Abstract
Closed supercritical carbon dioxide (S-CO2) Brayton cycle is a promising alternative to steam Rankine cycle due to higher cycle efficiency at equivalent turbine inlet conditions, which has been explored to apply to nuclear, solar power, waste heat recovery, and coal-fired power plant. This study establishes 300MW S-CO2 power system based on modified recompression Brayton cycle integrated with coal-fired circulating fluidized bed (CFB) boiler. The influences of two stages split flow on system performance have been investigated in detail. In addition, thermodynamic analysis of critical operating parameters has been carried out, including terminal temperature difference, turbine inlet pressure/temperature, reheat stages, and parameters as well as compressor inlet pressure/temperature. The results show that rational distribution of split ratio to the recompressor (SR1) achieves maximal cycle efficiency where heat capacities of both sides in the low temperature recuperator (LTR) realize an excellent matching. The optimal SR1 decreases in the approximately linear proportion to high pressure turbine (HPT) inlet pressure due to gradually narrowing specific heat differences in the LTR. Secondary split ratio to the economizer of CFB boiler (SR2) can recover moderate flue gas heat caused by narrow temperature range and improve boiler efficiency. Smaller terminal temperature difference corresponds to higher efficiency and brings about larger cost and pressure drops of the recuperators, which probably decrease efficiency conversely. Single reheat improves cycle efficiency by 1.5% under the condition of 600°C/600°C/25Mpa while efficiency improvement for double reheat is less obvious compared to steam Rankine cycle largely due to much lower pressure ratio. Reheat pressure and main compressor (MC) inlet pressure have corresponding optimal values. HPT and low pressure turbine (LPT) inlet temperature both have positive influences on system performance.
Highlights
High efficiency and clean coal-fired power generation technologies are priority research directions in the traditional energy industry
An additional high pressure CO2 split flow extracted from low temperature recuperator (LTR) outlet to the economizer (ECO) can utilize flue gas heat and increase high temperature recuperator (HTR) effectiveness, which is a valid method employed by aforementioned studies
Supercritical carbon dioxide concentrated solar power (CSP) (S-CO2) recompression Brayton cycle is a promising alternative to be applied in coal-fired power generation due to special
Summary
High efficiency and clean coal-fired power generation technologies are priority research directions in the traditional energy industry. Moullec [16] explored the potential performance of a coal-fired power plant based on double reheat recompression S-CO2 cycle integrated with a post-combustion carbon capture and storage (CCS). A high temperature air preheating combined with a fraction of fluid split from the main compressor (MC) to the economizer can effectively utilize 100∼ 500∘C flue gas heat. Li et al [18] set up an additional split flow economizer before the air preheater to heat the CO2 from low temperature recuperator (LTR) and had accomplished 5MWe fossil-based S-CO2 recompression and reheat integral test facility design. Bai et al [19] provided a novel S-CO2 intercooled recompression cycle with additional medium-temperature recuperator and an anabranch applied to a coal-fired power plant, which could achieve 49.5% net LHV efficiency with 29.6Mpa/650∘C. A series of parameters sensitivity analysis have been carried out, including two stages split ratio, terminal temperature difference, turbine inlet pressure/temperature, and reheat pressure/temperature as well as compressor inlet pressure/temperature
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