Coal is a sedimentary rock of organic origin, black or dark brown. It is used primarily as a fossil fuel because of its high calorific value due to the fact that it has a carbon content of majority. The coals can be classified by the percentage that contain carbon, which is related to the moisture content and impurities. According to this criterion, we can distinguish peat, lignite, bituminous coal and anthracite.
Composition of coal
This item appears in carbon coal at a rate greater than 50% by weight and 70% by volume. Water containing (humidity) is variable and it comes from the trapped during the formation of coal.
Other constituents are the coal mineral matter (various silicates) and mineral carbonate (siderite, calcite and aragonite). Pyrite is a mineral common in sulfur coals. There are small amounts of metals such as iron, uranium, cadmium, and very meager quantities, gold.
Methane is a gas found in coal mines and can be the source of dangerous explosions in underground mines. In this specific context is the & rsquo; often called firedamp.
Origin of coal
It is believed that most of the current coal was formed during the Carboniferous period (280 to 345 million years ago) was the primary. Also in the Permian, Triassic and Jurassic reservoirs formed. In the Cretaceous lignite was formed. There are currently forming peat bogs.
Coal Europe, Asia, and North America was formed mainly in the Carboniferous based tropical vegetation.
Coal southern hemisphere formed vegetation cold climate (tundra). Old plants through geological changes were compacted, hardened, chemically altered and undergoing a process of metamorphosis for high temperature and pressure.
Coal northern hemisphere formed in wetland ecosystems called carboniferous forests. In plants die and accumulate in aquatic environments with little oxygen (anaerobic environments) suffering from bacterial degradation. For the coal formation that these conditions must have a sufficient length of time, and without erosion in sedimentary conditions.
History of & rsquo; use of coal
The British Isles (especially rich in coal and where the industrial revolution began) is the first study which detected the use of this fossil fuel.
There, in the third millennium BC was found that was a component of funeral pyres and around the year 200 BC there is evidence in the same area, business activity and be used to dry cereals . Under Roman rule are sporadic mentions of the use of coal, but not until the Middle Ages acquired considerable importance.
The first coal used was just picked up from the beach, this source was depleted when it had happened to coal mining. He started using massively with the first applications of the steam engine, both in industry and transport, including trains and ships.
In the twentieth century, when coal became quite expensive, began to prefer liquid fossil fuels (petroleum) transport to and from the middle of the century the use of natural gas was in favor of increasing oil and coal industry and energy production. Despite this, the twenty-first century coal used for the production of & rsquo; thermal energy (heat) and electricity power plants and industrial boilers.
Currently the main problems are presented pollution and sustainability, which is a natural resource depletion in the process.
Use of coal
Coal is mainly used as a primary source of heat in industrial boilers for obtaining electricity from coal combustion chambers (fixed bed or fluidized bed) of power plants. It is therefore mainly a fuel that can be classified into fossil fuels. 75% of global coal used to produce electricity. The overall energy efficiency of coal plants is not very high, about 25% -27%.
Minority also has other applications, among which are, for example, cement kilns and production of coking coal from coal to produce steel.
Two technologies with great future prospects are gasification and coal liquefaction. The first is older, used since the eighteenth century to get what was then called the gas and water currently has interest to produce these synthetic gaseous fuels (natural gas or synthetic GNS, hydrogen, etc. ), which are intended to be easier to store and transport, as well as more environmentally friendly, solid coal. The liquefaction of coal began to do in Germany during World War II, not to depend on other countries for oil and its derivatives, because they did not have oil fields but coal mines. As the oil runs out in the world, this technique, directly or indirectly, it becomes increasingly advantageous and also allows to produce cleaner fuels and designed to make them more suitable for use in the automotive industry. The liquid fuel obtained by coal liquefaction has twice the calorific value coal used to make it.
Like other fossil fuels, coal burning emits mainly in the air of carbon dioxide (CO2), an atmospheric pollutant that is considered the main greenhouse gas. In addition, the extraction is increased radioactive radon in the air and depending on how you do, can contaminate soil and water to wastewater not treated properly.
A central thermal coal also produces nitrogen oxides (NO and NO2) and sulfur dioxide (SO2), which cause acid rain. Nitrogen oxides are also toxic. Sulfur dioxide can be reduced considerably through the desulphurisation of gases in the fireplace with limestone (CaCO3), but then there are important gypsum waste and carbon dioxide. This process is usually done unless required by law, because of its high cost. Chalk, ash and other solid particles emitted into the atmosphere can be reduced with filters. The plant also increases the series of natural radioactive pollutants, mainly family radon.
Last review: June 12, 2016