Aliran Fluida Pada Shell & Tube Heat Exchanger Rangkuman Diskusi KBK Proses 24 Januari 2007 26 Januari 2007 Milis Migas Indonesia : http://groups.yahoo.com/group/Migas_Indonesia Migas Indonesia Online : http://www.migas-indonesia.com Migas Indonesia Network : http://www.migas-indonesia.net Editor : Zulfan Adi Putra Swastioko Budhi Suryanto Moderator KBK Proses

Ahmed Syarif Jurusan Teknik Gas & Petrokimia UI Saya mahasiswa teknik kimia. Saya masih bingung tentang penentuan fluida yang dialirkan pada shell jika menggunakan heat exchanger jenis shell and tube. Bisa minta penjelasannya tentang penentuan kriteria dari dua jenis fluida yang akan ditransferkan panasnya dalam heat exchanger jenis tersebut. Yang mana yang akan dialirkan di shell dan yang mana yang akan dialirkan di tube. Terimakasih atas tanggapannya. Muchlis Nugroho Rekayasa Engineering Beberapa pertimbangan fluida ditempatkan di shell atau di tube :

1. Potensi fouling, jika salah satu fluida memiliki potensi fouling/scaling (misalnya karena punya komponen pengotor) maka sebaiknya ditempatkan di tube. Karena tube lebih mudah dibersihkan/dirawat dengan mudah.

2. Kebutuhan jenis material, jika suatu fluida memerlukan peralatan dengan jenis material khusus (misalnya harus alloy yang mahal) maka sebaiknya fluida itu di dalam tube. Karena material tube itu tersedia dalam berbagai variasi, sedangkan material shell biasanya cuma carbon steel.

3. Jenis fasa, jika dalam heat exchanger tersebut ada perubahan fasa maka sebaiknya fluida yang berubah fasa tersebut berada di shell (misalnya evaporator chiller dan surface condenser). Karena kalau di tube ada resiko hammering. Walaupun ada juga fluida yang berubah fasa berada di tube dengan arrangement khusus tentunya (misalnya HP boiler, dan air cooled condenser) karena pertimbangan perawatan, material, dsb.

Jadi pada intinya desain alat itu secara umum harus melalui pertimbangan maintainability, operability, reliability, constructability, safety, dan economy. Tapi ada cara lain yang lebih mudah (tapi kalau mahasiswa mungkin malah susah) untuk menentukan fluida itu berada di shell atau di tube adalah dengan mencari tahu heat exchanger sejenis yang sudah pernah dibuat dan beroperasi bagaimana arrangementnya, dan bagaimana performancenya. Short cut saja lah.

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Hasrat Magabe Harahap Inti Karya Persada Teknik Disamping yang sudah diuraikan mas Muchlis di atas, sederhananya sebagai "rule of thumb" nya dengan basis true countercurrent flow adalah : Tube side untuk fluida yang bersifat corrosive, fouling, scaling dan bertekanan lebih tinggi, Shell Side untuk fluida yang bersifat viscous dan condense. Enrico Yandie Pertafenikki Engineering I hope this rule of thumb can be useful hints for you. Fluids to be passed through the shell :

Fluids of which pressure drop should be low Highly viscous fluids Fluids which exhibit a low heat transfer rate Fluids which undergo the phase change

Fluids to be passed through the tube :

Dirty fluids Fluids at higher pressure Corrosive fluids Fluids which contain solids Cooling water

