Mass Transfer Performance and Modeling of CO2 Chemical Absorption from Simulated Biogas

As one of the robust CO2 separation technologies, CO2 chemical absorption method can fully meet the requirement of CO2 capture from biogas, which is deserved to pay more attention. In a chemical absorption process, CO2 absorption always happens in a packed column called CO2 absorber, and therefore the mass transfer performance of CO2 absorption into absorbent is of importance for the design of absorber. However, the study on CO2 mass transfer characteristics and correlations in a packed column under the biogas circumstance is relatively rare. Therefore, the mass transfer performance of CO2 absorption into monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA) and piperazine (PZ) from the simulated biogas was investigated in a random pall ring packed column in terms of the overall gas phase volumetric mass transfer coefficient (KGav). Additionally, the effects of the key operation parameters, including absorbent concentration, temperature, liquid flow rate, CO2 loading, gas flow rate and CO2 partial pressure in gas on KGav values were experimented. Based on these influences, the empirical correlations of the operation parameters on KGav for MEA, DEA and PZ were erected. Results showed that PZ possessed the best CO2 mass transfer performance under the same conditions, followed by MEA, DEA and TEA. With the increase of absorbent concentration, KGav values of MEA, DEA and PZ were risen greatly. Accordingly, CO2 volumetric fractions in the gas exiting the absorber decrease gigantically. If CO2 volumetric fraction of the outlet gas less than 1% was targeted, the concentrations of MEA, DEA and PZ should be increased to 1.38 mol/L, 1.43 mol/L and 0.88 mol/L, respectively. However, the KGav value of TEA was dropped slightly due to the increase of solvent viscosity. Among all the absorbents, MEA achieved the highest KGav value with about 1.37 kmol/(m3•h•kPa) at 3.27 mol/L. In addition, KGav values of all the absorbents tested were increased with the increase of liquid flow rate, liquid temperature and gas flow rate. However, the initial CO2 loading of absorbent had a negative impact on KGav. It should be noted that the influence of CO2 partial pressure in gas on KGav was not significant. Furthermore, the simplified empirical correlations for KGav as a function of the key operation parameters were proposed for MEA, DEA and PZ, and most of the calculated KGav values were in agreement with the experimental data with an absolute average deviation less than 14%. According to the individual degree of operation parameters on KGav, the rank order was liquid temperature, liquid flow rate, active MEA concentration and gas flow rate for MEA case. As for DEA, active DEA concentration was the most important, followed by liquid flow rate, gas flow rate and liquid temperature. And for PZ, the most important factor was the active PZ concentration, followed by liquid temperature, liquid flow rate and gas flow rate. © 2018, Chinese Society of Agricultural Machinery. All right reserved.