Vapor Liquid Separator

ExxonMobil Proprietary

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DRUMS DESIGN PRACTICESVAPOR - LIQUID SEPARATORS Section

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PROPRIETARY INFORMATION - For Authorized Company Use OnlyDate

December, 1999

EXXON RESEARCH AND ENGINEERING COMPANY - FLORHAM PARK, N.J.

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CONTENTSSection Page

SCOPE ............................................................................................................................................................3

REFERENCES ................................................................................................................................................3DESIGN PRACTICES .............................................................................................................................3OFFSITE DESIGN PRACTICES .............................................................................................................3INTERNATIONAL PRACTICES ..............................................................................................................3OTHER REFERENCES ..........................................................................................................................3

DEFINITIONS ..................................................................................................................................................4

APPLICATION.................................................................................................................................................5EXPERIENCE LIMITS FOR VAPOR-LIQUID SEPARATORS ................................................................5

BASIC DESIGN CONSIDERATIONS..............................................................................................................5FLOW REGIME IN THE INLET PIPING ..................................................................................................6DRUM ORIENTATION ............................................................................................................................6REENTRAINMENT AT THE LIQUID SURFACE.....................................................................................6NOZZLES................................................................................................................................................6DISTRIBUTORS......................................................................................................................................6LIQUID HOLDUP ....................................................................................................................................7ANTI-VORTEX BAFFLES .......................................................................................................................7

DESIGN CONSIDERATIONS FOR SELECTED SERVICES ..........................................................................7LIQUID SURGE AND DISTILLATE DRUMS...........................................................................................7COMPRESSOR SUCTION, COMPRESSOR INTERSTAGE, AND GAS TURBINE FUEL (GAS)SEPARATOR DRUMS ............................................................................................................................7LUBE OIL SEPARATORS FOR COMPRESSOR DISCHARGE .............................................................7FUEL GAS SEPARATOR DRUMS FOR FURNACES ............................................................................8FUEL GAS SYSTEM CENTRAL COLLECTION DRUMS .......................................................................8STEAM DRUMS IN BOILER SERVICE...................................................................................................8WATER DISENGAGING DRUMS ...........................................................................................................8BLOWDOWN DRUMS ............................................................................................................................9FEED SEPARATOR DRUMS FOR AMINE SCRUBBERS......................................................................9HIGH-PRESSURE SEPARATORS .........................................................................................................9CRUDE PREHEAT FLASH DRUMS .......................................................................................................9

DESIGN PROCEDURES ...............................................................................................................................10GUIDELINES FOR SPECIFIC SERVICES............................................................................................10DESIGN METHODS FOR ALL DRUMS................................................................................................11

Preventing Entrainment from the Liquid Surface ................................................................................11Maximum Permissible Velocity in Annular Flow Without Drop Formation ..........................................13Vertical Separator Drums With and Without CWMS...........................................................................13

Changes shown by ➧

DESIGN PRACTICES DRUMSSection

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CONTENTS (Cont)Section Page

Vertical Separator Drum with Horizontal Tangential Inlet and Annular Ring ......................................14Horizontal Separator Drums With and Without Horizontal CWMS .....................................................15Horizontal Separator Drums with Both Vertical and Horizontal CWMS..............................................15Distance from Top of CWMS to Gas Outlet Nozzle............................................................................15Design Criteria for Anti-Vortex Battles................................................................................................16

SAMPLE PROBLEM (CUSTOMARY UNITS)...............................................................................................17DESIGN BASIS.....................................................................................................................................17HOLDUP ...............................................................................................................................................17FEED RATES AND PROPERTIES .......................................................................................................17SOLUTION............................................................................................................................................17

SAMPLE PROBLEM (METRIC UNITS) ........................................................................................................21DESIGN BASIS.....................................................................................................................................21HOLDUP ...............................................................................................................................................21FEED RATES AND PROPERTIES .......................................................................................................21SOLUTION............................................................................................................................................21

NOMENCLATURE ........................................................................................................................................26

COMPUTER PROGRAMS ............................................................................................................................27

TABLESTable 1 Typical Design Criteria for Various Services....................................................................28Table 2 Areas and Volumes of Cylindrical Vessels (Customary Units).........................................30Table 2A Areas and Volumes of Cylindrical Vessels (Metric Units) ................................................31Table 3 Recommended Inlet Nozzle Types for Specific Services.................................................32Table 4 Dimensions of 90° Standard Welding Elbows as a Function of Nominal Pipe Size .........33Table 5 Chord Lengths And Segment Areas vs. Chord Heights...................................................34

FIGURESFigure 1 Vertical Drum Debottlenecking Considerations ...............................................................35Figure 2 Typical Dimensions of Vertical Cylindrical Drums............................................................36Figure 3 Surface Tension-Viscosity Parameter..............................................................................37Figure 4 Typical Dimensions of Horizontal Cylindrical Drums .......................................................38Figure 5 Dimensions of Horizontal Drums with both Vertical and Horizontal CWMS.....................39Figure 6 Amine Scrubber Feed Separator Drum ...........................................................................40Figure 7 Velocity Dissipation in Impinging Jets..............................................................................41Figure 8 Design Criteria for a Vertical Drum with Tangential Inlet Nozzle and Annular Ring.........42Figure 9 Gas Collector...................................................................................................................44Figure 10 Position of Side-Out Gas Outlet Nozzles In Vertical Drums with CWMS.........................45Figure 11 Anti-Vortex Baffle Design.................................................................................................46Figure 12 Design Criteria for Horizontal Crude Flash Drums...........................................................47Figure 13 Design Criteria for Vertical Crude Flash Drums...............................................................49

Revision Memo12/99 Highlights of this revision are:

1. Figure 1 and Reference 2 added: Vertical Drum Debottlenecking for Vapor /Liquid Services, EE.43E.99.

2. Experience limits added.3. References made to PEGASYS computer programs.4. Updated vendor-designed separators.5. Conservation reduced in Eq. (9).


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SCOPEThis section covers the design of vapor-liquid separator drums, including internals (such as distributors, anti-vortex baffles andcrinkled wire mesh screens). Information is also given on the influence of the flow characteristics in the inlet piping on separatordrum performance.

➧ This section does not include information pertaining to the design of drums for Environmental or Safety purposes. For blowdowndrums and flare seal drums, see Design Practice Sections XV-D and XV-E, respectively. For FCCU wet gas scrubber venturiseparators, see Environmental Design Practice Section XVIII-A5.In addition, this section does not discuss how to debottleneck existing drums when poor performance is observed or increasedrates are planned. Techniques to evaluate vertical drums in debottlenecking situations are discussed in Reference 2.Debottlenecking considerations from that report are shown in Figure 1. That report rates vertical drums using drop sizes, a morefundamentally sound basis than critical velocity, which is used in this subsection. The report also provides guidance onestimating the drop size distribution to a separator, and the drop size effectively removed by drum internals including crinkledwire mesh screens, vane-type mist eliminators, packing and grid. There is not yet an equivalent report or rating approach forhorizontal drums. For debottlenecking of drums for critical separations, engineers are advised to contact the Fractionation andThermodynamics Section at ER&E.

REFERENCESDESIGN PRACTICESSection lIl Fractionating TowersSection Xl CompressorsSection Xll InstrumentationSection XIV Fluid FlowSection XV Safety in Plant Design

OFFSITE DESIGN PRACTICESSection XXV Fuel SystemsSection XXVI Steam Facilities

INTERNATIONAL PRACTICESIP 5-1-1, Pressure VesselsIP 5-1-2, Additional Requirements for Heavy-Wall Pressure Vessels, Thickness Over 2 InchesIP 5-2-1, Internals for Towers, Drums and Fixed Bed ReactorsIP 7-2-1, Industrial Boilers

OTHER REFERENCES1. Harleman, D. R., Selective Withdrawal from a Vertically Stratified Fluid, Intern Assoc. Hydro. Research, 8th Congress,

August, 1959.➧ 2. Maloney, D. P., Pagendarm, S. M., and Peruyero, J. M. A., Vertical Drum Debottlenecking for Vapor / Liquid Services,

EE.43E.99, January 1999.3. Marut, T. P., Design Criteria for Flash Drums in Crude Preheat Service, EE.79E.85, December, 1985.4. Patterson, F. M., Experimental Investigation of Critical Submergence for Vortexing in a Vertical Cylindrical Tank, M.S.

Thesis, University of Southern California, 1967.5. Peruyero, J. M. A., Design Criteria for Liquid/Gas Vertical Separator Drums, EE.34E.73, April, 1973.6. Peruyero, J. M. A., Performance of Horizontal Liquid/Gas Separator Drums, EE.71E.75, August, 1975.7. Stober, B. K., Carryover Reduction from Refinery and Chemical Plant Steam Drums, EE.9lE.79, August, 1979.


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DEFINITIONSGeneral definitions applicable to the design of separator drums are presented below:Crinkled Wire Mesh Screen (CWMS) - Crinkled wire mesh screens are porous blankets of wire or plastic knitted mesh, whichare used for removing entrained liquid drops from a vapor stream. CWMS is available in a wide variety of densities and wirediameters. Recommended CWMS densities and wire diameters are given in IP 5-2-1, Internals for Towers, Drums and FixedBed Reactors. When vapor and entrained liquid drops pass through a CWMS, the vapor moves freely through the mesh pad, butthe drops, because of their greater inertia, cannot follow the gas stream and are collected on the screen wires. The liquidcollected on the wires runs down to the bottom surface and drops off the screen. If the liquid rate entrained to the CWMS is toohigh or if the vapor rate is too high, however, CWMS flooding will occur. To prevent this, the drum and the CWMS should besized using the criteria given in this section.

➧ Critical Velocity - Critical velocity is an empirically calculated vapor velocity used to specify the maximum superficial vaporvelocity through the separator drum. It is not related to sonic velocity, and at superficial velocities above the critical velocity thereis no step change in liquid entrainment. Critical velocity is defined by Eq. (1).

5.0

G

GL1C CV

ρ

ρ−ρ= Eq. (1)

where: VC = Critical velocity, ft/s (m/s)C1 = Empirical constant = 0.157 ft/s (0.048 m/s)ρL = Liquid density at conditions, Ib/ft3 (kg/m3)ρG = Vapor density at conditions, Ib/ft3 (kg/m3)

The area used for calculating vapor velocity in a horizontal drum is the vertical cross-sectional area above high liquid level (oremergency liquid level, if applicable); for a vertical drum, it is either the horizontal cross-sectional area of the drum or that of theCWMS if a CWMS is used.Liquid Separation Efficiency - Liquid Separation Efficiency is defined by Eq. (2).

−=

FCF100E Eq. (2)

where: E = Separation efficiency, %F = Liquid feed rate to the drum, Ib/h (kg/s)C = Liquid carryover in the drum overhead, Ib/h (kg/s)

Normal Gas Flow - Normal gas flow is the design gas rate fed to a separator drum at typical operating conditions (i.e., in theabsence of upsets such as surges due to process instabilities or to the loss of upstream condensing capacity). CWMS in drumssized for 100% of critical velocity and horizontal drums with both vertical CWMS and horizontal CWMS will be highly effective atgas throughputs of 150% of normal gas flow, and therefore, no surge allowance is typically required for sizing these drums. Ifsurges larger than 150% are anticipated for these drums, the Fractionation/Thermodynamics section of ER&E should beconsulted.Maximum Gas Flow - Maximum gas flow is equal to the sum of the design gas rate fed to a separator drum at typical operatingconditions plus the gas rate due to upsets such as surges due to process instabilities or the loss of upstream condensingcapacity. Maximum gas flow should be used for sizing CWMS in vertical drums via Eq. (4) when maximum separation efficiencyshould be maintained during upsets such as in reciprocating compressor services.Vane-Type Mist Eliminator - Vane-Type Mist Eliminators are zig-zag baffles which are used for removing entrained liquid dropsfrom a vapor stream. Spacing between the baffles, turning angles and number of passes are designed to satisfy specific removalrequirements. When the vapor and the entrained liquid drops pass through a vane-type mist eliminator, the vapor moves freelythrough the baffles, but the drops, because of their greater inertia, impinge upon the walls of the baffles. The liquid collected onthe baffles runs down to the bottom surface and drops off the mist eliminator. Typically a vane-type mist eliminator is moreresistant to fouling than a CWMS due to larger physical openings. Design and sizing of vane-type mist eliminators are carried outby the vendor. Typical vendors include Koch-Glitsch, Munters, and Peerless Manufacturing Co.


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APPLICATION

Ordinary vapor-liquid separator drums use gravity to separate liquid from vapor. Such drums are effective for removal of dropslarger than about 200 to 400 micrometers (microns) (µm). Use of crinkled wire mesh screen increases the separationeffectiveness so that drops down to about 5 to 10 µm can be removed. The liquid separation efficiency of ordinary drums withoutCWMS is typically 95 to 99.5%. Installation of a horizontal CWMS in the drum vapor space typically increases the liquidseparation efficiency to perhaps 99.9% or more.

Where plugging of the CWMS may occur, such as in RESIDFINER and slurry services, other devices are available for the 5 to10 µm drop size range; e.g., proprietary cyclone type separators, filter/separators and tailor designed vertical drums withtangential inlet nozzles and annular rings. For sizing the latter drums for these services, the Fractionation/ThermodynamicsSection of ER&E should be consulted. When extremely fine droplets are to be removed, e.g., fogs due to rapid condensationfrom saturated gas or due to a chemical reaction, more efficient proprietary equipment is available. Two-stage filter/separatorscan be effective on drops down to about 2 µm, while Venturi scrubbers and electrostatic precipitators separate drops significantlysmaller than 1 µm. Brownian diffusion can be utilized to separate smaller drops, e.g., Peerless Manufacturing Company'sabsolute separators which consist of minicyclones followed by a coalescer.

In selecting the proper separation device, the designer must consider both the desired degree of liquid removal from the gasstream and the acceptable droplet size. In some cases a fine mist may not be detrimental to downstream equipment, whereaslarge drops of liquid could be. On the other hand, even a fine mist may be a highly undesirable contaminant because ofcorrosiveness or catalyst poisoning.

➧ For foaming services, consultation with the Fractionation and Thermodynamics Section of ER&E is recommended. Drumdesigns for these services tend to be service specific. Porta-Test International manufactures centrifugal separators that havebeen applied in debottlenecking non-Exxon drums, and ER&E is currently evaluating their technology.In a few situations, it may be justified to install an inline separator to collect entrained liquid. Inline separators operate bycentrifugal force and have low liquid holdup. "T-type" separators, installed in horizontal pipe runs, are preferred because of theirhigher efficiency, especially at moderate and high liquid rates. In general, inline separators are capable of removing dropletslarger than approximately 10 µm in diameter; however, specific cut-point information should be obtained from the particularvendor. Vendors include: (1) Hayward Industrial Products (Wright Austin Division) of Elizabeth, New Jersey, and (2)Pennsylvania Separator Corp. of Brookville, Pennsylvania. Proposals for inline separators should be reviewed by an ER&ESeparation Specialist.Other technology is available from vendors that can be utilized in unique situations; for example, to remove solid particles as wellas liquid droplets from feed to hydrogen reciprocating compressors. These include filter/separators or filter coalescers fromPeco, King Tool and Pall. Each of these devices utilizes a filter coalescer in front to increase the size of the drops and to removesolid particles either to protect downstream processes, or to increase the run length of the mist eliminating element contained inthe vendor's package. An ER&E Separation Specialist should be consulted if any of these devices are being considered.

EXPERIENCE LIMITS FOR VAPOR-LIQUID SEPARATORSExperience limits for the design of vapor-liquid separators are provided in the following table. If an application is outside thesebands, contact an ER&E Separation Specialist.

VAPOR-LIQUID SEPARATOR EXPERIENCE LIMITS

PARAMETER LOWER LIMIT UPPER LIMITDrum Diameter, ft (m) 0.7 (0.2) 25 (7.6)Vapor Density, lb/ft3 (kg/m3) 0.005 (0.08) 5 (80)Liquid Density, lb/ft3 (kg/m3) 20 (320) 80 (1280)Surface Tension, dynes/cm or mN/m 2 75Liquid Viscosity, cP or mPa•s 0.05 2CWMS Liquid Loading, gpm/ft2 (dm3/s•m2) 0.0 (0.0) 20 (13.6)Foaming Tendency NONE, except for Crude Flash Drums

BASIC DESIGN CONSIDERATIONSThe considerations discussed below are the basis for the design procedures given later in this section for designing drums exceptfor those listed in Table 1 or for drums in foaming services. The Fractionation/Thermodynamics Section of ER&E should beconsulted for setting the design criteria for separator drums in foaming services. The design procedures for drums listed inTable 1 are covered in DESIGN PROCEDURES under GUIDELINES FOR SPECIFIC SERVICES.


