The present study was initiated to investigate the problems associated with recovery of CO2 from flue gases for enhanced oil recovery. In particular, MEA and activated K2CO3 absorbing solutions were evaluated.
In MEA, amine sulfite and amine sulfate are the dominant impurities formed with minor amounts of higher thiosulfates and oxidized amines. In activated potassium carbonate solutions, only sulfites and sulfates ions were found, without higher oxidation products. The absorption rate of CO2 in these solutions decreases with increasing loading of CO2 in almost a linear fashion. The absorption coefficients obtained were linear with respect to active uncombined solution species, in agreement with theory of chemical-reaction control at low CO2 partial pressures. The coefficients ranged from 50 × 10−5 lb mole/ft2-sec for 20% MEA to 2 × 10−5 for 9% K2CO3 (8% K2SO4, 0.9% MEA) at zero CO2 loadings. It was found that addition of EAE rather than MEA as an activator increased the absorption rate by a factor of 2-4. At high CO2 loadings, the absorption rate of EAE-activated potassium carbonate and MEA have almost the same values.
Alternative absorption systems were analyzed in a preliminary cost evaluation. It is recommended that a K2CO3 (EAE activated) solution be the process of choice. The impurity level in the recovered CO2 was estimated to be ≤ 100 ppm non-condensible gases, 20-200 ppm SO2, and < 20 ppm NOX. There is little cost differential between an amine process and a K2CO3 process; the final decision should be based on operating experience, operating ease, and corrosion problem minimization. The estimated cost of recovery was 0.88ȼ/MCF CO2 (available at 1 atm. pressure) for extraction from a large stream of flue gas.