Today, high prices of oil and gas and uncertainties about political stability in most of oil producing countries, have renewed interest in all kinds of fuel. A renewed interest in coal gasification is therefore not surprising. Further-more, hydrogen is now a welcome by-product because of the current interest in alternatively fueled vehicles. Underground Coal Gasification (UCG) is potentially the most important clean coal technology of the future with worldwide application. Ultimately, it could be a substitute for deep mining coal for power generation use. Clean coal technologies are several generations of technological advances that have led to more efficient combustion of coal with reduced emissions of sulfur dioxide and nitrogen oxide.
Worldwide, coal reserves are quite vast – over 10 trillion tones. However, unless cleaner and cheaper ways can be found to convert coal to gas or liquid fuels, coal is unlikely to become an acceptable replacement for dwindling and uncertain supplies of oil and natural gas. Mining coal is dangerous work. Coal is dirty to burn and much of the coal in the ground is too deep or too low in quality to be mined economically. Today, less than one sixth of the world’s coal is economically accessible. However, there is a renewed interest world over to revive the old technology that offers promise to substantially increase usable coal reserves and make coal a clean and economic alternative fuel. Known as underground coal gasification (UCG), this technology converts coal to a combustible gas underground.
UCG is the process by which coal is converted in situ into a combustible gas that can be used as a fuel or chemical feedstock. It is a process to convert un-minable underground coal/lignite into combustible gases (i.e., combustible syngas – a combination of hydrogen and carbon monoxide) by gasifying. UCG uses a similar process to surface gasification. The main difference between both gasification processes is that in UCG the cavity itself becomes the reactor so that the gasification of the coal takes place underground instead of at the surface.
As a method of exploiting coal, UCG represents an environmental improvement on the combination of coal mining and surface combustion of coal. It is also safer and intuitively more efficient. UCG technology will potentially enable large coal resources to be exploited without causing significant environmental impacts when compared with conventional coal mining. Controlling sulfur oxides, nitrogen oxides and other emissions, such as mercury and ash, from conventional coal-fired power stations is currently expensive requiring significant surface processing to control waste products. In contrast, most of these unwanted coal by-products are left underground during UCG achieving lower costs for gas cleanup. Moreover the surface impact of conventional coal utilization includes the coal mine, which may be a highly disruptive open cast type, the significant coal washing, processing and fines disposal plant, the coal stockpiles and the entire associated transportation infrastructure. UCG requires none of this. Lastly, Carbon dioxide can be captured using well established and readily available technologies. The high pressure and temperature of UCG syngas enables cost effective carbon dioxide capture.
Although coal should not be promoted as energy resource as its really very toxic and not environmental friendly but these days Pakistan is in the grip of a serious energy crisis that is affecting all sectors of the economy and the various segments of the society. Current power generation from the Thar reserves is less than 0.5 percent of the potential capacity of the deep and rich reserves, which are spread over 9,600 square kilometers (sq. km) with the potential to generate 100,000 Megawatts (MW) a year. Some estimates put the value of the reserves at US$30 trillion on a desert that encompasses nearly 200,000 sq. km of eastern Pakistan and the Indian state of Rajasthan. Chinese and other companies had not only carried out surveys and feasibilities of this project but also offered 100 percent investment in last 7 to 8 years but these initiatives become a target of political turmoil. However, keeping in view the need of the hour, the U.S. power industry has invested about $90 billion since 1990 to deploy clean coal technologies to reduce air emissions – while at the same time providing affordable, reliable electricity to meet growing energy needs.
Increasing the public awareness and acceptance of the importance in low emission, clean coal technologies are as critical as the technological developments themselves. Public confidence in these technologies is built on early, open and honest engagement, as well as evidence of effective and successful projects. A key initiative of the Techtalk-Clean Coal Technologies being carried out by NUST Science Society is to increase public awareness and acceptance of the importance of reducing greenhouse gas emissions through the use of low emission, clean coal technologies and adopting these in varying technological applications to implement solution focused mechanisms and strategies for government, society and industry.
Written by: Taimoor Ahmed (Executive Publications NUST Science Society)
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