Recovery of CO₂ from Flue Gas for Enhanced Oil Recovery

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 NO_X. 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.