Adhi Budhiarto Pertamina Unit Pengolahan II Dumai Beberapa hal yang perlu dipertimbangkan dalam menentukan aliran fluida dalam shell side dan tube side untuk shell and tube exchanger adalah (urut dari yang paling penting/prioritas utama) : Korosi Fluida korosif sebaiknya dialirkan di tube side untuk menghindari korosi pada kedua sisi, yaitu pada permukaan dalam shell dan pada permukaan luar tube. Jika fluida korosif dialirkan di tube, maka hanya permukaan tube bagian dalam saja yang mengalami korosi. Jika terjadi kebocoran pada tube, maka prop saja pada tube yang bocor, trus heat exchanger bisa difungsikan lagi. Jumlah tube yang di-prop maksimum 10 % atau tergantung kebutuhan heat exchange-nya. Sediment/ Suspended Solid / Fouling Fluida yang mengandung sediment/suspended solid atau yang menyebabkan fouling sebaiknya dialirkan di tube sehingga dapat memudahkan waktu cleaning (jika keadaan memungkinkan, tube bundle tidak perlu dicabut untuk cleaning, cukup dengan membuka channel cover terus tembak deh pakai water jet/mechanical cleaning atau dibantu dengan chemical cleaning). Jika fluida yang mengandung sediment dialirkan di shell, maka sediment/fouling tersebut akan terakumulasi pada stagnant zone di sekitar baffles, sehingga cleaning pada sisi shell menjadi tidak mungkin dilakukan tanpa mencabut tube bundle. Best practice fouling factor untuk Oil Refinery streams (dalam hr.ft2.oF/Btu) :

Gas dan vapor di Crude dan Vacuum unit : Atmospheric tower overhead vapours : 0,001

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Lght naphtha : 0,001 Vacuum overhead vapours : 0,002

Crude oil (0 s/d 232 oC) velocity < 2 ft/s : 0,003 velocity 2 s/d 4 ft/s : 0,002 velocity > 4 ft/s : 0,002

Gasoline : 0,002 Naphtha/light distillate/kerosene/light gas oil : 0,002 - 0,003 Heavy gas oil : 0,003 - 0,005 Heavy fuel oil : 0,005 - 0,007 Kerosene : 0,002 - 0,003

Viscosity Koefisien heat transfer yang lebih tinggi dapat diperoleh dengan menempatkan fluida yang lebih viscous pada shell side sebagai hasil dari peningkatan turbulensi akibat aliran crossflow (terutama karena pengaruh baffles). Biasanya fluida dengan viscosity > 2 cSt dialirkan di shell side untuk mengurangi luas permukaan perpindahan panas yang diminta. Koefisien perpindahan panas yang lebih tinggi terdapat pada shell side, karena aliran turbulen akan terjadi melintang melalui sisi luar tube dan baffle. Pressure Kecuali dipengaruhi oleh faktor lain, maka fluida dengan pressure yang lebih tinggi sebaiknya dialirkan di tube, sehingga shell dapat didesain untuk tekanan operasi yang lebih rendah dan heat exchanger menjadi lebih murah. Jika fluida dengan pressure yang lebih tinggi dialirkan di shell side, maka baik shell maupun tube bundle harus didesain untuk pressure yang tinggi. Sedangkan jika fluida dengan pressure yang lebih tinggi ditempatkan pada tube side, maka bagian-bagian yang harus didesain pada tekanan tinggi hanya channel, channel cover, dan tube bundle saja. Alasan lain adalah karena tekanan kerja yang diberikan pada internal tube dua kali tekanan kerja external tube. Condensing vapours Biasanya condensing vapours dialirkan di shell side untuk memfasilitasi penghilangan condensate. Temperatur Kecuali dipengaruhi oleh faktor lain, biasanya lebih ekonomis meletakkan fluida dengan temperatur lebih tinggi pada tube side, karena panasnya ditransfer seluruhnya ke arah permukaan luar tube/ke arah shell sehingga akan diserap sepenuhnya oleh fluida yang mengalir di shell. Jika fluida dengan temperatur lebih tinggi dialirkan pada shell side, maka transfer panas tidak hanya dilakukan ke arah tube, tapi ada kemungkinan transfer panas juga terjadi ke arah luar shell alias ke lingkungan (yah pengaruhnya kecil sih, makanya jadi prioritas terakhir untuk dipertimbangkan). Best practice penempatan fluida di shell atau di tube :

Fluida yang mengalir pada shell : Condensing vapours Allowable pressure drop yang lebih rendah Jumlah aliran yang lebih besar dengan sifat fisis yang sama dengan fluida di tube Fluida viscous yang clean Vaporizing

