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Here is a compilation of essays on ‘Coal’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Coal’ especially written for school and college students.
Essay on Coal
Essay Contents:
- Essay on the Introduction to Coal
- Essay on Coal Reserves
- Essay on Coal Production and Demand
- Essay on Coal Mining Practices
- Essay on Coal Quality
- Essay on Environmental Issues in Coal Mining
- Essay on Environmental Issues in Coal Based Power Generation
- Essay on the Benefits of Beneficiated Coal
- Essay on the Options for Beneficiation of Coal
- Essay on Clean Coal Combustion Technologies
Essay # 1. Introduction to Coal:
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Among the fossil fuels, coal has acquired the dubious distinction of being the dirtiest one. Such an attribute is on account of environmental damage and pollution problems caused during mining, processing, end use and wastes of coal.
Land subsidence in underground mines, ugly scars of land in abandoned open cast mines, emissions of fly ash during combustion of coal and huge quantities of ash generated from boilers of coal based power plants and industrial houses are among the hosts of problems associated with handling and use of coal. Emission of carbon dioxide, an important component of “Greenhouse Gases” (GHGs) and global warming is yet another emerging concern linked with burning of coal.
Essay # 2. Coal Reserves:
India with 2.7 percent of the world reserves ranks sixth in the world in coal resources, occurring in Gondwana and tertiary formations. The Gondwana coals are largely confined to river valleys such as the Damodar (West Bengal and Bihar), Mahanadi (Orissa), and Godavari (Maharashtra and Andhra Pradesh). Coal fields of Assam of Jaintia and Barail series belong to the Tertiary age. The lignite deposits of Jammu and Kashmir, Kerala, Tamil Nadu and Gujarat are also of the Tertiary age.
Most of the coal reserves in India are concentrated in the peninsular part within 78 to 88 degrees East longitude and 22 to 24 degrees North latitude. As per Geological Survey of India, the estimated coal reserves, down to a depth of 1,200 metre, stood at 208751.5 million tonnes as on 1.1.99.
Of these estimated reserves, down to a depth of 1,200 meters, which is considered economically viable are 90 percent of the total reserves. About 83 percent of total resources are non-coking coals and 14 percent belongs to coking coals.
Essay # 3. Coal Production and Demand:
Coal production in India sharply increased from 30 million tonnes in 1940 to over 290 million tonnes in 1998-99. Now, India ranks 3rd amongst the coal producing countries in the World. About 70 percent of total production is used by the power generation sector while steel and cement are also among the major consumers.
Essay # 4. Coal Mining Practices:
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India’s total land area is 3.29 million sq. km. and within this only 0.45% area (about 16,000 sq. km) is coal hearing. Out of this coal bearing area, active coal mining area is about 2500 sq. km. Maximum land degradation in coal mining is caused by open-cast mining and it is currently confined to 20% of the coal bearing land.
Additional areas that could be used for open-cast mining would be around 5 to 10% of the coal bearing land. Thus, the area where land degradation has taken place and is likely to take place is around 0.2% of the land mass.
Underground production of coal peaked in the late seventies and has fallen slowly since then. Surface mining, on the other hand, has soared from 16 to 160 million tonnes per annum. Of the 588 mines in India, 355 are underground, but opencast accounts for 75 percent of production and employs only 16 percent of the total mining work force. Productivity is higher in the opencast sector.
However, the pace of growth cannot be sustained for long, as stripping ratios will increase and mining operations run into land access and other environmental problems. Underground mining is largely a ‘board and pillar’ operation. Long-wall was introduced in 1978 and by 1993, 20 long-wall units were installed.
Essay # 5. Coal Quality:
The quality of Indian coal is mainly attributed to its origin. Due to drift origin of Indian coal, inorganic impurities are intimately mixed in the coal matrix, resulting in difficult beneficiation characteristics. Over 200 million tonnes of coal reach the consumers with ash content averaging 40 percent. Based on ash content, gross calorific value and useful heat value, Indian coal is classified in six categories.
