10.4　Dry Fly Ash Handling System

10.4.1　The fly ash handling system shall be either a vacuum conveying system，a positive pressure pneumatic system，an air slide，an en-masse scraper conveyor，a screw conveyor or a combination of the above，as justified through techno-economic comparison based on the amount and characteristics of fly ash，conveying distance，type of precipitator and layout of ash hoppers.

10.4.2　The design capacity of pneumatic fly ash handling system shall be determined according to the ash amount，type and operating mode of the system.For a system intended for continuous operation，its capacity shall not be less than 150% of the fly ash discharge of boilers when burning design coal under BRL condition and shall not be less than 120% of the ash discharge of boilers when burning check coal under BRL condition.For a system intended for intermittent operation，its output shall not be less than 200% of the ash discharge of boilers when burning design coal under BRL condition.The capacity of each ash hopper at the first electric field of electrostatic precipitator（ESP）should allow for ash collection of at least eight hours.

10.4.3　For a positive pressure pneumatic fly ash handling system，in case one or two compressors are in operation simultaneously，an additional one shall be set as standby，and if three or more are in operation simultaneously，two shall be set as standby.

10.4.4　The vacuum conveying fly ash handling system shall be furnished with dedicated vacuum evacuation equipment.Within one unit system，one additional piece of such equipment shall be set as standby if one or two are in frequent operation.

10.4.5　Air slides should be supplied with air by dedicated blowers with no standby.Air may also be provided by the FD fan of a boiler if possible.The arrangement of air slides shall comply with the following requirements:

1　The slope gradient shall not be less than 6%.

2　Damp-proof and thermal insulation measures should be considered.

3　Slide gates and motor-driven air lockers shall be installed between fly ash hoppers and air slides.

4　Flexible coupling should be adopted between fly ash discharge pipes and air slides and between blowers and air nozzles.

5　The conveying direction of the branch slides below the ESP should extend from the first electric field to the second（third）electric field.

10.4.6　The total capacity of fly ash silos should comply with the following requirements:

1　When used as transfer or buffer ash silo，the capacity should allow for storage of fly ash discharged from the system in eight hours.

2　When used as ash storage silo，the capacity should allow for storage of fly ash discharged from the system in 24hours-48hours.

10.4.7　If the fly ash silo is designed with a flat bottom，an aeration tank shall be furnished at the bottom.Aeration air shall be hot air.The aeration air system shall be furnished with dedicated air heaters，and pipes for conveying heated aeration air shall be thermally insulated.

10.4.8　The unloading facilities of the fly ash silo shall be provided according to the following requirements:

1　When hydraulic conveying is employed outside of the power plant，slurry preparation devices shall be provided.

2　When handling dry ash，truck or ship loading facilities that can prevent dry ash from escaping shall be provided.

3　When ash is wetted for transportation，water-ash agitating devices shall be provided and the water added should be 15%-30% of the fly ash weight.