Introduction: 1. This series boiler is horizontal three-return fire tube and water tube mixed hot water boiler. There is a bundle of spiral gas tube in the boiler drum. And the furnace of the boiler has water wall tubes at the both side. 2. The fire grate is light weight and blocky. Equipped with Induced draft fan and forced draft fan to make good ventilation. 3. Fuel fell on grate was burned, the flame through the combustion chamber ,the economizer and was drew forth by induced draft fan and