Definition and Types of Coal

Cranepedia - Coal is a fossil fuel. Understanding generally combustible sedimentary rock, sedimentary organic, primarily the remains of plants and are formed through a process pembatubaraan. The elements consists primarily of carbon, hydrogen and oxygen.

Coal also is an organic rock that have physical properties and chemical complex that can be found in various forms.

Elemental analysis gives empirical formula such C137H97O9NS formula for C240H90O4NS for bituminous and anthracite.

Coal Age 

Coal formation requires certain conditions and only occurs in certain eras in the history of geology. Carboniferous Period, about 340 million years ago (Mya), is the formation of the most productive coal which almost all deposits of coal (black coal) that is economical in the northern hemisphere formed.

In the Permian Period, about 270 Mya, also formed coal deposits economically in the southern hemisphere, such as Australia, and continues up to the Tertiary Period (70-13 Mya) in various other hemisphere.

Forming material Coal
Almost all the coal-forming plant origin. The types of coal-forming plants and generally according Diessel (1981) is as follows:

• Alga, from the Age of Pre-Cambrian to Ordovician and single-celled. Very few coal deposits of this period.
• Silofita, from the Silurian to the Middle Devon, is derived from algae. Little coal deposits of this period.
• Pteridofita, age of Upper Devonian to Upper Carboniferous. The main material Carbon-old coal-forming in Europe and North America. Plants without flowers and seeds, spores multiply and grow in warm climates.
• Gimnospermae, a period ranging from Permian to Cretaceous Period Central. Heterosexual plants, seeds encased in fruit, such as pine, contain levels of sap (resin) high. Type Pteridospermae like gangamopteris and Glossopteris is the main constituent of coal Permian such as in Australia, India and Africa.
• Angiosperms, from the Upper Cretaceous until now. Modern plant species, fruit covering seed, male and female in one interest, less gummy than gimnospermae so that, in general, less can be preserved.

Class and type of Coal

Based on the rate of formation process which is controlled by pressure, heat and time, coal is generally divided into five classes: anthracite, bituminous, sub-bituminous, lignite and peat.

1. Anthracite coal is the highest grade, with a shimmering black (luster) metallic, containing between 86% - 98% of the elements carbon (C) to a moisture content of less than 8%.

2. Bituminous containing 68-86% carbon element (C) and the water content of 8-10% by weight. Grade coal are the most widely mined in Australia.

3. Sub-bituminous coal contains less carbon and a lot of water, and therefore a source of heat is less efficient compared to bituminous.

4. Lignite or brown coal is very soft coal containing 35-75% water by weight.

 

5. Peat, porous and has a moisture content above 75% and the lowest calorific value.

Formation of Coal

The process of change remains of plants into peat to coal termed (coalification). In brief, there are two stages of processes that occur, namely:

• Diagenetik or Biochemistry stage, begins when the plant material deposited to form lignite. The main agents involved in the process of this change is the water content, degree of oxidation and biological disorder that can cause the process of decay (decomposition) and compacting the organic material and form peat.
• Metamorphic stage or geochemistry, covering the process of change of lignite into bituminous and finally anthracite.

Thus sundries glimpse of coal, may be useful!