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Boilers are required for all production units that require steam. Generally, coal-fired boilers are selected, such as pulverized coal furnaces, circulating fluidized bed boilers, chain furnaces, and boiling furnaces.
After the heat of the coal is converted, steam is generated or turned into hot water, but not all of the heat is effectively converted, and part of the heat is consumed. Generally, the heat conversion efficiency of a larger boiler is relatively high, at 60-80%.
1) Layer burning furnace:
After the raw coal is crushed into pieces with a particle size of 25-40 mm, it is layered on the chain grate by using a coal sluice or coal shovel in front of the coal hopper.
The advantage is that the accessory equipment is small, easy to manufacture and install, and easy to operate.
Suitable for small and medium capacity boilers.
The disadvantage is that the combustion of coal is incomplete, the content of combustibles in slag and fly ash is high, and the boiler efficiency is generally 75-85%. Usually you need to burn better coal.
2) Chamber burning furnace:
Also known as pulverized coal boiler. The raw coal is screened, crushed and ground into a majority of coal powder with a particle size of less than 0.1 mm, and then injected into the furnace through a burner for suspension combustion. After the pulverized coal is sprayed into the furnace, it can quickly catch fire, and the smoke can reach a high temperature of about 1500 °C. However, the relative movement between the pulverized coal and the surrounding gas is very weak. The pulverized coal stays in the larger furnace for about 2 to 3 seconds to be basically burned out. Therefore, the furnace volume of the pulverized coal furnace is often compared with the stratified furnace of the same evaporation amount. About doubled.
The advantage is that it can burn various coals and burn more completely, so the boiler capacity can be made very large, suitable for large, medium and extra large boilers. Boiler efficiency is generally up to 90 to 92%.
The shortcomings are that there are many auxiliary machinery, high automation level requirements, boiler feed water must be treated, and infrastructure investment is large.
3) Cyclone furnace:
The crushed coal or coarse pulverized coal with particle size less than 10 mm is first vortex-likely burned in the front-mounted cyclone, and the high-temperature flue gas generated enters the main furnace (cooling chamber) for radiation exchange. heat.
The utility model has the advantages that the furnace volume has high heat intensity and the furnace has small size; the excess air coefficient is small (only 1.05 to 1.10), which can reduce the loss of exhaust heat; the burning of coarse coal powder can simplify the milling equipment; the slag discharge rate is high, flying The ash concentration is low, and the flue gas speed is increased to enhance the heat transfer of the convection heating surface.
The disadvantage is that the applicable coal type is limited by the ash melting point and the viscosity of the slag, and the boiler load variation range is small;
Can't start and stop quickly;
Since the temperature in the furnace can reach about 1800 °C, the NOx emissions of harmful gases are large, and the air pollution is serious.