The circulating fluidized bed boiler includes five major systems: combustion system, material circulation system, coal preparation system, air and smoke system, and slag and ash removal system. The structure of the circulating fluidized bed boiler is as follows:
The boiler is mainly composed of the following three parts: furnace; solid circulation loop (mainly composed of Cyclone Separator, feeder and external fluidized bed); tail shaft.
The heart of the circulating fluidized bed boiler is the furnace, where fuel and limestone for desulfurization are fed. The primary air enters the furnace through the air distribution plate and serves as the primary combustion air. At the same time, the upward air current holds up (fluidized) the solid particles and fills the entire furnace volume. The secondary air is fed into the furnace in two stages, thereby realizing staged combustion. The high-efficiency cyclone separator captures the solid particles leaving the furnace, and distributes the flow of solid particles through the water-cooled cone valve. One part is directly sent into the lower furnace through the feeder to maintain the balance of the solid particles in the main circulation loop; The separated solid particles are sent into the furnace after releasing heat through an external heat exchanger arranged in a bubble-like bed. After separation, the clean flue gas containing a small amount of fly ash enters the tail shaft, passes through the air preheater and the fly ash collection system, and is finally discharged into the atmosphere through the chimney.
Boiler steam water system: The high-pressure system includes economizer, drum, evaporating heating surface and superheater. The water circulation system adopts natural circulation. The boiler feed water is first led to the economizer inlet header arranged in the tail flue, flows upward through the horizontally arranged economizer tube group, and then enters the Boiler Drum through the economizer outlet pipe. When there is no feed water flowing into the drum during the start-up phase, the economizer recirculation pipeline can lead the boiler water from the drum to the economizer inlet header to prevent the water in the economizer tube from vaporizing statically.
Circulating fluidized bed air and smoke system: The combustion of the boiler requires a relatively high air pressure head so that the particles can be fluidized in the bed, and the primary air from the primary and secondary fans is sent into the furnace after passing through the air preheater. Other air uses include fluidized air for external heat exchangers, feeders, and slag coolers. The fluidized air is all taken from high-pressure fluidized fans. The air preheater adopts a mature quarter-bin rotary air preheater.
Slag and ash removal system: During the normal operation of the boiler, a large number of solid particles circulate continuously in the main circulation loop composed of the furnace and the separator. A part of the very fine particles arrive at the tail flue along with the flue gas and enter the dust collector as fly ash; while most of the remaining particles are captured by the separator and returned to the furnace through the feeder or external heat exchanger. The slag discharged at the bottom of the furnace is cooled by a slag cooler and discharged.
In addition, the circulating fluidized bed boiler also includes an auxiliary fuel system and a coal preparation system.
