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Jan' 2005 PRESENTATION ON DESIGN OF FIRED HEATERS FOR ESSAR OIL ENGINEERS by S. Senthil Kumar 3 rd January 2005
Jan' 2005
PRESENTATION
ON
DESIGN OF FIRED HEATERSFOR ESSAR OIL ENGINEERS
by
S. Senthil Kumar
3rd January 2005
Jan' 2005
2OVERVIEW
INTRODUCTION
APPLICATIONS OF FIRED HEATER
FEATURES OF FIRED HEATER
TYPICAL CONFIGURATIONS OF FIRED HEATER
MODES OF OPERATION
HEATER COMPONENTS
COMBUSTION & RELATED SUBJECTS
PROCESS CONSIDERATION
Jan' 2005
3INTRODUCTION
WHAT IS A FIRED HEATER ?
MANY A TIMES IT IS REQUIRED TO RAISE THE TEMPERATURE OF
PROCESS FLUID, FOR EXAMPLE
REACTOR FEED PREHEATING
COLUMN BOTTOM REBOILER
HEATING HOT OIL TO EXCHANGE HEAT WITH PROCESS FLUID
TO ACHIEVE THIS, HEAT ENERGY HAS TO BE SUPPLIED TO THE
PROCESS FLUID
HEAT ENERGY IS OBTAINED BY COMBUSTION OF FUEL
Jan' 2005
4FIRED HEATER
IF COMBUSTION OF FUEL IS PERFORMED INSIDE AN INSULATED
ENCLOSURE, THEN GENERATED HEAT ENERGY CAN BE UTILIZED
EFFECTIVELY
THIS ENCLOSURE IS CALLED “FURNACE OR FIRED HEATER”
THIS EQUIPMENT IS USED TO COMBUST THE FUEL AND TRANSFER
THE HEAT GENERATED TO THE PROCESS FLUID FLOWING
THROUGH TUBES PLACED INSIDE THE HEATER
Jan' 2005
5UTILIZATION IN PROCESS INDUSTRY
FURNACES ARE MAINLY USED FOR FOLLOWING SERVICES:
PREHEATING REACTOR FEED
SOURCE OF HEAT IN DISTILLATION COLUMNS (BOTTOM REBOILERS)
HOT OIL HEATERS
THERMAL CRACKING SERVICES
ENDOTHERMIC CATALYTIC REATORS (REFORMERS)
MAINLY CLASSIFIED AS
REACTIVE FURNACES
NON REACTIVE FURNACES
FURNACES USED FOR NON REACTIVE SERVICES ARE GENERALLY
TERMED AS “FIRED HEATER”
Jan' 2005
6APPLICATION OF FIRED HEATER
FIRED HEATERS ARE USED FOR VARIOUS PURPOSES IN THE REFINING
& PETROCHEMICALS INDUSTRY, SUCH AS:
CRUDE FURNACE
VACUUM CHARGE HEATER
REACTOR CHARGE HEATER (HYDRO-DESULPHURIZATION REACTORS)
REFORMER FURNACE
HYDROCRACKER FURNACE
VISBREAKER FURNACE
AIR HEATER
AND MANY, MANY OTHERS
Jan' 2005
FEATURES OF FIRED HEATER
Jan' 2005
8FEATURES OF A FIRED HEATER
MAIN FEATURES
RADIANT SECTIONSHIELD SECTIONCONVECTION SECTIONFLUE GAS STACK
AUXILLIARY EQUIPMENT
BURNERAIR PREHEAT SYSTEMDRAFT SYSTEMS
FANS & BLOWERSDAMPER SOOT BLOWERSREFRACTORIES
Radiant
ShieldConvection
Stack
Burner
Jan' 2005
9FEATURES OF A FIRED HEATER
Jan' 2005
TYPICAL CONFIGURATIONS OF FIRED HEATER
Jan' 2005
11TYPICAL CONFIGURATIONS OF HEATER
SHAPE OF RADIANT SECTION
ONLY RADIANT OR RADIANT WITH CONVECTION
VARIATIONS IN PLACEMENT OF TUBES
PLACEMENT OF BURNERS IN RADIANT SECTION
VARIOUS FACTORS THAT CONTRIBUTE TO
DIFFERENT CONFIGURATIONS ARE
Jan' 2005
12TYPICAL CONFIGURATIONS OF HEATER
SHAPE OF RADIANT SECTIONCYLINDRICAL BOXCABIN
CONFIGURATION OF TUBES
TUBE PATTERNS VERTICAL HELICAL HORIZONTAL U-TUBE & INVERTED U-TUBE
VERTICAL TUBEHELICAL TUBE
INVERTED U TUBE
Jan' 2005
13TYPICAL CONFIGURATIONS OF HEATER
VARIATIONS IN PLACEMENT OF TUBES
LOCATION OF TUBES
REFRACTORY WALL BACKED
CENTRALLY PLACED
FIRING WITH RESPECT TO TUBES
SINGLE SIDE FIRING
DOUBLE SIDE FIRING
Jan' 2005
14TYPICAL CONFIGURATIONS OF HEATER
PLACEMENT OF BURNERS
IN RADIANT CHAMBER
FLOOR (UPFIRED)
SIDEWALL
SIDEWALL MULTILEVEL
ENDWALL
Jan' 2005
15TYPICAL CONFIGURATIONS OF HEATER
A A
Section A-A
CYLINDRICAL RADIANT WITH VERTICAL TUBES
Most commonly used where duties are
usually small
Tubes are
Vertically placed
Refractory backed
Placed along the inner
circumference of the cylindrical
radiant section
Shield & convection tubes are normally
horizontal
Only radiant configuration is also possible
Jan' 2005
