Effects of CO2-absorption control strategies on the dynamic performance of a supercritical pulverized-coal-fired power plant
Journal article, 2017
This work investigates the interactions that occur between a supercritical pulverized-coal-fired power plant and a downstream CO2-absorption process during load changes in the power plant, by linking the dynamic models of the two systems. The derived dynamic model for this integrated system is implemented in the dynamic modeling and simulation software Dymola. The operation of the integrated system is investigated in two modes of operation, considering various power plant loads and levels of steam availability for the CO2-absorption process. Several schemes for control of the CO2-absorption process, which have been suggested in the literature, are implemented for the integrated system and their effects on power plant operation are evaluated. Comparison of the simulation results obtained through varying the power plant load with and without CO2 absorption reveal that the CO2-absorption process has slower process dynamics than the power plant cycle, with the CO2 absorption stabilizing in more than 1 hour, while the power generation generally stabilizes in 6–9 minutes, in the power plant both with and without CO2 absorption. The control scheme used for the CO2-absorption process is important, as pairing of the control variables in relatively slow control loops increases the settling time of the power plant by up to 30 minutes with respect to power output. The results suggest that the investigated CO2-absorption process does not affect significantly the load-following capabilities of the power plant. Redirecting steam from the CO2-absorption process to the low-pressure turbine section in order to increase power generation (during a hypothetical peak-load demand) results in fluctuations of process variables in the power plant during the 2 hours of reduced steam availability to the CO2-absorption process. This is observed for both control schemes applied to the CO2-absorption process, and the power generation is not stabilized until the operation is restored to full load.