The combustion of coal produces carbon dioxide (CO2). CO2 produced by coal-fired power generators can be captured at the point of emission as a relatively pure gas and stored safely in underground reservoirs by injection or after conversion to rock-like solid materials. This process is known as carbon capture and storage (CCS), or geosequestration.
Carbon capture is proven technology. Carbon dioxide is currently separated and extracted from natural gas well heads around the world. Vattenfall, a Swedish power company, plans to start construction in 2006 of a coal-fired, CCS power station in Germany. But it is expensive, estimated to represent around 75 per cent of total CCS costs as against 25 per cent for the transport and storage of the captured material.
Major research efforts are underway to bring down these costs, led internationally by the International Energy Agency Clean Coal Centre and the Carbon Sequestration Leadership Forum, and in Australia by the Co-operative Research Centre for Greenhouse Gas Technologies and ACARP and COAL21.
Storing captured CO2 is feasible as well as safe and well established. In over 70 locations around the world, enhanced oil recovery (EOR), enhanced gas recovery (EGR) and enhanced coal bed methane recovery (ECBMR) is achieved by pumping CO2 under pressure into natural oil and gas reservoirs. CCS essentially replicates this.
Storage options for captured CO2 include the use of geological formations, saline formations, oil and gas reservoirs and unmineable coal seams. It is estimated that Australian geological formations have the capacity store over 1600 years’ worth of national carbon dioxide emissions. Underground saline formations associated with sedimentary geological basins offer the greatest capacity. They have also proved their safety by serving as a safe trap for natural gas over millions of years.