DCU Heater Mod

5/26/2018 DCU Heater Mod.

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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

NO


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



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S

NO


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



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S

NO


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



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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

Documents

DCU Heater Mod