Coal (from the Old English term col, which has meant "mineral of fossilized carbon" since the 13th century) is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams.

The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.

Coal is extracted from the ground by coal mining, either underground by shaft mining, or at ground level by open pit mining extraction. Since 1983 the world top coal producer has been China. In 2011 China produced 3,520 millions of tonnes of coal – 49.5% of 7,695 millions tonnes world coal production. In 2011 other large producers were United States (993 millions tonnes), India (589), European Union (576) and Australia (416). In 2010 the largest exporters were Australia with 328 million tonnes (27.1% of world coal export) and Indonesia with 316 millions tonnes (26.1%), while the largest importers were Japan with 207 million tonnes (17.5% of world coal import), China with 195 million tonnes (16.6%) and South Korea with 126 million tonnes (10.7%).

Coal is the largest source of energy for the generation of electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. In 1999, world gross carbon dioxide emissions from coal usage were 8,666 million tonnes of carbon dioxide. In 2011, world gross emissions from coal usage were 14,416 million tonnes. Coal-fired electric power generation emits around 2,000 pounds of carbon dioxide for every megawatt-hour generated, which is almost double the approximately 1100 pounds of carbon dioxide released by a natural gas-fired electric plant per megawatt-hour generated. Because of this higher carbon efficiency of natural gas generation, as the market in the United States has changed to reduce coal and increase natural gas generation, carbon dioxide emissions have fallen. Those measured in the first quarter of 2012 were the lowest of any recorded for the first quarter of any year since 1992. In 2013, the head of the UN climate agency advised that most of the world's coal reserves should be left in the ground to avoid catastrophic global warming.- taken from wikipedia.org

COAL MINING

Over 6185 million tonnes (Mt) of hard coal is currently produced worldwide and 1042 Mt of brown coal/lignite. The largest coal producing countries are not confined to one region - the top five hard coal producers are China, the USA, India, Australia and South Africa. Much of global coal production is used in the country in which it was produced; only around 15% of hard coal production is destined for the international coal market.

Surface Coal Mining Operations & Mine Rehabilitation

MINING METHODS

Coal is mined by two methods:

surface or 'opencast' mining
underground or 'deep' mining

The choice of mining method is largely determined by the geology of the coal deposit. Underground mining currently accounts for a bigger share of world coal production than opencast; although in several important coal producing countries surface mining is more common. For example, surface mining accounts for around 80% of production in Australia; while in the USA it is used for about 67% of production.

SURFACE MINING

Surface mining - also known as opencast or opencut mining - is only economic when the coal seam is near the surface. This method recovers a higher proportion of the coal deposit than underground mining as all coal seams are exploited - 90% or more of the coal can be recovered.

Large opencast mines can cover an area of many square kilometres and use very large pieces of equipment, including:

draglines, which remove the overburden
power shovels
large trucks, which transport overburden and coal
bucket wheel excavators
conveyors

The overburden of soil and rock is first broken up by explosives; it is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and systematically mined in strips. The coal is then loaded on to large trucks or conveyors for transport to either the coal preparation plant or direct to where it will be used.

UNDERGROUND MINING

There are two main methods of underground mining: room-and-pillar and longwall mining.

ROOM & PILLAR MINING

In room-and-pillar mining, coal deposits are mined by cutting a network of 'rooms' into the coal seam and leaving behind 'pillars' of coal to support the roof of the mine. These pillars can be up to 40% of the total coal in the seam - although this coal can sometimes be recovered at a later stage.

LONGWALL MINING

Longwall mining involves the full extraction of coal from a section of the seam, or 'face' using mechanical shearers. A longwall face requires careful planning to ensure favourable geology exists throughout the section before development work begins. The coal 'face' can vary in length from 100-350m. Self-advancing, hydraulically-powered supports temporarily hold up the roof while coal is extracted. When coal has been extracted from the area, the roof is allowed to collapse. Over 75% of the coal in the deposit can be extracted from panels of coal that can extend 3km through the coal seam.

Technological advancements have made coal mining today more productive than it has ever been. To keep up with technology and to extract coal as efficiently as possible modern mining personnel must be highly skilled and well-trained in the use of complex, state-of-the-art instruments and equipment.

Top Ten Hard Coal Producers (2011e)
PR China	3471Mt	Russia	334Mt
USA	1004Mt	South Africa	253Mt
India	585Mt	Germany	189Mt
Australia	414Mt	Poland	139Mt
Indonesia	376Mt	Kazakhstan	117Mt

Source: International Energy Agency 2012 - http://www.worldcoal.org/

Coal & Cement

The cement industry requires energy to produce cement and coal is an important source of the energy needed.

