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        2. Home > Operational Area > BOILER
          Slag-discharging, ash-discharging and coke-knocking-out of 220 tons circulating fluidized bed boiler

          1. For this boiler, the method of solid-state slag -discharging, ash-discharging in dry state is adopted, its temperature is higher, so the remote- control electrically discharging and automatic pneumatic ash-conveying shall be adopted. The operating shall be often monitored in order to ensure the safe operation of the boiler. 

          2. During operation, the slag cooler is controlled according to the differential pressure  of material layer in order to make the slag discharged uniformly and the differential pressure material layer stabilize around 8500 pa. Keep boiler operation normal and combustion stable. 

          3. In case of the following situations, the slag-discharging shall be stopped: 

          (1) The boiler combustion is not normal and fluidization is unstable.

          (2) The differential pressure of material layer is low, and is less than 8000 pa. 

          (3) the coal quality is better, under the lowest output, the slag-discharging continuously is still conducted when the differential pressure of material layer drops. At this moment, discontinuously discharging slag in less amount shall be adopted. 

          (4) Damping down and starting in hot start. 

          (5) Interrupting the coal feeding from the coal feeder. 

          (6) Without the consent of the stoker. 

          4. In case one of the following circumstances, the slag-discharging can be reinforced. 

          (1) confirm that there are big particles depositing in the bed, causing uneven fluidization.

          (2) During operating, the micro coking phenomenon is found. 

          (3) When the temperature difference of upper part and lower part  in the dense phase zone in the hearth is between 100-150 ℃. 

          (4)When the differential pressure of material layer is bigger, and is more than 9000 pa. 

          (5) When there are large amount of returning ash flowing back the hearth and making the differential pressure of  material layer increase suddenly. 

          (6) The coal quality is poorer, under the lowest output, the slag-discharging continuously is conducted when the differential pressure of material layer still increases. At this time, slag discharging artificial auxiliary shall be done. 

          5. Other precautions for slag-discharging: 

          (1) when the slag- discharging, the air chamber pressure reduction does not exceed 300-500 pa and shall not affect the boiler load. It is not allowed to increase the coal feeding amount by a large margin when the slag is discharged. 

          (2) It is forbidden to impact the slag -drop pipe forcibly. 

          (3) During the process of the slag- discharging, such as when there are refractory concrete, air hood, refractory brick and foreign body emitting, it is required to immediate notice the  stoker for processing, if the slag-pipe is blocked, it is required to report the shift chief-operator immediately for handling and to record the results in the handover book. 

          (4)If the slag-cooler and chain bucket slag-conveying machine have problems, it is required to report to the monitor and to notify the maintenance persons for handling immediately. And record the results in the handover record book. 

          (5) When the bypass slag -discharge pipe is used,  the operator shall wear the helmet, gloves, glasses and protective mask. The amount of slag -discharging shall be determined according to the capacity of air chamber pressure and the size of the load. 

          6. Precautions for operation of slag-conveying machine: 

          (1) When starting, it is required to firstly start # 3 slag-conveying machine. After it operates normally, then # 1 or # 2 slag-conveying machine are started. When stopping, firstly stop # 1 and # 2 slag-conveying, then stop # 3 slag-conveying machine. During outage, after the slag is discharged from the chain bucket, then stop operation. 

          (2)When the slag-conveying machine is operating, it is required to check the running status and check whether the bucket wheel derails or falls off. and check whether there is abnormal sound or not during operation.  and check whether the operation of motor reducer is normal or not. The rotating parts of the slag-conveying machine shall be lubricated on time. 

          (3) While inspecting or repairing, it is forbidden to run across the chain bucket in operation. 

          (4) The slag accumulated in the slag-conveying channel shall be cleaned on time. 

          (5) When it is found that there is overloading phenomenon in the slag-conveyor, the slag-discharging capacity shall be reduced and the slag shall be discharged artificially. 

          7. The person on-duty shall discharge the ash according to the specific factors of boiler load, temperature of returns, differential pressure of hearth and bed temperature, and determine the discharging capacity of ash. 

          8. In case one of the following circumstances, the ash can be discharged: 

          (1) the load is suddenly reduced. 

          (2) The cyclone separator is damaged or the return feeder  is blocked by ash or cokes. 

          (3) The pressure differential value of hearth exceeds 1400 pa. 

          (4) When the returns feeder is required for ignition. 

          (5) When the air for returns  is interrupted or the  small air hood in the returns feeder is seriously damaged. 

          (6) The combustion  and fluidization in the bed are not normal, and bed temperature is slightly high or low. 

          (7) Before the fire is damped down, part of the returns ash can be discharged. 

          9. Precautions for ash-discharging: 

          (1) Before the ash is manually discharged, it is required to get the consent of the stoker. The worker for discharging ash shall put on the helmet, gloves and protective glasses as well as protective mask. The amount of ash to be discharged is determined according to the specific factors of the boiler load, returns  temperature, differential pressure of hearth, boiler  bed temperature and inlet smoke temperature of cyclone separator. 

          (2) When the ash accumulated in returns feeder is discharged, the  boiler load shall not be affected. 

          (3) It is not allowed to cause the boiler bed temperature to fluctuate by a large margin.

          (4)  It is forbidden to impact the slag -drop pipe forcibly. 

          (5)The ash shall be discharged slowly in order to avoid fine ash flying and causing secondary pollution and to prevent the jetting of flame from injuring people. 

          (6) In the process of ash-discharging, it is required to  pay attention to the firmness of each welding point and ash door pin in order to prevent happening of abnormal accidents. 

          10. In the process of  ignition phase and normal operation of boiler, it is required to often monitor the boiler bed temperature and returns temperature, in order to prevent local over temperature and coking of material layer. When there is local and small range of coking in the material layer, it is required to immediately increase the primary air volume and to increasing the slag-discharging capacity in order to eliminate coking. 

          11. If the coking of materials layer is discovered, it is required to timely report the shift chief-operator for processing: 

          (1) Increasing air output, at the beginning of the coking, it is obvious to decoke by means of increasing air flow. 

          (2) If the coking cannot be eliminated by means of increasing air flow, the boiler shall be stopped for processing. 

          (3)When the coke is knocked out, the manhole of hearth shall be completely opened and the coke raked shall be transported immediately. When entering the hearth to knock out the coke, the manhole place must be monitored by special person in order to prevent  happening of emergency. 

          (4) It is forbidden to directly spray water for cooling the coke in the combustion chamber. When the coke raked from the hearth is cooled by water spraying, water vapor burns shall be avoided. 

          12. When coking appears in the return feeder, after the boiler is stopped, discharge the returns ash completely, then knock out the coke.  


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