Clean coal technology

CA 09/09/2015

Current Scenario

Half of the world’s electricity is generated by burning coal.
Coal will remain a dominant energy source for years to come.
Since CO2 contributes to global warming, reducing its release into the atmosphere has become a major international concern.

CO2 and CO (carbon monoxide) are the major greenhouse gas which are released during burning of coal.
Along with the above gases, nitrogen oxides (destroys ozone) and sulphur oxides (acid rains) are also released.

Coal mined in India is a poor quality coal with less carbon, high ash (hard to dispose) and high moisture content (more gases; less fuel efficiency) [India’s coal is not Carboniferous Coal].
To improve efficiency and reduce adverse effects, India should do away with its present sub-critical coal power plants and build more super-critical and ultra-super-critical ones (15-20% increase in efficiency).

Clean coal technology seeks to reduce harsh environmental effects by using multiple technologies to clean coal and contain its emissions.
Some clean coal technologies purify the coal before it burns. One type of coal preparation, coal washing, removes unwanted minerals by mixing crushed coal with a liquid and allowing the impurities to separate and settle.
Other systems control the coal burn to minimize emissions of sulfur dioxide, nitrogen oxides and particulates.
Electrostatic precipitators remove particulates that aggravate asthma and cause respiratory ailments by charging particles with an electrical field and then capturing them on collection plates.
Gasification avoids burning coal altogether. With gasification, steam and hot pressurized air or oxygen combine with coal in a reaction that forces carbon molecules apart. The resulting syngas, a mixture of carbon monoxide and hydrogen, is then cleaned and burned in a gas turbine to make electricity.
Wet scrubbers, or flue gas desulfurization systems, remove sulfur dioxide, a major cause of acid rain, by spraying flue gas with limestone and water.
Low-NOx (nitrogen oxide) burners reduce the creation of nitrogen oxides, a cause of ground-level ozone, by restricting oxygen and manipulating the combustion process.

Carbon capture and storage -- perhaps the most promising clean coal technology -- catches and sequesters carbon dioxide (CO2) emissions from stationary sources like power plants.
Flue-gas separation removes CO2 with a solvent, strips off the CO2 with steam, and condenses the steam into a concentrated stream. Flue gas separation renders commercially usable CO2, which helps offset its price.
After capture, secure containers sequester the collected CO2 to prevent or stall its reentry into the atmosphere.
The two storage options, geologic and oceanic, must contain the CO2 until peak emissions subside hundreds of years from now.
Geologic storage involves injecting CO2 into the earth. Depleted oil or gas fields and deep saline aquifers safely contain CO2 while unminable coal seams absorb it. A process called enhanced oil recovery already uses CO2 to maintain pressure and improve extraction in oil reservoirs.
Ocean storage, a technology still in its early stages, involves injecting liquid CO2 into waters 500 to 3,000 meters deep, where it dissolves under pressure. However, this method would slightly decrease pH and potentially harm marine habitats.
Cleaning coal and sequestering its emissions significantly raises the per-BTU price of what would otherwise be an inexpensive fuel. While selling byproducts like gypsum or commercial CO2 for sodas and dry ice can offset the price of clean coal technologies, a charge on carbon could make emission-reduction financially realistic.

Carbon sequestration is the process of capture and long-term storage of atmospheric carbon dioxide (CO2)
It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases
Carbon dioxide is naturally captured from the atmosphere through biological, chemical, or physical processes.

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