UG－200/9.8－M
Boiler Operation Instruction 355B－SM8
Design: Check: Review: Approve: Standards:
PEOPLE’S REPUBLIC OF CHINA
Wuxi Huaguang Boiler Co., Ltd (WUXI BOILER WORKS) Sep. 2014
Content 0. Preface ................................................................................................................................................................... 1 1. Preparation before Boiler Startup .......................................................................................................................... 1 1.1 Drying-out ........................................................................................................................................................... 1 1.2 Cold State Aerodynamic Aerodynamic Filed Test ..................................................................................................................... 3 2. Boiler Startup and Operation ................................................................................................................................. 4 2.1 Cold Startup ......................................................................................................................................................... 4 2.2 Warm Startup (Fuel cannot be fed if bed temperature <450 ℃)........................................................................... 8 2.3 Hot Startup ........................................................................................................................................................... 9 3. Normal Operation ................................................................................................................................................ 14 3.1Checking Procedures during B oiler Operation ................................................................................................... 14 3.2 Load Adjustment ................................................................................................................................................ 14 3.3 Water Level Adjustment Adjustment .......................... .......................................................................................................... 15 3.4 Bed Temperature Temperature Control................................................................................................................................... 15 3.5 Steam Pressure Control ...................................................................................................................................... 15 3.6 Steam Temperature Temperature Control ............................................................................................................................... 15 3.7 NOx and SO2 Emission C ontrol........................................................................................................................ 15 3.8 Air Distribution .................................................................................................................................................. 16 3.9 Others................................................................................................................................................................. 16 4. Boiler Shut-down ................................................................................................................................................. 17 4.1 Scheduled Shutdown of the Boiler to Cold State............................................................................................... 17 4.2 Shutdown to Hot Reserve .................................................................................................................................. 17 4.3 Emergency Emergency Shutdown ........................................................................................................................................ 18 4.4 Fast Cooling Down after Boiler Shut Down ...................................................................................................... 18 5． Precautions....................................................................................................................................................... Precautions....................................................................................................................................................... 19 6． Protection Protection during Boiler Shutdown ................................................................................................................. 20 6.1 Nitrogen Blanketing........................................................................................................................................... 20 6.2 Water Water Release and Drying under Hot State........................................................................................................ 20 6.3 Pressure Filli ng .................................................................................................................................................. 20 7. Trouble Shooting ................................................................................................................................................. 21 7.1 Abnormal Bed Temperature ............................................................................................................................... 21 7.2 Abnormal Bed Temperature ............................................................................................................................... 21 7.3 Water Wall Rupture............................................................................................................................................ 21 7.4Superheater 7.4Superheater Tube Rupture ..................................................................................................................... ............. 22 7.5 Bed Coking C oking ........................................................................................................................................................ 22 7.6 Re-burn i nside Flue Gas G as Duct ............................................................................................................................ 23 7.7Water 7.7Water Shortage Shortage.................................................................................................................................................... 23 7.8 Overflow ............................................................................................................................................................ 24 7.9 Water Impact...................................................................................................................................................... 24 7.10 Shortage of C oal Supply .................................................................................................................................. 24 7.11. Main Fuel Trip(MFT) ..................................................................................................................................... 24
Boiler Operation Instruction 355B-SM8
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0. Preface The 200t/h high temperature, high pressure Circulat ing Fluidized Bed (CFB) boiler is designed by Wuxi Huaguang Boiler Co., Ltd (WHBC) with licensed CFB combustion technology from Chinese Academy of Sciences (CAS) Institute of Engineering Thermophysics and WHBC’s years of experiences in CFB manufacturing. In this operation instruction, the major requirements for boiler application and operation are provided based on the design feature of CFB boiler, this instruction shall be applied only for reference by the user when prepar ing the boiler startup and operation manual.
1. Preparation before Boiler Startup In addition to the commissioning of main equipments for different boiler systems, following works have to be completed before boiler commissioning: Boiler flushing and Washing, Auxiliary Interlock Protection Test, Boiler Drying Out; Bo iler Cold Aerodynamic Field Test, Chemical Boiling, Steam Purging, Boiler Safety Valve Commissioning, Boiler Main Protection Test, etc. In this specification, detailed introduction is provided to boiler drying out and boiler cold aerodynamic field test. 1.1 Drying-out The drying out procedures is provided to dry out the linings and/ or refractory materials of the newly erected boiler before operation. Normally, the drying out procedures takes 120-150 hours. The newly constructed boiler wall contains some moisture, which is required to be dried out slowly, otherwise, when boiler put into operation, the moisture vaporizes and expands after heating, which generate a certain amount of pressure to the boiler wall, and it can result in cracking, deformation, damage and even falling out of the boiler wall. The drying out of the boiler can also accelerate the process of the physical and chemical changes of the boiler wall materials，the strength of the boiler wall material can be steadily increased during the drying out process, and the boiler wall can remain in good condition with a long service life under high temperature. Therefore, the drying out procedures must be made by low temperature with applicable requirements before formal operating of boiler. The instructions of this specification are provided only for reference.
