Factors affecting the heating surface layout of steam boilers
Influence of steam parameters on the heating surface layout of steam boiler The heating process of the steam boiler working fluid can be divided into three stages: preheating of water, evaporation of water and overheating of steam. The ratio of the heat absorption in these three stages varies with the change of steam pressure. The steam pressure is low, the proportion of heat of vaporization is large, the pressure is high, and the proportion of heat of vaporization is smaller. The ratio of preheating heat and heat of superheating The bigger. For example, the proportion of evaporative heat in a low-parameter boiler is 70% to 75%, and the heated surface is dominated by an evaporation heating surface. The heat of vaporization of the medium-pressure boiler accounts for about 66%, and the heat of overheating accounts for about 20%. Generally, the convection superheater can be arranged. Ultra-high pressure and subcritical pressure boilers are generally reheat boilers, and the superheating and reheating heat accounts for more than 45%. It is necessary to arrange a wall, screen and convection superheater combination system. Therefore, the boiler steam parameters have a great influence on the arrangement of the heating surface of the boiler, and the boilers with different parameters have different requirements for the arrangement of the heating surfaces. Influence of boiler capacity on the heating surface layout of steam boiler The steam boilers have different capacities and the arrangement of the heating surfaces of the boilers is also different. When the boiler capacity is increased, the increase in the wall area of ​​the furnace is slower than the increase in capacity. Therefore, the wall area of ​​the large-capacity boiler is relatively smaller than that of the small-capacity boiler. In small and medium-sized boilers, the furnace wall area is relatively large. After the water wall is arranged, the furnace outlet temperature is not too high. However, in the large-capacity boiler, after only the water wall is arranged, the furnace outlet temperature is still high, and the radiation must be arranged again. The superheater and semi-radiation superheater can reduce the furnace outlet temperature to reach the allowable value. Therefore, boiler capacity is also a major factor affecting the layout of the heating surface of the boiler. Influence of fuel properties on the heating surface layout of steam boilers The nature and type of fuel have a major impact on the way the boiler is placed. Taking solid fuels as an example, volatiles, moisture, ash and sulfur have a great influence on the boiler layout. Coal with low volatile content is generally not easy to catch fire and burn out, which requires a larger volume of the furnace to ensure that the fuel has sufficient burning time in the furnace. In addition, a higher hot air temperature is required, that is, the heating surface of the air preheater is increased. When the moisture of the fuel is large, the temperature of the furnace is lowered, and the heat absorption of the radiation is reduced, so that the air preheater should be arranged more. When the ash content of the fuel is large, the wear of the convective heating surface will be aggravated. In order to reduce the wear, a tower arrangement may be adopted. When the ash melting point is too low, in order to ensure that the furnace surface is not slagging at the outlet and the rear heating surface, a liquid row may be used. Slag method. When the sulfur content of the fuel is large, various measures to prevent low temperature corrosion and clogging are also required in the arrangement of the boiler. The ascending speed in the drum will increase, and there will be enough energy to bring out the highly dispersed water droplets on the water surface, which will deteriorate the steam quality, especially the load fluctuation or overload. During operation, even if the concentration of salt in the pot water is not large, the serious consequences of soda water will occur. When the water level of the steam boiler is too high, the steam space of the drum will shrink, and the amount of steam passing through the corresponding unit volume will increase. The steam flow rate will increase, and the free separation space of the water droplets will shrink, which will cause the water droplets to be carried out with the steam. It will also deteriorate the steam quality, and the fluctuation of the water level will cause the steam to bring water instantaneously. When the pressure of the steam boiler drops suddenly, the volume of steam of the same mass increases, and the volume of steam passing through the volume per unit volume increases. In this way, fine water droplets are also easily taken out, which affects the quality of the steam.
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