16TYPICAL CONFIGURATIONS OF HEATER
CYLINDRICAL RADIANT WITH HELICAL COILS
Commonly used where
Duties are small
Allowable pressure drop is limiting
Used in intermittent services
Tubes are
Helical
Multi-Helix are also used
With or without convection section
Jan' 2005
17TYPES OF HEATER
A A
Section A-A
BOX TYPE WITH VERTICAL TUBES & HORIZONTAL TUBES IN CONVECTION
BOX TYPE WITH INVERTED U TUBES & HORIZONTAL TUBES IN CONVECTION
Jan' 2005
18TYPES OF HEATER
TWIN CELL BOX TYPE WITH VERTICAL TUBES
TWIN CELL BOX TYPE WITH HORIZONTAL TUBES
CABIN TYPE WITH HORIZONTAL TUBES
Jan' 2005
MODES OF OPERATION
Jan' 2005
20MODES OF OPERATION
NATURAL DRAFT
FORCED DRAFT
INDUCED DRAFT
BALANCED DRAFT
Jan' 2005
21MODES OF OPERATION
NATURAL DRAFT OPERATION
In this system the air required for combustion is drawn by the burner
from the atmosphere due to the draft created by the stack
Radiant
ShieldConvection
Stack
Burner
Jan' 2005
22MODES OF OPERATION
FORCED DRAFT APH SYSTEMS
This system has only a forced fan to provide the combustion air
requirements. All the flue gases are removed by stack draft.
Because of the low draft generation capabilities of the stack, the
APH flue gas side pressure drop must be kept very low, thus
increasing the size & cost of APH
Radiant
ShieldConvection
Stack
Air
FD Fan
Jan' 2005
23MODES OF OPERATION
INDUCED DRAFT APH SYSTEMS
This system has only a induced draft fan removing the flue gases
from the heater and maintain the appropriate system draft.
Radiant
ShieldConvection Stack
Flue Gas
ID Fan
Jan' 2005
24MODES OF OPERATION
BALANCED DRAFT OPERATION WITH APH SYSTEMS
This system has both a forced draft (FD) fan and an induced draft (ID)
fan. The system is balanced because the combustion air, provided by
the forced draft fan, is balanced by the flue gas removal of the
induced draft fan.
Jan' 2005
HEATER COMPONENTS
Jan' 2005
26RADIANT SECTION
HEAT IS TRANSFERRED MAINLY BY DIRECT RADIATION
HEAT ABSORPTION IN THE RADIANT SECTION IS TYPICALLY
AROUND 60%
HEAT ABSORPTION DEPENDS ON
BODY TEMPERATURE & EMISSIVITIES
SHAPE & ARRANGEMENT OF SURFACES
CHARACTERISTICS OF COMBUSTION PRODCUTS
AREAS OF REFRACTORY
HEAT ABSORBING SURFACE
VIEW FACTORS
Jan' 2005
27SHIELD SECTION
THE SHIELD SECTION CONTAINS THE TUBE ROWS THAT "SHIELDS" THE CONVECTION ROWS FROM THE DIRECT RADIANT HEAT
Shield Tubes
Jan' 2005
28SHIELD SECTION
TWO IMPORTANT MONITORING POINTS JUST BELOW THE SHIELD
TUBES ARE
THE "BRIDGEWALL" TEMPERATURE WHICH IS THE TEMPERATURE
OF THE FLUE GAS AFTER THE RADIANT HEAT IS REMOVED
THE OTHER IS THE DRAFT MEASUREMENT AT THIS POINT
Jan' 2005
29CONVECTION SECTION
THE CONVECTION SECTION IS LOCATED AFTER SHIELD SECTION
IN THE CONVECTION SECTION, HEAT IS TRANSFERRED BY
CONVECTION
IT CONTAINS ROWS OF EXTENDED SURFACE TUBES TO IMPROVE THE
EFFICIENCY OF THE FURNACE
Shield Tubes
Convection Tubes
Jan' 2005
30
STACK :
IMPORTANT FOR GETTING THE FLUE GASSES OUT FROM HEATER INTO THE ATMOSPHERE TO SAFE LOCATION.
STACK
Jan' 2005
31BURNERS
TYPES OF BURNERS
BASED ON FUEL
– GAS FIRING
– OIL FIRING
– COMBINATION FIRING
BASED ON DRAFT
– NATURAL DRAFT BURNERS
– FORCED DRAFT BURNERS
TYPICAL BURNER COMPONENTS
MAIN GAS/OIL TIPS
PILOT TIP
FLAME SCANNER (IR / UV)
STEAM ATOMISERS
SIGHT PORTS
Jan' 2005
32BURNER TYPES
NATURAL DRAFT BURNER
REQUIRES LESS PRESSURE DIFFERENTIAL TO PROVIDE THE
REQUIRED AIR FOR COMBUSTION THAN THE FORCED DRAFT
BURNER
STACK EFFECT INDUCES THE COMBUSTION AIR
REQUIRED DRAFT/ PRESSURE DIFFERENTIAL AT BURNER,
TYPICALLY 0.1 – 1.0 IN H2O.
