Pilot plant modeling of Advanced Flash Stripper with piperazine
Joseph Selinger, 0000-0002-4185-8607 · 2018
Implementation of carbon capture using amine scrubbing is limited by the large energy penalty of CO₂ capture and compression. Alternative stripper designs can reduce lost work in the stripper by implementing heat recovery unit operations and reducing opportunities for solvent degradation. The advanced flash stripper (AFS) has reduced the required equivalent work by 12-15% compared to the simple stripper by using multiple solvent bypasses to equalize heat capacity across cross exchangers and minimizing lost latent heat of water vapor in the condenser. The Advanced Flash Stripper using 5 m piperazine was studied at the National Carbon Capture Center (NCCC) pilot plant, which presented the novel opportunity to test the solvent and design configuration with coal-fired power plant flue gas. Piperazine (PZ) solvent was stripped of CO₂ with an average stripper operating temperature of 150 °C The energy cost averaged 2.2 GJ/MT CO₂ for the AFS and 3.8 GJ/MT CO₂ for the simple stripper (SS). A temperature-control heuristic for controlling bypass flowrates was evaluated using five AFS test cases. Using bypass temperature differences of 7 °C, the bypass rates were automatically controlled to within 5% of the optimal bypass configuration. While the method was successful in simulations, unexpected heat loss in the NCCC plant limited the accuracy of the temperature-control heuristic due to the heat loss reducing the benefits of heat recovery unit operations. Overall energy balances of the AFS using the Independence model showed a positive heat gain of 65000 Btu/hr. The unexpected heat gain was attributed to an overestimated heat of absorption in the Independence model, as well as an underestimation of the total heat transferred from the process steam. A test AFS run was analyzed using three different assumption methods, with energy requirements varying from 2.1 – 3.0 GJ/MT CO₂.