10.2　Hydraulic Ash Handling System

10.2.1　If a hydraulic ash handling system is employed，water reclaimed from the power plant shall be used，and the slurry preparation mode and ash-water concentration shall be determined appropriately through techno-economic comparison.

10.2.2　Hydraulic ash conveying in the power plant can be through pressurized pipes or trenches，depending on the types of the bottom ash removal equipment and precipitator，layout of the boiler house and the plant area as well as the location of the ash yard.

10.2.3　If a hydraulic ash handling system equipped with centrifugal ash pumps is employed，the pumps should be directly connected in series if the head of a single-stage pump cannot meet the requirements.

10.2.4　If positive displacement ash pumps are used，the ash slurry shall be conveyed at a high concentration.

10.2.5　If concentrators are used to concentrate ash slurry，they shall be selected according to the following requirements:

1　The diameter of the concentrator shall be determined according to the ash discharged and unit output of the concentrator.

2　Concentrators should be above the ground level.

3　The slurry discharge pipes of concentrators shall be fitted with backwash pipes with reliable flushing water supply，the water pressure shall not be lower than 0.4 MPa.

10.2.6　The quantity of spare concentrators shall meet the following requirements:

1　When the plant-wide ash handling system is provided with spares or emergency ash removal provisions，no spare concentrator is required.

2　When the plant-wide ash handling system is not provided with spares or emergency ash removal provisions，at least two concentrators should be equipped；when either one is out of work，the total capacity of the rest concentrators shall not be less than 80% of the calculated ash amount of the ash handling system.

10.2.7　The ash slurry trenches of the ash handling system shall be designed according to the following requirements:

1　Ash slurry trenches require no spares and shall be short and straight.For convenience of connections during extension construction，the bottom of the trenches shall be built with anti-wearing panels such as cast stones.

2　Drainage and sewage discharged from other systems in the power plant should not be drained into ash slurry trenches.

3　The slope gradient of ash slurry trenches shall comply with the following requirements:

1）The slope of fly ash slurry trench should not be less than 1%.

2）The slope of solid bottom ash slurry trench should not be less than 1.5%.

3）The slope of liquid bottom ash slurry trench should not be less than 2%.

4）The slope gradient of trenches used to deliver high-concentration ash slurry should be appropriately increased.

10.2.8　In a hydraulic ash handling system，the quantity of spares for major equipment shall comply with the following requirements:

1　Each（group of）clean water pump（pumps）operated frequently shall be provided with one（group of）spare pump（pumps）.

2　In a pump house，the quantity of spares for centrifugal ash slurry pumps and positive displacement type ash slurry pumps shall be determined as follows:

1）When one（group of）pump（s）is（are）in operation，one（group of）spare pump（s）shall be provided.

2）When two to three（groups of）pumps are in operation，two（groups of）spare pumps shall be provided.

3）For positive displacement type ash slurry pumps，if only two（groups of）spare pumps are provided，the foundation for the second（second group of）spare pump（s）may be reserved.

10.2.9　If a bottom ash settling pond is used in a bottom ash handling system，it shall be sized based on factors such as the amount of bottom ash slurry，sizes of bottom ash particles，settling velocity and external conveying conditions.The settling pond should consist of two compartments each having an effective capacity sufficient to contain at least 24 hours of bottom ash discharge of the system.If a dewatering bin is used in a bottom ash handling system，its capacity shall be determined based on factors such as the amount of bottom ash discharged from the boiler and external conveying conditions.The effective capacity of each dewatering bin should allow it to contain at least 24 hours of bottom ash discharge of the system.

10.2.10　When one to three hydraulic ash slurry pipes are in operation，one spare pipe shall be provided.Measures shall be taken when the pipes suffer from severe wearing and scaling.

10.2.11　When common steel pipes are used as ash slurry pipes，the wall thickness shall meet the strength requirements.In addition，the pipes shall also meet the following requirements:

1　The wall thickness of fly ash slurry pipes shall not be less than 7mm.

2　The wall thickness of bottom ash slurry pipes shall not be less than 10mm.

3　Bends and fittings can be wear resistant.

4　If the ash is highly abrasive，wear-resistant materials may also be used for the straight pipe sections if justified through techno-economic comparison.