Aerosol formation in CO2 capture plants – aspen plus simulation model

Abstract

One of the most promising technologies available for decreasing CO2 concentration in the atmosphere is Post Combustion CO2 Capture (PCCC). The process is based on absorption-desorption of carbon dioxide by a solvent. Amine based aqueous solutions are considered as the state of the art solvent for PCCC. However, its use is associated with MEA emissions from an absorber column through vapour and aerosol phases. Aerosol emission has only recently been detected, and reported to be related to the degree of supersaturation of gas. The objective of this study was to develop a new conceptual model to estimate heat and mass transfer rates between gas and particulate phases using Aspen Plus simulation software. Also, validation of the model was performed by comparing it with results of an experimental mini-plant developed by TNO group in Netherlands. In the model presented in this study, interaction between the gas and the solvent, and the gas and the particles was split by modelling the gas-solvent interaction in the absorber and the gas-particles interaction in separate absorber columns representing sections of a discretised absorber. A method was presented to estimate particle formation due to nucleation and to correct the MEA loss predicted by Aspen Plus. The CO2 removal efficiency was estimated to be 95%. The estimated total molecular mass transfer rate from the gas phase at the top of the absorber column to the particle phase was found to be -7.3×10-10 kg/s, indicating net molecular mass transfer from the particle to the gas phase. The mass transfer due to nucleation was estimated to be 1.92487×10-6 kg/s. The amount of particle phase MEA emission was found to depend on the temperature inside the absorber, temperature bulge, gas supersaturation ratio, volume of particles entering the absorber and H2SO4 concentration in the entering gas. The particle phase MEA emission due to the molecular mass transfer from the gas phase to the particle phase was found to be 0.3 mg/Nm3gas, while particle phase MEA emission resulted from the nucleation mass transfer was 697.0 mg/Nm3gas. Thus, the total particle MEA emission was estimated to be 697.3 mg/Nm3gas. The estimated nucleation rate is approximately 2×1015 particles.cm-3.s-1. Gas phase MEA emission was found to be 1.3 mg/Nm3gas.