Cement is critical to the construction industry – mixed with water, and gravel it forms concrete, one of the key construction materials available today. Varying the mix of cement, sand and aggregate enables concrete to be used in a range of applications. Products can be designed, coloured and shaped to accommodate a variety of environmental conditions, architectural requirements and to withstand a wide range of loads, stresses and impacts.

Over 3.3 billion tonnes of cement were consumed globally in 2010. China's cement consumption alone reached over 1.8 billion tonnes.

What is Cement?

Cement is made from a mixture of calcium carbonate (generally in the form of limestone), silica, iron oxide and alumina. A high-temperature kiln, often fuelled by coal, heats the raw materials to a partial melt at 1450°C, transforming them chemically and physically into a substance known as clinker. This grey pebble-like material is comprised of special compounds that give cement its binding properties. Clinker is mixed with gypsum and ground to a fine powder to make cement.

Coal is used as an energy source in cement production. Large amounts of energy are required to produce cement. It takes about 200 kg of coal to produce one tonne of cement and about 300-400 kg of cement is needed to produce one cubic meter of concrete (World Business Council for Sustainable Development).

Coal combustion products (CCPs), such as Fly Ash also play an important role in cement manufacture and in the construction industry generally.

Coal & Steel

Steel is an essential material for modern life. The manufacture of steels delivers the goods and services that our societies need – healthcare, telecommunications, improved agricultural practices, better transport networks, clean water and access to reliable and affordable energy.

Global steel production is dependent on coal. 70% of the steel produced today uses coal. Metallurgical coal – or coking coal – is a vital ingredient in the steel making process. World crude steel production was 1.4 billion tonnes in 2010. Around 721 million tonnes of coking coal was used in the production of steel.

How is Steel Produced?

Steel is an alloy of iron and carbon. Steel is produced via two main routes

Integrated smelting involving blast furnace (BF) iron-making followed by basic oxygen furnace (BOF)
Electric arc furnaces (EAF).

Raw Materials

Steel is an alloy based primarily on iron. As iron occurs only as iron oxides in the earth’s crust, the ores must be converted, or ‘reduced’, using carbon. The primary source of this carbon is coking coal.

Coke Making
Coking coal is converted to coke by driving off impurities to leave almost pure carbon. The physical properties of coking coal cause the coal to soften, liquefy and then resolidify into hard but porous lumps when heated in the absence of air. Coking coal must also have low sulphur and phosphorous contents. Almost all metallurgical coal is used in coke ovens.

The coking process consists of heating coking coal to around 1000-1100ºC in the absence of oxygen to drive off the volatile compounds (pyrolysis). This process results in a hard porous material - coke. Coke is produced in a coke battery which is composed of many coke ovens stacked in rows into which coal is loaded.

The coking process takes place over long periods of time between 12-36 hours in the coke ovens. Once pushed out of the vessel the hot coke is then quenched with either water or air to cool it before storage or is transferred directly to the blast furnace for use in iron making.

Iron Making
Iron ore is mined in around 50 countries – the largest producers are Australia, Brazil and China. Around 98% of iron ore is used in steel-making.

During the iron-making process, a blast furnace is fed with the iron ore, coke and small quantities of fluxes (minerals, such as limestone, which are used to collect impurities). Air which is heated to about 1200°C is blown into the furnace through nozzles in the lower section. The air causes the coke to burn, producing carbon monoxide which reacts with the iron ore, as well as heat to melt the iron. Finally, the tap hole at the bottom of the furnace is opened and molten iron and slag (impurities) are drained off.

Basic Oxygen Furnace
The most commonly applied process for steel-making is the integrated steel-making process via the Blast Furnace – Basic Oxygen Furnace.

In the basic oxygen furnace, the iron is combined with varying amounts of steel scrap (less than 30%) and small amounts of flux. A lance is introduced in the vessel and blows 99% pure oxygen causing a temperature rise to 1700°C. The scrap melts, impurities are oxidised, and the carbon content is reduced by 90%, resulting in liquid steel.

Other processes can follow – secondary steel-making processes – where the properties of steel are determined by the addition of other elements, such as boron, chromium and molybdenum, amongst others, ensuring the exact specification can be met.

