Optimal Integration of Post-Combustion CO2 Capture Process with Natural Gas Fired Combined Cycle Power Plants

Post combustion CO2 capture (PCC) has been considered as one of the near term solutions to significantly reduce CO2 emissions associated with fossil fuels combustions. To accelerate the PCC incorporation into the energy market, various political, legal, economic and technical challenges and uncertainties should be successfully tackled. In relation to such, this thesis investigates methods to offer optimal incorporation of post-combustion CO2 capture process into natural gas fired combined cycle (NGCC) power plants. The objectives of this thesis is to develop and use thermodynamic models to study various process configurations, evaluate and quantify their benefits in terms of energy requirements on the performance of the integrated PCC-NGCC power plants. A detailed rate-based model of CO2 absorption/stripping process using 30 wt. % monoethanolamine (MEA) as solvent was developed in Aspen Plus® RateSepTM. The developed rate-based model was successfully validated in pilot scale using experimental data obtained from two pilot plants: (1) the UKCCSRC/PACT CO2 capture pilot plant, and (2) the pilot plant at the Laboratory of Engineering Thermodynamics in TU Kaiserslautern. The application and effectiveness of four alternative process configurations were studied: two absorber intercooling processes, i.e. “in-and-out” intercooling and “recycled intercooling”, and two stripper configurations: “advanced reboiled” stripper and “advanced flash” stripper. In addition, optimal incorporation of a large-scale PCC plant, including the CO2 compression unit, into a commercial-scale NGCC plant with a nominal power output of 650 MWe was investigated. The performance viability of the integrated NGCC-PCC plant was assessed at power plant full-load and part-load operations, to study the feasibility of the PCC operation at power plants full-load and part-loads, and recognise key performance parameters require careful consideration for a stable and efficient operation of the integrated plant at variable loads. In addition, the performance of the NGCC, especially the low pressure steam turbine, at various loads at times the power plant was integrated with the capture plant, and at times the CO2 capture plant was offline were investigated, and issues require careful considerations when operating the power plant in case of non-capture operation were addressed. This research also studied the relationship between the cost of CO2 capture and the flue gas CO2 concentration ranging from 4 to 14 %. For each case, the specific regeneration and cooling duties and total capital expenditure (CAPEX) and operational expenditures (OPEX) were calculated and compared. Accordingly, the total annual cost of each plant (TOTEX) was determined using the respective CAPEX and OPEX with taking into account an investment period of 20 years and an interest rate of 10 %. Finally, for each case the cost of CO2 captured was estimated and compared.