 |
|||||||||
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|||||||||
Information used with permission from:Australian Coal Association: http://www.australiancoal.com.au/
World Coal Institute: http://www.worldcoal.org/
FAQs
What is coal? READ MORE >>
How was coal formed? READ MORE >>
What is coal used for? READ MORE >>
Where is coal found? READ MORE >>
How is coal found? READ MORE >>
How does mining coal affect the environment? READ MORE >>
What is Clean Coal? READ MORE >>
Is coal mining dangerous? READ MORE >>
Coal is a fossil fuel. It’s combustible, sedimentary, organic rock formed from ancient vegetation that has been consolidated between other rock strata and transformed by pressure and heat over a considerable time period, a process known as coalification.
Layered between other sedimentary rocks, coal is found in seams ranging in thickness from less than a millimetre to many metres.
Coal is composed mainly of carbon (50-98%), hydrogen (3-13%) and oxygen, and smaller amounts of nitrogen, sulphur and other elements. It also contains a little water and grains of inorganic matter that remain as ash when coal is burnt.
Initially peat, the precursor of coal, was converted into lignite or brown coal—coal types with low organic ‘maturity’. Over many more millions of years, the continuing effects of temperature and pressure produced additional changes in the lignite, progressively increasing its maturity and transforming it into the range known as sub-bituminous coals.
As this process continued, further chemical and physical changes occurred until these coals became harder and more mature, at which point they are classified as bituminous or hard coals. Under the right conditions, the progressive increase in the organic maturity continued, ultimately to form anthracite.
Large coal deposits only started to be formed after the evolution of land plants in the Devonian period, some 400 million years ago. Significant accumulations of coal occurred during the Carboniferous period (350-280 million years ago) in the Northern Hemisphere, the Carboniferous/Permian period (350-225 million years ago) in the Southern Hemisphere and, more recently, the late Cretaceous period to early Tertiary era (approximately 100-115 million years ago) in areas as diverse as the USA, South America, Indonesia and New Zealand.
Australia’s oldest deposits of black coal, found in NSW and Queensland, were formed between 225 and 180 million years ago. However, younger black coals mined in Queensland, South Australia and Tasmania are between 140 and 180 million years old. Victoria’s brown coal deposits are young by comparison, formed less than 45 million years ago.
Coal has a wide range of important uses—the major ones being:
- Electricity generation
Forty percent of all the electricity generated worldwide is produced from coal. The earliest conventional method for generating electricity was by burning lump coal on a grate in boilers to raise steam. In modern, highly efficient, versions of this system, the coal is first milled to a fine powder in a pulveriser. This increases the surface area of the coal and hence the rate of combustion. The powdered coal is blown into the combustion chamber of a boiler where it is burnt at around 1400°C. The hot gases and radiant heat energy produced convert water in tubes lining the boiler into steam.
The high pressure steam is passed into a turbine containing thousands of propeller-like blades. The expanding steam hits these blades causing the turbine shaft to rotate at high speed. Mounted at the end of the turbine shaft is the generator, consisting of carefully wound wire coils. Electricity is generated when these are rapidly rotated in a strong magnetic field.
After passing through the turbine chamber, the steam is condensed and returned to the boiler to be heated once again.
The electricity is transformed into the higher voltages used for economic transmission via power line grids (400,000 volts and above). Near the point of consumption, the electricity is transformed down to the safer 100-250 voltage systems used in the domestic market.
- Steel production
Some 70% of total steel production is based on the smelting of iron ore in blast furnaces and the subsequent refining of the iron into steel, mainly in Basic Oxygen Furnaces (BOF). A blast furnace typically uses iron ore, coke (made from coal), small quantities of limestone, and, where Pulverised Coal Injection (PCI) is employed, pulverised or granulated thermal coal.
Source: World Coal Institute
Iron ore, mined in many countries, is a mineral containing iron oxides. Commercial ore grades usually have an iron or ferrous content of at least 58%. Most of the ore fed to the furnace is finely ground and then mixed and heated with coke fines to form 'sinter'. Smaller quantities of natural lump or pelletised ores are then added.