Sulphur content in Indian coal is generally less than 0.6 percent and the Chlorine content is less than 0.1 percent. Mercury in coal ranges from 0.01 to 1.1 ppm in Indian coals against upto 20 ppm in Russian coals, 0.2 to 2.0 ppm in Belgium coals, 0.03 to 1.3 ppm in Canadian coals and 0.01 to 2.0 ppm in American coals.
Essay # 6. Environmental Issues in Coal Mining:
i. Air Pollution:
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Air pollution in coal mines is mainly due to the fugitive emission of particulate matter and gases including methane, sulphur dioxide and oxides of nitrogen. The mining operations like drilling, blasting, movement of the heavy earth moving machinery on haul roads, collection, transportation and handling of coal, screening, sizing and segregation units are the major sources of such emissions. Under-ground mine fire is also a major source of air pollution in some of the coal fields.
High levels of suspended particulate matter increase respiratory diseases such as chronic bronchitis and asthma cases while gaseous emissions contribute towards global warming besides causing health hazards to the exposed population.
ii. Emission of Methane (CH4):
Methane emission from coal mining depends on the mining methods, depth of coal mining, coal quality and entrapped gas content in coal seams.
Degree I:
A seam in which the inflammable gas in the general body of air at any place in the underground working exceeds 0.1 % and rate of emission of gas is less than 1 m3 per tonne of coal mined.
Degree II:
A seam in which the inflammable gas in the general body of air at any place in the underground working exceeds 0.1% and rate of emission of gas is less than 1 m3 per tonne of coal mined or rate of emission of gas 1 m3 per tonne or more but less than 10 m3 per tonne of coal mined.
Degree III:
A seam in which the rate of emission of gas in more than 10 m3 per tonne of coal mined.
iii. Land Degradation:
As much 1, 40,771 hectares of total land covered under surface mining. Additionally 57,000 hectares of land will be required of which 13,000 hectares are in forest land.
Essay # 7. Environmental Issues in Coal Based Power Generation:
Seventy percent of total installed capacity of electricity generation in the country is from coal based thermal power plants. Increased dependence of power sector on the inferior quality of coal has been associated with the emissions from the power plants in the form of particulate matter, toxic elements, fly-ash, oxides of nitrogen, sulphur and carbon besides large volume of water for cooling and land requirement for ash disposal. Only twenty percent of total coal transported to the power plants is of superior grade with ash content 24% or less and remaining eighty percent is of inferior grade with ash ranging from 24 to 45 percent.
During 1998-99, the power stations consumed 208 million tonnes of coal, which in turn produced 80 million tonnes of ash. Mainly 80% of this ash is in the form of fly-ash and balance 20% in the form of bottom ash. Supply of high ash laden coal to power plants not only poses environmental problems but also causes poor plant performance and high cost for O&M and ash disposal.
The Ministry of Environment & Forests, Govt., of India constituted a Committee headed by the Chairman, Central Pollution Control Board (CPCB), to suggest the measures for improving the quality of coal supplied to the power plants.
On the recommendation of the Committee, Govt. of India has promulgated a Gazette Notification on use of beneficiated/blended coal containing ash not more than 34 percent w.e.f. June 2001 in the following power plants:
i. Power plants located beyond 1000 kms from pit head;
ii. Power plants located in critically polluted areas, urban areas and in ecologically sensitive areas.
The power plants using FBC (CFBC, PFBC & AFBC) and IGCC combustion technologies are exempted to use beneficiated coal irrespective of their locations.
Essay # 8. Benefits of Beneficiated Coal:
One of the solutions to the problems associated with the use of inferior grade coal is beneficiation for reduction in ash content. This will not only reduce the ash content to required level but also enrich the coal with reactive materials for better thermal efficiency, plant availability and plant output thereby reducing operating/maintenance costs, load on transport system and oil support in boiler.