Optimal operation of the blast furnace demands the highest quality of raw materials – the carbon content of coke therefore plays a crucial role in terms of its effect in the furnace and on the hot metal quality. A blast furnace fed with high quality coke requires less coke input, results in higher quality hot metal and better productivity. Overall costs may be lower, as fewer impurities in the coke mean smaller amounts of flux must be used.

Around 0.6 tonnes (600 kg) of coke produces 1 tonne (1000 kg) of steel, which means that around 770 kg of coal are used to produce 1 tonne of steel through this production route.

Basic Oxygen Furnaces currently produce about 70% of the world’s steel. A further 29% of steel is produced in Electric Arc Furnaces.

Electric Arc Furnaces
The Electric Arc Furnace process, or mini-mill, does not involve iron-making. It reuses existing steel, avoiding the need for raw materials and their processing. The furnace is charged with steel scrap, it can also include some direct reduced iron (DRI) or pig iron for chemical balance.

The EAF operates on the basis of an electrical charge between two electrodes providing the heat for the process. The power is supplied through the electrodes placed in the furnace, which produce an arc of electricity through the scrap steel (around 35 million watts), which raises the temperature to 1600˚C, melting the scrap. Any impurities may be removed through the use of fluxes and draining off slag through the taphole.

Electric Arc Furnaces do not use coal as a raw material, but many are reliant on the electricity generated by coal-fired power plant elsewhere in the grid.

Around 150 kg of coal are used to produce 1 tonne of steel in electric arc furnaces.

Pulverised Coal Injection

Pulverised Coal Injection (PCI) technology involves injecting coal directly into the blast furnace to provide the carbon for iron-making – displacing some of the coke required for the process. A wider range of coals can be used in PCI, including steam coal which has a lower carbon content than coking coal. This method has a number of advantages, including reducing overall costs and prolonging the life of existing coke batteries.

Recycling

Steel is 100% recyclable. The BOF process uses up to 30% recycled steel (scrap) and around 90-100% is used in EAF production.

Coal & Electricity

Modern life is unimaginable without electricity. It lights houses, buildings, streets, provides domestic and industrial heat, and powers most equipment used in homes, offices and machinery in factories. Improving access to electricity worldwide is critical to alleviating poverty.

Coal plays a vital role in electricity generation worldwide. Coal-fired power plants currently fuel 41% of global electricity. In some countries, coal fuels a higher percentage of electricity.

Coal in Electricity Generation
South Africa 93%	Poland 87%	PR China 79%
Australia 78%	Kazakhstan 75%	India 68%
Israel 58%	Czech Rep 51%	Morocco 51%
Greece 54%	USA 45%	Germany 41%

Source: IEA 2012

How is Coal Converted to Electricity?

Steam coal, also known as thermal coal, is used in power stations to generate electricity.

Coal is first milled to a fine powder, which increases the surface area and allows it to burn more quickly. In these pulverised coal combustion (PCC) systems, the powdered coal is blown into the combustion chamber of a boiler where it is burnt at high temperature (see diagram below). The hot gases and heat energy produced converts water – in tubes lining the boiler – into steam.

The high pressure steam is passed into a turbine containing thousands of propeller-like blades. The steam pushes these blades causing the turbine shaft to rotate at high speed. A generator is mounted at one end of the turbine shaft and consists of carefully wound wire coils. Electricity is generated when these are rapidly rotated in a strong magnetic field. After passing through the turbine, the steam is condensed and returned to the boiler to be heated once again.

The electricity generated is transformed into the higher voltages (up to 400,000 volts) used for economic, efficient transmission via power line grids. When it nears the point of consumption, such as our homes, the electricity is transformed down to the safer 100-250 voltage systems used in the domestic market.

Efficiency Improvements

Improvements continue to be made in conventional PCC power station design and new combustion technologies are being developed. These allow more electricity to be produced from less coal - known as improving the thermal efficiency of the power station. Efficiency gains in electricity generation from coal-fired power stations will play a crucial part in reducing CO2 emissions at a global level.

Efficiency improvements include the most cost-effective and shortest lead time actions for reducing emissions from coal-fired power generation. This is particularly the case in developing countries where existing power plant efficiencies are generally lower and coal use in electricity generation is increasing. Not only do higher efficiency coal-fired power plants emit less carbon dioxide per megawatt (MW), they are also more suited to retrofitting with CO2 capture systems.

