Unit Operating Procedure

TAB 10 - UNIT OPERATING PROCEDURES

TABLE TABL E OF CONTENTS TITLE

PAGE NO.

INTRODUCTION INTRODUCTION ................................................................................................................................. 1 GLOSSARY OF COMMON TERMS .................................................................................................... 1 PRE-OPERATIONAL PRE-OPERATIONAL PROCEDURES PROCEDURES ................................................................................................. 2 Cleanup Clean up ........................................................................................................................................... 2 Chemic Chem ic al Cleani Cl eaning ng ......................................................................................................................... 2 Steam Line Blowing ....................................................................................................................... 2 Setting Safety Valves ..................................................................................................................... 2 COLD START-UP ................................................................................................................................ 2 Cold Start Conditions .................................................................................................................... 2 Preparat io ns for fo r Li ght in g Off ............ .................. ............ ............ ............. ............. ............ ............ ............ ............ ............ ............. ............. ............ ............ ............ ......3 Warm Water Fil li ng of the th e Boi ler .......... ................ ............ ............ ............. ............. ............ ............ ............ ............ ............ ............ ............. ............. ............ ......... ... 7 Water Recir cul ation ati on via vi a Boi B oiler ler for fo r Clean-up ............ .................. ............ ............ ............ ............. ............. ............ ............ ............ ............ ............ ........ 7 Start of the th e B oi ler Recir culati cu lati on Pump (BRP) ............ .................. ............ ............ ............ ............ ............ ............. ............. ............ ............ ........... ..... 8 Initi Ini ti al Fir ing in g Precaut ions io ns ............ .................. ............ ............ ............. ............. ............ ............ ............ ............ ............ ............ ............. ............. ............ ............ ............ ........8 Superheat Steam Temperatur Temperatur e Cont rol (Prior to Unit Synchro nizatio n) ........ ........... ...... ....... ....... ...... ...... ...... ...... ..... .. 9 Air Ai r Pr eheater eheat er Prot Pr ot ect io n Duri Du ri ng Uni t Start St art -Ups On Oi l ............................................................... 9 Lighting Off .................................................................................................................................. 10

UNIT OPERATING PROCEDURES POST-TRIP PROCEDURES PROCEDURES ................................................................... ................................... 33 TURBINE PROTECTION UPON LOSS OF LOAD ..................................................................... 34 Master Fuel Trip ........................................................................................................................... 34 Low Waterwall Flow ..................................................................................................................... 38 High Waterw all Tube Temperatu re ............ .................. ............ ............. ............. ............ ............ ............ ............ ............ ............. ............. ............ ............ ........38 Evapor ator Inlet Inl et Sub-Cooli Sub-Coo li ng ............ .................. ............ ............. ............. ............ ............ ............ ............ ............ ............. ............. ............ ............ ............ .......... ....39 Los s of All Feedwater Pump s ............ .................. ............. ............. ............ ............ ............ ............ ............ ............ ............. ............. ............ ............ ............ ......... ...39 Low Lo w Airf l ow ................................................................................................................................... 39 Furnace Pressure High/Low ........................................................................................................ 39 Separat or St or age Tank Level Hi gh ............................................................................................ 40 Airh Ai rh eater Gas Outl Ou tl et Temper Tem peratu ature re Hi gh ..................................................................................... 40 Bot h FD Fans Off or Bot h ID Fans Off ............ .................. ............ ............ ............. ............. ............ ............ ............ ............ ............ ............ ............. ......... ..40 Bot h Secondary Second ary Air heaters Off ............ .................. ............ ............ ............. ............. ............ ............ ............ ............ ............ ............ ............. ............. ............ ........ 40 40 Load Lo ad Ru n-Back n-B acks s ........................................................................................................................... 40 Tube Failures ................................................................................................................................ 41 WATERWALL TUBES................................................................................................................ 41 ECONOMIZER ECONOMIZER TUBES .............................................................................................................. 41 SUPERHEATER SUPERHEATER AND REHEATER TUBES ............................................................................... 42 OPERATION WITHOUT BRP ............................................................................................................ 42 General Gener al Remar ks .......................................................................................................................... 42 Col d Star t Wit hout ho ut B RP ............................................................................................................... 42 Shutdown Without BRP ............................................................................................................... 43 Warm Start without BRP .............................................................................................................. 43 Hot Start Without BRP ................................................................................................................. 43 APPENDIX A - FEEDWATER FEEDWATER SPECIFICATIONS SPECIFICATIONS FOR FOR ONCE THRU THRU BOILERS BOIL ERS ..............................45

UNIT OPERATING PROCEDURES POST-TRIP PROCEDURES PROCEDURES ................................................................... ................................... 33 TURBINE PROTECTION UPON LOSS OF LOAD ..................................................................... 34 Master Fuel Trip ........................................................................................................................... 34 Low Waterwall Flow ..................................................................................................................... 38 High Waterw all Tube Temperatu re ............ .................. ............ ............. ............. ............ ............ ............ ............ ............ ............. ............. ............ ............ ........38 Evapor ator Inlet Inl et Sub-Cooli Sub-Coo li ng ............ .................. ............ ............. ............. ............ ............ ............ ............ ............ ............. ............. ............ ............ ............ .......... ....39 Los s of All Feedwater Pump s ............ .................. ............. ............. ............ ............ ............ ............ ............ ............ ............. ............. ............ ............ ............ ......... ...39 Low Lo w Airf l ow ................................................................................................................................... 39 Furnace Pressure High/Low ........................................................................................................ 39 Separat or St or age Tank Level Hi gh ............................................................................................ 40 Airh Ai rh eater Gas Outl Ou tl et Temper Tem peratu ature re Hi gh ..................................................................................... 40 Bot h FD Fans Off or Bot h ID Fans Off ............ .................. ............ ............ ............. ............. ............ ............ ............ ............ ............ ............ ............. ......... ..40 Bot h Secondary Second ary Air heaters Off ............ .................. ............ ............ ............. ............. ............ ............ ............ ............ ............ ............ ............. ............. ............ ........ 40 40 Load Lo ad Ru n-Back n-B acks s ........................................................................................................................... 40 Tube Failures ................................................................................................................................ 41 WATERWALL TUBES................................................................................................................ 41 ECONOMIZER ECONOMIZER TUBES .............................................................................................................. 41 SUPERHEATER SUPERHEATER AND REHEATER TUBES ............................................................................... 42 OPERATION WITHOUT BRP ............................................................................................................ 42 General Gener al Remar ks .......................................................................................................................... 42 Col d Star t Wit hout ho ut B RP ............................................................................................................... 42 Shutdown Without BRP ............................................................................................................... 43 Warm Start without BRP .............................................................................................................. 43 Hot Start Without BRP ................................................................................................................. 43 APPENDIX A - FEEDWATER FEEDWATER SPECIFICATIONS SPECIFICATIONS FOR FOR ONCE THRU THRU BOILERS BOIL ERS ..............................45

UNIT OPERATING PROCEDURES

LIST OF REFERENCES REFERENCES TITLE

LOCATION

Airf Ai rf lo w Contr Con tr ol and Dis tr ib ut io n ....................................................... Part 6

Sectio Sect io n 4

Boi ler Circu latin g Pump Operating Procedur es ...... ......... ...... ...... ...... ...... ...... ...... ...... ... Part Part 2

Secti Secti on 3

Recommend Recom mended ed Bur ner Management System Syst em ............ .................. ............ ............ .......... .... Part 7

Section Secti on 1

Pressure Part Part Connecti on and Expansion Movement Diagrams ... Part Part 2

Secti Secti on 5

Proc ess & Inst rument ru ment ation ati on Diagrams Diagr ams ............ .................. ............ ............. ............. ............ ......... ... Part 2

Section Secti on 7

Pulv erized eri zed Coal System Syst em ............ ................... ............. ............ ............ ............ ............ ............ ............. ............ ....... .. Part 6

Secti on 1

Pulv erizer eri zer Operati ng Proc edur es ............ .................. ............. ............. ............ ............ ............ .......... .... Part 6

Secti on 2

Soot Blow Bl ow in g Phil oso phy ............ ................... ............. ............ ............ ............ ............ ............ ............. ........... .... Part 5

Section Secti on 4

Steam Li ne Bl ow ing in g ............. ................... ............ ............ ............ ............ ............ ............. ............. ............ ............ ........ Part 2

Secti on 3

Tilti Til ti ng Tangenti al Firin Fir ing g System Syst em ............ .................. ............. ............. ............ ............ ............ ............ ...... Part 6

Secti on 4

Water Treatmen Treat ment..................................................... t..................................................... ............................ Part 2

