Volatile matter refers to that when the coal is kept at 900 ± 10[4]When heated at ℃ for 7 minutes, the organic matter and some minerals in the coal will be decomposed into gas (such ascarbon monoxide, methane and other combustible gases) and liquid overflow, and the water in the coal subtracted from the overflow is the volatile matter.The volatile content of coal for chain grate boiler should be above 20%.[1]
The mass loss of coal after moisture correction in isolation from air heating under specified conditions is called volatile matter.The residue after removing volatile matter is called coke residue.Volatile matter is not the original inherent volatile matter in coal, but the thermal decomposition product of coal when heated under strictly specified conditions. Therefore, volatile matter in coal should be called volatile matter yield.[2]
The yield of volatile matter of coal is closely related to the degree of coalification. The lower the degree of coalification, the higher the yield of volatile matter. As the degree of coalification deepens, the yield of volatile matter gradually decreases.Volatile matter yield is an index for evaluating coal quality.Coal with high volatile matter yield is prone to produce unburned carbon particles when burning, commonly known as "black smoke", with low thermal efficiency.If the volatile matter yield of coal is too low, the boiler is not easy to catch fire, and it is easy to extinguish the fire after catching fire, which is difficult to ensure the stable combustion of the boiler.The determination results of volatile matter yield of coal vary with different test conditions, especially the heating temperature and H, II Division. Therefore, the determination must be carried out in strict accordance with the standard experimental operating conditions.
Calculation formula
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In order to eliminate moisture and ash,
For the influence of change, the volatile matter of the analyzed coal sample must be converted into the volatile matter based on the combustiblerexpress.The conversion fraction is:
Vf——Volatile matter on analytical basis (air dry basis),%;
Wf——Analyze the moisture of coal sample,%;
Af——Ash content of analyzed coal sample,%.
Determination of volatile matter of coal
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Measurement principle
The mass loss of coal after moisture correction in isolation from air heating under specified conditions is called volatile matter.The residue after removing volatile matter is called coke residue.Volatile matter is not the original inherent volatile matter in coal, but the thermal decomposition product of coal during heating under strictly specified conditions. Specifically, volatile matter in coal should be called volatile matter yield.[3]
Coal is heated in isolation from air, and the general situation is as follows:
The gas adsorbed in the coal below 100 ℃ and part of the water escapes, the water escapes in the coal below 110 ℃, and the combined water escapes at 200 ℃;Gas escapes from the first pyrolysis at 250 ℃;Tar is generated when the temperature is higher than 350 ℃;550~600 ℃, the tar is exhausted;When the temperature is higher than 600 ℃, the second pyrolysis starts. The gas escapes again and condenses into high-temperature coke. The decomposition stops at 900~1000 ℃. The residue is coke.
The volatile matter of coal is mainly composed of water and carbonhydroxideAnd hydrocarbons (CHfourMainly), but physically adsorbed water (including external water and internal water) and mineral formationcarbon dioxideIt is not within the range of volatile matter.
The determination of volatile matter in coal is a highly standardized test, and its results depend entirely on the test conditions.The sample quality, heating temperature, heating time, heating speed, the material, shape and size of the crucible, the model of the test equipment and the size and material of the crucible frame can all affect the determination results of volatile matter to a certain extent.
Key points of method
Weigh a certain amount of general analysis test coal sample, place it in a porcelain crucible with a cover, heat it for 7 min in isolation from air at (900 ± 10) ℃, and then subtract the moisture content of the coal sample from the percentage of the reduced mass in the coal sample as the yield of volatile matter.
