Common faults of gasification units and their solutions
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Accident phenomena, causes, and handling methods:1. Bridge formation in the coal bin: a. Coal is too wet; a. Use an air cannon for vibration.
2. High current alarm in the ball mill: a. Power grid fluctuations; b. Excessive load; c. Poor bearing lubrication; a. Notify the substation promptly for handling; b. Adjust the load; c. Check the operation of the lubricating oil system.
3. High current alarm in the slurry tank mixer: a. Excessively high slurry viscosity; b. Foreign objects blocking the blades; a. Adjust the properties of the slurry; b. Check for foreign objects and remove them promptly.
4. Low-pressure slurry pump does not deliver fluid: a. Clogged inlet pipe; b. No liquid level in the mill’s discharge tank; c. Clogged inlet valve, pump malfunction; a. Clear the inlet pipe; b. Wait until a normal liquid level is established in the tank before pumping; c. Disassemble and clean the inlet valve, and repair the pump.
5. High-pressure slurry pump does not deliver fluid: a. Clogged inlet valve; b. Pump malfunction (such as clogged or damaged inlet/outlet valves, damaged diaphragms and hoses); a. Disassemble and clean the inlet valve; b. Inspect the pump. 6. High outlet pressure alarm for the high-pressure slurry pump: a. Excessively high system pressure; b. Blockage in the pipeline from the slurry pump outlet to the gasifier; c. One of the valves between the slurry pump and the gasifier is not open or not fully open; d. Mechanical failure of the pump itself. a. promptly check and adjust the operating conditions of the gasification system; b. clean and unblock the pipelines; c. check the opening status of the relevant valves and ensure they operate as required by the process; d. repair the pump. 7. Coarse particle size of the slurry: a. Excessive amount of coal being fed; b. Increased size of the coal particles entering the grinder; c. Severe wear of the steel balls; d. Changes in the quality of the coal. a. Adjust the amount of coal fed; b. check and adjust the operation of the coal screening equipment; c. add more steel balls; d. adjust the ratio of steel balls used. 8. Fine particle size of the slurry: a. Insufficient amount of coal being fed; b. Severe wear of the steel balls. a. Increase the amount of coal fed; b. Add more steel balls. 9. Increased viscosity of the slurry: a. Reduced dosage of additives; b. Fine particle size of the slurry; c. Excessively high concentration. a. Increase the dosage of additives; b. take appropriate actions based on the cause of the fine particle size; c. adjust the concentration. 10. High concentration of the slurry: a. Increased amount of coal fed; b. Reduced amount of water supplied; c. Inaccurate readings from the instruments. a. Reduce the amount of coal fed or increase the amount of water supplied; b. Increase the amount of water supplied or reduce the amount of coal fed; c. Notify the personnel responsible for maintaining the instruments. 11. Blockage in the slurry pipeline: a. Excessive residence time of the material inside the pipe; b. Entry of large debris into the pipe; c. Damaged pipe fittings. a. Flush the pipe with water; b. Clean the pipe by flushing it with water or removing it and cleaning it; c. Replace the damaged pipe fittings. 12. Low coal feeding rate to the grinder: 3. Blockage at the outlet of the coal hopper; 4. Blockage in the coal weighing feeder; 5. Blockage in the inlet chute of the grinder. 1. Use an air cannon to clear the blockage; 2. Stop the coal weighing feeder to remove the blockage. I. Handling of accidents in the slurry preparation system: Accident symptoms, causes, and solutions. 13. High water supply rate to the grinder: a. Fault in the grinder’s water supply valve FV1005. a. Check the regulating valve FV1005. 14. Low water supply rate to the grinder: a. Fault in the grinder’s water supply valve FV1005; b. Fault in the pump used to supply water to the grinder. a. Check the regulating valve FV1005; b. Check the pump used to supply water to the grinder