Jan' 2005
33BURNER TYPES
FORCED DRAFT BURNERS
COMBUSTION AIR IS SUPPLIED BY A FD FAN
NORMALLY REQUIRES 0.3 TO 4.0 IN H2O
BURNERS HAVE DIFFERENT AIR REGISTERS FOR PRIMARY AND
SECONDARY AIR INTAKE. THE AIR MAY BE DELIVERED TO THE
REGISTERS BY AN AIR PLENUM
INCORPORATES STAGED AIR OR FUEL DESIGNS (SPLITTING
COMBUSTION AIR OR FUEL WITHIN BURNER)
THESE BURNER TYPES HAVE BECOME STANDARD BECAUSE
ENVIRONMENTAL AIR STANDARDS DEMAND THE BEST
COMBUSTION TECHNOLOGY AVAILABLE
Jan' 2005
34AIR PREHEATERS
THE AIR PREHEAT SYSTEM IS USED TO PREHEAT THE
COMBUSTION AIR GOING TO THE BURNERS
SINCE IT COOLS THE FLUE GAS FURTHER, WHILE REMOVING
HEAT, IT IMPROVES THE EFFICIENCY OF THE FURNACE
USING AN AIR PREHEAT SYSTEM WILL RESULT IN OVERALL
EFFICIENCIES ABOVE 90%.
Jan' 2005
35AIR PREHEATERS
MERITS OF APH
ENHANCE EFFICIENCY ( ~ 90-93 %).
TO ENHANCE AIR-FUEL MIXING (HIGH AIR VELOCITY)
REDUCE OIL BURNER FOULING
MORE COMPLETE COMBUSTION OF HEAVY FUELS
DEMERITS OF APH
INCREASES POTENTIAL OF SO3 & NOX GENERATION AS
ADIABATIC FLAME TEMPERATURE IS HIGH
REDUCES THE STACK TEMP., SO EITHER ID FAN OR TALLER
STACK WILL BE REQUIRED
Jan' 2005
36TYPES OF AIR PREHEATER
DIRECT APH SYSTEMS
(MOST COMMON TYPE)
REGENERATIVE
RECUPERATIVE
– Tube type
– Plate type
INDIRECT APH SYSTEMS
EXTERNAL HEAT SOURCE
APH SYSTEMS
Direct APH systems
Jan' 2005
37TYPES OF AIR PREHEATER
DIRECT APH SYSTEMS
(MOST COMMON TYPE)
REGENERATIVE
RECUPERATIVE
– Tube type
– Plate type
INDIRECT APH SYSTEMS
EXTERNAL HEAT SOURCE
APH SYSTEMS
Indirect APH systems
Jan' 2005
38TYPES OF AIR PREHEATER
DIRECT APH SYSTEMS
(MOST COMMON TYPE)
REGENERATIVE
RECUPERATIVE
– Tube type
– Plate type
INDIRECT APH SYSTEMS
EXTERNAL HEAT SOURCE
APH SYSTEMS
External Heat Source APH systems
Jan' 2005
39TYPES OF AIR PREHEATER
TUBE TYPE
TUBES MADE OF CAST IRON OR GLASS
WHEN CAST IRON TUBES ARE PROVIDED, THE MIN. METAL TEMP
IS KEPT 10-15 0C ABOVE DEW POINT.
ADVANTAGES
VERY LOW LEAKAGE, EASY TO DESIGN & FABRICATE,
NORMALLY LOW UNIT COST, EASY FOR MAINTAINENCE
DISADVANTAGES
HIGHER PRESSURE DROP AS COMPARED TO PLATE TYPE
HEAVY, SO INCREASES THE STRUCTURAL COST IF PLACED
ON BOARD
GLASS TUBES MAY GET DAMAGE AND RESULT IN LEAKAGES
Jan' 2005
40TYPES OF AIR PREHEATER
PLATE TYPE
TYPICALLY IT CONTAINS CARBON STEEL PLATES (~ 2 mm THICK)
ASSEMBLED IN FRAME
THESE MODULES ARE STANDARD IN SIZE AND REQUIRED
CAPACITY IS OBTAINED BY INCREASING THE NUMBER OF
MODULES
ADV: LOW PRESSURE DROP, LIGHT IN WEIGHT & COMPACT,
SO MOSTLY USED AS ONBOARD UNIT
DISADV: DIFFICULT FOR MAINTENANCE
EASY TO FOUL & CORRODE(SOMETIMES PORCELAIN
ENAMELED PLATES ARE USED ) AND HIGH UNIT COST
Jan' 2005
41FANS & BLOWERS
USE OF FANS AND BLOWERS
FORCED DRAFT FANS
INDUCED DRAFT FANS
PURGE FANS
Jan' 2005
42FANS & BLOWERS
FORCED DRAFT FANS
FORCED DRAFT (FD) FANS ARE USED TO SUPPLY COMBUSTION AIR TO THE
BURNER(S)
THEY DRAW AMBIENT AIR AND FORCE IT TO THE BURNER SYSTEM VIA APH
FOR THE COMBUSTION OF FUEL.
THEY NORMALLY ARE NOT EMPLOYED TO MOVE THE FLUE GASES
THROUGH THE FURNACE.
