Startup, shutdown, and load-following simulations of a 10 MWe supercritical CO2 recompression closed Brayton cycle

This work describes improvements to dynamic process and control models developed previously for a 10 MWe supercritical CO2 recompression closed Brayton cycle pilot plant and highlights their use in the analysis of fast ramped-setpoint load-following operation and a warm shutdown and subsequent startup operation. One enhancement includes cooler and recuperators modeled as one-dimensional, compact, zig-zag type printed circuit heat exchangers optimized by minimizing metal mass and validated using dynamic data from a small-scale supercritical CO2 test loop. For the load-following ramps between 10 MWe and 4 MWe, an aggressive ramp rate of approximately 7.5%/min of full load is simulated using inventory management control and sliding-pressure operation, with the resulting net-load closely tracking the demand. The supercritical CO2 temperature at the inlet of the main compressor is controlled at 4 °C above the critical temperature using a water-cooled printed circuit heat exchanger. A high level of interaction between the cooler and inventory control is observed to intensify oscillatory behavior in the cycle load and compressor inlet temperature as control gains and/or ramp rates become more aggressive. Transient simulation procedures and results are also presented for a shutdown from 4 MWe to a warm condition. The warm shutdown is achieved in 30 min while satisfying the operating constraint limiting the rate of change in temperature at the primary heat exchanger inlet to less than 2 °C/min. The subsequent startup from warm conditions to positive load is reached in 45 min and minimum load of 4 MWe is achieved in 90 min.