This document provides operating procedures for a heat recovery steam generator (HRSG) unit, including: 1) Pre-operating procedures such as cleaning, chemical cleaning, blowing steam lines, setting safety valves, and filling the unit before cold startup. 2) Cold startup procedures such as adjusting water levels, purging the unit, gradually warming it up and introducing supplementary firing. 3) Guidelines for normal shutdown including stopping supplementary firing and slowly reducing gas flow and pressure. 4) Emergency procedures for low or high water levels and tube failures. 5) A walkdown checklist to inspect for leaks or abnormal conditions.

1. UNIT OPERATING PROCEDURE
INTRODUCTION :
The procedures included in this section are of basic nature, intended to serve as a guide in following proper
sequence and precautions during initial stages of operation. Since the Heat Recovery Steam generator is only
a part of the overall plant which must operate in unison, specific and detailed values are to be incorporated to
refine the procedure after sufficient experience is gained and the opportunity to fine tune the controlled to
confirm with actual operating requirements and characteristics.
Reference should be made to respective Manufacturer’s instructions regarding pre-operational and operational
procedures for auxiliary equipment.
PREOPERATING PROCEDURES
Clean – up :
Before initial startup with the admission of GT exhaust gas and prior to each subsequent cold start – up , after
maintenance has been done on the unit , it should be inspected and cleaned both internally and externally. All
foreign material should be removed from pressure parts. Any grating ,pipe lines, electric conduit etc. that
might restrict normal expansion of the unit, should be cleared. All personnel should be cleared from the hot
gas path inside the HRSG and Access doors closed.
Chemical cleaning :
Specific procedures for alkali boil out are given separately.
Blowing steam lines :
Prior to starting up a new unit or restarting an older unit following major pressure parts repairs, the main
steam line should be steam blown to remove scale and foreign matter. This should be done after chemical
cleaning and prior to setting safety valves. Detailed procedures for steam line blowing is given separately.
Setting of safety valves :
Setting of safety valves is carried out next.
Cold start up
Preparation for service :
Ensure that the unit has been chemically cleaned, that the steam lines have been blown, that the safety valves
have been set and that the unit has been filled to the start-up level with properly treated feed water.
Ensure that all instruments are calibrated and all instrumentation, control systems and interlocks have been
checked and are available for service.
Ensure that all-mechanical equipment have been checked and are available for service.
Ensure that the feed water system, equipment have been checked and is available fore operation. It is
recommended that during start-up , the feed water be controlled remote – manually until sufficient flow is
established. Ensure that feed water quality is as per the recommendation .
Ensure that the GT exhaust system has been checked and is available for service. Ensure proper operation of
GTG , its compressor cleanness, IGV opening, its steam water injection , divertor opening , to deliver the
required GTE gas flow at specified gas temperature and composition. Deviation if any shall be informed to
BHEL for review of further course of action.
It is assumed that smooth manual and remote operation of guillotine gate and divertor damper at HRSG inlet
has been checked and is available for service.
Ensure that SF system of HRSG has been checked as per Burner O & M and is available for service.

2. If the HRSG has been recently filled up with feed water or stored as per recommended preservation
procedures, the following steps ( 1 to 4 ) can be skipped and step 5 to be followed directly.
1. Open the entire vent and drain valves of economizers, evaporators and the drum.
2. Slowly fill the economizers and evaporators using the cold boiler feed water up to start-up level.
If cold boiler feed water is not available and hot boiler is to be used. The temperature difference
of metal and water should not be more than 30 deg C.
3. Close all the drain valves except SH drain valves after 5 minutes.
4. When the water level in drum reaches the start-up level, vent valves of economizer are to be
closed after ensuring that there is no air in the system.
5. Water level in drum can be adjusted to start-up level with the help of respective emergency drain
(intermittent blow drain valves).
Purge the HRSG as per NFPA requirements.
Now the HRSG is ready for receiving the GT exhaust gases. HRSG can be taken into service, in cold start-up
in the following mode.
Caution :
The procedure should ensure that no damage to the HRSG and its components is caused during start-ups. THE
HEATING RATE DURING START-UP AND THE COOLING RATE DURING SHUTDOWN IS ONE
MAJOR ASPECT TO BE TAKEN CARE OF. Variation in temperature during start-up or shutdown causes
stresses in the boiler components, particularly in the drum and can cause damage to the drum if the rate of
temperature rise / pressure rise is very high. During the initial start up of new unit, it is recommended that a
relatively slow rate of pressure increase be allowed in order to allow sufficient time for checking expansion
movements and to permit the operators to become familiar with the characteristics of the unit and its
auxiliaries.
Start up procedure ;
DIVERTER DAMPER OPENING :
1. Ensure Guillotine damper is opened.
2. Ensure any of the scanner fan is running.
3. HRSG drum level not low.
4. HRSG level not high.
5. All burner trip valves are closed.
6. GT is running.
HRSG TRIP INTERLOCKS
SL NO DESCRIPTION SETTING
1 Supplementary firing trip on gas pressure Very low 0.05 Kg/Cm2
2 Supplementary firing trip on gas pressure Very high 1.8 Kg/Cm2
3 HRSG trip on scanner air pressure very low 2/3. Only supplementary
firing trip is provided. Divertor will trip with both scanner air fans not
available.
4 HRSG trip on drum level very low 7 %
5 HRSG trip on drum level very high 95 %
6 HRSG trip on GT#3 trip
7 Start permissive for gas supply pressure 3 Kg/Cm2
8 Drum Level Permissive for Divertor damper opening towards HRSG 60 %
Cold startup in GT mode:
The GT load shall be adjusted such that the GT exhaust temperature is less than 400 deg C and open divertor
damper towards HRSG, as per start-up curve.

