Effects of relative volume-ratios on dynamic performance of a direct-heated supercritical carbon-dioxide closed Brayton cycle in a solar-thermal power plant

The effect of the relative hot-to-cold side volume-ratios on dynamic characteristics of a CBC (closed Brayton cycle) with sCO2 (supercritical carbon-dioxide) as the working-fluid is investigated in this study. The analysis of the CBC is conducted in the context of power generation in a direct-heated (no thermal-oil loop) and dry-cooled parabolic-trough solar thermal power plant, using a control-oriented model of the CBC. Dynamic performance of the sCO2 CBC with different relative volume-ratios between the hot and cold sides of the sCO2 CBC is compared using simulations for conditions on a representative summer day. The CBC hot-to-cold side volume-ratio influences CO2 mass movement and hence power output. Increasing the hot-to-cold side volume-ratio in the CBC results in a slower, more gradual dynamic response when there are fluctuations in solar heat input and ambient air temperatures. The dynamic response characteristics of a CBC with a hot-to-cold side volume-ratio less than one are shown to differ significantly from a CBC with a volume-ratio greater than or equal to one.