10.3　Mechanical Bottom Ash Handling System

10.3.1　When the boiler is provided with a mechanical bottom ash handling system，submerged scraper conveyors，dry-type air-cooled conveyors or en-masse scraper conveyors may be used to convey bottom ash through techno-economic comparison based on factors such as the amount and characteristics of bottom ash，conveying distance as well as bottom ash recycling requirements.If conditions permit，a mechanical system shall be preferred to lift bottom ash to the bottom ash silo.

10.3.2　If submerged scraper conveyors are used，the following requirements shall be met:

1　Single-step submerged scraper conveyors should be used to convey bottom ash to the bottom ash silo.The maximum capacity of the scraper conveyors should not be less than 400% of the bottom ash discharged from the boilers when burning design coal under the boiler rated load condition.Scraper conveyor components in contact with bottom ash shall be made of materials resistant to wear and corrosion.

2　The water channel of the scraper conveyor shall contain water deep enough to allow thorough granulation of bottom ash and a pressure larger than the maximum positive pressure in the boiler furnace.

3　The tilt angle of the head of scraper conveyors shall not be greater than 35°，and facilities for cleaning the chains shall be provided.

10.3.3　If dry-type air-cooled conveyors are used，the maximum capacity of the equipment should not be less than 250% of the bottom ash discharged from the boilers when operating design coal under BRL condition，and should not be less than 150% of the bottom ash discharged from the boilers when burning check coal under BRL condition.

10.3.4　Anti-wearing，low-velocity en-masse scraper conveyors special for power plants shall be used.Layout of en-masse scraper conveyors shall meet the following requirements:

1　En-masse conveyors may be in horizontal or tilted arrangement.When in tilted arrangement，the tilt angle should not be greater than 10°.

2　En-masse conveyors can be equipped with either horizontal or vertical driving devices depending on the specific conditions.When arranged at high level，a maintenance platform shall be provided.

3　En-masse conveyors should be arranged in a single line.

10.3.5　The bottom ash silo shall be arranged near the bottom ash discharge point.The capacity of the bottom ash silo shall be determined based on the amount of bottom ash discharged from the boilers and external conveying conditions.The effective capacity of the bottom ash silo should allow it to contain 24hours-48hours of bottom ash discharged from the system.When the bottom ash silo is only used as transfer or buffer bottom ash bin，its effective capacity should allow the silo to contain eight hours of bottom ash discharged from the system.