(264c) Comparison of Different Controller Designs for Plantwide IGCC Control

An IGCC plant is an assimilation of operating units or subsections which share characteristics such as tight energy integration, similar process objectives and/or time scales. These subsections closely interact among themselves through material and energy flows which in turn provide natural hierarchy for high level control structure design. An approach one takes in these scenarios can vary from simplistic single level fully-decentralized mode, which although simple to design and significantly intuitive and adherent to any operator, is far from the best possible operating route; to a complex multilayer control architecture, where a centralized supervisory layer keeps track of the overall economics, logistics and performance of the plant while providing best possible or ?optimized? setpoint signals to the lower level of controller hierarchy, which in turn are designed to meet the setpoints in the ?best? possible way. The focus of this paper is to investigate, through rigorous dynamic process modeling in Aspen Plus/Dynamics, a comparison of controller design performance among a fully-centralized model predictive controller (MPC) for the Air Separation?Gas Turbine/Combustor?Gasifier power loop; a semi-centralized design where each sub-section is controlled by centralized MPC passing setpoint information among each other; and a fully decentralized IMC based PID controller design where each control loop remains oblivious to others presence. It is apparent and has been shown that the process variables operating at different time-scales pose significant problems when operating in simple PID-based control schemes. Whereas this might seem intuitive for a complex integrating process, a sub-section operating at much faster rate as compared to others, such as the gas-turbine/combustor, does not provide much performance improvement when switching to more complex centralized design thus deteriorating the overall performance of IGCC power cycle. Lastly, we close with a discussion of future work on integration of heat-recovery-steam-generator subsection, the impact of current controller design on total power generation (including both gas and steam cycles), and simulation and control of an entire IGCC power plant.