Handling of accidents in the gasification and slag-water systems: Accident symptoms, causes, and corrective actions. 1. High differential pressure between the gasification furnace and the syngas outlet; blockage at the furnace’s slag outlet. a. Fluctuations in coal quality, excessively low operating temperature. b. Degraded performance of the burners, poor atomization. c. Improper adjustment of the central oxygen supply, resulting in poor atomization. d. Inadequate temperature increase and slag removal procedures during shutdown. e. Excessively high final temperature during furnace drying. a. Analyze the situation promptly and adjust the process parameters. b. Ensure proper installation of components and carry out regular replacements. c. Adjust the central oxygen supply, lengthen the flame, and improve atomization performance. d. Follow strict procedures for temperature increase and slag removal during shutdown. e. Keep the furnace drying temperature below 1200°C to prevent slag from flowing and blocking the slag outlet. When process adjustments are ineffective, the furnace should be stopped for manual intervention. 2. Excessively high wall temperature of the gasification furnace: a. Excessively high furnace temperature; b. Excessive load; c. High furnace pressure or a reduced slag outlet, leading to increased flow of syngas, or vibrations and impacts that widen the gaps between bricks, causing gas leakage; d. Local or overall thinning of the refractory bricks: a. Reduce the furnace temperature; b. Lower the load according to production requirements; c. Reduce the load to bring the furnace temperature to an appropriate level; over time, slag will form and fill these gaps; d. Replace the bricks. 3. Abnormally high local temperatures in the furnace chamber: a. Improper spraying from nozzles, resulting in localized excess oxygen; b. Instrumentation issues: a. Adjust the oxygen supply and the load on the gasification furnace; if this does not work, stop the furnace; b. Have instrumentation technicians check and repair the equipment. 4. Overload of the slag breaking machine, leading to shutdown: a. Falling refractory bricks inside the furnace; b. Falling metal components inside the quenching chamber; c. Faults with the slag breaking machine itself. Restart after 1 hour of shutdown; if it still doesn’t work, stop the furnace for inspection. 5. Inadequate operation or failure to operate of the lockhopper valve: a. Broken valve bearings; b. Hard objects stuck in the valve; c. Issues with the valve’s position sensor or other instrumentation problems: a. Stop the furnace for repairs; b. Try opening and closing the valve several times; if that doesn’t work, stop the furnace for cleaning; c. Have instrumentation technicians check and make adjustments. 6. Failures in the slag skimming machine: These include broken chains, broken gears connecting the skimmers, overly long chains, falling liner plates, burned-out motors, or gearbox failures, as well as the skimmer getting stuck and failing to function. In such cases, reduce the load on the gasification furnace, use the auxiliary slag discharge line to send the slag to the grinding tank, and then repair the slag skimming machine. 7. High liquid level alarm in the gasifier quench chamber: a. Excessive water flow into the quench chamber; b. Blockage in the outlet water pipe; c. Instrument failure (false liquid level) or blockage in the liquid level gauge connections. a. Adjust the water flow into the quench chamber; b. Adjust the valve opening for the water entering the flash tank – if this does not work, shut down the system; c. Have the instrumentation team handle the issue and make adjustments. 8. High pressure difference before and after the filter in the quench chamber: a. Too many impurities have accumulated in the separator, causing a blockage. a. Switch to another filter and clean the one that is in use. 9. High temperature of the cooling water at the nozzle: a. Low flow rate of cooling water to the nozzle; b. Poor heat exchange efficiency in the nozzle cooling water cooler, resulting in high temperature of the circulating water; c. Breakage in the coil, leading to synthesis gas leakage. a. Adjust the flow rate or start a backup pump; b. Increase the amount of circulating water, and if necessary, shut down the system to clean the heat exchanger; c. Shut down the system to replace the nozzle and repair any leaking nozzles
Accident phenomena, causes, and handling measures:
10. Fire in oxygen pipelines and valves
a. The oxygen pipeline is not cleaned properly; it contains slag, grease, etc.
b. The oxygen valve is opened too quickly, resulting in a high flow rate.
c. The anti-static facilities are damaged.
a. Perform nitrogen purging after an emergency shutdown.
b. The oxygen valve should be opened slowly.
c. Regularly inspect the anti-static facilities of the oxygen pipelines.