The anti-abrasive refractory material are mainly laid out inside the furnace, cyclone separator and material return leg, inlet and out let flue gas ducts, material return valve, and startup burners, etc. The curing method for anti-abrasive refractory material, including the drying out curves shall be jointly developed by the refractory material manufacturer, the user and the commissioning contractor. Holes of φ6～φ8 for steaming discharging with a pitch of 500mm shall be made for cyclone separator material return leg, material return valve, cyclone separator and outlet duct to discharge the moisture from refractory lining, those holes shall be seal welded after drying out procedures. Anti-abrasive material sampling points shall be provided on cyclone separator, material return device, outlet duct of the cyclone separator, and the moisture content of these points shall be measured to judge the effect of the drying out procedure. Normally, the startup burners are provided as the heat source for drying out, the neighboring boiler heating device (if applicable) can also help to get a better drying out
Boiler Operation Instruction 355B-SM8 2 / 26 effect, and firewood can be utilized for heating at the initial stage of drying out process. 1.1.1 The Preparation Work & the Pre-conditions for the Drying Out Process The erection work for the boiler proper, the material returning system and the air supply as well as the flue gas system is complete; and the air leakage and the air pressure testing are passed; the thermal insulation work is completed. All manholes, man doors are kept open for natural drying for no less than 72 hours. The internal inspection of furnace, air and gas duct, cyclone separator, material returning device, air preheater (APH) as well as electrostatic precipitator (ESP) shall be completed. Expansion indicators for different parts are installed and are set to “0” position. The construction of oil supply system is completed; the hydrostatic test is passed and capable of supplying oil properly. Relative thermodynamic and the electrical instruments are installed, trail tested, calibrated, and ready for use. The installation of drum internals is completed. The scale of the water level gauge is clear, correct and provided with proper lighting. Pump the softened water or de-mineralized (DM) water to steam drum to normal water level (NWL). The temperature difference between DM water and drum wall shall not exceed 50°C， normally the water temperature is 40°C ~60°C , and water level gauge shall be washed. The sampling points shall be provided for the anti-abrasive material at the bottom of furnace, cyclone separator and material returning device. 1.1.2 The Method and Process for Drying Out After build-up of the anti-abrasive and refractory lining materials, the boiler shall be dried naturally for at least 72 hours before starting the drying out process. The drying out process shall be conducted by 3 steps, namely low temperature drying out by the under bed startup burner, low temperature integral drying out and high temperature integral drying out. Low temperature drying out by the under bed startup burner The refractory and the thermal insulation bricks are lined inside the under bed startup burner pre-firing chamber and inside the mixing chamber. These areas are featured in high thermal load and temperature increasing speed is hard to control. The heat impact to the wall refractory material is heavy. If the moisture contains inside the joints of the refractory and the temperature increasing is too fast, the refractory material can fall down. Therefore before the overall drying out of the boiler by startup burner, it is recommend curing the refractory and the thermal insulation material of the startup burners by using the wood chips with temperature of 300°C (based on the air chamber temperature) Start by small fire with the initial temperature of 100°C. Slowly increase the temperature and keep at 160°C after 2 hours and continue for 6 hours. Increase the temperature by speed of 30°C /h till it reaches 300 °C, hold for 10 hours and complete. Low temperature (100-150 °C) Drying Out (Cyclone Separator Inlet Temperature) No bed material is allowed to fill into boiler. Build a non-completely sealed partition wall at the inlet section of the cyclone separator, by which majority part of flue gas is guided from the material return system to cyclone separator outlet. The under bed startup burners are provided with 300kg/h atomizer plates. During startup, the No. 1 under bed startup burner shall be started with lowest capacity, and the No.2 under
Boiler Operation Instruction 355B-SM8 3 / 26 bed startup burner shall be started about 30 minutes later and steadily operated for 3 hours. Increase the temperature with the speed of 28°C/h, till drum pressure reaches 1Mpa and then steadily operate for 6 hours. Continue increase the temperature with the speed of 28°C/h, when drum pressure reaches 4.15MPa，the oil guns shall be put into operation with the highest capacity and steadily operate for 24 hours. The cyclone separator inlet temperature shall reach about 150℃. The material return leg curing shall be made during the overall drying out of the boiler: the firewood shall be applied for drying out, and the temperature increase speed shall be controlled to be 30℃/h，the temperature shall be hold unchanged when it reaches 350℃, and the holding time is determined by the boiler drying out condition. The drying out procedures of steam & water system is the same with the procedures of drying out pulverized fuel boiler of same grade. After completion of boiler drying out at this stage, stop the boiler and remove the partition wall at the inlet section of the cyclone separator. Drying -out under High Temperature (300°C) Bed material shall be fed to the furnace with a thickness of 500mm, and 300kg/h atomizer plates must be provided to the under bed startup burners, the temperature increase speed shall be 28℃/h，the temperature shall be hold for 20 hours when it reaches 150℃. For The flue gas temperature variation ratio shall not exceed 28°C/h, the atomizer plates shall be changed to 800kg/h to meet this requirement, when the oil gun reaches its maximum capacity, it shall be steadily operated for 24 hours, and the cyclone separator inlet temperature is about300℃. The drying out process must be restarted from beginning in case of any interrupt due to any reason. The moisture content sampling test of the refractory material shall be made in accordance with the requirements of the material supplier. The drying out process can be regarded as finished when the manufacturer’s requirements are satisfied. 1.2 Cold State Aerodynamic Filed Test 1.2.1 Purpose The purposes of the aerodynamic field test is to determine the pressure drops for empty bed and material layer, to work out the critical fluidize flow, and to provide reference information for boiler hot state operation, and consequently guarantee the safety of the boiler combustion; prevent the bed from coke agglomerating, and to ensure a stable steam pressure and temperature. 1.2.2 Content and Method Air flow calibration: air flow in the main air ducts for primary and secondary air. Empty Bed Pressure Drop Characteristics Test When grid is free of bed material, start the ID fan and PA fan, adjust the PA flow, record the pressure difference value of the grid and draw the relationship curve between the pressure drop of the grid and the supplied air flow based on t he recorded data. Testing of the Relationship between the t hickness of the material and the bed pressure With certain amount of air flow (normally the design value is recommended) and the static bed height of 500mm,600mm,700mm,and 800mm, the bed pressure value shall be recorded, and then draw the relationship curve for the material layer thickness and the bed pressure. Critical Fluidizing Air Flow Test The critical fluidizing air flow is the air flow by which the bed material started to fluidize, slagging can be detected when fluidizing air flow lower than the critical fluidizing air flow.
Boiler Operation Instruction 355B-SM8 4 / 26 Different static bed height, e.g. 500mm,600mm,700mm,800mm shall be selected to measure the critical fluidizing air flow, record values like bed pressure and bed temperature, etc, and corresponding bed material and air flow curve s hall be made according to the recorded data. Fluidization Quality Test When bed material is under fluidizing state, stop the air supply and observe the plainness of the bed material layer to determine the uniformity of the grid air distribution. If the bed material layer is not even, the reason shall be determined and relative solutions shall be carried out.
2. Boiler Startup and Operation 2.1 Cold Startup Inside the boiler, large amount of wear-resistant refractory materials are lined, especially on locations like material return leg, material return valve and outlet duct. Due to the requirement of temperature increasing speed of these internal linings, the startup speed of CFB boiler is limited. The flue gas temperature speed variation is the key factor for thermal stress, and excessive thermal stress can be avoided by a proper startup mode. Normally, the maximum allowable temperature change ratio of the refractory manufacturer is ±150°C/h, therefore, the temperature change have to be controlled not exceed 150 °C/h during operation. During boiler startup, due to required minimum primary air flow for the bed material fluidization and the required air distribution of the oil burner, the boiler can be operated under high excess air factor. The flow of the two (2) under bed ignition burners is 800× 2Kg/h; the operation oil pressure is 2.5Mpa. The under bed igniting combustion rate takes 12% of total combustion rate, when the bed temperature maintained to be above the level by which the coal is allowed to be fed into boiler, put the No.1 coal feeder into operation by low speed, and the bed temperature increased speed can be based on coal ignition condition, and then start other coal feeders to increase the combustion rate. 2.1.1 Preparation Work before the Ignition 2.1.1.1 Inspection before Ignition
The ignition and startup of the boiler can only be start ed after completion of followings step: The drying out of the boiler; The boiling of the boiler; The flushing & cleaning of the piping; The steam sealing property testing; The Safety valve calibration; All the temporary facilities are thoroughly removed; The hydrostatic testing has passed; And the following works have to be finished: All the boiler proper equipment has been inspected and under working condition, the flue gas duct is through and no human beings are staying inside the furnace and the erection tooling and affiliated items are completely removed from the furnace. Check for correctness of the installation of all the parts; All the auxiliary equipments are under optimal working condition and the operation of these equipments are strictly in accordance with the manufacturer’s instruction. Check the water level gauge installation as per the drawings provided by the manufacturer.
