Techno-economic analysis of supercritical carbon dioxide cycle integrated with coal-fired power plant

Highlights: • Integration of four novel sCO₂ cycles with coal-fired power plant. • Efficiency of sCO₂ cycle is higher than steam Rankine cycle by 3–4%pts. • sCO₂ cycles can reduce the cost of electricity by 6–8% than steam Rankine cycle. • Increasing turbine inlet temperature by 140 °C increases efficiency by 3–4%pts. • Increasing turbine inlet temperature doesn't show reduction in cost of electricity. Supercritical carbon dioxide (sCO₂) cycles can achieve higher efficiencies than an equivalent steam Rankine cycle at higher turbine inlet temperatures (>550 °C) with a compact footprint (tenfold). sCO₂ cycles are low-pressure ratio cycles (~4–7), therefore recuperation is necessary, which reduces the heat-addition temperature range. Integration of sCO₂ cycles with the boiler requires careful management of low-temperature heat to achieve higher plant efficiency. This study analyses four novel sCO₂ cycle configurations which capture the low-temperature heat in an efficient way and the performance is benchmarked against the state-of-the-art steam Rankine cycle. The process parameters (13–16 variables) of all the cycle configurations are optimised using a genetic algorithm for two different turbine inlet temperatures (620 °C and 760 °C) and their techno-economic performance are compared against the advanced ultra-supercritical steam Rankine cycle. A sCO₂ power cycle can achieve a higher efficiency than a steam Rankine cycle by about 3–4% points, which is correspond to a plant level efficiency of 2–3% points, leading to cost of electricity (COE) reduction. Although the cycle efficiency has increased when increasing turbine inlet temperature from 620 °C to 760 °C, the COE does not notably reduce owing to the increased capital cost. A detailed sensitivity study is performed for variations in compressor and turbine isentropic efficiency, pressure drop, recuperator approach temperature and capacity factor. The Monte-Carlo analysis shows that the COE can be reduced up to 6–8% compared to steam Rankine cycle, however, the uncertainty of the sCO₂ cycle cost functions can diminish this to 0–3% at 95% percentile cumulative probability.