Mining of coal is one of the most destructive activity for the environment. Whatever the method of mining be—opencast or underground, green fields and forests cannot remain untouched. Since one has to rip off the surface layer to gain access beneath, a cavity results during and after mining. When monsoon rains fill these up, the waters percolate through resulting in land subsidence. Moreover, when there is underground mining, once the coal is exhausted and supports withdrawn, the soil caves in causing a depression. Mining often changes the hydrological regime of regions, affecting the courses of local streams and minor rivers. Underground mining can extend up to aquifers and can hamper their normal functions, thus causing ponds to dry up and rivers to divert. Topographical changes, landslides, loss of valuable agricultural land and lush vegetation are all a part and parcel of the mining process. Additionally, mining of coal exposes the region to the danger of devastating coal seam fires, sometimes naturally through spontaneous combustion caused by the friction between gases in mines, and at others, induced by man.
Coal Mine Hazards
Firedamp present in mines containing bituminous coal have been historically known to cause explosions and hence, miners’ deaths. Firedamp is the name given to the group of inflammable hydrocarbons, prominently comprising methane, found in mines Firedamp accumulates in pockets in the coal and adjacent strata, and when penetrated, can trigger explosions. Variations of firedamp are ‘black damp’ which is a mix of carbon dioxide and nitrogen caused by corrosion, ‘after damp’ which includes the same gases as a black damp, plus carbon monoxide, and ‘stink damp’, which reeks of rotten eggs, and is mostly hydrogen sulphide. Each of these can explode and cause accidental deaths. ‘White damp’, is another major variation which is totally indiscernible since it lacks a scent, but contains carbon monoxide, and can be toxic at even low concentrations, causing death.
At times, digging for coal can result in a wrong blow hitting a groundwater aquifer. This results in the punctured water table giving way, flooding the mine and killing thousands at one go.
Even otherwise, dusts in mines have a high amount of suspended particulate matter (SPM), which, along with other gaseous hydrocarbons, especially methane and ethane, make a volatile composition. This exposes miners to the risk of respiratory and bronchial ailments, as also cancer.
The processing of coal is another very polluting affair. After being mined, coal requires to be washed with water sourced from rivers, ponds, or lakes. The water that flows into the washeries and the water that flows out are vastly different in composition. Apart from the dust and the grime which covers coal, several other chemicals invisible to the eye dissolve in the water. Sulphates of ammonia, sulphur dioxide, carbon monoxide, methane and various other hydrocarbons are released from the washeries into local water sources. Consequently, Damodar, which flows through the coal producing Chhotanagpur plateau spread over Jharkhand and West Bengal, is one of the most polluted rivers in India.
If mining is not done scientifically, or safety measures ignored, coal seam fires can result. Once ignited such a fire can burn for decades or centuries, until the entire coal reserve is exhausted. Such a fire remains unmonitored and can be extremely dangerous. It can cause land subsidence and kill by suffocation and exposure to toxic gases. In the Indian context pollution from burning coal has become a matter of grave concern. Thermal power plants are the main source of such pollution as 80 per cent of the power generated by India’s thermal power plants is coal-based.
After being treated in washeries, the coal is readied for use in the power, and other sectors. The combustion of coal, particularly in thermal power, results in four major components being emitted—SOx, NOx, suspended particulate matter and carbon monoxide.
Flyash, which is generated on combustion of coal, is a major source of worry, particularly since Indian coal has more than 45 per cent ash content. At the moment, India’s coal based thermal power plants produce more than 112 million tonnes of flyash, for which 65000 acres is being used for dumping. By 2017, the amount of flyash is expected to cross 225 million tonnes.
I Nawaz, in an article, ‘Disposal and utilisation of flyash to protect the environment’, in the International Journal of Innovative Research in Science, Engineering and Technology, (October 2013), points out, “When pulverized coal is burnt to generate heat, the residue contains 80 per cent flyash and 20 per cent bottom ash”. Being just 0.5 -300 micron in diameter, and lightweight flyash particles are easily airborne and can hence pollute the environment.
Flyash dumps are always lined in the US, and kept moist. Since such lining is not done in India, flyash can seep through and severely pollute water by blocking the air spaces in the soil apart from causing siltation. Flyash turns soils acidic, and can mar soil fertility. It also interferes with the photosysnthesis of aquatic plants, and affects the food chain.
The Central Electricity Authority (CEA) which manages thermal power plants has issued directives for 100 per cent utilisation of flyash through recycling and other uses. However, it recently took several defaulting power plants to task for not having done so.
