Thermodynamic and economic analysis of the different variants of a coal-fired, 460 MW power plant using oxy-combustion technology

Highlights: • Mathematical models of an integrated oxy-combustion power plant. • Thermodynamic analysis of the modeled different cases of the plant. • Analysis of the methods of increasing the net efficiency of the plant. • Economic comparative analysis of the air-type and oxy-type plants. - Abstract: In the face of existing international provisions limiting the emissions of greenhouse gases, primarily carbon dioxide, it is necessary to introduce solutions that will allow the production of electricity from coal with high efficiency and low emissions. Oxy-combustion systems integrated with carbon capture and storage (CCS) installations may prove to be such a solution. This paper presents the main results from a thermodynamic analysis of a supercritical unit operating in oxy-combustion technology, fueled with pulverized coal with a power output of 460 MW. The parameters of the live steam in the analyzed system are 600 °C/30 MPa. To perform the numerical analyses, models of the individual components were built, including an oxygen production installation (ASU), a boiler, a steam cycle and a flue gas conditioning system (CPU). The models were built in the commercial programs GateCycle and Aspen and then integrated into the Excel environment. In this paper, different structures for an integrated oxy-type system were analyzed and compared. The auxiliary power rates were determined for individual technological installations of the oxy-combustion power plant. The highest value of this indicator, in the range between 15.65% and 19.10% was calculated for the cryogenic ASU. The total value of this index for the whole installation reaches as high as 35% for the base case. The use of waste heat from the interstage cooling of compressors in the air separation installation and flue gas conditioning system was considered as the methods of counteracting the efficiency decrease resulting from the introduction of ASU and CPU. The proposed configurations and optimization allow a significant reduction of the auxiliary power of the considered unit. In consequence, the efficiency decrease was reduced by approximately 3.5% points. An economic analysis of the different structures of the oxy-fuel system and the reference air-fired power plant was also conducted using a newly developed computational algorithm built in the Excel environment. The algorithm uses a Break Even Point (BEP) method, focusing mainly on determining a break-even price of electricity. It was found that about the profitability of this investment will mainly decide the price of emission allowances. For the assumptions made, the oxy-combustion power plant will be economically comparable with a reference plant without carbon dioxide capture when the price of allowances would be between 34 and 41 €/tonne. A sensitivity analysis concerning the influence of selected components of the cash flows on the break-even price of electricity was also performed. The main results of the calculations are presented in the paper