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BASIC DESIGN CONSIDERATIONS (Cont)

FLOW REGIME IN THE INLET PIPINGDifferent flow regimes may be present in the inlet piping of process separator drums. These flow regimes are defined in SectionXIV-D, Two-Phase (Vapor-Liquid) Flow.Separator drums are normally designed with annular/spray or spray flow in the inlet piping. With this type of flow, liquid carryoverincreases with increasing gas velocity in the inlet piping. The presence of stratified flow, annular flow below onset of liquidentrainment, or wavy flow in the inlet piping of separator drums would increase the liquid separation efficiency of the drum toperhaps 99.8%. However, these types of flow are not usually encountered in process operations, because relatively large pipediameters would be required. Nevertheless, the design of inlet piping to achieve these flow regimes should be considered forspecial services in which low entrainment rates are essential but a CWMS or other internals are not permitted; e.g., because it isa severely fouling service. Conservative estimates of the mixture velocities in the inlet piping for which drops are not entrained inannular pipe flow are given in DESIGN PROCEDURES, under Maximum Permissible Velocity in Annular Flow Without DropFormation.Slug flow or bubble flow should be avoided in the inlet piping to vertical separator drums. These flow regimes result in excessiveliquid carryover and vibration. If these flow regimes cannot be avoided at the drum inlet, liquid carryover can be minimized byuse of a horizontal drum with two inlet nozzles and a central vapor outlet nozzle (preferred choice) or a vertical drum with aslotted distributor (second choice). If only slug flow is typically present in the inlet piping, a vertical drum with a tangential inletnozzle and an annular ring will be more effective than one with a slotted distributor.

DRUM ORIENTATIONSeparator drums are generally oriented with their axes horizontal or vertical. Vertical drums require less plot area, but horizontaldrums typically are smaller in volume for high liquid loading service. Horizontal drums erected below other equipment such ascondensers will reduce the structural material needed to support the entire circuit equipment. Because interfaces are morequiescent, horizontal drums are preferred where two liquid phases are separated and for services in which the flow regime in theinlet piping is slug flow or bubble flow.Horizontal drums with one inlet nozzle will be more effective than vertical drums whenever the ratio of drum length to vapor spaceheight is greater than one. Horizontal drums with two inlet nozzles will be more effective than vertical drums whenever the ratioof the drum length to vapor space height is two or greater. This improved effectiveness of horizontal drums results from thedrops settling perpendicular to the gas flow, rather than countercurrent to gas flow as in vertical drums.

REENTRAINMENT AT THE LIQUID SURFACEIn many operations, especially at high pressure and temperature, liquid can be reentrained from the liquid surface and carriedoverhead. Reentrainment rate depends on the gas velocity in the inlet piping, the inlet nozzle type, the distance from the inletnozzle to the liquid level or impinging surface, the surface tension of the liquid, and the densities and viscosities of the liquid andgas. Criteria for estimating the maximum mixture velocity leaving the inlet nozzle below which reentrainment will not occur aregiven in DESIGN PROCEDURES under Preventing Entrainment from the Liquid Surface.

NOZZLES➧ Size - Inlet and outlet nozzles typically are line size. However, if reentrainment at the liquid surface might occur, the inlet nozzle

diameter may be increased upstream of the drum (five line diameters in length). Generally the smallest instrument connectionused for process vessels is 2 in. (50 mm) except for thermowells which are 1 1/2 in. (40 mm).Inlet Nozzle Type and Orientation - Inlet nozzle type depends on the flow regime in the inlet piping, on the separator internalsand the type of service. Recommended inlet nozzle types are given in Table 3. Inlet nozzle orientations are shown in Figures 2,4, 5, 8 and A (under SAMPLE PROBLEM).

DISTRIBUTORS➧ Distributors for vapor-liquid separators are not designed for good distribution. Instead they are designed for low slot (or hole)

velocity to minimize the formation and entrainment of small bubbles or droplets, see Eqs. (3d), (3e) and (3f).Perforated-pipe distributors should be T-shaped, with feed entering at the center and flowing toward both ends. For verticaldrums, the distributor slots (or holes) should be located within a 120° included angle on the bottom portion of the header (Figure2). For horizontal drums, the distributor slots (or holes) should point toward the near head of the drum, within 60° of thehorizontal (see Figure A under SAMPLE PROBLEM). No openings should be placed directly opposite the entrance leg. Formechanical strength the minimum permissible distance between two adjacent slots (or holes) is equal to the distributor pipethickness.


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BASIC DESIGN CONSIDERATIONS (Cont)LIQUID HOLDUPDesign liquid holdup is usually determined by process, control or emergency requirements. Process requirements for varioustypical services are given in Table 1. Control and emergency requirements are covered in Design Practices Sections Xll,Instrumentation, and XV-D, Safety in Plant Design-Disposal Systems, respectively. The Fractionation/ Thermodynamics Sectionof ER&E should be consulted for setting the minimum permissible liquid holdup time for new services, especially for potentiallyfoaming services. Holdup in vertical and horizontal drums may be calculated using the values given in Tables 2 and 5,respectively.

ANTI-VORTEX BAFFLESAnti-vortex baffles should be installed above all liquid outlets to minimize vortex formation with subsequent gas carryunder.Design criteria for anti-vortex baffles are given in DESIGN PROCEDURES, under Design Criteria for Anti-Vortex Baffles.

DESIGN CONSIDERATIONS FOR SELECTED SERVICES

LIQUID SURGE AND DISTILLATE DRUMSHorizontal separator drums with CWMS are used for clean services; filter/separators or proprietary multiple cyclones arerecommended for services in which solids or fouling materials are present.

COMPRESSOR SUCTION, COMPRESSOR INTERSTAGE, AND GAS TURBINE FUEL (GAS) SEPARATORDRUMSVertical separator drums with CWMS are used for clean services; however, the CWMS should be composed of two 6-in.(150 mm) thick layers with 10 Ib/ft3 (160 kg/m3) material on the top and 5 Ib/ft3 (80 kg/m3) material on the bottom. The presenceof solids, typically due to excessive corrosion problems, should be avoided by selecting adequate piping materials. When this isimpractical, proprietary filter/separators (such as Peco filters) or gas scrubbers should be provided upstream of the compressoror gas turbine to mitigate compressor or fuel nozzle fouling problems.The designer should also consider the installation of a vertical drum with a horizontal tangential inlet and an annular ringupstream of the filter/separator. This will significantly reduce the solids content in the feed to the filter/separator, therebyincreasing the total gas volume that can be processed by the filter elements. The Machinery Engineering Section or theFractionation/Thermodynamics Section of ER&E should be consulted for specific design criteria for separators in servicescontaining solids.To eliminate the presence of liquid in the feed to the compressor or gas turbine, the following steps should also be taken:• The designer should ensure that the drum will operate satisfactorily under all process conditions, e.g., regeneration (if

applicable), startup, normal operation, upsets, etc.• Level High Alarms and Level High Cut Outs should be properly located in the drum.• The distance from the drum to the compressor should be minimized. In addition, the suction line should be insulated and

sloped away from the compressor. Heat tracing of the line should also be specified if calculations show that line insulationwill not prevent condensation.

• In addition to the above, for reciprocating compressors, the compressor cylinder jacket inlet water temperature should bemaintained between 10 to 15°F (6 to 8°C) above the gas inlet temperature to prevent condensation in the cylinder and valveareas.

• In addition to the above, for gas turbines, the fuel should be superheated 50°F (28°C) above its dew point.It is sometimes economical to combine the compressor suction drum service with another drum service, such as in the distillatedrum of a catalytic cracking unit primary fractionator. In such cases, the emergency liquid surge requirements for compressorsuction service are added to the other service requirements. Horizontal drums with CWMS are common in this type ofcombination service.

LUBE OIL SEPARATORS FOR COMPRESSOR DISCHARGELubricating oil from reciprocating and sliding-vane compressors can be carried into the compressor discharge gas stream asextremely fine droplets. Lube oil separators should be specified for instrument air and for processes which cannot tolerate thepresence of this oil. Section Xl-O, Compressor Unit Piping and Process Train Equipment, covers the types of lube oil separatorscommercially available, their estimated separation efficiency, pressure drop, and relative cost.


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DESIGN CONSIDERATIONS FOR SELECTED SERVICES (Cont)FUEL GAS SEPARATOR DRUMS FOR FURNACESSeparator drums should be located on the fuel supply to the furnaces to collect slugs of condensate during upsets and to preventexcessive liquid entrainment to the furnace burners. For clean fuel gas service, a vertical separator drum with CWMS and sizedfor 100% of critical velocity at normal gas flow rate should be used. For sour and corrosive fuel gas services, the use of verticaldrums with tangential inlet nozzles and annular rings or separator drums with proprietary multiple cyclones, such as Peerless dryscrubber or U.O.P. Multiclones or demonstrated equivalent, are recommended to minimize fouling and plugging of burners.

FUEL GAS SYSTEM CENTRAL COLLECTION DRUMSA fuel gas system central collection drum (see Offsite Design Practices Section XXV, Fuel Systems) is designed to removegross liquid entrainment. Either a vertical or a horizontal separator drum without CWMS is recommended for this service. Theallowable vapor velocity through the drum is 100% of critical velocity at design gas flow rate. The allowable velocity through thevertical drum could be increased to 200% of critical velocity at maximum gas flow rate if a tangential inlet nozzle and an annularring are used. Five minutes liquid holdup at the maximum liquid rate is provided. Other design criteria are given in OffsiteDesign Practices Section XXV.

STEAM DRUMS IN BOILER SERVICEWhen steam is fed to a superheater, a steam turbine, or a reformer, steam drums should be designed as follows:1. For waste heat boilers of the shell and tube or kettle reboiler type operating with steam pressures less than 700 psig (4820

kPa gage), vertical or horizontal separator drums with CWMS should be used.a. For vertical separator drums, the CWMS and the drum vapor space are sized for 100% of critical velocity at design

steam flow rate. The design shown in Figure 2 is preferred; however, the CWMS should be composed of two 6-in.(150 mm) thick layers with 10 lb/ft3 (160 kg/m3) material on the top and 5 Ib/ft3 (80 kg/m3) material on the bottom.

b. For horizontal separator drums, a combination of vertical and horizontal CWMS as shown in Figure 5 is preferred.However, the vapor space and CWMS areas should be based on 100% of critical velocity at design steam rate. Thedensity of the vertical and horizontal CWMS should be 5 lb/ft3 (80 kg/m3) and 10 lb/ft3 (160 kg/m3), respectively.Because of the potential foaminess of the boiler water, the minimum permissible distance between CWMS bottom andthe water is 18 in. (450 mm). When these criteria are satisfied in the absence of foaming, the liquid entrainment in thedrum overhead should be less than 150 to 300 weight ppm (mg/kg).

c. For both horizontal and vertical separator drums, the maximum permissible velocity in the inlet piping depends on steampressure as shown below:

STEAM PRESSURE MIXTURE VELOCITY IN INLET PIPINGpsig kPa gage ft/s m/s100 690 30 9.1200 1380 20 6.1400 2760 15 4.6600 4100 10 3.0

600+ 4100+ (1)

Note:(1) The Fractionation/Thermodynamics Section of ER&E should be consulted for sizing

steam drums at pressures higher than 600 psig (4100 kPa gage).2. Steam drums for any other boiler type, e.g., fired boilers, should be designed by the boiler vendor according to

specifications given in IP 7-2-1, Industrial Boilers.Impurities - The maximum permissible solids, alkalinity and silica content of the boiler water is a function of the boiler operatingpressure as shown in Offsite Design Practices Section XXVI-A, Boiler Feedwater Treating.

WATER DISENGAGING DRUMSDisengaging drums are provided to remove small amounts of hydrocarbon liquid and vapor contaminants from aqueous planteffluent streams to permit them to be safely discharged to the sewer. The design basis for these disengaging drums is describedin Section XV-D.


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DESIGN CONSIDERATIONS FOR SELECTED SERVICES (Cont)BLOWDOWN DRUMSThe main purpose of a blowdown drum is to disengage fluid streams from closed safety valve releases and from various drainageblowdowns, and to convert them into liquid and vapor streams which can be safely disposed of. Criteria for selection and designof blowdown drums are given in Section XV-D.

FEED SEPARATOR DRUMS FOR AMINE SCRUBBERSHydrocarbon entrainment in the gas feed to amine scrubbers can result in foaming, with subsequent excessive carryover in thescrubber. In refineries, an integral separator drum in the bottom of the amine scrubber is used for the removal of most of theliquid entrainment due to condensation in the line. A schematic diagram of this drum is given in Figure 6. This separator shouldcontain a CWMS in its vapor space and the gas velocity through the drum and the CWMS should be 100% of critical velocity atdesign gas rate. In chemical plants (steam crackers), a superheater in lieu of a separator drum may be used to preventcondensation in the scrubber.

HIGH-PRESSURE SEPARATORSHigh-pressure separators, e.g., hot, high-pressure separators in hydrodesulfurization units, are designed to minimize both gascarryunder and liquid holdup volume, because of process debits of lost gas (H2) and high drum costs, respectively.A horizontal separator drum with either a horizontal CWMS or a combination of two vertical and one horizontal CWMS should beused for clean services (see Figure 5).When entrainment should be reduced to a value equal to or less than 1 lb (1 kg) of liquid per 100 lb (100 kg) of gas and a CWMScannot be used because of the possibility of plugging by coking, the mixture velocity in the inlet piping should not exceed 20 ft/s(6.1 m/s) to prevent forming very small drops. In addition, the vapor space should be sized for 100% of critical velocity at designgas rate, a slotted distributor inlet should be installed at each end of the drum, and the drum should have a single vapor outletnozzle. Design criteria for preventing gas carryunder in the underflow of these drums are given in Table 1 under High-PressureSeparators.The following criteria, which allow for the foaming potential of liquids, are recommended for the design of separator drums inRESIDFINER service:• A horizontal separator drum with two inlet nozzles and one vapor outlet nozzle should be used.• The vapor space area should be sized for 100% of critical velocity at design gas rate.• Reentrainment at the liquid surface should be prevented using appropriate equations given in DESIGN PROCEDURES

under Preventing Entrainment from the Liquid Surface.• The maximum mixture velocity in the inlet piping should be 16 ft/s (4.9 m/s).• The minimum liquid residence time below low liquid level should be two minutes and the minimum vertical height below low

liquid level should be 18 in. (450 mm).• Facilities should be provided for the injection of anti-foaming agents into the feeds to the separator drums.• Two or three gage glasses at various overlapping elevations should be installed to detect the presence of foam.The Fractionation/Thermodynamics Section of ER&E should be consulted for design criteria for high pressure separators insynthetic fuels plants since they should be handled on a case by case basis.

➧ CRUDE PREHEAT FLASH DRUMSThese drums can experience severe foaming, which can result in both vapor carryunder and overhead liquid entrainment. Thesephenomena can reduce refinery crude capacity by as much as 30% by such mechanisms as downstream pump cavitation,uneven furnace pass balancing, reduced APS flash zone temperature, and system upsets too severe to control.To cope with foaming, crude flash drums require high liquid holdup, low superficial liquid and vapor velocities, as well as otherdesign features. In most cases, the use of an antifoam agent cannot be economically justified or may have adverse processconsequences. The design criteria detailed below are specific for refinery services, and therefore, are not applicable to crude oilproduction separators. The Fractionation / Thermodynamics Section of ER&E should be consulted on crude preheat flash drumdesign since emerging technology may result in drum size reduction.Horizontal Crude Flash Drum Design Criteria - A horizontal separator with two inlet nozzles (see Figure 12) is recommendedfor this service since, compared to a vertical separator, it maximizes the surface area available for vapor/liquid separation,minimizes foam height, and provides a quiescent zone that enhances bubble disengagement. A horizontal CWMS or vane typemist eliminator is provided to remove small drops that would otherwise be entrained in the vapor leaving the drum.Other key design criteria are summarized in Figure 12 and its attached notes.