Boiler Operation Instruction 355B-SM8 5 / 26 All the steam exhaust piping, drains piping, pressure release piping, safety valve piping, instruments cleaning pipes should be easy to be accessed and correctly and properly connected to the blow down system or other piping. All the thermodynamic and auto controlled instruments are calibrated with the specified and correct measuring precision. The control interlock system is under working condition. All the manholes, man doors, peep holes are c losed. All equipments related to the thermal expansion e.g. temporary frame used for erection, ladders, etc, are removed. Peep holes of the oil burner and the flame detector must be fully cleaned by cleaning air. The atomizer nozzles of startup burner shall be inspected for blockage. Fuel feeding system is under perfect condition and no-load operation is carried out for 15 to 20 minutes. 2.1.1.2 Water Filling
For the first time of water filling, the water shall be filled to a level 50mm lower than the normal water level, the feed water shall be chemical treated and chemical content shall meet all the requirements for boiler normal operation, the intake water temperature shall not exceed 70. Open drum vent valves; Close all the water side drain valves; Open all the superheater vent valves; Open superheater drain valves and the drain valves of the main steam piping; Open boiler feed water bypass valves and manually control the feed water device, make sure the feed water flow is 10% to 15%; Open the economizer vent valves and close the same after the air is released; The drum shall be filled to the minimum level; Manually close the attemperator; Confirm that the recirculation stop valve between the drum and the inlet of the economizer is at open position. 2.1.1.3 Fans
The startup sequence of the air fans is: ID fan ---- High Pressure Fluidizing Fan --- SA fan ---PA fan ID fan Startup
During the startup of the boiler, the ID fan is the first fan to be started in the circulation fluidization system and the flue gas system. Before startup of the ID fan, its inlet baffle plate shall be positioned at the MINIMUM place to prevent the motor from over current. When ID fan is started, special attentions shall be paid to the indication of bearing vibration indicator to ensure that the voltage and the current values are within the specified range. Slowly open the inlet baffle plate and set the furnace negative control at AUTO position, monitor the furnace pressure and then adjust the damper to supply air till a proper furnace pressure is achieved. In case the ID fan tripped or stopped due to certain reasons the PA fan, SA fan and the fuel feeding system shall be inter lock stopped. HP Fan Startup During boiler startup, the high pressure fluidizing fan shall be started after ID fan, and air flows of different chambers the material return valve shall be checked. During normal
Boiler Operation Instruction 355B-SM8 6 / 26 operation, the HP air flows continuously to the sealing device, and the operator shall monitor the temperature of the seal leg to ensure a reasonable circulating flow to the combustion chamber. The HP air fan is of quantitative type, when a proper air flow is ensured, the extra air enters primary air duct via bypass duct. PA Fan Startup
During boiler startup, the primary air fan shall be started after the starting of ID fan and high pressure fluidizing fan. Before the startup, the inlet dampers, downstream primary air duct dampers and different air duct dampers of the startup burners shall be adjusted to the minimum position to avoid motor overload. After the primary fan put into operation, the primary air fan inlet vane control damper shall be opened slowly, and the furnace pressure shall be monitored. SA Fan Startup
Before the startup of the secondary air fan, make sure the inlet damper of the fan is in close position to avoid motor overload.
2.1.1.4 Bed Material Feeding Before the startup of the boiler, the furnace is empty, a certain amount of bed material can be fed inside the furnace on condition of fans are already put into operation. The initial bed material shall be furnace slag with the carbon content of less than 3% and the size of 0~5mm. Because the air fan are being operated and the bed materials will be evenly distributed on the air grid. Check the bed pressure indication to determine the amount the bed material accumulated on grid. When bed material increases the bed press ure indication will increase accordingly. The bed material shall be fed into furnace to make sure the bed pressure reaches the minimum requirement of the bed pressure, i.e. 3.5KPa. 2.1.1.5 Air Purging PA flow shall be controlled to maintain at 30% ( set the PA control at manual position ) Open the oil burner damper. Start oil burner purging 2.1.2 Oil Supply
PA flow shall reaches to 30% of the total air flow; Bed pressure shall be kept to about 4KPa（ bed material shall be fed when necessary）; Oil control valve outlet pressure shall a bove1.5MPa; Set oil burner air flow control to “AUTO “mode; Set the furnace pressure control to “AUTO” mode; Close SA damper by “AUTO” mode; Close PA damper; The openness of the under bed igniter shall be maintained by 30%. Start the first bed start up oil burner (300kg/h atomizer plate), when it burns steadily and t he air supply to the oil burner shall be set at AUTO mode; The oil supply of the oil burner shall be adjusted to the minimum value ( the oil pressure of oil burner must be larger than the lowest oil pressure ); The maximum bed temperature increase speed shall be 80°C/h( as per the requirement of the refractory material supplier ); Start the second oil burner 15 minutes after the ignition of the first oil burner and increase
Boiler Operation Instruction 355B-SM8 7 / 26 the oil supply based on the liner temperature increasing function curve. In case temperature increase is not obvious, the oil burner atomizer plate shall be changed to the 800Kg/h one. Control the mixed air flow of the burners ，and make sure the water cooled chamber temperature less than 900℃. Attentions shall be paid to expansion of drum, header, etc. the expansion indicator shall be checked regularly, any displacement shall be recorded. Bed material feeding shall be made if the bed pressure less t han3.5KPa. Vent valves of drum and superheater shall be closed when steam pressure reac hes 0.1MPa. When the steam pressure reaches 0.15 ~ 0.2 MPa, flush the pressure gauge and cross check with the neighboring pressure gauge to ensure that t he readings are accurate. When the drum pressure reaches 0.3Mpa and the superheater temperature is higher than the saturated steam temperature and then open the motorized valve on 20% When the steam flow is more than 7% and then closes the stop valve between drum and re-circulation piping of the economizer. When the steam pressure reaches 0.3Mpa ~ 0.5 MPa, the water wall lower header shall be drain and blow down, inspection the blow down valves for the flexibility and leakage. During blow down, the drum level cannot lower than the minimum level; otherwise the drum shall be filled with proper amount of water. Close the superheater drain valves. Adjust the steam discharge valve, make sure the SH steam outlet temperature exceed the saturated temperature in no less than 15°C , the steam flow shall be more than 10% to cool the SH. When requirements for steam turbine rolling parameter are reached, the steam shall be supplied to the turbine. 2.1.3 Coal
The coal delivery system operates properly. Coal of proper particle size is sent to boiler. Coal feeding can be started when bed temperature >450 ℃ (reference value, actual value is to be determined during commissioning). Coal feeders are in MANUAL condition. Gate valve of the coal feeding hopper is in open position. Start the sealing air to coal feeder and isolation gate valve. Start No.2 coal feeder (under the minimum rotation speed), coal shall be fed for 90 seconds each time with an interval of 90 seconds, pulse feeding for three times. The increasing of bed temperature (>5℃/min) and the light from combustion of the particles inside the furnace can be based in determination of ignition. The coal feeder shall be operated under the minimum RPM after confirmation of the ignition. Open the No.3 isolation gate valve. Start the No. 3 coal feeder (under the minimum RPM). The capacity of the oil burner can be decreased with actual requirements, at the same time increase coal feeder rotation speed or put No.1 and No.4 coal feeder into operation. Check the bed temperature increase rate and further increase the fuel flow. Start the limestone feeder function group (Manual mode), and adjust the limestone feeder capacity to 10%.
