Power Plant with CO2 Capture based on Absorption: Integration Study
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This thesis gives a detailed evaluation of the integration of power plants and post-combustion CO2 capture based on absorption. The study looks at natural gas combined cycles and pulverized coal power plants. Also the absorption process has been evaluated separately, aiming at reducing energy requirements in the capture process. In the first part of the thesis a theoretical part was given on fundamentals of CO2 capture by absorption, power generation, and process integration. Based on this theory, several case studies were defined for each of the three main processes. Simulation models were built accordingly and investigated. Simulation results from the capture process showed that there was a reboiler energy saving potential of 29% and 27% for NGCC and PC plant, respectively, when including vapor compression and absorption intercooling in the capture process. Another interesting observation made was reduced cooling duty in the overhead condenser of the stripper when applying vapor compression.Analysis of steam extraction from the NGCC plant showed it was possible to cover 1 MJ/kg CO2 directly from the HRSG. This steam can be provided directly from the LPB. For duties above 1 MJ/kg CO2 a secondary extraction point was required. In this study the IP/LP crossover was considered the most appropriate point to extract the remaining steam. The efficiency penalty when integrated with the different CO2 capture cases ranged from 7-8%, giving a net plant efficiency of 49.6-50.5%. At part load it was shown that the LPT should be throttled in order to secure constant pressure at the extraction point.For the PC plant the feedwater heat system showed potential in terms heat recovery in the return stream from the capture process. By integrating the return stream with FWH2, energy savings of 11.9% compared to the base case plant were found. Also it was found that the IP/LP crossover pressure should be set to 4.5 bar, since the IPT has the highest efficiency and therefore power production in this unit should be maximized. The final results for the PC plant efficiency range from 30-31.7% and the percentual efficiency penalty was 10-11.7% for the four capture case studies. As was the case for the NGCC plant, the LPT should be throttled when operating at part load.