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DESIGN CONSIDERATIONS FOR SELECTED SERVICES (Cont)Vertical Crude Flash Drum Design Criteria - Although a horizontal drum configuration is preferred for crude flash service, if plotspace limitations do not allow a horizontal drum design, then a vertical drum design can be used (see Figure 13). However, avertical drum will typically be larger, more expensive and less tolerant of upsets than a horizontal drum. The design criteria forvertical crude flash drums is basically the same as for horizontal drums with the following exceptions:• A tangential inlet nozzle with an annular ring should be provided.• A distance equivalent to 0.8 times the drum diameter should be provided between the bottom of the annular ring and the

HLL.• Four vertical anti-swirl baffles should be provided below the NLL. These baffles should extend from 6 in. (150 mm) below

the NLL to the bottom tangent line. The baffle width should be about 10% of the drum diameter. Their purpose is to preventvortex formation which may result in vapor carryunder.

• The horizontal CWMS or vane-type mist eliminator below the vapor outlet should occupy the entire drum cross sectionalarea.

• Minimum vertical height from the LLL to the bottom tangent line should be 3 ft (900 mm).A complete list of design criteria for the vertical crude flash drum is given in Figure 13 and its attached notes.

DESIGN PROCEDURESGUIDELINES FOR SPECIFIC SERVICESThe procedure given below is recommended for designing a separator drum for any of the following services:• Liquid surge and distillate drums.• Compressor suction, compressor interstage, and gas turbine fuel (gas) separator drums.• Lube oil separators for compressor discharge.• Fuel gas separator drums for furnaces.• Steam drums in boiler service.• Feed separator drums for amine scrubbers.• High-Pressure separators.• Crude preheat flash drums.Step 1 - Locate in Table 1 the typical design criteria for the service. Additional design criteria are given in the main text underDESIGN CONSIDERATIONS FOR SELECTED SERVICES.

Step 2 - Based on the drum configuration selected in Step 1, use the corresponding drum drawing (Figures 2, 4, 5, 8 and Aunder SAMPLE PROBLEM) as a guide for drum design. In addition, see the specific design criteria given below for the type ofdrum selected, e.g., Vertical Separator Drums With and Without CWMS.Step 3 - Size the drum vapor space using the area for calculating vapor velocity given under Definitions, Critical Velocity. Forhorizontal drums, use a length to diameter ratio of 3 to 4. Generally this results in minimum size and lowest cost. The diameterof a vertical drum is typically based on critical velocity criteria, other drum dimensions should be sized per Figure 2. Table 2shows areas and volumes of various size drums with 2:1 ellipsoidal heads.Step 4 - Select the type of inlet nozzle using criteria given in Tables 1 and 3, and herein for specific types of separator drums.Step 5 - Calculate the inlet nozzle diameter using criteria given below under Preventing Entrainment from the Liquid Surface.Step 6 - For drums with CWMS, estimate the minimum permissible distance between the top of the CWMS and the gas outletnozzle, based on criteria given below under Distance from Top of CWMS to Gas Outlet Nozzle. For corrosive services, theCWMS should be made of suitable materials of construction. Suitable grating supports should be provided at the top and bottomof horizontal CWMS, and at the sides of vertical CWMS. Grids recommended for these services are described in IP 5-2-1,Internals for Towers, Drums and Fixed Bed Reactors.Step 7 - Size the anti-vortex baffles and estimate the minimum permissible distance from LLL (low liquid level) to liquid outletnozzle, using criteria given under Design Criteria for Anti-Vortex Baffles.For services not covered in Table 1 select the type of separator drum using the criteria given in BASIC DESIGNCONSIDERATIONS. However, the Fractionation/Thermodynamics Section of ER&E should be consulted for setting theminimum permissible liquid holdup time, especially for potentially foaming services. Then proceed with the drum design followingSteps 2 to 7, above.For critical services in which entrainment must be minimized and/or plugging of CWMS due to solids or fouling may occur, theFractionation/Thermodynamics Section of ER&E should be consulted.


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DESIGN PROCEDURES (Cont)

DESIGN METHODS FOR ALL DRUMSThe following design methods, equations, and guidelines must be used for all drum designs.

Preventing Entrainment from the Liquid Surface

Criteria for estimating the maximum mixture velocity leaving the inlet nozzle, such that entrainment will not occur at the liquidsurface, are given below:1. Vertical Drums

a. Flush Inlet Nozzles

5.0

L

GG

2E

f

)C(V

ρρµ

σ= pd5.2hfor ≤ Eq. (3a)

and

5.0

p

p5.0

L

GG

3E

d5.0hd

f

)C(V

−

ρρµ

σ= pd5.2hfor > Eq. (3b)

b. 90° Elbow Inlet Nozzles

5.0

L

GG

4E

f

)C(V

ρρµ

σ= Eq. (3c)

c. Slotted Distributors

5.0

L

GG

5E

)C(V

ρρµ

σ= 5s

xforslot

≤ Eq. (3d)

and

5.0slot

5.0

L

GG

6E

xs

)C(V

ρρµ

σ= 5s

xforslot

> Eq. (3e)

d. Holed Distributors

Use Eq. (3d) for 5dxh

≤

and

ρρ

µ

σ=

xd

)C(Vh

5.0

L

GG

7E 5

dxforh

> Eq. (3f)

e. Tangential Inlet Nozzle with Annular Ring.


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DESIGN PROCEDURES (Cont)The mixture velocity in the inlet piping should not exceed 220 ft/s (67m/s) or the value given by Eq. (3g) below, whichever issmaller.

G

5.0

G

L8

E

CV

µ

ρρσ

= Eq. (3g)

The nomenclature for Eqs. (3a) to (3g) is:

VE = Maximum mixture velocity at the exit of the inlet nozzle, such that entrainment will not occur at the liquid surface, ft/s (m/s)

f = Jet velocity dissipation factor. As shown in Figure 7, f is a function of the distance x from the inlet nozzle to the impinging surface and the inlet nozzle diameter, dp. [f is not used in Eqs. (3d), (3e), and (3f).]

h = Distance from bottom of inlet nozzle to high liquid level (HLL), in. (mm)dp = Inlet nozzle diameter, in. (mm)dh = Hole diameter, in. (mm)sslot = Slot height, in. (mm). Typically, slots are long and narrow. Slot height is the narrow

dimension.x = Distance from the inlet nozzle to the impinging surface, in. (mm) (see Figure 7). For

vertical drums with flush inlets, x is the drum diameter. x is equal to h for vertical drumswith either slotted (or holed) distributors or 90° elbows.

µG = Vapor viscosity at conditions, cP (mPa•s)ρG = Vapor density at conditions, Ib/ft3 (kg/m3)ρL = Liquid density at conditions, Ib/ft3 (kg/m3)σ = Liquid surface tension at conditions, dynes/cm (mN/m)

EMPIRICAL CONSTANTS CUSTOMARY UNITS METRIC UNITSC2 6.8 x 10-4 2.1 x 10-4

C3 4.6 x 10-4 1.4 x 10-4

C4 5.3 x 10-4 1.6 x 10-4

C5 5.3 x 10-4 1.6 x 10-4

C6 2.3 x 10-4 7.0 x 10-5

C7 1.0 x 10-4 3.1 x 10-5

C8 6.3 x 10-3 1.9 x 10-3

2. Horizontal Drumsa. 90° Elbow Inlet Nozzles - Use Eq. (3c). However, for this case, x (in Figure 7) is the distance from the nozzle to the

near head of the drum.With a combination of vertical and horizontal CWMS, the maximum permissible mixture velocity is five times the valuecalculated using Eq. (3c).Without vertical CWMS (with or without horizontal CWMS), the maximum permissible mixture velocity is twice the valuecalculated using Eq. (3c).

b. Slotted or Holed Distributors - Use Eqs. (3d), (3e) or (3f), whichever is applicable. However, in this case, x is thedistance from the distributor to the near head of the drum.With a combination of vertical and horizontal CWMS, the maximum permissible mixture velocity is five times the valuecalculated using the appropriate equation.Without vertical CWMS (with or without horizontal CWMS), the maximum permissible mixture velocity is twice the valuecalculated using the appropriate equation.


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DESIGN PROCEDURES (Cont)

Maximum Permissible Velocity in Annular Flow Without Drop Formation

A conservative estimate of this mixture velocity is given by Eq. (3h):

5.0

L

GG

9I

)C(V

ρρµ

σ= Eq. (3h)

where: VI = Mixture velocity in the inlet piping, below which velocity liquid drops are not entrained in annular pipe flow, ft/s (m/s)

C9 = Empirical constant = 5.9 x 10-4 Customary units (1.8 x 10-4 Metric units)Other terms are described in the nomenclature.

Vertical Separator Drums With and Without CWMS

For services in which a moderate liquid carryover of up to 5 lb (5 kg) of liquid per 100 lb (100 kg) of gas is permissible, CWMSare not required and the vapor space in the drum should be sized for 100% of critical velocity at design gas flow rate. For criticalservices in which liquid entrainment should be reduced to less than 1 lb (1 kg) of liquid per 100 lb (100 kg) of gas, a 5 Ib/ft3, 6 in.(80 kg/m3, 150 mm) thick CWMS is recommended. For foaming services, both the drum and the CWMS horizontal cross-sectional area should be sized for 100% of critical velocity at design gas flow rate. Specific design criteria for sizing CWMS invertical drums in selected services are detailed in Table 1 and under DESIGN CONSIDERATIONS FOR SELECTEDSERVICES. For all other services, the drum and the CWMS should be sized for either 100% of critical velocity at normal gasflow rate or the value given by Eq. (4) below, whichever is larger.

( )

−= σ 2

2L10uMAX,C

D)W2D()C(K225%V L Eq. (4)

where: VC,MAX(%) = Maximum allowable percent of critical velocity at maximum gas flow rate, %Kσµ = Surface tension - viscosity parameter, dimensionless, see Figure 3LL = Maximum liquid loading which is the maximum liquid feed rate divided by the

drum horizontal cross-sectional area, gpm/ft2 (dm3/s•m2)D = Drum diameter, ft (mm)W = CWMS support ring width, ft (mm)C10 = Empirical constant = 0.953 Customary units (0.932 Metric units)

The last term in Eq. (4) accounts for the reduction in area for vapor flow at the bottom of the CWMS due to the presence of theCWMS support ring. A support ring 2 in. (50 mm) wide is typically recommended for these services.The procedure for calculating both the vertical drum diameter and the CWMS diameter using Eq. (4) is detailed below.1. Calculate the maximum vapor flow rate, ft3/s (dm3/s).2. Calculate critical velocity, ft/s (m/s).3. From Figure 3 read Kσµ at the viscosity of the liquid (µL) and surface tension (σ), or calculate Kσµ using Eqs. (5), (6), and (7)

below.

µ−

=σ45.0)(

276.068.1

STDL10 Eq. (5)

( ) [ ] 5.0STD

STDfσσ

σ−σ=σµ Eq. (6)

( )µσ=σµ,f

24.1K Eq. (7)


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DESIGN PROCEDURES (Cont)4. Assume a trial diameter (D) and calculate its corresponding cross-sectional area.5. Calculate the maximum liquid loading, LL.6. Calculate the actual percent of critical velocity (VC,ACTUAL%) at the trial diameter.7. Calculate the maximum allowable percent of critical velocity using Eq. (4).8. Calculate the ratio of the actual percent of critical velocity to the maximum allowable percent of critical velocity.9. Approximate the next trial drum diameter using the ratio calculated in Step 8 as given below.

( )( )

5.0

MAX,C

ACTUAL,CNEW %V

%VDD

= Eq. (8)

10. Repeat calculations starting from Step 5 until actual percent of critical velocity is in reasonably good agreement with themaximum permissible percent of critical velocity.The above steps assume that the drum cross-sectional area is determined by the vapor loading. A larger drum diameter willbe required if the liquid holdup requirement sets the drum cross-sectional area.For cases in which the turndown ratio is between three and six, two CWMSs should be used in series. The cross-sectionalarea of the bottom CWMS should be based on 100% of critical velocity or the value calculated using Eq. (4), whichever islarger. The cross-sectional area of the top CWMS should be one-third of the bottom CWMS cross-sectional area. Thedistance between the two CWMSs should be about 2 ft (600 mm).Since the liquid loading which a CWMS can handle without flooding decreases with increasing density of the CWMS, theFractionation/Thermodynamics Section of ER&E should be consulted for the design of separator drums with any other typeof CWMS. Additional design criteria are given in Figure 2.

Vertical Separator Drum with Horizontal Tangential Inlet and Annular Ring

This type of drum is currently recommended for the following services: 1) fouling and corrosive fuel gas services (see Fuel GasSeparator Drums for Furnaces), 2) central collection drum for fuel gas system, 3) services in which slug flow regime is present inthe inlet piping (see Table 3); and 4) non-condensible blowdown services (see Section XV-D, Safety in Plant Design - DisposalSystems).The designer should also consider the use of this drum upstream of a Peco filter for compressor services in which solids orfouling materials are present. It will significantly reduce the solids loading into the Peco filter, thereby increasing the total gasvolume that can be processed by its filter elements which require replacement when fouled. Finally, tailor-designed verticaldrums with tangential inlet nozzles and an annular ring are currently being used in slurry services such as Flexicoker Venturiseparator drums. The Fractionation/Thermodynamics Section of ER&E should be consulted for developing specific designcriteria for slurry services.The following design criteria should be used for sizing a vertical drum with horizontal tangential inlet(s) and an annular ring:• The horizontal cross-sectional area for vapor flow should not exceed 200% of critical velocity at maximum gas flow rate.• The core area for upward vapor flow, i.e. the drum cross-sectional area minus the annular ring area, should not exceed

300% of critical velocity at maximum gas flow rate (see Figure 8).• A distance equivalent to the drum diameter should be provided between the bottom of the annular ring and the solid circular

baffle.• To prevent reentrainment of the liquid film which collects on the separator wall, the mixture velocity in the inlet piping should

not exceed 220 ft/s (67 m/s) or the value given by Eq. (3g), whichever is smaller.When the drops are formed by the interaction between the liquid and the vapor in the inlet piping, liquid separation efficiencies of99.8% plus can be attained if the calculated value for the following expression exceeds C11.

( )113

s2

GG

2LT C

)V()(Dn1C

≥ρµ

+σρ Eq. (9)

where: CT = Annular ring configuration factor, dimensionlessn = Vortex exponent, dimensionless

Vs = Mixture velocity in inlet piping, ft/s (m/s)➧ C11 = Empirical constant = 500 Customary units (3.6 Metric units)


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DateDecember, 1999


DESIGN PROCEDURES (Cont)When only one inlet nozzle is used, CT is given by the following expression

−+=

D12d3

dD12216C p

pT Eq. (10)

For two inlet nozzles, the value of CT is 50% of the value calculated using Eq. (10). The value of the vortex exponent, n, is givenby the following expression:

n = C12 D0.14 Eq. (11)

where: C12 = Empirical constant = 0.567 Customary units (0.255 Metric units)

Horizontal Separator Drums With and Without Horizontal CWMS

For services in which a moderate amount of entrainment is permissible [e.g., up to 5 lb (5 kg) of liquid per 100 lb (100 kg) of gas],CWMSs are not required and the vapor space in the drum should be sized for 100% of critical velocity at normal gas flow rate.The inlet nozzle(s) should terminate in either a 90° elbow or a slotted distributor, pointing toward the near head of the drum.For clean, low entrainment services, a 6-in. thick, 5 Ib/ft3 horizontal (150 mm thick, 80 kg/m3) CWMS should be installed in thevapor space, to reduce liquid carryover to less than 1 lb (1 kg) of liquid per 100 lb (100 kg) of gas. In addition, drums larger than3 ft (1 m) in diameter should have an inlet nozzle at each end and a single central vapor outlet nozzle. The drum and the CWMSarea for vapor flow should be sized for 100% of critical velocity at design gas flow rate. Additional design criteria are given inFigure 4.

Horizontal Separator Drums with Both Vertical and Horizontal CWMS

For clean services in which liquid carryover should be reduced to less than 1 lb (1 kg) of liquid per 100 lb (100 kg) of gas, thevapor velocity through the drum vapor space can be increased by 25% (to 125% of Vc) if two vertical and one horizontal CWMSare installed in the vapor space (see Figure 5). The drum should have an inlet nozzle at each end, terminating in either a 90°elbow or a slotted distributor, and a single central vapor outlet nozzle. A 6-in. thick, 5 Ib/ft3 (150 mm thick, 80 kg/m3), verticalCWMS should be located between each inlet nozzle and the 6 in. thick, 5 Ib/ft3 (150 mm thick, 80 kg/m3), horizontal CWMS. Thevertical CWMS should cover the area for vapor flow and should extend at least 6 in. (150 mm) below the low liquid level. Thearea for vapor flow (in the drum and through the CWMS) should be sized for 125% of critical velocity at design gas flow rate.Horizontal drums with both vertical CWMS and horizontal CWMS are smaller than horizontal drums with horizontal CWMS.However, with small low-pressure drums, the savings from the smaller diameter may be offset by the extra cost of the verticalCWMS.

