Reducing CO2 regeneration heat requirement through waste heat recovery from hot stripping gas using nanoporous ceramic membrane

Abstract

In CO2 chemical absorption process, bypassing the unheated rich solvent before the lean/rich heat exchanger to recover the waste heat of the stripping gas (i.e., rich-split process) can reduce CO2 regeneration heat requirement. In this study, we introduce the hydrophilic mono-channel tubular ceramic membranes for recovering the waste heat from stripping gas using CO2-rich monoethanolamine (MEA) solvent. Heat recovery performance (qrec) of the ceramic membrane heat exchanger (CMHE) is systematically investigated with various operating parameters. Results show that an increase in the rich solvent flow rate can lead to a great increase of qrec value, however may inversely generate a higher CO2 regeneration heat consumption than that w/o rich-split process, particularly at higher solvent flow rates. So the flow rate of bypassed rich solvent in CMHE should be optimized. Meanwhile, increasing the water vapor molar fraction or the inlet stripping gas pressure can increase qrec value as well. Additionally, it is mandatory to reduce the temperature of cold rich solvent because its increase can generate the great drop of qrec value. Furthermore, the CMHE with 4 nm mean pore size of the separation layer of the ceramic membrane performs better than 10 nm CMHE in terms of qrec value, meaning the required membrane area of 4 nm CMHE is 14.9–60.54% smaller than 10 nm CMHE for recovering the same waste heat. The mass transfer of MEA and CO2 can be neglected due to the blocking effect of the condensate in the membrane nanopores. To allow the heat transfer data readily utilized, the empirical correlations with high accuracy for predicting qrec are proposed for 4 nm and 10 nm CMHEs.