Modeling of absorber pilot plant performance for CO2 capture with aqueous piperazine

Abstract

A CO2 capture pilot plant with the advanced flash stripper was operated with aqueous piperazine (PZ) at The University of Texas Separations Research Program (UT-SRP) in March 2015. A wide range of absorber operating conditions (solvent concentration, lean loading, flue gas CO2, gas rate, liquid-to-gas ratio) and intercooling configurations was tested in the pilot plant campaign.The pilot plant measurements closed the material balance (±2%) around the absorber. 5m PZ was tested for the first time and outperformed 8m PZ at comparable absorber conditions due to enhanced mass transfer rates in the absorber. Operating with 5m PZ increased the number of transfer units (NTU) by ∼20% for each of 3 tests even though 8m PZ was operated with greater solvent capacity and greater driving force. Operation with full spray intercooling doubled the NTU compared to operation without spray or intercooling at identical absorber conditions.The pilot plant data were used for further validation of the rigorous rate-based absorber model in Aspen Plus®. The pilot plant absorber model has been developed over several pilot plant campaigns, and a consistent method for absorber model validation and correction utilizing a rigorous data reconciliation method with the Independence PZ model was used to predict pilot plant performance for the March 2015 campaign. Pilot plant data suggested that interfacial area correction and CO2 correction provided similar predictions of pilot plant absorber performance and could be used interchangeably to correct the model. The inhibitor correction to density-predicted loadings was consistent with model-predicted correction to titration data and might provide an explanation for pilot-model offsets. Pilot plant data also suggested a possible time dependence, and absorber NTU values were slightly over-predicted (mean ratio of model-predicted NTU to pilot plant-measured NTU=1.08). A possible explanation is that several high CO2 removal cases in the March 2015 campaign were outside the range where the previous model corrections were developed, where the controlling mass transfer resistance in the absorber differed. This observation provides an opportunity to investigate future model corrections at different column mass transfer limiting mechanisms. The column temperature profiles of different intercooling configurations were matched within 2% mean absolute percentage error.