HRSG
7 Start-up
Prior to proceeding further in the User Manual it is essential that personnel are familiar
with the safety, warnings and procedures for this installation.
Therefore proceed to view the safety, warnings and procedures in chapter 2 “SAFETY
MEASURES” before undertaking any task.
I have read and understood the Safety Measures and Procedures and wish to proceed.
7.1 START-UP GENERAL INFORMATION
Thermal stresses are induced in the boiler during start-up and shutdown. Greater is the
temperature rise rate (or fall) during these periods, greater will be the stress. If ignored, these
stresses can cause fatigue and premature mechanical problems.
In this regard the HRSG has been designed for 10-12 cold start-ups a year.
It is of paramount importance to limit the fatigue stresses induced by cold start-up to provide:
Limit the temperature ramp rate to 120°C/h.
During idle periods, box-up the HRSG to retain as much heat as possible. This is not
applied during shutdowns for inspection activities.
1) The heat input to the HRSG should be controlled by monitoring the rate at which the
saturation temperature rises in the drum (the ramp rate). This rate should be limited by:
a) limiting the turbine exhaust flue gas flow going through the HRSG by the HRSG
damper.
b) releasing steam through the start-up vent.
c) controlling the rate at which heat enters the HRSG by limiting the turbine loading.
2) If the gas turbine is not yet running, then it should be held at full speed no load condition until
the steam drum operating pressure is reached. When this condition is achieved the gas
turbine can be loaded up to minimum load (GT parallel, breaker closed).
NOTE: It is preferable to start to admit GT exhaust gas in the HRSG with the HRSG
temperature as hot as possible. Hot starts induce lower stresses in the HRSG than
cold starts.
3) When main steam temperature is suitable, line up HRSG to steam network.
NOTE: Maintaining proper drum water levels is critical during start-up and operation of the
HRSG. High water levels can cause carryover and leave deposits in superheater. Low water
levels can result in damage due to overheating and can lead to forced or automatic
shutdowns.
4) The start-up valve may be closed in 5/10% steps to allow quicker start-up as long as the
ramp rate is not exceeded. In no case should the valve be operated at less than 10% open.
CAUTION: valves should not be operated at less than 10% open to avoid erosion of
the seat.
7.2 PREPARATION FOR START-UP
Before the boiler start-up the following checks should be done:
1) Check for and remove any foreign or loose material in all HRSG flue gas path including
stack. All manways, duct openings and inspection doors should be secured, except where
manways require further tightening. All gags should be removed from safety valves.
2) Walk down the entire unit to verify the general readiness of the HRSG. The DCS indications
should be verified with local gauges comparisons. Manual valves with no remote indication
should be checked locally, particularly isolation valves which may impede an important
boiler function.
3) The boiler has been filled with water up to “start-up level” (5% above the low level alarm) as
described in paragraph 6.4. It is important to ensure that boiler water does not spill over into
the superheater section of the boiler. During commissioning the initial level could be
adjusted on future startups so the peak will occur close to normal level.
4) All control systems and emergency shutdown system/devices have been checked out and
are available for service.
5) All instrumentation is available for service.
6) The feedwater system is ready for operation.
7) The supplementary firing system is ready for operation.
8) The valves are in position for start-up (see the check list in appendix “C”).
9) Utilities like cooling water, fuel gas are available at their respective systems under operating
conditions.
10) If any repair work has occurred since the last hydrotest, the unit should be checked for
leaks.
11) If drum manways were opened, they may need to be re-tightened when the pressure
reaches 2 kg/cm2g to completely seal.
12) Before the very first start-up and before to start the boiler after an outage, ensure proper
sampling line flushing in order to avoid any inaccurate measurement from analyzer and
potential damage to the analyzer.
7.3 COLD START-UP PROCEDURE IN CLOSE CYCLE (GT EXHAUST GAS
TO HRSG)
Boiler is in operation! Fluids under pressure, surfaces at hot temperature,
rotating machinery in service, fuels present!
In this paragraph is described the procedure for boiler start-up. For more detailed information
refer to the documents: “Control functional description” doc. No. 1211-0-S-030 (26071-V7A-A-
331-07A/B-WHB-01-00136) and “Description of BMS operation” doc. No. 1211-0-S-031 (26071-
V7A-A-331-07A/B-WHB-01-00137) attached in appendix “A” and appendix “B” respectively of
this manual.
For detailed start-up/operating information regarding auxiliary equipment such as FA fan, etc.
refer to the relevant manufacturers manual included in Boiler Auxiliaries Technical Catalogue
doc. No. 1211-0-A-501 (26071-V7A-A-331-07A/B-WHB-01-00002).
PROCEDURE
1) If the unit has been standing full of water for some time, before the start-up it is a good
practice to open the drains on the evaporator (tag No.036A, 037A) for a short period to
drain any eventual build-up. Blowdown all gauge glasses and water columns and observe
water levels. Verify the functioning of the water level alarm system at the existing drum
water level and check the set point. Open saturated steam line vents (tag No.146A, 296A)
and the superheater drains (tag No.153A, 149A, 155A, 159A) in order to evacuate all
condensate from the superheater.
2) Fully open the start-up vent (PV-0255A).
3) HRSG damper fully open with relevant sealing system operating. Guillotine damper is in
open position.
4) Perform the boiler purge by means of FA fan. When the boiler purge is completed throttle
HRSG damper to admit flue gas in the HRSG.
