Coal is the single largest fuel used for power generation all over the world, due to its abundant availability and established infrastructure and technology. However, greenhouse gas emission poses a significant challenge in continuing the usage of coal as prime fuel. Currently, Natural gas is favored as fuel for power generation and number of LNG (liquefied natural gas) plants have been set up in many parts of the world. Coal seam methane gas is another potential source that competes with natural gas. Basically, Methane is the major constituent of such gases in the form of Hydrogen and they are suitable for both combustion as well as for gasification for power generation. Countries who are endowed with large deposits of coal such as Australia, South Africa, Indonesia have advantages in clean coal technologies and in reducing their greenhouse gas emissions. There is an opportunity for coal-fired power plants to continue their operations, if they can solve the greenhouse gas emission and other pollution problems associated with coal. Number of companies are now re-evaluating clean coal technologies such as IGCC and carbon capture and reuse.
As we have seen in previous articles, Hydrogen is the key in developing clean coal technology of the future. That is why, gasification technology such as IGCC (Integrated Gasification and Combined Cycle) is gaining importance over combustion technologies because that is the only way we can introduce a Hydrogen molecule in the combustion by way of ‘Syngas’. By introducing Hydrogen, we not only can improve the thermal efficiency but also use the heat of combustion to the most by combined cycle with reduced GHG emission. It also facilitates the usage of existing and known power generation technologies such as, steam turbine and gas turbine, as well as, new technologies such as Fuel cell and Hydrogen turbines.
Coal in the form of pumpable liquid (CWS –coal water slurry) is another key milestone in developing a clean coal technology. Countries like China and Indonesia have been using coal water slurry for power generation successfully. Finely powdered coal is mixed with water in the ratio of 60:40 along with dispersant such as Lignosulfonate as additives to make a finely dispersed, viscous liquid that resembles heavy petroleum oil, ready for combustion. It is easier to handle pumpable oil than a solid coal.
A novel products called ‘colloidal coal water’ (CCW) is a finely dispersed colloidal coal in water with additives such as surfactants and dispersants with specific formulating agents leading to certain rheological properties is a key development in clean coal technology. The coal water slurry now used does not have long-term stability and storage properties like colloidal coal water fuel. The work is under development and it is expected that such finely dispersed colloidal coal water mix resembling a liquid hydrocarbon may be named as ‘liquid coal’ for all practical purposes will become a low-cost fuel in the future power generation.
This ‘colloidal coal liquid’ can be easily gasified or used as liquid fuel for combustion equipment such as boilers and also serve as precursor for a number of chemical product synthesis as downstream products. The emitted Carbon dioxide can be captured cryogenically and separated in a pure form for potential application such as ‘Natural Refrigerant’ and to synthesize number of chemical products. Clean coal can become a commercial reality provided we re-evaluate the coal preparation, gasification methods and to contain emitted carbon into a useful product of commerce.