BUT IN SPECIAL CASES, SUCH AS A POSITIVE PRESSURE, SINGLE FAN AIR
PREHEAT SYSTEM, THEY MAY ALSO SERVE THIS PURPOSE.
INDUCED DRAFT FANS
INDUCED DRAFT (ID) FANS ARE GENERALLY USED TO PULL THE
FLUE GAS FROM THE HEATER AND DISCHARGE IT TO ATMOSPHERE
DIRECTLY OR THROUGH AN AIR PREHEATER
Jan' 2005
43FANS & BLOWERS
PURGE FANS
THE PURPOSE OF THE PURGE FAN IS TO DISPLACE ANY
POTENTIALLY EXPLOSIVE GAS MIXTURES FROM
HEATER FIREBOX, PRIOR TO LIGHTING OF THE
BURNERS
PURGE FANS ARE ESPECIALLY DESIRABLE ON HEATERS
THAT ARE SHUT DOWN AND RELIGHTED ON A
REGULAR BASIS
HEATERS EMPLOYING FD OR ID FANS DO NOT NORMALLY
REQUIRE ADDITIONAL PURGE FANS. RUNNING THE
FD OR ID FAN USUALLY WILL PURGE THE SYSTEM
Jan' 2005
44DAMPER
FUNCTIONS OF DAMPER ARE
CONTROL OF FLUID FLOW THROUGH ANY DUCT (CONTROL DAMPER)
NORMALLY USED IN STACK, FD/ID FAN
AND COMBUSTION AIR BYPASS
AROUND THE APH
MAIN DAMPER IN THE STACK IS USED
TO CONTROL DRAFT AT ARCH PREVENT FLOW OF FLUID THROUGH ANY DUCT (ISOLATION DAMPER)
NORMALLY USED IN FLUE GAS/
COMBUSTION AIR DUCT FOR ISOLATION
PURPOSE OF APH
BYPASS DUCT
Jan' 2005
45TYPES OF DAMPER
CONTROL DAMPER
IT CAN BE EITHER MANUAL OR AUTOMATIC IN OPERATION
IT ALWAYS HAS SOME LEAKAGE ( ~3%)
IT CAN BE SINGLE BLADE ( LIKE BUTTERFLY DAMPER ) OR
MULTIPLE BLADE ( LIKE LOUVER DAMPER )
1.2
NO. OF BLADES ~ INSIDE AREA OF THE DUCT OR STACK (M2)
Jan' 2005
46TYPE OF DAMPERS
SHUT OFF DAMPER
IT CAN BE OPERABLE MANUALLY BY CHAIN & PULLEY
ARRANGEMENT (GUILLOTINE BLIND) OR BY AN ELECTRIC
MOTOR (SWING GATE)
IT IS DESIGNED FOR A HIGH SEALING EFFICIENCY ( ~99.9%).
Jan' 2005
47SOOT BLOWERS
SOOT IS GENERATED AS A RESULT OF IMPROPER
COMBUSTION
THIS SOOTS DEPOSITS OVER EXTENDED SURFACE AND
DECREASES HEAT TRANSFER RATE
SOOT HAS TO BE REMOVED TO MAINTAIN HEAT TRANSFER
COEFFICIENT
TYPE OF SOOT BLOWERS
RETRACTABLE TYPE
FIXED ROTARY TYPE
VIBRATION TYPE
Jan' 2005
48SOOT BLOWERS
RETRACTABLE TYPE
MOSTLY USED FOR HIGH TEMPERATURE & DIRTIER FUEL
APPLICATION. IT IS MORE COSTLY BUT HAS BETTER CLEANING
CHARACTERISTICS
FIXED ROTARY TYPEIT IS CHEAPER THAN RETRACTABLE TYPE BUT CAN NOT BE USED
IN HIGH TEMPERATURE OR DIRTY FUEL SERVICES
VIBRATION TYPE
ULTRASOUND WAVES ARE USED IN THIS TYPE TO CREATE
VIBRATION TO DISENGAGE THE SOOT FROM THE COILS. VERY
LIMITED EXPERIENCE IS AVAILABLE FOR THIS TYPE
Jan' 2005
49REFRACTORY
REFRACTORY : TO REDUCE THE HEAT LOSS TO
ATMOSPHERE.
THREE COMMON TYPES:
FIREBRICKS GENERALLY USED FOR BRIDGEWALLS AND FLOORS WITH
DENSITY ABOUT 150 LB/CUFT, MUST BE DRIED OUT SLOWLY
CASTABLES IT IS A MIXTURE OF LUMNITE(CEMENT),HAYDITE (AGGREGATE)
AND VERMICULITE(INSULATION) WITH DENSITY OF ABOUT 55
LB/CUFT. NEEDS CURING & DRYOUT BEFORE STARTUP
CERAMIC FIBRE IT IS AVAILABLE IN LAYERED & MODULAR TYPE. A SANDWICH
CONSTRUCTION OF THIS MATERIAL IN TWO DENSITIES (2-
3INCHES LAYER OF 4 LB/CUFT AND 1 INCH LAYER OF 8
LB/CUFT) IS USED.