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Fluida yang mengalir pada tube : Cooling water Fluida tekanan tinggi Fluida korosif/alloy construction

Khusus untuk cooling water, pertimbangkan penggunaannya jika temperatur proses tinggi, karena temperatur proses yang tinggi dalam water-cooled exchanger dapat menyebabkan :

Overheating cooling water pada tube wall (akan menyebabkan mineral scaling) Perbedaan temperatur yang tinggi antara shell dan tube (mechanical problem)

Best practice-nya, jangan gunakan cooling water jika fluida panas > 200 oC untuk mencegah terjadinya fouling yang disebabkan oleh hardness salts dalam air. Selain itu, temperatur air keluar dibatasi maksimum 50 oC. Semoga bermanfaat.

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How to Select Shell and Tube Heat Exchanger Classes and Types

Drajad Agus Widodo (drajad_aw@yahoo.com)

Fundamentals of Shell and Tube Heat Exchangers

A shell and tube heat exchanger is a cylindrical vessel housing a set of tubes (called the tube bundle) containing a fluid at some temperature and immersed in another fluid at a different temperature. The transfer of heat occurs between the fluid flowing over the tubes and the fluid flowing inside the tubes. The fluid flow inside the tubes is said to be tube side and the fluid flow external to the tube bundle is said to be shell side

Basic Components of Shell and Tube Heat Exchangers

Fig. 1 Shell and Tube Exchanger Components

While there is an enormous variety of specific design features that can be used in shell and tube exchangers, the number of basic components is relatively small.

Tubes

The tubes are the basic component of the shell and tube exchanger, providing the heat transfer surface between one fluid flowing inside the tube and the other fluid flowing across the outside of the tubes. The tubes may be

seamless or welded and most commonly made of copper or steel alloys. Other alloys of nickel, titanium, or aluminum may also be required for specific applications.

The tubes may be either bare or with extended or enhanced surfaces on the outside. Extended or enhanced surface tubes are used when one fluid has a substantially lower heat transfer coefficient than the other fluid. Extended surfaces, (finned tubes) provide two or four times as much heat transfer area on the outside as the corresponding bare tube, and this area ratio helps to outside heat transfer coefficient.

Fig. 2 Finned Tube

More recent developments are: a corrugated tube which has both inside and outside heat transfer enhancement, a finned tube which integral inside turbulators as well as extended outside surface, and tubing which has outside surfaces designed to promote nucleate boiling.

Tube Sheets

The tubes are held in place by being inserted into holes in the tube sheet and there either expanded into grooves cut into the holes or welded to be tube sheet where the tube protrudes from the surface. The tube sheet is usually a single round plate of metal that has been suitably drilled and grooved to take the tubes (in the desired pattern), the gaskets, the spacer rods, and the bolt circle where it is fastened to the shell. However, where mixing between

the two fluids (in the event of leaks where the tube is sealed into the tube sheet) must be avoided, a double tube sheet may be provided.

Fig. 3 Tube Sheet

The space between the tube sheets is open to the atmosphere so any leakage of either fluid should be quickly detected. Triple tube sheets

(to allow each fluid to leak separately to the atmosphere without mixing) and even more exotic designs with inert gas shrouds and/or leakage recycling systems are used in cases of extreme hazard or high value of the fluid.

The tube sheet, in addition to its mechanical requirements, must withstand corrosive attach by both fluids in the heat exchanger and must be electrochemically compatible with the tube and all tube-side material. Tube sheets are sometimes made from low carbon steel with a thin layer of corrosion-resisting alloy metallurgically bonded to one side.

Shell and Shell-side Nozzles

The shell is simply the container for the shell-side fluid, and the nozzles are the inlet and exit ports. The shall normally has a circular cross section and is commonly made by rolling a metal plate of the appropriate dimensions into a cylinder and welding the longitudinal joint (rolled shells). Small diameter shells (up to around 24 inches in diameter) can be made by cutting pipe of the desired diameter to the correct length (pipe shells). The roundness of the shell is important in fixing the maximum diameter of the baffles that can be inserted and therefore the effect of shell-to-shell baffle leakage. Pipe shells are more nearly round than rolled shells unless particular care is taken in rolling.

