Coal Gasification and Coal-bed Methane

Context: India aims for 100 million tones (MT) coal gasification by 2030.

  • The Government of India’s big plan to push coal gasification to replace natural gas in the fertiliser sector would help square energy and food security objectives.
  • However, ammonia produced from coal gasification has a carbon footprint that is 1.8 times higher than that produced from the conventional process using natural gas.

Analysis

Coal gasification

  • Coal gasification is a thermo-chemical process in which the gasifier’s heat and pressure break down coal into its chemical constituents.
  • The resulting “syngas” or synthetic natural gas (SNG) is comprised primarily of carbon monoxide and hydrogen, and occasionally other gaseous compounds.
  • Proponents of coal gasification say that syngas can be used for electricity production, used in energy-efficient fuel cell technology, or as chemical “building blocks” for industrial purposes.
  • The hydrogen can also be extracted for use in fueling a hydrogen economy.
  • Coal gas can also be converted into a transportation fuel as a substitute for gasoline in vehicles, but it is far less efficient than the current production and burning of petroleum-based gasoline.
  • Coal gasification is said to have greater efficiency than conventional coal-burning because it can effectively use the gases twice: the coal gases are first cleansed of impurities and fired in a turbine to generate electricity.
  • Then, the exhaust heat from the gas turbine can be captured and used to generate steam for a steam turbine-generator.
  • This is called a combined cycle, and a coal gasification plant using this dual process can potentially achieve an efficiency of 50 percent or more, compared with a conventional coal power plant, which is often just above 30 percent.
  • Transporting gas is a lot cheaper than transporting coal.
  • Coal gasification can also help address local pollution problems.
  • Coal gasification and liquefaction facilitate the removal of Sulphur and ash and produce valuable chemical by-products.

But there are two big problems.

  • First, coal gasification actually produces more CO2 than a traditional coal plant.
  • Synthetic natural gas emits seven times more greenhouse gases than natural gas, and almost twice as much carbon as a coal plant.
  • The second problem is water use. Coal gasification is one of the more water-intensive forms of energy production.

Coal-bed methane

  • Other countries are looking at different ways to get gas from coal. One method, particularly popular in Australia, is coal-bed methane, a process allowing access to coal deposits that are too deep to mine.
  • Water is sucked out of the seam and the methane attached to the surface of the coal is freed and then collected.
  • Very little CO2 is emitted, but the process is not without controversy. Opponents highlight concerns about water contamination, land subsidence and disposing of waste water safely, while the water intensive process sometimes involves fracking.
  • Coalbed Methane (CBM) is an unconventional source of natural gas.
  • India has the fifth largest proven coal reserves in the world and thus holds significant prospects for exploration and exploitation of CBM.
  • The Gondwana sediments of eastern India host the bulk of India’s coal reserves and all the current CBM producing blocks.

Underground coal gasification

  • A very different way to produce gas from coal is known as underground coal gasification (UCG), a process that has been around since the 19th Century but which has yet to become commercially viable on a grand scale.
  • The process involves pumping oxygen and steam through a small borehole into the coal seam to produce a small and controlled combustion.
  • Unlike coal-bed methane, therefore, the actual coal is converted from a solid state into gas.
  • The hydrogen, methane, carbon monoxide and CO2 are then siphoned off through a second borehole.
  • Coal Gasification in India
  • Coal is the most abundant fuel resource in India with a cumulative total reserve of nearly 307 Billion tonnes, estimated up to the maximum depth of 1200m.
  • In view of the limited reserves of petroleum and natural gas in the country, coal has the potential to be the major energy, ammonia/urea and organic chemicals resource.
  • However, the following factors restrict its use for alternate energy over imported crude oil and LNG:
  • the low calorific value (GCV about 3600);
  • high levels of inorganic impurities (35-45%) of the Indian coal;
  • unavailability of suitable technology to process high ash coal
  • At present the 60% of available coal is consumed by the power production units, while steel and cement industry consume around 4% and 7% respectively. Other 29% is used as feedstock for producing various chemicals.
  • The high ash content in the Indian coal still remains a major hindrance towards developing an appropriate technology which can be run on commercial basis.
  • The three units of FCIL at Ramagundam, Sindri and Talcher which were setup during 1970-80 using coal gasification technology failed to achieve commercial success due to high ash content of coal feed.
  • It is understood the technology available so far restricts the use of coal with ash content above 30%.
  • Recently, contract for coal gasification plant for urea project at the erstwhile Talcher in Odisha was awarded.

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