3. Hold the GT at the above load. During the warming up period, maintain the drum water level. Initially water
level will raise and continuous blow down, if required, emergency blow down also can be used to maintain
water level in sight in the water level guage glass. Continue warming up at this rate till steaming starts.
After warming up, increase rate of flow of gases through the HRSG, as per the start-up curve, by opening the
divertor damper more towards HRSG. Steaming will start with resultant increase in drum pressure. Regarding
the startup, vent controls the pressure rise.
Close the drum vents when continuos flow of steam is established and drum pressure is around 2.0 kg / cm2
(g).
While the unit is heating up, frequent checks of the expansion movements of drum, vents, hanger rods and
columns also restrain in vents and drain lines should be made.
Maintain drum water level at normal. Adjust the feed water supply to the unit as necessary to maintain normal
water level. Feed water control should be placed on automatic as soon as possible and practicable after
continuos feed water flow has been established.
As drum pressure increases, progressively adjust the main stream line start up vent ensuring drum water level
and rate of pressure rise are within limits.
Open the divertor damper completely towards HRSG as and when startup curve dictates.
Increase GT load gradually up to full load ( 33.89 MW at ambient temperature of 38 deg C) ensuring that
steam pressure, temperature and flow rates do not exceed the values given in startup curve. The position of the
divertor damper shall be maintained as per startup curve.
Check all operating instruments and controls and ensure their correctness in unfired mode of operation. Any
deviations to be informed to BHEL (T).
Introduction of supplementary firing :
For introduction of SF system, the following instructions / operations shall be carefully followed.
GT load minimum – 33.89 MW and GT exhaust flow of 131.111 kg / sec and GT exhaust temp. of 549 deg C
at an ambient temperature of 38 deg C. however in case of operational limitations on Gas Turbine loading,
supplementary firing can be introduced with HRSG steam flow rates of 50 tph or more.
Divertor damper shall be fully open towards HRSG.
Feed water temperature entering economizer shall be less than 138 deg C.
The GT and HRSG fuel are naphtha and Bombay high Associated gas resply.
Start SF system by opening the isolation valve of the burner system in case of Bombay High Associated gas.
While starting the fuel control valve shall be corresponding to the minimum flow condition. This fuel pressure
shall be kept at minimum when the burner elements are being brought into service. The fuel pressure at burner
shall not exceed 0.6 kg / cm2 (g) for Bombay high associated gas / reformed gas (minimum pressure) while
bringing the SF system in to service. The value may require refinement based on trial operation. Upward
revision shall however be with the approval of BHEL.
Further increase in firing shall be gradually till the steam generates reaches the rated parameters and not
exceeding MCR steam flow.
The flue gas temperature after the duct burner and the superheated metal temp. shall be periodically,
particularly when load on HRSG is raised. In case the flue gas temperature exceeds 875 deg C or the
superheated metal temp. exceeds 490 deg C the firing rate control shall become stayput and control changed
over to manual.

4. Reasons for increase in gas / metal temperature shall be checked before putting back the firing system on auto.
In case firing rate shall be restricted such that the gas / metal temp. is within acceptable limit specified above.
GT load may be reduced to the required level ( but in any case not less than 25 % load) after reaching the
reqd. steam generation at full load but not exceeding MCR steam generation with GTE temp. Always above
steam outlet temp. During this period of GT load reduction , supplementary firing shall be constant and shall
be increased , even if the steam output decreases. Firing rate may be increased gradually to meet steam
demand ( but not exceeding MCR steam generation) ensuring the gas temp. and metal temp. do not exceed
the above values. Sufficient care shall be taken to ensure steam generation not less than 50 tph at any point of
SF mode operation.
HOT STARTUP IN GT MODE : ( AFTER 4 HOURS OF SHUTDOWN)
Open the divertor damper and guillotine gate at HRSG inlet.
Purge the HRSG as per NFPA requirements.
Reduce the GT load such that the GT exhaust temp. is less than 400 deg C
Adjust divertor damper position as per startup curve matching residual drain pressure with cold startup curve.
After ensuring continuous steam flow through superheated, GT load shall be increased gradually to reach
33.89 MW. Divertor damper shall be fully open towards HRSG. Ensure that the rate of increase of steam
generation, steam pressure and temperature are within limits.
Introduce SF system to increase the steam generation. For introducing the SF system, inststructions /
operations specified under startup procedure shall be strictly adhered to.
Shutting down :
The following procedure is for normal; shutdown. This is based on the assumption that the unit is operating
and it is intended to reduce the pressure to zero and cool the unit completely.
Stop supplementary firing. Slowly close deviator damper towards HRSG. This reduces the gas flow thorough
HRSG. Allow the pressure to drop with reduction in load to accelerate cooling. The load reduction should be
slow enough to ensure that the HRSG cooling rate is not more than 100 deg C per hour. Once the pressure
drops by 2 kg / cm2 below the normal operating pressure close the main steam stop valve and the divertor.
Emergency procedures :
Low water level:
If the water level falls out of sight in the water level gauge, due to failure of feed water supply or some other
fault, except in the case of momentary fluctuations that might occur with extraordinary changes in load,
appropriate action should be taken at once to stop supplementary firing, if SF system is in service and also to
close the divertor damper towards HRSG . In case of
Difficulties in closing the divertor damper within the normal closing time, GT shall be tripped.
If someone in the authority, who is familiar with the circumstances and guide to the emergency and positively
certain that the water level can be restored immediately without damaging the unit is available, he can take the
decision to keep the divertor damper in an intermediate position so that only a limited gas flow passes
through the HRSG after ensuring that SF system is not in service.

