What are the 3 ways by which coal is mined?

Coal can be mined through three main methods:

1.Surface Mining: This method is used when coal deposits are located close to the Earth's surface. There are two types of surface mining techniques:

a. Strip Mining: This method involves removing the overlying layers of soil and rock (known as overburden) to expose the coal seam. Large machinery, such as draglines, shovels, or bucket-wheel excavators, is used to remove the overburden and extract the coal.

b. Open-Pit Mining: Similar to strip mining, open-pit mining involves the removal of overburden to access the coal seam. However, instead of removing the overburden in strips, a large open pit is excavated, and the coal is extracted from the pit.

Surface mining methods are typically used to extract coal reserves that are near the surface and cover vast areas. They are less expensive and more efficient than underground mining but can have significant environmental impacts.

2.Underground Mining: This method is employed when coal deposits are deep below the surface and cannot be accessed through surface mining. There are several underground mining techniques:

a. Room and Pillar Mining: In this method, tunnels, or "rooms," are created into the coal seam, leaving "pillars" of coal to support the roof. The coal is extracted by removing the pillars, allowing the roof to collapse. This technique is commonly used for shallow coal deposits.

b. Longwall Mining: Longwall mining involves the use of a continuous mining machine called a shearer that moves back and forth along the coal seam. As the machine cuts the coal, hydraulic-powered supports (known as chocks or shields) are used to hold up the roof. The extracted coal is transported to the surface via a conveyor belt.

c. Retreat Mining: This method is a variation of room and pillar mining. It involves extracting the remaining coal from pillars after the initial room and pillar mining is complete. This can be a dangerous method as the roof can collapse while the pillars are being extracted.

Underground mining methods are more expensive and complex compared to surface mining but are necessary for accessing deeper coal deposits.

3.Coal Gasification and Liquefaction: These methods involve converting coal into synthetic gases or liquid fuels.

a. Coal Gasification: Coal is reacted with oxygen and steam at high temperatures to produce a gas known as syngas. Syngas can be further processed to remove impurities and used as a fuel for electricity generation or chemical production.

b. Coal Liquefaction: Coal can be converted into liquid fuels through a process called coal liquefaction. There are two main techniques: direct liquefaction and indirect liquefaction. Direct liquefaction involves subjecting coal to high pressures and temperatures in the presence of a solvent to produce liquid hydrocarbons. Indirect liquefaction involves gasifying coal to produce syngas and then converting the syngas into liquid fuels.

Gasification and liquefaction methods are typically used for coal that is not suitable for conventional mining or for converting coal into more versatile forms for various applications.

Each mining method has its advantages and disadvantages, and the choice of method depends on factors such as coal seam depth, thickness, quality, and environmental considerations.