Following are some of the benefits of using washed coal:
i. Increased generation efficiency, mainly due to the reduction in energy loss as less inert material passes through the combustion process;
ii. Increased plant availability;
iii. Reduced investment costs due, as an example, to reduced costs for fuel and ash handling equipment;
iv. Reduced operation and maintenance (O & M) costs due to less wear and reduced costs for fuel and ash handling;
v. Energy conservation in the transportation sector and lower transportation costs;
vi. Less impurities and a more even coal quality;
vii. Reduced load on the particulate removal equipment in existing plants; and
viii. Reduction in the amount of solid waste that has to be taken care of at the plant.
According to the Central Fuel Research Institute, Dhanbad, if the entire power coals which are to be transported over 1000 kms in the year 2001-02 are washed and the ash level is brought down from 40 to 34%, it is likely to reduce 11 million tonnes in transport, 8 million tonnes fly ash and 23 million tonnes of carbon dioxide (a greenhouse gas) emissions.
There is a general recognition that improvements in the quality of coal utilized in power generation would not only reduce environmental pollution but also lead to improvements in power plant operational efficiencies.
Coal preparation has been the subject of various studies and pilot plant tests carried out by Indian and International Institutions. These studies have highlighted that, in the majority of cases, it is technically feasible and economically viable to reduce the ash content of raw coal to 32-34% range, with net benefits to power plants.
Essay # 9. Options for Beneficiation of Coal:
i. Blending of Selected Raw Coals with Clean Products:
As most of the washeries are used to get feed from multiple sources, the process which was once applied to coking coal beneficiation seems least promising.
ii. Mixing the Untreated Smaller Fractions with Beneficiated Coarse Coal Fractions of a Raw Coal Feed
As is practised in Piparwar and Bina washeries. Earlier studies at CFRI on the washability characteristics of some non-coking coals showed that the amount of free dirt/sand having relative density greater than 1.80-1.85 may be very high. About 20-45% of the finer fractions (5-10% of the whole coal) that is included in the prepared coal enhance the wear and tear of the boiler tubes and auxiliary units.
iii. Blending the Low Ash Foreign Coal (Raw/Clean) with Raw Indigenous Coal of High Ash:
Mixing of one tonne of imported coal of 10% ash content with 4 tonnes of Indian coal at ash level 40% results in a blend of 34% ash content. Though not practised in general, this may be an option in near future, particularly for the thermal power stations in coastal areas.
The reduction in import duty on thermal coal from 85percent in 1993-1994 to 10% in 1997-1998 has been an incentive for import of coal particularly for the coal based power stations. However, blending of coals of widely different ranks may cause undesirable differential combustion behaviour in the burners, which need to be taken into account during blending of coal.
iv. Mixing of Coarser and Finer Size Beneficiated Coal:
With the advent of modern High Capacity Processor (HCP) including efficient cyclone circuit, it is possible to commission 350-600 tonne per hour washing system for beneficiation of both coarse and intermediate fractions. In the economic analysis for the Bilaspur Coal Washery Project, despite limitations in density of separation, the H.M. Cyclone was found to more efficient than the jigs.
In first two cases, the desired overall ash content and the level of moisture content are maintained but the quality of the washed coal in terms of its end utilization in power stations may not be always assured. Washing of such coals down to an ash level of 34% reduces the transport cost and environmental pollution.
However, it may not assure quality of the washed coal in terms of combustion behavior. Beneficiation of the finer fractions becomes one of the important considerations in the coal preparation strategy. The limit to which coal needs washing or preparation has to be justified from the specific qualities that are demanded for the boilers.
Essay # 10. Clean Coal Combustion Technologies:
Steam turbines can run on a variety of fuels but coal continues to remain a popular choice. However, the traditional coal-fired plants suffer from two major drawback overall efficiency levels are low and pollution levels are high.
Growing environmental concerns and the need to improve conversion efficiency levels have led to the development of clean coal technologies. The most popular of these technologies are Fluidised Bed Combustion (FBC), Pressurised Fluidised Bed Combustion Combined Cycle (PFBC) and Integrated Gasification Combined Cycle (IGCC).
