Simple model for water wash performance in amine scrubbing for CO2 capture

Abstract

In amine-based capture systems, a water wash is necessary to remove gaseous amine to minimize atmospheric emissions and maximize amine recovery. Water wash simulation requires rigorous thermodynamic and kinetic models like those for absorption and stripping systems. An offline water wash model has been developed based on simplified thermodynamic and mass transfer assumptions to simulate a single-stage water wash for flue gas from gas-fired turbines with little or no aerosol, and to expedite simulations without needing to utilize process modeling software. Calculation of activity coefficients using both Pitzer–Debye–Hückel and Debye–Hückel theory suggest that the liquid phase in a typical water wash will be ideal due to the dilute concentration of molecular and ionic species.

Vapor phase piperazine (PZ) is predicted with a driving force based on the volatility of the free amine that has not reacted with other species or dissociated into its ionic form, and the predicted outlet concentration is nearly identical to that predicted by rigorous Aspen Plus^Ⓡ simulations. The predicted UT FEED outlet concentration is 220 ppb compared to 260 ppb predicted by Aspen Plus^Ⓡ.

Single-stage water washes are predicted to have single ppm concentration of MEA leaving the wash outlet flue gas. Amino-methyl-propanol (AMP) is predicted to be reduced to 10–30 ppm by a single-stage wash, and is predicted to be a difficult-to-capture amine without further washing steps. This prediction correlates with published TCM data from an ALIGN-CCUS campaign. Amine compounds at a similar or lower volatility to that of PZ are predicted to be reduced to ppb levels via a single-stage wash.