When the boiler is running, three processes are carried out at the same time, namely, the combustion process of fuel, the heat transfer process from flame and flue gas to boiler water, and the heating, vaporization and overheating process of water.

Second, the combustion process of fuel

The combustion process of fuel refers to the process that the fuel reacts with oxygen in the air at a certain temperature in the furnace to release heat. Whether the combustion process is perfect is one of the fundamental conditions for the normal operation of the boiler. To ensure good combustion, it is necessary to have a high temperature environment, to meet the requirements of proper air and good air-fuel mixing, and to allow enough time and space for fuel in the combustion process. In order to make the boiler combustion stable and continuous, fuel, air, flue gas and ash should be continuously supplied.

Thirdly, the heat transfer process from flame and flue gas to boiler water.

The process of transferring the heat released after fuel combustion to boiler water through the water wall heating surface arranged in the furnace and the convection heating surface arranged in the flue.

The heat transfer process is mainly carried out in the furnace by radiation. In the convection flue, due to the gradual decrease of flue gas temperature, the heat release of flue gas to the heating surface is mainly carried out by convection; In the metal inside the heating surface, heat is mainly transferred from the high temperature side to the low temperature side (water side) by conduction, and then absorbed by the flow and circulation of boiler water.

Whether the conversion process can be carried out smoothly directly affects the safety and economy of boiler operation. When there is dust accumulation on the flue gas side of the heating surface or scaling on the water side of the heating surface, the metal wall temperature of the heating surface will rise and be overheated, which will reduce the thermal efficiency of the boiler and waste fuel.

Four, water heating, gasification and overheating process

For hot water boiler, it refers to the process that boiler water absorbs heat from the metal on the heating surface, raises the water temperature to the required level, and outputs it from the boiler outlet. For a steam boiler, it is a process that boiler water absorbs heat from the metal on the heating surface and becomes saturated water, and then becomes a mixture of steam and water. Steam and water are separated in the boiler and output as clean steam from the boiler outlet. Therefore, for steam boilers, a steam-water separation device should be installed at the steam outlet in the drum. For boilers with superheaters, it also includes the process that saturated steam is heated to the overheating temperature in the superheater.