(29a) Evaluation of an Integrated Vacuum Carbonate Absorption Process for Post-Combustion Co2 Capture

The monoethanolamine (MEA) absorption processes are currently available technology for post-combustion CO2 capture. However, the MEA process is extremely energy intensive, contributing to more than half of the CO2 avoidance cost. Reducing the energy consumption is the key to the success of CO2 separation processes.

The proposed vacuum carbonate process employs a potassium carbonate (K2CO3) aqueous solution for CO2 absorption. While the absorption takes place at the atmospheric pressure, the stripper is operated under a vacuum condition. The low heat of reaction between CO2 and K2CO3 favors a stripping process operated at a low temperature and the low quality steam (close to the exhaust end of low pressure turbine) can thus be used as a heat source for stripping process.

The objective of this study is to evaluate the energy performance of the proposed vacuum process applied to a 528 MW (gross) pulverized coal-fired power plant. The steady state process simulations were performed to calculate the mass and energy balances of the process, and a conventional MEA process as a comparison. The vacuum process extracted the power plant steam at 2-8 psia, of which 2/3 was directly introduced into the stripper and 1/3 was used in the reboiler. Compared to the MEA process, both the quality and quantity of the steam heat were reduced in the vacuum process. When the vacuum stripper operated at 4 pisa, the total electricity loss due to CO2 capture and compression was reduced by 27% compared to the MEA process. The CO2 stripping pressure and the CO2 loading in solution are two important operating parameters for the vacuum process. The total electricity loss increased with increasing stripping pressure at a power of 0.22. The CO2 loading in the lean solution impacted the liquid to gas ratio. A decrease of the lean CO2 loading from 1.5% to 0.5% almost doubled the electricity of steam extraction, while a lean loading higher than 1.5% didn't further improve the energy performance. The preliminary cost analysis showed the vacuum process is economically attractive for post-combustion CO2 capture.