Oxy-combustion turbines

Publication Overview

Post combustion capture is usually considered to be the leading option for capture of CO₂ at natural gas fired power plants but there is increasing interest in the alternative of oxy-combustion turbines which use recycled CO₂ and/or H2O as the working fluid instead of air. Large component tests have taken place and a 50 MWth demonstration plant is scheduled to be commissioned in 2017. Oxy-combustion turbines can also be combined with solid fuel gasification as an alternative to IGCC with pre-combustion capture. This study provides an independent evaluation of the performance and costs of a range of oxy-combustion turbine cycles, mainly for utility scale power generation. The study was carried out by Amec Foster Wheeler in collaboration with Politecnico di Milano.

Publication Summary

• The predicted thermal efficiencies of the oxy-combustion turbine power cycles assessed in this study range from 55% (LHV basis) for the NET Power cycle to around 49% for the other base case cycles. For comparison, a recent IEAGHG study predicted an efficiency of 52% for a natural gas combined cycle plant with post combustion capture using a proprietary solvent.
• There is scope for improving the thermal efficiencies in future, for example by making use of materials capable of withstanding higher temperatures. Proprietary improvements by process developers may also result in higher efficiencies.
• The levelised cost of electricity (LCOE) of base-load plants using natural gas at 8 €/GJ are estimated to be 84-95 €/MWh, including CO₂ transport and storage costs. The lowest cost oxy-combustion plant (NET Power) has a slightly lower LCOE than a conventional gas turbine combined cycle with post combustion capture using a proprietary solvent.
• The cost of CO₂ emission avoidance of the various cycles compared to a reference conventional natural gas combined cycle plant is 68-106 €/t CO₂ avoided.
• The base case percentage capture of CO₂ in this study was set at 90% but it was determined that it could be increased to 98% without increasing the cost per tonne of CO₂ avoided, or essentially 100% if lower purity CO₂ was acceptable.
• The water formed by combustion is condensed in oxy-combustion turbine cycles, which would mean that if air cooling was used the power plants could be net producers of water. This could be an advantage in places where water is scarce, although air cooling would reduce the thermal efficiency.
• Oxy-combustion cycles could have advantages at compact sites. The total area of an oxy-combustion combined cycle plant is estimated to be slightly less than that of a conventional combined cycle with post combustion capture. The ASU could be located off-site if required to further reduce the power plant area. In addition, regenerative oxy-combustion cycles are significantly more compact than combined cycles.
• Oxy-combustion turbines could be combined with coal gasification. The predicted thermal efficiency of a coal gasification plant with a semi-closed oxy-combustion combined cycle (SCOC-CC) is 34% (LHV basis). This is similar to that of more conventional CCS technologies (IGCC with pre-combustion capture and supercritical pulverised coal with post combustion amine scrubbing) but the estimated capital cost and cost of electricity of the oxy-combustion turbine plant are significantly higher.