In large exchangers, the shall is made out of low carbon steel wherever possible for reasons of economy, though other alloys can be and are used when corrosion or high temperature strength demands must be met.

Tube-Side Channel and Nozzles

Tube-side channels and nozzles control the flow of the tube-side fluid into and out of the tubes of the exchanger. Since the tube-side fluid is generally the more corrosive, these channels and clan instead of solid alloy.

Channel Covers

The channel covers are round plates that bolt to the channel flanges and can be removed for tube inspection without disturbing the tube-side piping. In smaller heat exchangers, bonnets with flanged nozzles or threaded connections for the tube-side piping or often used instead of channels and channel covers

Pass Divider

A pass divider is needed in one channel or bonnet for an exchanger having two tube-side passes, and they are needed in both channels or bonnets for an exchanger having more than two passes.

The arrangement of the dividers in multiple-pass exchangers is somewhat arbitrary, the usual intent being to provide nearly the same number of tubes in each pass, to minimize the number of tubes lost from the tube count, to minimize the pressure difference across any pass divider (to minimize leakage and therefore the violation of the MTD derivation), to provide adequate bearing surface for the gasket and to minimize fabrication complexity and cost.

Baffles

Baffles serve two functions; Most importantly, they support the tubes in the proper position during assembly and operation and prevent vibration of the tubes caused by flow-induced eddies, and secondly, they guide the shell-side flow back and forth across the tube field, increasing the velocity and the heat transfer coefficient.

Fig. 4 Baffle cuts (a) Baffle cuts for single segmental baffles. (b) Baffle cuts for double segmental baffles. (c) Baffle cuts for triple segmental baffles.

Selection of Shell and Tube Heat Exchanger Classes

TEMA Standards provide a Recommended Good Practice for the designers consideration in areas outside of the limits of the specified standards. Guidance and references are noted for seismic design, large diameter exchangers, tube vibration, tube-to-tube sheet stress analysis, nozzle loading analysis, and numerous other design-limiting features.

Shell and tube heat exchanger technology for gas, chemical, and petroleum plants has developed a broad. exchangers, tube vibration, tube-to-tube sheet stress analysis, nozzle loading analysis, and numerous other design-limiting features. basis of common understanding through the Standards of Tubular Exchangers Manufacturers Association (TEMA). These TEMA Standards provide nomenclature, dimensional tolerances, manufacturers and purchasers responsibilities, general installation and operating guidelines, and specific design and fabrication practices.

The design and fabrication practices of TEMA are in three classifications, called Class R, C, or B.

Class R includes heat exchangers specified for the most severe service in the petroleum-chemical processing industry. Safety and durability are required for exchangers designed for such rigorous condition.

Class C includes heat exchangers designed for the generally moderate services and requirements. Economy and overall compactness are the two essential features of this class.

Class B are heat exchangers specified for general process service. Maximum economy and optimum compactness are the main criteria of design.

Table 1 Comparison of TEMA Classes R, C and B Exchangers

Para. Topic R C B 1.12 Definition For the generally severe

requirement of petroleum and related processing application

For the generally moderate requirements of commercial and general process application

For chemical process service

1.51 Corrosion allowance on carbon steel

1/8 inch 1/16 inch 1/16 inch

2.5 Tube pitch and minimum cleaning lane

1.25 x tube OD. 1/4 inch lane.

1.25 x tube OD. Tube OD = 5/8 or less, may be located 1.2 x tube OD

1.25 x tube OD. Lane may be 3/16 inch in 12 inch and smaller shells. Minimum cleaning lanes 1/4" for shell diameter greater 12

4.42 Longitudinal baffle thickness

1/4 inch minimum 1/8 inch alloy, 1/4 inch CS 1/8 inch alloy, 1/4 inch carbon steel

4.71 Minimum tie rod diameter 3/8 inch in 6 15 inch Shells Diameter

1/4 inch in 6-15 inch Shells Diameter

1/4 inch in 6-15 inch Shells Diameter

5.11 Floating head cover cross-over area

1.3 times tube flow area Same as tube flow area Same as tube flow area

5.31 Lantern ring construction 375 oF maxi. 300 psi up to 24 inch diam. Shell 150 psi for 25-42 inch shells 75 psi for 43-60 inch shells

600 psi maximum (same as TEMA R)

6.2 Gasket materials Metal jacketed or solid metal for (a) internal floating head

cover (b) 300 psi and up. (c) All hydrocarbons

Metal jacketed or solid metal (a) internal floating head (b) 300 psi and up.

