二、 Classified by structure

1. Fire tube boiler:flue gas flows through the fire tube, generally small capacity, low parameter boiler, low thermal efficiency, but simple structure, low water quality requirements, convenient operation and maintenance; 2. water tube boiler:steam water flows through the tube, can It can be made into a small-capacity, low-parameter boiler, and can also be made into a large-capacity, high-parameter boiler. Power station boilers are generally water tube boilers with high thermal efficiency, but also have high requirements on water quality and operating level.