The work presented in this paper aims to examine and analyse a novel concept dealing with the carbonation-calcination process of lime for CO2 capture from coal-fired power plants. The scheme is based on a novel steam gasification process of low rank coals with calcined limestone where in-situ CO2 capture and steam reforming are performed in a single reactor. CO2 is separated reacting exothermically with CaO based sorbents, providing also the necessary heat for the gasification reactions. The produced gas is a H2-rich gas with low carbon or near zero carbon content, depending on the ratio of lime added to the process. The produced fuel gas can be used in state-of-the-art combined cycles where it is converted to electricity, generating almost no CO2 emissions. After being captured in the gasification process, CO2 is released in a separate reactor where extra energy is provided through the combustion of low rank coal. Regenerated CaO is produced in this reactor and is continuously recycled within the process. The key element of the concept is the high-pressure steam gasification process where CO2 is captured by CaO based sorbents and fuel gas with high hydrogen content is produced, without using additional shift reactors. Two optimised power plant configurations are presented in detail and examined. In the first case, pure oxygen is utilised for the low rank coal combustion in the limestone regeneration process, while in the second case fuel is combusted with air instead. Results from the equilibrium based mass balance of the two reactors as well as the power plant thermodynamic simulations, dealing with the most important features for CO2 reduction are presented concerning the two different options. The energy penalties are quantified and the power plant efficiencies are calculated. The calculated results demonstrate the capability of the power plant to deliver decarbonised electricity while achieving high overall electrical efficiencies, comparable to other technological alternatives for CO2 capture power plants. The Aspen Plus software is used for the equilibrium based mass balance of the gasifier and the regenerator while the combined cycle power plant cycle calculations are performed with the thermodynamic cycle calculation software ENBIPRO (ENergie-BIllanz-PROgram), a powerful tool for heat and mass balance solving of complex thermodynamic circuits, calculation of efficiency, exergetic and exergoeconomic analysis of power plants [1].
Flexible operation of coal-fired power plant integrated with post-combustion CO2 capture