Boiler Operation Instruction 355B-SM8 8 / 26 When oil pressure lower than the minimum required value, and the bed temperature higher than 820, oil flow can be decreased gradually and stop one of the oil burners, at the same time the coal feeding flow has to be increased to maintain load increasing. After stopping the oil burner, the corresponding PA damper shall be opened slowly. Gradually close under bed burner air damper, for the mixed air nozzle of the burner requires cooling with certain amount of air, the air da mper shall not be closed completely. Stop the other oil burners while the bed temperature is maintained, and the coal feeding flow shall be adjusted to increase the load steadily. Corresponding curves shall be based to increase the PA flow with the boiler load. When the set value of the main steam is reached, start load control and coal feeder control. Set the limestone feeder to “AUTO” mode, and start the SO2control. By discharging ash or adding bed material, a bed pressure about 6KPa shall be kept. The main steam pressure shall be increased by 9.8MPa with the pressure r ising curve. Set the main steam pressure control to “AUTO” mode. 2.2 Warm Startup (Fuel cannot be fed if bed temperature <450) For warm startup, air purging by PA and SA shall be made before starting the under bed startup burners. For the bed temperature is already high before air purging, the temperature increase speed is not required to be checked. After that, the startup sequence shall be made as per the startup of the boiler under cold state. 2.2.1 Fans
Keep the inlet guide vane of the ID fan and PA fan at close position. Keep SA damper and the oil burner at MANUAL position and fully closed. Keep the ID and PA control system at MANUAL mode. Start up the ID fan (Close the inlet guide vane of the ID fan at first). Furnace pressure control at AUTO mode. Startup the high pressure air fan for the material return valve and the open the air damper. Check the air flow in the material returning valve. Startup the PA fan. Startup the SA fan. Slowly open the inlet guide vane of the ID fan and check t he furnace pressure. Adjust the fans and ID fan and set at them AUTO mode. 2.2.2Air Purging
Manually adjust the PA flow to 30%. Open SA damper and oil burner air damper. Start air purging. 2.2.3 Fuel Oil
A PA flow higher than 30% shall be maintained. The oil control valve shall be set at MANUAL position. The outlet pressure of the control valve shall be more than 1.5 MPa. Set the oil burner air flow control at AUTO mode. Startup the No.1 oil burner (site inspection is required). Slowly increase the PA flow, and check the stability of the flame. Increase the oil supply, second oil burner shall be put into operation when necessary. Coal feeding shall be started when bed temperature higher than 450 (recommended value, the actual value shall be determined after commissioning).
Boiler Operation Instruction 355B-SM8 9 / 26 Drum upper and lower wall temperature shall be checked, and the temperature difference shall be less than 50. Limestone shall be fed with required proportion ( SO 2 value shall be checked) 2.2.4 Coal
Coal feeding shall be started when bed temperature higher than 450 (recommended value, the actual value shall be determined after commissioning). Coal feed set to “MANUAL “mode. Open coal hopper isolation valve. Start the sealing air to coal feeder and isolation gate valve. Start No.2 coal feeder (under the minimum rotation speed), coal shall be fed for 90 seconds each time with an interval of 90 seconds, pulse feeding for three times. The increasing of bed temperature (>5/min) and the light from combustion of the particles inside the furnace can be based in determination of the success of ignition. The coal feeder shall be operated under the minimum RPM after confirmation of the ignition. Start the No. 3 coal feeder (under the minimum RPM). The capacity of the oil burner can be decreased with actual requirements, at the same time increase coal feeder rotation speed or put No.1 and No.4 coal feeder into operation. Check the bed temperature increase rate and further increase the fuel flow, make sure the bed pressure increase to 6Kpa. Start the limestone feeder function group (Manual mode), and adjust the limestone feeder capacity to 10%. When oil pressure lower than the minimum requirement, and the bed temperature higher than 850，the oil flow can be decreased gradually and stop one of the oil burner, at the same time, in order to maintain the load increasing, the coal feeding flow has to be increased. Stop the other oil burners while the bed temperature is maintained, and the coal feeding flow shall be adjusted to increase the load steadily. Corresponding curves shall be based to increase the PA flow with the boiler load. When the set values of the main steam are reached, the load control and coal feeder control shall be started. Set the limestone feeder to “AUTO” mode, and start the SO2control. By discharging ash or adding bed material, a bed pressure about 6KPa shall be kept. Bed temperature, main steam temperature and main steam pressure shall be supervised. Set the main steam pressure control to “AUTO” mode. 2.3 Hot Startup After startup of fans, when bed temperature higher than 450 ℃ (coal feeding is acceptable), the hot startup sequences can be started. When boiler startup under hot state, the bed temperature is always higher than the temperature required for the fuel feeding and hence the coal feeding can be immediately started without air cleaning and ignition. Once the fed coal is ignited under the lowest RPM of the feeder the combustion ratio shall be increased, and the boiler can reach full load about 35 minutes later. These processes are possible for cyclone separat or is under hot state and has large heat reservation. That means that the temperature rising speed of refractory lining is not necessary to be taken into consideration during hot startup.
