--> Abstract: An Overview of Clean Coal Technologies and Carbon Capture and Storage (CCS), by Ian J. Duncan and William A. Ambrose; #90124 (2011)

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AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

An Overview of Clean Coal Technologies and Carbon Capture and Storage (CCS)

Ian J. Duncan1; William A. Ambrose1

(1) Bureau of Economic Geology, Austin, TX.

Carbon Capture and Storage or CCS is a general term that applies to a set of integrated technologies that capture CO2 from carbon based fuels, compress the CO2, transport it and finally sequester it in a form of long term storage such as in depleted oil and gas fields, or deep brine reservoirs. CCS involves capture from fossil fuel fired electric plants (coal or natural gas), chemical plants, refineries, cement plants, or even biofuel-fired electric plants. Clean Coal Technologies (CCT) are a subset of CCS that address the specific issue of decarbonizing energy production (in the form of electricity or transportation fuels) from coal in a environmentally acceptable way. CCT can be divided into those based on either post-combustion or pre-combustion capture. Post-combustion capture occurs when the coal is combusted in air (conventional coal plants) or oxygen (oxy-fired technology) and resultant combustion products are processed to separate the CO2. Post-combustion capture from conventional coal plants is likely to be expensive (on the order of $40 to 50 per metric ton) because their flue gas typically contains 88% N2 and only 12% CO2. Although post-combustion capture is often presented as synonymous with retrofitting existing plants, it will be most efficient when implemented in new super-critical or ultra-super-critical coal plants (such as proposed for Sweetwater Texas by Tenaska). Pre-combustion capture occurs in plants where carbon-based fuels are gasified in a limited oxygen environment. This process produces a mixture of H2 and CO2 in roughly equal portions. After separating the CO2 the H2 is used to fuel a combined cycle turbine. This type of installation is known as an Integrated Gasification and Combined Cycle plant or IGCC (such a plant is currently being planned for Odessa, Texas by Summit Power Group). Post combustion capture plants are thought to have capture costs about half or less than those for pre-combustion capture although capital costs for IGCC plants are higher than for conventional coal plants. CCT provide the promise for environmentally sound production of energy from the large US coal reserve. The Department of Energy has sponsored a set of demonstration projects that will test various aspects of CCS and CCT. Several of these projects in Texas integrate CO2 enhanced oil recovery projects for potential CO2 storage sites.