5. If feed water has become available, gradually re-establish the level in the drum. If feed water is not available
fast close divertor damper towards the HRSG, if HRSG is in GT mode, seal air fan and scanner air fan shall
be kept in operation.
If tube failure is suspected reduce the steam pressure gradually by opening the main steam line drain. Open
the drum vent when the pressure drops below 1.5 kg/cm2 and drain the unit following normal draining
procedure once pressure drops to atmospheric pressure. Determine the cause of low water level and examine
the unit for the effects of possible overheating such as leaks and distortion of pressure parts.
Repair any leaks.
After the repairs, hydrostatically test the unit at working pressure before putting the unit back in service.
High water level :
Abnormally high water level should be avoided as it may lead to moisture carryover. If the water level rises
above the recommended normal operating range, proceed as follows:
1. Reduce the water level immediately by opening the emergency blow down valves.
2. Reduce the steaming rate, if necessary and place feed water control on manual. If water carryover
should occur, as indicated by rapid fluctuations in the outlet steam temperature, proceed as
follows:
3. Reduce the steam rate.
4. If the water level is abnormally high, reduce the level by opening the emergency blow down
valves and place feed water control on manual.
5. Investigate the water conditions ( alkalinity and solids)
6. Investigate the water condition of the drum as soon as opportunity is there.
Tube failures:
The following instructions regarding tube failures are of a general nature. It must be understood that
conditions may arise which will require exercise of judgement by the operators. Trip SF system once a tube
failure is suspected. Never continue HRSG operation with supplementary firing in service under such tube
failure conditions.
Superheated tubes :
In case of a leak or tube failure, which does not involve a serious, drain on the feed water supply the water
level should be maintained and the unit taken out in normal manner. If the tube failure results in a loss of
steam as great that water level cannot be maintained with the feed water supply available, use the methods
outlined below.
1. Close the divertor damper towards HRSG to isolate it from GT.
2. Shut off feed water to the unit.
After the unit is cooled enough to permit a man to enter it, make a thorough inspection of pressure parts for
any indication of damage resulting from loss of water level. Report the tube failure and operated data to
BHEL in the format enclosed elsewhere in the O & M. after necessary reports have been made apply a
hydrostatic test and obtain the approval of proper authorities before putting the unit back in service.
Evaporator tubes :

6. In case of a leak or tube failure, which does not involve a serious drain on the feed water supply, the water
level should be maintained, and the unit taken out in normal manner. If the tube failure results in a loss of
steam as great that water level cannot be maintained with the feed water supply available, use the method
outlined below :
1. Close the diverter damper towards HRSG to isolate it from GT.
2. Shut off feed water to the unit.
3. After the unit is cooled enough to permit a man to enter it, make a thorough inspection of damage
resulting from water level. After necessary repairs have been made, apply a hydrostatic test and
obtain the approval of proper authorities before putting back the unit in service.
Economizer :
An economizer tube leak can be detected by sound and increased feed water requirements. The leak should be
investigated at the earliest possible time and the unit shut down in a normal manner. Water leaks in
economizer can cause considerable corrosion damage to adjacent tubes. Any decision to continue operation
with known leaks should be made with this in mind.
Walk down check- off list :
One of the most important benefits of a “ walk down check- off “ of an unit is derived from the operator
keeping his eyes and ears open for any unusual condition and reporting his findings to his supervisor.
Potential damage to equipment can be avoided if abnormal conditions are detected in time.
The following are some of the items that an operator should be looking for :
1. Look foe any unusual traces of water on the floor or leaking from casing joints.
2. Look for valve and valve packing leaks.
3. Be on the look-out for any unusual condition (discoloration, hot spots etc. ) on boiler casing.
4. Check for unusual noises, overheating of bearings and for adequate lubrication of all motors and
driven equipment.
The following are the some specific items that should be observed at least once a day:
1. Look for leaks in gauge glasses and water column.
2. Check for broken observation port glasses.
3. Check for broken seal air and gas pipe hoses.
4. Look for leakage of gases through casing joints.
The following more extensive checking should be done at least once a week :
1. Listen for leaking safety valves.
2. Look for non-operating equipments.
3. Trail operates non-operating stand-by equipment.
During every startup from cold:

7. 1. Check for proper expansions of HRSG to ensure no hang-ups to occur.
2. Check spring hangers on boiler support and on steam lines for proper functioning.
HEAT TRANSFER SURFACE DETAILS
SECTION TYPE TUBE SIZE AREA ( SQ. M)
SUPERHEATER SERRATED & SOLID
SPIRAL FINNED
51.0 X 3.6 1000
EVAPORATOR PLAIN & SERRATED
FINNED TUBE
51.0 X 3.6 7065
ECONOMISER SERRATED FINNED 38.1 X 3.6 1165
MUH SERRATED FINNED 38.1 X 3.6 1640
SAFETY VALVES
LOCATION MAKE SET PRESSURE
KG/SQCM (G)
OPEN CLOSE
STEAM DRUM
VALVE 1
BHEL 30.0 28.5
STEAM DRUM
VALVE II
BHEL 30.6 29.1
STEAM DRUM
VALVE III
BHEL 30.9 29.4
STEAM DRUM
VALVE I
BHEL 25.6 29.4
STEAM DRUM
VALVE II
BHEL 26.3 25.0
SAFETY RELIEF VALVES
LOCATION MAKE SETPRESSURE
KG/SQCM (G)
TYPE
MUH BHEL 25.0 1910 -K
WATER LEVEL GAUGES
LOCATION MAKE VISIBILITY
(MM)
NUMBERS MODEL
STEAM DRUM
- LOCAL
BHEL 686 TWO TYPE 0479 (RH)
STEAM DRUM
-REMOTE
YARWAY
USA
- ONE -
STEAM DRUM
- ELECTRONIC
YARWAY
USA
953 ONE AQUARIAN
3000
CBD TANK -
LOCAL
LEVCON 762 ONE -

8. STEAM GENERATION UNIT
UNIT DESCRIPTION: The heat recovery Steam Generator (HRSG) is a horizontal, natural circulation,
single drum, single pressure, fired, water tube boiler. It is designed to generate steam quantities as
furnished in the predicted operation. Feed water temperature is 138 deg C.
SALIENT FEATURES : The Heat recovery Steam Generator (HRSG) consists of the following main
components .
Screen and components
Superheated and components
Evaporator and components
Economizer and components
Makeup water heater and components
Attemperator
Expansion joints
Supplementary Firing system
Steel chimney
SCREEN AND COMPONENTS : Screen is the first heat transfer surface arranged in the direction of the gas
flow. Two numbers of screen modules are located immediately after the Duct Burner. Superheater is located
after the screen module. The high temperature gases leaving duct burner enter screen module and then
Superheater. Screen module contains two rows of plain tubes. The screen module is connected to drum by
means of riser at top and to common feeder by means of individual feeders at bottom.
Details of the screen system are as follows.
Tubes in a module :
1. Tube Outer Diameter , 51.0 mm
2. Tube Thickness , 3.6 mm
3. Fin specification : Plain tubes
4. Tube Material : SA 213 T11
5. Tube type plain tubes
Headers Top Bottom
Outside diameter 219.1 219.1
Thickness 25.0 14.2
Material SA 335 P12
Riser tubes
1. Pipe size 159 x 10
2. Number of risers four
3. Material SA 106 GrB
Individual feeders
1. Pipe size 159 X 12.5
2. Number of feeders Two
3. Material SA 106 GrB

9. SUPERHEATER AND COMPONENTS
Superheater is the second heat transfer surface arranged in the direction of gas flow. Superheater is
constructed of modules consisting of spiral finned tubes welded to top and bottom headers , two rows per
module. The Superheater is designed for single pass flow on the gas side as well as on the tube side.
Interconnection of modules are by multiple 180 degrees bent pipes of similar material as header.
The superheater modules are equipped with low point 1” drains for a fully drainable design. The superheater
outlet is equipped with a vent for start up. The inlet and outlet piping are selected based on steam design
pressure and design temperature.
Details of the superheater system are as follows :
Main steam line :
1. Pipe size 406.4 X 22.2 mm
2. Material SA 335 P22
Tubes in a module :
SH II SH I
Tube outside diameter 51.0 51.0
Tube thickness 3.6 3.6
Tube length 10000 10000
Fin specification
Type : Solid Serrated
Density fins / m 110 200
Height mm 12.5 12.5
Thickness mm 1.25 1.25
Tube material SA213T22 SA213T22
Fin material SA240 TP 409
Top headers
1. Outside diameter x thick 219.1 x 32.0 219.1x32.0
2. Material SA335 P22 SA335 P22
Bottom headers
1. Outside diameter x thick 219.1 x 12.7 219.1 x 12.7
2. Material SA 335 P22 SA 335 P 22
Drum to SH link
1. Pipe size 159 x 10.0 mm
2. Number of pipes Six
3. Material SA 106 GR. B
Connecting links
1. Pipe size 159 x 12.5 mm
2. Number of pipes six
3. Material SA 335 P22
DESH links
1. Pipe size 406. X 22.2 mm
2. Number of pipes one
3. Material SA 335 P 22