Improvement in overall performance of steam turbines for thermal power plants can be brought about largely through two kinds of advancement. Firstly, through improvement in mechanical efficiency by reducing aerodynamic and leakage losses as the steam expands through the turbine. Secondly, through improvement in thermodynamic efficiency by increasing the temperature and pressure at which heat is added to the power cycle.
i. Supercritical Technology:
The steam temperature can be raised to levels as high as 580 to 600°C and pressure over 300 bars. Under these conditions, water enters a phase called “supercritical” with properties in between those of liquid and gas. This supercritical water can dissolve a variety of organic compounds and gases, and when hydrogen per-oxide and liquid oxygen are added, combustion is triggered. Turbines based on this principle are called Supercritical Turbines. These turbines offer outputs of over 500 MW. Some manufacturers are planning to commission steam turbines of 800-1,000 MW output in the next few years.
The supercritical turbines can burn low grade fossil fuels and can completely stop Oxides of Nitrogen (NOx) emissions and keep emissions of sulphur dioxide to a minimum. For example, lignite or brown coal has high water content.
So, it is normally not used for power generation. Yet, when lignite is added to water that has been heated to 600°C at a pressure of 300 bars, it will completely burn up in one minute while emitting no NOx and only 1 percent of its original sulphur content as SOx.
This also eliminates the need for desulphurization and denitrification equipment and soot collectors. Although large amounts of energy are required to create supercritical water, operating costs could be significantly different from existing power generating facilities because there would be no need to control gas emissions. The demand for cooling water is also reduced, almost proportionally to an increase in the efficiency.
Currently, supercritical power plants reach thermal efficiencies of just over 40 percent, although a few of the more plants have attained high efficiency upto 45 percent. A number of steam generator and turbine manufacturers around the world now claim that steam temperatures upto 700°C (“ultra” supercritical conditions) are possible which might raise plant efficiencies to over 50 percent, but by using expensive nickel-based alloys. Because supercritical water is corrosive, expensive nickel alloys must be used for the reaction equipment and power generators.
The main competition to supercritical system is from new gas turbine combined cycle plants which are now expedited to achieve an overall efficiency of 60 percent, making a huge difference in generating and life-cycle costs. However, the new gas turbines will release exhaust into waste heat recovery steam generator at temperatures above 600°C, thus necessitating the use of the high chromium steel and nickel alloys as used in the supercritical coal-fired plants.
The economic benefits of taking steam temperature above 635°C, the costs of nickel-based alloys are yet to be resolved. The extra costs of using nickel-based alloys can probably be compensated by reduction in the amount of material required through thinner tube walls and smaller overall dimensions of both plant and site requirements. Efforts are also afoot to develop materials which can withstand high temperatures and pressures to improve thermal efficiency.
However, increased live steam pressure may lower potential for improved performance due to auxiliary power consumption. In addition, increased pressure leads to a loss of thermal flexibility and this can also increase costs.
ii. Fluidised Bed Combustion:
During the seventies and also in eighties, it appeared that conventional pulverised coal-fired power plants had reached a plateau in terms of thermal efficiency. The efficiency levels achieved were of the order of 40 percent in the US and the UK. The corresponding figures for India, however, were lower at 36 to 37 percent.
An alternative technology, Fluidised Bed Combustion (FBC), was developed to raise the efficiency levels. In this technology, high pressure air is blown through finely ground coal. The particles become entrained in the air and form a floating or fluidised bed. This bed behaves like a fluid in which the constituent particles move to and fro and collide with one another.
Fluidised bed can burn a variety of fuels-coal as well other non- conventional fuels like biomass, petro-coke, and coal cleaning waste and wood. This bed contains only around 5 percent coal or fuel. The rest of the bed is primarily an inert material such as ash or sand.
The temperature in FBC is around 800-900°C compared with 1,300-1,500°C in Pulverised Coal Combustion (PCC). Low temperature helps minimise the production of NOx. With the addition of a sorbent into the bed (mostly limestone), much of the SO2 formed can be captured.
The other advantages of FBC are compactness, ability to burn low calorific values (as low as 1,800 kcal/kg) and production of ash which is less erosive. Moreover, in FBC, oil support is needed for 20-30 percent of the load versus 40-60 percent in PCC. FBC-based plants also have lower capital costs compared to PCC-based plants. The capital costs could be 8-15 percent lower.