Boiler Operation Instruction 355B-SM8 10 / 26 Consumption Data of Boiler Fatigue Life OPERATION CONDITIONS
TIMES DESIGNED
WASTING EACH TIME (%)
Cold startup (metal temperature < 40% of full load)
200
0.01022
Warm startup (metal temperature: 40-80% of full load)
3000
0.00876
Hot startup (metal temperature: >80% of full load)
4000
0.00759
Extremely hot startup (metal temperature: around full load)
5000
0.00426
Step break load (10% of turbine rated power)
12000
0.000675
Boiler Operation Instruction 355B-SM8
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D= Main Steam Flow Tb=Boiler Bed Temperature Ts=Main Steam Temperature P=Main Steam Pressure R=Coal Combustion Rate
Coal feeding
Boiler Operation Instruction 355B-SM8
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D= Main Steam Flow Tb=Boiler Bed Temperature Ts=Main Steam Temperature P=Main Steam Pressure R=Coal Combustion Rate
Coal feeding
Boiler Operation Instruction 355B-SM8
H o t a n d e x t r e m e l y h o t s t a r t u p c u r v e
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D= Main Steam Flow Tb=Boiler Bed Temperature Ts=Main Steam Temperature P=Main Steam Pressure R=Coal Combustion Rate
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3. Normal Operation 3.1Inspection Procedures for Boiler Operation Check the inlet flue gas temperature of the cyclone separator; make sure it not exceeds 1050 °C, for excessive temperature may damage the refractory or metal pressure parts. Check the bed temperature thermocouple and the related instruments; make sure they are under normal working condition. Check the PA flow to the grid to ensure that the normal distribution ratio between the PA flow and the SA flow. Check the oxygen content in the flue gas to ensure that the measuring gauge for oxygen is working properly. Check the bed pressure of the furnace to verify the chocking of the pressure measuring points and its piping to ensure that the bed pressure indication is working properly. Monitor the proper function of bottom ash discharge system and monitor the discharge temperature. Check the drum water level. If required to blow down the water level gauge and verify the normal functioning of the feed water control valve. Regularly sampling the fuel in front of the boiler to verify the size distribution and ingredients variations. Regularly sampling of the feed water, drum water, saturated steam, superheated steam and analyze the changes. Regularly check the affect of the feed water quality against the steam quality and timely chemical treatment of the drum water. Regularly check the function of the soot blowing system. When the boiler is under normal operation and if the outlet temperature of the economizer is 16 °C higher than the normal temperature and then the soot blowing shall be executed. Check if there is any abnormal sound, vibration or displacement around the boiler area. 3.2 Load Adjusting The boiler load is adjusted by manual or automatically changing of fuel feeding speed and/or corresponding air flow .The adjustment of air flow and fuel feeding speed shall be made within small adjustment range each time and made for multiple times to avoid the bed temperature variation. The major adjustment means of the boiler load is bed height controlling, whereas the bed temperature control can also be used as an auxiliary means. For load pickup, the fuel flow and air flow shall be increased, and the bed height shall be increased without change the bed temperature to increase the heat absorption of the evaporation heating surface. On contrary, decrease coal feed flow, air supply and bed height can reduce the boiler capacity. For load pickup, PA and SA flow shall be increased slightly before increasing the coal feeding flow, gradually increase material pressure difference and then slightly increase the air and coal feeding flow till the required capacity is reached. When cutting load, the coal feeding flow shall be decreased first, and properly decrease PA and SA flow, slowly discharge certain amount of recirculation ash to decrease the bed material pressure difference, repeat those procedures till the required capacity is met. Boiler load can be controlled by changing bed temperature. In principle the high load represents the high bed temperature and the low load represents the low bed temperature. While the bed temperature is constrained by many elements, and the variation range is
Boiler Operation Instruction 355B-SM8 15 / 26 limited, therefore, the load adjustment function by changing bed temperature is less effective than the function by changing the bed height. 3.3 Water Level Adjustment Rapid variation of drum level can result in fluctuation in steam pressure and temperature. And the boiler has to be stopped in case of overflow or water shortage. Therefore, a balance and continue water supply shall be provided during operation to make sure the drum level within the normal scope.
The normal drum level is 180mm below the drum centerline. Levels of + 50mm are the maximum and the minimum water level. Drum level scope: DCS sound and light alarm when drum level reaches -100 mm or +100mm. MFT function when drum level reaches -200mm or +250mm. During boiler partial load, the drum level shall be slightly higher than normal level to avoid the low level caused by increasing of load; on contrary, during high load, the drum level shall be slightly lower than normal level to avoid excessive water level caused by decreasing of the load, while the variat ion scope shall not exceed the allowable value.
3.4 Bed Temperature Control Normally, boiler bed temperature is 880℃，in consideration of load variation and other requirements, the bed temperature shall be controlled between ±40℃. Long term excessive high bed temperature can result in bed coking and boiler fail in operation, whereas, an excessive low bed temperature can cause incomplete combustion and fire extinction. The bed temperature is mainly controlled by adjusting the coal feeding flow and PA flow to air grid. If a bed temperature higher than 990 ℃ (the limit temperature is1050℃) cannot be maintained, the air flow must be controlled by PA flow to grids and reducing SA flow. 3.5 Steam Pressure Control With the requirements of different load condition for bed height and bed temperature, the coal feeding flow shall be adjusted to stabilize boiler combustion and control the steam pressure fluctuation range, which shall be maintained at 9.8Mpa ±0.1MPa. The steam pressure variation range shall be controlled based on the requirements of bed height and temperature of different load conditions, the boiler coal feeding flow shall be controlled to stabilize the boiler co mbustion and control the steam pressure range The adjustment of the feed water flow can be used as an alternative method to control the steam pressure. With this method the drum water level shall be controlled within the permissible range. 3.6 Steam Temperature Control The boiler steam temperature is controlled by the spray attemperator installed between the superheater I &II; the feature of this method is adjusted agilely without delay. The superheater outlet temperature shall be maintained at 535℃ ± 5℃. 3.7 NOx and SO2 Emission Control Check SO2 emission, manually or automatically adjust limestone feeding speed, make sure relative local laws and regulations are conformed; the SO2 emission value cannot lower than 75% of local regulations for long time, which may decrease the boiler operation efficiency. One of the method to control flue gas NO x concentration is to control bed temperature, when the bed temperature higher than 900 ℃, NOx content will increase obviously. The
Boiler Operation Instruction 355B-SM8 16 / 26 NOx content can also be controlled by changing PA /SA ratio, and controlling t he excess air coefficient. The minimum NOx emission value can be obtained when bed temperature is variable within the scope of 820~900℃. 3.8 Air Distribution The principle for adjusting of the PA and SA air is: The SA is applied to control the total air flow, under the condition that the requirements for fluidization, bed temperature and bed material pressure difference are met and when the total air flow is insufficient, the SA damper can be opened gradually, and the SA flow shall be increased gradually along with the load increasing. Monitor bed fluidization conditions, combustion conditions, and material recirculation situation, any problem shall be eliminated immediately. PA/SA ratio or coal feeding flow shall be timely adjusted for bed temperature variation. 3.9 Others Startup burner shall be put into operation when bed temperature is lower than 800℃. During boiler operation, the variations in temperature and pressure drop in different parts shall be inspected, any abnormal condition shall be checked for air leakage, excessive excess air, coking or abnormal combustion, and proper measures shall be carried out to remove the problem. It is recommended to conduct the integral soot blowing in every shift. During boiler operation, special attention shall be paid to variation of the coal quality and the boiler shall be adjusted accordingly.
