Coal bed methane (CBM) drainage - Potential uses of coal mines methane:

Coal bed methane (CBM) drainage - Potential uses of coal mines methane:

One of the major decisions facing a mine owner, when considering the implementation of a CBM drainage program is the potential use for the gas. The gas is a clean energy resource. However, the location of the mine and the ability to convert the gas into a marketable product may severely test the mine planners’ perseverance in finding an economic way of using the gas and producing the accompanying reduction in greenhouse gases. Here we would try to outline some possibilities for the gas whether it is a high-Btu, medium-Btu, or low-Btu product.

(1) High-Btu Gas (> 950 Btu/scf) - High-Btu gas is generally defined as having enough heat content to be used in a natural gas pipeline. Several potential uses exist for high-Btu gas. If the drainage system provides primarily CH4 and little in the way of inert gas, the product may be gathered, compressed, and marketed to a pipeline company. This is one of the most desirable options if natural gas pipelines are located near the mine. Thus, marketing of coal mines methane to a pipeline company would be a very desirable goal.

In case, pipelines are not readily available or the pipeline companies are not ready to buy coal mines methane, several other options are available for high-Btu gas. The first of these would be to use the gas as a feedstock to produce ammonia, methanol, or acetic acid. Currently, these chemicals are produced from natural gas, but coal-bed methane would be equally useful if it is available in sufficient quantities and if the chemical plants were in a favorable location. Another potential method of using CBM would be to compress or liquefy it for use in buses, trucks, and automobiles. This implementation has been successfully used in many of the CIS countries like Ukraine, Czech Republic etc.

(2) Medium-Btu Gas (300 to 950 Btu/scf) - There are many possible uses for medium-Btu gas. If the gas is at the high end of the heat content scale, enrichment by blending with a higher-quality gas or ‘spiking’ of the gas to produce a gas of pipeline quality is possible. Enrichment is the removal of gases like nitrogen, oxygen, and carbon dioxide to improve the heat content of the gas. ‘Spiking’ is the process of combining another fuel gas (like propane) with the methane to increase the heat content. Spiking will normally be economic only if the supplement gas is available cheaply in the area. A major and growing use of medium-Btu gas is as a substitute for other fuels in space heating and other applications where natural gas, fuel oil, or coal is normally used. For example, CBM can be used for heating mine facilities, heating mine intake air, heating greenhouses and institutional facilities, as a heat source in a thermal dryer and as a heat source for treating brine water.

Another use for medium-Btu methane is in electric power production. Using methane in coal-fired utility and industrial boilers and as a supplement to natural gas in blast furnaces is common where methane is extracted from coal mines.

(3) Low-Btu Gas (<>

Summery of specific options for utilization of Coal-bed methane from mines: a. Power Generation - CBM can be ideal fuel for co-generation Power plants to bring in higher efficiency and is preferred fuel for new thermal power plant on count of lower capital investment and higher operational efficiency. b. Auto Fuel in form of Compressed Natural Gas (CNG) - CNG is already an established clean and environment friendly fuel. Depending upon the availability of CBM, this could be a good end use. Utilization of recovered CBM as fuel in form of CNG for mine dump truck is a good option. c. Feed stock for Fertilizer – Many of the fertilizer plants in the vicinity of coal mines where coal-bed methane is drained, have started utilizing fuel oil as feedstock for its cracker complex. d. Use of CBM at Steel Plants - Blast furnace operations use metallurgical coke to produce most of the energy required to melt the iron ore to iron. Since coke is becoming increasingly expensive, in the countries where CBM is available, the steel industry is seeking low-capital options that reduce coke consumption, increase productivity and reduce operating costs. e. Fuel for Industrial Use - It may provide an economical fuel for a number of industries like cement plant, refractory, steel rolling mills etc. f. CBM use in Methanol production - Methanol is a key component of many products. Methanol and gasoline blends are common in many countries for use in road vehicles. Formaldehyde resins and acetic acid are the major raw material in the chemical industry, manufactured from methanol. g. Other uses - Besides above, option for linkages of coal-bed methane produced by coal mines, through cross country pipe lines may be considered.

Use of methane as a fuel and for other purposes:

Use of methane as a fuel and for other purposes:

Methane (CH4) is the simplest alkane, used as a fuel for various use. Apart from methane being principal constituent of natural gas, it is obtained from coal seams (as coal bed methane, CBM) and also it is obtained from bio-mass. At room temperature, methane is a gas less dense than air. Methane's relative abundance and clean burning process makes it a very attractive fuel. Burning one molecule of methane in the presence of O2 (oxygen) releases one molecule of CO2 (carbon dioxide) and two molecules of H2O (water). Methane being gas in ordinary temperature, its transportation and storage is difficult. Methane is a powerful greenhouse gas. Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO₂)

Some methane is manufactured synthetically by the distillation of coal. Coal also contains hydrogen and oxygen, with small concentrations of nitrogen, chlorine, sulfur, and several metals. Coals are classified by the amount of volatile material they contain. Volatile substances released from coal when it is distilled, in addition to methane, include water, carbon dioxide, ammonia, benzene, toluene, naphthalene, and anthracene. In addition, the distillation also yields oils, tars, and sulfur-containing products. The non-volatile component of coal, which remains after distillation, is coke.

