Requirements for coal quality of boilers in therma

2022-08-07
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Requirements for coal quality of power plant boilers

the type and nature of coal have a great impact on the structure, type selection, heating surface layout, economy and reliability of operation of power plant boiler combustion equipment; Therefore, large and medium-sized power plant boilers are designed based on certain coal types. The main indicators that have a great impact on the thermal work of power plant boilers are: volatile matter on dry ash free basis, ash on received basis, moisture on received basis, total sulfur on dry basis, low calorific value on received basis and ash fusibility

(1) volatile matter. Different power plant boilers have requirements for volatile matter. Designing boilers that use low volatile coal and burning high volatile coal will greatly affect their safety and economy; Therefore, the coal of power plant shall be selected and supplied according to the volatile requirements of design. From the analysis of furnace type, it shows that the volatile siloxane of coal in the furnace type of layer combustion furnace and chamber combustion furnace is inorganic and requires selection and supply. According to the analysis of furnace type, the requirements for volatile matter of coal are more strict for layer combustion furnace and chamber combustion furnace; Cyclone boiler, fluidized bed boiler and circulating fluidized bed boiler have relatively loose requirements for coal type. The volatile zones of coal available are large and coal type adaptability is strong. In particular, the newly-built circulating fluidized bed boiler in recent years has relatively loose requirements for volatile content

(2) ash. The effects of ash on combustion are as follows: high ash content will slow down the flame propagation speed, delay the ignition point, reduce the combustion temperature, deteriorate the combustion stability, and even cause fire extinguishing; At the same time, the ash content is too high, which is easy to aggravate the wear of the equipment and shorten the service life of the equipment. The ash content of this part is called "Dragonfly", which is too low. During layered combustion, the grate is easy to burn out because the ash is too thin. In terms of ash adaptability, circulating fluidized bed boiler has the strongest adaptability to ash

(3) moisture. Moisture is both a quantity index and a quality index. As the moisture content of coal increases, the calorific value decreases, and the exhaust gas temperature of boiler increases, which affects the combustion efficiency of power generation boiler. In the boiler using pulverized coal combustion, the pulverized coal shall be dried before entering the boiler to reduce the impact of moisture on the combustion of the power boiler

(4) sulfur. After sulfur combustion, S02 and S03 are generated. They are very easy to synthesize h2s04 steam with the water in the flue gas, causing corrosion to the power generation equipment. At the same time, S02 and S03 are discharged into the air, causing serious pollution to the atmospheric environment. In addition, high sulfur coal is prone to metamorphism and spontaneous combustion during storage, which affects the combustion effect of coal

(5) calorific value. The calorific value of coal is an important index in the design of power generation boiler. If the calorific value of coal is lower than the design index, the temperature level in the boiler will be reduced, which will affect the ignition point and burnout of pulverized coal, and the thermal efficiency of the boiler will be reduced. When the calorific value is low to a certain extent, it will cause unstable combustion, fire fighting and blasting, and oil must be used for combustion support; On the contrary, if the calorific value of coal is higher than the design level, the furnace temperature will inevitably rise, and most of the coal ash will soften and melt, which is easy to form slagging

(6) ash fusibility. This is the target combustion mode proposed by Northeast Light Alloy Co., Ltd. at the recent scientific and Technological Innovation Conference. The ash fusibility of coal is not high; The suspension combustion adopts the fixed slag discharge method. The ash fusibility softening temperature st 1350 ~ ℃ may cause furnace slagging and hinder the continuous and safe operation of the boiler. Suspension combustion adopts liquid slagging method, and generally uses coal with low ash fusibility

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