Improving the efficiency of pulverised coal-fired power plants has been the focus of considerable efforts by the coal industry. There is huge scope for achieving significant efficiency improvements as the existing fleet of power plants are replaced over the next 10-20 years with new, higher efficiency supercritical and ultra-supercritical plants and through the wider use of Integrated Gasification Combined Cycle (IGCC) systems for power generation.

A one percentage point improvement in the efficiency of a conventional pulverised coal combustion plant results in a 2-3% reduction in CO2 emissions.

USES OF COAL

Access to modern energy services not only contributes to economic growth and household incomes but also to the improved quality of life that comes with better education and health services. All sources of energy will be needed to meet future energy demand, including coal.

WHAT IS COAL USED FOR?

Coal has many important uses worldwide. The most significant uses of coal are in electricity generation, steel production, cement manufacturing and as a liquid fuel. Around 6.6 billion tonnes of hard coal were used worldwide last year and 1 billion tonnes of brown coal.

Since 2000, global coal consumption has grown faster than any other fuel. The five largest coal users - China, USA, India, Russia and Japan - account for 76% of total global coal use.

Different types of coal have different uses. Steam coal - also known as thermal coal - is mainly used in power generation. Coking coal - also known as metallurgical coal - is mainly used in steel production.

The biggest market for coal is Asia, which currently accounts for over 67% of global coal consumption; although China is responsible for a significant proportion of this. Many countries do not have natural energy resources sufficient to cover their energy needs, and therefore need to import energy to help meet their requirements. Japan, Chinese Taipei and Korea, for example, import significant quantities of steam coal for electricity generation and coking coal for steel production.

Other important users of coal include alumina refineries, paper manufacturers, and the chemical and pharmaceutical industries. Several chemical products can be produced from the by-products of coal. Refined coal tar is used in the manufacture of chemicals, such as creosote oil, naphthalene, phenol, and benzene. Ammonia gas recovered from coke ovens is used to manufacture ammonia salts, nitric acid and agricultural fertilisers. Thousands of different products have coal or coal by-products as components: soap, aspirins, solvents, dyes, plastics and fibres, such as rayon and nylon. Coal is also an essential ingredient in the production of specialist products:

Activated carbon - used in filters for water and air purification and in kidney dialysis machines.
Carbon fibre - an extremely strong but light weight reinforcement material used in construction, mountain bikes and tennis rackets.
Silicon metal - used to produce silicones and silanes, which are in turn used to make lubricants, water repellents, resins, cosmetics, hair shampoos and toothpastes.

It has been estimated that there are over 861 billion tonnes of proven coal reserves worldwide. This means that there is enough coal to last us around 112 years at current rates of production. In contrast, proven oil and gas reserves are equivalent to around 46 and 54 years at current production levels. Coal reserves are available in almost every country worldwide, with recoverable reserves in around 70 countries. The biggest reserves are in the USA, Russia, China and India. After centuries of mineral exploration, the location, size and characteristics of most countries' coal resources are quite well known. What tends to vary much more than the assessed level of the resource - i.e. the potentially accessible coal in the ground - is the level classified as proved recoverable reserves. Proved recoverable reserves is the tonnage of coal that has been proved by drilling etc. and is economically and technically extractable. DEFINITIONS Resource The amount of coal that may be present in a deposit or coalfield. This does not take into account the feasibility of mining the coal economically. Not all resources are recoverable using current technology. Reserves Reserves can be defined in terms of proved (or measured) reserves and probable (or indicated) reserves. Probable results have been estimated with a lower degree of confidence than proved reserves. Proved Reserves Reserves that are not only considered to be recoverable but can also be recovered economically. This means they take into account what current mining technology can achieve and the economics of recovery. Proved reserves will therefore change according to the price of coal; if the price of coal is low proved reserves will decrease. Over recent years there has been a fall in the reserves to production (RP) ratio, which has prompted questions over whether we have reached 'peak coal'. Peak coal is the point in time at which the maximum global coal production rate is reached after which the rate of production will enter irreversible decline. However, recent falls in the RP ratio can be attributed to the lack of incentives to prove up reserves, rather than a lack of coal resources. Exploration activity is typically carried out by mining companies with short planning horizons rather than state-funded geological surveys. There is no economic need for companies to prove long-term reserves. All fossil fuels will eventually run out and it is essential that we use them as efficiently as possible. Coal reserves could be extended further through a number of developments including: the discovery of new reserves through ongoing and improved exploration activities; advances in mining techniques, which will allow previously inaccessible reserves to be reached. 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 EXPLORATION 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.

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What is Coal ?

Coal Mining