Absorber and aerosol modeling in amine scrubbing for carbon capture
A rate-based PZ aerosol growth model was developed in gPROMS [superscript ®] ModelBuilder. Amine Aerosol growth was simulated at the unique conditions of piperazine (PZ) and the pilot plant absorber configurations at the National Carbon Capture Center. Amine aerosol growth is driven by amine-limited diffusion. As aerosol concentration increases, aerosol growth decreases due to the depletion of the amine driving force in the gas phase. Aerosol growth can be increased by enhancing the gas-film mass transfer coefficient of packing. A solvent with moderate volatility, like PZ, will produce aerosol that grows to larger size and is easier to collect. Solvents with low volatility should be avoided as they produce aerosol that is hard to collect. Process configurations that provide greater water partial pressure in the water wash, such as higher operating temperature and pre-humidified empty space, will help aerosol grow. Two pilot plant campaigns were designed and conducted in this work. 5 molal (m) PZ was operated for the first time and provided significant absorber performance benefits over 8 m PZ due to enhanced mass transfer rates from lower solvent viscosity. Parametric tests were performed with a wide range of absorber operating conditions. With the existing model correction, the pilot plant absorber model could reasonably capture the measured absorber performance. For future campaigns, this work recommended that the pilot plant absorber should be operated at both pinched and not pinched conditions. Both equilibrium correction (correct for errors in solvent loading measurements and effects of degradation) and packing correction (correct for effects of rivulets and drop and additional mass transfer caused by distributors and chimney trays) should be utilized in the data reconciliation process. A membrane-amine hybrid carbon capture system for natural gas combined cycle (NGCC) power plants was proposed and evaluated. When the inlet CO2 increases from 4% to 18%, the total absorption costs decrease by 60% and the total regeneration costs remain the same. Amine scrubbing without the direct contact cooler was found to be a superior design for NGCC carbon capture. The absorber gas inlet must be designed to avoid excessive localized temperature and solvent evaporation.