What is coal gasification?
• Coal gasification is the process of producing syngas [a mixture consisting primarily of methane (CH4), carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2) and water vapor (H2O)], from coal, water, air and/or oxygen.
What are its usages?
• In current practice, large-scale instances of coal gasification are primarily for electricity generation, for production of chemical feedstocks, or for production of synthetic natural gas.
• The hydrogen obtained from coal gasification can be used for various purposes such as making ammonia, powering a hydrogen economy, or upgrading fossil fuels.
• Alternatively, coal-derived syngas can be converted into transportation fuels such as gasoline and diesel or into methanol which itself can be used as transportation fuel or fuel additive
• Methane or natural gas extracted from coal gasification can be converted into LNG for direct use as fuel in transport sector.
What is underground coal gasification process?
• Underground coal gasification (UCG) is an industrial process which converts coal into product gas (predominant product gases are methane, hydrogen, carbon monoxide and carbon dioxide)
• UCG is an in-situ gasification process carried out in non-mined coal seams using injection of oxidants, and bringing the product gas to surface through production wells drilled from the surface.
• About 350 m3 gas can be produced per tonne of coal.
• Bye products of significant commercial value will be hydrocarbons, phenols, anhydrous NH3 and clean water.
• UCG overcomes hazards of underground and open cast mining operations. Ƒ
• In UCG process, ash/ slug removal is not required as they remain in the cavities.
• Cost of production for this energy resource could be as low as US$ 1.0-1.5 per MMBTU
• Gas output may be combusted for electricity production.
• Gas can be used to produce synthetic natural gas.
• Hydrogen and carbon monoxide can be used as a chemical feedstock for the production of fuels (e.g. diesel), fertilizer, explosives and other products
What are the advantages of UGC?
• UCG is the only feasible technology, which enables exploitation of deep (> 700m) coal reserves, which are not amenable to known conventional mining methods.
• UCG offers an environmentally clean way to harness energy from coal.
• UCG produces insignificant surface disruption and brings no solid waste to the surface.
• Even at shallower depths (< 500m), UCG can be more economical than conventional mining.
• UCG reduces capital investment, operating costs, and the output gases cost by 25 to 50% as compared to surface gasification.
• Possibilities of transport of medium calorific value gas over a distance of 100 km. exist.
• Possibilities of using CO2 from the gas for enhanced oil recovery exist.
• Increases worker safety as no mining operations involved.
• Compared to traditional coal mining and processing, the underground coal gasification eliminates surface damage and solid waste discharge, and reduces sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions.
What are the disadvantages of UGC?
• Difficult to control the operation.
• Contamination of aquifer if not decommissioned properly. Case study: cougar energy plant Queensland (Australia) exploded and subsequently benzene was found in ground water
• Void left over can cause subsidence.
What are the Applications of byproducts of UGC?
• Urea for Fertilizer:
In the longer term, fuel for urea will be switched over to Natural Gas. With no committed supply assurance of Natural Gas, Syngas from Underground Coal Gasification can be an alternative as a feed stock.
• Chemicals (Ammonia and Methanol):
Two notable uses of syngas are in producing ammonia and methanol and their derivatives. Natural gas based methanol plants are of small size. Syngas from UCG provides good options for producing these valuable chemicals without getting exposed to international feedstock price fluctuations.
Syngas from UCG can be used as a feed stock for CTL for production of clean synthetic liquid fuels using Fischer Tropsch process. The syngas is converted into liquid hydrocarbons, through a catalytic reaction using cobalt as catalyst by Fischer-Tropsch (F-T) Synthesis.
What is the INDIA’s potential in this field?
• Coal in India is constrained by growing land acquisition problem and stringent environmental laws. UCG requires much less surface area, thus representing potential method to extract energy from India’s deep seated untapped coal reserve.
• It will also strengthen “national policy on sustainable energy resource” through clean coal.
• India has a coal reserve of 285 billion tonnes.80 % is non metallurgical (high ash content).out of this non-metallurgical coal India’s coal is largely dominated by inferior coal (80%), found in the depth of 300-1200 met.
• 40 billion tonnes of lignite coal (most of which is found below 300 met).e.g Kalol basin.
• ONGC has taken Skochinsky Institute of Mining, Russia, and world’s foremost leaders in UCG Technology, as its technical collaborator. ONGC is working in partnership with a number of leading Coal / Power companies in this project viz. CIL, NLC, SCCL, GMDC and GIPCL. Fifteen different probable sites in India in the states of Maharashtra, West Bengal, Jharkhand, Andhra Pradesh, Gujarat, Rajasthan and Tamil Nadu have already been studied for suitability to UCG.
• ONGC drilled two pilot wells near Mehsana city, in North Gujarat.
• The Ministry of Coal, Government of India, has awarded an S&T study project to the Neyveli Lignite Corporation.
• Environmental concern: As many of the coal blocks are in ecologically sensitive areas,environment safety is a concern.
• Suitable coal deposit: Though technically feasible,number of sites geologically and hydrologically suitable are limited.
• Inconsistent supply of syngas: Both the flow and heating value of gas will vary
• Economies of scale: Without economies of scale operation, the project will render uneconomical.
Benefits of gasification:
- Transporting gas is a lot cheaper than transporting coal.
- Help address local pollution problems.
- Has 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.
Concerns and challenges:
- Coal gasification is one of the more water-intensive forms of energy production.
- There are concerns about water contamination, land subsidence and disposing of waste water safely.
What is Underground coal gasification?
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.
With limited reserve potentiality of petroleum & natural gas, eco-conservation restriction on hydel project, improvement in technology for harnessing renewable energy and geo-political perception of nuclear power, it is becoming increasingly evident that coal will continue to occupy centre-stage of India’s energy scenario. India is well positioned to take up UCG for extracting energy from isolated geographical locations. This will help in meeting the energy demands.