Process control of the advanced flash stripper for CO2 solvent regeneration

The advanced flash stripper (AFS) is an intensified process design for CO2 solvent regeneration in amine scrubbing. This work identified self-optimizing controlled variables for the energy recovery bypass flowrates of the AFS, as well as a controller configuration for the steam extraction flowrate. Two self-optimizing variables were selected using a high-fidelity steady state process model: the temperature difference at the top of the stripper packing and the temperature difference on the hot end of the stripper overhead heat exchanger. Ranges of possible off-design conditions for the rich loading, absorber temperature, rich flowrate, and flash tank operating temperature were evaluated, and the worst case heat duty for CO2 stripping of the self-optimizing control scheme was within 1% of the true system optimum. A low-order dynamic model was used to test the proposed self-optimizing control strategy and showed no significant control loop interactions in the closed-loop response. Cascade control, where the inner loop controlled the steam heater effluent temperature and the outer loop controlled the flash tank temperature, was found to have favorable dynamic performance compared to a non-cascaded structure with uncontrolled flash tank temperature.