Sectio Sect io n 3

SSC SSC and Pulverizer Rejects Syst em

Tab Tab 9 Tab Tab 1

Tab 2 Tab 8 Tab 3


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INTRODUCTION These procedures are intended to serve as a guide during the initial stages of operation. They include precautions, which must be observed, and the proper operating sequences of the steam generator, fuel firing equipment and auxiliary equipment. Refer to the General Arrangement Drawings. The sequential procedures do not include all detailed reference to equipment such as the feed pumps, condensate pumps, or the turbine. Because the steam generator is only one part of a complex power station and all equipment must operate in unison, all specific procedures and detailed values cannot be included in this manual. As operating experience is gained and the controls are fine-tuned, the characteristics and operating requirements of the unit will become apparent. Refer to the manufacturer’s instructions in the Maintenance and Vendor Manual for further operating details for specific equipment, including pre-operational and operational procedures. References to other sections included in these operating procedures are listed in the Table of Contents. GLOSSARY OF COMMON

UNIT OPERATING PROCEDURES CCOFA

Close-Coupled Overfire Air

SSC

Submerged Scraper Conveyor

BMS

Burner Management System

PRE-OPERATIONAL PROCEDURES Cleanup The furnace should be inspected and cleaned both internally and externally before initial firing and prior to each subsequent cold start-up after maintenance. Remove all foreign material from the pressure parts. Clear any grating, pipe lines and electric conduit which may restrict normal expansion of the steam generator. All personnel should be clear, and the access doors closed. A complete check list should be prepared by operating personnel. Chemical Cleaning Specific pre-operational chemical cleaning procedures are included elsewhere in this manual. The fuel firing and boiler circulating pump operating procedures, outlined under COLD START_UP, Lighting Off, should be used as a guide when operating the fuel firing equipment. Steam Line Blowi ng Prior to starting up a new steam generator, or following a major pressure part repair, the main steam and reheat steam lines should be blown out to remove scale and other foreign matter. Steam line blowing,

UNIT OPERATING PROCEDURES Preparations for Lighting Off Before lighting off the steam generator, verify that the following steps have been completed: CAUTION: The differential temperature between the feedwater and boiler metal must never exceed 200°F (111°C) (check the separator during initial filling or separator and superheater outlet header during filling for hydrostatic test). If the metal temperature is less than 100°F (38°C) and the feedwater temperature is higher, a minimum fill rate should be used. 1.

The unit has been chemically cleaned, and the steam lines have been blown and safety valves have been set (before initial turbine operation).

2.

All control systems have been checked and are available for service. All safety interlock systems should be checked prior to start-up to ensure proper functioning. Exercise the systems by creating the actual interlock actuating conditions. Simulate the activating condition if the actual condition cannot be created.

3.

All instrumentation and associated mechanical equipment has been checked out and is available for service.

4.

The auxiliary fuel firing equipment has been checked out to ensure it is properly functioning. Recheck the following items to make sure that:

UNIT OPERATING PROCEDURES f.

The pulverizer lube oil systems are available for service.

6.

The windboxes have been checked for proper damper positioning and the tilts are set at horizontal.

7.

The feedwater system and at least one feedwater pump, including the instrumentation and equipment, has been checked out and is available for operation. During a start-up, the feedwater flow should be controlled in automatic mode for best results.

8.

The deaerator auxiliary steam supply is operational and deaerated feedwater at 220°F (104°C) is available. To avoid oxygen corrosion in the boiler, the use of deaerated feedwater with a temperature of greater than 215°F (102°C) is recommended. Refer to Water Treatment instructions.

9.

The boiler recirculating pump (BRP) has been checked out, the suction and discharge isolation valves are open, and all pump instrumentation is available for service. The pump differential pressure monitoring must be in service. Ensure that the proper trip settings have been made.

10. The steam generator start-up system valves are ready for operation (MEFCV, HWL-1, HWL-2, WKFCV), with isolation valves open. The SST level control using HWL-1 and HWL-2 valves has been checked and is available for service. 11. The Startup system drain transfer system is ready for operation. This system includes the flash tank, condensate receiving tank, and drain transfer pumps. 12. Auxiliary steam is available from another operating boiler or common system for supplying the deaerator, and feedwater tank.


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NOTE: It is assumed that the unit will be started with two ID fans, two FD fans, two PA fans, and two SA air heaters, and two PA air heaters in service. If the unit is started with only one ID and FD fan, one PA fan in service, the following damper positions apply to the equipment to be started. Dampers associated with the idle equipment should be closed. Refer to the fan manufacturer's instructions for operating details.

14. All air and gas handling equipment has been checked out and is available for service. Air and gas duct dampers should be in the start-up position as follows: a.

For the first draft group to be started (ID and FD fans), the fan outlet shutoff dampers are closed and the flow control device is at minimum.

b.

For the second draft group (opposite ID and FD fans), the outlet shutoff dampers are open to provide a flow path through the unit.

c.

The PA fan outlet shutoff dampers and flow control device are closed or at the minimum position.

d.

The steam coil airheater inlet and outlet dampers are open and the bypass dampers are closed. Alternately, if steam airpreheating is not desired, then the steam coil airheater inlet and outlet dampers are closed and the bypass dampers are open. Steam coil airheater usage should be based on maintaining average cold end temperature of the airheaters above the recommended level for oil firing and coal firing. Refer to the airheater operating manual for recommended setpoints.

UNIT OPERATING PROCEDURES tracted and the main supply valve closed. Refer to the soot blower instructions. 17. All desuperheater spray water control and block valves are closed. CAUTION: Prevent possible water damage to the turbine by taking extreme care to eliminate all water from the main steam line(s), cold and hot reheat lines, and the superheater and reheater elements and headers before the turbine is rolled. Refer to the turbine manufacturer's instructions and the Valve Operating Diagram for proper drain valve settings. 18. Position superheater, and reheater and economizer drain valves, and vent valves in startup position. Refer to the Valve Operating table figure 6. 19. The auxiliary steam extraction line from superheater is isolated. 20. The warming-keeping system for the boiler start-up system is isolated (supply is from economizer outlet links and discharge is to SH desuperheater). 21. The acoustic pyrometer or other measuring device for measuring furnace outlet temperature is in working order and available for service. 22. The HP and LP bypass stations are available for service, and hydraulic stations are in operation. The water supply for desuperheating has been established. 23. The condenser is available for service, with circulation water flow

UNIT OPERATING PROCEDURES Warm Water Filling of th e Boiler The entire economizer, furnace wall, and separator system must be filled with warm deaerated water (220 F (104°C)) and be free of air. °

The following procedure shall be carried out to ensure the water system is free of air: 1.

The economizer outlet vent valve and waterwall outlet vent valve is open.

2.

BFPM is started at minimum setting and flow according to feed pump operating procedures.

3.

The drain transfer pumps between receiving tank and condenser are switched to automatic control in start-up position.

4.

If the water system of the boiler is empty (economizer, furnace walls, separators), then the system is to be filled with approximately 10% BMCR feedwater flow. Feedwater flow is preferably controlled using automatic feedwater control with a set point of 10% BMCR.

5.

Close the economizer outlet and waterwall outlet vent valve as soon as a clear stream of water is discharged.

6.

When the level in the SST reaches the high water level setpoint, the HWL-1 valve will begin to open. Increase boiler feedwater flow to 30% BMCR and ensure that the HWL-1 valve reaches >30% open for more than 2 minutes. The water system is considered full when: a.

The SST water level remains stable for 2 minutes with feedwa-

UNIT OPERATING PROCEDURES tank and condensate drain pump back to the condenser (reference figure 4 phase II). 3.

Water flow circulation is continued through the entire pre-boiler system, including the condensate polisher, to remove impurities.

4.

During this time, constant boiler feedwater flow of 10% BMCR or more is maintained.

5.

The recirculation is continued until the water quality is within the specified limits, based on samples taken at the HP feedwater heater discharge and SST discharge.

1.

It is assumed that the following preparatory work has been completed:

Start of the Boiler Recirc ulation Pump (BRP)

a.

Feedwater quality within specified limits.

b.

Boiler Feedwater flow setpoint at 10% BMCR.

c.

Water SST level stable with HWL-1 at stable opening.

d.

Cooling water flow to the hp cooler of the BRP adequate.

e.

Suction valves and discharge valves are open.

2.

Set the MEFCV valve at minimum (pump start) position, select MEFCV to auto, and start BRP per pump operating instructions.

3.