FBCs are essentially of two types bubbling and circulating. While bubbling beds have low fluidisation velocities to prevent solids from being elutriated, circulating beds employ high velocities to actually promote elutriation. Both these technologies operate on atmospheric temperature. The circulating bed can remove 90-95 percent of the sulphur content from the coal while the bubbling bed can achieve 70-90 percent removal.
FBC thus offers an option for burning fuels economically, efficiently and in an environmentally acceptable way. Currently, size is the only limitation of this technology. While the maximum size of a PCC-based power plant unit could be 1,300 MW, FBC has achieved a maximum unit size of 250 MW.
According to some estimates, FBC represents only about 2 percent of the total coal fired capacity worldwide, but is of particular interest and significance for use of those coals which are difficult to mill and fire in PCC boilers.
iii. Circulating Fluidised Bed Combustion (CFBC):
Unlike conventional PC-fired boiler, the CFBC boiler is capable of burning fuel with volatile content as low as 8 to 9 percent (e.g., anthracite coke, petroleum etc., with minimal carbon loss). Fuels with low ash-melting temperature such as wood, and bio-mass have been proved to be feedstock’s in CFBC due to the low operating temperature of 850-900°C. CFBC boiler is not bound by the tight restrictions on ash content either. It can effectively burn fuels with ash content upto 70 percent.
CFBC can successfully burn agricultural wastes, urban waste, wood, bio-mass, etc., which are the low melting temperature as fuels. The low furnace temperature precludes the production of “thermal NOX” which appears above a temperature of 1200 to 1300°C.
Besides, in a CFBC boiler, the lower bed is operated at near sub-stoichiometric conditions to minimise the oxidation of “fuel-bound nitrogen.” The remainder of the combustion air is added higher up in the furnace to complete the combustion. With the staged-combustion about 90 percent of fuel-bound nitrogen is converted to elemental nitrogen (N2) as main product.
In India, Bharat Heavy Electricals Limited (BHEL) has developed bubbling fluid bed boilers upto capacity rating of 150 tonne per hour for high ash coals and washery rejects. For units of capacity higher than 30 MW, circulating fluidised bed combustion (CFBC) technology is more economical for high ash coals and/or high sulfur coals.
For higher capacity CFBC boilers, BHEL has entered into a technical collaboration agreement with M/s Lurgi Babcock Energy Technik, Germany to make boilers upto 200 MW. BHEL is currently executing an order for two units of Lignite fired CFBC boilers of 125 MWe each (390 tph steam flow) in Gujarat and has commissioned one coal fired unit of 30 MWe (175 tph) capacity in Maharashtra in 1996.
The first CFBC power plant of 110 MW at Nuclu. Colorado, USA is operating since 1990. Several such CFBC power plants are operating in Germany, UK, Canada and Japan using various kinds of coal and bio-mass fuels. The largest CFBC power plant is the 250 MWe units in Gardane, France, commissioned in 1996. Presently, 350 MWe units are being constructed in Canada and Japan.
CFBC is a mature technology with more than 300 CFBC boilers in operation world wide ranging from 5 MWe to 250 MWe. With line stone addition, 90 percent of the sulfur emission can be retained. With staged combustion and with relatively low combustion temperature of 850/900°C, NO2 formation is about 300 to 400 mg/Nm3 only against 500 to 1000 mg/Nm3 in conventional PF fired boilers.
iv. Pressurised Fluidised Bed Combustion Combined Cycle (PFBC):
A new type of fluidised bed design, the pressurised bed, was developed in the late eighties to further improve the efficiency levels in coal-fired plants.
In this concept, the conventional combustion chamber of the gas turbine is replaced by a pressurised fluidised bed combustor. The products of combustion pass through a hot gas cleaning system before entering the turbine. The heat of the exhaust gas from the gas turbine is utilised in the downstream steam turbine. This technology is called pressurised fluidised bed combustion combined cycle (PFBC).
