This is apropos of the statement (March 28) by the Sindh mines department secretary that the federal government had given approval to a 100MW power plant at Thar at which coal gas would be extracted through underground coal gasification (UCG) technology.
The project would be based on latest technology known as integrated gasification combined cycle (IGCC), which would capture carbon dioxide.
While the secretary deserves credit for being environment-conscious, the capturing and storing of carbon dioxide will be done on the asking of the World Bank. The bank's insistence on capturing carbon dioxide is understandable, as the gas has international implications.
There are other environmental concerns associated with UCG technology that need to be addressed. While carbon dioxide will be captured, UCG also cause emissions of sulphur oxides, nitrogen oxides and particulates.
Volatile organic compounds (VOCs) derived from coal travel to groundwater resources, causing their contamination. The contaminated groundwater may move upward due to buoyancy, resulting from changing fluid density gradients and thermal environment. Loss of syngas into the surrounding geological formations and leaching of residual ash or tars remaining in a spent UCG cavity are also the sources of groundwater contamination. In the US, a UCG plant at Hoe Creek in Wyoming resulted in the contamination of aquifers used for drinking water.
Groundwater in the Thar area is already contaminated. Any further contamination will make the groundwater poisonous. Groundwater constituents like magnesium, sodium, calcium, bicarbonates, sulphates, total dissolved solids, etc, increase many times owing to UCG.
Lowering of the water table is a potential impact of UCG. Some groundwater is drawn into the UCG process and used in gasification reactions. This will be critical in case of Thar. Aqueous solubility of organic compounds is the function of temperature. The higher the temperature, the greater is the solubility of organic compounds.
Land subsidence is a major environmental concern when UCG technology is used. In fact, UCG has produced significant land subsidence and groundwater contamination, in many operations in the world.
Environmental protection concerns pose constraints on the hydrological and geological aspects of the site, reducing production of exploitable coal. Subsidence is the lowering of the ground surface caused by a collapse or compression of underlying rock strata.
During the process, ash in coal is converted to inert, glassy slag. If the coal contains mercury, the synthesis gas (syngas) is passed through a bed of activated charcoal, for its removal. The spent activated charcoal has to be disposed of carefully, as mercury is a major environment pollutant.
Syngas is the product of UCG. The gas comprises hydrogen, carbon monoxide, nitrogen, carbon dioxide and methane. Methane is an explosive gas. On April 5, nearly 25 people died in West Virginia, USA, in coal mine accident, due to the explosion of methane gas.
Likewise, in China, on the same day, underground floods trapped over 110 workers in coal mine in Shanxi province.
These incidents highlight hazards with coal mining. UCG is a non teady state process. The operations cannot be controlled to the same extent as surface gasification.
Coal gasification is a promising option for the future economic development of Thar. The environmental impacts, however, must be adequately addressed.
F. H. MUGHAL
Karachi
