High CO2 removal with aqueous piperazine at the NCCC pilot plant under NGCC conditions

Abstract

A pilot plant campaign at the National Carbon Capture Center (NCCC) used the Piperazine with the Advanced Stripper (PZAS) treating gas with 4.3 mol % (dry) CO₂ and 8 mol % H₂O at 110 °C. The absorber with pump-around intercooling (PA IC) maintained 95.5 % CO₂ removal for 4000 h. The lean loading was 0.2 mol/equiv N with an average rich loading of 0.4 mol/equiv N. The heat duty was minimized with sequential steps changes in bypass flowrates. The minimum net heat duty was 2.43 GJ/tonne, at 5 % cold and 64 % warm rich bypass. Parametric testing during the campaign included operation without a lean solvent cooler and at a low lean loading of 0.18 mol/equiv N.

Rigorous rate-based models predicted the performance of the stripper and absorber within ± 5 %. These models were used to study process design. In the absence of a lean solvent cooler, PA IC temperatures between 26.6 and 40 °C produced a CO₂ removal between 97 and 90 %, at a constant rich loading of 0.4 mol/equiv N. The feasibility of this design is contingent on the ability to maintain the PA IC temperature. The NCCC system could achieve 98.6 % CO₂ removal without causing water to condense in the absorber. Water condensation will limit all aqueous capture solvents with equilibrium constraints. Operating above this limit requires process modifications to enable water balance control and removal of volatile amine in the water wash or the addition of a direct contact cooler upstream of the absorber to avoid water condensation.