Coal-fired boiler people should know

Coal burning index
First index: moisture
Water in coal is divided into internal water, external water, crystal water and decomposition water. Excessive moisture in coal is unfavorable to processing, transportation, etc. it will affect thermal stability and heat conduction during combustion, reduce coke yield and prolong coking cycle during coking. Now we often report the following moisture indicators: 1. Total moisture (MT), which is the sum of all internal and external moisture in coal, is also commonly expressed by Mar. It is generally specified to be below 8%. 2. Air dry basis moisture (MAD) refers to the moisture content of coal in the air dry state. It can also be considered as internal moisture, which is called "analysis based moisture" in the old national standards.
Second index: Ash
Refers to the residue left by coal after combustion. It is not the sum of minerals in coal, but the residue of these minerals after chemical and decomposition. The high ash content indicates that the combustible content in coal is low. The calorific value is low. At the same time, in the coking of clean coal, the ash content of coke is determined by the ash content. Common ash indexes include air dry basis ash (AAD) and dry basis ash (AD). It is also useful to receive (AAR) based on ash.
The third index: volatile
It refers to the products of heating and decomposition of organics and some minerals in coal, not all of which are inherent components of coal, but also some of which are pyrolysis products, so it is called volatile yield. The size of volatile matter is related to the degree of coal metamorphism. The higher the degree of coal metamorphism, the lower the yield of volatile matter. In combustion, it is used to determine the boiler model; In coking, it is used to determine the proportion of coal blending; At the same time, it is also an important indicator of vaporization and liquefaction. Commonly used are air dried based volatile (VAD), dry based volatile (VD), dry ash free based volatile (Vdaf) and received based volatile (VaR). Among them, Vdaf is one of the important indicators of coal classification.
The fourth indicator: fixed carbon
Carbon, which is different from element analysis, is calculated according to moisture, ash and volatile. The relevant formula of FC + A + V + M = 100 is as follows: FCAD = 100 mad aad VAD FCD = 100 ad VD fcdaf = 100 Vdaf
Fifth indicator: total sulfur
It is a harmful element in coal, including organic sulfur and inorganic sulfur. Less than 1% can be used as fuel. In some areas, it is required to be below 0.6 and 0.8. Now, the environmental protection coal and green energy often used refer to coal with low sulfur content. Common indicators include: Total Sulfur on air drying basis (st, AD), total sulfur on dry basis (St.d) and total sulfur on received basis (st, AR).
Sixth index: calorific value
The calorific value of coal, also known as the calorific value of coal, is the heat emitted by the complete combustion of coal per unit mass. The calorific value of coal is the basic index of coal pricing by calorific value. As a power fuel, coal mainly uses the calorific value of coal. The higher the calorific value, the greater its economic value. At the same time, the calorific value is also the basis for calculating the heat balance, thermal efficiency and coal consumption, as well as the parameters for boiler design. The calorific value of coal represents the degree of deterioration (degree of coalification) of coal. The calorific value of coal mentioned here refers to the calorific value of floating coal (or the calorific value of raw coal with ash content no more than 10%) after separation with 1.4 specific gravity liquid. Peat with the latest coal formation age and the lowest degree of coalification has the lowest calorific value, generally 20.9 ~ 25.1mj/kg. Lignite with coal formation earlier than peat has increased to 25 ~ 31mj / kg, and bituminous coal has continued to increase. When coking coal and lean coal are used, the carbon content has increased, but due to the decrease of volatile matter, especially the hydrogen content is much lower than bituminous coal, some of which are less than 1%, equivalent to 1 / 6 of bituminous coal, Therefore, the coal with the highest calorific value is still some of the bituminous coal. In view of the fact that the calorific value of coal with low degree of coalification varies greatly with the degree of coalification, some countries often use the high calorific value of coal on a constant humidity ash free basis as an index to distinguish the types of coal with low degree of coalification. In China, lignite and long flame coal are divided by the high calorific value of ash free basis at constant humidity of coal.