11. Over-oxygen explosion in the system (often occurs during startup in the quench chamber and scrubber tower)
a. The drain valve on the coal slurry pipeline is not closed, or the flow meter reading does not match the actual amount of fuel in the furnace.
b. The flushing water valve for the coal slurry pipeline is not closed, causing the coal slurry to become diluted and leading to an excess of oxygen.
c. During startup and shutdown, low-pressure N2 purging is incomplete or there are areas where purging does not occur properly.
a. Verify all valves before startup; if over-oxygen levels are detected after feeding starts, stop the machine manually immediately.
b. Verify all valves before startup; stop the machine as appropriate after feeding starts.
c. Ensure proper low-pressure N2 purging; O2 and flammable substances must be analyzed to ensure they are within acceptable limits.
12. High CO level detected above the burner cooling water separation tank
a. The burner cooling water coil is damaged.
b. Instrumentation failure.
a. Stop the machine, replace the burner, and repair the damaged coil.
b. Notify the instrumentation team to conduct inspections after stopping the machine.
13. Excessively high temperature at the syngas outlet of the quench chamber
a. Low liquid level in the quench chamber.
b. Insufficient amount of cooling water.
c. The downcomer in the quench chamber is damaged or broken.
d. Low flow rate or no flow of condensate at the syngas outlet.
a. Increase the amount of cooling water, reduce the flow rate of the black water outlet valve, and adjust the liquid level to normal levels.
b. Increase the amount of cooling water.
c. Stop the machine, repair the issue, and adjust the spray volume to normal levels.
d. Adjust the spray volume to normal levels.
14. Blockage in the syngas outlet pipe of the quench chamber, resulting in increased pressure difference between the gasifier and the scrubber tower
a. Low flow rate or no flow of condensate at the syngas outlet of the quench chamber.
b. Damage to the baffle plates at the top of the quench chamber.
a. Increase the spray volume; if that doesn’t work, stop the machine and carry out repairs to clear the blockage.
b. Repair the issue after stopping the machine.
15. Water contamination in the gasifier quench chamber, manifested as: large fluctuations in venturi pressure difference, rising liquid level in the scrubber tower, significant reduction in water flow into the tower despite attempts to control it, dropping and fluctuating temperatures at the top of the quench chamber, and reduced amount of black water exiting the gasifier.
a. Excessively high actual liquid level in the quench chamber.
b. Blockages in the gaps around the upcomer and downcomer, reducing the flow area and causing high gas flow rates.
c. The upcomer is misaligned, reducing the flow area.
d. Damage to the baffle plates on the gas exit side of the quench chamber.
a. Lower the liquid level in the quench chamber.
b. Stop the machine and clear the blockage.
c. Slightly lower the liquid level and reduce the load; repair the issue after stopping the machine.
d. Stop the machine and carry out repairs.
16. Excessively high pressure difference in the venturi scrubber, exceeding 0.2 MPa; the gas exiting the scrubber tower contains excessive dust, pressure in the gasifier increases, and the amount of cooling water decreases.
a. The gray water is too dirty, resulting in poor sedimentation in the sedimentation tank.
b. Severe contamination of the syngas with ash.
c. High hardness in the gray water, causing scaling in the venturi scrubber.
a. Adjust the flocculant used in the sedimentation tank.
b. Increase the amount of water sprayed in the syngas quench chamber.
c. Add scale inhibitors to the gray water
10. Fire in oxygen pipelines and valves
a. The oxygen pipeline is not cleaned properly; it contains slag, grease, etc.
b. The oxygen valve is opened too quickly, resulting in a high flow rate.
c. The anti-static facilities are damaged.
a. Perform nitrogen purging after an emergency shutdown.
b. The oxygen valve should be opened slowly.
c. Regularly inspect the anti-static facilities of the oxygen pipelines.