The bed is operated at a pressure of between 5 bars and 20 bars and operating the plant at such low pressures allows some additional energy to be captured by venting the exhaust gases through a gas turbine which is then combined with the normal steam turbine to achieve plant efficiency levels of upto 50 percent. The steam turbine is the major source of power in PFBC, contributing about 80 percent of the total power output. The remaining 20 percent is produced in gas turbines.
PFBC plants are smaller in size than the atmospheric FBC and PCC plants and therefore have the advantage of siting in urban areas. The fuel consumption is about 10-15 percent lower than in PCC technology.
PFBC has been used only over the last few years. The development of this technology is dependent upon the compatibility of the hog gas clean-up system with the gas turbine inlet temperatures and maximum particulate size. Improvements on these two fronts would lead to greater acceptance of PFBC.
v. Status of PFBC Technology Development:
The first demonstration plant of capacity of 130 MWe (+224 M W, co-generation) has been operating in Stockholm, Sweden since 1991 meeting all the stringent environmental conditions. Another demonstration plant of 80 MWe capacities is operating in Escatron, Spain using 36% ash black lignite.
The third demonstration plant of 70 MWe at TIDD station, OHIO, USA was shut down in 1994 after eight years demonstration period in which a large amount of useful data and experience were obtained. A 70 MWe demo plant has been operated at Wakamatsu from 1993 to 1996.
Presently, a 350 MWe PFBC power plant is planned in Japan and another is on or der in USA (to be operated at SPORN). UK has gathered a large amount of data on an 80 MWe PFBC plant in Grimethrope during its operation from 1980-1992 and is now offering commercial PFBC plants and developing second generation PFBC. ABB-Sweden is the leading international manufacturer which has supplied the first three demonstration plants in the world and is now offering 300 MWe units plants.
In India, BHEL-Hyderabad has been operating a 400 mm PFBC for the last eight years and has collected useful research data. IIT Madras has a 300 mm diameter research facility built with NSF (USA) grant. A proposal by BHEL for a 60 MWe PFBC plant is under consideration with the Government of India.
vi. Integrated Gasification Combined Cycle (IGCC):
The integrated gasification combined cycle is a process in which the fuel is gasified in an oxygen or air-blown gasifier operating at high pressure. The raw gas thus produced is cleaned of most pollutants (almost 99 percent of its sulphur and 90 percent of nitrogen pollutants).
It is then burned in the combustion chamber of the gas turbine generator for power generation. The heat from the raw gas and hot exhaust gas from the turbine is used to generate steam which is fed into the steam turbine for power generation.
Often, IGCC is referred to as “Cool Water” technology, a name drawn from the ranch in California’s Mojave Desert that once occupied the site where it was developed. Coal all shorts burns so well with the Cool Water technology—upto 99 percent of sulphur contamination is eliminated.
The main subsystems of a power plant with integrated gasification are:
i. Gasification plant.
ii. Raw gas heat recovery systems.
iii. Gas purification with sulphur recovery.
iv. Air separation plant (only for oxygen blown gasification).
v. Gas turbine with heat recovery steam generator.
vi. Steam turbine generator.
The feedstock which is fed into the gasifier is more or less completely gasified to synthesis gas (syngas) with the addition of steam and enriched oxygen or air. The gasifier can be fixed bed, entrained or fluidised bed. The selection of the gasifier to achieve best cost efficiency and emission levels depends upon the type of fuel.
In the gas purification system, initial dust is removed from the cooled raw gas. Chemical pollutants such as hydrogen sulphide, hydrogen chloride and others are also removed. Downstream of the gas purification system, the purified gas is reheated, saturated with water if necessary (for reduction of the oxides of nitrogen) and supplied to the gas turbine combustion chamber.
The IGCC technology scores over others as it are not sensitive with regard to fuel quality. Depending on the type of gasifier, liquid residues, slurries or a mixture of petcoke and coal can be used. In fact, the IGCC technology was developed to take advantage of combined cycle efficiency of such low-grade fuels.
IGCC technology is also environment friendly. In IGCC, pollutants like sulphur dioxide and oxides of nitrogen are reduced to very low levels by primary measures alone, without down-stream plant components and additives like limestone.