At high temperatures (700 to 1100 degree Celsius) in the presence of nickel catalyst, steam reacts with methane to yield CO (carbon monoxide) and H2 (hydrogen). This hydrogen is used for manufacturing of ammonia (NH3). In near future, one of the greatest uses of hydrogen would be for running vehicle by using environment-friendly hydrogen cell technology.

Methane is important for electrical generation by burning it as a fuel in a gas turbine or steam boiler. Compared to other hydrocarbon fuels, burning methane produces less carbon dioxide for each unit of heat released. In many cities, methane is piped into homes for domestic heating and cooking purposes. Methane in the form of compressed natural gas (CNG) is used as a fuel for vehicles, and is claimed to be more environmentally friendly than alternatives such as gasoline/petrol and diesel.

Note: NASA is developing LOX/methane engines as an option for the future rocket engine, as methane is abundant in the outer solar system.

Underground coal mining:

Underground coal mining:

When coal seams obtained at a great depth, surface coal mining is not feasible; the extraction of coal is done by a method called underground mining. Underground mining currently accounts for about 60% of world coal production.

In underground coal mining, there are two system of working – (1) board and pillar method; (2) Longwall method.

A. In board and pillar method, all along the coal seam, coal pillars are formed by developing drives. Drives are supported by timbers. The coal pillars thus formed kept standing till the development is done upto the mine boundary in a certain portion of the block called ’district’. Once, full area is developed in several districts, the pillars are to be extracted by a method called ‘depillaring’.

B. In Longwall (retreat) method of coal mining, drives are made at the two periphery of a district till end and these two drives are joined by another drive. This drive becomes the coal production face, where continuous machines like shearer loader, chain conveyors etc., are put. The hydraulic supports are made at the face. This is a high productive method for coal extraction from underground coal mines.

C. In underground coal mines, methane gas present in the originally formed coal seam gets released in to the mine atmosphere during excavation of coal. Methane when mixed with air in the proportions between 5 and 14 % forms an explosive mixture. Hence, there is possibility of a methane-air mixture being dangerously formed in the working areas. In underground coal mines, there is also an additional risk as ‘coal-dust’, when mixed with air, can undergo a dust explosion when suitably ignited. Both methane-air and coal dust explosions cause loss of life and extensive damage to the underground mines. Therefore, avoidance of such incidences is to be observed essentially by taking suitable safety measures. Keeping proper ventilation is again very important aspect in underground mines. Sufficient ventilation air dilutes the noxious gases generated in the coal seams and also due to blasting operation.

Formation of Fossil Fuels (Coal, Petroleum):

Formation of Fossil Fuels (Coal, Petroleum):

Energy and minerals are the life-blood of modern day world. Rapid industrial growth and growth in human population has brought the consumption of energy and mineral to a very high level. Ironically, resources are not unlimited. We know, the fossil fuels – coal, petroleum and natural gas – provide most of our needs of energy; till recently, coal used to be major source of energy. Due to recent hike in price of petroleum products, coal again is getting importance as major source of energy.

Geologically fossil fuels (coal and petroleum) have been originated from very old-buried (more than hundreds of million years old) of plants, animals and microorganisms and overlaid with sediments. This burial protected these vegetation and microorganism from oxygen, which would have completed its breakdown, and preserved it instead it into partially decayed form as coal and petroleum. Coal originated from plants & trees, whereas petroleum & natural gas originated from marine organism. Chemically, all fossil fuels consist largely of hydrocarbons, which are compounds composed of hydrogen and carbon.

The various stages of coal formation are:

(a) Peat - partially carbonized plant matter,

(b) Lignite - soft brownish-black coal with low carbon content,

(c) Sub-bituminous coal - soft coal with intermediate carbon content,

(d) Bituminous coal - soft coal with higher carbon and lower moisture content than sub-bituminous coal,

(e) Anthracite coal - hard coal with highest carbon content and lowest moisture content.

Methane (CH4) gas, which is a hydrocarbon compound, is also entrapped in most of the coal seams; is now finding importance in recovery from coal seam due to recent energy crisis.

The petroleum and gas deposits are particularly prevalent in coastal zones. Largely, our cars and vehicles are powered by diesel, gasoline and natural gas.

Vast quantity of oil is locked-up in a fine grained sedimentary rock called oil shale. This contains high proportion of ‘kerogen’, a solid organic material, when heated produces oil vapour from which oil can be recovered.