Six basic indicators of coal

Six basic indicators of coal:
The first indicator: water content.
Water in coal is divided into internal water, external water, crystal water and decomposition water.
Excessive moisture in coal is not conducive to processing, transportation, etc. It will affect thermal stability and heat conduction during combustion, reduce coke yield and prolong coking period during coking.
Now we often report the following water indicators:
1. The total moisture (Mt) is the sum of all the internal and external moisture in the coal, which is also commonly expressed as Mar. It is usually specified below 8%.
2. Air drying basis moisture (Mad) refers to the moisture content of coal in the air drying state. It can also be considered as internal moisture, which is called "analytical basis moisture" in the old national standard.
Second indicator: ash content
Refers to the residue of coal after burning.
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 component in coal is low. Calorific value is low.
At the same time, in coking with clean coal, the ash content determines the ash content of coke.
Energy indexes of ash include air dry ash (Aad), dry ash (Ad), etc. It is also useful to receive the basis ash (Aar).
Third index: volatile matter (full name is volatile matter yield) V
It refers to the product of thermal decomposition of organic matter and some minerals in coal, which is not all the inherent components of coal, but also some of the 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; It is also an important indicator of vaporization and liquefaction.
Air dried volatile matter (Vad), dried volatile matter (Vd), dried ash free volatile matter (Vdaf) and received volatile matter (Var) are commonly used.
Vdaf is one of the important indexes of coal classification.
The fourth indicator: fixed carbon
Carbon, which is different from elemental analysis, is calculated according to moisture, ash and volatile matter.
FC+A+V+M=100
The relevant formula is as follows: FCad=100 Mad Aad Vad
FCd=100-Ad-Vd
FCdaf=100-Vdaf
Fifth index: total sulfur St
It is a harmful element in coal, including organic sulfur and inorganic sulfur. Less than 1% can be used for fuel. In some areas, it is required to be less than 0.6 and 0.8. Now, green coal and green energy often refer to coal with low sulfur content.
Common indicators include: air dried total sulfur (St, ad), dried total sulfur (St. d) and received total sulfur
(St,ar) 。
Sixth index: calorific value of coal
The calorific value of coal, also known as the calorific value of coal, is the heat generated by the complete combustion of coal of unit mass. The calorific value of coal is the basic index of coal pricing based on calorific value. As a power fuel, coal mainly uses its calorific value. 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 parameter for boiler design.
The calorific value of coal represents the degree of metamorphism (coalification degree) of coal. The calorific value of coal here refers to the calorific value of float coal separated with 1.4 specific gravity solution (or the calorific value of raw coal with ash content not exceeding 10%). The peat with the lowest coalification degree at the latest coal forming age has the lowest calorific value, generally 20.9~25.1MJ/Kg. The calorific value of lignite with coal forming earlier than peat increases to 25~31MJ/Kg. The calorific value of bituminous coal continues to increase, and the calorific value of lignite with coal forming earlier than peat increases to 25~31MJ/Kg
Although the carbon content of lean coal increases, the hydrogen content is lower than that of bituminous coal due to the reduction of volatile matter
Some of them are less than 1%, equivalent to 1/6 of bituminous coal, so the coal with the highest calorific value is still one of bituminous coal
Some kinds of coal. Since the calorific value of coal with low coal degree varies greatly with coal degree, some countries
The constant moisture ash free basis gross calorific value of coal is used as the index to distinguish the low coal rank coals. Constant coal consumption in China
The high calorific value on wet ash free basis is used to classify lignite and long flame coal.