Distance from Top of CWMS to Gas Outlet Nozzle

For both vertical and horizontal drums, the distance from the top of the CWMS to the gas outlet nozzle should be adequate toprevent flow maldistribution through the CWMS. The minimum distance for this purpose is given by Eq. (12a):

2dDC

h oCWMS13o

−= Eq. (12a)

where: ho = Minimum distance from top of CWMS to gas outlet nozzle, in. (mm)DCWMS = Diameter of a round CWMS, or long side of a rectangular CWMS, ft (mm)do = Outlet nozzle diameter, in. (mm)C13 = Constant = 12 for Customary units (1 for Metric units)

If this distance is impractical, a slotted gas collector (preferred choice) or a solid circular baffle located between the CWMS andthe gas outlet nozzle, should be used. If neither of these two alternatives is satisfactory, contact the Fractionation andThermodynamics Section of ER&E for a perforated plate vapor distributor.


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DESIGN PROCEDURES (Cont)With a slotted gas collector, a rectangular CWMS (Figure 9) should be used. The side branch of the collector should have thesame diameter as that of the outlet nozzle, and should extend along the long side of the CWMS. As shown in Figure 9, the slotsshould be located in the top portion of the collector pipe, at least 30° above horizontal. The slots should be sized using the orificepressure drop equation of Section XIV with a discharge coefficient of 0.6. Normal pressure drop through the slots is in the rangeof 1 to 7 in. of water (0.25 to 1.75 kPa). The minimum permissible vertical distance between the top of the CWMS and thenearest slot opening is given by the larger of the two values calculated from Eqs. (12b) and (12c):

2

sNLC

hslot

s

CWMS14

o

−

= Eq. (12b)

2)N(SC

h rslotCWMS14o

l−= Eq. (12c)

where: ho = Minimum distance from top of CWMS to near edge of slot in outlet collector, in. (mm)LCWMS = Long side of rectangular CWMS, ft (mm)Ns = Number of slots per rowSCWMS = Short side of rectangular CWMS, ft (mm)l slot = Long side of rectangular slot, in. (mm)sslot = Short side of rectangular slot, in. (mm)Nr = Number of rows of slots in gas collectorC14 = Constant = 12 Customary units (1 Metric unit)

If a solid circular baffle is used, its diameter should be 1.5 times the outlet nozzle diameter. The distance between the baffle andthe outlet nozzle should be such that the peripheral area for vapor flow between the baffle and the outlet nozzle is three times theoutlet nozzle area. (The peripheral area is equal to the product of the baffle circumference and the vertical distance from thebaffle to the top of the drum.)The minimum distance between the baffle and the top of the CWMS should be 12 in. (300 mm) or 1.5 times the outlet nozzlediameter, whichever is smaller.Specific design criteria for a vertical drum with CWMS and a side-out gas outlet nozzle are shown in Figure 10.

Design Criteria for Anti-Vortex Baffles

Design criteria of anti-vortex baffles are given below:Three evenly-distributed square tiers of subway grating should be located between the liquid outlet nozzle and the low liquidlevel. The maximum distance between two adjacent gratings should be 6 in. (150 mm). For vertical drums, the lowest gratingshould be located at a distance of half a nozzle diameter above the liquid outlet nozzle. For horizontal drums, the lowest gratingshould be located 2 in. (50 mm) above the liquid outlet nozzle.The length of the sides of each grating should be 4 times the outlet nozzle diameter or half the drum diameter, whichever issmaller.The grating should consist of parallel 1 in. x 1/8 in. (25 mm x 3 mm) bars spaced as shown in Figure 11.The minimum distance from the low liquid level to the liquid outlet nozzle is 9 in. (225 mm), or the value of hLL calculated fromEq. (13), whichever is greater.

2.0

L

G

4.015

LL

1

QCh

ρρ

−

= Eq. (13)

where: hLL = Minimum permissible height from low liquid level to liquid outlet nozzle, in. (mm)Q = Liquid discharge rate, ft3/s (dm3/s)ρG = Vapor density at conditions, lb/ft3 (kg/m3)ρL = Liquid density at conditions, lb/ft3 (kg/m3)C15 = Empirical constant - 8.4 Customary units (56 Metric units)


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DateDecember, 1999


SAMPLE PROBLEM (CUSTOMARY UNITS)(Powerformer Separator Drum)

DESIGN BASISLiquid Carryover - This is a critical service, in which liquid carryover in the drum overhead should be significantly less than 1weight %, since the overhead (recycle gas) is fed first to a drier and then to a compressor.

HOLDUP1. Ten minutes holdup between ELL (emergency liquid level) and HLL (high liquid level). See Table 1 under Special Design

Considerations for Liquid Surge and Distillate Drums.2. Fifteen minutes holdup between HLL and LLL (low liquid level) on a product feeding a subsequent tower, such as in this

service. This holdup time ranges from 5 to 15 minutes depending on the controlling process (see Table 1 and SectionXII-C, Level Measurement and Control).

FEED RATES AND PROPERTIES

Normal gas flow rate, ft3/s 212.9Vapor density at drum conditions, Ib/ft3 0.443Vapor viscosity at drum conditions, cP 0.01Liquid feed rate, gpm 1024.0Liquid density at drum conditions, Ib/ft3 46.3Liquid surface tension at drum conditions, dynes/cm 15.0

SOLUTION(See Figure A, at the end of this SAMPLE PROBLEM.)A horizontal drum with split flow (two inlet nozzles) and with either a horizontal CWMS or a combination of both vertical andhorizontal CWMS is preferred for this service. (See Horizontal Versus Vertical Separator Drums, Table 3, Horizontal SeparatorDrums With and Without Horizontal CWMS, and Horizontal Separator Drums with Both Vertical and Horizontal CWMS.)Although the arrangement of CWMS should be based on an economic comparison, a horizontal drum with only a horizontalCWMS is used in this example.Minimum Permissible Distance Between LLL and Bottom of Drum - This distance, hLL, is calculated from Eq. (13):

.in12call.;in7.11

3.46443.01

60x48.710244.8

1

Q4.8h 2.0

4.0

2.0

L

G

4.0

LL =

−

=

ρρ−

=

Vertical Height Required for Vapor Flow - The vertical height required for vapor flow must satisfy both of the following criteria:1) The normal vapor velocity in the drum vapor space ≤ 100% of Vc, and 2) The minimum permissible vertical height for vaporflow is either 20% of the drum diameter or 12 in., whichever is larger (see Figure 4 and DESIGN PROCEDURES underHorizontal Separator Drums With and Without Horizontal CWMS).The critical velocity is calculated from Eq. (1) (see DEFINITIONS).

s/ft6.1443.0

443.03.46157.0157.0V5.05.0

G

GLc =

−=

ρ

ρ−ρ=

The vertical area for vapor flow Av above ELL required to satisfy the critical velocity criteria is obtained by dividing the gas flowrate per nozzle by the critical velocity:

2v ft5.66

)2()6.1(9.212A ==

Drum Sizing - The estimate of the optimum drum size is a trial-and-error procedure. First, a drum size is assumed, then theadequacy of this drum for the service is checked. This procedure should be repeated until the drum size is optimized, since theobjective is to design the smallest drum adequate for the service.


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SAMPLE PROBLEM (CUSTOMARY UNITS) (Cont)1. First Trial - Check the adequacy of a 15-ft diameter, 45-ft long drum (length/diameter ratio of 3:1).

a. Vertical Area Between LLL and ELL (ALLL-ELL) - The required holdup time between LLL and ELL = 15 + 10 = 25minutes. Liquid holdup volume between ELL and LLL is obtained by multiplying the liquid feed rate by the holdup time:

(1024) (25) = 25,600 gal

Therefore, the vertical area required between LLL and ELL is obtained by dividing the holdup volume by the drum lengthand the gal/ft3 conversion factor:

2ELLLLL ft1.76

)45()48.7(600,25A ==− (neglecting the holdup in the drum heads)

b. Vertical Area Between LLL and Bottom of Drum (ABtm-LLL) - Use Table 5 to calculate the cross-sectional areabetween the drum bottom and LLL (ABtm-LLL) at the LLL height (hLL) of one foot.

R* = h / D = 1.0/15 = 0.06667; A* = AChord / ACircle = 0.0286

ABtm-LLL = (0.0286) (ADrum) = (0.0286) (π/4) (15)2 = (0.0286) (176.7) = 5.1 ft2

(Note: Table 5 will be used for all subsequent drum diameter and cross-sectional area ratio calculations.)c. Vertical Area Available for Vapor Flow - The vertical cross-sectional area available for flow, Av, is:

Av = ADrum – [ABtm-LLL + ALLL-ELL]

= 176.7 – [5.1 + 76.1] = 95.5 ft2

Since Av is significantly greater than the required area of 66.5 ft2, the assumed drum size is too large for this service.2. Second Trial - Check the adequacy of a 14 ft diameter, 42-ft long drum using the equations from the first trial.

2ELLLLL ft5.81

)42()48.7(600,25A ==−

R* = 1.0/14 = 0.07143; A* = 0.0317

ABtm-LLL = (0.0317)

π

4 (14)2 = (0.0317) (153.9) = 4.9 ft2

Av = 153.9 – [4.9 + 81.5] = 67.5 ft2

This is only slightly larger than the required area of 66.5 ft2. Therefore, 14 ft is an optimum diameter for this service. FigureA shows the final drum design.

Vertical Distance Between Bottom of Drum and HLL (hBtm-HLL) - The required vertical area between LLL and HLL (ALLL-HLL)is given by the following equation:

)lengthdrum()ft/gal48.7()holdup()rateliquid(A 3HLLLLL =−

2ft9.48)42()48.7()15()1024( ==


V-APage


DateDecember, 1999


SAMPLE PROBLEM (CUSTOMARY UNITS) (Cont)The vertical area required between the bottom of the drum and HLL (ABtm-HLL) is given by the following equation:

ABtm-HLL = ABtm-LLL + ALLL-HLL

= 4.9 + 48.9 = 53.8 ft2

380.0*R;3496.09.1538.53*A ===

Therefore, the vertical distance between the bottom of the drum and HLL is:

hBtm-HLL = (0.380) (14) = 5.32 ft = 64 in.

Also, to find the vertical distance between the bottom of the drum and ELL, subtract the distance from ELL to the top of the drumfrom the drum diameter:

452.0R;4386.09.1535.67A;ft5.67A 2

v ==== ∗∗

.in92ft67.7)14()452.0(14h ELLBtm ==−=−

Inlet Nozzle Selection - Either 90°-elbow or slotted distributor inlets can be used for this service (see Table 3). One should tryto use 90°-elbow inlets since they are easier to fabricate than slotted distributors. The 90°-elbow inlets will be adequate for thisservice if the mixture velocity VE is below the maximum value for which entrainment will not occur at the liquid surface.From Table 1 of DP Section XIV-B, the permissible pressure drop in the inlet line is 0.2 psi per 100 ft of line. Pressure dropcalculations with two inlet nozzles would show that two 24 in. lines satisfy this requirement. Let the inlet nozzles be line size, i.e.,24 in. diameter.VE at the exit of 90°-elbow inlets is calculated from Eq. (3c), corrected for horizontal drum application (multiplier of 2) and with aconservative assumed value of 1.0 for f.

( )

ρρ

µ

σ=−

5.0

L

Gg

4

E

f

10x3.52V

( ) ( )

( ) ( )s/ft3.16

3.46443.001.00.1

1510x3.52 5.0

4=

=−

The feed, which consists of 212.9 ft3/s vapor and 1024 gpm liquid, has a total volume flow rate of:

( ) ( ) s/ft2.21548.760

10249.212 3=+

with two 24 in. inlet nozzles, the mixture velocity Vs at the inlet is:

( ) s/ft3.34

1224

4

2/2.215V 2s =

π

=

Since the velocity in the 90°-elbow inlets greatly exceeds the maximum allowable velocity, slotted distributor inlets must be used.


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SAMPLE PROBLEM (CUSTOMARY UNITS) (Cont)Design of Slotted Distributor Inlets - Assume that:

.in24x.;in5.0sslot ==

5485.0

24s

xslot

>==

Estimate the maximum permissible mixture velocity VE at the slotted distributor exit using Eq. (3e) since x / sslot > 5:

( ) ( ) ( ) s/ft9.48

245.0

3.46443.001.0

1510x3.22

xs

10x3.22V 5.05.0

4

5.0slot

5.0

L

GG

4

E =

=

ρρµ

σ=−−

With a 24 in. pipe diameter and assuming that the slots are cut within an included angle of 120° (± 60° from horizontal), the slotlength slotl is:

slotl ( ) ( ) .in2524360120 =π

=

Therefore, the area of a slot is:

( ) ( ) 2slotslotslot .in5.12255.0sa === l

Since there is only one row of slots per distributor, the number of slots required for each inlet is:

3.25)9.48()144/5.12()2/1()/sft2.215(

VaQN

3

Eslot

Ms ===

Use 26 slots, with 13 slots in each branch of the distributor. With a distance between adjacent slots of one in., the requiredslotted distributor length is 65.5 in. (Figure A), assuming that the inlet nozzle has a wall thickness of 0.25 in.Check the width of the vapor space for mounting the slotted distributors. Using Table 5, the chord length available for theinstallation of a 24-in. diameter slotted distributor at a level 6 in. above the emergency liquid level is 12.5 ft, which is more thanadequate.CWMS Design - The CWMS is based on 100% of critical velocity.

2ft1336.1

9.212areaCWMS ==

Use a 6-in. thick, 5 Ib/ft3 CWMS (see DESIGN PROCEDURES under Horizontal Separator Drums With and Without HorizontalCWMS.)Assume a square CWMS. Its width is then:

CWMS side = (133)0.5 = 11.5 ft = 138 in.

The minimum permissible distance ho between the top of the CWMS and the gas outlet nozzle is obtained from Eq. (12a), andassuming that the outlet nozzle diameter is 30 in.:

.in542

301382

dD12h oCWMSo =−=−=

Locate the top of the CWMS 54 in. below the outlet nozzle (Figure A).


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DateDecember, 1999


SAMPLE PROBLEM (CUSTOMARY UNITS) (Cont)The vertical distance available between the bottom of the CWMS and the ELL (hCWMS-ELL) is:

hCWMS-ELL = (DDrum – hBtm-ELL) – (ho + CWMS thickness)

= (168 – 92) – (54 + 6) = 16 in.

This exceeds the required minimum of 12 in., for preventing excessive splashing into the CWMS.Check the adequacy of the vapor space for mounting a 138 in. square CWMS 54 in. below the vapor outlet nozzle. Using Table5, one finds that the chord length at a level 54 in. below the gas outlet nozzle is 13.1 ft. This is more than adequate for the 138in. wide CWMS.Design of Anti-Vortex Baffles - Assume that the liquid outlet is an 8 in. nozzle. Three square tiers of subway gratings should beused. The length of the sides of each grating should be 32 in. (four times the liquid outlet nozzle diameter). The bottom of thelowest, intermediate and top gratings should be located at 2, 6.5 and 11 in. above the liquid outlet nozzle, respectively.

SAMPLE PROBLEM (METRIC UNITS)(Powerformer Separator Drum)

DESIGN BASISLiquid Carryover - This is a critical service, in which liquid carryover in the drum overhead should be significantly less than 1weight %, since the overhead (recycle gas) is fed first to a drier and then to a compressor.

HOLDUP1. Ten minutes holdup between ELL (emergency liquid level) and HLL (high liquid level). See Table 1 under Special Design

Considerations for Liquid Surge and Distillate Drums.2. Fifteen minutes holdup between HLL and LLL (low liquid level) on a product feeding a subsequent tower, such as in this

service. This holdup time ranges from 5 to 15 minutes depending on the controlling process (see Table 1 and SectionXII-C, Level Measurement and Control).