As soon as the BRP is running, SST level will decrease as the upper circuits are filled. Maintain 10% BMCR boiler feedwater flow until SST level shows sustained increase. Monitor the


Superheat Steam Temperature Contro l (Prior to Unit Synchronization) The boiler will normally be started-up de-coupled from the turbine using the HP and LP bypass systems, which provide a steam flow path through the superheater, to the reheater, and to the condenser. This provides additional flexibility for adjusting steam temperatures to match turbine requirements at start-up. The primary methods for controlling steam temperature will be firing rate and airflow adjustment. Air Pr eheater Protec ti on During Unit Start-Ups On Oil It is ALSTOM’s strong recommendation to have the airheater soot blowing system continuously in service when firing oil to start up a boiler. This measure is intended to help avoid airheater fires due to accumulation of oil vapor on heating surfaces or ash particles in the airheater baskets. A retractable soot blower is normally installed at the cold end of the airheater on the gas side, arranged close to the changeover of air to gas side when looking in direction of rotation, opposite the hot spot detection device. This soot blower is primarily designed to reduce and/or control ash build-up in the airheater surface. It is not a cleaning device such as the stationary wash down nozzles. Steam is the preferred soot blowing media. However, on some units auxiliary steam sources are not available when starting a unit, and normal sootblowing steam requirements are not reached until a later stage

UNIT OPERATING PROCEDURES For unit loads below 10% BMCR steam flow, excessive combustion air (more than the required 30% minimum air flow) or unnecessary high furnace draft (more negative than -.062 kPa / -0.25 w.g.) should be avoided. Burner tilts should not go above the horizontal position. Changes in the firing pattern should be closely observed in respect to possible carryover. Also, any steam that is available - including saturated steam - can and should be used for airheater soot blowing as long as sufficient steam pressure is available (at least 9 bar / 130 psig). When this minimum steam pressure has been reached, continuous cold end blowing should be initiated and continued until 10% BMCR steam flow is reached. After that airheater soot blowing can be reduced to intermittent operation, once every four to eight hours or as required, depending on the fuel being fired. ″

Once the unit is above 10% BMCR steam flow, normal soot blowing can be followed using the units own auxiliary steam source as temperature and pressure is built up. WARNING: The greatest danger of developing an airheater fire is in the initial stages of boiler operation, i.e. chemical cleaning and steam blowing. Experience has shown that during these stages more than the normal precautions need to be taken. Continuous plant observations must be undertaken so the risk of a airheater fire can be kept to its very minimum. Airheater surfaces should be waterwashed between these initial start-ups if auxiliary steam was not available or used to clean the airheater prior to shutdown. Once the unit has seasoned on coal, fly ash will have


CAUTION: The ID fans may be capable of developing drafts that exceed the furnace design pressure. Therefore, an airflow path through the unit must be established and maintained before starting an ID fan and before opening the ID fan flow control device by ensuring that other dampers in the system are in the start-up positions indicated in Preparations for Lighting Off, page 3. The ID fan flow control device must be kept closed or at the minimum open position until after the fan is started. This minimizes the possibility of developing excessive negative pressure in the unit during the starting procedure. Furnace draft must be maintained within safe limits at all times. Extreme care should be taken when draft and airflow controls are in the manual mode. Be alert for possible malfunctions of automatic control equipment resulting in abnormal excursions, negative or positive, in furnace pressure. 2.

Start the first draft group: Start one ID fan, then the corresponding FD fan. Open the outlet shut-off dampers. Adjust the ID fan for proper furnace draft, and set furnace pressure control to automatic. Adjust unit airflow to minimum 30%, and set unit airflow control to automatic.

3.

Start the second draft group: After closing the outlet shut-off dampers, start the other ID fan, then the corresponding FD fan. Open the shut-off dampers and adjust the flow control device to balance the draft groups, and place the second group into auto-

UNIT OPERATING PROCEDURES Excess Air Versus Load curve, and to Airflow Control and Distribution in the Tilting Tangential Firing System section. 6.

When the fans are started, the secondary air damper control should modulate the auxiliary air dampers to maintain a programmed set point differential pressure between the windbox and furnace.

7.

Check that all other purge permissives are satisfied.

8.

Place the thermoprobe into service to measure furnace exit gas temperature.

9.

Initiate a furnace purge (timer in BMS).

10. Upon completion of the purge cycle, check that all firing prerequisites are satisfied, including the following control settings: a.

Boiler feedwater control setpoint is maintained at 5% to 10% BMCR with HWL-1 active and limiting SST level to continuously purge the solids that may concentrate in the separator storage tank during startup and thereby continuously cleans the fluid in the furnace walls. If water quality is confirmed, this setpoint can be reduced to zero to reduce water losses.

b.

Start-up system (BRP and MEFCV valve) is on automatic maintaining minimum economizer inlet flow setpoint. CAUTION: It is extremely important that minimum economizer inlet (ie. Waterwall) flow be maintained at all times when firing the boiler to prevent tube damage due to overheating. If waterwall flow falls below the low setpoint, all fuel must be automatically tripped with a maxi-

UNIT OPERATING PROCEDURES (1) Open LP bypass bypass stop valve valve after establishing sufficient condenser vacuum and water supply for desuperheating. (2) Adjust to pre-set minimum position, position, and adjust pressure setpoint of LP bypass valve to minimum (app. 30 psig). (3) Place control on automatic. h.

Open SH SH backpass drain valves, valves, and RH outlet vent vent valves. valves.

11. Start one seal air fan. 12. When the seal air to pulverizer pulverizer underbowl pressure dfferential is adequate (>8 in.wg (203 mm.wg)), open the cold air gates to provide a purge air flow path through the pulverizers and confirm that the cold air dampers are less than 5% open. If the pulverizers are out of service, the pulverizer discharge gates must be fully open. The cold air inlet control dampers must be set to the minimum position. The pulverizer discharge gates are only closed during pulverizer maintenance, or when the pulverizers are idle and full of coal and other pulverizers are being started after a unit trip. Refer to EMERGENCY PROCEDURES PROCEDURES,, Master Fuel Trip. 13. For cold start-ups, the fuel startup sequence should follow this table (A elevation is the bottom elevation in the windbox): Sequence Step 1 2

Elevation AB warmup CD warmup

Notes

UNIT OPERATING PROCEDURES sure/temperature at the desired rate (400°F/hr max (222°C/hr)) and without exceeding the furnace exit gas temperature limitation (1100°F (593°C)). 17. To ensure stable operation of the water circulation system and to ensure sufficient steam flow through the superheater, firing rate should not be further increased until 100 psig (7 kg/cm2)is measured in the water separator. 18. As the pressure is raised and saturation temperature increases, SST water level increase due to boiler water swell, and some HWL-1 and HWL-2 action may occur to limit SST water level. As pressure further increases, the HWL-2 and then HWL-1 valves will start to close as the water level (swell) decreases. 19. During all start-ups, control the firing rate to keep the maximum furnace exit gas temperature below 1100°F (593°C), as measured by the thermoprobe until approximately 10% steam generation or the turbine is synchronized or flow is established through the HP/LP bypass system. Sufficient steam flow must be maintained at all times to assure clearing the superheater and reheater elements of condensate. Do not close the startup drains completely until steam flow through the HP/LP bypass is established. Once flow is established, progressively close startup drains and vents to transfer flow to the HP bypass. 20. The superheat backpass drain valve valve can be closed when separator pressure reaches 75 psig (5.3 kg/cm2) (or before as desired after all condensate is removed). 21. Progressively increase LP bypass setpoint to 170 psig (12 kg/cm2). As the HP bypass opens, the reheater will be warmed

UNIT OPERATING PROCEDURES maintains a constant pressure during turbine rolling, synchronization, and initial loading. 28. After the required startup pressure is attained, the firing rate can be adjusted to achieve the required steam temperature for turbine rolling. Refer to the start-up curves for the target steam conditions. 29. Do not exceed the furnace exit exit gas temperature limit of 1100°F (593°C) below 10% boiler load. Above 10% boiler load, automatic interlocks provide protection from over-firing. If it is desirable to supplement the warm up fuel, the pulverizer serving a lower elevation of coal nozzles should be prepared for operation and started in accordance with Introducing Coal,. Adjacent warm-up fuel should be in service to supply the required ignition energy. The feeder should be set to keep the furnace exit gas temperature from exceeding 1100°F (593°C). The condition may exist when an upper elevation of coal will be placed in service for start-up, with ignition provided by the associated elevation of warm-up fuel. Start-up by this procedure is allowable, however, if utilized, care must be exercised not to exceed the furnace exit gas temperature limitation of 1100°F (593°C) as applicable, or the steam temperature values shown in the Steam Temperature Versus Load curve.

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NOTE: The NOTE: The steam pressure should be increased slowly during the initial start of a new steam generator. This allows sufficient time for checking expansion movements and permits the operators to become familiar with the characteristics of the steam generator and auxiliary

UNIT OPERATING PROCEDURES 30. While the unit is heating up, check the boiler expansion movements frequently. Special attention should be given to expansion of the boiler relative to the building steel. Expansion movements should be recorded for comparison with future start-ups. Refer to the Pressure Parts Connection and Expansion Movement Diagrams. 31. Maintain SST water level at normal setpoint via auto feedwater flow control and check the water concentrations and constituents as frequently as necessary to maintain proper boiler water conditions. Sample connections are located on the SST. Rolling and Synchronizing the Turbine 1.