Jan' 2005
55
COMBUSTION AND RELATED SUBJECTS
Jan' 2005
56COMBUSTION AND RELATED SUBJECTS
NOX
PURPOSE OF EXCESS AIR
ACID DEW POINT OF FLUE GAS
Jan' 2005
57NOX AND OTHER CONSIDERATIONS
THE FIRED HEATER INDUSTRY HAS CONCENTRATED ON THE
TWO PRIMARY SOURCES OF NITROGEN OXIDES (NOX)
THESE ARE NORMALLY REFERRED TO AS THERMAL NOX AND
FUEL NOX
THE THREE MAIN STRATEGIES FOR REDUCING NOX
EMISSIONS: REDUCE PEAK TEMPERATURES OF THE FLAME ZONE
REDUCE GAS RESIDENCE TIME IN FLAME ZONE
REDUCE OXYGEN CONCENTRATION IN THE FLAME ZONE
Jan' 2005
58NOX AND OTHER CONSIDERATIONS
MAIN STRATEGIES FOR REDUCING NOX EMISSIONS
REDUCE PEAK TEMPERATURES
– USING A FUEL-RICH PRIMARY FLAME ZONE
– DECREASING THE ADIABATIC FLAME TEMPERATURE BY DILUTION
– DILUTING AIR-FUEL MIXTURE BY FLUE GAS MIXING
REDUCE THE GAS RESIDENCE TIME IN THE HOTTEST PART OF THE
FLAME ZONE
– CHANGING THE SHAPE OF THE FLAME ZONE
– USING THE STEPS LISTED IN STRATEGY 1
REDUCE THE O2 CONTENT IN THE PRIMARY FLAME ZONE
– DECREASING THE OVERALL EXCESS AIR RATES
– CONTROLLED MIXING OF FUEL AND AIR
– USING A FUEL-RICH PRIMARY FLAME ZONE
Jan' 2005
59PURPOSE OF EXCESS AIR
PERFECT COMBUSTION
PERFECT COMBUSTION IS ACHIEVED WHEN ALL THE FUEL IS
BURNED USING ONLY THE THEORETICAL AMOUNT OF AIR
PERFECT COMBUSTION CANNOT BE ACHIEVED IN A FIRED
HEATER
INCOMPLETE COMBUSTION INCOMPLETE COMBUSTION OCCURS WHEN ALL THE FUEL IS NOT
BURNED, WHICH RESULTS IN THE FORMATION OF CO, SOOT
AND SMOKE
Jan' 2005
60PURPOSE OF EXCESS AIR
COMPLETE COMBUSTION
COMPLETE COMBUSTION IS ACHIEVED WHEN ALL THE FUEL IS
BURNED USING THE MINIMAL AMOUNT OF AIR ABOVE THE
THEORETICAL AMOUNT OF AIR NEEDED TO BURN THE FUEL
THIS MINIMAL AMOUNT IS CALLED THE “EXCESS AIR”
PERCENTAGE OF EXCESS AIR RANGES FROM 10 TO 25%
WITH COMPLETE COMBUSTION, THE FUEL IS BURNED AT THE HIGHEST COMBUSTION EFFICIENCY
Jan' 2005
61ACID DEW POINT
SULFUR DIOXIDE PRODUCED AS A RESULT OF COMBUSTION GETS CONVERTED INTO SO3 AND REACTS WITH WATER VAPOR PRESENT IN THE FLUE GAS TO FORM SULFURIC ACID
SULFURIC ACID AT LOW TEMPERATURE CONDENSES ON THE INSIDE SURFACE OF THE REFRACTORY
HARMFUL FOR TUBES, REFRACTORY & THE CASING
Jan' 2005
62ACID DEW POINT
FLUE GAS DEW POINT DEPENDS ON FUEL SULFUR CONTENT FLUE GAS O2 CONTENT FLUE GAS MOISTURE CONTENT COMBUSTION TEMP FUEL & FLUE GAS ADDITIVES
TO AVOID FLUE GAS CONDENSATION, THE MIN. METAL TEMP IS KEPT 10-15 deg C ABOVE THE FLUE GAS DEW POINT
Jan' 2005
63
PROCESS CONSIDERATIONS
Jan' 2005
64PROCESS CONSIDERATIONS
PRIMARY CONSIDERATIONS
CLIENTS REQUIREMENTS
APPLICABLE STANDARDS
API STANDARD 560
(FIRED HEATERS FOR GENERAL REFINERY SERVICE)
THIS STANDARD COVERS THE MINIMUM REQUIREMENTS FOR THE
DESIGN, MATERIALS, FABRICATION, INSPECTION, TESTING,
PREPARATION FOR SHIPMENT AND ERECTION OF FIRED HEATERS,
AIR PREHEATERS, FANS AND BURNERS FOR GENERAL REFINERY
SERVICE.
