Guide: The high-temperature flue gas released by the combustion of coal is transported to the inlet of the waste heat boiler through the flue, and then flows through the heater, evaporator and economizer, and finally discharged into the atmosphere through the chimney. The flue gas temperature is generally 150～180℃. The heat released when the temperature drops from high temperature to exhaust temperature is used to turn water into steam.

　　The high-temperature flue gas released by the combustion of coal is transported to the inlet of the waste heat boiler through the flue, and then flows through the heater, evaporator and economizer, and finally discharged into the atmosphere through the chimney. The flue gas temperature is generally 150～180℃. The heat released when the temperature drops from high temperature to exhaust temperature is used to turn water into steam. The boiler feed water first enters the economizer, and the water absorbs heat in the economizer and rises to a temperature slightly lower than the saturation temperature under the pressure of the steam drum and enters the drum.

　　After the water entering the drum is mixed with the saturated water in the drum, it enters the evaporator along the downcomer below the drum to absorb heat and starts to produce steam. Usually only a part of the water becomes steam, so soda water flows in the evaporator mixture. The steam-water mixture leaves the evaporator and enters the upper drum and is separated by steam-water separation equipment. The water falls into the water space in the drum and enters the downcomer to continue to absorb heat and produce steam, while the steam enters the superheater from the upper part of the drum and absorbs heat to turn saturated steam into superheated steam. . According to the three stages of the steam production process, there are three heating surfaces corresponding to the economizer, evaporator and superheater. If superheated steam is not needed, only saturated steam is needed, and no superheater is required.