Coal is the most common and longest used fossil energy fuel. Coal, oil and natural gas will still exist when depleted, and coal prices are stable compared to other energy sources. Coal is a safe and reliable product because of its ease of transportation, ease of storage and long life. It is also easy to process and deliver coal to users. With such properties, coal is an indispensable source of energy.
World oil reserves will run out in 40 years, according to estimates. Natural gas reserves will be exhausted after 60 years. Estimates for coal reserves are around 200 years. It has been the fastest-growing energy source worldwide in the 21st century and also it will be the long-term efficient energy product in the near future.
Coal is a fossil fuel. Its main components are; carbon, hydrogen, and oxygen. Steam coal is also known as thermal coal. It’s mostly used in electricity generation.
Thermal Coal products in South Africa
South Africa is the 6th biggest coal exporter country with 6,23 billion USD export value. 1/4 of South African coal is exported to energy providers and metallurgical plants in mostly Europe, South America, and India.
Coal is highly used as energy source in South Africa, almost 90% of South Africa electricity being obtained from coal-fired power stations.
Supporters of environmentalist products compare wind and solar power and electricity generation capacity and storage issues with the cost of natural gas production and the security risks posed by nuclear power plants. The result is clear, coal will remain an economic and reliable source of energy for the next 50 years.
It is no coincidence that South African coal is used in the energy sector and especially in electricity generation. South Africa's RB1 and RB3 type coals offer high-calorific value and high energy efficiency. Other features that make South African coal advantageous are its ability to burn easily and fast, soft and brittle.
Analysing and specification of Coal
The type and basic properties of coal are determined by the properties measured in 8 main titles. Such as: "gross calorific value", "total moisture", "volatile matter", ash, "total sulphur" and so on.
The specification for thermal coal is defined in terms of its typical quality. Coal trading companies request additional analyses and test records on milling, ash composition, and ash fusion temperatures as a standard procedure.
SOUTH AFRICAN COAL SPECIFICATIONS - RB1, RB3, RB4/4800
The value and treatment of coal is affected by many properties, such as listed below:
Total moisture: The total moisture in the coal is represented by measuring weight loss from aggressive drying in an air atmosphere under strictly controlled temperature, time and airflow conditions. The presence of moisture is an important factor both in the storage and utilization of coal, as it adds unnecessary weight during transportation, reduces calorific value and presents some usage problems.
Inherent moisture: It means moisture, except those found in fractures that are present as an integral part of the natural seam of coal, including water in the pores, but which are macroscopically visible.
Ash: Its content is the non-combustible residue that remains after the combustion of the coal. Ash reduces the carrying and burning capacity, affects the combustion efficiency and boiler efficiency and therefore increases transportation costs.
Volatile matter: It is the material released when the coal is heated to 950 °C in the absence of air under the specified conditions. It consists of a gas mixture, low boiling organic compounds and tars which, after cooling, are mixed into oils. In general, coals containing high volatiles are highly flammable and highly reactive in combustion applications.
Fixed carbon: It’s a solid combustible residue that remains in the furnace after distillation of the volatile material, mostly carbon, but also contains a quantity of hydrogen, oxygen, sulphur and nitrogen which is not exhausted by the gases. It provides a rough estimate of the heating value of coal.
Total Sulphur: Since the sulphur content in coal causes corrosion and contamination of boiler pipes and atmospheric contamination when released in flue gases, it presents problems with the use and consequent pollution.
HGI: Coal can be pulverized depending its own strength. and this process can measure by the Hardgrove Grindability Index testing.
Gross Calorific Value (ADB): The calorific value is the heat capacity of the coal per unit weight after it has completely burned. It is often referred to as the gross calorific value.
Uses of Coal & Product Types
Coal is mainly used in electricity production, iron and steel industry, cement industry, heating and other industrial plants. Coal is also used in the production of aluminium refineries, paper mills, chemical plants and pharmaceuticals. Many chemicals are obtained from the by-products of coal. Coal and coal by-products are used in thousands of products, such as soap, aspirins, solvents, dyes, plastics and fiber such as rayon and nylon.
Coal is also using as an essential ingredient in many kinds of new and technological knowhow-based products such as activated carbon, carbon fibre and silicon metal.
Coal properties classified by its rank dependent. at the same time, some of the other factors could be effective for example "maceral composition" and "the presence of mineral"
Coals basically categorised with its physical properties such as coal preparation and utilisation.
For example, coal density ranges could be 1.1 to 1.5 megagrams per cubic meter.
Coal density is determined by the dimensions of the pores and voids in the coal mass. Coal is a flexible material and generally has three different sizes of pores: macropores (diameter bigger than 50 nanometres), mesopores (diameter between 2 to 50 nanometres), micropores (diameter less than 2 nanometres).
An important property of coal is Its ability to reflect light. Reflectivity is measured by shining a beam of monochromatic light on a polished surface of the vitrinite macerals in a coal sample R-max, R-mean, R-random, and R-min reflection values are measured in coals. Reflection values allow us to determine the process of coal formation.
In coal mined from different mineral deposits, properties such as hardness, grindability, ash fusion temperature, and free swelling index are measured. Accurate determination of these properties ensures accurate determination of coal extraction, processing and usage areas.
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