5) Pressurize the HRSG.
a) In order to not exceed the ramp rate (120°C/h), it is possible to bring the HRSG damper
at 50% opening.
b) In order to increase the ramp rate, start up vent valve can be throttled (maximum of
120°C/h shall be respected).
6) Monitor the water temperature and level in the steam drum. When the boiling is reached,
drum level will swell as steam is produced. For initial start-up of the HRSG, drum water level
should be set 5% above the minimum level. It is important to ensure that boiler water does
not spill over into the superheater section of the HRSG. Adjust the initial level on future
startups so the peak will occur close to normal level.
7) When pressure has reached 1.5-2 kg/cm2g, close the saturated steam line vents
and the superheater drains.
NOTE: during the start-up phase continuously check the steam temperatures are matching with
the DCS set point values. If necessary operate the DSH in manual mode in order to keep the
steam temperature within the normal operating range (ref. to docs. 1211-0-S-100 - 26071-
V7AA-
331-07A/B-WHB-01-00146 in appendix “D” and 1211-0-C-311 - 26071-V7A-A-331-07A/BWHB-
01-00011 in appendix “E”).
It is of paramount importance to keep flushed and therefore cooled the
SH coils to prevent tubes overheating by guaranteeing in any
condition the presence of steam flow through SH coils. When there is
no steam demand by main header this goal can be achieved by
throttling start up vent valve
8) Client to evaluate if the steam temperature is suitable for steam header before to put in line
the HRSG. If necessary provide to increase the GT load to achieve the required steam
temperature (GT parallel, breaker closed). The operations are the following:
a) If the main header is not yet pressurized open the by-pass stop valve
(tag No. 010A) in order to warm-up the line. When warm-up is completed and the
pressure upstream and downstream of the stop valve (tag No.HV-0251A) is balanced,
open this valve and close its by-pass valve.
b) If the main header is already pressurized, when the pressures upstream and
downstream the valve HV-0251A are similar open this valve.
These operating modes are suggested in order to allow a smooth opening of the main
steam stop valve avoiding any eventual overloading on this valve.
9) Be sure that the steam traps are in operation. Field operator to crack open manual drains to
verify presence of water.
10) Begin to bring on line the ancillary equipment, instruments and control system. After the
HRSG is in stable operation, visually inspect the entire unit. During operation, steam flow,
pressure and temperature must not exceed the design conditions specified by MACCHI
(refer to boiler performance data sheet doc. 1211-0-C-311 - 26071-V7A-A-331-07A/B-WHB-
01-00011).
11) When the steam flow is greater than 20%-25%MCR it is possible to close the start-up vent.
12) When stable operating conditions are reached the operator can proceed to:
Release in auto mode all control loops;
Put in service the blowdown system;
Check the chemicals for water conditioning. In the first days of operation make frequent
analysis of water, saturated and superheated steam chemical conditions in order to
optimize chemicals dosing.
13) During every cold start-up verify for:
Proper expansion of boiler to ensure no hang-up occurs.
Spring hangers on piping, etc. for proper functioning.
The movement from cold to hot of the boiler. Be certain that free expansion occurs.
14) Notes should be kept during this procedure to develop and refine the process during future
startups. In particular, note the time to begin boiling, and the highest level caused by the
drum swell. Initial fill level can then be adjusted accordingly.
7.4 COLD START-UP PROCEDURE IN FA MODE
This section outlines the procedures for starting a unit in Fresh Air mode.
1) If the unit has been standing full of water for some time, before the start-up it is a good
practice to open the drains on the evaporator (tag No.036A, 037A) for a short period to
drain any eventual build-up. Blowdown all gauge glasses and water columns and observe
water levels. Verify the functioning of the water level alarm system at the existing drum
water level and check the set point. Open saturated steam line vents (tag.No.146A, 296A)
and the superheater drains (tag No.153A, 149A, 155A, 159A) in order to evacuate all
condensate from the superheater.
2) Start BFW pump. Fully open the start-up vent (PV-0255A).
3) For initial start-up of the HRSG, drum water level should be set 5% above the minimum
level. It is important to ensure that boiler water does not spill over into the superheater
section of the HRSG. Adjust the initial level on future startups so the peak will occur close to
normal level.
4) HRSG damper fully closed with relevant sealing system operating. Guillotine damper is in
open position. Perform the boiler purge by means of FA fan. The purge sequence is
automatically started when all permissive are satisfied.
5) When purge is completed, the operator can proceed to start the duct burner at minimum
firing:
a) Press the “Pilots light-off” push-button 331-HS-0291AA on BCS HMI to start the pilots
or automatically by the duct burner light-off sequence.
b) When pilot ignition control time is expired, if flame is detected, the pilots are considered
“ON”, the cumulative “Pilots ON” lamp on BCS 331-BL-0292AA will stop flashing and
remain steady “ON”.
NOTE: The duct burner cannot be started if all pilots has not been started.
c) Press the “Duct burner light-off” push-button HS-6736-A3 on BLP to start the duct
burner. If all duct burner rows are “OFF”, it is allowed to light-off the duct burner from
BLP only by means of the “Duct burner light-off” push-button HS-6736-A3.
d) When the duct burner ignition control time is expired, if at least five duct burner rows
flames are detected, the “Duct burner ON” lamp on BLP XL-6730-A3 will stop flashing
