Heat Exchanger Performance in Pilot Plant Testing of Piperazine with the Advanced Stripper™

Abstract

The performance of four key heat exchangers at the National Carbon Capture Center (NCCC) during 4000 hours of operation is analyzed in this paper. A 0.5 MW integrated absorption-stripping pilot plant using Piperazine with the Advanced StripperTM (PZASTM) was used, with 5 m piperazine (PZ) as the capture solvent. Data from the coal and Natural Gas Combined Cycle (NGCC) campaigns were used, with flue gas compositions of 12% and 4% CO2. For the steam heater, data from multiple campaigns at the Separations Research Program (SRP) at the University of Texas J. J. Pickle Research Campus were used. All the exchangers were simulated in Aspen Plus®, and the IndependenceTM model was used to estimate properties not measured on-site. The performance metric used was the number of transfer units (NTU) for the cold, hot, and CO2 exchangers, and the overall heat transfer coefficient for the steam heater. The cold and hot exchangers exhibited similar performance throughout both campaigns, averaging a lean side NTU of 13.4 and 4, respectively. The pressure drop on both sides of both exchangers was correlated with the operating variables, with an added term to represent the flashing of the rich stream in the hot exchanger. Model deviations were under ± 25% for both units. The steam heater at NCCC underperformed in relation to design expectations. When compared to the performance of the steam heater at SRP, the low fluid velocities measured at NCCC suggest pool boiling operation, which is characterized by low thermal performance. The CO2 exchanger performed better than expected, with average NTU of 3.7 and 5.4 on the CO2 and rich sides. The cold, hot, and CO2 exchangers were analyzed for performance loss during the NCCC campaigns. The cold and CO2 exchangers did not show any statistically significant loss of performance during the campaigns, but the performance of the hot exchanger degraded slightly over time, suggesting the presence of fouling or leaking due to corrosion of the SS316L plates by the flashing rich stream.