dcu heater mod
DESCRIPTION
DCUTRANSCRIPT
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PRESENTATION ON
DCU HEATER
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Presentation Context
1. Heater and its classification
2. Heater configuration
3. Heater section details4. Heater Inspection check points
5. Safety Interlocks
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What is a Heater?
A heater is a heat transfer equipment where heat
of combustion of fuel oil/fuel gas is used to
increase the temperature of the desired fluid.
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Classification of Heaters
1. On the basis of Draft (Natural, Forced,
Induced and Balanced Draft)
2. On the basis of Structural Configuration
(Cylindrical, Cabin, Multi cell)
3. On the basis of Radiant Tube Configuration
(Vertical, Horizontal, Helical and Wicket
Type)
4. On the Basis of Burner position (Bottom
fired, Top fired and Side fired)
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Design of Heater
API 560 : Fired Heater for Refinery
API 530 : Heater Tube thickness in Refinery
API RP 550 : Installation of Instruments and
Control System for Fired heater and SteamGeneration
EA 7301 : Guidelines for Noise
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DCU HEATER(14-FF-00-101 A/B)
CONFIGURATION
Balanced Draft, Twin Cell, Cabin Type,
Horizontal Tubes Double Fired.
Heat Absorption :- 17.2 MMKcal/Hr
No of Tubes in Radiation Zone:- Total-64
(32 / Cell)
No of Tubes in Convection Zone:-56
No of Soot Blowers:-16/heater
No of Burners:-32/heater
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Fluid Handled
Heater Feed:- VR from VDU column
IN OUT
1. Liquid (Kg/hr) 179605 143676
2. HC Vapor (Kg/hr) - 359293. Operating pressure 22-28 5.25
(kg/cm2abs)
4. Operating temperature(oC) 297.2 506
5. Liquid density (kg/m3) 908.5 751.3
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Heat Distribution in Heater Section
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Radiant Section : 70-75%
Convection Section : 30-25%
Heat Distribution in Heater Section
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DCU-Heater configuration & Air Flow
RADIATION
ZONE
FUEL OIL
FUEL GAS
STEAM
PLENUM
CHAMBER
CONVECTION
ZONE
STACK
AIR PREHEATER
ID FAN
FD FAN
DAMPER
B
R
I
D
G
E
W
A
L
L
GAPH
CAPH
AIR
327 C
163 C
Amb
215 C
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CAPH
GAPH
IGV
IGV SOB-02
UV-22
UV-18
SOB-01
SOB-04
SOB-07
SOB-05
SOB-16
SOB-17
SOB-08SOB-14
SOB-03
UV-20
UV-19
UV-21
UV-16
UV-17
UV-04 UV-06
UV-10
UV-11
UV-12
UV-13
14-FF-00-
101A
14-FF-00-
101B
UV-08UV-09
UV-15UV-14
UV-03
UV-
SOB-09 SOB-15
Bird
screen
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Why Two Heater ?
Normally both heater in operation
To allow one heater to be offline for
decoking while other heater is on 50-60%
operation
Heater can be decoked by pigging
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DCU Heater sections
1. Convection Zone
2. Radiation Zone
3. Soot Blowers
4. Air Preheater Including Glass APH and Cast APH5. FD Fan
6. ID Fan
7. Superheater
8. Burners
9. Snuffing Steam
10. Stack
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DCU Heater sections
1. Convection Zone:-
DCU heater convection zone having 56 tubes
Feed is preheated with flue gases. High skin temp. of convection tubes indicates more negative
draft.
Lower skin temp. of convection tubes indicates soot
deposition. MP steam is superheated in the convection section.
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2. Radiation Zone:-
DCU heater radiation zone having 32 tubes/pass
The radiant tubes are horizontal, and double fired. In the radiant section of the heater it receive radiant heat
directly from the flames, gas and wall.
The radiant zone with its refractory lining is called the firebox.
Most of the heat is gained there.
DCU Heater sections
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3. Soot Blowers
Soot blowers are used for removing of soot deposited on
finned tubes in convection zone
DCU heater having 32 soot blowers During the soot blowing period keep close watch on the
heater parameters (Furnace arch press high, draft)
Bypass the Air Pre-Heater Section.
Open stack damper slowly to maximum extent keeping closewatch on Furnace draft.