Jan' 2005
65
(A) NATURAL DRAFT:-
GAS FIRING : 20%
OIL FIRING : 25%
(B) FORCED DRAFT:-
GAS FIRING : 15%
OIL FIRING : 20%
EXCESS AIR CONSIDERATIONS
Jan' 2005
66GENERAL CONSIDERATIONS
MAINTAIN HYDRAULIC SYMMETRY IN INLET/ OUTLET MANIFOLDS:
PIPE LENGTHS, FITTINGS SHALL BE SAME FOR ALL PASSES
MIN.NO. OF PASSES FOR VAPORIZING FLUIDS
MIN. RADIATION LOSS ( BASED ON LHV):
WITHOUT APH=1.5% WITH APH=2.5%
ARCH PRESSURE:
NORMAL VALUE -2.5 mm WG
Jan' 2005
67
GENERALLY THERE SHOULD BE MORE THAN ONE BURNER IN A
FURNACE
NO. OF BURNERS IN A CYLINDRICAL FURNACE SHOULD
PREFERABLY BE A MULTIPLE OF THE NO. OF PROCESS PASSES
FOR EVEN HEAT DISTRIBUTION
IN A CYLINDRICAL FURNACE WITH SEVERAL BURNERS
ARRANGED IN A CIRCLE, THERE IS A MINIMUM DIMENSION OF
THE BURNER CIRCLE
BURNER
Jan' 2005
68BURNER
NO. OF BURNERS REQUIRED FOR A GIVEN HEAT RELEASE
SHALL BE OPTIMIZED BASED ON FOLLOWING CRITERIA:
IN NORMAL CASES, MAX HEAT RELEASE PER BURNER
SHALL NOT EXCEED 3.0 MMKCAL/HR.
TURNDOWN REQUIREMENTS TO BE CONSIDERED
FLAME DIMENSION: FLAME IMPINGEMENT ON TUBES,
REFRACTORY & ADJACENT BURNERS SHALL BE AVOIDED
Jan' 2005
69BURNER
NO. OF BURNERS MAX./NOR. HEAT RELEASE <5 1.25
6-7 1.20 >8 1.15
MIN PILOT HEAT RELEASE20000 KCAL/HR
OIL ATOMIZATION:
STEAM ATOMIZATION : STEAM/OIL ~ 0.3 KG/KG
PRESSURE DIFFERENTIAL BETWEEN FUEL OIL & STEAM
~2.1 kg/cm2g
FOR OIL FIRED BURNERS, MAX. VISCOSITY IS 43 CST.
Jan' 2005
70BURNER
POLLUTANTS FROM COMBUSTION:
SOX : SOX (SO2 & SO3 ) GENERATION DEPENDS THE SULFUR
CONTENT OF THE FUEL
NOX :NOX (NO & NO2 ) IS GENERATED THERMALLY BY THE REACTION OCCURRING ABOVE 700-800 0C
UNBURNT HYDROCARBON:RESULT OF IMPROPER MIXING OF FUEL WITH AIR
SPM: SOOT, ASH ETC.
Jan' 2005
71BURNER
MIN PARAMETERS REQUIRED FOR BURNER SELECTION
HEAT RELEASE : MIN / NOR / MAX
TYPE OF BURNER : NATURAL DRAFT, FORCED DRAFT, LOW
NOX, COMBINATION
FUEL DETAILS : COMPOSITION, LHV, PRESSURE,
TEMPERATURE
COMBUSTION AIR : TEMPERATURE, PRESSURE, RELATIVE HUMIDITY
NO. OF BURNERS, IGNITION DETAIL
EMISSION REQUIREMENTS: SOX, NOX, UHC, SPM, CO ETC
NOISE LIMITATION: 85 DBA AT 1M FROM BURNER
Jan' 2005
72RADIANT SECTION DESIGN
RADIANT AVERAGE FLUX ( KCAL/HR/M2 ):
CRUDE 32500
VACUUM / NAPHTHA / DHDS 27100
DELAYED COKER / VISBREAKER 25000
PROCESS MASS VELOCITY (KG/S/M2)
CRUDE HEATER 1200 TO 1700
REBOILERS 700 TO 1200
HOT OIL HEATERS 1700 TO 2200
HYDROTREATERS 700 TO 1000
MAXIMUM FILM TEMP SHALL NOT BE EXCEEDED
MAXIMUM METAL TEMP SHALL NOT BE EXCEEDED
Jan' 2005
73RADIANT SECTION DESIGN
VERTICAL CYLINDRICAL HEATERS: H / D < 2.75
HORIZONTAL TUBE HEATERS: H / W < 2.75
MAX. LENGTH FOR VERTICAL TUBES = 18.3 M
MAX. UNSUPPORTED LENGTH FOR HORIZONTAL TUBES
SHALL BE 35 TIMES OD OR 6M WHICHEVER IS LESS
MIN. DISTANCE B/W REFRACTORY & TUBE CENTER =
1.5 x NOMINAL DIAMETER
DUTY ABSORBED IN RADIANT = AROUND 60% OF TOTAL
ABSORBED DUTY
NORMAL BRIDGE WALL TEMP = 600 TO 800 DEG C
Jan' 2005
74CONVECTION SECTION DESIGN
FLUE GAS MASS VELOCITY ( KG/S/M2):
NATURAL DRAFT : 1.5 - 3.0
FORCED DRAFT : 3.0 - 4.5
TYPES OF EXTENDED SURFACES:
STUDS : FOR HEAVY FUELS ( e.g. FUEL OIL )
FINS : FOR LIGHTER FUELS ( e.g FUEL GAS)
STUDS SOLID FINS SERRATED FINS
