Pneumatic conveying of calcium desulfurization and limestone powder in power plants
? ? ?China strictly controls the SOz emission standards in the atmosphere of power plants. Power plants with high sulfur content in coal require the use of desulfurization technology. There are currently two commonly used desulfurization methods: one is to use a circulating fluidized bed boiler, in which limestone powder is mixed and burned inside the boiler; The second is to set up a separate flue gas desulfurization system behind the flue. The transportation of limestone powder in the former adoptspneumatic conveyingMethod: Limestone powder contains calcium carbonate and calcium oxide. Physical properties of limestone powder: bulk density of 1.2~1.5vm, resting angle of 30 °~35 °, moisture content (mass fraction)
? ? The system includes two 300m limestone powder warehouses, which are pneumatic transported by bulk wheat tankers to the warehouses, and then pneumatic transported to a 40m limestone powder transfer warehouse. The system uses dense phase pneumatic conveying, with a system output of 15t/h. Each set of furnace front limestone powder feeding system has an output of 2-9.6/h. The system is equipped with two sets of furnace front limestone powder conveying systems, each set including a screw feeder, bin pump, powder feeding fan, electric butterfly valve, conveying pipeline, expansion joint, etc. Main parameters: coal consumption of 62t/h, designed Ca/S molar ratio of 2.5, designed desulfurization rate ≥ 95%, limestone powder consumption of 9.6/h, SOz mass emission of ≤ 760/a, limestone powder conveying capacity of 42/h, limestone powder conveying airflow of 3200m/h under standard conditions, and 8 nozzles. Two circulating fluidized bed boilers (2x310v h) are installed in the Shanghai Petrochemical Thermal Power Plant, which uses a pneumatic conveying system for limestone powder granules. The system has an output of 30t/h, 2 downward fluidized bed pumps of 5 ㎡, 2 conveying pipes, a horizontal conveying distance of 210m, a lifting height of 38m, 8 90 ° elbows, and a conveying pipe diameter of $168x9 seamless steel pipe.
The pneumatic conveying of limestone powder granules should pay attention to the following points:
? 1) Due to the higher density of limestone powder compared to fly ash, based on usage experience, it is recommended to use a down draft fluidized bed pump or jet pump. 2) Limestone powder granules have the characteristic of being easily affected by moisture in a cold state. When designing, attention should be paid to moisture-proof measures. The storage hopper should be insulated, and hot air should be introduced at the bottom of the powder warehouse to prevent moisture and clumping.
? 3) Limestone powder granules have a high degree of dispersion in particle distribution, with large particle sizes of about 2mm and small particle sizes below 50um. The suspension velocity gradient is large, which makes it difficult to select the appropriate air velocity for the conveying pipeline and even causes pipeline blockage.
? 4) The air purification requirements are high. It is recommended to use a screw air compressor, equipped with a refrigerated dryer and air filter, to improve the quality of the transported air.
? 5) Full consideration should be given to limestone powder granulespneumatic conveyingThe difficulty of designing conveying speed, mixing concentration ratio, gas consumption and output must be left with margin or appropriately increased.