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The truth about ash: What can the residue left behind after burning coal tell us?
As the global demand for renewable energy continues to increase, the use of coal and its chemical and physical properties remain an important topic of discussion. The ash left behind after burning coal, while seemingly useless, actually provides crucial information about the quality and properties of the coal. This article will explore analytical techniques for coal and its physical and chemical properties, and provide insights into how these properties affect coal's applications and environmental impacts.
Chemical properties of coal
Coal is generally divided into four categories: lignite, bituminous coal, anthracite and graphite. Each type has unique physical characteristics that are largely controlled by moisture, volatile matter, and carbon content. Understanding these properties can not only determine the suitability of coal, but also infer its ash composition after combustion.
Moisture content is an important property of coal and all coal is moist when mined. The moisture in coal can be divided into surface moisture, hygroscopic moisture, decomposed moisture and mineral moisture.
Water
Moisture content can affect coal's energy production capacity and combustion efficiency. The total moisture content of coal is analyzed by the mass loss of coal samples before and after combustion. Moisture is usually determined by heating or drying methods, the choice of which depends on the rank of the coal. For example, low-rank coals require special drying processes to prevent oxidation.
Volatile matter
The volatile matter of coal refers to the volatile components in coal except water under high temperature and oxygen-free conditions. These components include various hydrocarbons and a small amount of sulfur. The determination of volatile matter can provide a basis for the processing and use of coal.
Ash content of coal
Coal ash refers to the incombustible residue remaining after coal is burned. This value can help determine the quality of the coal and is usually expressed as a percentage of the coal's original mass.
The ash analysis of coal is relatively simple, and the mass of the ash remaining after the coal is completely burned is calculated. Coal with a high ash content tends to produce more waste after combustion, which affects its economic value and environmental impact, so it is very important to understand the ash content of coal.
Physical and mechanical properties of coal
The physical properties of coal, such as relative density and particle size distribution, directly affect the handling and combustion properties of coal. Measurement of relative density helps determine the properties and performance of coal. Generally speaking, density increases with the rank of coal.
Particle size distribution
The particle size distribution of coal depends on the rank of the coal and the processing it has undergone. During the combustion process, this characteristic affects the combustion efficiency and combustion characteristics of coal, so it is crucial to understand and control the particle size distribution of coal.
Float and sink test
Float and sink tests can be used to identify and wash coal to increase its heating value and energy output. This process removes high-ash coal particles and improves the overall quality of the coal.
Special combustion tests
The energy output of coal can be measured through specialized combustion tests that help understand the combustion behavior of different types of coal.
The melting behavior of fly ash in a hot cone environment is an important factor in setting boiler operating points.
Coal Grade Classification
Coal is classified according to its carbon content and volatile matter. As the rank of coal increases, the carbon content rises, which means that the energy produced by its combustion is also relatively high.
ConclusionThe analysis of coal is not limited to its chemical and physical properties but also includes the effects of ash content. The presence of ash itself can provide insight into coal quality. In the global push for green energy, do we need to re-evaluate the role of coal and the value of its future applications?