Coke is made from coking coals, which have certain physical properties that cause them to soften, liquefy and then resolidify into hard but porous lumps when heated in the absence of air. Coking coals must also have low sulphur and phosphorous contents.
Coal is carbonised in batteries of coke ovens. The coal blend, crushed to a maximum size of 3 mm, is poured into the top of the ovens and heated to above 1200°C over a period of 18-20 hours. The volatile contents of the coal are driven off as coke oven gas, which is first cleaned to remove impurities and yield by-products such as tar and benzole; then used to heat the ovens themselves and as fuel elsewhere in the steelworks. The red-hot coke is pushed out of the ovens, cooled and screened to remove the smaller sizes. The larger sized material - typically above 30 mm - goes to the blast furnace, where it:
- supplies carbon as a reducing agent, removing the oxygen from the ore;
- provides heat to melt the iron;
- acts as a load-bearing but permeable layer, supporting the burden whilst allowing the reducing gases to pass through.
Ore, coke and limestone are fed into the top of the furnace. The hot air blast and, if PCI is installed, the pulverised coal, are injected through nozzles into the base of the furnace. The pulverised coal injected in this way is used as a less expensive source of carbon and fuel. The molten iron or hot metal are periodically tapped from the bottom of the furnace and taken directly to the Basic Oxygen Furnace. Steel scrap and more limestone are added, and oxygen is blown onto the liquid metal, which is 93-95% pure iron at this stage. The reaction with the oxygen raises the temperature to 1600-1650°C and oxidises the impurities to leave almost pure liquid steel.
Blast furnaces with PCI require 350-400 kg of coke, made from 525-600 kg of coking coal, plus 100-200 kg of cheaper PCI coal - around 700 kg of coal for each tonne of hot metal produced. Furnaces without PCI use more coke, also equivalent to some 700 kg of coal, but all of it the more expensive coking coal. As each tonne of steel uses approximately 90% hot metal and 10% scrap, about 630 kg of coal are used per tonne of steel.
About 630 kg of coal are used to produce 1,000 kg of steel.
Some 30% of world steel is produced in Electric Arc Furnaces, which melt scrap iron and steel. Much of the electricity used in arc furnaces is generated in coal-fired power stations.
New processes are being developed for the direct reduction of iron (DRI), eliminating blast furnaces and coke ovens and the need for coke. For examples of such technologies in Australia, see: Coal Use and the Environment - Reducing the Environmental Impacts of Coal Use. However, DRI plants will still use coal as a fuel and a reductant, and will account for only a small percentage of the world steel output for many years.
For the foreseeable future, coal will remain indispensable to the production of steel.
- Cement manufacture
Cement is the main binding ingredient in concrete, the most common building and construction material in the world. Major uses include buildings, both commercial and homes, manufacturing, mining and tourism facilities, and infrastructure development such as roads, airports, bridges, harbours, reservoirs and dams.
The world uses more than 1,350 million tonnes of cement every year.
Cement is made from a mixture of calcium carbonate (generally in the form of limestone), silica, iron oxide and alumina.
A high-temperature kiln fuelled by coal, natural gas or alternative fuels (waste tyres, oils and solvents) heats the raw materials to a partial melt at 1450°C, transforming them chemically and physically into clinker. This grey pebble-like material comprises the special compounds that give cement its binding properties. Clinker is mixed with gypsum and ground to a fine powder to make cement.
The cement industry requires energy to produce cement and coal will remain an important input for the global cement industry. A number of coal producers and cement plant operators have identified and developed strong long-term relationships for the supply of coal to meet all or part of the energy needs of the plant.
Coal combustion products (CCPs), such as Fly Ash also play an important role in cement manufacture and in the construction industry generally. When Fly Ash is added to concrete, for example, the spherical particles act like ball bearings in the mix, improving the workability and fluidity of concrete as well as the grading curve of the concrete mixture.
Other important users of coal in Australia include the alumina refineries in Queensland and Western Australia, paper manufacturers, breweries and the chemical and pharmaceutical industries.
