Development and comparison of control schemes for the off-design operation of a recompression supercritical CO2 cycle with an intercooled main compressor

Abstract

Four control schemes with different main compressor outlet pressure control modes and/or parametric optimization options are developed for the off-design operation of a supercritical carbon dioxide cycle with an intercooled main compressor. The cycle performance under four control schemes is first evaluated under possible off-design conditions and then compared with two case studies on annual performance. The off-design results indicate that the parametric optimization can simplify the main compressor control during the off-design operation regarding the surge risk control. The results also indicate that parametric optimization under different pressure control mode results in significant differences regarding the cycle performance improvement. The parametric optimization under the variable pressure control mode leads to more noticeable cycle efficiency improvement (0.02%–23.1%) than under the fixed pressure mode (0.02%–16.7%), but also larger reductions in net output power and temperature differential compared to those with the latter scheme (8.4–47.7 MW and 6.1–26.1 °C). The hybrid scheme of these two modes is recommended to accommodate different operating scenarios. The optimum annual cycle efficiency with an efficiency improvement up to 11% is obtained with the parametric optimization under the variable pressure control mode at the design-point main compressor inlet temperature of 41 °C.