Boiler auxiliary machine
The device heats the feed water in the tail flue of the boiler. Its role is to absorb part of the heat in the flue gas at the tail of the boiler and reduce the exhaust temperature to save fuel. Modern boilers generally have economizers. The term economizer comes from coal-fired boilers, and boilers for fuel oil, gas, and other fuels are also commonly referred to as economizers. The economizer is divided into boiling type and non-boiling type according to whether the outlet water is vaporized. The boiling rate of the boiling economizer (mass percentage of the vaporized part of the outlet water) should not exceed 20%. If the flow resistance is increased, the flow of each tube in the pipe group will alternately pulsate, causing the economizer to vibrate, which will cause damage. The economizers for medium pressure boilers are often boiling, while other pressure boilers are often non-boiling. The economizer can be divided into cast iron type and steel tube type according to structure and material. The cast iron economizer (see figure [cast iron economizer]) is not high in strength and is used for boilers with a pressure of less than 2.5 MPa. To enhance heat transfer, there are a large number of fins outside the tube. The cast iron economizer has a poor ability to withstand vibration and shock, so it cannot be used as a boiling type; however, it has good corrosion resistance and can be used in industrial boilers without deoxidation of feed water. The steel tube economizer is not limited by pressure and can be used as a boiling type. Generally, it is made of carbon steel pipe with an outer diameter of 32 to 51 mm. Sometimes fins and fins are added to the tube to improve the heat transfer effect. The steel pipe economizer consists of horizontally arranged parallel elbow pipes (referred to as serpentine pipes).
The economizer has two functions. The first function is to increase the temperature of the feed water. The boiling economizer can also generate a small amount of steam. The feed water entering the economizer comes from the deaerator. The water temperature of the low-pressure deaerator is generally 104 ° C, and the water temperature of the high-pressure deaerator is about 158 ° C. The saturation temperature of the medium-pressure furnace (4.4Mpa) is about 256 ° C, and the saturation temperature of the high-pressure furnace (11Mpa) is 317 ° C, which is much higher than the temperature of deoxygenated water. If there is no economizer, the feed water directly enters the drum, because the water entering the downcomer is underheated, a large part of the heating surface of the water-cooled wall is used to increase the water temperature, and the heating surface used to generate steam is reduced, which causes the boiler to evaporate. The amount is reduced. After installing the economizer, the water temperature can be significantly increased. For the boiling economizer, the water temperature can be increased to the saturation temperature under the boiler pressure, and a small amount of steam can be generated (about 10% to 20% of the boiler's evaporation). When water is fed into the water wall to absorb heat, it can be vaporized, and the boiler's evaporation capacity is significantly increased.
The second function is to reduce the temperature of the flue gas, recover the heat of the flue gas, improve the thermal efficiency of the boiler, and save fuel. The temperature of the flue gas at the outlet of the superheater is about 700 ° C. Even if a large number of convection tube bundles are arranged after the superheater, the temperature of the flue gas leaving the convection tube bundle is still 250-350 ° C because the temperature of the boiler water is the saturation temperature under the pressure of the drum. Contains a lot of calories. Installing a economizer after a superheater or a convection tube bundle can effectively reduce the flue gas temperature, recover a lot of heat, and save a lot of fuel. Because early boilers usually used coal as fuel, they were called economizers.
After the economizer is installed in the boiler, the temperature of the feed water entering the drum is greatly increased. For a boiling economizer, the temperature of the feed water entering the drum is the saturation temperature under the pressure of the drum. For a non-boiling economizer, the feed water temperature entering the drum is not yet reached, but it is also close to the saturation temperature. Therefore, after the feed water is heated by the economizer, because the water temperature is equal to or close to the saturation temperature under the pressure of the drum, the thermal stress caused by the temperature difference can be reduced and the working conditions of the drum can be improved.