REVIEW OF COz CAPTURE TECHNOLOGJES AND SOME IMPROVEMENT OPPORTUNITIES

Reducing C02 emissions for addressing climate change concerns is becoming increasingly important as the C02 concentration in the atmosphere has increased rapidly since the industrial revolution. Many mitigation methods, including C02 sequestration and novel C02 utilization, are currently-under investigation. Most of these processes require C02 in a concentrated form. However the C02 from large sources such as fossil fueled power plants is mixed with nitrogen, water vapor, oxygen, and other impurities. A typical C02 concentration from coal fired power plants is around 15 %, while C02 concentrations for natural gas fired plants are less than I O %. Therefore, capturing C02 from flue gas is an important common link for many mitigation methods. The current commercial operations for capturing COz from flue gas use a chemical absorption method with Monoethanol Amine (MEA) as the sorbent. The method is expensive and energy intensive. The cost of capturing a ton of C02 including removing impurities and compressing C02 to supercritical pressure using existing MEA technology would be in the order of $40, and the power output would be significantly reduced by the energy consumption in capturing and compressing C02. The high capture cost and energy consumption would be a major barrier for implementing C02 mitigation methods. Alternative technologies may offer improvement. This paper reviews several separation technologies applicable to caphue C& from flue gas, and discusses improvement opportunities and research needs. MTRODUCTION Concern over the increased concentration of C02 in the atmosphere and its effect on global climate change has increased the awareness and investigation for reducing COz emissions. Most of the methods for mitigation require C02 in a concentrated form, while the C02 from fossil fueled power plants is mixed with nitrogen, water vapor, oxygen, and other impurities and bas low concentrations (15 % for coal fired power plants, and less than 10 % for natural gas fired plants). Therefore, capturing COz from flue gas is an important common link. The current commercial operations for capturing C02 fiom flue gas use a chemical absorption method with Monoethanol Amine (MEA) as the sorbent. The method is expensive and energy intensive. An estimate by Pergman et a1 [l] using data fiom an Af3BLummus Crest brochure [2] indicated the cost of capturing a ton of COz including removing impurities and compressing C02 to a supercritical pressure would be in the order of $40. While compression is an energy intensive and expensive component, the capture part of MEA method actually uses more energy and costs more than compression. The high capture cost is a major barrier for implementing near term carbon sequestration methods such as injecting C02 for enhanced oil recovery [l]. The other major shortcoming of the current technology is its high-energy consumption. The amine based method uses a large amount of low-pressure steam for sorbent regeneration, and the total power output is significantly reduced. It could lead to ' 20% reduction in electricity production for a PC plant (107MW/S54MW) as a study by Booras and Smelser indicated [3]. Following is a preliminary analysis of several separation technologies applicable to C02 capture, new power generation configurations that may simplify C02 capture, as well as a discussion of some improvement opportunities GAS SEPARATION METHODS APPLICABLE FOR C02 CAPTURE Capturing COz from the flue gas is essentially a gas separation process. Several separation methods, including Chemical Absorption, Physical Absorption, Physical Adsorption, Membrane Technologies, and Cryogenic Separation, can achieve such a goal. The judging criteria are capture effectiveness, process economy, energy consumption, and other technical and operational issues. Other measures such as modifying of power generation configurations by using OdCOz Combustion mode and oxygen blown Gasification Combined Circle, could alter the flue gas composition and pressure that could help the C02 capture. Such strategy has some benefit but also raises new technical challenges.