An Advanced Pccc Control Scheme Utilizing Predictive Control and System-Dependent Fast-Response Variables at the Uky-Caer 0.7 MWe Small Pilot Scale CO2 Capture Facility

With regard to post combustion CO₂ capture (PCCC) processes, the cost of capture is of vital importance to mitigating emissions. Economic implications present themselves if the capture system is often operated off of the best performance curve at given flue gas compositions and ambient conditions. Current process control methods involve the use of simple feedback controllers and proportional–integral–derivative (PID) controllers. While these methods are industry proven for systems with low fluid inventory, improvements in control system response time for large fluid inventory systems, such as aqueous carbon capture units, can be made by using a form of feed-forward control that is based off of a process data generated model.

With the University of Kentucky Center for Applied Energy Research (UKy-CAER) PCCC process, there are many factors affecting system performance that are difficult to consistently control. These include: capture solvent concentration and CO₂ loading, system water balance, ambient conditions, solvent degradation and emission rates, and differences in manual responses. By utilizing a control system based model predictive control algorithm and selecting gas-side fast-response variables that are indicative of future system performance, these factors can be more precisely controlled. With conventional PID control using liquid-side variables, changes in system operation can only be realized after the solvent inventory has completely cycled. This leads to overshooting and undershooting energy requirements from 2-5% to reach 90% CO₂ capture. UKy-CAER has developed an approach for an advanced control scheme utilizing the CO₂ product flow rate at the stripper exhaust and real-time calculated solvent quality analysis to control the 0.7 MWe small pilot scale CO₂ capture process. Through use of a fast-response and predictive control approach, UKy-CAER can realize a 3-4x increase in the process state response time, and the specific reboiler duty requirement can be tuned to the real-time solvent quality.