Amine aerosol in aqueous scrubbing for CO₂ capture

Sustained amine emissions above one ppm are prohibitive to amine scrubbing and prevalent with aerosol in the flue gas. The development, demonstration, and quantification of mitigation strategies for amine aerosol will ensure sustainable CO₂ capture operations. This work supports that goal by conducting systematic aerosol tests and developing aerosol models for 2nd and 3rd generation CO₂ capture solvents. SO₃ generation by catalytic conversion and plasma oxidation of SO₂ were compared and adapted for aerosol tests. The catalytic bed was proven highly effective at pilot scale with the demonstration of 97% conversion and 8 ppm SO₃ injection into 4000 lb/hr flue gas. Plasma oxidation had a much lower conversion but showed great promise due to its relative cost and ease of start-up/shut down. Amine aerosol can be sustainably mitigated upstream of CO₂ capture or within the absorber and water wash and are reduced at NGCC conditions. The hydrated lime addition rate is the critical indicator for upstream SO₃ reduction and inlet aerosol mitigation in baghouse operations. The threshold for SO₃ slippage is at half the normal lime rate. As inlet flue gas SO₃ increases, amine emissions increase, and the water wash performance decreases. There exists a tradeoff between capital or energy costs and amine aerosol control. A 98% reduction in PZ aerosol was demonstrated for flue gas with 2 ppm SO₃ by increasing the lean solvent to 58 °C and using a 2-stage water wash. Particulate measurements showed that PZ aerosol grows and gets collected at higher lean solvent temperatures. The growth of amine aerosol in the absorber is driven by amine-limited diffusion, and the aerosol is in equilibrium with water in the bulk gas phase. More volatile solvents grow bigger drops due to the larger driving force for amine transfer, and the effect of aerosol concentration on drop size is diminished. Therefore, aerosol mitigation with mist eliminators should be feasible for highly volatile solvents. As the volatility of the amine in a solvent system increases, vapor emissions will become more significant than aerosol emissions.