(493e) Dynamic Modeling and Control of Post-Combustion CO2 Capture Process Integrated With Supercritical Pulverized Coal Plant

Dynamic Modeling and Control of Post-Combustion CO₂ Capture Process Integrated with Supercritical Pulverized Coal Plant

Qiang Zhang, Debangsu Bhattacharyya, and Richard Turton

Department of Chemical Engineering, West Virginia University,

Morgantown WV, 26506, USA

The process of CO₂ capture and storage is a promising and effective way to control the emission of CO₂ from large-scale, stationary sources such as conventional, pulverized-coal, power plants. In this work, a liquid MEA-based, post-combustion CO₂ capture and compression system, was simulated in Aspen Plus and Aspen Plus Dynamics. The process was also integrated with the steam system of a 550 MWe supercritical pulverized coal power plant. The steady state simulation was carried out in Aspen Plus using rate-based separation processes for the absorber and stripper columns under a constraint of 90% capture efficiency. The thermal energy for CO₂ recovery was provided by extracting steam before the low-pressure turbine. With optimized parameters for the capture process, the integrated coal-fired power plant had a net power of 420.9 MWe and the efficiency was 30.08% (HHV), which was 9.22% less than the values reported in the case without CO₂ capture.

The steady state model developed in Aspen Plus was converted to a dynamic model in Aspen Plus Dynamics with appropriate modifications in the plant configuration for a pressure-driven dynamic simulation. The rate-based separation calculation method was also replaced by equilibrium-based method since rate-based unit operations are  not supported in Aspen Plus Dynamic. A formulation for component efficiency was generated from the rate-based simulation in the face of typical disturbances such as changes in the flue gas flowrate and composition. This formulation was then applied in the dynamic simulation to minimize the discrepancy between rate-based and equilibrium-based absorber models.

For even modest sized power plants, the volume of flue gas generated requires that multiple parallel trains of absorption and stripping columns are needed in order to capture the majority of the carbon dioxide in the gas.  For the current study, six trains of CO₂ absorption and stripping columns were coupled together to investigate the controllability of such systems. Due to the pressure-flow dynamics, a precise distribution of the flue gas between the trains is a challenge for this highly interactive system. Variations in distribution of the flue gas in the absorbers can lead to variations in CO₂ capture achieved in any column. Thus it can be difficult to achieve the overall goal of CO₂ capture.  In addition, the control of liquid inventory and the regulation of the stripper efficiency pose further challenges. The presentation will include results from a number of control strategies for maintaining the desired CO₂ capture efficiency in the face of typical disturbances for this highly interactive process.