(Same as TEMA C)

6.32 Peripheral gasket contact surface

Flatness tolerance specified No tolerance specified No tolerance specified

7.131 Minimum tube sheet thickness with expanded tube joints

Outside diameter of the tube 0.75 x tube OD for 1 inch and smaller. 7/8 inch for 1 1/4 OD 1 inch for 1 1/2 OD 1.25 inch for 2 OD

(Same as TEMA C) + In no case shall the total tube sheet thickness, including corrosion allowance, be less than 3/4"

7.44 Tube Hole Grooving Two grooves Above 300 psi design pressure and/or above 350 oF design temp: 2 grooves

(Same as TEMA R)

7.51 Length of expansion Smaller of 2 inch or tube sheet thickness 1/8

Smaller of 2 x tube OD or tube sheet thickness 1/8

(Same as TEMA R)

7.6 Tube sheet pass partition grooves

3/16 inch deep grooves required

Over 300 psi 3/16 inch deep grooves required or other suitable means for retaining gaskets in place

(Same as TEMA C)

10.3 Pipe Tap Connections 6000 psi coupling with bar stock plug

3000 psi coupling 3000 psi coupling with bar stock plug

10.32 Pressure Gauge connections Required in nozzle 2 inch & up with one connection of 3/4 minimum NPS

(shall be specified by purchaser)

Required in nozzle 2 inch & up with one connection of 1/2 minimum NPS

10.33 Thermometer Connections Required in nozzles 4 inch & up with one connection of 1 minimum NPS

(shall be specified by purchaser)

(Same as TEMA R)

11.1 Minimum bolt size 3/4 inch 1/2 inch recommended, smaller bolting may be used

5/8 inch

Selection of Shell and Tube Heat Exchanger Types

Nomenclature

Fig 5 summarizes the major shell-and-tube exchanger components other than tubes and baffles. The letters are used for a standard nomenclature in the industry. A three-letter type designation in the order of front head type, shell type, and rear head is used. For example, an AJS would have a front head that is removable with a removable cover, a shell that is arranged for divided flow, and a rear floating head with a backing device (usually a split-ring).

Fig. 5 TEMA-type designations for shell and tube heat

exchangers.

Principal Type of Construction

Fig. 5 shown details of the construction of the TEMA types of shell-and-tube heat exchangers. These and other types are discussed in the following paragraphs. Fixed-Tube-Sheet Heat Exchanger Fixed-tube-sheet exchanger Fig. 6b are used more often than any other type, and the frequency of use has been increasing in recent years. The tube sheets are welded to the shell. Usually these extend beyond the shell and serve as flanges to which to tube-side header are bolted. This construction requires that the shell and tube-sheet materials be weldable to each other. When such welding is not possible, a blind gasket type of construction is utilized. The blind gasket is not accessible for maintenance or replacement once the unit has been constructed. This construction is used for steam surface condensers, which operate under vacuum. The tube-side header (or channel) may be welded to the tube sheet, as shown in Fig 5 for type C and N heads. This type of construction is less costly than types B and M or A and L and still offers the advantage that tubes may be examined and replaced without disturbing the tube-side piping connections. There is no limitation on the number of tube-side passes. Shell-side passes can be one or more, although shells with more than two shell-side passes are rarely used. Tubes can completely fill the heat-exchanger shell. Clearance between the outermost tubes and the shell is only the minimum necessary for fabrication. Between the inside of the shell and the baffles some clearance must be provided so that baffles can slide into the shell. Fabrication tolerances then require some additional clearance between the outside of the baffles and the outermost tubes. The edge distance between the outer of the baffles and the outer tube limit (OTL) and the baffle diameter must be sufficient to prevent vibration of the tube from breaking through the baffle holes. The outermost tube must be contained within the OTL. Tubes can replaced. Tube-side headers, channel covers, gaskets etc., are accessible for maintenance and replacement. Neither the shell-side baffle structure nor the blind gasket is accessible. During tube removal, a tube may break within the shell. When this occurs, it is most difficult to remove or to replace the tube. The usual is to plug the appropriate holes in the tube sheets. U-Tube Heat Exchanger (Fig. 6d) The tube bundle consists of the stationary tube sheet, U tubes (or hairpin tubes), baffles or support plates, and

