PRE-, POST- AND OXY-COMBUSTION APPROACHES TO MITIGATE CO2 EMISSIONS: TECHNO-ECONOMIC COMPARISON

Worldwide energy production requirements could not be fully satisfied by nuclear and renewables sources. Therefore a sustainable use of fossil fuels (coal in particular) will be required for several decades. In this scenario, carbon capture and storage (CCS) represents a key solution to control the global warming reducing carbon dioxide emissions. Currently, the integration between CCS technologies and power generation plants has not been demonstrated yet at commercial scale; therefore, technological risks, which enhance the already significant cost, represent the main near-term barrier to commercial diffusion of CCS. With the aim to comparing them and to estimate the current potential application of CCS technologies, this study reports a performance assessment of different coal-fired power generation technologies. In particular, different plant configurations including (i) integrated gasification combined cycle (IGCC) with pre-combustion capture, (ii) ultra-supercritical (USC) combustion with postcombustion capture and (iii) oxy-coal combustion (OCC) have been compared from both the technical and economic points of view. Each power generation technology has been analysed with reference to both the conventional configuration (without CO2 capture and storage systems) and the more complex configuration with integrated CO2 removal sections, considering a reference thermal input of 1000 MW. As for CO2 storage, the sequestration in saline aquifers has been considered, being this technique characterized by the higher storage capacity in Italy. Performance assessment has been carried out by using simulation models implemented through commercial tools, such as Aspen Plus and Gate Cycle. On the other hand, the economic assessment has been performed through a detailed simulation model, properly developed by Sotacarbo for feasibility studies on CCS power generation plants. The model estimates the annual cash flow and the main typical indicators (such as net present value, internal rate of return, and cost of electricity) on the basis of plant performance and economic parameters. The integration between technical and economic simulation models allows a detailed feasibility assessment. Being the economic assessment strongly influenced by the fluctuation of several parameters (mainly the prices of both electrical energy and CO2 allowances, governed by local and international markets), a sensitivity analysis has been carried out to estimate the impact of these parameters on plant economics. The analysis shows that USC plants are less expensive than IGCC in their basis configuration (without CCS), whereas the costs of the same power generation technologies equipped with CCS configurations are comparable. Moreover, in a short term future, oxy-fuel promises to became one of the most competitive technologies for a CO2-free power generation.