What is the difference between CFB boiler and pulverized coal boiler in combustion system?

Pulverized coal boiler grinds coal into fine pulverized coal with particle size of about 1 ~ 300μ m through pulverizing system, and then it is injected into the furnace together with hot primary air through burner to deliver powder. Pulverized coal and combustion-supporting hot air are strongly mixed and suspended in the furnace, and the fuel combustion process is completed in a few seconds. About 90% of the ash produced after combustion passes through the heating surfaces at all levels of the boiler together with the flue gas in the form of fine ash and leaves the furnace body after heat exchange. After the flue gas is removed by electrostatic precipitator, it is discharged into the atmosphere from the chimney by induced draft fan. The representative equipment of pulverized coal boiler combustion system includes blower, induced draft fan, pulverizing system (coal feeder, coal mill, powder exhauster and coarse and fine powder separator), burner, etc.

CFB boiler cancels pulverized coal boiler pulverizing system. Coal is directly finely divided into coal particles with a particle size of 0 ~ 8 mm, and then sent to the hearth bed (dense phase area) through the coal feeder belt. The hot primary air entering from under the bed makes the bed material and coal particles fully fluidized, and the coal particles collide with the bed material for heat exchange, which is quickly ignited and ignited. Large particles burn in the bed; Fine particles flow with the flue gas to the upper part of the furnace (dilute phase area) to continue combustion and heat transfer. Some fine particles gather into large particle clusters, which move downward near the furnace wall because they can't overcome the action of gravity, while the relatively thin gas-solid phase in the center of the furnace continues to move upward, forming a strong particle circulation in the furnace; After the relatively diluted gas-solid phase leaves the furnace with a large number of unburned particles, it enters the cyclone separator to separate most of the material particles entrained in the flue gas, and then it is sent back to the furnace bed through the J valve feeding device to continue combustion and utilization, forming an external circulation of large materials. After that, the flue gas also leaves the furnace body after heat exchange by heating surfaces at all levels of the boiler, is removed by electrostatic precipitator, and is discharged into the atmosphere from the chimney through induced draft fan. The representative equipment of CFB boiler combustion system includes blower, induced draft fan, J valve blower, coal feeder, cyclone separator, J valve return device, slag cooler and ignition air duct under the bed.