appropriate tie rods and spacers. The tube bundle can be removed from the heat-exchanger shell. A tube-side header (stationary head) and a shell with integral shell cover, which is welded to the shell, are provided. Each tube is free to expand or contract without any limitation being placed upon it by the other tubes. The U-tube bundle has the advantage of providing minimum clearance between the outer tube limit and the inside of the shell for any of the removable-tube-bundle constructions. Clearances are of the same magnitude as for fixed-tube-sheet heat exchangers. The number of tube holes in a given shell is less than that for a fixed-tube-sheet exchanger because of limitation of bending tubes of a very short radius. The U-tube design offers the advantage of reducing the number of joints. In high-pressure construction this feature becomes of considerable importance in reducing both initial and maintenance costs. The use of U-tube construction has increased significantly with the development of hydraulic tube cleaners, which can remove fouling residues from both the straight and the U-bend portions of the tubes. Kettle-type reboilers, evaporators, etc., are often U-tube exchangers with enlarged shell sections for vapor-liquid separation. The U-tube bundle replaces the floating-heat bundle of Fig.6e. The U-tube exchanger with copper tubes, cast-iron header, and other parts of carbon steel is used for water and steam services in office buildings, schools, hospitals, hotel, etc. Nonferrous tube sheets and admiralty or 90-10 copper-nickel tubes are the most frequently used substitute materials. These standard exchangers are available from a number of manufacturers at costs far below those of custom-built process-industry equipment. Packed-Lantern-Ring Exchanger (Fig. 6f) This construction is the least costly of the straight-tube removable bundle types. The shell-and tube-side fluids are each contained by separate rings of packing separated by a lantern ring and are installed at the floating tube sheet. The lantern ring is provided with weep holes. Any leakage passing the packing goes through the weep holes and then drops to the ground. Leakage at the packing will not result in mixing within the exchanger of two fluids. The width of the floating tube sheet must be great enough to allow for the packings, the lantern ring, and differential expansion. Sometimes a small skirt is attached to a thin tube sheet to provide the required bearing surface for packings and lantern ring.

The clearance between the outer tube limit and the inside of the shell is slightly larger than that for fixed-tube-sheet and U-tube exchangers. The use of a floating-tube-sheet skirt increases this clearance. Without the skirt the clearance must make allowance for tubeholes distortion during tube rolling near the outside edge of the tube-sheet or tube-end welding at the floating tube sheet. The packed-lantern-ring construction is generally limited to design temperatures below 191 oC (375 oF)and to the mild services of water, steam, air, lubricating oil, etc. Design gauge pressure does not exceed 2068 kPa (300 lbf/in2) for pipe shell exchangers and is limited to 1034 kPa (150 lbf/in2) for 610 to 1067 mm (24 to 42 in.) diameter shells. Outside-Packed Floating-Head Exchanger (Fig. 6c) The shell-side fluid is contained by rings of packing, which are compressed within a stuffing box by a packing follower ring. This construction was frequently used in the chemical industry, but in recent years usage has decreased. The removable-bundle construction accommodates differential expansion between shell and tubes and is used for shell-side service up to 4137 kPa gauge pressure (600 lbf/in2) at 316 oC (600 oF). There are no limitations upon the number of tube-side passes or upon the tube-side design pressure and temperature. The outside-packed floating-head exchanger was the most commonly used type of removable-bundle construction in chemical-plant service. The floating-tube-sheet skirt, where in contact with the rings of packing, has fine machine finish. A split shear ring is inserted into a groove in the floating-tube-sheet skirt. A slip-on backing flange, which in service is held in place by the shear ring, bolts to the external floating-head cover. The floating-head cover is usually a circular disk. With an odd number of tube-side passes, an axial nozzle can be installed in such a floating-head cover. If a side nozzle is required, the circular disk is replaced by either a disked head or a channel barrel (similar to Fig. 6f) bolted between floating-head cover and floating-tube-sheet skirt. Internal Floating-Head Exchanger (Fig. 6a) The internal floating-head design is used extensively in petroleum-refinery service, but in recent years there has been a decline in usage.

