Boiler basic structure
The overall structure of the boiler includes two parts: the boiler body and auxiliary equipment.

Boiler Body

The main components of the boiler, such as the hearth, drum, burner, water wall, superheater, economizer, air preheater, frame and furnace wall, constitute the core part of steam production, which is called the boiler body. The two most important parts in the boiler body are the furnace and the drum.

Hearth

Also known as the combustion chamber, it is the space for fuel combustion. The furnace where the solid fuel is put on the grate for fire-bed combustion is called the stratified furnace, also known as the fire-bed furnace; the furnace where the liquid, gas or solid fuel ground into powder is sprayed into the fire chamber for combustion is called the chamber furnace , Also known as the fire chamber furnace; the air lifts up the coal particles to make them burn in a boiling state, and the furnace suitable for burning inferior fuel is called a fluidized bed furnace;

the use of air flow to make the coal particles rotate at a high speed and burn strongly The cylindrical furnace is called a cyclone furnace. The cross section of the furnace is generally square or rectangular. The fuel burns in the furnace to form flames and high-temperature flue gas, so the furnace wall around the furnace is composed of high-temperature resistant materials and insulation materials. Water wall pipes are often laid on the inner surface of the furnace wall, which not only protects the furnace wall from burning, but also absorbs a large amount of radiant heat from flames and high-temperature flue gas. The structure, shape, volume and height of the furnace must ensure that the fuel is fully burned, and the temperature of the flue gas at the exit of the furnace should be lowered below the temperature at which the slag starts to condense.

When the temperature in the furnace exceeds the melting point of the ash, the ash is in a molten state. The molten ash particles will stick to the water wall tube or other components in the furnace. The bonded ash particles gradually increase, and slag blocks are formed, which is called slagging. Slagging will reduce the heat transfer effect of the heating surface of the boiler. In severe cases, the flue gas flow channel will be blocked, affecting the safe and economic operation of the boiler. Generally, the heat load of the furnace volume and the heat load of the furnace section or the heat load of the grate are used to express the intensity of combustion.

The furnace volume heat load is the heat released per unit time in the unit furnace volume. In boiler technology, the furnace volume heat load is often used to measure whether the furnace size is appropriate. If the volumetric heat load is too large, it means that the furnace volume is too small, and the fuel residence time in the furnace is too short, which cannot guarantee the complete combustion of the fuel and reduces the combustion efficiency; at the same time, it also means that the furnace wall area is too small and it is difficult to lay enough water walls.

As a result, the temperature of the smoke in the furnace and the exit of the furnace is too high, and slagging is prone to occur on the heating surface. The heat load of the furnace section of a chamber combustion furnace is the heat released by fuel combustion on a unit furnace cross section per unit time. After the furnace volume is determined, the excessive heat load of the furnace section will cause the wall temperature in the local area to be too high and cause slagging. The grate heat load of a stratified furnace is the ratio of the heat released by fuel combustion per unit time to the area of ​​the grate. Excessive heat load of the grate will greatly increase the fly ash.

Furnace design needs to fully consider the characteristics of the fuel used. Each boiler should try to burn the fuel originally designed. When fuels with relatively different characteristics are used, the economy and reliability of boiler operation may be reduced.