Inform Utility about increase in steam consumption during
soot blowing operation
DCU Heater sections
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Before starting the soot blowing, the steam line should be
drained thoroughly. Any water carryover will damage the
Refractory lining
After line condensate draining open gradually steam valve
fully
Start soot-blowing operation one by one by keeping watch
on furnace pressures. Still in case if any excess
pressurization is observed soot blower to be stopped and
further condensate removal process is to be repeated
DCU Heater sections
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4. Air Preheater Including Glass APH and Cast APH
An air preheater improves the efficiency of a furnace
sometimes by as much as 5 to 10%.
a) GAPH GAPH is the first inlet of fresh air in tube side while shell
side having flue gas
No of glass tubes : 1850
OD & thickness : 32 mm , 2 mm
Heating surface area : 394 M2
DCU Heater sections
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b) CAPH
Preheated air from GAPH enters the tube side of CAPH
The cast iron tubes have integral fins on both internal andexternal surfaces
Heating surface area is 1960 M2
DCU Heater sections
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5. FD & ID fan
FD fan :
To provide combustion air to burners by two nos of FD fan
Total air requirement is 61372 kg/hr Both fan are running at 50% capacity
In case of tripping of one fan other fan will auto start
ID fan remove flue gas from heater, maintained draft in
heater The ID fan and FD fan regulate the flow of air to the
combustion chamber
The ID fan and FD fan supplying combustion air under
balanced draft condition
DCU Heater sections
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6. Superheater
In convection zone above the feed convection bank
superheater is provided
Saturated MP steam being fed and utilized flue gas heatinto superheated MP steam
7. Snuffing steam
Snuffing is the action of smothering a fire by using steam. Assteam is inert and will not burn, it replaces the air around the
fire causing it to suffocate.
Snuffing steam is provided on the fire box side
DCU Heater sections
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S
NO
DESCRIPTION OF CAUSES CONSEQUENCES
1 Emergency switch If there is manually activated emergency switch either
from the DCS or field, the fuel gas, fuel oil supply to all
burners including pilot are cut off
2 Low-Low heater feed flow In case of low-low heater feed flow through any of the
coil, the fuel gas and fuel oil to all burners of the furnace
is cut off
3 High-High combustion pressure It is dangerous when the combustion chamber pressure
becomes higher than atmospheric pressure since hot
flue gas may leak to atmosphere thereby causing a risk
to operating personnel and furnace out side wall. In this
event damper of ID fan are open. If the condition remain
same for 30 second then FD fan tripped and fuel gas and
fuel oil supply to all burners including pilot is cut-off
Heater Safety Interlocks
The heater safeguarding system has the following trip
initiators
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S
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DESCRIPTION OF CAUSES CONSEQUENCES
4 Low-Low combustion air pressure In case of low-low combustion air flow, caused for
instance by a failure of the FD fan, combustion of fuel is
not possible. In this event fuel gas and fuel oil supply to
all burners including pilot is cut-off5 High-High fuel gas KO drum level If there is a high level in the fuel gas KO drum there ia a
chance of liquid fuel carryover which dose not combust
completely in the burners. This is dangerous situation.
Therefore, in the event of this condition the fuel gas and
fuel oil supply to all burners including pilot is cut-off
6 High-High fuel gas pressure In case of the pressure of the fuel gas going to theburners can become higher than the maximum pressure
for which the burners designed, the fuel gas firing has to
be tripped
Heater Safety Interlocks
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S
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DESCRIPTION OF CAUSES CONSEQUENCES
7 Low atomizing steam/fuel oil
differential pressure
If the differential pressure between the steam and fuel oil
falls becomes too low, there may be insufficient steam
being supplied to the burner to provide sufficient
atomizing of the fuel oil. In this case the fuel oil supply toburners are cut-off
8 High-High heater outlet temperature In case of high-high heater outlet temp., the fuel gas and
fuel oil supply to all burners is cut-off
9 Forced draft fan low speed In case of failure or mechanical problems with the FD fan
the other fan will take full load(100%), if even speed not
recovered then fuel gas and fuel oil supply to all burners
including pilot is cut-off
10 Air/fuel ratio If the air to fuel ratio is too low, complete combustion of
the fuel may not occur. In this event the fuel gas and fuel
oil supply to all burners including pilot is cut-off
11 Loss of ID fan detection When ID fan is not in operation , draft is lost then by pass
around APH will open to ensure air circulation. Bypass
auto close when the ID fan restart within 30second
Heater Safety Interlocks
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S
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DESCRIPTION OF CAUSES CONSEQUENCES
12 High-high heater outlet pressure During steam spalling of the heater coils, spalled coke
may cause blockage of the coil. This causes
overpressure the coils. In this event In this event the fuel
gas and fuel oil supply to all burners is cut-off. This trip
only be activated during spalling. It shall be bypassedduring normal operation to avoid spurious trips due to
pressure fluctuation during coke drum switching
13 High-High fuel oil pressure In this case fuel oil supply to all burners is cut-off
14 High-High pilot gas pressure In this case the fuel oil and fuel gas supply to all burners
is cut-off
15 Low-Low fuel gas pressure Fuel gas supply to burners will cut-off
16 Low-Low fuel oil pressure If the pressure of the fuel oil to the main burners falls
below the minimum pressure for which the burners
designed, the fuel oil supply is cut-off
17 Low-Low pilot gas pressure The fuel gas and fuel oil supply is cut-off
Heater Safety Interlocks
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Commission steam tracing on fuel gas & fuel oil lines to the
heater and check that the fuel gas knock-out drum is free of
liquid.