Jan' 2005
75CONVECTION SECTION DESIGN
NORMALLY FIRST 3 ROWS ARE CONSIDERED AS SHIELD
TUBES. HENCE NO EXTENDED SURFACES ARE PROVIDED TO
PREVENT OVERHEATING OF THESE TUBES
NEVER EXCEED CRITICAL VELOCITY
MAXIMUM FILM TEMP SHALL NOT BE EXCEEDED
MAXIMUM METAL (TUBE & EXTENDED SURFACES) TEMP
SHALL NOT BE EXCEEDED
Jan' 2005
76STACK DESIGNSTACK DESIGN
STACK IS DESIGNED TO MAINTAIN -2.5 MMWG PRESSURE AT
MINIMUM 120% OF DESIGN HEAT RELEASE WITH DESIGN EXCESS AIR &
MAX. AMBIENT TEMP
• TOTAL DRAFT GAIN = DRAFT GAIN IN CONVECTION +
DRAFT GAIN IN STACK
• TOTAL PRESSURE LOSS = PRESSURE LOSS IN CONVECTION (ENTRY LOSS, LOSS ACROSS TUBES & EXIT LOSS)
+ PRESSURE LOSS IN STACK (ENTRY & EXIT LOSSES,DAMPER LOSS, FRICTION LOSS)
• NORMAL FLUE GAS VELOCITY IN STACK:
NATURAL DRAFT 8 M / SINDUCED DRAFT 15 - 20 M / S
Jan' 2005
77FORCED DRAFT FANFORCED DRAFT FAN
FD FANS ARE DESIGNED WITH MIN 15 % MARGIN OVERAIR FLOW RATE CORRESPONDING TO DESIGN HEAT RELEASE
FD FAN DISCHARGE PRESSURE SHOULD BE CAPABLE ENOUGH TO OVER COME:
• COMBUSTION AIR DUCT PRESSURE LOSS (STRAIGHT& FITTINGS)• APH• BURNERS
DESIGN VELOCITIES IN COMBUSTION AIR DUCT:STRAIGHT, TEE, TURNS ~15 M / SBURNER AIR SUPPLY & PLENUM DUCT 7.5 - 10.5 M / S
NORMALLY CENTRIFUGAL FAN WITH FIXED SPEED DRIVE ARE USED
Jan' 2005
78FORCED DRAFT FANFORCED DRAFT FAN
• ONE FAN IS RUNNING, OTHER IS STANDBY - SIMPLE &
CHEAPER BUT LESS RELIABLE
FOR CRITICAL APPLICATIONS ( VIZ. CDU/VDU ETC.) 2 FD FANS ARE PROVIDED
TWO OPTIONS ARE AVAILABLE IN CASE OF 2 FD FANS
PROVIDED:
• BOTH THE FANS ARE RUNNING AT 50 % LOAD - COSTLY
BUT MORE RELIABLE
MOC OF CASING - CS
MOC OF IMPELLER - CS
Jan' 2005
79FORCED DRAFT FANFORCED DRAFT FAN
FOLLOWING PARAMETERS TO BE SPECIFIED FOR THE
SELECTION OF FD FAN:
(A) FLOW RATE: MIN / NOR / MAX
(B) TEMP: MIN / NOR / MAX / DESIGN
(C) INLET PRESSURE: MIN / NOR
(D) OUTLET PRESSURE : NOR / MAX
(E) HUMIDITY
(F) DRIVER : MOTOR / STEAM TURBINE
(G) SPARES
Jan' 2005
80INDUCED DRAFT FANINDUCED DRAFT FAN
- ID FANS ARE DESIGNED WITH MIN 20 % MARGIN
OVER FLUE GAS FLOW RATE CORRESPONDING TO
DESIGN HEAT RELEASE
- NORMAL DISCHARGE PRESSURE OF ID FAN IS
AMBIENT PRESSURE
-SUCTION PRESSURE = ARCH PRESSURE -
TOTAL PRESSURE LOSS IN CONVECTION -
TOTAL PRESSURE LOSS IN OFF TAKE DUCT -
PRESSURE DROP IN INLET DAMPER
- DESIGN VELOCITIES IN OFF TAKE DUCT:
STRAIGHT, TEE, TURNS ~12 M / S
- MOC OF CASING - CS / SS
- MOC OF IMPELLER - CS / SS / CORTEN STEEL
Jan' 2005
81INDUCED DRAFT FANINDUCED DRAFT FAN
FOLLOWING PARAMETERS TO BE SPECIFIED FOR THE SELECTION OF ID FAN:
(A) FLOW RATE: MIN / NOR / MAX
(B) TEMP: MIN / NOR / MAX / DESIGN
(C) INLET PRESSURE: MIN / NOR
(D) OUTLET PRESSURE : NOR / MAX
(E) FLUE GAS COMPOSITION
(F) DRIVER : MOTOR / STEAM TURBINE
(G) SPARES
Jan' 2005
82DRIVES FOR FANDRIVES FOR FAN
FIXED SPEED MOTOR (1000 OR 1500 RPM ) - CAPACITY CONTROL
BY INLET GUIDE VANS/ INLET DAMPER
TYPE OF DRIVE:
VARIABLE SPEED DRIVE (FLUID COUPLING, VFD) -
CAPACITY CONTROL BY VARYING SPEED
Q N , H N2 , P N3
Jan' 2005
83AIR PREHEATERSAIR PREHEATERS
• AIR / FLUE GAS FLOWRATES : MIN / NOR / MAX
• AIR / FLUE GAS TEMPERATURES (IN/OUT): MIN / NOR @ MAX / DES