11. Over-oxygen explosion in the system (often occurs during startup in the quench chamber and scrubber tower)
a. The drain valve on the coal slurry pipeline is not closed, or the flow meter reading does not match the actual amount of fuel in the furnace.
b. The flushing water valve for the coal slurry pipeline is not closed, causing the coal slurry to become diluted and leading to an excess of oxygen.
c. During startup and shutdown, low-pressure N2 purging is incomplete or there are areas where purging does not occur properly.
a. Verify all valves before startup; if over-oxygen levels are detected after feeding starts, stop the machine manually immediately.
b. Verify all valves before startup; stop the machine as appropriate after feeding starts.
c. Ensure proper low-pressure N2 purging; O2 and flammable substances must be analyzed to ensure they are within acceptable limits.
12. High CO level detected above the burner cooling water separation tank
a. The burner cooling water coil is damaged.
b. Instrumentation failure.
a. Stop the machine, replace the burner, and repair the damaged coil.
b. Notify the instrumentation team to conduct inspections after stopping the machine.
13. Excessively high temperature at the syngas outlet of the quench chamber
a. Low liquid level in the quench chamber.
b. Insufficient amount of cooling water.
c. The downcomer in the quench chamber is damaged or broken.
d. Low flow rate or no flow of condensate at the syngas outlet.
a. Increase the amount of cooling water, reduce the flow rate of the black water outlet valve, and adjust the liquid level to normal levels.
b. Increase the amount of cooling water.
c. Stop the machine, repair the issue, and adjust the spray volume to normal levels.
d. Adjust the spray volume to normal levels.
14. Blockage in the syngas outlet pipe of the quench chamber, resulting in increased pressure difference between the gasifier and the scrubber tower
a. Low flow rate or no flow of condensate at the syngas outlet of the quench chamber.
b. Damage to the baffle plates at the top of the quench chamber.
a. Increase the spray volume; if that doesn’t work, stop the machine and carry out repairs to clear the blockage.
b. Repair the issue after stopping the machine.
15. Water contamination in the gasifier quench chamber, manifested as: large fluctuations in venturi pressure difference, rising liquid level in the scrubber tower, significant reduction in water flow into the tower despite attempts to control it, dropping and fluctuating temperatures at the top of the quench chamber, and reduced amount of black water exiting the gasifier.
a. Excessively high actual liquid level in the quench chamber.
b. Blockages in the gaps around the upcomer and downcomer, reducing the flow area and causing high gas flow rates.
c. The upcomer is misaligned, reducing the flow area.
d. Damage to the baffle plates on the gas exit side of the quench chamber.
a. Lower the liquid level in the quench chamber.
b. Stop the machine and clear the blockage.
c. Slightly lower the liquid level and reduce the load; repair the issue after stopping the machine.
d. Stop the machine and carry out repairs.
16. Excessively high pressure difference in the venturi scrubber, exceeding 0.2 MPa; the gas exiting the scrubber tower contains excessive dust, pressure in the gasifier increases, and the amount of cooling water decreases.
a. The gray water is too dirty, resulting in poor sedimentation in the sedimentation tank.
b. Severe contamination of the syngas with ash.
c. High hardness in the gray water, causing scaling in the venturi scrubber.
a. Adjust the flocculant used in the sedimentation tank.
b. Increase the amount of water sprayed in the syngas quench chamber.
