Coal is the largest source of electricity supply in the world with 41% of the global power coming from the burning of coal.The Pros of Coal have made the growth of Thermal Power Plants accelerate in developing countries like China and India.This has made Coal Stocks run up by more than 150% in 2010 and  another 30% in 2010.With little alternative in terms of a cheap energy choice,Steel Makers,Power Utilities are rushing to secure Coal Mines by buying them up.This has led to a steep increase in the price of coal and it does not look like it will come down anytime soon.However Coal is also the greatest contributor to Greenhouse Gas Emissions.Coal is also responsible for thousands of deaths directly and indirectly due to Coal Mining and Coal Combustion which leads to waste products like Mercury,Arsenic etc which are extremely toxic to human health.To solve the  problems of getting cheap energy without global warming, a number of technologies have been been proposed which would reduce the harmful effects of Coal combustion..These are known as Clean Coal Technologies and a number of private companies are engaged in their development.However sceptics have dismissed Clean Coal as nothing but putting lipstick on the Carbon Pig.Here is a list of Clean Coal Technologies and Processes

Clean Coal Technoly in Coal Mining

Coal Washing – Coal Washing is a method of reducing the amount of ash in raw coal which helps in efficient combustion and increases the energy content per ton. It also reduces the sulphur content in coal in order to decrease the production of sulphur dioxide which is harmful to the environment.

Methane Gas Capture – Reducing greenhouse gas emissions during mining by capturing methane gas and using it to provide power for input to the electricity grid

Underground Coal Gasification (UCG) – In the UCG process, water/steam and air or oxygen are injected into a coal seam. The injected gases react with coal to form a combustible gas which is brought to the surface and cleaned prior to utilisation.

Clean Coal Technologies used During Combustion

Combined Heat and Power (CHP) involves the use of a steam turbine which is designed not only to drive a generator, but also to produce steam or hot water. It can provide power more efficiently and economically where there is a steady demand for the heat.They incorporate turbines which are specially designed to provide flexibility in operation, so that they can be run solely to provide power (for example if district heating is not required) or to provide a consistent and secure supply of steam (for example to an industrial plant) while also generating power.

Fluidised-Bed Combustion (FBC) –FBC reduces emissions of SO2 and NOx by the controlled combustion of crushed coal in a bed fluidised with jets of air. Sulphur released from coal as SO2 is absorbed by a sorbent such as limestone, which is injected into the combustion chamber along with the coal. Around 90% of the sulphur can be removed as a solid compound with the ash. FBCs operate at a much lower temperature than conventional pulverised coal boilers, greatly reducing the amount of thermal NOx formed.

Integrated Gasification Combined Cycle (IGCC) – IGCC  involves gasification of coal  cleaning the gas produced, and combusting it in a gas turbine to produce electricity. Residual heat in the exhaust gas from the gas turbine is recovered in a heat recovery boiler as steam, which can be used to produce  additional electricity in a steam turbine generator.Sulphur, nitrogen compounds, and particulates are removed

Use of Supercritical Boilers,Efficient Coal Combustion Technology – Developed countries use Thermal Power Plants with higher efficiency of around 36% compared to around 30% in Developing Countries.This means that the Coal Power Plants burn more Carbon Dioxide per Kwh in Developing Countries.India and China have started building mega power plants using supercritical boiler technology which burns coal more efficiently.Some of these UMPPs have even gotten carbon credits from UN CDM council drawing criticism from green activists

Clean Coal Technologies used During Emission

Particulate emissions control technologies – Primary particulate matter is generated by a variety of physical and chemical processes. During coal combustion, the mineral matter (inorganic impurities) is converted to ash. Part of the ash is discharged from the bottom of the furnace as bottom ash. The particles suspended in the flue gas are known as fly ash.The technologies used to control this use filters,electrostatic,mechanical and thermal techniques

Flue gas desulfurization – This technology is used to control the emission of Sulphur Dioxide which is emitted during combustion of the sulphur found in coal as impurity.Scrubbers and other process are used in this method.

Low NOx Burners – These 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.

Ultra-clean coal (UCC) – New processing technologies which reduce ash below 0.25% and sulfur to very low levels mean that pulverised coal might be used as fuel for very large marine engines, in place of heavy fuel oil.  There are at least two UCC technologies under development.

Clean Coal Technologies used post Combustion

Carbon Capture and Storage (CCS) – As the name implies,these technologies try and capture the carbon which is emitted during emission of Coal.The Coal is then stored in underground caverns or Oil Wells.However the technical feasibility of various CCS approaches  have been found to be unworkable.Many grants have been given by the government but it is a technology still in the far future.

Summary

Despite a number of Clean Coal Technologies being developed and employed,carbon emissions from Coal Ming and Use can only be partly reduced and will not make a major impact on the problem of Climate Change.Clean Coal Technology is not a Green Solution to the Disadvantages of Coal.Saying that implementing Clean Coal Technology will result in Climate Change Mitigation is Greenwashing.That said these technologies need to be implemented till the world is ready to move away from its addiction to cheap energy provided by Coal even though it has a deleterious long term affect.