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4. Boiler Shut-down 4.1 Scheduled Shutdown of the Boiler to Cold State By adjusting the set value of boiler master controller while maintain normal bed temperature, gradually reduce the fuel feeding and the air supply to reduce the boiler load to 50%. During the load reducing process the drum upper and lower wall temperature difference shall not exceed 50 °C. Soot blowing must be carried out when load is reduced to 50% and before boiler stop to avoid the Sulfur contained ash to absorb the moisture from the air to result in the erosion of the tubes. Continue to reduce the boiler load and reduce the fuel feeding flow with a speed of no more than 10% per minute. During load reducing, a steam temperature higher than the saturated steam temperature shall be maintained. Startup burners shall be put into operation before the bed temperature decreases to a value lower than 450, and keep reduce the feeding flow of solid fuel. When the flue gas temperature and the metal temperature of the cyclone separator are maintained not exceed the temperature reducing limit of 100 ℃ /h and 50 ℃ /h correspondingly, reduce the oil burner combustion speed. Limestone feeding shall be set at AUTO state until the solid fuel feeding is stopped. When necessary, the drum level controller shall be set at MANUAL state, and the normal drum level shall be maintained. Stop fuel feeding, limestone feeding and bed material discharge. During boiler shut down, the drum level shall be kept at the upper limit of the level gauge’s visible scope. Continue the fluidization of the bed material and maintain a pressure parts temperature reducing speed less than 40 °C/h. The startup burner shall be stopped when bed temperature is around 450 ℃. When the bed temperature reduces to 400 °C, stop the PA fan and SA fan inlet control damper. All fans shall be stopped after closing of fan inlet damper. Discharge all water inside the boiler or provide nitrogen blanket protection in case of long time shut down. 4.2 Shutdown to Hot Reserve In case of temporary shutdown, fire bank is applicable, so that the boiler is under hot reserve condition, and can be started at any time. When preparing fire bank, decrease the boiler load to the minimum value and the bed fuel shall be burn out, when indicated oxygen content increases to two times of normal value, supply air to furnace to reduce the heat loss; close the inlet vane and air duct control damper of the fan, and the furnace shall be kept without any fire or ignition. For boiler startup, when the bed temperature is lower than 450 ℃, the oil burner can be applied to increase the bed temperature to a value higher than 450 ℃ and then start the coal feeding. Normal drum level shall be maintained during the whole fire bank and hot startup process.
Boiler Operation Instruction 355B-SM8 18 / 26 4.3 Emergency Shutdown Boiler operation shall be stopped immediately upon any of the following conditions: Shortage of drum water, and the drum water level is not visible eve n after water make up. Serious water overflow, drum water level increases above the maximum visible water level and the water level is not visible after the emergency water discharge. Heating surface tube rupture and the normal drum level cannot be maintained. Heavy slag agglomeration. All water level gauges fail, impossible to monitor drum water level. Abnormal increasing of flue gas te mperature due to back firing inside outlet flue gas duct . Boiler wall rupture and in danger of collapsing, which is hazardous to personal and property safety. The system incurs the load throw-off and the safety valves does not function even when the steam pressure is beyond the limit value and the steam release to air could not reduce the pressure. When system load rejecting, malfunction of the safety valve due to exceeding of steam pressure limit and pressure release requirement cannot be met by steam relief. During emergency shutdown the boiler condition changes fast, certain measures shall be taken to prevent the emergency from worsening: Immediately cut off the fuel supply and timely reduce t he boiler load. Adjust the feed water to maintain the normal water level. In case of serious leakage of furnace, feed water to boiler shall be stopped immediately discharge the bed material from the bed. In case of leakage inside the convection duct, normal level of drum shall be maintained. The cooling process for the emergency shutdown is the same as the scheduled shutdown but the time maybe shortened. 4.4 Fast Cooling Down after Boiler Shut Down Close each damper of air and flue gas system after falling down of bed material. When the bed temperature reduces to 400 °C, start the ID fan, the high pressure air fan, the PA fan and the SA fan and compulsory cooling the furnace, however, the opening of air damper cannot be too large, the temperature reducing speed shall be controlled to less than 150/h ( as per the requirement of the refractory supplier ). When the bed temperature reduces to 150 °C, stop high pressure air fan, SA fan and PA fan and open the manhole at the lower portion of the furnace wall, and properly increase the furnace negative pressure according to the requirement for temperature reducing speed. Stop the ID fan when furnace temperature reduces to less than 60 °C. If the boiler is shutdown for hot reserve or it is not required to speed up the cooling of the boiler, the compulsory cooling of the boiler may not required. When boiler shutdown for more than 5 days, the bed material shall be discharged and recycle the bed material of small particle size otherwise the bed material is unnecessary to be discharged. The above procedures are recommended to guarantee the safety and correct startup and operating of the boiler. Proper alternation of those procedures may be made by the user with the actual operation experience. The operation of the auxiliary equipment affiliated with the boiler please refer to the operation manuals of the equipment provided by the manufacturer.
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Precautions
Following precautions shall be observed by the operators for different conditions: During boiler operation, the furnace, especially the lower part of the furnace shall be in positive pressure, and furnace doors are prohibited to be opened to avoid personal injury. Furnace pressure limitation: both excessive positive and negative pressure of furnace may result in damage of equipment, therefore the furnace pressure shall be controlled during operation, before boiler start, following control shall be put into operation. a． monitor the furnace negative pressure(outlet balance point measurement), the negative pressure shall be controlled within the scope of -100～-250Pa，the furnace balance point pressure is not allowed to exceed ±500Pa (alarming value). b．Set value of pressure at the outlet of the furnace for main fuel trip (MFT) is ±2500Pa with 5 seconds of delay. c． Set value of pressure at the outlet of the furnace for blower and ID fan trip is ±4000Pa, without delay. After MFT, heat is reserved with a large amount of recirculating material inside the furnace, therefore special attention shall be paid to water level and steam pressure, drum level control and alarm value please see3.3. Safety Valve Adjustment All the safety valves have been calibrated in the manufacturer’s workshop but the same shall be rechecked during the startup of the boiler. Any defect should be rectified. Excess Air Requirement In order to maintain the proper combustion conditions the excess air factor inside furnace shall be controlled to guarantee a suitable fuel/air ratio. Under rated load, the corresponding oxygen content shall be controlled at 3.2% , this value is provided for reference only, the actual value shall be adjusted according to the combustion situation. Temperature Distribution Around the furnace, thermocouples are installed above the grid to closely monitor the temperature variation. The average value of the 6 measuring points (or the average value of 4 points without maximum and minimum values) shall be taken as coal feeding control temperature. The normal operation scope of the bed temperature is 880 ～960℃, the high bed temperature alarming value is 990℃. Main fuel trip （MFT）when temperature exceed 1050℃.Minimum operation bed temperature is 840 ℃, the bed temperature shall not lower than this value without supporting combustion. main fuel trip (MFT) with a bed temperature lower than 800℃, unless under bed igniting burners are put into operation, however, when bed temperature decreased to a value lower than 450 ℃, coal feeder will trip automatically no matter whether t he under bed igniting burner are running. Protection of Cyclone Separator Heating Surface Tubes In case of unit trip, the temperature of cyclone separator heating surface tubes may increase very fast, if the steam temperature indicated by thermocouples on the ring header on top of cyclone separator is higher than 500 ℃，the control system shall increase steam relief flow automatically to increase steam flow speed and cool off the cyclone separator heating surface tubes. In order to monitor the startup and the operation conditions, thermocouples are provided on steam side piping to monitor the operation as well as control startup speed. Details refer to the following table:
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Protection during Boiler Shutdown
6.1 Nitrogen Blanketing For a shutdown period of more than one week, Nitrogen blanketing is applicable. After boiler shutdown, when drum pressure reduce to 0.3MPa, nitrogen shall be injected into the boiler, the drain gates shall be opened with a nitrogen pressure of 0.3—0.5 MPa, and each drain gates shall be closed when all boiler water is discharged by nitrogen. The boiler steam/water system shall be completely checked, all air valves, drain valves, blowdown valves, valves for feed water and main steam piping as well as the drain valves for these piping shall be strictly closed. During nitrogen blanketing, the nitrogen pressure of the boiler shall be ensure to higher than 0.03MPa (gauge), and the purity of the nitrogen shall be higher than 98%. 6.2 Water Release and Drying under Hot State During boiler shutdown period, water release and drying method can be utilized for pressure parts maintenance or when the boiler shutdown period is within one week. After the bed is fall down, all air and flue gas dampers shall be closed, and the flue gas and air system shall be closed. When drum pressure reduces to 0.5 MPa ~ 0.8 MPa, open the drain and water release gates, and the water in the boiler shall be released as soon as possible. When the drum pressure reduced to 0.1 MPa ~ 0.2 MPa open all air gates of boiler proper. When the drum water is almost fully release and the bed temperature is reduced to 120 °C, start the ID fan, the High voltage air fan, the PA fan the SA fan, put two oil burners into operation to maintain the fluidization air flow and the temperature of 220 °C- 300 °C. Continuously drying the boiler for 10 to 12 hours by means of the hot air and then stop and close the boiler. When the outlet flue gas temperature of the economizer is reduced below 120 °C, close all the air gates of the boiler proper and the drain and water release gates. During the drying of the boiler the relative humidity inside the boiler shall be less than 70% or equal to the environmental relative humidity. 6.3 Pressure Filling The pressure filling is applied when the shutdown period of the boiler is only 2 to 3 days. After the stop of the operation, naturally reduce the boiler pressure (the CBD may not be stopped). When the boiler pressure reduces to 5.8Mpa, analysis shall be made by chemical personnel for the boiler water quality. The boiler water shall be changed if not qualified. When the boiler water meet the quality requirement, close the first and second gate of the IBD as well as the main gate of the IBD to stop the IBD function. The boiler water must be qualified before boiler pressure decreases to 0.5Mpa. When boiler pressure is above 0.5Mpa and the superheater wall temperature is below 200 °C the water maybe fed to the boiler to start the pressure increasing. The anti-corrosion pressure is generally maintained at 2.0Mpa ~ 3.0 MPa, with maximum value of 5.8Mpa and minimum value of 0.5Mpa. In case of certain reason, the pressure decreases to a value to below 0.5Mpa (the pressure reaches 0), re-ignition is required to increase the pressure to 4.0 Mpa and repeat the above procedures. Once the pressure filling is completed, a record shall be kept and notice shall be made to
Boiler Operation Instruction 355B-SM8 the relative section for analyze the dissolved oxygen.
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7. Trouble Shooting 7.1 Abnormal Bed Temperature Phenomenon: The indication of bed temperature is high or low. High bed temperature alarm. Load increase or reduce. Reasons： The fuel particles may be oversize or downsized. The measuring fault of thermocouples. Failure of fuel feeders. Improper PA /SA ratio Failure of ash discharge system. Failure of limestone feeding system Solutions: Check the thermocouples for the bed temperature measuring. Check the fuel feeder performance and control. Adjust PA / SA ratio. Oil gun shall be provided in case of unstable co mbustion caused by low bed temperature. 7.2 Abnormal Bed Temperature Phenomenon: Alarm due to high or low bed pressure Load of ash cooler increased seriously, or stop of ash discharging. Bottom air box pressure is too high or too low. Reasons： Bed pressure measuring failure. Failure of ash cooler, excessive discharge or discharge too little. Abnormal limestone or fuel feeding. Abnormal PA flow. Boiler loads varies too fast or coal quality changes too much. Solutions： For an excessive high bed pressure, ash cooler discharge flow shall be increased while fuel feeding flow shall be reduced; for an excessive low bed pressure, ash cooler discharge flow shall be reduced and limestone feeding shall be increased when necessary. Bed pressure measuring points shall be inspected and any failure shall be eliminated. If the problem of ash discharge cannot be removed, and the bed pressure continuously increases, the boiler must be stopped to solve the problem. 7.3 Water Wall Rupture Phenomenon: In case of slight rupture, special sound of steam may indicate the leakage of the weld, and feed water flow will slightly increased. If the tube rupture is serious there is the obvious cracking sound and the steam sound and the furnace pressure will become positive instead of negative and the feed water flow will be abnormally larger than the steam flow. Reasons：
Boiler Operation Instruction 355B-SM8 22 / 26 The boiler water and the feed water quality is fail to meet the standard for a long time, fouling has been built inside the tube and resulted in increasing of the thermal resistance locally to form the local over heated. Improper water circulation caused local overheating. Unqualified tube material, unqualified bed welds or serious erosion of tube outer wall. Solutions： Serious water wall rupture： a. Increase feed water flow to maintain the drum level; actual condition shall be based to make the boiler operate in partial low or shutdown the boiler in accordance with normal procedures. b. Oil shall be provided for support combustion in case of unstable co mbustion. Normal level cannot be maintained in case of serious damage of water wall: a. Emergency shutdown of the boiler, and stop feed wat er supply. b. Maintain the operation of the ID fan to remove the steam inside the boiler and stop the ID fan if the bed temperature decreasing speed is beyond the permissible value. c. Immediately remove the bed material after boiler shutdown. d. Other operations please refer to the shutdown normal shutdown of the boiler under). 7.4Superheater Tube Rupture Phenomenon： Sound of steam injection can be detected, and the water flow is larger than the steam flow. Furnace negative pressure decreases or become positive pressure, the pressure of superheated steam decrease. Reasons： Deterioration of heat transfer due to fouling built inside t furnace wall or tube blockage by foreign substances Wearing of tube outer wall or high temperature corrosion. Boiler operates for long time under excessive steam or wall temperature. Unqualified tube material, bed welding quality or improper soot blowing. Solutions： In case the tube rupture is not very serious, the boiler is allowed to operate for certain time, while the load shall be reasonably reduced, and the boiler shall be prepared for shutdown. Serious tube rupture: a. ID fan shall be kept for operation, and the bed temperature decrease speed shall be control not exceed the design value. b. A normal water level shall be maintained by keeping a small feed wat er flow. c. Normal boiler shutdown procedures shall be taken for other operations. 7.5 Bed Coking Phenomenon： Indications of one or more thermocouples has large difference with the average value ( with the difference>100 °C ) Air chamber pressure increases under the normal bed pressure. Indications of one or more bed pressure keep static, which are not the fluctuation reading during the normal operation. White flash can be detected within the fluidized bed, and coking can be seen from the peephole, in case of serious coking, it is hard to carry load. Reasons:
Boiler Operation Instruction 355B-SM8 23 / 26 Excessive bed temperature or excessive low bed material melting points. Improper air/coal ratio for long time during operation. Many fluidizing air nozzles are blocked before boiler start or foreign substances like refractory material blocks are left inside the boiler. Solutions： Increase the PA flow. Reasonable decrease the bed temperature, special attention shall be paid during coal feed for bed temperature increase speed. Boiler shall be shut down immediately in case o f no improvement after adjusting. 7.6 Re-burn inside Flue Gas Duct Phenomenon: Abnormal increase of flue gas exit temperature. In case of re-burn inside flue gas duct, the oxygen content of flue gas decreases, and main steam temperature increases abnormally. In case of combustion in side back pass, PA and SA temperature increases, and economizer outlet water temperature increases. Large variation of furnace negative pressure. Fire and flue gas comes out of the duct where is not properly sealed. Reasons Serious improper air/coal ratio for long time during operation. Improper oil gun atomization during the startup, while operates with oil combustion for long time. Solutions: Start the soot blowing for flue gas duct heating surface and reduce load when necessary. If the above measurement does not help and the discharge flue gas temperature is increased to 200 °C, the boiler has to be emergency shutdown. Stop all the air fans and close t he boiler combustion and the flue gas, air supply system. Maintain the continuous feed water supply to t he boiler. 7.7Water Shortage Phenomenon：
Drum level lower than the normal value, or water level cannot be detected from the Low level alarm. Steam flow suddenly largely higher than actual effective feed water flow. Reasons:
Negligence of the operator in monitory of water level. Failure of certain equipment, e.g. automatic feed water failure, or fake level indication due to blockage of water level gauge. Leakage of boiler drain or blowdown system, or excessive discharge. Rupture of boiler feed water t ubes or rupture in heating surface. Solutions: Indications of all water level gauges shall be cross checked to judge verify the authenticity of the water level or the seriousness of the shortage. Immediately shutdown shall be made in case of serious water shortage. Slightly shortages of water, which may not affect the boiler operation, are usually caused by improper operation. And in such cases, the feed water flow shall be manually increased
Boiler Operation Instruction 355B-SM8 24 / 26 to guarantee that the water level is go back to the normal position. 7.8 Overflow Phenomenon:
Water level is not visible and drum water is not clear. High level alarm. Superheated steam temperature decreases and steam salt content increases. Feed water flow suddenly largely higher than Steam flow Reasons:
Negligence of the operator in monitory of water level. Failure of feed water automatic control or excessive feed water pressure. Solutions: Indications of all water level gauges shall be cross checked to judge verify the authenticity of the water level or the seriousness of overflow. The automatic feed water control shall be shifted to manual feed water control. Slightly overflow can be controlled manually, and the flow for blow down, drain and emergency water discharge shall be increased. Immediately shutdown shall be made in case of serious overflow. 7.9 Water Impact Reasons: The pipes are not properly heated and drained before carrying the steam or there is air left inside the piping. The intermittent close and open of the BFP to create t he unstable water pressure. Solutions: In case of the water impact, open the drain valve of the superheater system to smooth the drainage and timely release the air from inside the superheater piping system. For the feed water piping, the water pressure should be stabilized and the air should be released completely. 7.10 Shortage of Coal Supply Reasons: The bunker is chocked. Feeder failure The moisture of the fuel result in a blockage The furnace back pressure is too high. Solutions: O2 meters shall be checked for oxygen indications, in case of any indication obviously high than normal value, the coal shortage shall be checked at first, ( it will be a waste of time to judge the coal shortage after continuously decrease of bed temperature), routine check shall be conducted to locate the blockage of coal, and mean while increase the speed of other coal feeders to maintain the total coal feeding flow, in case the back pressure of the furnace is too high, the ash cooler discharge flow shall be increas ed. 7.11. Main Fuel Trip(MFT) The MFT incurs along with the following activities: 1．Main fuel trip 2．Limestone system trip 3．Under bed ignition system trip
Boiler Operation Instruction 355B-SM8 25 / 26 4．All air flow control are shifted to manual mode and kept at final position. 5．Unless the fans are trip, all fan control will be shifted to manual mode and be kept at final position, when fans are trip, the control logic of fan will be followed. 6．ID fan automatic control is limited by combustion output signal to make sure furnace pressure not exceed the limited value. 7．Unless the boiler is under the hot restart condition, otherwise the “specified boiler purging” logic will be established. 8．Print MFT time and reason. Any of following conditions will result in main fuel tr ip（MFT） 1．Both boiler MFT buttons are pressed. 2．Bed temperature higher than 1050 ℃（signal from CCS） 3．Logic control power lost. 4．2 of the 3 logic controls show that furnace outlet pressure is high high value +2500Pa (delay) 5．2 of the 3 logic controls show that furnace outlet pressure is low low value -2500Pa (de lay) 6．2 of the 3 logic controls show that drum level is high high value +250mm (delay) 7．2 of the 3 logic controls show that drum level is low low value -200mm (delay) 8．ID fan trips. 9．PA fan and SA fan trip. 10． Excessive low total air flow, less than 25% (with delay) (signal from CCS). 11． CCS power lost (signal from CCS). 12． Air /coal ratio less than the minimum value. (Signal from CCS). 13． Bed temperature less than800℃，under bed igniter start (signal from CCS). 14． Material recirculation air trip. 15． Gas turbine trip. Solutions after MFT active. 1．If MFT is not caused by trip of ID fan, trip of PA or SA fan or due to failure of DCS system, following principles can be followed directly: a) Adjust the air dampers to maintain normal furnace negative pressure. b) Adjust the feed water flow to maintain the normal drum level. c) Immediately find the cause of MFT. d) In case the cause of MFT cannot be detected or eliminated within a proper time window, the boiler shall be shutdown to hot reserve condition. e) If the cause of MFT can be detected and removed within a short period, the boiler can be restarted under hot state. 2．If MFT is caused by trip of ID fan, trip of PA or SA fan or due to failure of DCS system, in addition to the abovementioned principles, local bed material pilling and local stoppage of fluidization shall be taken into consideration, the phenomenon is as follows: a) One or more bed temperature indication is largely varied from the other indications of bed temperature. b) All the readings of the bed temperature are static (normally, the bed temperature fluctuates). 3．Steps for automatic fluidization of bed material:
a)
Shift the boiler air flow control to manual operation.
b)
The general gate of PA shall be opened fatly and close to its original position to observe
Boiler Operation Instruction 355B-SM8 26 / 26 whether the indication of bed pressure returns to normal value.
c)
Repeat the abovementioned movement for 3 times in 10min, if the situation does not improve further steps of discharging the bed material shall be taken to fluidize the startup bed material, till the result are satisfied.
d)
Boiler air flow control shall be switched to AUTO mode.