• AIR / FLUE GAS PRESSURES (IN) : MIN / NOR / MAX / DES
• TYPE OF APH
• DUTY : NOR/ MAX
• ALLOWABLE PRESSURE DROP (AIR SIDE / FLUE GAS SIDE)
• SULFUR DEW POINT OF FLUE GAS
• FLUE GAS COMPOSITION
• REQUIREMENTS OF TUBE SKIN THERMOCOUPLE
MIN DATA REQUIRED FOR AIR PREHEATER SPECIFICATION
Jan' 2005
84SOOT BLOWERSSOOT BLOWERS
• MIN STEAM FLOWRATE REQUIRED : 4535 KG/HR
• MIN STEAM PRESSURE REQUIRED : 10 KG/CM2 G
• EACH SOOT BLOWER SHOULD COVER MAXIMUM
1.2M OR 5 TUBE ROWS, WHICHEVER IS LESS
• SOME TIMES STEAM LANCING NOZZLES ARE
PROVIDED TO REMOVE SOOT FOR SMALLER
INSTALLATIONS
Jan' 2005
85
• VANADIUM & SODIUM ATTACK IN PRESENCE OF SULFUR
• OXIDATION AT HIGH TEMPERATURE
• ATTACK BY H2S
• ATTACK BY POLYTHIONIC ACID
• ATTACK BY CHLORINE
• ATTACK BY H2
• CARBURISATION
PROCESS FLUID GOVERNS THE MATERIAL SELECTION
HEATER COIL METALLURGYHEATER COIL METALLURGY
Jan' 2005
86
- CARBON STEEL ~ 540 DEG C
- LOW ALLOY STEEL (P11,P22) ~ 650 DEG C
- HIGH ALLOY STEEL ( P5, P9) ~ 650- 705 DEG C
- AUSTENITIC STAINLESS STEEL ~ 815 DEG C
( SS304 / 310 / 321 / 347)
FOLLOWING TUBE MATERIALS ARE NORMALLY USED:
FOLLOWING SUPPORT MATERIALS ARE NORMALLY USED:
CS : 427OC,
25CR-20NI : 871OC,
50CR-50NI-CB : 982OC
HEATER CASING IS ALWAYS MADE OF CARBON STEEL
METALLURGYMETALLURGY
Jan' 2005
87METALLURGYMETALLURGY
CRUDE P5
VACUUM P9
DELAYED COKER / VISBREAKER P9
HYDROTREATER SS 321 / SS
347
HOT OIL HEATER CS
REBOILERS CS
TYPICAL TUBE MATERIAL FOR VARIOUS SERVICES:
Jan' 2005
88TYPICAL INPUT DATA FOR THERMAL DESIGN OF FIRED HEATERS
HEATER DESIGN DUTY AND THROUGHPUT
PROCESS INLET AND OUTLET TEMPERATURES
PROCESS INLET OR OUTLET PRESSURE
PROCESS FLUID ENTHALPY CURVE AT OPERATING CONDITIONS
PROCESS FLUID TRANSPORT PROPERTIES AT OPERATING
CONDITIONS
FLASH VAPORISATION CURVE FOR 2-PHASE HEATERS WHERE
FLASHING OCCURS (E.G. VACUUM FURNACES AND CRUDE
FURNACES
FUEL TYPE AND COMPOSITION
CORROSIVE ELEMENTS IN FUEL (SULPHUR, VANADIUM)
Jan' 2005
89TYPICAL INPUT DATA FOR THERMAL DESIGN OF FIRED HEATERS
ALLOWABLE PRESSURE DROP
AVERAGE ALLOWABLE RADIANT HEAT TRANSFER RATE
MAXIMUM ALLOWED FILM TEMPERATURES FOR FEEDSTOCK IF THE
SERVICE IS SUSCEPTIBLE TO COKE FORMATION
TUBE MATERIAL
TYPE OF HEATER TO BE USED (e.g ALL-RADIANT, CYLINDRICAL,
BOX/ CABIN TYPE)
DESIRED OVERALL FURNACE EFFICIENCY
Jan' 2005
90TYPICAL INPUT DATA FOR THERMAL DESIGN OF FIRED HEATERS
EXCESS AIR TO BE USED
TYPE OF BURNERS : FORCED OR NATURAL DRAFT
FURNACE HEAT LOSSES AS PERCENT OF HEAT LIBERATION
DETAILS OF ANY LONG-TERM TURN-DOWN CONDITIONS TO BE TAKEN
INTO ACCOUNT IN DESIGN
AVAILABLE PLOT AREA FOR HEATER
Jan' 2005
91THERMAL DESIGN OUTPUT FOR FIRED HEATER
API DATASHEET
PROCESS PARAMETERS (FLOW, TEMPERATURE, PRESSURE,
COMPOSITION, ETC OF PROCESS FLUID AS WELL AS FLUE GAS
AND AIR) IN COILS AND FIREBOX
COIL DETAILS (DIAMETER, LENGTH, THICKNESS, MOC, NO OF
PASSES, ROWS, ETC.)
AVERAGE/ MAXIMUM RADIANT FLUX, MAX. TUBE METAL TEMP.,
INSIDE FILM TEMP.,
REFRACTORY (THICKNESS, TYPE, ETC.)
STACK (DIAMETER, HEIGHT)
BURNERS (DUTY, NUMBER)
Jan' 2005
92THERMAL DESIGN OUTPUT FOR FIRED HEATER
DATA SHEETS FOR BOUGHT OUT ITEMS
BURNERS
FANS
DAMPER
SOOT BLOWER
APH
