11　Flue Gas Desulfurization System

11.0.1　The flue gas desulfurization（FGD）process shall be selected through techno-economic comparison by comprehensively taking into account such factors as boiler capacity and type，sulfur content in coal，requirements for desulfurization efficiency approved in the environmental impact assessment report，availability and transportation conditions of desulfurizer，water supply conditions，wastewater and bottom ash discharge conditions，recycling conditions of FGD by-products as well as maturity level of FGD process.For expanded or modified power plants，the layout of the plant site shall also be considered.The FGD process shall also be selected in accordance with the following requirements:

1　For CFB boilers with a medium or small capacity，in-boiler desulfurization should be given priority.

2　For units burning coal with a sulfur content not less than 2%，the limestone-gypsum wet FGD process shall be given priority.

3　For units burning coal with a sulfur content less than 2%，or units with a remaining service life less than 10years，or when an FGD system is to be installed in an existing power plant with restricted site conditions，semi-dry or dry FGD process or other proven and less costly FGD process should be employed provided that environmental protection requirements are satisfied.

4　Ammonia scrubbing FGD process may be used if justified through techno-economic comparison.

5　For coastal power plants burning coal with a sulfur content not more than 1%，seawater FGD process may be employed on condition that the alkalinity of seawater meets the process requirements and the assessment on the impact on the sea areas has passed the review of the state authorities.For coastal power plants burning coal with the sulfur content exceeding 1%，seawater FGD process can also be employed if justified through techno-economic comparison and the above conditions are met.

6　For thermal power plants located in regions where water is in extremely short supply，dry and semidry FGD processes that consume less water should be employed.

7　The availability of the FGD plant shall be higher than 95%.

11.0.2　The desulfurization absorbent shall meet the following requirements:

1　A reliable supply source of absorbent shall be available，and ready-to-use absorbent meeting the relevant requirements should be commercially available.When the condition permits，an absorbent preparation workshop may be built in the power plant if justified reasonable.If an absorbent preparation plant has to be built，priority shall be given to cooperation with other power plants in this region and a comprehensive techno-economic justification is required taking into account the investment and management mode，processes，plant site，transportation conditions and other factors.

2　The absorbent storage volume in the power plant shall be determined according to the supply continuity，distance of supply source from the power plant，transportation conditions and other factors，and should accommodate at least three days'absorbent consumption.

3　Measures against re-entrainment of dust and volatilization and leakage shall be taken for the absorbent preparation，storage and handling system to ensure safety.

4　For CFB boilers，the storage and conveying system of pulverized limestone used for desulfurization shall meet the following requirements:

1）After being transported to the power plant，finished product limestone powder may be conveyed pneumatically into the pulverized limestone silo for storage.Limestone pulverized in the power plant should also be conveyed pneumatically，and if the condition permits，enclosed scraper conveyer or spiral conveyer may be used and should be arranged in a single line.

2）Single-stage or two-stage pulverized limestone conveying system may be employed.

3）The pulverized limestone silo for one-stage conveying system should have a capacity sufficient to accommodate 24 hours of the consumption by boiler operating under BRL condition；and the pulverized limestone silo for two-stage conveying system should have a capacity sufficient to accommodate 3hours-4hours of the consumption by boiler operating under BRL condition.

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

5）If pneumatic conveying is used，the output design of the system shall be determined according to the boiler consumption of pulverized limestone and operating mode.The design output of the conveying system shall not be less than 150% of consumption of limestone powder in continuous operation mode，and shall not be less than 200% of consumption of limestone powder in intermittent operation mode.

6）If pulverized limestone is conveyed through two-stage conveying system using fans，one or two constant-capacity conveying fans should be provided.

11.0.3　The quantity and capacity of the FGD plant shall meet the following requirements:

1　The rated capacity of the FGD plant should be determined according to the amount of flue gas produced by the boiler burning design coal or check coal under BRL conditions，whichever is the greater.No margin shall be provided.

2　Sulfur dioxide concentration at the inlet of FGD plant（both design value and check value）shall be determined through investigation，and in consideration of the purchase conditions of coal and variation trend of sulfur content，shall be taken as a larger value within the variation range.