Confirm the steam conditions, pressure, temperature, and steam purity, at the turbine are correct for turbine roll. (See turbine manufacturers recommendations and startup curves in figure 3).

2.

Roll the turbine per the Turbine manufacturers procedures .

3.

SH and RH steam temperatures are maintained by adjusting firing rate and airflow.

4.

When the turbine is warmed-up, synchronize the generator and put on initial load according to turbine/generator startup instructions.

5.

If the startup is done without the HP/LP bypass, the restriction on furnace gas temperature must be maintained until the turbine is synchronized and RH flow is established.


CAUTION: Operators should be alert to detect the symptoms of water carry-over from the boiler and introduction of water into the turbine, such as: a. A sudden, unexplained drop in steam temperature in either the main steam or hot reheat line. b. Vibration in the steam piping resulting from water hammer. c. Abnormal vibration and differential expansion readings from the turbine supervisory instrumentation. Operators must be prepared to take necessary steps to prevent turbine damage upon detecting the introduction of water. Refer to the turbine manufacturer’s instructions for specific actions to be taken. 10. The firing rate should never exceed the rate necessary to match the total steam generation (steam to bypass plus steam to turbine). If the unit is put on line before design operating pressure/temperature is reached, a further increase of firing rate should be in accordance with a gradual rate of pressure/temperature increase consistent with increasing load. Do not allow steam temperature to exceed the values shown in the Steam Temperature Versus Load curve. 11. If the unit was started with one set of fans in service, start the second set of fans as required. Refer to the fan manufacturer's instructions for operating details.

UNIT OPERATING PROCEDURES lowable, however, if utilized, care must be exercised not to exceed the steam temperature values shown in the Steam Temperature Versus Load curve. 5.

Confirm that the pulverizer reject hopper is ready for service (discharge valve closed, loop seal full, and inlet valve open). Place the pulverizer reject sluicing system in service (refer to SSC and Pulverizer Reject System …..)

6.

Check that the pulverizer start permissives are satisfied. Refer to the Control System instructions. The coal fuel-air dampers should remain closed until ignition is established. Refer to Airflow Control and Distribution in the Tilting Tangential Firing System section. Maintain the nozzle tilts at horizontal (+/- 10 degrees). At least one PA fan must be in service. If the unit start-up follows a master fuel trip, the pulverizer may not be empty. Clear the pulverizer of excess coal per recommended clearing procedures before starting the pulverizer. Refer to the Design and Operation manual, for the pulverizer clearing procedures. During this procedure, the pulverizer discharge gates of all other idle pulverizers must be closed. This prevents hot furnace gases from entering the coal piping and the idle pulverizers. (See EMERGENCY PROCEDURES,.) When the coal has been removed from the pulverizer, the feeder can be started at minimum speed and then adjusted to a speed which provides the stable flame required to meet unit load requirements. Be sure the ignition energy in the furnace is established before starting the pulverizer.

7.

Start the pulverizer. Open the hot air shutoff gate. Place the pulverizer airflow and temperature control on automatic.and bring the pulverizer up to the required operating temperature without

UNIT OPERATING PROCEDURES 9.

Increase unit load as required by increasing the boiler inputs: feedwater, fuel, and air in coordinated automatic mode.

10. When the feeder rating of the first pulverizer has reached approximately 80%, place the second pulverizer, which supplies the ad jacent elevation of coal nozzles, in service in a similar manner. When the second adjacent pulverizer is proven in service, equalize the feeder rating of both. The warm-up fuel must remain in service until both feeders achieve 50% rating. If the adjacent pulverizer is not available for service, place the pulverizer serving the next closest elevation of coal nozzles in service. Do not remove the warm-up fuel from service until the two adjacent coal elevations are in service with feeder ratings greater than 50%. 11. When the unit load reaches 30% of full load, the Burner Management System and secondary air damper controls should close the auxiliary air dampers which serve the compartments adjacent to the coal nozzles out of service. The Windbox to Furnace Differential Controller, provided in the Closed Loop Control System should gradually increase the windbox-to-furnace differential pressure to approximately 4 in. w.g.(102 mm H 2O) as load is increased per the prescribed curve. 12. The airflow to the furnace must be sufficient for the firing rate. Automatic control equipment is normally arranged to maintain such a balanced condition. The operation of the O 2 measuring devices, often tied in with the airflow control, should be checked periodically for proper operation. Initial Load Increase to


Reduce warm up fuel firing to minimum. Warm up elevation CD is issued an elevation stop command.

7.

At app. 40% BMCR, the firing rate matches the economizer inlet flow. The steam temperature at the separator outlet will reach a stable superheated condition, causing the level in the SST to decrease, and the boiler will enter the once-through (dry) mode. The boiler is proven in once-through (dry) mode when all the following conditions exist: a.

Steam flow > 40% for 5 minutes.

b.

Separator storage tank level < 39 inches (1 meter).

c.

Separator outlet temperature is superheated by >30°F (17°C).

d.

The difference between economizer inlet temperature and feed water temperature leaving the HP feedwater heater < 10°F (6°C).

When the controls swithch from wet to dry mode, FW flow control will be released from SST level control to FW-Firing Rate coordination to control separator outlet steam temperature, and the BRP will be auto-stopped (note that BRP operation can continue with the unit is dry mode if desired). 8.

When the BRP stops, the warm-keeping system for the start-up system should be put into operation. The warm-keeping system maintains the start-up system in a warm condition so that it can be immediately put into service. This system uses water from the economizer outlet link as the source of heat. A wet-leg fluid level is maintained in the startup system by automatically draining fluid to the superheat desuperheaters via the WKFCV valve.

UNIT OPERATING PROCEDURES 14. Place the feedwater-firing rate ratio control in auto. Place windbox tilts in auto control (RH temperature) at 30% load. Place combustion control on automatic when firing conditions are stable. Refer to the control manufacturer's instructions for specific procedures. 15. Make frequent visual observations of furnace conditions to ensure that no excessive slag build-up is developing. This is especially important when burning coal with low ash fusion temperatures. Operate the soot blowers as required to keep the steam temperature control (nozzle tilts, desuperheaters) within operating range. If response to soot blowing is sluggish or insignificant, reduce unit load or increase excess air to assist in lowering steam temperature and take steps to eliminate the cause of the erratic steam temperatures. Refer to Soot Blowing/Water Cannon Philosophy. WARNING: The coutant bottom of the furnace is designed only to transfer ash to the bottom ash removal system and is not designed to store accumulated ash. Under no circumstances should the level of ash in the bottom ash hopper or submerged scrapper conveyor be allowed to reach the level of the coutant opening, thus blocking further removal of ash from the furnace. Under no circumstances should ash or slag be allowed to bridge across the coutant opening. If bridging starts to occur, load should be reduced in an attempt to shed the buildup. If complete bridging across the coutant opening does occur, immediate steps should be taken to shut the

UNIT OPERATING PROCEDURES NORMAL OPERATION UNIT LOAD CHANGES The normal load range under automatic control is 40% to 100%. The boiler load change rates should not exceed 3% per minute (20 MW per minute) between 40% and 50% load, and should not exceed 5% per minute (33 MW per minute) above 50% load. These maximum load change rates can only be achieved if control actions are well coordinated and well tuned. Below 40% load, the change rates should not exceed that shown on the prescribed start-up curves. During normal operation, unit load changes may alter pulverizer loading rate and/or the number of pulverizers in service. A wide range of load control can be achieved with the pulverizers on automatic. During normal operation, the FD fans are modulated to supply the required combustion airflow and excess air as a function of unit load. The PA fans are modulated to supply the required airflow to the pulverizers that are in service. Decreasing Load If the unit load decreases to a point at which the feeder rating of the pulverizers in service is reduced to 40%, a pulverizer should be taken out of service. Normally the pulverizer serving the lower-most coal elevation is removed in order to maximize steam temperature by maintaining heat release higher in the furnace. To remove the pulverizer from service, proceed as follows: 1.

Ensure that pulverizer ignition energy is available in the furnace. Start the warm-up elevation associated with the coal elevation served by the selected pulverizer.

UNIT OPERATING PROCEDURES tions is not recommended and is only permissible through the use of the associated warm up fuel elevation(s) to provide support ignition energy. If the unit load is reduced to a point at which only two pulverizers are required, the associated warm up fuel adjacent to the coal nozzles in service must be placed in service to ensure support ignition when the feeder ratings drop to 50% or less. Auxiliary supporting fuel should be used whenever, in the operator's judgment, ignition stabilization is necessary. Increasing Load If, after several pulverizers have been taken out of service due to a load decrease, load increases again to a point at which the feeder rating of the pulverizers in service exceeds 80% of maximum, place an additional pulverizer in service as follows 1.

