For CO2 removal from flue gases containing SO2 at thermal power plants, secondary alkanolamine with high molecular weight (abb. HIA) was selected as an absorbent because of low utility consumption. SO2 forms sulfite salt in absorbent and it is oxidized with O2 to form the sulfate. These salts called Heat Stable Salts (HSS) reduce CO2 removal ratio. On the other hand, the sulfite consumes O2 in the absorbent and the resistance to oxidation of HIA can be expected. We estimated the relationship between concentration of HSS and CO2 removal ratio, and the resistance to oxidation of HIA absorbent by the presence of SO2 in treated gas. Based on these results, pilot testing (flue gas capacity: 1, 000 Nm3/h, CO2 removal ratio: 90%) was carried using coal oil mixture-fired power plant flue gas for continuous 2, 000 hours (accumulating time of 2, 441 h) to evaluate the resistance to oxidation and regeneration heat of HIA.
Oxalic acid by oxidative degradation was accumulated 0.0095% after completion of pilot testing, and its amount was 0.1 times as low as that of LNG-fired flue gas. Furthermore, four kinds of cyclic amines were detected by GC-MS analyses and three of them were compounds by oxidative degradation. Their amounts of the mixture were spectrophotometrically determined to be 0.19% based on a reasonable assumption of the average molar absorptivity of the mixture. Average oxidation rate of the mixture was estimated 8.8x10-5%/h. This was 0.4% of the total loss of HIA.
Regeneration heat of HIA was 20% as low as that of the conventional absorbent even in the case of accumulation of HSS up to 2% as the reduced concentration of H2SO4.