Absorption of CO2 in microchannel-performance

Abstract

Chemical absorption using alkanolamine solution can be significantly enhanced in micro reactors that offer high surface area per unit volume. These micro reactors can offer higher absorption efficiency and substantial reduction in the size of equipment. In the present study, the fluid flow and mass transfer characteristics of CO2 absorption using microchannel technology were studied and an economic analysis was presented to demonstrate the feasibility of using microchannel technology in gas sweetening process. Chemical absorption of CO2 mixed with N2 into alkanolamine solution was investigated in microchannels with circular cross-section. Pressure drop, CO2 loading, absorption efficiency and liquid side volumetric mass transfer coefficient were studied by varying the phase superficial velocity, phase concentration, channel length, channel diameter and temperature. The experimental results showed that liquid side volumetric mass transfer coefficient increased with gas and liquid phase superficial velocity in slug flow regime and achieved its maximum value in the slug-annular flow and churn flow regimes. Also the results showed the shorter length channel has a higher mass transfer coefficient and higher diethanolamine (DEA) concentration enhanced the absorption efficiency and volumetric mass transfer coefficient due to enhancement in reaction kinetics. The smaller diameter channel achieved a higher absorption efficiency and mass transfer coefficient than the larger diameter channel due to larger interfacial area of smaller diameter channel while mass transfer coefficient decreased with increasing temperature. The values of mass transfer coefficient in this study were 1 to 2 orders of magnitude higher than those in conventional gas-liquid absorption systems. Individual empirical correlations were proposed for different flow regimes to predict the liquid side volumetric mass transfer coefficient. Similarly, an empirical correlation to predict CO2 loading was proposed based on Reynolds number, Schmidt number and the aspect ratio defined by channel length and diameter. The prediction of the correlations agreed with the experimental data well. An economic analysis model was developed to study the feasibility of gas sweetening process using microchannel technology. A new gas sweetening system model based on the conventional gas sweetening system integrated with microchannel technology with the same solvent regeneration section was developed. In this model, the maximum pressure drop was set as a constraint, while the operating and capital costs were calculated by adjusting the liquid flow rate and the number of the stacks. The analysis has shown that the microchannel reactors are economically feasible to be used in gas sweetening plants, especially for the relatively low capacity plants.

Date of Award	2016
Original language	American English
Supervisor	Mohamed Alshehhi (Supervisor)