In alumina refineries coal is used to generate process heat to separate alumina from the impurities in the ore. Under high temperatures and pressure the alumina is dissolved while the impurities remain solid.
Paper manufacturers and breweries use coal for steam raising and for heating and processing, and bricks, tiles and earthenware pipes are fired at high temperatures, often in coal fired kilns.
Several chemical products can be produced from the by-products of coal. Refined coal tar is used in the manufacture of a range of chemicals - pitch, creosote oil, naphthalene, phenol, pyridine, benzene and toluene. Ammonia gas recovered from coke ovens is used to manufacture ammonia salts, nitric acid and agricultural fertilisers - sulphate of ammonia and ammonium nitrate.
Thousands of different products have coal or coal by-products as components. Soap, aspirin, solvents, dyes, plastics and fibres like rayon and nylon are some of them.
Where is coal found?
It has been estimated that there are over 909 billion tonnes of proven coal reserves worldwide. This means that there is enough coal to last us over 155 years on current global usage projections. Coal can be found on every continent in over 70 countries, with the biggest reserves in the USA, Russia, China and India.
Additionally, significant improvements continue to be made in how efficiently coal is used so that more energy can be generated from each tonne of coal produced.
Coal reserves are discovered through exploration activities. The process usually involves creating a geological map of the area, then carrying out geochemical and geophysical surveys, followed by exploration drilling. This allows an accurate picture of the area to be developed.
The area will only ever become a mine if it is large enough and of sufficient quality that the coal can be economically recovered. Once this has been confirmed, mining operations begin.
How does mining coal affect the environment?
Coal, like all other sources of energy, has a number of environmental impacts, from both coal mining and coal use.
Coal mining raises a number of environmental challenges, including soil erosion, dust, noise and water pollution, and impacts on local biodiversity. Steps are taken in modern mining operations to minimise these impacts.
The coal industry recognises it must meet the challenge of environmental sustainability—in particular coal must significantly reduce its greenhouse gas (GHG) emissions.
Technological innovation will allow demand for coal to be met without an unacceptable environmental impact. The wider deployment of clean coal technologies will have a significant impact on the environmental performance of coal in both developed and developing countries.
The development and deployment of best practice clean coal technologies must continue and further development of advanced coal technology is needed. Carbon capture and storage will also be required if substantial cuts in GHG emissions are to be achieved.
Using complementary aspects of coal and renewable energy can improve the environmental performance and reliability of the energy system.
Clean Coal Technologies (CCTs) are defined as technologies designed to enhance both the efficiency and the environmental acceptability of coal extraction, preparation and use. These technologies reduce emissions, reduce waste, and increase the amount of energy gained from each tonne of coal.
CCT programmes are being vigorously pursued by many countries, with hundreds of millions of dollars being spent annually on developments in utilisation techniques. These technologies will enable coal use to be increasingly efficient and environmentally acceptable as a vital world energy source throughout this century.
Most CCTs concentrate on power generation from coal, as more than 50% of coal produced is used to generate electricity. An impressive array of technologies is already commercially viable, and a large number of others will become available in the near future.
The safety of employees and a mine’s neighbouring community is a primary focus for the entire coal industry. New operational and work practices aimed at providing a safer and healthier work environment are constantly sought. The industry’s pollution control initiatives are an integral part of stringent management measures adopted at each site.
The number of accidents and injuries in the industry is declining rapidly. However, management and employees believe that the accident rate remains too high, in both human and productivity terms, and are continuously working to reduce it.
Company initiatives in this area include the progressive introduction of new technology, work methods and job design, detailed company safety plans and programmes and systematic risk, claims, accident and injury management.
The industry’s strategic direction, increased senior and line management involvement and commitment to occupational health and safety have seen the rise of an improved culture throughout the industry.
Coal companies are translating commitment into effective action with substantial results. Considerable effort is being made to provide a safe and healthy workplace through fundamental organisational reform.
As well as commitment to occupational health and safety (OH&S) by senior management, active participation and commitment is being fostered at all work levels. Detailed OH&S plans and programmes are developed and communicated to all employees and are subject to stringent check and control systems.