Coal Gasification : All you need to know about

Do you know what is coal gasification? can you mention the types of coal found in India? Read further to know more.

Coal Gasification is the process of converting coal into synthetic gas(syngas) which is a mixture of hydrogen(H2), Carbon Monoxide(CO), and Carbon dioxide(CO2).

It is an in situ process in which oxygen is injected into the seam along with water and ignited at a high temperature, which causes the coal to partially oxidize into hydrogen, Carbon monoxide, carbon dioxide, methane, and hydrogen sulphide.

Coal in India

About:

• Coal is a readily combustible, black or brownish-black sedimentary rock, predominantly made of carbon.

Major uses of coal:

• Power generation in Thermal Power Plants.
• Steel production with the help of coking coal.
• Synthetic fuel by gasification and coal liquefaction.
• In alumina refineries, paper manufacturing, and chemical and pharmaceutical industries.

Types of coal found in India

• Anthracite: It is the highest grade of coal containing a high percentage of fixed carbon. It is hard, brittle, black, and lustrous. It is found in smaller quantities in regions of Jammu and Kashmir.
• Bituminous: It is a medium grade of coal having high heating capacity. It is the most commonly used type of coal for electricity generation in India. Most bituminous coal is found in Jharkhand, Odisha, West Bengal, Chhattisgarh, and Madhya Pradesh.
• Bituminous: It is black in color, dull (not shiny), and has a higher heating value than lignite.
• Lignite: It is the lowest grade coal with the least carbon content. It is found in the regions of Rajasthan, Tamil Nadu, and Jammu & Kashmir.

Process of Coal Gasification

During the process the coal is blown through with oxygen and steam (water vapor) while also being heated (and in some cases pressurized). When the coal is heated by external heat sources, it is called “allothermal”, while “autothermal” is the process of heating of the coal via exothermal chemical reactions occurring inside the gasifier itself.

It is essential that the oxidizer supplied is insufficient for complete oxidizing (combustion) of the fuel. During the reactions, oxygen and water molecules oxidize the coal and produce a gaseous mixture of carbon dioxide (CO₂), carbon monoxide (CO), water vapor (H₂O), and molecular hydrogen (H₂).

The process has been conducted in situ within natural coal seams (referred to as underground coal gasification) and in coal refineries. The desired end product is usually syngas (i.e., a combination of H₂ + CO), but the produced coal gas may also be further refined to produce additional quantities of H₂

Types of Gasifiers

• Fixed bed gasifiers-here, the flow of gas is independent of the flow of gas, requires minimal pre-treatment of feed coal, and has high terminal efficiency.
• Fluidized bed gasifiers-It is characterized by uniform particle mixing and uniform temperature gradient with a high char recycling rate.
• Entertained Flow Gasifiers-It has the ability to handle practically any feed and syngas obtained is free of oil and tars.

Importance of Coal Gasification

• Achieve INDC targets-Under Paris Agreement,2016 India has committed to certain targets. In achieving these targets, coal gasification may be of use as it helps in reducing emission intensity.
• Reduce import dependency-Syngas may be used to produce urea and obtain multiple products like methanol, Dimethyl Ether(DME), and olefins which may help India to reduce its import.
• Steel Industry-The carbon monoxide and hydrogen are important reducing agents for steel making and are considered environment-friendly methods of coal making. This may further reduce the import of furnace oil.

Challenges

• Capital intensive-setting up of coal gasification plants is capital intensive as it requires land, water, and electricity and also a long gestation period.
• Inadequate expertise-It requires highly skilled engineers and workers for the installation and successful execution of the project
• Quality of coal-The quality of coal available in India is mostly of low rank with high ash content. The conversion of high ash coal to syngas is a major challenge.

Government Measures

• National Coal Gasification mission-The policy sets an ambitious target of achieving 100MT coal gasification by the year 2030
• Concession of 20% on revenue share: For encouraging the use of clean sources of fuel, the government has provided for a concession of 20% on the revenue share of coal used for gasification.
• SHAKTI policy-For allocation of long-term coal linkages through auction, SHAKTI policy was adopted in coal gasification projects to reduce operational expenditure.
• Coal India Ltd has also planned to set up at least 3 gasification plants (besides Dankuni) on Built-own-operate(BOO)  basis through global tendering and has signed an MOU with GAIL for marketing synthetic natural gas.

Wayforward

• Inter stakeholder approach-the coordination between various agencies of the government like Coal India ltd, the Ministry of petroleum and natural gas, Ministry of chemicals and fertilizers along with private sector participation may be considered,
• Indigenous technology-Technology suitable for gasification of high ash content coal found in India is the need of the hour.
• Investment in research and development-Annual budgetary allocation for funding research and development can significantly contribute toward the success of projects

Article written by: Vivek Rajasekharan