Coal Gasification

Coal is fossil fuel which has vast reserves. Sources of coal are from around the world, more than 100 countries. Therefore, supply of coal is certainty resulting to lower price relative to other fuels, especially natural gas and fuel oil. The properties of coal can be classified as shown in below table.

Gasification exposes coal to temperatures that would normally cause the coal to combust but by carefully regulating the amount of oxygen in the gasifier and adding steam, the coal does not burn but rather separates into syngas. Syngas is a mixture of carbon monoxide (CO) and hydrogen (H2). The syngas can then be ‘shifted’ with the addition of more steam to produce more hydrogen and to convert the carbon monoxide into carbon dioxide (CO2).
The gasification of coal and other substances (petcoke, refinery bottom waste, biomass etc.) is not new. For example, China has been successfully gasifying coal for decades for ‘town gas’, chemical feedstock and for its domestic fertiliser industry.
Town gas – another name for syngas – was also widely used in North American and Europe for domestic heating and lighting and public street lighting. The popularity of town gas decreased significantly by the 1950s as natural gas became widely available. Natural gas was favoured over town gas because of its greater heating value and fewer contaminants.
Gasification is the first step for IGCC electricity generation, which is more efficient than conventional coal combustion. Gasification also produces a much higher concentration of carbon dioxide than direct combustion of coal in air, which makes carbon capture and storage more economical.

Coal gasification is also the first half of the indirect coal liquefaction process.

Currently there are 117 modern gasification plants operational worldwide, using 385 gasifiers of various designs – 49% of the total capacity is coal-fed. An additional ten coal-based plants are expected to come on-line in the near future, in North America, Europe and China.

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