Oxy-combustion Processes for CO₂ Capture from Power Plant

Publication Overview

The IEAGHG R&D programme has completed several studies on the costs of CO₂ capture from power plants using post combustion and pre-combustion capture technology. The costs of oxy-combustion capture have not been studied to the same depth because of the immaturity of the technology. Although commercial examples of the technology are still not in existence it is now felt that there has been sufficient advance in knowledge to attempt a cost study of similar accuracy. The process is applicable to both natural gas and coal fired power plant although the equipment used for the different fuels is quite different. There are many oxy-combustion process variants some of which are still in early stages of development. For example processes are proposed which use dense oxygen conducting membranes or recycle of water rather than CO₂. It would be difficult to generate firm costs for process using such novel elements. The brief given to the contractor was to select a gas fired and a coal fired process which would make use of existing designs and not represent any significant stepout beyond accepted limits. For the coal fired case this essentially means maintaining sufficient CO₂ recirculation so as not to radically alter velocities and heat fluxes in the radiant and convective parts of a conventional pulverized coal boiler. For the gas fired case which would be a combined cycle gas turbine with CO₂ recycle the situation is more difficult since a new gas turbine model would have to be developed. The brief was to base this machine on existing design limitations and practices so that the changes would be minimized. The commercial costing of this machine remains difficult since the price will be highly dependent on the size of the market.

Publication Summary

The main conclusion is that the extra costs of electricity in CO₂ capturing oxy-combustion processes are similar to those for coal fired pre and post combustion options but somewhat higher for gas fired plant. Efficiency losses and costs of CO₂ avoidance are also of similar magnitude for coal fired plant but significantly higher for the gas fired process. As yet there is no obvious CO₂ capture technology preference, thus choices seem likely to determined by factors other than cost and efficiency at this stage. IEAGHG is preparing a comparison of the performance of all the processes which have been studied by the programme and this will be issued in due course.

The need for a completely new gas turbine remains a major hurdle for application of this technology to a gas fired CCGT process.