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The Secret of Coal: Do you know what's special about different types of coal?
Coal, used extensively in energy production and industrial processes, is a fascinating natural resource. With environmental concerns growing in severity, various techniques are used to analyze the physical and chemical properties of coal to assess its suitability for different uses. Different types of coal are worthy of in-depth study, both in terms of efficiency and environmental impact.
Chemical properties
There are four main types of coal: lignite, bituminous coal, anthracite and graphite, and the physical parameters of each type are affected by moisture, volatile matter content and carbon content.
Water
Moisture content is an important property of coal. All coal has some moisture in it, which is called natural moisture. Water can be divided into the following forms:
- Surface moisture: moisture present on the surface of coal particles.
- Hygroscopic moisture: Moisture retained in micro-cracks of coal by capillary action.
- Decomposition moisture: Moisture retained during the decomposition of organic matter.
- Mineral water: The crystalline structure of water, such as that found in clay.
Through heating, drying and other methods, the total moisture content can be measured to assess the quality of the coal.
Volatiles
Volatile matter refers to components released from coal under high temperature and oxygen-free environment. Most volatiles consist of short-chain and long-chain hydrocarbons, aromatics, and some sulfur content. As the rank of coal increases, the volatile matter content decreases.
Ash content
The ash of coal is the incombustible residue left after combustion. Analyzing the ash can give the quality index of coal. Ash determination involves calculation of the ratio between air drying and oven drying and is usually carried out using a high temperature combustion method.
Fixed Carbon
Fixed carbon refers to the carbon that remains in coal after the volatile substances disappear. It is an important basis for further estimating the amount of coke that can be produced from coal.
Physical and mechanical properties
Relative density
The relative density, or specific gravity, of coal varies with the grade of the coal and the mineral impurities present. This data can assist in converting resource to reserve estimates.
Particle size distribution
The particle size distribution of coal depends on its grade, and coal usually needs to be processed to a corresponding size so that it can be used more efficiently in combustion and refining.
Flotation test
Different particles of coal will have different relative densities, making flotation testing critical in improving the energy efficiency and sale value of coal.
Wear test
Wear testing assesses the effect of coal on mechanical operations and its potential for wear and tear, and is critical to the continued operation of equipment.
Special combustion tests
Specific Energy
Bomb calorimeters are used to measure the specific energy output of coal, which is particularly important in steam generators.
Ash Fusion Test
The behavior of coal ash at high temperatures is critical to the selection of coal for steam power generation. Different melting points affect the function and efficiency of the boiler.
Kettle Swell Index
The Kettle Swelling Index test heats coal in a standardized test tube to assess its potential to make coke.
Coal Grade Classification
Coal is classified according to various international standards. Higher-grade coal has a higher carbon content and is usually evaluated differently on its environmental impact and energy use.
In this rapidly changing world, different types of coal are compared not only in terms of their chemical and physical properties, but also in terms of how these properties can be used to meet society's current demand for clean energy. Have you ever thought about what role coal will play in the future energy transition?
