(445e) Dynamic Simulation and Load-Following Control of an IGCC Power Plant with CO2 Capture

Load-following control of future integrated gasification combined cycle (IGCC) plants with pre-combustion CO₂ capture is expected to be far more challenging as electricity produced by renewable energy is connected to the grid and strict environmental limits become mandatory requirements.  To study control performance during load following, a plant-wide dynamic simulation of a coal-fed IGCC plant with CO₂ capture has been developed. The slurry-fed gasifier is a single-stage, downward-fired, oxygen-blown, entrained-flow type with a radiant syngas cooler (RSC).  The syngas from the outlet of the RSC goes to a scrubber followed by a two-stage sour shift process with inter-stage cooling. The acid gas removal (AGR) process is a dual-stage physical solvent-based process for selective removal of H₂S in the first stage and CO₂ in the second stage. Sulfur is recovered using a Claus unit with tail gas recycle to the AGR. The recovered CO₂ is compressed by a split-shaft multistage compressor and sent for sequestration after being treated in an absorber with triethylene glycol for dehydration.  The clean syngas is sent to two advanced “F”-class gas turbines (GTs) partially integrated with an elevated-pressure air separation unit. A subcritical steam cycle is used for heat recovery steam generation. A treatment unit for the sour water strips off the acid gases for utilization in the Claus unit. The steady-state model developed in Aspen Plus^® is converted to an Aspen Plus Dynamics^® simulation and integrated with MATLAB^® for control studies. The results from the plant-wide dynamic model are compared qualitatively with the data from a commercial plant having different configuration, operating condition, and feed quality than what has been considered in this work.

For load-following control, the GT-lead with gasifier-follow control strategy is considered. A modified proportional–integral–derivative (PID) control is considered for the syngas pressure control. For maintaining the desired CO₂ capture rate while load-following, a linear model predictive controller (LMPC) is implemented in MATLAB^®. A combined process and disturbance model is identified by considering a number of model forms and choosing the final model based on an information-theoretic criterion.  The performance of the LMPC is found to be superior to the conventional PID control for maintaining CO₂ capture rates in an IGCC power plant while load following.