Coal, as a source of energy, is firmly out of favour now due to climate change considerations. Most countries, including India, have plans to phase out coal over the next few decades. India, in fact, has officially announced that it would not set up any new coal-fired power plants after 2022. Show
However, we still have to live with coal for some more time at least. In spite of the rapid increase in power generation from renewable sources like wind and solar, over 60% of India’s electricity is still generated in thermal power plants. And it is estimated that even in the best-case scenario, coal would continue to be the mainstay of India’s energy mix for at least three more decades. Efforts are on to ensure that pollution emanating from coal is at least reduced a bit in these intervening years. A variety of “clean coal technologies” is being deployed or experimented with to realise the objective. The modern “super-critical” power plants also emit lesser pollutants. Follow @ieexplained The varieties of coal found in India have an additional problem. They have high ash content. Burning coal in the conventional pulverised mode results in the release of a lot of fly ash, a major contributor to air pollution and a health hazard. Several techniques have been put in place to capture this fly ash after it is produced, but they are not very efficient. Alternatively, coal is passed through an extensive “pre-processing” process called “washing” to remove some of the ash content before it is burnt, which is also not very effective. A group of researchers at IIT Madras has now come up with a more effective way of managing this problem. Apart from ensuring that the ash is removed as chunks from the reactor bed itself, their procedure reduces the formation of CO2, and instead generates synthetic gas (syngas), which is a mixture of clean fuel gases like carbon monoxide and hydrogen, as by-products which can then be put to a variety of uses. The group utilised a well-known coal gasification technique in which coal is only partially burnt with a very limited supply of oxygen in the ‘bubbling fluidized bed gasification reactor’. At about 100 degree celsius, all moisture from the coal is drained out. At higher temperatures, between 300 and 400 degree celsius, gaseous fuels trapped inside coal, like nitrogen, methane and a mixture of many other hydrocarbons, are released. When temperatures reach between 800-900 degree celsius, the carbon in the coal starts reacting with oxygen in the air, as well as steam supplied along with air, to form carbon monoxide (CO), hydrogen and carbon dioxide (CO2). By controlling the amount of air and steam, it can be ensured that significant amounts of carbon monoxide (CO) and hydrogen (H2) are formed. Production of CO2, which is a greenhouse gas, can be minimized. Careful systematic studies have been conducted to arrive at the regime of operation, air to coal and steam to coal ratios. It has been found that the addition of steam becomes favourable in the case of high-ash Indian coals. Therefore, optimized performance can be established in the case of Indian coal by following this operational procedure. In fact, this technique can be extended to produce syngas of high calorific value by enhancing the oxygen content in the oxidizer, and the H2 to CO ratio can be improved by adding steam in appropriate quantities. The researchers also showed that adding biomass, like rice husk along with Indian coal imparts catalytic effect and improves the gasification performance significantly. Vasudevan Raghavan, one of the researchers associated with the experiment, said that the process would improve the attractiveness of Indian coal for use in power plants. Coal is cheaply available in India in very large quantity, but it is not preferred due to the high ash and low energy content. Raghavan added that existing power plants would need to replace their traditional reactors with gasification reactors, and operate them as illustrated by his team to take advantage of this procedure. In Indian coal mine mouths, such gasification reactors can be established to take care of rural power needs.
Published Jul 28, 2008 Updated Dec 19, 2017
Air pollution from coal-fired power plants is linked with asthma, cancer, heart and lung ailments, neurological problems, acid rain, global warming, and other severe environmental and public health impacts.
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Coal is an abundant fuel source that is relatively inexpensive to produce and convert to useful energy. However, producing and using coal affects the environment. Effects of coal miningSurface mines (sometimes called strip mines) were the source of about 64% of the coal mined in the United States in 2020. These mining operations remove the soil and rock above coal deposits, or seams. The largest surface mines in the United States are in Wyoming's Powder River Basin, where coal deposits are close to the surface and are up to 70 feet thick. Mountaintop removal and valley fill mining has affected large areas of the Appalachian Mountains in West Virginia and Kentucky. In this form of coal extraction, the tops of mountains are removed using explosives. This technique changes the landscape, and streams are sometimes covered with rock and dirt. The water draining from these filled valleys may contain pollutants that can harm aquatic wildlife downstream. Although mountaintop mining has existed since the 1970s, its use became more widespread and controversial beginning in the 1990s. U.S. laws require that dust and water runoff from areas affected by coal mining operations must be controlled, and the area must be reclaimed close to its original condition.
Underground mines generally affect the landscape less than surface mines. However, the ground above mine tunnels can collapse, and acidic water can drain from abandoned underground mines. Methane gas that occurs in coal deposits can explode if it concentrates in underground mines. This coalbed methane must be vented out of mines to make mines safer places to work. In 2019, methane emissions from coal mining and abandoned coal mines accounted for about 8% of total U.S. methane emissions and about 1% of total U.S. greenhouse gas emissions (based on global warming potential). Some mines capture and use or sell the coalbed methane extracted from mines. Emissions from burning coal
In the past, fly ash was released into the air through the smokestack, but laws now require that most emissions of fly ash be captured by pollution control devices. In the United States, fly ash and bottom ash are generally stored near power plants or placed in landfills. Pollution leaching from coal ash storage and landfills into groundwater and several large impoundments of coal ash that ruptured are environmental concerns. Reducing the environmental effects of coal useThe Clean Air Act and The Clean Water Act require industries to reduce pollutants released into the air and water. The coal industry has found several ways to reduce sulfur and other impurities from coal. The industry has also found more effective ways of cleaning coal after it is mined, and some coal consumers use low sulfur coal. Power plants use flue gas desulfurization equipment, also known as scrubbers, to clean sulfur from the smoke before it leaves their smokestacks. In addition, the coal industry and the U.S. government have cooperated to develop technologies that can remove impurities from coal or that can make coal more energy efficient, which reduces the amount of coal that is burned per unit of useful energy produced. Equipment intended mainly to reduce SO2, NOx, and particulate matter can also be used to reduce mercury emissions from some types of coal. Scientists are also working on new ways to reduce mercury emissions from coal-burning power plants. Research is underway to address emissions of CO2 from coal combustion. One method is carbon capture, which separates CO2 from emissions sources and recovers it in a concentrated stream. The CO2 can then be injected underground for permanent storage, or sequestration. Reuse and recycling can also reduce the environmental effects of coal production and use. Land that was previously used for coal mining can be reclaimed and used for airports, landfills, and golf courses. Waste products captured by scrubbers can be used to produce products such as cement and synthetic gypsum for wallboard. Last updated: December 2, 2021 |
Ii. describe one method to reduce the air pollutants released from a coal-burning power plant.
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