8.9　Circulating Fluidized Bed（CFB）Boilers

8.9.1　The ignition and combustion supporting oil system shall comply with the following requirements:

1　Light oil should be used for ignition and combustion supporting purpose,and combustible gas may be adopted instead.

2　The boiler ignition and combustion supporting mode and system output should be determined according to the type of boiler fuel,type of burner and requirements of boiler manufacturer.

8.9.2　The coal feeding system shall comply with the following requirements:

1　For CFB boilers with external beds and double air distribution plates type in form of trouser legs,four lines of coal feeding system should be provided,each having a capacity sufficient to supply design coal flow consumed by the boilers operating at 50%of the BMCR.

2　For other types of CFB boilers,when no more than four lines of coal feeding system are provided,the design output of the lines of coal feeding system in front of the boilers should be such that,when one line fails,the remaining lines shall be able to supply design coal flow consumed by the boilers operating at the BMCR；when more than four lines of coal feeding system are provided,the design output of the lines in front of the boilers should be such that,in the event that two lines fail,the remaining lines shall be able to supply design coal flow consumed by the boilers operating at the BMCR.

8.9.3　The storage and conveying system of pulverized limestone shall meet the following requirement:

1　One-stage pulverized limestone conveying system should be adopted.

2　The pulverized limestone silo for one-stage conveying system should have a capacity sufficient to accommodate the consumption by boilers operating at MCR for 20-24 hours；the pulverized limestone bin for two-stage conveying system should have a capacity sufficient to accommodate the consumption by boilers operating at MCR for 2-4 hours.

3　The pulverized limestone fed to boiler furnaces should be conveyed pneumatically,with the various conveying pipes being arranged symmetrically.

4　If pulverized limestone is conveyed with two-stage fan conveying system,2×100%constantcapacity conveying fans should be provided.

5　Pulverized limestone silo and bin should be provided with anti-corrosion and anti-dust measures.The included angle between the inclined wall of discharge port and the horizontal plane should not be less than 60°.The necessity for providing gasifying air system and anti-freezing measures shall be determined according to the local meteorological conditions and system arrangement.

8.9.4　Flue gas and air system shall comply with the following requirements:

1　The types,number,air flow,and pressure heads of primary air fans shall comply with the following requirements:

1）Primary air fans should be of speed-adjustable centrifugal type.

2）Each boiler should be provided with 2×50%capacity primary air fans.

3）The basic air flow of primary air fans shall be determined to be the sum of the air flow required by the boiler when operating on design coal under the BMCR condition,the net leakage at primary air side of air preheater after one-year operation as guaranteed by the manufacturer.The basic pressure head of primary air fans shall be the sum of resistance from the fan inlet to primary air nozzle outlet and the resistance of boiler furnace when the boiler operates on design coal under the BMCR condition.

4）The primary air fan should be selected with an air flow margin of no less than 20%plus a temperature margin（which can be determined based on"outdoor air temperature used for ventilation calculation during summer"）；the pressure head shall be equal to the basic pressure head plus a pressure head margin.The margins for pressure head should be determined by sections.In particular,the margin for furnace resistance shall be provided by the boiler manufacturer；margin for resistance from the air pre-heater inlet to the primary air nozzle outlet should be 44%；for boiler system with double air distributors in form of trouser legs,margin should not be added for the resistance of the regulating damper after the air pre-heater and before primary air box；margin for 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 basic air flow.

2　The types,number,air flows,and pressure heads of secondary air fans shall comply with the following requirements:

1）Secondary air fans should be of speed-adjustable centrifugal type.

2）Each boiler should be provided with 2×50%secondary air fans.

3）The basic air flow of secondary air fans shall be determined to be the sum of the air flow required by the boiler when operating on design coal under the BMCR condition,the net leakage at secondary air side of air preheater after operation for one year as guaranteed by the manufacturer.The basic pressure head of secondary air fans shall be the sum of resistance from the fan inlet to secondary air nozzle outlet and the resistance of boiler furnace when the boiler operates on design coal under the BMCR condition.

4）The secondary air fan should be selected with an air flow margin of no less than 20%plus a temperature margin（which can be determined based on"outdoor air temperature used for ventilation calculation during summer"）；the pressure head shall be equal to the basic pressure head plus a pressure head margin.The margins for pressure head should be determined by section.In particular,the margin for furnace resistance shall be provided by the boiler manufacturer；margin for resistance from the air pre-heater inlet to the secondary air nozzle outlet should be 44%；margin for 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 basic air flow.

3　The types,number,air flows and pressure heads of high-pressure fluidizing fans shall comply with the following requirements:

1）High-pressure fluidizing fan may be of centrifugal type or Roots fan.

2）The number of high-pressure fluidizing fans should be determined through techno-economic analysis and one additional fan with the same capacity should be provided for standby.

3）The basic air flow of high-pressure fluidizing fans shall be calculated based on the fluidizing air flow required by the boilers when operating on design coal under the BMCR condition.Both the air flow margin and head margin should not be less than 20%.

8.9.5　The bed material feeding system shall comply with the following requirements:

1　When burning fuel characterized by low ash content or high abrasiveness,stationary mechanical bed material feeding system should be adopted.

2　When burning fuel which allows self-balance of bed materials during boiler operation,one temporary bed material conveying system operating intermittently may be provided.

3　Other types of bed material conveying system may be adopted depending upon the characteristics of bed material and the requirements on boiler fuel feeding.

8.9.6　The bottom ash cooler of boilers shall comply with the following requirements:

1　When the converted ash content of burned fuel is excessive,or the ash formation characteristics is poor and the conditions for arrangement permit,roller type bottom ash cooler should be adopted,or,if the conditions are favorable,air-water bottom ash cooler may be adopted instead.

2　The total design output of bottom ash cooler of boilers should not be less than 150%the bottom ash discharge amount when the boilers operate on design coal at BMCR condition,and should not be less than 120%the bottom ash discharge amount when the boilers operate on check coal at BMCR condition.

3　Under normal conditions,the bottom ash discharging temperature shall be lower than 150℃.When one bottom ash cooler is stopped for a short time for repair or if it fails,the bottom ash discharging temperature of the remaining bottom ash coolers shall be lower than 200℃.