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Thursday, May 22, 2008

Clean coal technology (CCT) – To mitigate Global warming and climate change - A discussion



Clean coal technology (CCT) – To mitigate Global warming and climate change - A discussion

Coal when burned is the dirtiest of all fossil fuels. A range of technologies are being used and developed to reduce the environmental impact of coal-fired power stations. Thus, clean coal technology (CCT) is the name attributed to coal chemically washed of minerals and impurities, sometimes gasified, burned and the resulting flue gases treated with steam with the purpose of removing sulfur dioxide, and reburned so as to make the carbon dioxide in the flue gas economically recoverable.

A. It is a known fact that, the burning of coal, a fossil fuel, is the principal causes of anthropogenic climate change and global warming. In fact, the byproducts of coal combustion are very hazardous to the environment if not properly contained. This is seen to be the technology's largest challenge, both from the practical and public relations perspectives. While it is possible to remove most of the sulfur dioxide (SO2), nitrogen oxides (NOx) and particulate (PM) emissions from the coal-burning process, carbon dioxide (CO2) emissions will be more difficult to address. Therefore, fact regarding the coal remains:

(a) Coal is a vital fuel in most parts of the world.

(b) Burning coal without adding to global carbon dioxide levels is a major technological challenge which is being addressed.

(c) The most promising "clean coal" technology involves using the coal to make hydrogen from water, then burying the resultant carbon dioxide by-product and burning the hydrogen.

(d) The greatest challenge is bringing the cost of this down sufficiently for "clean coal" to compete with nuclear power on the basis of near-zero emissions for base-load power.

B. In relation to clean coal technology, a terminology ‘carbon capture and storage’ (CCS) is being discussed. CCS is nothing but method of capturing the carbon dioxide, preventing the greenhouse gas entering the atmosphere, and storing it deep underground by various ways, such as

(a) CO2 pumped into disused coal fields displaces methane which can be used as fuel,

(b) CO2 may be pumped into and stored safely in saline aquifers, or

(c) CO2 pumped into oil fields helps maintain pressure, making extraction easier.

A range of approaches of CCS have been developed and have proved to be technically feasible. They have yet to be made available on a large-scale commercial basis because of the costs involved.

C. Clean coal technologies are continually developing. Today, efficiencies of 46% can be achieved by implementing the best available technology. With further research into techniques such as Ultra-supercritical combustion, efficiencies above 50% are envisaged in the near future. Work is underway to exploit the opportunities of capturing and storing CO2, which is an inevitable by-product of the thermal use of all fossil fuels. Coupled with integrated gasification, coal could in this way provide a source of low-carbon hydrogen for fuelling transport without producing local emissions. There will be challenges in bringing these technologies to market, but with the right mix of research investment and market incentives, coal may stake a place in a sustainable and secure energy future.

D. To summarise, burning coal, such as for power generation, gives rise to a variety of wastes which must be controlled or at least accounted for. So-called "clean coal" technologies are a variety of evolving responses to late 20th century environmental concerns, including that of global warming due to carbon dioxide releases to the atmosphere. However, many of the elements have in fact been applied for many years, and they will be only briefly mentioned here:

(i) Coal cleaning by 'washing' has been standard practice in developed countries for some time. It reduces emissions of ash and sulfur dioxide when the coal is burned.

(ii) Electrostatic precipitators and fabric filters can remove 99% of the fly ash from the flue gases - these technologies are in widespread use.

(iii) Flue gas desulfurisation reduces the output of sulfur dioxide to the atmosphere by up to 97%, the task depending on the level of sulfur in the coal and the extent of the reduction. It is widely used where needed in developed countries.

(iv) Low-NOx burners allow coal-fired plants to reduce nitrogen oxide emissions by up to 40%. Coupled with re-burning techniques NOx can be reduced 70% and selective catalytic reduction can clean up 90% of NOx emissions.

(v) Increased efficiency of plant - up to 45% thermal efficiency now (and 50% expected in future) means that newer plants create less emissions per kWh than older ones.

(vi) Advanced technologies such as Integrated Gasification Combined Cycle (IGCC) and Pressurised Fluidised Bed Combustion (PFBC) will enable higher thermal efficiencies still - up to 50% in the future.

(vii) Ultra-clean coal from new processing technologies which reduce ash below 0.25% and sulfur to very low levels mean that pulverised coal might be fed directly into gas turbines with combined cycle and burned at high thermal efficiency.

(viii) Gasification, including underground gasification in situ, uses steam and oxygen to turn the coal into carbon monoxide and hydrogen.

(ix) Sequestration refers to disposal of liquid carbon dioxide, once captured, into deep geological strata.

E. Discussion - Many experts think, the concept of clean coal is said to be a solution to climate change and global warming. Whereas, environmental groups believe it is nothing but another way of making everybody fool, in other words, it is ‘green-wash’. Environmentalists say, with this technology emission and wastes are not avoided, but are transferred from one waste stream to another. They opine that, coal can never be clean. Critics of the planned power plants assert that there is no such thing as "clean coal" and that the plant will still release large amounts of pollutants compared to renewable energy sources such as wind power and solar power. A good deal of investment in research and development and also in implementation of pollutant free renewable energy (such as wind power and solar power) has to augmented, to make the world very clean, to make the required electricity generation fully green.

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