Establish the ignition energy required for the coal elevation served by the selected pulverizer.

2.

Start the pulverizer.

3.

Open the hot air shutoff gate and place the Pulverizer Airflow and Temperature Control into automatic and bring the pulverizer up to operating temperature (Refer to the Pulverizer and Pulverized Coal System sections of this manual).

4.

Start the coal feeder. The feeder control should be on manual and at minimum feeder rating.

5.

When the pulverizer is grinding and coal ignition has been established, gradually increase the feeder rating until it equals that of the other feeders in service. Then, place the feeder on automatic


CAUTION: Exercise care to prevent water from entering the turbine through the main steam line(s), the hot reheat line(s), or the cold reheat line(s) during and after the shutdown process. This prevents water damage to the turbine during a subsequent restart. Possible water sources are: a. Overflow from the separator into the superheater when a high water level exists. b. Water entering the superheater or reheater through the desuperheaters due to open desuperheater control valves or valve leakage with the feed pumps running. 1.

The rate at which load is reduced will be a function of the turbine requirements. The operator determines the required trip load and the rate of load decrease as input, then the control system will automatically reduce boiler inputs at the required rate. Feedwater, air flow, fuel flow, and steam temperature should remain on automatic control during the shutdown for best coordinated control.

2.

Reduce the unit load to 60% Tmcr following the prescribed sliding pressure vs. load curve (for a shutdown to hot, a higher pressure may be desirable to preserve energy in the unit).

3.

To maintain constant steam temperature while the turbine is shutdown, decouple the turbine and boiler using the HP/LP bypass. Hold boiler load constant, transfer pressure control to the HP bypass, reduce turbine load at a rate prescribed by the turbine supplier while transfering steam flow from the turbine to the HP/LP bypass.

UNIT OPERATING PROCEDURES the spout and feeder are empty, and then stop the feeder. Make sure the pulverizer is completely empty by running it for at least 3 minutes. Then, stop the pulverizer. Unless an emergency condition exists, the pulverizer should always be emptied in this manner before being stopped. Refer to the shutdown procedures in the Pulverizer and Pulverized Coal System sections in of this manual. 8.

As pulverizers are taken out of service, the secondary air damper control system should close the associated windbox dampers and adjust the other dampers to compensate for the reduced firing rate.

9.

Take the second pulverizer supplying the next highest elevation of coal nozzles out of service when the feeder rating on all remaining pulverizers reaches 40%. Continue taking additional pulverizers out of service in the same manner. When only two pulverizers remain in service, the adjacent warm up fuel must be placed in service prior to reducing the feeder rating of either pulverizer to below 50%. It is recommended that this consecutive elevation shutdown sequence be followed. Firing coal at separated coal nozzle elevations without auxiliary supporting fuel is not permitted.

10. Overfire air will be reduced automatically as the unit load is reduced per the prescribed control curves. Below approximately 30% load, overfire will be closed to a minimum position. Keep the overfire air dampers at minimum open position to prevent the nozzle tips from overheating. 11. Operate all soot blowers as load is reduced. Refer to the Soot

UNIT OPERATING PROCEDURES the SST. The boiler will now be returned to recirculation (wet) mode. The boiler is proven in recirculation (wet) mode when all the following conditions exist: a.

Steam flow < 40%,

b.

Separator storage tank level > 39 inches (1 meter)

c.

Separator outlet temperature < saturation temperature + 30°F (17°C),

d.

Difference between economizer inlet temperature and feedwater inlet temperature >10°F (6°C).

When recirculation mode is logically proven, FW flow control will switch from coordination of FW-Firing Rate controlling steam temperature to SST level control. The BRP will be auto started to provide minimum waterwall flow. 16. Continue to reduce load to the predetermined load where the turbine will be taken off-line. 17. After the last pulverizer is shut down, remove the warm up fuel from service. All fires should be extinguished when the unit is off the line. With no pulverizers in service, the PA fans and the pulverizer seal air fans may also be shut down. The PA fans should not be shut down if the air heater gas inlet temperature is above 400°F (205°C) 18. After all fuel firing is removed, close the HP and LP bypass valves. 19. Immediately after closing the HP/LP bypass valves, open the su-

UNIT OPERATING PROCEDURES a.

Complete a post trip purge of the unit by running the ID and FD fans for at least 5 minutes at 30% airflow after the fires are extinguished.

b.

If not already done, reduce the airflow through the unit to 30% minimum airflow. Keep the fans and air heaters in service until the unit has cooled to the desired temperature. Air heaters and fans should not be taken out of service until the air heater gas inlet temperatures have dropped below 400°F (205°C).

c.

Keep the BRP in service until the boiler water temperature is reduced to the desired point. Keep the water level near normal in the SST, adding makeup water as required.

26. If the cooling process must be accelerated to permit entry into the steam generator for maintenance, proceed as in step 25, except: a.

Continue running the fans at the desired rate to cool the unit. The air heaters may be shut down when the gas entering temperature has dropped below 400°F (205°C). Refer to the air heater instructions. With the air heaters stopped and the fans running, deposits of fly ash may accumulate in the air heater and cause a rotor unbalance.

b.

Keep the BRP in service to increase recirculation. Keep the water level near normal in the separator storage tank. Shut down the pump when the boiler water temperature is reduced to the desired level.

27. Do not shut down the scanner/ignitor air fan until the furnace temperature has dropped to below 300°F (149°C).

UNIT OPERATING PROCEDURES During a shutdown to hot standby, it is assumed that the unit will be shut down for a relatively short period of time and that the existing pressure and temperature conditions will be substantially maintained. A procedure similar to that for normal shutdown should be used, with the following exceptions: 1.

Reduce steam pressure in line with unit load reduction, following the prescribed sliding pressure curve. To preserve energy in the boiler, maintain a higher pressure (approximately 2000 psig (141 kg/cm2)) until the boiler is taken off line. After the boiler is off the line and fires removed and HP/LP bypass closed, the boiler may be bottled up by closing all superheater drains and vents. Reheater drains and vents should be opened to relieve pressure in the reheater.

2.

It is not necessary to close the feeder inlet gates and run the spouts and feeders empty. As each pulverizer is taken out of service, close the hot air shutoff gate. Stop the feeder when the coal/air temperature drops to 130°F (54 deg C). Run the pulverizer for a 3 minute period until it is empty, and then stop the pulverizer.

3.

The BRP should be kept in operation to ensure uniform boiler metal temperatures. This will prevent possible local overheating due to hot slag deposits. WARNING: If the fans are shut down with an air heater gas inlet temperature above 400°F (205°C), the air heater must be kept rotating. However, running an air heater with the gas inlet temperature above 400°F (205°C) and no air flow through it will cause seal damage fol-


CAUTION: The differential temperature between the feedwater and boiler metal must never exceed 200°F (111°C) (separator storage tank during initial filling or separator storage tank and superheater outlet header during filling for hydrostatic test). 6.

The operator should observe the SST level periodically so that he is always aware of the actual level and can take the appropriate action to re-establish the water level when the unit is being restarted. When the BRP is shut down, the water level will rise. As the unit cools and the water shrinks, makeup water should be added intermittently to prevent the water from dropping below normal level. Adding relatively cold feedwater will establish a reservoir of cooler water in the system. If the BRP is then started, this cooler water will produce a cycle of cool and hot temperature transients to the pump casing and other pressure parts of the boiler. The BRP should be operating when makeup water is added to minimize the temperature stratification.

WARM START-UP Assuming that the unit has been down for a short period of time (less than approximately 36 hours), the unit can be re-started in a similar sequence to Cold Start-up procedure as outlined below:

Warm Start Conditio ns


Main steam pressure >= 1200 psig (84 kg/cm2). and

3.

Turbine requirements are met.

1.

Make a general inspection of the steam generator and check the points outlined in the Preparations for Lighting Off for Cold Start Ups.

2.

The BRP should still be in service.

3.

If the air heaters and fans were shut down at reduced temperature (see NORMAL SHUTDOWN TO HOT STANDBY,), start the air heaters and fans as outlined under COLD START-UP, Lighting Off. If the unit was bottled up hot with the air heaters still running, start the fans in the normal sequence.

Preparations , Lightin g Off, and Load Incr ease

CAUTION: Prevent possible water damage to the turbine by using extreme care to eliminate all water from the main steam line(s), cold and hot reheat lines, and superheater and reheater elements and headers before the turbine is rolled. Refer to the turbine manufacturer's instructions and to the Valve Operating Diagram for the proper drain valve settings. 4.

