The air equipment using waste heat of boiler to heat the equipment for combustion is known as the air preheater. 

The application of air preheater can reduce the exhaust fume temperature, so as to improve the efficiency of the boiler. The air preheaters for circulating fluidized bed boiler are three kinds. Most of the circulating fluidized bed boiler uses tubular air preheaters, which are divided into vertical pipe and horizontal pipe air preheater. Less amount of circulating fluidized bed boiler uses hot pipe air preheater, the advantages of which is less air leakage coefficient. The third kind is the rotary air preheater, the advantages of which is relatively smaller volume, it is suitable for circulating fluidized bed boiler with large capacity Such as the introduced 300 mw circulating fluidized bed boiler for Baima Power Plant. Due to higher air pressure of circulating fluidized bed boiler, in order to avoid too large air leakage coefficient, separate parts and sealing mode are adopted for the rotary air preheater of the CFB. For an example, the tubular air preheater of a certain power plant is arrangement as follows: The upper level is secondary air preheater, the lower level is primary air preheater; the preheater tube is Φ 40 mmx1. 5 mm. The flue gas in pipe flows from top to bottom, and the air outside laterally erodes. After the secondary air passes two strokes, it enters to the secondary air duct, enters three strokes once and enters to the primary air duct. In order to facilitate replacement and repair, two groups are arranged, the upper group includes two strokes, and the lower group includes one stroke.