CO2-free power generation in combined cycles - Integration of post-combustion separation of carbon dioxide in the steam cycle

Ever since the release of the Kyoto protocol the demand for CO2-free processes have been increasing. One of the most expanding sources of electric power in the industrialised world today is the gas-fired combined cycle, combining high efficiency and low investment cost. In this paper, the integration of a post-combustion CO2-separation unit into a combined cycle is studied from a thermodynamic and economic point-of-view. A standard dual-pressure combined cycle is chosen as a reference cycle. It is compared to a dual-pressure combined cycle and a triple-pressure combined cycle with the lowest pressure level producing steam for a CO2-separation unit. The steam pressure levels in the different cycles are optimised for maximum efficiency and minimum specific cost, respectively, using genetic algorithms. The efficiency drop due to CO2-separation is approximately 8% points, from 54 to 46%. The specific cost of the power plant is expected to increase with almost 100% and the cost of electricity with approximately 30%. In several countries a carbon dioxide tax is already introduced as an incentive for more efficient power cycles and use of fuels with lower content of coal. The result above implies that the level of such a tax would be in the order of 30% of the price of electricity to encourage CO2-free power generation.