Fuel and smoke system

　　Fuel and smoke system4wrBoiler Burner

　　The main fuel used in China's boilers is coal.Generally large boilers and power station boilers often use pulverized coal, so it is necessary to have a pulverized coal grinding system.As shown in the figure, the coal falling through the original bunker is sent by the coal feeder to the coal mill for grinding.The coal is dried at the same time during the coal grinding process. The drying medium is usually hot air.The cold air is fed into the air preheater by the blower, where it absorbs the heat from the exhaust and becomes hot air.Part of the hot air through the pulverizer after the high pressure head into the coal mill, in the coal heating and drying at the same time with the pulverized coal away from the mill, it can be seen that this part of the hot air as a drying medium, but also play a role in conveying pulverized coal, usually called this part of the hot air primary wind.In the direct blowing system shown in the figure, the mixture of air and powder comes out of the coal mill and is fed directly into the burner through the pulverized coal pipe and is sprayed into the furnace by the burner for combustion.It should be noted that in an intermediate silo pulverizing system, a primary wind carries pulverized coal into a pulverized coal separator, where the pulverized coal is separated from the airflow and stored in the pulverized coal bunker, and an appropriate amount of pulverized coal is supplied to the burner from the pulverized coal bunker by a pulverized coal feeder according to load requirements.It can also be seen from the figure that another part of the hot air from the air preheater enters the furnace directly through the distribution outlet of the burner to provide the air needed for pulverized coal combustion. This part of the hot air is called secondary air.4wrBoiler Burner

　　Pulverized coal gives off a lot of heat when burning in the furnace.The inner side of the furnace is laid with a water-cooling tube wall composed of metal pipes.However, due to the limitation of the heat load and the volume of the furnace, the smoke temperature at the outlet of the furnace is generally still high.In order to make use of this high temperature flue gas, the flue is also equipped with superheater (divided into several stages), reheater, economizer and air preheater and other heating surface.The flue gas of high temperature flows through these heating surfaces in turn and releases heat to these heating surfaces by convection, radiation and other heat transfer methods.The exhaust temperature from the air preheater is generally around.At this time, the flue gas can no longer be reused, it is sent into the dust collector for separation, the vast majority of the fly ash carried by the flue gas is removed, and then by the induced fan into the chimney, and finally discharged into the atmosphere.4wrBoiler Burner

　　Soda system4wrBoiler Burner

　　During the whole process of steam generation, the working medium goes through three heating stages in the boiler.First, the boiler feed water is heated into saturated water, then in turn is heated into saturated steam and superheated steam with a certain superheated temperature.These three processes are usually completed in the economizer, water wall and superheater heating surface respectively.4wrBoiler Burner

　　When the boiler is in operation, after water treatment and deoxygenation, the feed water is boosted by the feed pump and then passes through the high pressure heater and enters the header at the inlet of the economizer.In general, the feedwater is heated into saturated water in the economizer.But actually different boilers have different conditions.For example, low-pressure small industrial boilers using cast iron economizers do not generally heat the feedwater to saturated water;For medium pressure boilers, it may be required that the working medium at the economizer outlet header has up to saturated steam content;For boilers above subcritical pressure, it may be required that the working medium of the outlet header of the economizer is unsaturated water with large underenthalpy.The working medium flows from the economizer outlet header through a conduit into the drum, where it is forced to flow by the feed pump.After entering the drum, the working medium flows into the water-cooled wall lower header along the descending tube, from which it is distributed to each water-cooled wall tube (i.e.The flow in this section is maintained by the density difference between the soda mixture in the descending tube and the ascending tube.After the soda mixture returns to the drum, it is separated by the soda separation device in the drum. The steam concentrates in the steam space in the upper part of the drum, while the water enters the water space in the lower part of the drum and starts a new natural circulation flow.For high pressure boilers, some water usually evaporates into saturated steam every cycle.4wrBoiler Burner

　　After the saturated steam in the drum is separated, it is introduced into the superheater through the conduit for overheating.When the superheated steam is heated to the rated temperature, it is transferred to the turbine for work.The boiler shown has a reheater in the convection flue.The steam from the outlet of the steam turbine high-pressure cylinder is diverted to the reheater for reheating.When the required temperature is reached, the reheated steam is reintroduced through the reheated steam outlet into the middle and low pressure cylinders of the turbine for expansion work.4wrBoiler Burner