Pilot plant demonstration of piperazine with the advanced flash stripper

Abstract

Amine scrubbing is an important alternative for CO2 capture from coal- and gas-fired power plants. 5 m piperazine (PZ) with the Advanced Flash Stripper (AFS) has all the attributes of a benchmark system for the second-generation amine scrubbing process for CO2 capture. This process has been demonstrated with more than 2000 h of operation on 0.6 MWe of coal-fired flue gas at the National Carbon Capture Center. In the first 600 h, the AFS configuration was used, and the stripper sump level was kept high at 80%. From 600 to 850 h, the system switched to simple stripper configuration and from 850 to 1100 h, switched back to AFS. After 1100 h, the mitigation methods for oxidation were tested with the AFS, including nitrogen sparging, applying the SO2 prescrubber to remove NO2, and lowering the stripper sump level to 15%. The energy required per tonne CO2 removed was less than 2.1 GJ steam and less than 232 kW h total equivalent work. The stripper operated at 150 °C, producing CO2 up to 6 bara. The 5 m PZ solvent was used reliably with little solids precipitation. CO2 removal from 90 to 99% was achieved with less than 12 m of packing. PZ oxidation was less than 0.1 kg PZ/tonne CO2 with the AFS and the absence of NO2. As estimated from NH3 production, the mitigation methods reduced the PZ oxidation rate by 13%. The trends in dissolved iron correlated with the PZ oxidation rate rather than the extent of oxidation. PZ emissions were managed to less than 1 ppm with water wash and an elevated lean solvent temperature. With aqueous PZ, carbon steel was frequently protected by deposition of FeCO3, making it an attractive alternative to stainless steel.