9.3　Flue Gas and Air System

9.3.1　The types，number，flow，and pressure of FD fans of pulverized coal fired boilers shall be determined in accordance with the following requirements:

1　FD fans should be high-efficiency centrifugal fans.Speed-regulating fans should be used if justified through techno-economic comparison.

2　For boilers rated 130t/h and below，each boiler shall be provided with one FD fan.For boilers rated 220t/h and above，each boiler should be provided with one or two FD fans and no standby fan is required.

3　The flow and pressure of FD fans shall be determined in accordance with the following requirements:

1）The base flow of the FD fan is calculated assuming that the boiler operates on design coal type，and shall include the flow required when boiler operates under the boiler rated load condition and the net air leakage at the air inlet side of air preheater after one-year operation as guaranteed by the manufacturer.

2）If trisector air preheaters are used，the FD fans should be selected with a flow margin of not less than 5% plus a temperature margin，which can be determined based on the"outdoor air temperature used for ventilation calculation during summer"，as well as a pressure margins of not less than 15%.

3）If bisector or tubular air preheaters are used，the FD fans should be selected with a flow margin of 10% and a pressure margin of 20%.

4）When a hot air recirculating system is employed，the flow margin of FD fans shall not be less than the hot air recirculating flow under operating conditions in winter.

4　For the boilers burning low calorific value or low volatile coals，if each boiler is equipped with two FD fans，the selected fan margins shall be checked such that the boiler minimum stable load without oil supporting can be reached when only one FD fan is put into service.

9.3.2　The types，number，flow，and pressure of ID fans shall be determined in accordance with the following requirements:

1　ID fans should be high-efficiency centrifugal fans.Speed-regulating fans should be used if justified through techno-economic comparison.

2　For boilers rated 65t/h and below，each boiler shall be provided with one ID fan.For boilers rated 130t/h and above，each boiler should be provided with one or two ID fans and no standby fan is required.

3　The flow and pressure of ID fans shall be determined in accordance with the following requirements:

1）The base flow of ID fan should be determined to be the sum of the flow of flue gas produced when the boiler operates on design coal under the boiler rated load condition，the leakage at flue gas side of air preheater after one-year operation as guaranteed by the manufacturer，and the leakage of the boiler flue gas system.

2）The flow margin shall not be less than 10% and the temperature margin shall be 10℃-15℃.

3）The pressure margin shall not be less than 20%.

4　For boilers burning low calorific value or low volatile coal，if each boiler is equipped with two ID fans，it shall be checked that the boiler minimum stable load without oil supporting can be reached when only a single ID fan is put into service.

9.3.3　The primary/secondary air fans of CFB boilers should be high-efficiency centrifugal fans.Speedregulating fans should be used if justified through techno-economic comparison.For boiler rated 220t/h and below，each boiler shall be provided with one primary/secondary air fan.For boilers rated 410t/h，each boiler shall be provided with one or two primary/secondary air fans and no standby fan is required.The air flow and pressure of primary/secondary air fans shall be determined in accordance with the following requirements:

1　The base flow is calculated assuming that the boiler operates on design coal type，and shall include the flow required when boiler operates under the boiler rated load condition and the net air leakage at primary air side of the air preheater（secondary air side of secondary air fan）after one-year operation as guaranteed by the manufacturer.

2　The fan should be selected with a flow margin of 20% plus a temperature margin which can be determined based on"outdoor air temperature used for ventilation calculation during summers".

3　The margins for the pressure of the fan should be determined by sections.In particular，the margin corresponding to the furnace back pressure（resistance resulting from the bed layer etc.）shall be provided by the boiler manufacturer；margin corresponding to the resistance from the air preheater inlet to the primary/secondary air nozzle outlet shall be 44%；margin corresponding to the resistance from fan inlet to air preheater inlet should be equal to the square of the ratio of air flow used for fan type selection to base flow.

9.3.4　If CFB boilers need to be provided with high-pressure fluidizing fans，centrifugal or Roots blowers should be used.For boilers rated 220 t/h and below，each boiler should be provided with two 50% capacity fans.For boilers rated 410 t/h，each boiler should be provided with three 50% capacity fans.The margins for flow and pressure of fans shall not be less than 20%.

9.3.5　If the monitoring and protection system of boilers needs to be provided with cooling fans，each boiler should be provided with two centrifugal fans，one in operation and the other for standby.The flow and pressure margins of fans shall accommodate the requirements for cooling of the monitoring and protection system.

9.3.6　The type of precipitator shall be determined through techno-economic comparison taking into account the requirements on the flow and concentration of dust emission set forth in the environmental impact assessment report，coal ash characteristics，boiler combustion mode，process，site conditions，and the requirements on comprehensive utilization of ash.The selected precipitator shall be able to achieve the guaranteed efficiency under either of the conditions below:

1　The flue gas flow of precipitator is the flow of flue gas leaving air preheater when boiler operates on design coal under BRL condition，plus a margin of 10%；the flue gas temperature is the temperature of flue gas leaving air preheater when boiler operates on design coal under BRL condition，plus a margin of 10℃-15℃.

2　The flue gas flow of precipitator is the flow of flue gas leaving air preheater when boiler operates on check coal under BRL condition；and the flue gas temperature is the temperature of flue gas leaving air preheater when boiler operates on check coal under BRL condition.

9.3.7　Sampling holes and platforms shall be provided on the flue before and after precipitator.

9.3.8　The number，type，height of chimneys and velocity of flue gas leaving the chimneys shall be determined according to the environmental impact assessment results and anti-corrosion requirements of the chimneys，while taking into consideration the number of boilers installed synchronously，arrangement of chimneys and their economic rationality of structure.The number of boilers sharing the same chimney should be two to four.