The air preheater is a boiler auxiliary equipment that uses the heat of the flue gas to increase the air temperature and reduce the exhaust gas temperature. After the preheated air is fed into the furnace, the process of drying, ignition and combustion of the fuel is accelerated. At the same time, it strengthens radiation heat exchange, maintains stable combustion, and reduces chemical incomplete combustion losses. For burning inferior fuels with high moisture, ash and low volatile content, the setting of air preheater is more necessary.
There are two main types of air preheaters: tubular and rotary.
Tubular air preheaters are welded from steel pipes and thicker tube sheets at both ends. Sometimes there are intermediate tube sheets between the tube sheets to separate the airflow into several processes. Some steel frames are sometimes welded on the outside to enhance its rigidity. The tubes are staggered. Expansion joints should be installed between the tube sheet and the outer shell, and between the outer shell and the steel frame of the boiler, in order to prevent air leakage between the tubes, the outer shell and the steel frame of the air preheater due to different expansions. The flue gas flow rate of the air preheater can not be too high or too low, too high wear too fast, too low easy to block ash. The flue gas velocity is generally 10-14m/s, and the air velocity is 45% of the flue gas velocity.