Open snuffing steam to the fire box and purge the heater
for 15 minutes minimum
Gas test the firebox at representative points for the
presence of inflammable gas/vapour. Use inspection ports
Start FD fan and ensure the FD fan discharge dampers are
in open condition. Purge the heater with 6 times of furnace
volume of air for 15 minutes to eliminate explosive mixture
and followed by a gas free test. If not done there will be
accumulation of fuel gas inside the heater
Heater Start-up
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Heater Start-up
due to passing of fuel gas block valve, which results in theformation of explosive mixture and it may explode while
introducing igniter for lighting burner.
Open the stack or flue gas damper fully and ensure the
damper indications in field and control room are in ONcondition.
If there is a delay between the gas free test, and lighting of
the burners, the fire box must be re-purged and retested.
Bypass the APH initially and start ID fan Bypass fuel shutoff interlocks
Drain condensate from the fuel gas pilot line before light-up
pilot burners. same procedure is applicable to fuel gas line
Gas oil would be utilized for the cold & hot oil circulation
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Open pilot gas main block valve.
Open gas to the pilot burner and press the igniters.
Observe that the pilot burner has ignited. If necessary,
adjust the air control of the pilot burner, so that the flame is
stable and satisfactorily
Do not attempt to light pilot burners from an adjacent pilot
burner
If the initial pilot fails to ignite, shut off the gas supply to that
burner, try the adjacent pilot and repeat the sequence
Ignite all pilot burners individually and adjust the pressure in
the pilot fuel gas header to obtain steady flames
Heater Start-up
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Slowly open the main fuel gas supply valve. Reset the
shutdown valve and pressurise the system up to the burner
valves. Drain condensate from the header. Condensate
carryover inside the fire box will result in explosion and back
fire which may damage to the equipment and the personsemployed.
Gradually open the burner gas valve until the burner ignites
from the pilot Continue opening the valve until a stable
flame is obtained. Ignite remaining burners as required and regulate to slowly
increase the heater COT to about 90 C
Residual water in the equipment and circulating gas oil
(cold oil circulation- 50 % of normal feed rate) may start
Heater Start-up
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vaporizing in the towers.
Now ready to start fuel oil burner
The fuel oil system must be circulating steadily at the
required temperature, pressure and at a sufficient rate of
flow. Check that the steam tracing on the heater fuel oil
supply system is in commission and operating satisfactorily
Commission the atomizing steam supply to all burners, then
adjust the desired light up pressure
Slowly open the main fuel oil supply valve, reset the shut-
down valve and pressurise the system up to the burner
valves - check for leaks. Adjust the main fuel oil supply valve
(such that) to give the recommended fuel oil pressure at the
burner
Heater Start-up
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Gradually open the burner oil valve until the oil spray ignites
from the pilot flame. Continue opening oil to the gun until a
stable flame is obtained. Adjust air registers for proper flame
shape
Inspect the flames frequently. If any one of them isunsatisfactory or goes out, shut off the fuel, replace the oil
gun with a clean one, and re-ignite.
After satisfactory ignition of all burners check for heater
outlet temp. and rate of vaporization in coker fractionatorcolumn
High vaporisation may cause rapid overfilling of overhead
system and tube fouling
Heater Start-up
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Make sure that this vaporization is not excessive by
checking the overhead separator levels
Drain off water as required
Then increase the heater outlet temp. @ 10 C/hr
Light up additional burners as necessary
when heater outlet temp have reached 150 C then hold this
temp. for 4 hour or until the temp. of all circulating systems
have stabilized
Start HP steam injection to the inlet tubes of coker heater
Start MP steam flow through the steam superheater coil if
necessary and vent to atmosphere until the product
strippers are ready
Heater Start-up
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When the temp has risen sufficiently some vaporization willoccur in the coker fractionator and will flow to the overhead
condensing system
The heater outlet temp is raised up to 290 0C @ 30 0C /hr. now
VR can be line up When flue gas temp reached to 300 0C then line-up APH
Increase the firing rate to bring the COT to 493 0C in about 2 hr
Commission the heater outlet temp controller
Closely monitor the heater firing conditions both from field &from DCS
Switch all fuel firing controls from manual to automatic
After getting desired heater outlet temp.(506 0C) optimize heat
load on heater
Heater Start-up
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Take the heater coil outlet TIC in manual mode and place
the fuel on manual pressure control
The firing rate on the burners is decreased under manual
control lowering the process outlet temperature at a rate of
25-30 C per hour till 426 C
Shut down main burners as and when required and keep
pilot burner in service
As COT reaches 426 C bypass coke drum
Discontinue fresh feed to feed surge drum
Continues reduce COT to 385 C @ 70 C/hr (max) and
stop HP steam injection to heater
Reduce heater coil HC flow rate to 60% of design flow
Heater Shutdown
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After attaining COT of 285 C isolate main feed valve and
flush the line with FO for 15 minutes
Vent the superheater MP steam to atmosphere
At COT of 230 C actuate the ESD of fuel gas
Purge coil inlet with steam to displace HC from the coil
tubing for 30 min(min)
Stop pilot burners
Heater Shutdown
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Thanks