Clean coal is likely to remain a chimera rather than a real solution to carbon emissions, a new study suggests, because the much-touted process of carbon capture and sequestration simply wonât prove to be feasible.
Proponents of coal have held out CCS as the key to a future use of coal in keeping with efforts to combat global warming, but the technology remains unproven and has long faced skepticism.
In theory, carbon dioxide given off during combustion would be captured and injected in either liquid or âsupercriticalâ state into an underground rock formation so that it would not disperse into the atmosphere.
The new study on CCS by Michael Economides of the University of Houston and Christine Ehlig-Economides of Texas A&M University says that proponents of CCS have underestimated the amount of reservoir space that will be required because the volume of carbon dioxide to be stored cannot exceed more than 1% of pore space, and perhaps much less, rather than the 1-4% in most calculations.
âThis will require from 5 to 20 times more underground reservoir volume than has been envisioned by many,â the authors write, âand it renders geologic sequestration of CO2 a profoundly non-feasible option for the management of CO2 emissions.â
Michael Economides himself is a self-declared skeptic of global warming and long has argued that traditional fossil fuels must continue to provide the bulk of our energy needs.
The mistaken calculations are due to the assumption that the CO2 can be injected into a reservoir formation at a constant pressure, the authors say. But in fact, pressure will vary, affecting the rate of injection. Excessive pressure could fracture the formation, says the study, published in the Journal of Petroleum Science and Engineering.
âIn applying this to a commercial power plant, the findings suggest that for a small number of wells the areal extent of the reservoir would be enormous, the size of a small U.S. state,â the authors say.
Several government-sponsored experiments in CCS are under way in various countries, including the U.S.Â The New York Times reported last week on a project in Germany that has been injecting carbon into a sandstone reservoir for the past 22 months and is attempting to monitor any leakage.
By. Darrell Delamaide