UCG cost effective alternative to Reactor Gasification
 

An alternative to coal gasification in 
 reactors is underground coal gasi-
 fication (UCG).
This method of coal gasification has the potential to reduce capital costs significantly, as the costs associated with surface gasification and conventional coal-mining are removed, because coal extraction and gasification occur in a single phase. 
A further economic benefit of UCG is that it provides the opportunity to extract stranded coal reserves that would otherwise be unmineable.


The burning coal in the seam mitigates the environmental impact of surface coal combustion and the associated release of large quantities of carbon dioxide. Further, UCG reduces the potential for soil contamination, as no handling and storage of large volumes of ash and slag in ash dumps is required. 
The method also allows for the removal of polluting constituents, such as sulphur oxides, particulates and heavy metals, from the production of synthetic gas (syngas).


The UCG process is initiated by drilling two adjacent boreholes into the coal seam. A pressurised oxidant, such as air or oxygen, is injected into one of the boreholes and ignited at the coal seam. 
The resulting chemical reaction converts the coal to gas, which is extracted from the second borehole. 
The product gas is collected at the surface and treated to remove contamin-ants and residues, after which it can be used as syngas for synthetic fuels production. 
The expansion of the process is achieved by the addition and linkage 
of further injection and production 
wells.


In South Africa, petrochemicals company Sasol has completed the basic engineering designs for a demonstration-scale UCG plant, to be built on a stranded deep coal seam near its coal-to-liquids facility in Secunda.
Further, State-owned power utility Eskom is developing a UCG project, with the first ignition of the coal seam having occurred at the Majuba operation in January 2007. 
The project is being developed in a series of stages to ultimately produce 2 100 MW of power using UCG in a combined-cycle power plant.


From miningweekly