Tackling Flyash through Technology
For several years, flyash has been used as landfills. Of late, flyash bricks are becoming popular as a building material. This technology, developed by Indian Institute of Technology (IIT), Delhi, involves replacing flyash for cement in mortar. Flyash bricks have been successfully used for the construction of roads and embankments in the country and the technology is gaining ground.
The Energy Research Institute (TERI) has proven that flyash dumps can be reclaimed by adding organic matter and symbiotic fungi, making them commercially viable for floriculture and silviculture. An ash pond at the Badarpur Thermal Power Station has been reclaimed using mycorrhizal fungi based organic biofertilizer. As the fungus germinates, it sustains the partner plant and quickly spreads to the roots and beyond, improving the plant’s water and nutrient intake, storing carbohydrates and oils for use when needed, protecting the plant from disease, and detoxifying contaminated soils. This keeps both air and water pollution under control. The demonstration site at the Badarpur power station now grows marigold, tuberose, gladioli, sunflower, and carnations apart from trees such as Indian rosewood, poplar and eucalyptus.
Being rich in oxides, flyash has been found suitable for agricultural applications as well, and is fast gaining acceptability among farmers.
The National Thermal Power Corporation (NTPC) has also developed a dry ash technology, wherein flyash is collected in huge mounds, and a filter bed is provided at the bottom (of each mound). Grass is then planted on the slopes of the mounds and a polymer layering is provided to prevent the ash from being blown off by the wind. Flyash thus treated develops certain physical properties that make it more suitable for commercial use.
Liquid Coal vs Petroleum
Coal-to-liquid (CTL) technology or the ‘Fischer-Tropsch’ technology offers a range of important environment friendly synthetic fuels and products produced by liquefying coal.
The technology was first developed in the 1920’s by German scientists at the Kaiser Wilhelm Institute. The process became known as ‘Fischer-Tropsch Synthesis’ after its creators, chemists Franz Fischer and Hans Tropsch. During World War II, Fischer-Tropsch fuels were used to power planes and tanks for the German army.
In this method, coal is fed into a gasifier. Within the gasifier, controlled amounts of heat, pressure and oxygen are added to break up the molecular structure of the coal. The gasifier only allows a portion of the coal to burn, resulting in the partial oxidation of the coal. This reaction produces carbon monoxide and hydrogen rich synthesis gas.
Synthesis gas, or syngas, is then fed into a reactor where it is condensed over a catalyst, which is typically iron or cobalt. The exposure to the catalyst converts the syngas into liquid and wax products that can be refined into synthetic fuels.
CTL fuels can be used to run a variety of vehicles including cars, trucks, tanks and jets, while the waxes produced may be stored indefinitely. Depending on the catalyst and conditions in the reactor, CTL products vary in density, composition and prospective use. Excess steam from the gasification process can be used to produce electricity.
With CTL technology, emissions are removed before the fuel is burned. Because coal gasification uses oxygen rather than air to produce syngas, the resulting gas stream is smaller, and emissions from it can be stripped off easily and efficiently. Hence, the resulting fuel products are clean. CTL diesel, for example, is sulphur free.
At the moment, scientists are trying to limit the production of carbon dioxide, which is released when the coal is liquefied and again, when CTL fuel is burned. There are several methods of carbon dioxide capture and sequestration that are under development. These processes and technologies would capture and condense carbon dioxide during coal gasification, and then store it safely in underground structures such as saline aquifers. The captured carbon dioxide could then be sold to oil companies to increase oil field yield by injecting it into depleted oil wells. However, building a CTL plants can cost billions of dollars, and investors are not yet forthcoming.
Central Mine Planning and Design Institute (CMPDI) is planning to put its first coal-to-liquid research project in Digwadi, Dhanbad, by August 2015, in collaboration with Central Institute of Mines and Fuel Research. Speaking with the G’nY correspondent, Prabhat Shanker, General Manager, CMPDI said, “our research is focussed on finding the right catalyst for India’s bituminous, so that the process is extremely cost effective.” He claims that once the breakthrough is made and costs ascertained, not only will petroleum become easily accessible and perhaps cheaper, but it will also reduce the environmental repercussions of burning coal. The future, thus, could prove bright for this technology which is being seen as the best modification to a polluting, but indispensable fossil fuel.
Notwithstanding its polluting nature and processes involved, coal remains the cheapest and most abundant fuel for meeting India’s energy needs. Although the government has been exploring alternatives such as renewable sources to produce green energy, these are still expensive. At the same time, hydroelectricity and nuclear power have environmental and safety aspects that are difficult to ignore. The answer hence, lies, in working towards cleaner coal-based technology to minimise health hazards from the processes involved in mining and processing coal for thermal power generation.