A split backing ring and bolting usually hold the floating-head cover at the floating tube sheet. These are located beyond the end of the shell and within the larger-diameter shell cover. Shell cover, split backing ring, and floating-head cover must be removed before the tube bundle can pass through the exchanger shell. With an even number of tube-side passes the floating-head cover serves as return cover for the tube-side fluid. With an odd number of passes a nozzle pipe must extend from the floating-head cover through the shell cover. Provision for both differential expansion and tube-bundle removal must be made. Pull-Through Floating-Head Exchanger (Fig. 6e) Construction is similar to that of the internal-floating-head split-backing-ring exchanger except that the floating-head cover bolts directly to the floating tube sheet. The tube bundle can be withdrawn from the shell without removing either shell cover or floating-head cover. This feature reduces maintenance time during inspection and repair. The large clearance between the tubes and the shell must provide for both the gasket and the bolting at the floating-head cover. This clearance is about 2 to 2 times that required by the split-ring design. Sealing strips or dummy tubes are often installed to reduce bypassing of the tube bundle.

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1. Stationary Head Channel 20. Slip-On Backing Flange 2. Stationary Head Bonnet 21. Floating Head Cover - External 3. Stationary Head Flange Channel or Bonnet 22. Floating Tube sheet Skirt 4. Channel Cover 23. Packing Box Flange 5. Stationary Head Nozzle 24. Packing 6. Stationary Tube sheet 25. Packing Gland 7. Tubes 26. Lantern Ring 8. Shell 27. Tie-Rods and Spacers 9. Shell Cover 28. Transverse Baffles or Support Plates 10. Shell Flange Stationary Head End 29. Impingement Plate 11. Shell Flange Rear Head End 30. Longitudinal Baffle 12. Shell Nozzle 31. Pass Partition 13. Shell Cover Flange 32. Vent Connection 14. Expansion Joint 33. Drain Connection 15. Floating Tube sheet 34. Instrument Connection 16. Floating Head Cover 35. Support Saddle

17. Floating Head Flange 36. Lifting Lug 18. Floating Head Backing Device 37. Support Bracket 19. Split Shear Ring 38. Weir 39. Liquid Level Connection Fig. 6 Heat-Exchanger-Component nomenclature. (a) Internal-floating-heat exchanger (with floating-head backing device). Type AES. (b) Fixed-tube-sheet exchanger. Type BEM. (c) Outside-packed floating-head exchanger. Type AEP. (d) U-tube heat exchanger. Type CFU. (e) Kettle-type floating-head reboiler. Type AKT. (f) Exchanger with packed floating tube sheet and lantern ring. Type AJW. (Standard of Tubular Exchanger Manufacturers Association)

Table 2 Features of TEMA Shell and Tube Type Exchangers

Type of design Fixed tubesheet

U-tube Packed lantern-ring floating head

Internal floating head (split backing ring)

Outside-packed floating head

Pull-through floating head

TEMA rear-head type

L or M or N U W S P T

Relative cost increases from A (least expensive) through E (most expensive)