10. EVAPORATOR AND COMPONENTS – CIRCULATION SYSTEM
Evaporator is the third heat transfer surface arranged in the direction of the gas flow. In the circulation system,
the heated feed water from Economizer goes to the steam drum. The boiler water from the steam drum flows
to the common feed header through a large downcomer and is distributed to the bottom headers of the
evaporators through the individual feeders. Steam water mixture generated in the evaporator tubes, due to heat
transfer from the gas turbine exhaust, flows back to the drum through the riser tubes. The saturated steam is
separated by the centrifugal separators and final scrubbers placed inside the drum. The separated boiler water
is ricirculated through the downcomer, common feeder, individual feeders, and evaporator tubes and risers.
The saturated steam flows to the Main steam line. Details system are as follows:
Steam Drum (TYPICAL)
1. Inner diameter 1828.8 ( 72”) mm
2. Thickness 38 mm (min)
3. Material SA 515 Gr. 70
4. Internals Baffle Screen and centrifugal seperators
5. Internals material Carbon Steel
Tubes in a module:
1. Tube Outer Diameter 51.0 mm
2. Tube Thickness 3.6 mm
` 3. Fin specification
Module no 03 to 05 06 to 14
Type Serrated fins
Density fins / m 120 200
Height mm 12.5 12.5
Thickness mm 1.25 1.25
Tube material SA 210 Gr A1
Fin Material IS 513 Gr. EDD
Top and bottom Headers
1. Outside Diameter x thick 219.1 x 14.2
2. Material SA 106 Gr B
Down comer
1. Pipe size 406.4 x 32
2. Number of downcomer TWO
3. Material SA 106 Gr C
4. Type Plain, gas touched
Common feeders
1. Pipe size 406.4 x 32
2. Number of downcomer TWO
3. Material SA 106 Gr C
4. Type Plain, gas touched

11. ECONOMISER AND COMPONENTS
Economizer is the fourth heat transfer surface arranged in the direction of gas flow. The economizer is
constructed of modules, consisting of spirals finned tubes welded to the top and bottom headers, two rows
(max.) per module. the economizer is designed for single pass flow on the gas side and multipass flow on the
tube side. The economizer modules are equipped with high point 1” vents and low point 1” drains for a fully
drainable design.
The modules shall be interconnected with multiple 180 degrees bent tubes of similar material as headers.
Top and bottom headers
Top Bottom
1. Outside Diameter mm 219.1 219.1
2. Thickness mm 22.23 14.20
3. Material SA 106 Gr. B SA 106 Gr. B
Tubes in a module
1. Tube Outer Diameter 38.1
2. Tube Thickness 3.6
3. Fin specification :
Module No. 01 to 02
No. of tubes per module 68
Type Serrated tube
Density, Fins /m 180
Height, mm 12.5
Thickness, mm 1.25
Tube material SA 210 Gr. A1
Fin material IS 513 Gr. EDD
Connecting Links inlet outlet
From feed pump economizer
To economizer drum
Pipe size mm 159 x 10, 1 no 159 x 10, 1 no
Material SA 106 Gr.B SA 106 Gr.B
CROSS OVER PIPES :
1. Pipe size 159 x 10.0
2. Number of downcomer ONE per module
3. Material SA 106 Gr C
MUH is the fifth heat transfer surface arranged in the direction of the gas flow. The MUH is constructed of
modules , consisting of spiral finned tubes welded to the top and bottom headers, two rows per modules.
The MUH is designed for single pass flow on the gas side and multipass flow on the tube side.
The MUH modules are equipped with high point 1” vents and low point 1
drain for a “ fully drainable” design.
The modules shall be interconnected with multiple 180 degrease bent tubes of similar material as headers.

12. Top and bottom headers
Top Bottom
1. Outside Diameter mm 219.1 219.1
2. Thickness mm 22.23 12.70
3. Material SA 312 P 316 SA 312 P 316
Tubes in a module
1. Tube Outer Diameter 38.1
2. Tube Thickness 3.6
4. Fin specification :
Module No. 01 to 02
No. of tubes per module 68
Type Serrated tube
Density, Fins /m 130
Height, mm 15.9
Thickness, mm 1.25
Tube material SA 213 TP 316
Fin material SA 240 TP 316
Connecting Links inlet outlet
From feed pump economizer
To economizer drum
Pipe size mm 159 x 10, 1 no 159 x 10, 1 no
Material SA 213 TP 316 SA 240 TP 316
CROSS OVER PIPES
1. Pipe size 159 x 10.0
2. Number of downcomer ONE per module
ATTEMPERATOR
Spray attemperator is utilized to control the final steam temperature to 385 deg C . for this application an
attemperator is used after the superheater. The attemperator piping is furnished and is designed with an
internal sleeve for the first 3 m down stream of the spray nozzle to protect against thermal shock.
EXPANSION JOINTS
One expansion joint at HRSG inlet and one more expansion joint at chimney inlet are provided as shown in
company’s GA drg. to take care of the expansions.
SUPPLEMENTARY FIRING SYSTEMS
A supplementary firing system capable of firing Refinery gas and Bombay high associated gas as fuels heats
up the GT. Exhaust to the required temperature whenever reqd. the duct burners are located at the inlet of the
HRSG. The supplementary firing system is supplied by M/S BHEL. Constructional details of burner system
may be seen in burner area enclosed in the O & M manual.

