Coal washing is a process through the impact of water flow, raw coal with different components and specific gravity is separated into different grades. It can remove dust and waste rock and reduce the ash and sulfur content.
Coal washing is an indispensable link in coal processing. The coal after coal washing is called clean coal. Coal washing can achieve the purpose of environmental protection, and also improve the utilization rate of coal.
Why is Coal Washing Necessary?
Raw coal extracted from mines often contains a significant amount of impurities, including:
▪ Ash: Inorganic minerals such as silica, alumina, and iron oxide reduce the energy content of coal and cause operational problems in power plants.
▪ Sulfur: A pollutant that can contribute to acid rain and air pollution when burned.
▪ Moisture: Excess water that can reduce the energy content of coal and make it more difficult to handle and store.
▪ Rock and other contaminants: Non-coal materials such as rocks, clay, and other minerals that can reduce the quality of coal.
These impurities can affect the performance and efficiency of power plants, industrial processes, and other coal-using applications. Coal washing helps to remove these impurities, resulting in higher-quality coal.
Coal Washing Process
Coal washing involves several stages, each designed to remove specific impurities. Here are the primary steps:
1. Crushing and Screening
The raw coal is first crushed into smaller pieces to facilitate further processing. It is then screened to separate particles of different sizes. Larger particles may require additional crushing.
2. Gravity Separation
This method uses the difference in density between coal and impurities to separate them. Dense media separation and jigging are common gravity-based techniques. In dense media separation, a liquid medium with a specific density of coal from heavier impurities.
3. Flotation
Flotation is a chemical process that separates fine particles based on their hydrophobic (water-repelling) properties. Chemicals called reagents are added to a slurry of coal and water, causing the coal particles to attach to air bubbles and float to the surface, where they are collected.
4. Magnetic Separation
Magnetic separation removes ferrous (iron-containing) impurities from coal. Magnetic separators attract and remove these particles from the coal stream.
5. Dewatering
After the impurities have been removed, the cleaned coal is often wet. Dewatering processes, such as centrifugation and filtration, are employed to reduce the moisture content of the coal, making it suitable for storage and transportation.
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