Coal combustion products (CCPs) can play an important role in concrete production. CCPs are the by-products generated from burning coal in coal-fired power plants. These by-products include:

• fly ash
• bottom ash
• boiler slag
• flue gas desulphurisation gypsum
• others types of material such as fluidised bed combustion ash, cenospheres, and scrubber residues

Fly ash can be used to replace or supplement cement in concrete. In the USA, for example, more than half of the concrete produced is blended with fly ash.

Among the most significant environmental benefits of using fly ash over conventional cement is that greenhouse gas (GHG) emissions can be significantly reduced. For every tonne of fly ash used for a tonne of portland cement (the most common type of cement in general use around the world) approximately one tonne of carbon dioxide is prevented from entering the earth’s atmosphere. Fly ash does not require the energy-intensive kilning process required by portland cement.

Using CCPs reduces GHG emissions, reduces the need for landfill space, and eliminates the need to use primary raw materials. Fly ash produces a concrete that is strong and durable, with resistance to corrosion, alkali-aggregate expansion, sulphate and other forms of chemical attack.

Coal combustion products are expected to continue to play a major role in the concrete market. Their use in other building products is also expected to grow as sustainable construction becomes more prominent, and more architects and building owners understand the benefits of using CCPs.

Underground Coal Gasification (UCG) is a method of converting unworked coal – coal still in the ground – into a combustible gas which can be used for industrial heating, power generation or the manufacture of hydrogen, synthetic natural gas or diesel fuel.

UCG technology allows countries that are endowed with coal to fully utilise their resource from otherwise unrecoverable coal deposits in an economically viable and environmentally safe way. UCG turns this resource into high value products:

• clean power
• liquid fuels
• syngas
• fertilisers and other chemical feedstocks.

UCG uses a similar process to surface gasification. The main difference between both gasification processes is that in UCG the cavity itself becomes the reactor so that the gasification of coal takes place underground instead of at the surface.

[Source:  http://www.worldcoal.org/]

South Africa has been producing coal-derived fuels since 1955 and has the only commercial coal to liquids industry in operation today. Not only are CTL fuels used in cars and other vehicles, South African energy company Sasol’s CTL fuels also have approval to be utilised in commercial jets. Currently around 30% of the country’s gasoline and diesel needs are produced from indigenous coal. The total capacity of the South African CTL operations now stands in excess of 160,000bbl/d.

CTL is particularly suited to countries that rely heavily on oil imports and that have large domestic reserves of coal. There are a number of CTL projects around the world at various stages of development. Liquid fuels from coal can be delivered from an existing pump at a filling station via existing distribution infrastructure and used, without modification, in the current vehicle fleet.

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.

[Source:  http://www.worldcoal.org/]