13. CHIMNEY
The GT exhaust gases, after passing through all the heat transfer surfaces are discharged into the atmosphere
at the safe height through a 60 m high steel chimney of dia 3.5 m . The chimney externally insulated to a safe
height for personnel protection.
SAFETY PRECAUTIONS
Safety is everyone’s business. While at BHEL boilers have been operating safely over decades, this section’s
purpose is to draw the operator’s attention of the necessary precautions to be taken for the safe operation and
maintenance of HRSG. By observing these simple precautions one can have safe and happy operations of the
HRSG throughout the life period.
NOTE: THIS SECTION IS SUGGESTIVE AND SHALL NOT BE CONSIDERED AS A SAFETY
OR PROCEDURE. THE SECTION INCLUDES MINIMUM REQUIREMENTS BUT IS NOT
ALL-INCLUSIVE.
Proper installations, operation and maintenance are essential for safe and reliable HRSG operation.
Precautions taken should consist of but not limited to , hearing protection, eye protection, protective
clothing(i.e. gloves, hard hat) as reqd for the task being preformed. Due to the various circumstances and
conditions in which plant personnel may be working and the consequences of each, BHEL cannot possibly
evaluate all conditions that may injure personnel or equipment. Nevertheless, BHEL is offering the following
safety precautions for plant personnel as matter of information only.
When replacing instrumentation, always isolate the instrument with root valves and release the pressure with
the instrument vent or the blow off line.
CAUTION : DO NOT TRY TO REPAIR AN INSTRUMENT WHEN UNDER PRESSURE.
It is reqd. to ensure that all control systems and safety interlocks have been checked and are available for
service. Loss of control power should be alarmed and its availability to be ensured. If any interlock is
bypassed or removed from service for testing or repair, other means need to be substituted to supervise this
interlock manually and caution should be made in the log book as per NFPA requirement.
HRSG ACCESS:
When entering ductwork or boiler casing through the access doors during outage for routine maintenance or
inspections, operators should ensure that the environment has been checked for man safe conditions. When
entering the cavity. Look around to be sure there are no loose liner pads or other boiler components overhead.
Extended outages for major HRSG upgrades or maintenance require the installation of blank-off plates. The
blank-off plates provide a positive gas flow interruption between the divertor damper outlet and the HRSG
inlet duct flange. This provides a means for simple cycle GT operation and operator’s safety during extended
HRSG outages.
After safe entry has been gained, ensure proper lighting and ventilation have been installed to perform the
task.
When entering steam drums, operators should mechanically ensure that drum access doors can not be
inadvertently closed trapping personnel inside.
Operators should be alert for grating not properly fastened down. Loose grating can result in tripping hazards.

14. When HRSG are in operation, never touch an exposed piece of process pipe or tubing without first testing for
temperature.
Do not touch the HRSG casing while in operation without making sure that the temperature of the surface is
tolerable to the human skin.
WARNING: DISCOLOURED CASING AREA IS INDICTIVE OF HOT SPOTS CAUSED BY
INSULATION SYSTEM FAILURE OR GAS LEAK.
VALVES:
Never repack or perform maintenance while the valves are under pressure unless a special procedure exists.
( i.e. setting of safety valves) and qualified personnel are performing the task.
Always be sure that all safety relief valves are in working order to start-up.
CAUTION: HRSG OPERATION WITH SAFETY RELIEF VALVES IN NON- OPERATIONAL
CONDITION COULD CAUSE SERIOUS INJURY AND EXCESSIVE DAMAGE TO HRSG PRESSURE
PARTS. MOTOR OPERATED VALVE SETTING (ACTAUTOR) ARE TO BE DONE AS PER O & M
AND SHALL NOT BE CHANGED DO NOT EXCEED THE TORQUE LIMITS WHILE CLOSING.
HRSG DUCTING
The ducting is a gas tight system and any hot gas leakage or gaps in insulation will cause hot spots and
discoloring in the duct. It needs to be attended.
WARNING: DISCOLOURED CASING AREA IS INDICTIVE OF HOT SPOTS CAUSED BY
INSULATION SYSTEM FAILURE OR GAS LEAK.
INSULATION:
Repair damaged insulation and lagging as soon as possible, particularly in areas where personnel could be
injured (i.e. near aisles, areas easily reached from platforms, ladders, stairs, etc.). The insulation specified is
non-asbestos bearing ceramic fibers.
CAUTION: DO NOT WALK ON CLADDING SHEET INSIDE THE DUCT. USE LONG WOODEN
PLATE OVER THE PIN FOR STANDING OR WALKING.
Follow guidelines as described in vendor manuals found in the HRSG operation and maintenance instruction
manual.
When examining high-pressure steam lines for leaks, extreme care should be taken particularly if the leak is
heard but not seen.
DIVERTOR DAMPER IN BY-PASS STACK :
Divertor damper is to be kept fully open towards HRSG during supplementary firing. No modification is
permitted during the operation.
DIVERTOR : Closing of divertor damper towards by-pass stack when guillotine gate at HRSG inlet is not
opened will cause major problem in GT.
CAUTION : DO NOT CLOSE DIVERTOR ON BY-PASS STACK SIDE WHEN GUILLOTINE GATE AT
HRSG INLET IS NOT OPENED.
GAS TURBINES :
Also the reduction in GT exhaust gas flow through HRSG with divertor damper modulation at any GT
operating point in SF mode can damage HRSG. Ensure divertor damper full open towards HRSG during SF
mode of operation.
CAUTION : DO NOT OPERATE HRSG IN SF MODE WHEN EXHAUST GAS FLOWS FROM GT IS
REDUCED WITH DIVERTOR DAMPER MODULATION.