B A C E D E

Provision for differential expansion

Expansion joint in shell

Individual tubes free to expand

Floating head Floating head Floating head

Floating head

Removable bundle

No Yes Yes Yes Yes Yes

Replacement bundle possible

No Yes Yes Yes Yes Yes

Individual tubes replaceable

Yes Only those in outside row

Yes Yes Yes Yes

Tube cleaning by chemicals inside and outside

Yes Yes Yes Yes Yes Yes

Interior tube cleaning mechanically

Yes Special tools required

Yes Yes Yes Yes

Exterior tube cleaning mechanically:

Triangular pitch

No No No No No No

Square pitch Yes Yes Yes Yes Yes Yes Hydraulic-jet cleaning:

Tube interior Yes Special tools required

Yes Yes Yes Yes

Tube exterior No Yes Yes Yes Yes Yes Double tubesheet feasible

Yes Yes No No Yes No

Number of tube passes

No practical limitations

Any even number possible

Limited to one or two passes

No practical limitations

No practical limitations

No practical limitations

Internal gaskets eliminated

Yes Yes Yes No Yes No

NOTE : Relative costs A and B are not significantly different and interchange for long lengths of tubing. U-tube bundles have been built with tube supports which permit the U-bends to be spread apart and tubes inside of the bundle replaced. Normal triangular pitch does not permit mechanical cleaning. With a wide triangular pitch, which is equal to 2 (tube diameter plus cleaning lane)/ 3, mechanical cleaning is possible on removable bundles. This wide spacing is infrequently used. For odd number of tube side passes, floating head requires packed joint or expansion joint.

Table 3 Application Shell and Tube Types

Type Designation

Significant Feature Applications Best Suited Limitation Relative Cost in Carbon Steel Construction

Fixed Tubesheet

Both tube sheets fixed to shell

Condensers; liquid-liquid; gas-gas; cooling and heating, horizontal or vertical, reboiling

Temperature difference at extremes of about 200 oF. Due to differential expansion

1.0

Floating Head or Tube sheet (removable and non-removable bundles)

One tube sheet floats in shell or with shell, tube bundle may or may not be removable from shell, but back cover can be removed to expose tube ends

High temperature differentials, above about 200 oF. Extremes; dirty fluids requiring cleaning of inside as well as outside of shell, horizontal or vertical.

Internal gaskets offer danger of leaking. Corrosiveness of fluids on shell side floating parts. Usually confined to horizontal units

1.28

U-Tube; U-Bundle

Only one tube sheet required. Tubes bent in U-shape. Bundle is removable

High temperature differentials which might require provision for expansion in fixed tube units. Clean service or easily cleaned conditions on both tube side and shell side. Horizontal or vertical.

Bends must be carefully made or mechanical damage and danger of rupture can result. Tube side velocities can cause erosion of inside of bends. Fluid should be free of suspended particles

1.08

Kettle Tube bundle removable as U-type or floating head. Shell enlarged to allow boiling and vapor disengaging

Boiling fluid on shell side, as refrigerant, or process fluid being vaporized. Chilling or cooling of tube side fluid in refrigerant evaporation on shell side

For horizontal installation. Physically large for other applications

1.2 1.4

References

1. Standard of Tubular Exchanger Manufacturers Association, Eight Edition 1999

2. Perrys Chemical Engineers Handbook, Copyright 1999 by The McGraw-Hill Company, Inc.

3. A. Keith Escoe, Mechanical Design of Process Systems Volume 2, 1986

4. Wolverine Engineering Data Book II by Wolverine Tube, Inc Research and Development Team, 2001

Please send your thought and suggest to drajad_aw@yahoo.com

THE AUTHOR

Drajad AW is a Mechanical Engineer with PT Technip Indonesia responsible for Package Equipments. After graduating from Sepuluh Nopember Institute of Technology (ITS) with a B.Sc degree in Marine Engineering, he joined PT. Mafhindo Utama, PT Indo-Laval, PT. Erraenersi Konstruksindo, PT. Rekayasa

Industri, PT. Istana Karang Laut, Malaysia Marine and Heavy Engineering SDN BHD. He was for eight years the Static Engineer (Pressure Vessels, Tanks, Filters, etc) and Package Equipments Engineer.

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