FEED RATES AND PROPERTIES

Normal gas flow rate, dm3/s 6030.0Vapor density at drum conditions, kg/m3 7.10

Vapor viscosity at drum conditions, mPa•s 0.01

Liquid feed rate, dm3/s 65.0Liquid density at drum conditions, kg/m3 742.0Liquid surface tension at drum conditions, mN/m 15.0

SOLUTION(See Figure A, at the end of this SAMPLE PROBLEM.)A horizontal drum with split flow (two inlet nozzles) and with either a horizontal CWMS or a combination of both vertical andhorizontal CWMS is preferred for this service. (See Horizontal Versus Vertical Separator Drums, Table 3, Horizontal SeparatorDrums With and Without Horizontal CWMS, and Horizontal Separator Drums with Both Vertical and Horizontal CWMS.)Although the arrangement of CWMS should be based on an economic comparison, a horizontal drum with only a horizontalCWMS is used in this example.Minimum Permissible Distance Between LLL and Bottom of Drum - This distance, hLL, is calculated from Eq. (13):

( ) mm300call;mm298

7421.71

6556

1

Q56h 2.0

4.0

2.0

L

G

4.0

LL =

−

=

ρρ−

=

Vertical Height Required for Vapor Flow - The vertical height required for vapor flow must satisfy both of the following criteria:1) The normal vapor velocity in the drum vapor space ≤ 100% of Vc, and 2) The minimum permissible vertical height for vaporflow is either 20% of the drum diameter or 300 mm, whichever is larger (see Figure 4 and DESIGN PROCEDURES underHorizontal Separator Drums With and Without Horizontal CWMS.)


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SAMPLE PROBLEM (METRIC UNITS) (Cont)The critical velocity is calculated from Eq. (1) (see DEFINITIONS).

m/s49.01.7

1.7742048.0048.0V5.05.0

G

GLc =

−=

ρ

ρ−ρ=

The vertical area for vapor flow Av above ELL required to satisfy the critical velocity criteria is obtained by dividing the gas flowrate per nozzle by the critical velocity:

( ) ( )( ) ( )

233

v m15.62m/s49.010/sdm6030A ==

−

Drum Sizing - The estimate of the optimum drum size is a trial-and-error procedure. First, a drum size is assumed, then theadequacy of this drum for the service is checked. This procedure should be repeated until the drum size is optimized, since theobjective is to design the smallest drum adequate for the service.1. First Trial - Check the adequacy of a 4600-mm diameter, 13,800-mm long drum (length/diameter ratio of 3:1).

a. Vertical Area Between LLL and ELL (ALLL-ELL) - The required holdup time between LLL and ELL = 15 + 10 = 25minutes. Liquid holdup volume between ELL and LLL is obtained by multiplying the liquid feed rate by the holdup time:

(65 dm3/s) (25 min) (60 s/min) = 97,500 dm3

Therefore, the vertical area required between LLL and ELL is obtained by dividing the holdup volume by the drum lengthand the appropriate conversion factor:

heads) drum thein holduptheg(neglectinm07.7)10()mm800,13()10()dm500,97(A 2

3

33

ELLLLL == −

−

−

b. Vertical Area Between LLL and Bottom of Drum (ABtm LLL) - Use Table 5 to calculate the cross-sectional areabetween the drum bottom and LLL (ABtm-LLL) at the LLL height (hLL) of 300 mm.

R* = h / D = 300 / 4600 = 0.0652; A* = AChord / ACircle = 0.0278

222DrumLLLBtm m46.0)m62.16()0278.0()m6.4(

4)0278.0()A()0278.0(A ==

π==−

(Note: Table 5 will be used for all subsequent drum diameter and cross-sectional area ratio calculations.)c. Vertical Area Available for Vapor Flow - The vertical cross-sectional area available for flow, Av, is:

Av = ADrum – [ABtm-LLL + ALLL-ELL] = 16.62 – [0.46 + 7.07] = 9.09 m2

Since Av is significantly greater than the required area of 6.15 m2, the assumed drum size is too large for this service.2. Second Trial - Check the adequacy of a 4300 mm diameter, 12,900 mm long drum using the equations from the first trial.

23

33

ELLLLL m56.7)10()mm900,12()10()dm500,97(A == −

−

−

R* = 300 / 4300 = 0.0698; A* = 0.0307

223LLLBtm m45.0)52.14()0307.0()10x4300(

4)0307.0(A ==

π= −

−

Av = 14.52 – [0.45 + 7.56] = 6.51 m2 vs. 6.15 m2 required

A third trial, assuming D = 4200 mm, yields Av = 5.68 m2. Therefore, 4300 mm is an optimum diameter for this service. Figure Ashows the final drum design.


V-APage


DateDecember, 1999


SAMPLE PROBLEM (METRIC UNITS) (Cont)Vertical Distance Between Bottom of Drum and HLL (hBtm-HLL) - The required vertical area between LLL and HLL (ALLL-HLL)is given by the following equation:

23

HLLLLL m53.4)m9.12(

)s900()/sm065.0()lengthdrum(

)holdup()rateliquid(A ===−

The vertical area required between the bottom of the drum and HLL (ABtm-HLL) is given by the following equation:

2HLLLLLLLLBtmHLLBtm m98.453.445.0AAA =+=+= −−−

375.0R;343.052.1498.4A === ∗∗

Therefore, the vertical distance between the bottom of the drum and HLL is:

hBtm-HLL = (0.375) (4300) = 1612 mm; = call 1610 mm

Also, to find the vertical distance between the bottom of the drum and ELL, subtract the distance from ELL to the top of the drumfrom the drum diameter:

459.0R;448.052.1451.6A;m51.6A 2

v ==== ∗∗

hBtm-ELL = 4300 – (0.459) (4300) = 2326 mm = call 2330 mm

Inlet Nozzle Selection - Either 90° -elbow or slotted distributor inlets can be used for this service (see Table 3). One should tryto use 90° -elbow inlets since they are easier to fabricate than slotted distributors. The 90° -elbow inlets will be adequate for thisservice if the mixture velocity VE is below the maximum value for which entrainment will not occur at the liquid surface.From Table 1 of DP Section XIV-B, the permissible pressure drop in the inlet line is 0.045 kPa per meter of line. Pressure dropcalculations with two inlet nozzles would show that two 600 mm lines satisfy this requirement. Let the inlet nozzles be line size,i.e., 600 mm diameter.VE at the exit of 90° -elbow inlets is calculated from Eq. (3c), corrected for horizontal drum application (multiplier of 2) and with aconservative assumed value of 1.0 for f.

5.0

L

GG

4

E

f

)10x6.1()2(V

ρρ

µ

σ=−

m/s0.5

7421.7)01.0()0.1(

)15()10x6.1()2(5.0

4=

=−

The feed, which consists of 6030 dm3/s vapor and 65 dm3/s liquid, has a total volume flow rate of:

QM = 6030 + 65 = 6095 dm3/s = 6.095 m3/s

with two 600-mm inlet nozzles, (inside diameter = 574.7 mm) the mixture velocity Vs at the inlet is:

m/s7.11)m5747.0(

4

)/sm095.6()5.0(V2

3

s =

π

=

Since the velocity in the 90° -elbow inlets greatly exceeds the maximum allowable velocity, slotted distributor inlets must be used.


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SAMPLE PROBLEM (METRIC UNITS) (Cont)Design of Slotted Distributor Inlets - Assume that:

sslot = 15 mm; x = 600 mm

54015600

sxslot

>==

Estimate the maximum permissible mixture velocity VE at the slotted distributor exit using Eq. (3e) since x / sslot > 5:

m/s6.13

60015

7421.701.0

)15()10x0.7()2(

xs

)10x0.7()2(V 5.05.0

5

5.0slot

5.0

L

GG

5

E =

=

ρρµ

σ=−−

With a 600 mm pipe (diameter = 574.7 mm) and assuming that the slots are cut within an included angle of 120° (± 60° fromhorizontal), the slot length slotl is:

( ) ( ) mm6027.574360120

slot =π

=l

Therefore, the area of a slot is:

aslot = sslot slotl = (15) (602) = 9030 mm2 = 0.00903 m2

Since there is only one row of slots per distributor, the number of slots required for each inlet is:

slots8.24)m/s6.13()m00903.0(

)2/1()/sm095.6(Va

QN 2

3

Eslot

Ms ===

Use 26 slots, with 13 slots in each branch of the distributor. With a distance between adjacent slots of 25 mm, the requiredslotted distributor length is 1700 mm (Figure A), assuming that the inlet nozzle has an outside diameter of 610 mm.Check the width of the vapor space for mounting the slotted distributors. Using Table 5, the chord length available for theinstallation of a 610 mm diameter slotted distributor at a level 150 mm above the emergency liquid level is 4250 mm, which ismore than adequate.CWMS Design - The CWMS area is based on 100% of critical velocity.

23

m31.12m/s49.0

/sm030.6areaCWMS ==

Use a 150-mm thick, 80 kg/m3 CWMS (see DESIGN PROCEDURES under Horizontal Separator Drums With and WithoutHorizontal CWMS.)Assume a square CWMS. Its width is then:

CWMS side = (12.31)0.5 = 3.51 m = 3510 mm

The minimum permissible distance ho between the top of the CWMS and the gas outlet nozzle is obtained from Eq. (12a), andassuming that the outlet nozzle diameter is a nominal 750 mm (O.D. = 762 mm):

mm13742

76235102

dDh oCWMSo =−=−=

Locate the top of the CWMS 1380 mm below the outlet nozzle (Figure A).The vertical distance available between the bottom of the CWMS and the ELL (hCWMS-ELL) is:

hCWMS-ELL = (DDrum – hBtm ELL) – (ho + CWMS thickness) = (4300 – 2330) – (1380 + 150) = 440 mm

This exceeds the required minimum of 300 mm for preventing excessive splashing into the CWMS.


V-APage


DateDecember, 1999


SAMPLE PROBLEM (METRIC UNITS) (Cont)Check the adequacy of the vapor space for mounting a 3510 mm square CWMS 1380 mm below the vapor outlet nozzle. UsingTable 5, one finds that the chord length at a level 1374 mm below the gas outlet nozzle is 4016 mm. This is more than adequatefor the 3510 mm wide CWMS.Design of Anti-Vortex Baffles - Assume that the liquid outlet is a 200 mm nozzle. Three square tiers of subway gratings shouldbe used. The length of the sides of each grating should be 800 mm (four times the liquid outlet nozzle diameter). The bottom ofthe lowest, intermediate and top gratings should be located at 50, 165 and 280 mm above the liquid outlet nozzle, respectively.

FIGURE ASAMPLE PROBLEM (POWERFORMER SEPARATOR DRUM)

��

Anti-vortex Baffles

8 in. φ (200 mm)

32 in.(800 mm) LLL

12 in. (300 mm)

HLL

ELL

120°Slot

Angle

6 in. (150 mm)

24 in. (600 mm) φ 30 in. (750 mm) φ

138 in.(3510 mm)

24 in. (600 mm)Minimum

6 in. (150 mm) Minimum

24 in. (600 mm)

0.5 in. (15 mm)

1 in. (25 mm) DistributorDetail

1 in. (25 mm)

1 in. (25 mm)

24 in.(600 mm)

DP5AFa

168 in.(4300 mm)

64 in.(1610 m)

Note:(1) Some of the metric values don't agree with their corresponding customary values because the entire sample problem was

carried out in both customary and metric units.

42 ft (12900 mm)

92 in.(2330 mm)

54 in. (1380 mm)

16 in. (440 mm)

65.5 in. (1700 mm)

20.75 in. (550 mm)20.75 in. (550 mm)

Section A-A

A

A


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NOMENCLATUREAv = Cross-sectional area for vapor flow, ft2 (m2)aslot = Flow area of a slot in gas collector or distributor, in.2 (mm2)C = Liquid carryover in drum overhead, Ib/h (kg/s) [see Eq. (2)]CI to C15 = Constants used for equations given under DEFINITIONS and DESIGN PROCEDURESCT = Annular ring configuration factor, dimensionlessD = Drum diameter, ft (mm)DCWMS = Diameter of circular CWMS, ft (mm)dh = Hole diameter, in. (mm)do = Outlet nozzle diameter or chimney width in chimney tray, in. (mm)dp = Inlet nozzle or pipe diameter, in. (mm)E = Separation efficiency, % [see Eq. (2)]F = Liquid feed rate to drum Ib/h (kg/s) [see Eq. (2)]f = Jet velocity dissipation factor given in Figure 7, dimensionless

f(σ,µ) = ( ) essdimensionl,5.0STD

STD

σσσ−σ

h = Distance from bottom of inlet nozzle to high liquid level (HLL), in. (mm)hLL = Minimum permissible height from low liquid level to liquid outlet nozzle, in. (mm)hT = Minimum permissible distance from drum head to side-out outlet nozzle, in. (mm) (see Figure 10)ho = Minimum permissible distance from top of CWMS to gas outlet nozzle (or to near edge of slot in outlet

collectors), in. (mm)Kσµ = Surface tension - viscosity parameter, dimensionlessL = Drum length, ft (mm) (shown in various figures)LL = Maximum liquid loading, gpm/ft2 (dm3/s/m2)LCWMS = Length of long side of rectangular CWMS, ft (mm)

slotl = Long side of rectangular slot, in. (mm)n = Vortex exponent, dimensionlessNr = Number of rows of slots in gas collectorNs = Number of slots per row in gas collector or distributorQ = Liquid discharge rate, ft3/s (dm3/s).QM = Mixture rate per inlet nozzle, ft3/s (dm3/s)SCWMS = Short side of rectangular CWMS, ft (mm)sslot = Short side of rectangular slot, in. (mm)VE = Maximum mixture velocity at the exit of the inlet nozzle, such that entrainment will not occur at the liquid

surface, ft/s (m/s)VI = Mixture velocity in the inlet piping, below which velocity liquid drops are not entrained in annular pipe flow, ft/s

(m/s)VC = Critical velocity, ft/s (m/s)VC,ACTUAL(%) = Actual percent of critical velocity at maximum gas flow rate, %VC,MAX(%) = Maximum allowable percent of critical velocity at maximum gas flow rate, %VG = Superficial vapor velocity, ft/s (m/s)Vs = Superficial velocity of mixture in the inlet piping, ft/s (m/s)x = Distance from the inlet nozzle to the impinging surface, in. (mm) (see Figure 7). For vertical drums with flush

inlets, x is the drum diameter. x is equal to h for vertical drums with either slotted (or holed) distributors, or 90°elbows. For horizontal drums with either 90° elbows or slotted (or holed) distributors, x is the distance from theinlet nozzle to the near head of the drum.

W = CWMS support ring width, ft (mm)ρG = Vapor density at conditions, Ib/ft3 (kg/m3)ρL = Liquid density at conditions, Ib/ft3 (kg/m3)σ = Liquid surface tension at conditions, dynes/cm (mN/m)σSTD = Standard surface tension, dynes/cm (mN/m)µG = Vapor viscosity at conditions, cP (mPa•s)µL = Liquid viscosity at conditions, cP (mPa•s)


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DateDecember, 1999


COMPUTER PROGRAMS➧ For up-to-date information on available programs and how to use them, affiliate personnel should contact their SEPARATION

SPECIALIST. A site's TECHNICAL COMPUTING CONTACT can also provide help on accessing available programs. There areseveral programs in the PEGASYS system for PC technical programs that are useful for design or rating of drums. Theseinclude:

PROGRAM NAME FUNCTION VERSION NUMBER

Horizontal Drum Design & Rating Designs and rates horizontal separation drums for thefollowing services: General, Distillate, CompressorFeed, Steam, High Pressure Separators (HPS), andHPS - RESIDFINER service.

5.0

Vertical Drum Design & Rating Designs and rates vertical vapor-liquid separatordrums, with and without CWMS, for General andSteam services.

5.0

Segment of Circle Given circle diameter (or area) and either rise, chordlength, segment area, or subtended angle; thisprogram calculates the missing variables.

5.0

Drum Volume Calculates the liquid volume in a drum given the liquidlevels.

5.0


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TABLE 1TYPICAL DESIGN CRITERA FOR VARIOUS SERVICES

DESIGN PARAMETER

FEED SEPARATORDRUMS FOR AMINE

SCRUBBERSHIGH-PRESSURE

SEPARATORSHORIZONTAL CRUDE

FLASH DRUMVERTICAL CRUDE

FLASH DRUM

Normal Drum Position Vertical Horizontal Horizontal VerticalAllowable VaporVelocity, % of Vc + Without CWMS 100 + With CWMS(1) 100(2) 100-125(2) 40 40Liquid Holdup The greater of:

1. Equal to or greaterthan the volume ofa 50 ft (15 m) slugof liquid in the inletpiping.

2. Ten minutesholdup based onthe largest liquidspill from upstreamunits.

Adequate for completeseparation of 220 µmbubbles based onsettling (rising) rateequations given inSection V-B.Minimum height at lowliquid level = 18 in.(450 mm).

Liquid holdup at NLLshould be 5 minutes.Minimum vertical heightin the vapor spaceabove the HLL shouldbe 25% of the drumdiameter. The minimumholdup time between theHLL and NLL is 1minute.Minimum height andholdup time between thebottom of the drum andthe LLL is 3 ft (900 mm)and 2 minutes,respectively.