15. DEARATOR: If the dearator is not proper, it will reduce its outlet temperature and increased oxygen content
in feed water. It is not desirable for proper HRSG operation. If need to be checked during operation and the
design values are to be maintained particularly when GT or SF system is fired with fuel oil to avoid back end
corrosion.
DOSING SYSTEM:
The dosing system including blow down C.B.D. and I.B.D. system should be available for service prior to
start up procedure.
DO’s
PREPARATION OF HRSG FOR STARTUP
• Check and remove any foreign material from HRSG.
• Ensure all manholes, access doors and openings in the HRSG ducting area are securely closed. Remove
any restrictions for free expansions of HRSG module expansion and drum. They should be free to expand
in lateral direction.
• Ensure proper functioning of all interlocks and protections of HRSG, all auxiliaries, dampers and valves.
• Ensure availability of seal air, scanner air, instrument air, power, chemicals, cooling water etc.
• Keep & operate all vents and drains as specified in unit operating procedure.
• Check up and keep ready the supplementary fuel systems.
• Check up correct functioning of all mechanical equipment and associated instrumentation.
• Check 100& tightness of divertor damper towards HRSG as well as Bypass Stack side and confirm with
the remote and local indications.
• Keep all dampers in air and gas system in start up condition.
• Fill the HRSG up to the start up water level.
• Ensure block valve upstream of spray control station and spray control is in fully closed condition.
• Familiarize with operation and maintenance.
START UP OF HRSG – UNFIRED MODE (COLD START)
Check that no HRSG trip condition exists.
GT to run in appropriate condition to purge the HRSG limiting the GAS temperature as indicted in GT
supplier / logic / NFPA requirement.
Purge the HRSG for a time duration as specified in NFPA.
After purge completion, ensure GT exhaust gas temperature is less than 400 deg. C for startup.
Admit the GT exhaust gas as per startup curve, by suitably operating the divertor damper to HRSG.
All air vents to be closed at 2 kg/sq.cm(g) ( except startup vent).
Bring the HRSG to the rated steam condition as per startup curve by suitably throttling the startup vent.
Taking more time the one specified in startup curve is better.
SH and DESH drains to be closed only after closing of all vents with five minutes delay, after well
establishing steam flow through superheater.
Charge derator and admit rated feed water temperature to HRSG 138 deg. C for continuos operation.
Check the free expansion of drum, Superheater, evaporator module economizer and MUH.
Drum level control and superheater steam temperature control to be taken on Auto mode after reaching rated
parameters.
On drum level low down trip, if the divertor damper is not closing towards HRSG within the stipulated time,
the GT shall be tripped.

16. DO’S
Familiarize with the operation and maintenance manual of duct burner.
Ensure readiness of selected fuel systems.
Check the igniters and scanners for the corresponding fuel.
Ensure all interlocks and protections to be in operation, to trip or stay put / decrease firing corresponding to
SH metal temp. gas temp and fuel pressure as per the control scheme.
BOMBAY HIGH ASSOCIATED GAS
Keep GT load at minimum of 25 %. raise steam generation to its full in unfired mode at rated pressure.
Ensure Divertor Damper 100 % open position towards HRSG both through indication and physical
verification.
Introduce burners.
The fuel pressure at burner shall not exceed 0.07 kg.cm2 (g) for Refinery gas and Bombay high associated gas
while bringing the SF system in to service.
Gradually increase the firing rate, not exceeding 3% MCR steam generation per minute, limited to the
maximum steam output of 108.0 tph at GT load of 33.89 MV monitoring continuously the following:
1. SH-MTM not to exceed 490 deg. C in any case.
2. Main steam temperature not to exceed 385 deg.C
3. Flue gas steam temperature not to exceed 875 deg.C
4. Fuel gas pressure alarm and trip set values.
DO’S
For further increase in steam output to meet steam demand, increase the GT load to meet the required steam
generation, keeping the supplementary heat input constant. However, in GT mode with Refinery gas /
Bombay high associated gas firing, the maximum steam output shall not exceed 108.0 tph.
Ensure that all the gas runners are in clean condition and in service by seeing through the view ports.
Flame shape has to be observed frequently for proper combustion and hence the flame length.
On fuel gas pressure high alarm, reduce the fuel-firing rate by 10% of the instantaneous value and control
shall become stay put and changed over to manual.
GENERAL
Check and control boiler water, feed water and steam conditions as recommended.
Keep drum level and SH temperature controls in auto during supplementary firing.
NORMAL REDUCTION OF BOILER LOAD
Reduce the load in step of 2.5% per minute for load down to 50 % MCR. Reduce supplementary firing
accordingly.
Check and take the controls on manual at a point where better control can be obtained manually.