Open wide all superheater drains to allow complete draining of superheater headers and/or elements. After draining, close all drains except the superheater back pass lower header drains and


Initiate a furnace purge and a normal light off sequence of the warm-up fuel following the sequence noted above.

8.

Set warm-up flow control to auto and increase fuel flow set point to 5% of BMCR firing rate.

9.

After a 5 minute stabilization period, Progressively increase firing rate to 10% BMCR. Increase separator pressure/temperature at the desired rate (400 F/hr (222°C/hr)) and without exceeding the furnace exit gas temperature limitation (1100 F (593°C)). °

10. When steam pressure at HP bypass begins to increase, the HP bypass valve is released to “pressure ramp” mode. The valves will then control the boiler pressure ramp-up to startup pressure or to existing pressure if greater than startup pressure. 11. As the HP bypass opens, the reheater will be pressurized as steam is passed through the reheat vents and drains. Set the LP bypass station to minimum setpoint in auto mode. The LP bypass will open in response to increasing reheat pressure. Progressively throttle the reheat vents and drains to transfer flow and pressure control to the LP bypass station. 12. Initiate an elevation start command for warm-up elevation EF. 13. Progressively increase firing rate to 15% BMCR. 14. Increase the firing rate, as prescribed, to raise the pressure and steam production. The rate of pressure rise should follow the prescribed start-up curves. 15. When boiler pressure reaches startup pressure (or existing pressure), the HP bypass valve is released to “pressure control” mode, and maintains a constant pressure during turbine rolling,


Synchronize the generator and put on initial load according to turbine/generator startup instructions.

5.

During a hot restart, the turbine metal temperature will normally require a rapid reloading of the unit.

6.

After synchronization, all superheat and reheat vent and drain valves should be confirmed closed.

7.

As steam is transferred to the turbine, the HP/LP bypass will close while maintaining main steam pressure and RH pressure at 170 psig (12 kg/cm2).

8.

As turbine conditions permit, put feedwater heaters into service per manufacturers instructions. Monitor the fluid condition entering the evaporator to ensure that subcooled conditions are at least 10 deg F (6°C). The HP heater should be put into service when load is above 20%.

9.

Deaerator heating steam source is transferred from auxiliary steam system to LP extraction when LP extraction pressure is adequate.

10. Commence coal firing as required to support load increase. 11. Coal firing and load increases generally follow the procedures outlined for cold start-ups and normal load changes. EMERGENCY

UNIT OPERATING PROCEDURES quick-opens and the balance of SG flow (70%Tmcr less ST house load) is transferred to the bypass. 2.

SG Load is held at 60%Tmcr for a stabilization period.

After stabilization, if desired the SG load and pressure can be reduced at a controlled rate of <3% per minute within SG temperature gradient limitations and within the bypass capacity limitation. ST load is maintained at house load, while the balance of SG flow is controlled by the bypass. If the HP bypass is not proven open within a short time delay, then all fuel should be tripped automatically and instantaneously. When a master fuel trip is caused by turbine control valve closure, an immediate restart is feasible in most instances because the turbine is still rolling and will be available to take steam as soon as the governor has the turbine speed under control. (Refer to turbine manufacturer's instructions for no-load operating procedures and limitations.) If an immediate turbine restart is not possible and the turbine is tripped, the reheater condenser drains should be opened (refer to Turbine Trip below). TURBINE TRIP If a loss of load occurs in which the turbine is tripped, then boiler should be rundown to match the capacity of the HP bypass (65%). For the case of ST trip from 100%Tmcr: 1.

Initially the SG is runback to 70%Tmcr (equal to bypass capacity) at a target rate of 50% per minute at constant pressure MS pres-

UNIT OPERATING PROCEDURES To permit firing during start-up, the initiating fuel trip circuits associated with the turbine must be disarmed before opening the turbine valves. They must then be rearmed at a suitable point in the start-up sequence, such as when synchronizing the turbine. CAUTION: Operators should be alert to detect the symptoms of water carry-over from the boiler and introduction of water into the turbine, such as: a. A sudden, unexplained drop in steam temperature in either the main steam or hot reheat line. b. Vibration in the steam piping resulting from water hammer. c. Abnormal vibration and differential expansion readings from the turbine supervisory instrumentation. Operators must be prepared to take necessary steps to prevent turbine damage upon detecting the introduction of water. Refer to the turbine manufacturer’s instructions for specific actions to be taken. TURBINE PROTECTION UPON LOSS OF LOAD Extreme care must be taken following a trip of the turbine and boiler to prevent water from entering the turbine during a unit restart. Condensation may cause water to collect in the main steam line(s) and cold reheat lines. Water may be introduced into the superheater due to overflow from the separator (inadvertent high water level). Water may be introduced into the superheater and/or reheater through the desuperheaters due to open or leaking spray water control valves.


Maintain the unit airflow at the pre-trip value for at least 1 minute and then gradually reduce the airflow to the purge rate (30% airflow) and complete a unit post trip purge.

2.

Procedure after Master Fuel Trip when all ID and FD Fans are off: The ID and FD fans discharge dampers shall be opened to allow natural ventilation of the unit. Opening of fan(s) dampers shall be timed or controlled to avoid excessive furnace pressure excursions during fan(s) coast-down. The fans discharge dampers shall remain open for a period of at least 15 minutes. During this 15-minute period, the ID and FD fans shall not be started. At the end of the 15-minute period, the ID/FD fans may be started in accordance with ID/FD fan(s) start-up procedures. If the unit will not be re-started for an extended time, a flow of air through the unit shall be maintained.

3.

If warm-up fuel is in service when the fuel trip occurred, make sure the warm-up header trip valve and individual nozzle shutoff valves are closed.

4.

If all auxiliaries are lost during a fuel trip, refer to the Boiler Circulating Pump Operating Procedures for handling the low pressure cooling water. The cooling flow must be maintained.

5.

If all auxiliary power sources were lost during a trip, after completing the 15 minute natural draft purge described above, start the fans and air heaters when power is restored, increase the unit airflow to the purge rate and complete a 5 minute purge. Observe the hot restart precautions in the air heater instructions. The BRP,


Check that the startup system is ready for operation (HWL-1 isolation valve open, HWL-2 is interlocked to prevent opening at high pressure to protect the flash tank) and the drain transfer system is ready for operation. Place the BFPM in service, stabilize deaerator conditions, and establish feedwater flow of 10% BMCR to the boiler to refill to normal SST level. Follow the same procedure for boiler filling as outlined previously. When SST level is stable with HWL-1 at stable opening and all BRP start permissives are satisfied, start the BRP (Refer to Boiler Circulating Pump Operating Procedures). Zero the feedwater flow as SST level recovers and attains the operational setpoint. If restart of the BRP is delayed, excessive HWL action will result in draining of water at pressure, oscillatory dump-feed action, with further reduction in boiler pressure and extension of startup time

10. The pre-firing furnace purge can be initiated once all purge permissives are met. 11. If the boiler can be immediately restarted, then raise load to >20% on auxiliary fuel utilizing th e HP/LP bypass and successively clear the pulverizers serving at least the 2 lower coal elevations using the steam transport system prior to re-synchronizing the turbine. The remaining pulverizers can be cleared using steam transport before or after the turbine is synchronized. Refer to the pulverizer clearing procedure located in the steam inerting section of the Design and Operations manual for additional details: a.

Close the pulverizer discharge gates on all other idle pulverizers containing coal during each steam transport procedure. This prevents hot furnace gases from being carried back into the pulverizers in the event of a furnace pressure rise when a

UNIT OPERATING PROCEDURES procedure and returned to normal service or shut down in a normal fashion if not required for load regulation. i.

If the pulverizer will be retained in service, when the pulverizer has completed the clearing process, open the hot air shutoff gate, bring the pulverizer up to normal operating temperature and start the associated feeder

j.

If the pulverizer will not be retained in service, stop it after completely clearing the coal. The pulverizer discharge gates should remain open to allow a flow of cooling air through the empty pulverizer.

12. If, due to load conditions and/or requirements to the Burner Management System, it is impossible to establish ignition permissives to allow steam transport, inerting steam shall be maintained until each pulverizer can be cleared of coal using steam transport or cooled to ambient 13. If the boiler cannot be re-started and the aurxiliary steam source cannot be continued indefinitely, then the pulverizers (those still containing coal) must be switched to an alternate steam inerting source or to an alternate inerting medium until they can be cooled to ambient and manually emptied. Refer to the clearing procedure located in the Pulverizer Inerting and Fire Fighting section of the Design and Operations manual for additional details.