Liquid holdup at NLLshould be 5 minutes.The minimum holduptime between the HLLand NLL is 1 minute.Minimum height andholdup time between thebottom of the Drum andthe LLL is 3 ft (900 mm)and 2 minutes,respectively.

Type of Nozzle Inlet(Vapor/Liquid)

Slotted tee distributor Slotted tee distributor(split flow)

Slotted tee distributor Horizontal tangentialwith annular ring

Outlet (Vapor) Flush Flush Flush FlushOutlet (Liquid) Flush Flush Flush FlushSpecial Considerations See MEA Scrubber

Feed Separator Drumsunder DESIGNCONSIDERATIONSFOR SELECTEDSERVICES.

See High-PressureSeparators underDESIGNCONSIDERATIONSFOR SELECTEDSERVICES.

See Crude PreheatFlash Drums underDESIGNCONSIDERATIONSFOR SELECTEDSERVICES.

See Crude PreheatFlash Drums underDESIGNCONSIDERATIONSFOR SELECTEDSERVICES.

Notes:(1) CWMS should not be used in dirty services.(2) See DESIGN CONSIDERATIONS FOR SELECTED SERVICES and DESIGN PROCEDURES for the specific type of drum.(3) Measured between the low liquid level in the drum and a point one pipe diameter below the inlet nozzle.


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DateDecember, 1999


TABLE 1TYPICAL DESIGN CRITERA FOR VARIOUS SERVICES (Cont)

DESIGN PARAMETERLIQUID SURGE DRUMS,

DISTILLATE DRUMS

COMPRESSOR SUC-TION, COMPRESSOR

INTERSTAGE, AND GASTURBINE FUEL (GAS)

DRUMSFUEL GAS SEPARATOR

DRUMS STEAM DRUMS

Normal Drum Position Horizontal Vertical Vertical Vertical or HorizontalAllowable VaporVelocity, % of Vc + Without CWMS + With CWMS(1) 100- 125(2) 100-225(2) 100(2) 100(2)

Liquid Holdup The greater of:1. Water settling

requirements (belowlow oil level).

2. Minimum instrumentdimensions given inSection XII-C, LevelMeasurement andControl.

3. Holdup requirement forthe controlling processgiven in Section XII-C,Level Measurementand Control.

4. Inventory requirementsfor startup, shutdown,makeup, etc.

Ten minutes liquid spillfrom the largest singleproducing unit ahead ofthe compressor.(3)

When taking suctionfrom absorbers, 5minutes based on totallean oil circulationrate.(3)

For closed looprefrigeration systems,see Section XII-C,Level Measurement andControl under Figure16, Case 14.

For interstage separatordrums, 10 minutesbased on maximuminterstage condensateproduction rate shouldbe provided betweenHLL and the high levelcut out located at a pointone pipe diameter belowthe inlet nozzle

Equal to or greater thanthe volume of a 50 ft(15 m) slug ofcondensate in theadjacent fuel header.(3)

Following an absorber,5 minutes on total leanoil circulation rate.(3)

One-third the volume ofthe steam generatorand piping or 2 minutesbased on feedwaterrate, whichever isgreater.

If damage can occurdue to loss of water insevere services suchas Flexicracker orFlexicoker flue gascoolers or hydrogenreformer effluent steamgenerators, additionalholdup should beprovided. Recentdesigns have provided5 to 10 minutes holdupin the control rangebetween high and lowliquid levels and a totalholdup in the range of15 to 45 minutesbetween low level cutoff and emergency highlevel.

Type of Nozzle Inlet(Vapor/Liquid)

90° elbow or slotted teedistributor

Slotted tee distributor Slotted tee distributor One slotted teedistributor (verticaldrum). Two slotted teedistributors or two 90°elbows with split flow(horizontal drum).

Outlet (Vapor) Flush Flush Flush FlushOutlet (Liquid) Flush or straight extension Flush Flush FlushSpecial Considerations If the drum feeds a com-

pressor or a fuel gas sys-tem, an additional 10minutes holdup based oncondensate rate should beprovided between HLLand a point 6 in. (150 mm)below the lower edge ofthe inlet nozzle. Thevapor space in this caseshould be sized inaccordance with com-pressor suction drumcriteria.

See CompressorSuction, CompressorInterstage, and GasTurbine Fuel (Gas)Separator Drums underDESIGNCONSIDERATIONSFOR SELECTEDSERVICES.

See Fuel GasSeparators Ahead ofFurnaces and Fuel GasCentral CollectionDrums under DESIGNCONSIDERATIONSFOR SELECTEDSERVICES. Also seeSection XV-B, Mini-mizing the Risks of Fire,Explosion or Accidentunder Preventing Entryof Fuel Gas Condensateinto Furnaces.

See Steam Drumsunder DESIGNCONSIDERATIONSFOR SELECTEDSERVICES.


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EXXONENGINEERING


TABLE 2AREAS AND VOLUMES OF CYLINDRICAL VESSELS (CUSTOMARY UNITS)

CYLINDRICAL PART OF VESSEL 2:1 ELLIPSOIDAL HEADS (EACH)VESSELDIAMETER AREA ft2 VOLUME

ft in. SURFACE*CROSS-

SECTIONALVOLUME*GALLONS

SURFACEAREA, ft2 ft3 GALLONS BARRELS

1 0 3.14 0.79 5.88 1.08 0.13 0.98 0.026 4.71 1.77 13.2 2.44 0.44 3.30 0.08

2 0 6.28 3.14 23.5 4.34 1.05 7.83 0.196 7.85 4.91 36.7 6.78 2.05 15.3 0.36

3 0 9.42 7.07 52.9 9.76 3.53 26.4 0.636 11.0 9.62 72.0 13.3 5.61 42.0 1.00

4 0 12.6 12.6 94.0 17.3 8.38 62.7 1.496 14.1 15.9 119.0 22.0 11.9 89.2 2.13

5 0 15.7 19.6 146.9 27.1 16.4 122.4 2.916 17.3 23.8 177.7 32.8 21.8 162.9 3.88

6 0 18.8 28.3 211.5 39.0 28.3 211.5 5.046 20.4 33.2 248.2 45.8 35.9 268.9 6.40

7 0 22.0 38.5 287.9 53.1 44.9 335.9 8.006 23.6 44.2 330.5 61.0 55.2 413.1 9.84

8 0 25.1 50.3 376.0 69.4 67.0 501.3 11.96 26.7 56.7 424.5 78.3 80.4 601.4 14.3

9 0 28.3 63.6 475.9 87.8 95.4 713.8 17.06 29.8 70.9 530.2 97.8 112.2 839.5 20.0

10 0 31.4 78.5 587.5 108.4 130.9 979.2 23.36 33.0 86.6 647.4 119.5 151.5 1,134 27.0

11 0 34.6 95.0 710.9 131.2 174.2 1,303 31.06 36.1 103.9 777.0 143.4 199.1 1,489 35.5

12 0 37.7 113.1 846.0 156.1 226.2 1,692 40.36 39.3 122.7 918.0 169.4 255.7 1,912 45.5

13 0 40.8 132.7 992.9 183.2 287.6 2,151 51.26 42.4 143.1 1,071 197.6 322.1 2,409 57.4

14 0 44.0 153.9 1,152 212.5 359.2 2,687 64.06 45.6 165.1 1,235 227.9 399.1 2,985 71.1

15 0 47.1 176.7 1,322 243.9 441.8 3,305 78.16 48.7 188.7 1,412 260.4 487.5 3,646 86.8

16 0 50.3 201.1 1,504 277.5 536.2 4,011 95.56 51.8 213.8 1,600 295.1 588.0 4,399 104.7

17 0 53.4 227.0 1,698 313.3 643.1 4,811 114.66 55.0 240.5 1,799 332.0 701.5 5,248 125.0

18 0 56.5 254.5 1,904 351.2 763.4 5,711 136.06 58.1 268.8 2,011 371.0 828.8 6,200 147.6

19 0 59.7 283.5 2,121 391.3 897.8 6,716 159.96 61.3 298.6 2,234 412.2 970.6 7,261 172.9

20 0 62.8 314.2 2,350 433.6 1,047 7,834 186.56 64.4 330.1 2,469 455.6 1,128 8,436 200.9

21 0 66.0 346.4 2,591 478.0 1,212 9,066 215.96 67.5 363.1 2,716 501.1 1,301 9,732 231.7

22 0 69.1 380.1 2,844 524.7 1,394 10,430 248.36 70.7 397.6 2,974 548.8 1,491 11,150 265.6

23 0 72.3 415.5 3,108 573.4 1,593 11,910 283.76 73.8 433.7 3,245 598.6 1,699 12,710 307.6

24 0 75.4 452.4 3,384 624.4 1,810 13,540 322.36 77.0 471.4 3,527 650.7 1,925 14,400 342.9

25 0 78.5 490.9 3,672 677.5 2,045 15,300 364.3

* Per foot of vessel straight side.


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DateDecember, 1999


TABLE 2AAREAS AND VOLUMES OF CYLINDRICAL VESSELS (METRIC UNITS)

CYLINDRICAL PART OF VESSEL 2:1 ELLIPSOIDAL HEAD(1)

DRUMDIAMETER, mm

SURFACEAREA,(2) m2

CROSS-SECTIONALAREA, m2

VOLUME,(2)m3

SURFACEAREA, m2

VOLUME,m3

300 0.94 0.071 0.071 0.098 0.004400 1.25 0.126 0.126 0.173 0.008500 1.57 0.196 0.196 0.271 0.016600 1.88 0.283 0.283 0.390 0.028700 2.19 0.385 0.385 0.531 0.045800 2.51 0.503 0.503 0.694 0.067900 2.827 0.636 0.636 0.878 0.095

1000 3.14 0.785 0.785 1.08 0.1311100 3.46 0.950 0.950 1.31 0.1741200 3.77 1.13 1.13 1.56 0.2261300 4.08 1.33 1.33 1.83 0.2881400 4.40 1.54 1.54 2.12 0.3591500 4.71 1.77 1.77 2.44 0.4421600 5.03 2.01 2.01 2.78 0.5361700 5.34 2.27 2.27 3.13 0.6431800 5.65 2.54 2.54 3.51 0.7631900 5.97 2.84 2.84 3.91 0.8982000 6.28 3.14 3.14 4.33 1.052100 6.80 3.46 3.46 4.78 1.212200 6.91 3.80 3.80 5.25 1.392300 7.23 4.15 4.15 5.73 1.592400 7.54 4.52 4.52 6.24 1.812500 7.85 4.91 4.91 6.77 2.052600 8.17 5.31 5.31 7.33 2.302700 8.48 5.73 5.73 7.90 2.582800 8.80 6.16 6.16 8.50 2.872900 9.11 6.61 6.61 9.12 3.193000 9.42 7.07 7.07 9.76 3.533200 10.05 8.04 8.04 11.10 4.293400 10.68 9.08 9.08 12.53 5.143600 11.31 10.18 10.18 14.05 6.113800 11.94 11.34 11.34 15.65 7.184000 12.56 12.56 12.56 17.34 8.384200 13.19 13.85 13.85 19.12 9.704400 13.82 15.21 15.21 20.99 11.154600 14.45 16.62 16.62 22.94 12.744800 15.08 18.10 18.10 24.98 14.485000 15.71 19.63 19.63 27.10 16.365200 16.34 21.24 21.24 29.31 18.415400 16.96 22.90 22.90 31.61 20.615600 17.59 24.63 24.63 34.00 22.995800 18.22 26.42 26.42 36.47 25.546000 18.85 28.27 28.27 39.02 28.276200 19.48 30.19 30.19 41.67 31.206400 20.11 32.17 32.17 44.40 34.316600 20.73 34.21 34.21 47.22 37.636800 21.36 36.32 36.32 50.12 41.167000 21.99 38.48 38.48 53.11 44.907200 22.62 40.72 40.72 56.19 48.867400 23.25 43.01 43.01 59.36 53.047600 23.88 45.36 45.36 62.61 57.467800 24.50 47.78 47.78 65.95 62.128000 25.13 50.27 50.27 69.38 67.02

Notes:(1) Each head.(2) Per meter of straight side.


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TABLE 3RECOMMENDED INLET NOZZLE TYPES FOR SPECIFIC SERVICES

SEPARATOR DRUM TYPE APPLICATION TYPE OF INLET NOZZLE

Vertical • All drums with CWMS. Slotted tee distributor.

• When bubble flow regime is present inthe inlet piping.

Slotted tee distributor.(1)

• When slug flow regime is present in theinlet piping.

Slotted tee distributor or tangential inletnozzle with annular ring.(1)

• When high liquid separation efficiency isrequired and a CWMS cannot be used.

Tangential inlet nozzle with annular ring.

Horizontal • Drums with CWMS. A slotted tee distributor or 90° elbow at eachend of drum. These inlets should pointtoward the nearer head.

• Drums without CWMS Slotted distributor(s) or 90° elbow(s) pointingtoward the nearer head.

Note:(1) A horizontal drum is preferred for this flow regime if sufficient plot area is available.


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DateDecember, 1999


TABLE 4DIMENSIONS OF 90°°°° STANDARD WELDING

ELBOWS AS A FUNCTION OF NOMINAL PIPE SIZE

Center-To-EndDistance

DP5AT4

NOMINALCENTER-TO-END DISTANCE, in. (mm)

PIPE SIZE, in. (mm) Long-Radius Elbows Short-Radius Elbows

1122334568

1012141618202224

1/2

1/2

1/2

(25)(40)(50)(65)(80)(90)

(100)(125)(150)(200)(250)(300)(350)(400)(450)(500)(550)(600)

123345679

121518212427303336

1/4(38)(57)(76)(95)

(114)(133)(152)(191)(229)(305)(381)(457)(533)(610)(686)(762)(838)(914)

1/2

1/4

3/41/2

1/2

1122334568

1012141618202224

1/2

1/2

1/2

(25)(38)(51)(64)(76)(89)

(102)(127)(152)(203)(254)(305)(356)(406)(457)(508)(559)(610)


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EXXONENGINEERING


R* =Chord Height

Diameter =hD

A* =Achord

Acircle=

θ – sin θ2π

; θ = 2 cos–1 (1-2R* ) , θ in Radians

L* =Chord Length

Diameter =lD

= sinθ2

= sin cos–1 (1–2R*)