17. NORMAL SHUT DOWN TO COLD
Shutdown supplementary firing at appropriate time.
Reduce the load gradually below 50% MCR. 10% per minute with one minute hold up time for every 10% load
reduction.
Check the normal drum level and maintain. When the pressure is 2kg/cm2 open all vents.
Stop scanner air fan when gas temperature after duct burner reaches 60deg.C. Open SH & DESH drain valves
and evaporator and economizer vent valves. Do not open evaporator, economizer & MUH valves.
DON’T’S
UNFIRED MODE :
Do not continue HRSG operation if the drum water level is near low low condition.
Do not purge HRSG with gas temperature above NFPA /GT supplier recommendation.
Till HRSG startup parameters reaching the nominal shown in startup curve. Exhaust gas temp. should not be
increased beyond 400 deg.C.
Do not increase the rate of steam pressure and temperature than recommended value as per startup curve.
Feed water temperature not below 138 deg.C.
SUPPLEMENTARY FIRING MODE :
HRSG#3 BMS LOGIC
LOGICS FOR PURGING
• Pilot MTV should be closed.
• Main gas MTV closed.
• All burner BTVs’ closed.
• Scanner air pressure ok.
• Seal air pressure ok.
• Showing no flame.
• Main gas pressure ok.
• Emergency trip PB is not operated.
• Main gas pressure is not very low and not very high.
• Scanner air pressure is not very low and any scanner air fan running feedback.
• Purge not completed.
• Loss of all fuel trip should not be there.
• Unit flame failure should not be there.
• External trip signal should not be there.

18. Once all the above conditions are satisfied, select LOCAL or REMOTE (selector switch in the
hardware console) in the control room and accordingly, press START PURGE PB in local BMS
panel or in the control room.
 LOSS OF ALL FUEL TRIP conditions :
• All pilot BTVs’ closed.
• Pilot MTV closed.
• All main gas BTVs’ closed.
• Main gas MTV closed.
• Any scanner is showing flame for 10 secs.(assuming gas passing)
 EXTERNAL TRIP conditions :
• GT should be running.
• GFD open towards HRSG.
• Drum level not very low.
• Drum level not very high.
 UNIT FLAME FAILURE TRIP conditions :All burners unsuccessful start or trip.
 BURNER UNSUCCESSFUL START / TRIP conditions :
• Particular burner BTV opened.
• Burner trial time elapsed.
• No flame for that Particular burner.
LOGICS FOR BURNER STARTING :
 PILOT MTV / BTV OPENING :
• MFT should not be there.
• Particular burner BTV ready.
1. pilot manual valve open.
2. Pilot burner stop PB not pressed.
3. Firing mode selected.
4. Select local or remote in the hardware selector switch.
PHILOSOPHY: Press start PB for any particular pilot burner.
• Same burner BTV ready will come.
• Once BTV ready comes , pilot MTV will open.
• Once pilot MTV open feedback is received, PLC will give command for opening BTV within 10
secs.

19.  MAIN GAS MTV & BTV OPENING :
• Main gas pressure ok.
• Main gas manual valve open.
• Main gas vent valve closed.
• firing mode selected.
• Any burner pilot on or burner on (for 2nd
burner).
• FCV in minimum position or any burner in service.
• MFT should not be there.
• Main gas pressure not very low and not very high.
• Burner stop PB not operated.
Burner unsuccessful start/trip should not be there.
Introduction of supplementary firing shall be at GT. Base load or at loads with corresponding steam
generation not less than 50 tph.
Do not exceed SH metal temp. of 490 deg C.
Do not reduce the GT load 25% Associated with steam generation not below 50 tph.
Do not move away from 100 % open position of divertor damper towards boiler when SF system on.
Do not put on manual. The superheater steams temp. Control & water level control.
Do not keep the fuel flow control valves above specified minimum position while introducing SF system for
startup.
Do not operate SF system beyond specified capacities.
Do not operate HRSG beyond specified capacity.
SHUT DOWN
Do not open vents(except startup vent) and drain.
Operate seal air fan and scanner air fan for cooling the glass & scanner.
Do not start closing divertor damper towards HRSG until supplementary firing is fully shutdown.
WATER VOLUME OF VARIOUS SECTIONS OF HRSG
SUPERHEATER AND COMPONENTS 8.00 CUB. M
EVAPORATOR AND COMPONENTS 36.00 CUB. M
ECONOMIZER AND COMPONENTS 2.00 CUB. M
MUH AND COMPONENTS 3.00 CUB. M
STEAM DRUM
TOTAL VOLUME- COMPLETELY FILLED 17.0 CUB. M
VOLUME UPTO NORMAL WATER LEVEL 10.0 CUB. M
VOLUME UPTO CENTRE LINE 8.5 CUB. M