The low NOx values are achieved by dilution of the purified syngas with nitrogen from air separation unit and by saturation with water. The direct removal of sulphur compounds from the syngas results in the effective recovery of elemental sulphur, yielding a saleable raw chemical product. Gasification and gas cleaning is an extremely effective filter for contaminants harmful to both gas turbines as well as environment. The IGCC technology is not only environment friendly, but also efficient in power generation (upto 50 percent).
However, IGCC is an expensive option. Some companies claim that they have found an answer to the cost issue with a new technology for producing methanol. They believe that fitting this system, which produces methanol at twice the rate of conventional methods, on the back end of the gasifier units on an IGCC plant can cut the capital cost by 25 percent.
The technology achieves this saving by reducing the number of gasifiers the IGCC plant needs—provided the full capacity of the power station is not required for base load running. This enables the operator to make full use of the gasifiers, which account for 50- 60 percent of the cost of an IGCC and become prohibitively expensive under part-time operation. When power is not required, they can be switched to methanol production. This provides the additional fuel to meet full power output at time of peak demand.
The additional benefits will not make an IGCC unit competitive with a Combined Cycle Gas Turbine (CCGT) plant where there is adequate supply of natural gas. However, a 500 MW unit could compete with traditional coal-fired technology. The biggest difficulty may arise in securing a long-term purchase contract for methanol that will allow the plant operator to keep the gasifiers in continuous operation.
The use of gasification for power generation is perceived by many as a complex and expensive technology. However, recent experience in both developed and developing countries reinforces its relevance to power generation. In India, in particular, the IGCC technology is of great relevance as we do not have huge reserves of hydrocarbons. Since coal is available, more project developers can go in for coal-based IGCC plants.
vii. Coal Bed Methane (CBM) Recovery:
It is well known that coal is framed due to bio conversion of fossilised organic matter, In the process of coal formation, anaerobic conditions led to generation and trapping of methane in this coal seams. The pressure exerted by naturally formed water keeps the methane “absorbed” on internal surfaces of coal.
Thus, coal bed gas is in mono-molecular state and not as free gas, as in natural oil/gas fields. Therefore, all coal fields of the world have coal bed methane, the only difference being the quantity of gas in individual coal seams.
Porosity plays an important role in building up methane gas reserves in the coal bed. Unlike the conventional reservoirs, in coal the methane is not compressed in the pore space (porosity) but physically attached to the coal at molecular level (micro-porosity).
Micro-porosity makes up about 70 percent of the total porosity in coal bed and is equivalent to a conventional reservoir having 20 percent porosity, saturated with 100 percent gas. On account of this difference, coal has higher gas storage capacity than sands containing petroleum gas.
The existence of gas in coal has been known for many decades. It is only in the last decade and a half that this gas has emerged as a viable energy source with coal as both source and reservoir rocks. In USA, the CBM exploration was first initiated and an energy resource has also been recognized.
By 1995, USA has produced about 2.5 Bcfd (billion cubic feet per day) of CBM from 9000 wells, which is about 5 percent of the total gas consumption of USA. In CBM exploration, China is emerging as a major player and Australia is on the threshold of commercial production.
The generation of methane gas results from high temperature and pressure due to continuous burial. During the transformation process, coal becomes rich in carbon and large amount of fluid matter is released like methane, carbon dioxide and water. Such generation of fluid is significant in bituminous and higher rank coal with maximum yield of 150-200 cm3 per gram of coal. Indian’s coals have gas content values ranging from 1 to 23m3/tonne.
In India, the Reliance Gas has carried out comprehensive geologic assessment of coal/lignite basins based on which about 20,000 km2 of area has been identified as prospective for CBM with estimated in place resource of about 2000 billion cubic meters.
The recoverable reserve of about 800 billion cubic meters and gas production potential of about 105 million metre cum per day over a period of 20 years has been estimated. CBM potential is thus about 1.5 times the present natural gas production in India, which is capable of generating about 19000 MW of electricity.