��

Diameter, D

Chord Length, l

θ2

Chord Height, h

Chord Area

DP5AT5

TABLE 5CHORD LENGTHS AND SEGMENT AREAS VS. CHORD HEIGHTS

R✶ L✶ A✶ R✶ L✶ A✶ R✶ L✶ A✶ R✶ L✶ A✶ R✶ L✶ A✶ R✶ L✶ A✶

0.030 0.341 0.0087 0.090 0.572 0.0446 0.150 0.714 0.0941 0.210 0.815 0.153 0.255 0.872 0.201 0.340 0.947 0.3000.031 0.347 0.0092 0.091 0.575 0.0453 0.151 0.716 0.0950 0.211 0.816 0.154 0.256 0.873 0.202 0.342 0.949 0.3020.032 0.352 0.0096 0.092 0.578 0.0460 0.152 0.718 0.0959 0.212 0.817 0.155 0.257 0.874 0.203 0.344 0.950 0.3050.033 0.357 0.0101 0.093 0.581 0.0468 0.153 0.720 0.0968 0.213 0.819 0.156 0.258 0.875 0.204 0.346 0.951 0.3070.034 0.362 0.0105 0.094 0.584 0.0475 0.154 0.722 0.0977 0.214 0.820 0.157 0.259 0.876 0.205 0.348 0.953 0.3090.035 0.368 0.0110 0.095 0.586 0.0483 0.155 0.724 0.0986 0.215 0.822 0.158 0.260 0.877 0.207 0.350 0.954 0.3120.036 0.373 0.0115 0.096 0.589 0.0490 0.156 0.726 0.0996 0.216 0.823 0.159 0.262 0.879 0.209 0.355 0.957 0.3180.037 0.378 0.0119 0.097 0.592 0.0498 0.157 0.728 0.1005 0.217 0.824 0.160 0.264 0.882 0.2110.038 0.382 0.0124 0.098 0.595 0.0505 0.158 0.729 0.1014 0.218 0.826 0.161 0.266 0.884 0.213 0.360 0.960 0.3240.039 0.387 0.0129 0.099 0.597 0.0513 0.159 0.731 0.1023 0.219 0.827 0.162 0.268 0.886 0.216 0.365 0.963 0.3300.040 0.392 0.0134 0.100 0.600 0.0520 0.160 0.733 0.1033 0.220 0.828 0.163 0.270 0.888 0.218 0.370 0.966 0.3360.041 0.397 0.0139 0.101 0.603 0.0528 0.161 0.735 0.1042 0.221 0.830 0.164 0.272 0.890 0.220 0.375 0.968 0.3430.042 0.401 0.0144 0.102 0.605 0.0536 0.162 0.737 0.1051 0.222 0.831 0.165 0.274 0.892 0.2220.043 0.406 0.0149 0.103 0.608 0.0544 0.163 0.739 0.1061 0.223 0.833 0.166 0.276 0.894 0.225 0.380 0.971 0.3490.044 0.410 0.0155 0.104 0.611 0.0551 0.164 0.741 0.1070 0.224 0.834 0.167 0.278 0.896 0.227 0.385 0.973 0.3550.045 0.415 0.0160 0.105 0.613 0.0559 0.165 0.742 0.1080 0.225 0.835 0.168 0.280 0.898 0.229 0.390 0.975 0.3610.046 0.419 0.0165 0.106 0.616 0.0567 0.166 0.744 0.1089 0.226 0.836 0.169 0.282 0.900 0.231 0.395 0.978 0.3670.047 0.423 0.0171 0.107 0.618 0.0575 0.167 0.746 0.1099 0.227 0.838 0.171 0.284 0.902 0.2340.048 0.428 0.0176 0.108 0.621 0.0583 0.168 0.748 0.1108 0.228 0.839 0.172 0.286 0.904 0.236 0.400 0.980 0.3740.049 0.432 0.0181 0.109 0.623 0.0591 0.169 0.750 0.1118 0.229 0.840 0.173 0.288 0.906 0.238 0.405 0.982 0.3800.050 0.436 0.0187 0.110 0.626 0.0598 0.170 0.751 0.1127 0.230 0.842 0.174 0.290 0.908 0.241 0.410 0.984 0.3860.051 0.440 0.0193 0.111 0.628 0.0606 0.171 0.753 0.1137 0.231 0.843 0.175 0.292 0.909 0.243 0.415 0.985 0.3920.052 0.444 0.0198 0.112 0.631 0.0614 0.172 0.755 0.1146 0.232 0.844 0.176 0.294 0.911 0.2450.053 0.448 0.0204 0.113 0.633 0.0623 0.173 0.756 0.1156 0.233 0.845 0.177 0.296 0.913 0.248 0.420 0.987 0.3990.054 0.452 0.0210 0.114 0.636 0.0631 0.174 0.758 0.1166 0.234 0.847 0.178 0.298 0.915 0.250 0.425 0.989 0.4050.055 0.456 0.0215 0.115 0.638 0.0639 0.175 0.760 0.1175 0.235 0.848 0.179 0.300 0.917 0.252 0.430 0.990 0.4110.056 0.460 0.0221 0.116 0.640 0.0647 0.176 0.762 0.1185 0.236 0.849 0.180 0.302 0.918 0.255 0.435 0.992 0.4170.057 0.464 0.0227 0.117 0.643 0.0655 0.177 0.763 0.1195 0.237 0.850 0.181 0.304 0.920 0.2570.058 0.467 0.0233 0.118 0.645 0.0663 0.178 0.765 0.1204 0.238 0.852 0.182 0.306 0.922 0.259 0.440 0.993 0.4240.059 0.471 0.0239 0.119 0.648 0.0671 0.179 0.767 0.1214 0.239 0.853 0.183 0.308 0.923 0.262 0.445 0.994 0.4300.060 0.475 0.0245 0.120 0.650 0.0680 0.180 0.768 0.1224 0.240 0.854 0.185 0.310 0.925 0.264 0.450 0.995 0.4360.061 0.479 0.0251 0.121 0.652 0.0688 0.181 0.770 0.1234 0.241 0.855 0.186 0.312 0.927 0.266 0.455 0.996 0.4430.062 0.482 0.0257 0.122 0.655 0.0696 0.182 0.772 0.1244 0.242 0.857 0.187 0.314 0.928 0.2690.063 0.486 0.0263 0.123 0.657 0.0705 0.183 0.773 0.1253 0.243 0.858 0.188 0.316 0.930 0.271 0.460 0.997 0.4490.064 0.490 0.0270 0.124 0.659 0.0713 0.184 0.775 0.1263 0.244 0.859 0.189 0.318 0.931 0.273 0.465 0.998 0.4550.065 0.493 0.0276 0.125 0.661 0.0721 0.185 0.777 0.1273 0.245 0.860 0.190 0.320 0.933 0.276 0.470 0.998 0.4620.066 0.497 0.0282 0.126 0.664 0.0730 0.186 0.778 0.1283 0.246 0.861 0.191 0.322 0.934 0.278 0.475 0.999 0.4680.067 0.500 0.0288 0.127 0.666 0.0738 0.187 0.780 0.1293 0.247 0.863 0.192 0.324 0.936 0.2810.068 0.503 0.0295 0.128 0.668 0.0747 0.188 0.781 0.1303 0.248 0.864 0.193 0.326 0.937 0.283 0.480 0.999 0.4750.069 0.507 0.0301 0.129 0.670 0.0755 0.189 0.783 0.1313 0.249 0.865 0.194 0.328 0.939 0.285 0.485 1.000 0.4810.070 0.510 0.0308 0.130 0.673 0.0764 0.190 0.785 0.1323 0.250 0.866 0.196 0.330 0.940 0.288 0.490 1.000 0.4870.071 0.514 0.0314 0.131 0.675 0.0773 0.191 0.786 0.1333 0.251 0.867 0.197 0.332 0.942 0.290 0.495 1.000 0.4940.072 0.517 0.0321 0.132 0.677 0.0781 0.192 0.788 0.1343 0.252 0.868 0.198 0.334 0.943 0.2930.073 0.520 0.0327 0.133 0.679 0.0790 0.193 0.789 0.1353 0.253 0.869 0.199 0.336 0.945 0.295 0.500 1.000 0.5000.074 0.524 0.0334 0.134 0.681 0.0798 0.194 0.791 0.1363 0.254 0.871 0.200 0.338 0.946 0.297

0.075 0.527 0.0341 0.135 0.683 0.0807 0.195 0.792 0.13730.076 0.530 0.0347 0.136 0.686 0.0816 0.196 0.794 0.13830.077 0.533 0.0354 0.137 0.688 0.0825 0.197 0.795 0.13930.078 0.536 0.0361 0.138 0.690 0.0833 0.198 0.797 0.14030.079 0.539 0.0368 0.139 0.692 0.0842 0.199 0.798 0.14140.080 0.543 0.0375 0.140 0.694 0.0851 0.200 0.800 0.14240.081 0.546 0.0382 0.141 0.696 0.0860 0.201 0.801 0.14340.082 0.549 0.0389 0.142 0.698 0.0869 0.202 0.803 0.14440.083 0.552 0.0395 0.143 0.700 0.0878 0.203 0.804 0.14540.084 0.555 0.0403 0.144 0.702 0.0886 0.204 0.806 0.14650.085 0.558 0.0410 0.145 0.704 0.0895 0.205 0.807 0.14750.086 0.561 0.0417 0.146 0.706 0.0904 0.206 0.809 0.14850.087 0.564 0.0424 0.147 0.708 0.0913 0.207 0.810 0.14960.088 0.567 0.0431 0.148 0.710 0.0922 0.208 0.812 0.15060.089 0.569 0.0439 0.149 0.712 0.0932 0.209 0.813 0.1516


V-APage


DateDecember, 1999


➧ FIGURE 1VERTICAL DRUM DEBOTTLENECKING CONSIDERATIONS (1)

Compare drum toDesign Practices Section V-A Criteria

YesNoAre

criteriaexceeded

?

Yes

Evaluate potential impactof entrainment (Liquid CarryOver or Vapor Carry Under)

YesNoContactER&E Process or

SeparationSpecialist

Estimate amountof entrainment

No YesIs

separationadequate

?

Nochangesneeded

Modify drum usingtechniques described inReport EE.43E.99 untilseparation is adequate.

If separation is notadequate, contact a

Separation Specialist orreplace drum

Modify or replace drumto Design Practices

Standards, or contactER&E Process or

Separation Specialist

Nochangesneeded

NoAre therecurrent

operatingproblems

?

Are thereOIMS; or significantcorrosion, fouling, or

mechanical damage issuesassociated with

entrainment?

(1) Report EE.43E.99 is not intended for flare seal and blow down drums or vertical drums withtangential inlets (contact Separation Specialist). DP5Af01


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EXXONENGINEERING


FIGURE 2TYPICAL DIMENSIONS OF VERTICAL CYLINDRICAL DRUMS

��

Section B-B

30°(Min.)

Section A-A

B B

Condensate OutletNozzle

Anti-VortexBaffles

See Table 1

A Adp

Emergency LevelHLL

NLLLLL

Inlet Nozzle (3)18 in.

(450 mm)

dp

36 in.(900 mm)

CWMS

With CWMSWithout CWMS (6)do Vapor Outlet Nozzle

DP5AF2

30°

(5)

(1)(4)

(7)

D (2)

Notes:(1) See DESIGN CONSIDERATIONS FOR SELECTED SERVICES and Table 1.(2) Recommended % of Vc is given in Table 1 and in the Design Procedures for Vertical Separator Drums With and Without

CWMS.(3) Inlet nozzle type depends on service, as shown in Table 3.(4) Minimum distance from bottom of inlet nozzle to HLL should be adequate to prevent or minimize reentrainment at the

liquid surface (see Preventing Entrainment from the Liquid Surface, under DESIGN PROCEDURES).(5) The minimum distance between the low liquid level and the liquid outlet nozzle is given in the DESIGN PROCEDURES

under Design Criteria for Anti-Vortex Baffles.(6) The minimum distance between the top of an inlet nozzle and the top tangent line of the drum should be 36 in. (900 mm).(7) The minimum permissible distance between the top of the CWMS and the gas outlet nozzle is set by criteria given in

DESIGN PROCEDURES under Distance from Top of CWMS to Gas Outlet Nozzle.


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DateDecember, 1999


FIGURE 3SURFACE TENSION-VISCOSITY PARAMETER

100101

0.5

Surface Tension (σ), dynes/cm (mN/m)

Surfa

ce T

ensi

on -

Visc

osity

Par

amet

er (K

σµ)

0.4

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.6

0.8

0.4

0.2

0.1

µL = 0.05

DP5Af3

Liquid Viscosity (µL), cP (mPa • s)

Legend:

σSTD = 101.68 - (0.276 / µ L

0.45 )

Kσµ = 1.24f(σ,µ)

f (σ,µ) = (σ σ STD)0.5σ - σ STD


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FIGURE 4TYPICAL DIMENSIONS OF HORIZONTAL CYLINDRICAL DRUMS

DP5AF4

��Emergency Liquid Level

HLL

LLL

CWMS

Min. (4)

Inlet Nozzle

See Table 1

Anti-Vortex Baffles Liquid Outlet Nozzle (3)

Vapor Outlet Nozzle Inlet Nozzle

L = 3 to 4D

D

(5)

(8)

(6)

(1)

(2)

(7)

12 in. (300 mm) Min.6 in. (150 mm) Min.

Notes:(1) Recommended % of Vc is given in Table 1, in DESIGN CONSIDERATIONS FOR SELECTED SERVICES, and in the

DESIGN PROCEDURES, under Horizontal Separator Drums With and Without Horizontal CWMS. The minimum verticaldistance between the emergency liquid level and the drum top should be sized for 12 in. (300 mm) or 20% of the drumdiameter, whichever is larger.

(2) Ten minutes holdup, if applicable; otherwise, emergency liquid level is high liquid level (Table 1).(3) If water drawoff is present, the hydrocarbon liquid outlet nozzle should be extended above the bottom of the drum. This

dimension should be adequate to permit water drawoff without entraining hydrocarbon (see DESIGN PROCEDURES inSection V-B).

(4) Minimum distance considering reinforcement and fabrication requirements. Piping elbow center-to-end dimensions areshown in Table 4.

(5) Refer to Table 3 and DESIGN PROCEDURES for Horizontal Separator Drums With and Without Horizontal CWMS, forinlet nozzle selection. Either one or two inlet nozzles may be used for drums without CWMS. Design criteria for inletnozzles are given in the DESIGN PROCEDURES under Preventing Entrainment from the Liquid Surface.

(6) The minimum distance between the CWMS and the gas outlet nozzle is given in the DESIGN PROCEDURES underDistance from Top of CWMS to Gas Outlet Nozzle.

(7) The minimum distance between the low liquid level and the liquid outlet nozzle is given in the DESIGN PROCEDURESunder Design Criteria for Anti-Vortex Baffles.

(8) Impingement baffles [1/4 in. (6 mm) thick unless otherwise specified] should be installed opposite 90° elbow inlet nozzlesto protect the drum shell. The baffle diameter should be twice the inlet nozzle diameter.


V-APage


DateDecember, 1999


FIGURE 5DIMENSIONS OF HORIZONTAL DRUMS

WITH BOTH VERTICAL AND HORIZONTAL CWMS

��

Liquid Outlet Nozzle (3)

Vapor OutletNozzle

Inlet Nozzle

L = 3 to 4D

Emergency Liquid Level

HLL

LLL

��

��

D

10 Minutes(2)

6 in. (150 mm)Min.

6 in. (150 mm)Min.

Min. (4)

Inlet Nozzle (5)

DP5AF5

(7)

(8)

(6)

(9)

(1)

12 in. (300 mm) Min.

See Table 1

Notes:(1) Vertical and horizontal CWMS areas for vapor flow should be sized for 125% of critical velocity at design flow rate. The

minimum vertical distance between the drum top and the ELL emergency liquid level shall be 12 in. (300 mm) or 20% ofthe drum diameter, whichever is larger.

(2) If applicable, otherwise emergency liquid level is high liquid level (Table 1).(3) If a water drawoff nozzle is present, the hydrocarbon liquid outlet nozzle should be extended above the bottom of the

drum. This dimension should be adequate to permit water drawoff without entraining hydrocarbon (see DESIGNPROCEDURES in Section V-B under Prevention of Liquid Reentrainment).

(4) Minimum distance considering reinforcement and fabrication requirements.(5) The inlet nozzle should consist of either a slotted distributor or a 90° elbow at each end of the drum. Inlet nozzle design

criteria are given in the Design Procedures under Preventing Entrainment from the Liquid Surface and under HorizontalSeparator Drums with Vertical and Horizontal CWMS.

(6) The minimum distance between the CWMS and the gas outlet nozzle is given in the DESIGN PROCEDURES underDistance From Top of CWMS to Gas Outlet Nozzle.

(7) The minimum distance between the low liquid level and the liquid outlet nozzle is given in the DESIGN PROCEDURESunder Design Criteria for Anti-Vortex Baffles.

(8) Impingement baffles [1/4 in. (6 mm)] thick unless otherwise specified) should be installed opposite 90° elbow inlet nozzlesto protect the drum shell. The baffle diameter should be twice the inlet nozzle diameter.

(9) A vertical CWMS should be located immediately downstream of each inlet nozzle.


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FIGURE 6AMINE SCRUBBER FEED SEPARATOR DRUM(1)

��

Tray 1

do

Chimney Tray (2)

Rich Amine Outlet

6 in. (150 mm)CWMSDCWMS

Slotted Distributor

HLL

LLL

Anti-VortexBaffles

18 in.(450 mm)

Gas Inlet

Sepa

rato

r Dru

mSc

rubb

er

Hydrocarbon

DP5AF6

(3)

See Table 1

Notes:(1) Remaining design criteria are given in Table 1, in Figure 2 and in Feed Separator Drums for Amine Scrubbers under

DESIGN CONSIDERATIONS.(2) See Section III-H for design details.(3) For a chimney tray with a single chimney (vapor outlet nozzle), use Eq. (12a). For a chimney tray containing multiple

vapor outlet nozzles, use Eq. (12a) for each chimney. For a given distance between the top of the CWMS and thechimney pan, determine the maximum permissible "diameter" of the CWMS section underneath each chimney. This"diameter" should be equal to or greater than the center to center distance between chimneys. It also should be equal toor greater than 50% of the distance from the center of any of the outer chimneys to the nearest tower shell.