Low Waterwall Flow The flow entering the economizer is monitored continuously to direct and alert the operator of abnormal flow conditions. Low flow could be the result of a malfunction of BRP, MEFCV, feedwater pump, controls, or operator neglect. Low flow subjects the waterwall tubing to overheating, and potential for failures. The minumum operational setpoint is 40% BMCR flow. If the flow drops below the alarm setpoint of 39% BMCR, the operator must investigate the above listed items. If the flow continues to drop below the trip setpoint of 38% BMCR, automatically trip the fuel following a maximum 10 second time delay. The time delay allows for momentary fluctuations due to valve transfers, etc.: 1.

Trip all fuel immediately.

2.

Shut off all steam being discharged from the unit (trip turbine, steam driven auxiliaries, and such).

3.

Leave the BRP in service as long as it is operating normally. CAUTION: The differential temperature between feedwater and boiler metal must never exceed 200°F (111°C) (separator during initial filling or separator and superheater outlet header during filling for hydrostatic test.)

4.

If the problem is rectified, re-establish minimum waterwall flow.

5.

If the BRP cannot be kept in service, do not admit feedwater to

UNIT OPERATING PROCEDURES the operator to any abnormal condition of excessive heat absorption or low fluid flow. High waterwall tube temperatures are an indication of an imbalance between firing rate and waterwall flow (over-firing, low waterwall flow, or a combination of both). Over-firing could be a result of extreme load change rates. Low waterwall flow could be a result of excessive SH spray flow, BRP trouble, MEFCV trouble, feedwater pump trouble, control system trouble, or tube blockage. If any spiral waterwall tube metal temperature exceeds the alarm setpoint of 463°C, then the operator should investigate the above listed items. If any 4 spiral waterwall tube metal temperatures exceed the trip setpoint of 477°C, automatically trip the fuel following a maximum 3second time delay. This trip protects the tubes from overheating damage, and potential failure, and therefore immediate action is required. Investigate the above listed parameters and their control before re-firing the boiler. Evaporator Inlet SubCooling The fluid condition entering the evaporator is monitored to alert the operator to abnormal conditions. If the fluid entering the evaporator is allowed to rise into the saturation region, the flow distribution in the evaporator will be detrimentally affected, causing tube temperatures to increase. If the fluid condition at the evaporator inlet is sub-cooled by less than 10°F (6°C), an alarm is generated. The operator should take steps to


Separator Storage Tank Level High If the SST level exceeds the high-high level setpoint 548 inches (13.9 meters), then all fuel shall be tripped immediately. A warning alarm is generated at high setpoint of 509 inches (12.9 meters), at which time the operator should check operation of the HWL valves, SST level control, or the balance of feedwater and firing rate (possible that firing rate is too low for feedwater flow). Airh eater Gas Outl et Temperature High If the gas temperature leaving the airheater exceeds the high setpoint, all fuel shall be tripped immediately. This is to protect downstream equipment from over-temperature. Both FD Fans Off or Both ID Fans Off If at any time both FD or both ID fans are off while firing the boiler, then all fuel shall be automatically tripped immediately. Both Secondary Airh eaters Of f If at any time both secondary airheaters are off while firing the boiler, then all fuel should be automatically tripper immediately. Load Run-Backs

UNIT OPERATING PROCEDURES Tube Failures If any water or steam carrying tube fails, the best shutdown method will be dictated by the size of the failure, the ability to maintain a normal water flow (or level if the boiler is in the recirculation mode) and the demand for the unit to remain in service. The following instructions are general since most of the conditions will require the judgment of the operators. WATERWALL TUBES If a leak or tube failure does not involve a serious drain on the feedwater supply, the water flow/level should be maintained and the unit taken out of service in the normal manner: 1.

Operate the soot blowers if conditions permit.

2.

Switch the combustion control equipment to manual control and proceed to reduce the firing rate and air flow in a normal manner.

3.

When all fires are extinguished continue the airflow through the unit at a reduced rate to purge all combustible gases, vapors, etc. Shut down the fans when the unit is cooled sufficiently.

4.

Feed water to the boiler by manual control. To speed cooling, boiler pressure can be reduced by opening the superheater outlet drains.

5.

Allow the boiler to cool at least to 200°F (93°C) (separator metal temperature); before draining.

If there is a serious water loss and the water flow/level cannot be maintained with the feedwater supply available. Use the following method:

UNIT OPERATING PROCEDURES operation with known leaks should be made with this in mind. The unit should be shut down in a normal manner. SUPERHEATER AND REHEATER TUBES A leak in a superheater or reheater element should be checked as soon as possible. Steam leaks in the superheater or reheater can cause considerable erosion damage to adjacent tubes. Any decision to continue operation with known leaks should be made with this in mind. The unit should be shut down in a normal manner. A major superheater or reheater tube failure may require an emergency unit shutdown. The operator must judge the degree of failure, its consequences, and then decide what type of shut down is required.

OPERATION WITHOUT BRP General Remarks Starting the boiler without the BRP is an unusual activity, and should therefore be carried out in exceptional cases only. The minimum economizer flow must be supplied by the BFPM, and in lieu of recirculation, water is drained through the start-up system HWL valves to the flash tank, receiving tank, transfer pumps, and returned to the condenser. Because there is no water recirculation, heat and water losses will be


When the pressure in the reheater reaches approximately 70 psig 4.9 kg/cm2) with the HP/LP bypass system in operation, feedwater heater no. 7 can be placed into operation to preheat the feedwater and raise steam production. Care must be taken to control the steam flow to FWH no. 7 during this period such that the LP bypass valve does not close too much, disabling both the cooling flow through the reheater and LP pressure control. In addition, monitor the fluid condition entering the evaporator. If sub-cooling is less than 10 deg F (6°C), then increase the economizer inlet flow or decrease the feedwater temperature.

8.

Roll and synchronize the turbine following the normal procedure.

9.

Increase load to 40% following the normal procedure.

10. At approximately 40% load the boiler will enter the once-through mode. When once-through mode is proven, the warm-keeping system should be put into operation. 11. Follow normal operation for unit load changes. Shutdown Witho ut BRP 1.

Reduce load in auto mode following the normal procedure.

2.

At approximately 40% load, the boiler will transfer to the recirculation mode. With the BRP off, the feedwater flow setpoint will automatically control the BFP loading to maintain the minimum economizer flow setpoint.

3.

The HWL-1 will open in auto mode when the level in the SST reaches the high setpoint. If additional drain capacity is needed, HWL-2 will open when HWL-1 reaches full open and level contin-

UNIT OPERATING PROCEDURES fact that cold water will be fed to the economizer, instead of recirculated water from the SST via the BRP. 1.

Prepare the unit for light-off following the normal procedure.

2.

Close the BRP suction and discharge isolation valves, and the BRP bypass valve.

3.

Set the feedwater flow setpoint to 40%. The HWL-1 and HWL-2 will open in auto mode when the level in the SST reaches the high setpoint, and will drain the full capacity of 40%.

4.

Note that the start up system valves (HWL-1, HWL-2) are interlocked to prevent opening above 2100 psig (148 kg/cm2) to protect the flash tank, so pressure must be less than this value before initiating the startup.

5.

Light-off the boiler following the normal procedure. When the first ignitor is proven in service, the feedwater flow setpoint will automatically be controlled to 40%. Warm-up the boiler following the normal procedure.

6.

When the pressure in the reheater reaches approximately 70 psig (4.9 kg/cm2) with the HP/LP bypass system in operation, feedwater heater no. 7 can be placed into operation to preheat the feedwater and raise steam production. Care must be taken to control the steam flow to FWH no. 7 during this period such that the LP bypass valve does not close too much, disabling both the cooling flow through the reheater and LP pressure control. In addition, monitor the fluid condition entering the evaporator and ensure that this temperature is always sub-cooled at least 10 deg F. If sub-cooling is less than 10 deg F (6 deg C), then increase the economizer inlet flow or decrease the feedwater temperature.


APPENDIX A FEEDWATER SPECIFICATIONS FOR ONCE THRU BOILERS

Refer to Water Chemistry Control for Once-Through Utility Boiler SYstems.


Figure 1. Airflo w Curve.

