What is the working principle of gas boiler?

The fuel used in boilers is mainly coal. Generally, large boilers and utility boilers often burn pulverized coal, so there should be a pulverizing system that grinds raw coal into pulverized coal. In the process of grinding coal, coal is dried at the same time, and hot air is usually used as the drying medium. The cold air is sent to the air preheater by the blower, where it absorbs the heat of the exhaust smoke and becomes hot air. Part of the hot air enters the coal mill after the pressure head is lifted by the powder exhauster, and leaves the coal mill with pulverized coal while heating and drying the coal. It can be seen that this part of hot air is not only used as a drying medium, but also plays a role in conveying pulverized coal, which is usually called primary air. In the direct blowing system as shown in the figure, after the gas-powder mixture comes out of the coal mill, it is directly sent to the burner through the pulverized coal pipeline, and the burner injects it into the furnace for combustion. It should be pointed out that in the pulverized coal pulverizing system of intermediate storage bin, the primary air carries pulverized coal into the pulverized coal separator, and the pulverized coal is separated from the airflow in the separator and stored in the pulverized coal bin. According to the load requirements, a proper amount of pulverized coal is supplied to the burner from the pulverized coal bin by the pulverized coal feeder. It can also be seen from the figure that another part of the hot air from the air preheater directly enters the furnace through the air distribution port of the burner to provide the air needed for pulverized coal combustion, which is called secondary air.

The combustion of pulverized coal in the furnace releases a lot of heat, and the flame center temperature reaches. The inside of the furnace is covered with a water wall composed of metal pipes, and the heat released by combustion is strongly absorbed by the heating surface of the water wall in the form of thermal radiation. However, due to the limitation of heat load and furnace volume, the smoke temperature at the furnace outlet is still as high as 30%. In order to make use of this high-temperature flue gas, the flue is also provided with superheater (in several stages), reheater, economizer, air preheater and other heating surfaces in turn. High temperature flue gas flows through these heating surfaces in turn, and releases heat to these heating surfaces through convection, radiation and other heat exchange methods. The temperature of flue gas discharged from air preheater is generally at. At this time, the flue gas can't be reused, so it is sent to the dust collector for separation, and most of the fly ash carried by the flue gas is removed, and then introduced into the chimney by the induced draft fan, and finally discharged into the atmosphere.