c. Add scale inhibitors to the gray water
17. The temperature of the syngas exiting the scrubber tower is unstable, the water vapor ratio increases, and the system pressure is unstable. a. The actual liquid level in the scrubber tower is too high, resulting in liquid entrainment. b. The scrubber tower trays are damaged. c. Improper operation of the scrubber tower causes flooding. d. The flow rate of water entering the venturi is low. e. The mist removal outlet at the top of the scrubber tower is blocked or damaged. a. Lower the liquid level in the scrubber tower. b. Shut down the system for maintenance. c. Adjust the amount of liquid flowing onto the scrubber tower trays. d. Adjust the flow rate of water entering the venturi scrubber. e. Shut down the system for maintenance. 18. The differential pressure in the scrubber tower decreases, the trays get flooded, the syngas temperature is high, and the dust content exceeds the specified limits. a. The trays are not installed properly. b. The feed load is too high, causing severe stress on the trays. c. The pressure is released too quickly when shutting down the system. a. Install the trays according to the design specifications and conduct a thorough inspection after installation. b. The feed load should not be too high; it should be kept between 50–60% of the normal level. c. Control the pressure release rate to less than 0.1 MPa/min. 19. An alarm is triggered due to an excessively high liquid level in the scrubber tower. a. The syngas contains excessive water. b. The flow rate of water entering the tower is too high. c. The water pipes at the bottom of the tower are blocked. d. The flow rate at the outlet of the quench water pump has decreased. a. Control the liquid level in the quench chamber. b. Adjust the flow rates of condensate and ash water entering the tower. c. If adjusting the outlet valve for the black water still doesn’t work, shut down the system. d. Adjust the flow rate of the quench water pump. 20. The black water pipeline is blocked. a. The black water pipeline isn’t thoroughly flushed during shutdown. b. There are faults with the lock hoppers or slag breakers, allowing slag from the quench chamber to enter the flash vaporization system. c. The black water pipeline isn’t switched regularly. d. The gasifier is not operating properly. a. Follow the requirements for proper shutdown flushing procedures. b. If the slag in the lock hoppers isn’t removed within one hour, shut down the system. c. Switch the black water pipeline regularly. d. Adjust the process parameters to identify the root cause; shut down the system if necessary for inspection. 21. The flow rate of quench water is too low. a. The quench water pump is faulty. b. The quench water filter is blocked. c. The operating pressure in the gasifier is too high. d. The pipeline from the quench water pump to the gasifier is blocked. a. Start the backup pump. b. Switch to the backup filter and clean the blocked filter. c. Reduce the operating pressure appropriately. d. If these measures don’t work, shut down the system for maintenance. 22. The proportion of glassy slag in the slag decreases, while carbon black slurry increases. Analysis shows that the carbon content in the slag has increased significantly, and the gas composition fluctuates, resulting in a low carbon conversion rate. a. The nozzles are worn, reducing the atomization effect. b. The oxygen level in the burner isn’t adjusted properly. c. The oxygen-to-coal ratio isn’t adjusted properly, resulting in a low furnace temperature. a. Replace the nozzles. b. Adjust the flow rate of central oxygen and monitor the furnace conditions. c. Adjust the oxygen-to-coal ratio and control the furnace temperature. 23. Vibration occurs in the flare pipeline, with water hammer sounds, and a large amount of water overflows from the flare separation tank. a. The liquid level in the syngas scrubber tower is too high, allowing water to enter the syngas flare pipeline. a. Quickly shut off the water supply to the scrubber tower and increase the drainage rate. Once the liquid level returns to normal, adjust the water flow rate accordingly. 24. Backflow occurs in the flare, and the flare vent pipeline turns red and extends back along the pipeline. a. Negative pressure is generated in the flare pipeline. b. The liquid level in the flare water seal tank is too low. c. Nitrogen supply is interrupted. a. Keep the temperature in the downstream system from dropping too low, to prevent excessive water vapor from condensing and causing pressure drops. b. The liquid level in the flare water seal tank must not be too low; conduct regular inspections and address any issues promptly. c. When tempering is detected, quickly open the nitrogen valve to extinguish the flame