V-APage


DateDecember, 1999


FIGURE 7VELOCITY DISSIPATION IN IMPINGING JETS

DP5AF7

0 2 4 6 8 10 12 14 160

0.2

0.4

0.6

0.8

1.0

x + dpdp

Velo

city

Dis

sipa

tion

Fact

or, f

dp

x


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EXXONENGINEERING


FIGURE 8DESIGN CRITERIA FOR A VERTICAL DRUM WITH

TANGENTIAL INLET NOZZLE AND ANNULAR RING

1N

(Not

e 2)

DP5AF8

��

��

��

��

45°

Detail A

Section A-A

Location ofSecond InletNozzle ifRequired

Core Area(Note 1)

Annular Ring(Closed at Top)(Note 1)

Tangential InletNozzle (Note 1)

1N

Anti-Swirl Baffles(Note 3)

Section B-B

Anti-Vortex Baffles(Note 5)


BB

0.1D

2N

LLL

NLL

HLLSolid Circular Baffle(Note 4)

Annular Ring(Note 1)

Tangential InletNozzle (Note 1)

A

dp

Vapor OutletNozzle Skirt(Note 6)

See Detail A

D

3N2do

do

dp

A

1.0D

2.5d

p36

in.

(900

mm

)M

in.

6 in. (150 mm)

Wear Plate(Note 1)

Nozzles & Connections

ServiceNo.

Feed InletLiquid OutletVapor Outlet

1N2N3N

(Not

e 3)

(Note 5)

(Note 4)

L


V-APage


DateDecember, 1999


FIGURE 8 – DESIGN CRITERIA FOR A VERTICAL DRUM WITHTANGENTIAL INLET NOZZLE AND ANNULAR RING (Cont)

Notes for Figure 8:(1) A tangential inlet nozzle with an annular ring and wear plate should be provided. The inlet should be sized per Eq. (3g).

The core area for upward vapor flow, i.e., the drum cross sectional area minus the annular ring area, should be designedfor 300% of Vc (maximum). If 300% is exceeded, then two smaller tangential inlet nozzles should be provided, located180° apart and orientated to direct flow in the same direction of rotation. The annular ring width should be the same as theinlet nozzle diameter and the annular ring vertical height should be 2.5 times the inlet nozzle diameter. A distanceequivalent to the drum diameter should be provided between the bottom of the annular ring and the solid circular baffle.No support members should be present within the annular ring area or between the bottom of the annular ring and theliquid level. The need for a wear plate should be determined by the Owner's Engineer. Figure 8 shows the positioningand length of the wear plate if needed. Materials and thickness of the annular ring and wear plate should be specified bythe Owner's Engineer.

(2) The minimum permissible vertical distance between the top of the annular ring and the top tangent line should be 3 ft(900 mm).

(3) Four vertical anti-swirl baffles should be provided below the NLL. These baffles should extend from 6 in. (150 mm) belowthe NLL to the bottom tangent line. The baffle width should be about 10% of the drum diameter.

(4) One solid circular baffle is recommended. The baffle diameter is sized to allow a superficial liquid velocity of 0.15 ft/sec(45 mm/s) through the annular gap between the baffle edge and the drum shell assuming all the liquid flows through theannular gap. However, the minimum permissible annular gap is 2 in. (50 mm). If feasible, the solid circular baffle shouldbe supported from the anti-swirl baffles. The supports should be located at least 2 in. (50 mm) away from the drum shell.

(5) The location of the LLL is set by the minimum height required to prevent vapor carryunder (see Design Criteria for Anti-Vortex Baffles). However, in no case should the LLL be located below the bottom tangent line.

(6) A skirt should be positioned at the vapor outlet nozzle entrance.


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FIGURE 9GAS COLLECTOR

DP5AF9

��

��

2 in. (50 mm) (Min.)Min.

BlankEnds

Provide 1/2 in. (13 mm) φDrain Hole in Each End ofCollector

Min.Min.

LCWMS

CWMS

lslot

Sslot

Drum Top

Each Leg of Distributorto Have 2 Rows ofEqually Spaced Slots

Gas OutletNozzle

1 in. (25 mm) Min.

Solid Vertical SupportBaffle on 4 Sides ofCWMS SCWMS

2 Drain Holes

Gas OutletNozzle

Drum Shell

30° (Min.) 30° (Min.)

ho

ho


V-APage


DateDecember, 1999


FIGURE 10POSITION OF SIDE-OUT GAS OUTLET NOZZLES IN VERTICAL DRUMS WITH CWMS

DP5AF10

��

Gas OutletNozzle, do

CWMS

ho

hT(2)

(1)

Notes:

(1)

where: ho = Minimum permissible distance from top of CWMS to gas outlet nozzle, in. (mm)DCWMS = CWMS diameter, ft (mm)do = Gas outlet nozzle diameter, in. (mm)C13 = 12 Customary units (1 Metric units)

(2)

where: hT = Minimum permissible distance from drum head to gas outlet nozzle, in. (mm)

2dDCh oCWMS13

o−=

oT d75.0h =


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EXXONENGINEERING


FIGURE 11ANTI-VORTEX BAFFLE DESIGN

DP5AF11

2

Notes:(1) Dimension E is set by holdup requirements (see Table 1) or reentrainment criteria (see Design Criteria for Anti-Vortex Baffles ). The top tier should be at or below LLL.(2) Dimension B is based on criteria for straight extension of outlet nozzles when two liquid phases are present (see Section V-B

under Straight Extension of Outlet Nozzle ).(3) Tiers should be evenly spaced and the maximum distance between the adjacent tiers should be 6 in. (150 mm) (see DESIGN

PROCEDURES under Design Criteria for Anti-Vortex Baffles ).

��

��

A

B

C

Tier B

4 do

4 do1 in. x 4 in.

(25 mm x 100 mm)Spacing

Tier A and C

4 do

4 do1 in. x 4 in.

(25 mm x 100 mm)Spacing

B (2)

LLL1 in. (25 mm)

2 in. (50 mm)Min. (3)

~ 2 in. (50 mm) (Horizontal Drums)

do ~ (Vertical Drums)do

E (1)

D


V-APage


DateDecember, 1999


FIGURE 12DESIGN CRITERIA FOR HORIZONTAL CRUDE FLASH DRUMS

2 in. (50 mm) Pall Ringsor DemonstratedEquivalent(Note 3)

DP5AF12

��

��

��

��

��

��

��

HLLNLL

LLL

1N3N

HLLNLL

LLL

CWMS orVane-TypeMist Eliminator(Note 2)

See DistributorDetail(Note 5)

2NSection B-B

Section A-A(Distributor Not Shown)

2 in. (50 mm)Pall Rings orDemonstratedEquivalent(Note 3)

1N4CN

3CN

B

3N

1N

C

A

2CN

2N1

CN

HLL

NLL

LLL

Min.

ImpingementBaffle

(Note 9)

Anti-VortexBaffles(Note 8)

BA

L/2 L/2

L

CWMS or Vane-TypeMist Eliminator(Note 2)

Section C-C

Closed End

1 in. (25 mm) Min. 1 in.(25 mm) Min.

Distributor Detail

CWMS or Vane-TypeMist Eliminator (Note 2)

120°Spray Angle

(Note 4)Note

5

D

Note 8

Note 3

Note 7Note 1

Note 8

Note 3 Note10

Notes11 & 13

Note 5

NOZZLES & CONNECTIONSNO. SERVICE1N Feed Inlet (2)2N Liquid Outlet3N Vapor Outlet

1CN LC/LLA/LHA (2)2CN LG (2)3CN LG (2)4CN LG (2)

C

Note 6

Note 12

Notes:(1) The vertical cross-sectional area for vapor flow above the high liquid level (HLL) should be designed for 40% of critical

velocity at normal gas rate. The minimum vertical height between the drum top and the HLL should be 25% of the drumdiameter.

(2) A 6 in. thick, 5 Ib/ft3 (150 mm thick, 80 kg/m3) horizontal CWMS should be located below the vapor outlet nozzle. TheCWMS should be sized for 100% of critical velocity at normal gas rate. For crudes which may foul or plug the CWMS, ahorizontal vane-type mist eliminator, i.e., Koch Flexichevron (Style 1, Model 4C2, without hooks), or demonstratedequivalent should be used. The thickness of the vane-type mist eliminator should be 10 in. (250 mm) with a 2 in. (50 mm)spacing between adjacent blades. It should be sized for 180% of critical velocity.

(3) A 24 in. (600 mm) thick section of 2 in. (50 mm) Pall Rings or demonstrated equivalent (such as #50 Metal-lntalox or #2Nutter Ring packing) should be located immediately downstream of each inlet nozzle. The packed sections should extendfrom the top of the drum to 4 in. (100 mm) below the LLL.

(4) Minimum distance considering reinforcement and fabrication requirements.


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EXXONENGINEERING


FIGURE 12 – DESIGN CRITERIA FOR HORIZONTAL CRUDE FLASH DRUMS (Cont)

Notes for Figure 12 (Cont):(5) The inlet nozzles should connect to a slotted pipe distributor at each end of the drum with a maximum slot velocity of 30

ft/sec (9.1 m/s). Inlet nozzle design criteria are given in DESIGN PROCEDURES under Preventing Entrainment From theLiquid Surface. The slots should be spread out as uniformly as possible along the length of the distributor. Both ends ofthe distributors should be attached to the drum shell. The distance between the distributor and the HLL should bemaximized; minimum distance is 6 in. (150 mm).

(6) The minimum permissible distance between the top of either the CWMS or vane-type mist eliminator and the gas outletnozzle is set by criteria given in DESIGN PROCEDURES under Distance From Top of CWMS to Gas Outlet Nozzle.

(7) The minimum permissible distance between the bottom of the CWMS or vane-type mist eliminator and the HLL is 24 in.(600 mm). The minimum holdup time between the HLL and NLL is 1 minute.

(8) The minimum liquid holdup time below the LLL is 2 minutes and the minimum vertical height below the LLL is 3 ft (900mm). Anti-vortex baffles are required above the liquid outlet nozzle (see Design Criteria for Anti-Vortex Baffles).

(9) Impingement baffles should be installed opposite the slotted distributors to protect the drum shell. Materials and thicknessof the impingement baffles should be specified by the Owner's Engineer.

(10) A liquid holdup of 5 minutes should be provided between the bottom of the drum and the NLL. The NLL should be locatedbetween 40 to 60% of the drum diameter, preferably at the drum centerline. Maximum downward liquid velocity is 2 ft/min(0.6 m/min) based on the drum's horizontal cross-sectional area at the NLL.

(11) The maximum permissible two-phase velocity in the feed piping downstream of the control valve is 30 ft/sec (9.1 m/s). Ifthis results in the presence of slug flow (see Section XIV-D), piping reinforcement may be required to prevent excessivevibration. Another option would be to use a larger pipe diameter to ensure the absence of slug flow at typical operatingconditions. A control valve upstream of the drum should be located at least 20 line diameters from the drum inlet to allowthe flow regime to reestablish before entering the drum.

(12) Two or three gage glasses at various overlapping elevations should be installed to detect the presence of foam. If thelevel in each of the gage glasses is the same, no foam is present. Conversely, if the levels are different, this indicates thepresence of foam.

(13) Facilities should be provided for the injection of antifoam into the feed line to the drum, downstream of the desalters andupstream of the control valve. It is important to provide antifoam pump recycle facilities to ensure that the injection pipingis completely filled for immediate injection in emergency situations. Although silicone-type antifoams are the most costeffective, they may break down at temperatures above 600°F (315°C) and there is a potential for contamination of someatmospheric and vacuum pipestill products. For example, the product quality of lube distillates and asphalt (penetrationtest) may be affected. The Fractionation/Thermodynamic Section of ER&E or the vendors should be consulted onantifoam selection.


V-APage


DateDecember, 1999


FIGURE 13DESIGN CRITERIA FOR VERTICAL CRUDE FLASH DRUMS

��

��

��

��

��

��

DP5AF13

Nozzles & Connections

ServiceNo.

Feed InletLiquid OutletVapor Outlet

LC/LLA/LHA (2)LG (2)LG (2)LG (2)

1N2N3N

1CN2CN3CN4CN

0.1D

2N

1CN

2CN

3CN

4CN

Anti-Vortex Baffles(Note 7)


C CLLL

NLL

HLL

4CN

1CN

3CN

2CN

SubwayGrating

6 in.(150 mm)

0.8DL

B Bdp

dp

Tangential InletNozzle (Notes 3 & 10)

Annular Ring(Note 3)

1NAA

2.5

d p

3N CWMS or VaneTypeMist Eliminator(Note 2)

D

CWMS orVaneTypeMist Eliminator(Note 2)

Section A-A

Wear Plate(Note 3)

1N

Location ofSecond InletNozzle ifRequired(Note 3)

Core Area(Note 3)

Annular Ring(Closed at Top)

(Note 3)

Tangential InletNozzle

Section B-B

Anti-SwirlBaffles(Note 8)

Section C-C

Notes 3,10 & 12

(Note 4)

(Not

e 5)

(Note 1)

(Note 9)

(Note 7)

(Note 6)

(Note 11)

(Note 7)

(Not

e 8)

(Note 9)


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EXXONENGINEERING


FIGURE 13 – DESIGN CRITERIA FOR VERTICAL CRUDE FLASH DRUMS (Cont)

Notes for Figure 13:(1) The horizontal cross sectional area for vapor flow should be designed for 40% of critical velocity at normal gas rate.(2) A 6-in. thick, 5 Ib/ft3 (150 mm thick, 80 kg/m3) horizontal CWMS should be located below the vapor outlet nozzle and

should occupy the entire drum cross sectional area. For crudes which may foul or plug the CWMS, a horizontal vane-typemist eliminator, i.e., Koch Flexichevron (Style 1, Model 4C2, without hooks), or demonstrated equivalent should be used.The thickness of the vane-type mist eliminator should be 10 in. (250 mm) with a 2 in. (50 mm) spacing between adjacentblades.

(3) A tangential inlet nozzle with an annular ring and wear plate should be provided. The inlet should be sized for a maximumvelocity of 30 ft/sec. (9.1 m/s). The core area for upward vapor flow, i.e., the tower cross sectional area minus the annularring area should be designed for 80% of critical velocity at normal flow rate; if greater than 80%, then two smallertangential inlet nozzles should be provided, located 180° apart and orientated to direct flow in the same direction ofrotation. The annular baffle width should be the same as the inlet nozzle diameter and the annular ring vertical heightshould be 2.5 times the inlet nozzle diameter. A distance equivalent to 0.8 times the drum diameter should be providedbetween the bottom of the annular baffle and the subway grating. No support members should be present within theannular ring area or between the bottom of the annular ring and the liquid level. Materials and thicknesses of the annularring and wear plate should be specified by the Owner's Engineer.

(4) The minimum distance between the top of either the CWMS or vane-type mist eliminator and the gas outlet nozzle is givenin DESIGN PROCEDURES under Distance From Top of CWMS to Gas Outlet Nozzle.

(5) The minimum distance between the bottom of the CWMS or vane-type mist eliminator and the top of the annular ring is24 in. (600 mm).

(6) One circular tier of subway grating is recommended. The tier diameter should be equal to the drum diameter minus twicethe inlet nozzle diameter. Grating spacing and tier thickness are the same as for anti-vortex baffles. If feasible, thesubway grating should be supported from the anti-swirl baffles. The supports should be located at least 2 in. (50 mm)away from the drum shell.

(7) The minimum liquid holdup time between the LLL and the bottom tangent line is 2 minutes and the minimum verticalheight between the LLL and bottom tangent line is 3 ft (900 mm). Anti-vortex baffles are required above the liquid outletnozzle (see Design Criteria for Anti-Vortex Baffles).

(8) Four vertical anti-swirl baffles should be provided below the NLL. These baffles should extend from 6 in. (150 mm) belowthe NLL to the bottom tangent line. The baffle width should be about 10% of the drum diameter.

(9) A liquid holdup time of 5 minutes should be provided between the bottom tangent line and the NLL. Maximum downwardliquid velocity is 2 ft/min (0.6 m/min) (Note that this criteria may set the drum diameter). A minimum liquid holdup of 1minute should be provided between the HLL and NLL.

(10) The maximum permissible two-phase velocity in the feed piping downstream of the control valve is 30 ft/sec (9.1 m/s). Acontrol valve upstream of the drum should be at least 20 line diameters from the drum inlet to allow the flow regime toreestablish before entering the drum.

(11) Two or three gage glasses at various overlapping elevations should be installed to detect the presence of foam.(12) Facilities should be provided for the injection of antifoam into the feed line to the drum, downstream of the desalters and

upstream of the control valve. It is important to provide antifoam pump recycle facilities to ensure that the injection pipingis completely filled for immediate injection in emergency situations.

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Vapor Liquid Separator

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