AIR FLOW CURVE FOR COLD START-UP

100 N G I S E D . X A M F O % W O L F R I A

90 80 70 60 50 40 30 20

PURGE AIRFLOW

10 0 0

10

20

30

40

50

60

70

80

BOILER LOAD - % OF MAX. DESIGN

90

100

110

UNIT OPERATING PROCEDURES Figure 2. Mill Operating Diagram NTPC BARH II PREDICTED PERFORMANCE Mill Operating Diagram with Design Coal 150 140

NOMAL OPERATING RANGE 40% TO 85% MILL CAPACITY

130 120

Seven Mills

110

Six Mills

R C 100 M B 90 % - 80 d a 70 o L r 60 e l i 50 o B

Five Mills

Four Mills

Three Mills

40 Two Mills

30 20

One Mill

10 0 0

10

20

30

40

50

60

70

80

90

100

110

120

Mill Capacity - % Curve S-xxxx

Alstom Power, Inc. Contract 00108

NTPC BARH II PREDICTED PERFORMANCE Mill Operating Diagram w ith Worst Coal

UNIT OPERATING PROCEDURES Figure 3: Startup Curves


UNIT OPERATING PROCEDURES Figure 4: Boiler Cleanup Diagram

START-UP SYSTEM WITH RECIRCIRCULATION PUMP WATER CLEAN-UP 4

3

1 2 5

1

7

6

MEFCV 8 16

ECONOMIZER

2

WATERWALLS

3

WATER SEPARATOR STORAGE TANK

4

CONDENSER

5

CONDENSATE PUMPS

6

CONDENSATE DEMINERALIZ ER

7

LP HEATERS

8

FEEDWATER TANK WITH DEAERATOR

9

FEED PUMPS

10 HP HEATERS 11 RECIRCULAT ION LINE FOR PRE-BOILER CLEAN-UP 12 FLASH TANK M

9

M

HWL-

HWL-

1

2

13 RECEIVING TANK 14 MIXING PIECE / FILTER

14

16 CIRCULATING PUMP 12

17 DRAIN TRANSFER PUMP 10

HWL-1 HWL-2 MEFCV 13

M 17

PHASE II PHASE III

LEVEL CONTROL VALVE LEVEL CONTROL VALVE MINIMUM ECONOMIZER FLOW CONTROL VALVE

UNIT OPERATING PROCEDURES Figure 5: Recommended Startup, Shutdow n, and Loading Guidelines

RECOMMENDED STARTUP, SHUTDOWN, and LOADING GUIDELINES and LIMITATIONS Material Temperature Gradient Limitatio n All Boiler Components

Temperature <450°F (232°C) increasing

400°F (222°C )/hr

100°F (56°C)/15 minutes

decreasing

300°F (167°C )//hr

75°F(42°C )//15 minutes

increasing

600°F (333°C )//hr

150°F(83°C )//15 minutes

decreasing

600°F(333°C )//hr

150°F(83°C )//15 minutes

Temperature >450°F (232°C)

Startup Firing Rate Limitation (to avoid overheating SH/RH tubing)

<1100°F(593°C )/ furnace exit gas temperature prior to establishing RH flow (via turbine synchronization or HP/LP Bypass open)

Typical Coordinated Startup Load Gradients (%MCR/min ) (refer to the relevant startup curves)

Maximum Load Gradients

Load Range

Cold

Hot

0-10%

0.50%

0.50%

10-40%

1%

1%

40-100%

1-2%

3-4%

Load Range

Sliding Pressure Operation

40-50%

3% MCR/min

50-100%

5% MCR/min (avoid turbin e holds, etc near 40% load during tran-

UNIT OPERATING PROCEDURES THIS PAGE INTENTIONALLY LEFT BLANK

FIGURE 6 VALVE OPERATION FOR UNIT COLD START

Description/Location

Valve Open

Valve Closed

Separator High Water Limit Valves HWL-1, HWL-2 Isolation Valves for HWL-1. HWL-2

Open for SST high level control

Closed all other times



Minimum Economizer Flow Control Valve, MEFCV

Closed when in once-through mode

Boiler Recirculation Isolation

Open for control of minimum economizer flow when in recirculation mode Open before starting BRP

BRP Suction Isolation

Open before starting BRP

Close if BRP trips

BRP Discharge Isolation


Close if BRP trips

Warmkeeping System Supply Isolation

Closed when in recirculation mode

Open when in once-through mode

Warmkeeping System Control, WKFCV


Warmkeeping System Discharge Isolation



Open at all other times

SH Connecting Link Vents

Open before lighting off

SH Furnace Roof Inlet Header drain


SH Backpass lower rear Header Drains


SH Backpass lower front Header Drains


Closed when transfer to once-through mode is complete

Open for control of warm-keeping flow when in once-through mode Open when in once-through mode Closed for maitaianance Throttle as pressure increases, verify closed completely when separator pressure > 5 psig Throttle as pressure increases, verify closed completely when separator pressure > 25 psig Close immediately after synchronization of the unit. See note 1. Operate in conjunction with SH Backpass lower front Header Drains

Link to steam inerting system SH link from Desuperheater 1 vents


SH link to SH Platen


Main steam line vents


Main steam line drains


Cold reheat line drains


Hot reheat line drains


Throttle as pressure increases, verify closed completely when separator pressure > 50 psig Throttle as pressure increases, verify closed completely when separator pressure > 25 psig Throttle as pressure increases, verify closed completely when separator pressure > 75 psig Throttle as pressure increases, close completely when turbine is under light load Keep open to condenser until turbine is under light load. See note 2. Keep open to condenser until turbine is under light load. See note 2.

Note 1: Valves may be used during warmup to obtain the required outlet steam temperatures (approx 100 deg F superheat) for turbine rolling. Steam is diverted by sequencing valves open and closed. Valves should be either fully open or fully closed. Valves must be closed immediately upon synchronization (before appreciable load is picked up) to prevent possible overheating of superheater elements. If additional backpass system valves are supplied by the customer, they may be used in place of these valves for superheat control. Note 2: Reheater drains and vents that are not connected to the condenser must be closed prior to establishing vacuum. BARHII_00108_ UOP_REV02A.DOC-6/2/11

1


VALVE OPERATION FOR UNIT HOT START

Description/Location

Valve Open

Valve Closed






Minimum Economizer Flow Control Valve, MEFCV

Closed when in once-through mode


Open for control of minimum economizer flow when in recirculation mode Open before starting BRP



Close if BRP trips



Close if BRP trips



Open when in once-through mode






Open at all other times

SH Connecting Link Vents


SH Furnace Roof Inlet Header drain


SH Backpass lower rear Header Drains


SH Backpass lower front Header Drains


Closed when transfer to once-through mode is complete

Open for control of warm-keeping flow when in once-through mode Open when in once-through mode Closed for maintainance Throttle as pressure increases, verify closed completely when separator pressure > 25 psig Throttle as pressure increases, verify closed completely when separator pressure > 25 psig Close immediately after synchronization of the unit. See note 1. Operate in conjunction with SH Backpass lower front Header Drains

Link to steam inerting system SH link from Desuperheater 1 vents


SH link to SH Platen


Main steam line vents


Main steam line drains


Cold reheat line drains


Hot reheat line drains


Throttle as pressure increases, verify closed completely when separator pressure > 25 psig Throttle as pressure increases, verify closed completely when separator pressure > 25 psig Throttle as pressure increases, verify closed completely when separator pressure > 50 psig Throttle as pressure increases, close completely when turbine is under light load Keep open to condenser until turbine is under light load. See note 2. Keep open to condenser until turbine is under light load. See note 2.

Note 1: Valves may be used during warmup to obtain the required outlet steam temperatures (approx 100 deg F superheat) for turbine rolling. Steam is diverted by sequencing valves open and closed. Valves should be either fully open or fully closed. Valves must be closed immediately upon synchronization (before appreciable load is picked up) to prevent possible overheating of superheater elements. If additional backpass system valves are supplied by the customer, they may be used in place of these valves for s uperheat control. Note 2: Reheater drains and vents that are not connected to the condenser must be closed prior to establishing vacuum.

2

BARHII_00108_ UOP_REV02A.DO C-6/2/11


GENERAL VALVE OPERATION

Descritpion/Location

Valve Operation


Open for SST high level control, closed at all other times

Link to Flash Tank drains

Open when draining unit, closed at all other times

Economizer Flow Control Valve, MEFCV

Modulated to control minimum flow to economizer,

SST Downcomer Sampling

Open for water sampling, closed at all other times


Open before starting BRP, close when transfer to once-through mode is complete





BRP Motor Cavity drains

Open when filling or draining BRP, locked closed at all other times

BRP Motor Cavity Fill lines

Open when filling BRP, closed at all other times


Open when startup system is out of service above 30% load, closed at all other times


Modulated to control warmkeeping system flow


Open when startup system is out of service above 30% load, closed at all other times


Closed for maintainance, open at all other times

Warmkeeping System Drains

Open when draining warm-keeping system, closed at all other times.

Furnace Lower Sphere Drains


Furnace lower Header Drains


Furnace Wall Riser Vent

Open when filling and draining unit, closed at all other times

Economizer inlet header drain

Open when draining unit, closed at all other times.

Economizer outlet link vents

Open when filling and draining unit, closed at all other times.

BRP Discharge Line Drain


MEFCV Discharge Line Drain


Boiler Recircuation link to Economizer drain


Boiler Main FW Line Drain


BARHII_00108_ UOP_REV02A.DOC-6/2/11

Open for SST high level control, closed at all other times

3

Unit Operating Procedure

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