3　The FGD plant shall be able to operate safely and continuously under any load ranging from the boiler minimum load rating（BMLR）to BRL.The change rate of load of the FGD plant shall be commensurate with that of the boiler.

4　The design temperature of flue gas at the inlet of the FGD plant shall be the temperature of flue gas flowing from the main flue duct to the inlet of the FGD plant when the boiler operates on design coal under BRL conditions plus 10℃（50℃during a short time）.Proper measures shall be taken when boiler operates under abnormal conditions so as to protect equipment from being damaged.

5　The quantity of FGD plant shall be determined based on the capacity of the boiler，and the capacity and reliability of the FGD plant.When a wet FGD process is employed，two boilers should be provided with one FGD scrubber；when a semi-dry FGD process is employed，one FGD scrubber may serve one boiler，or two boilers if the process condition permits.

6　Reliable anti-corrosion measures shall be taken inside the FGD plant according to the features of the FGD process.

11.0.4　If the FGD system is equipped with a booster fan，the capacity of the booster fan shall be determined according to the flue gas treatment amount，with a flow rate margin not less than 10%，a temperature margin not less than 10℃-15℃，and a pressure margin not less than 20%.When the FGD booster fan and ID fan are combined，the selection of the furnace transient explosion proof pressure shall take a larger pressure of the fan into consideration.

11.0.5　When a wet FGD process is employed，the necessity for installing a gas-gas heater（GGH）shall be determined according to approval comments on the environmental impact assessment reports of the project.

11.0.6　The necessity for providing a bypass flue duct for the FGD plant should be determined according to the technical features of the FGD process and reliability of the FGD plant.If the condition permits，bypass flue duct may be eliminated.If no bypass flue duct is provided，the availability of the FGD plant shall accommodate the requirements for the operation of the units.If a bypass flue duct is provided，the dampers（or gates）equipped at inlet and outlet of the FGD plant and at the bypass shall be airtight and have good operational performance.The opening time of the bypass damper（or slide plate gate）shall be designed such that failure of the FGD plant will not result in tripping of the boiler.

11.0.7　The flue duct from the outlet of the FGD plant to the chimney shall be subject to anti-corrosion treatment suitable for the FGD process because of the low temperature.

11.0.8　The FGD process shall be designed to facilitate recycling of FGD by-products.If justified reasonable through techno-economic comparison，FGD by-products may be appropriately processed before being transported outside，the processing depth，type and quantity of which shall be determined based on reliable market surveys.If the conditions for recycling the by-products are temporarily unavailable，they may be transported to a storage yard and should be stored separately from the ash for possible recycling in the future.In addition，measures shall be taken to avoid secondary pollution caused by the by-products.In the power plant，the by-products may be stored in the storage room depending on their properties.The capacity of the storage room shall be determined according to the transportation mode and should be sufficient to accommodate at least 24 hours of by-products produced.

11.0.9　If the absorbent and by-products are in the form of slurry，the conveying system shall be provided with anti-clogging measures and pipe cleaning facilities.

11.0.10　The arrangement and control level of the FGD control room shall comply with the following requirements:

1　The FGD control room should be combined with the ash handling air compressor room and dedusting switchgear room and arranged close to the FGD plant，or may be arranged independently according to the process flow and site conditions.

2　The control level of the FGD system shall be commensurate with that of the unit.

11.0.11　The voltage level and neutral grounding mode of the HV and LV auxiliary electrical systems of the FGD plant shall be the same as that of the main works of the power plant.The HV loads of the FGD plant are powered directly by the HV segment in the main power building.An LV transformer is provided in the FGD area to supply power to the LV loads of the FGD plant，with the HV power supply connected from the HV segment in the main power building.

11.0.12　The FGD system shall be arranged in accordance with the following requirements:

1　The FGD plant should be arranged near the flue duct at rear of boiler and chimney.

2　Absorbent preparation and by-product processing area should be arranged centrally near the FGD plant or at other suitable locations.

3　The FGD plant should be arranged outdoors and shall be provided with necessary protective measures.