Effects of flue gas impurities on amine stability in C02 capture process

Abstract

Amine stability in a post-combustion carbon capture plant is considered one of the most essential parameters tracked to keep the process running at peak efficiency. The presence of impurities in exhaust gases (O2, SOx, NOx) is known to undergo undesired irreversible reactions with the amine to form products leading to solvent loss which impedes the optimum operation of the plant. Metal oxides (the main constituents of industrial exhaust gas fly ash) influence on solvent degradation however have not been reported extensively and hence this study aims at investigating the effects of different metal oxides common in the blast furnace exhaust gas of iron and steel mills on the degradation of the amine solvent. In this study, oxygen-induced degradation of 0.28 CO2 loaded 5M MEA-DMAE (3M:2M) solvent under 0.12g of different metal oxides was quantified by NH3 emissions measured using an ammonia-nitrate analyzer. The effect of oxygen concentrations, temperatures, and the different metal oxides on the solvent stability were studied. The experiment was performed with four different systems each containing amine solution unique with a metal oxide constituent of ZnO, Fe2O3, and Al2O3 and a reference system containing no metal oxides(blank). The solubility of the metal oxides in the amine solution obtained using ICP-MS analysis from the experimental run conducted 10% O2 at 60oC showed that the solubility of ZnO > Fe2O3 > Al2O3 in the amine solution. ZnO and Fe2O3 systems showed catalytic effects in increasing the rate of NH3 emissions whereas the Al2O3 showed a relatively low NH3 emissions to the blank system. However, the specific rates of emissions with respect to the mass of dissolved metals showed that the Fe2O3 system had the highest catalytic effect compared to the ZnO system in increasing the rate of NH3 emissions. The time weighted NH3 emissions rates observed in this study ranged from 0.21-5.99 ppmV/hr. The studies showed that, the rate of NH3 emissions increased with increasing oxygen partial pressure and temperature. The relationship between solubility of various metal oxides in amine and the degradation of amine under typical conditions common to real life post combustion capture plants have been established.