Sustainability Assessment of a Solar Energy-Assisted Flue Gas Amine-Based CO2 Capture Process Using Fully Dynamic Process Models

Abstract

A new methodology to assess the feasibility and sustainability of the solar energy-assisted CO2 capture process using amine solution was developed that combined a conventional steady-state process model approximation, rigorous dynamic controllability study to handle external disturbances due to the renewable energy source integration, transient process inventory estimation, and the environmental impact assessment using life cycle analysis. In particular, a fully dynamic pressure-driven design of the postcombustion carbon dioxide (CO2) capture process based on solar energy-assisted amine absorption/stripping was performed to provide the techno-economic assessment based on realistic winter/summer daily flue gas feed patterns, natural fluctuations of solar irradiance, as well as the CO2 capture process disturbances resulting from those dynamic externalities. A steady-state design was performed to remove >90% by weight of CO2 from a pilot-plant scale flue gas source located in Al-Ahsa, Saudi Arabia, and compress it to ∼140 bar to supply for the enhanced oil recovery process. To decrease parasitic energy consumption in the stripper reboiler, steady-state design included a parabolic trough collector (PTC) that utilized ethylene glycol as a solar energy carrier at 153 °C. A dynamic process control structure was implemented to effectively handle (a) flue gas feed and (b) direct normal irradiance fluctuation disturbances during the daily cycles, and a complete process techno-economic assessment was performed using the obtained dynamic simulations data. For incomplete CO2 removal described here, dynamic fluctuations in the CO2 fraction removed were found to be proportional to the flue gas daily fluctuations. Environmental impacts based on a life cycle analysis showed a resulting environmental impact in all the measured categories compared to the steam-based scenario. For every 1000 kg of CO2 emissions averted, overall greenhouse emission savings of only 175 kg CO2 equivalent were obtained without PTC as obtained from the dynamically modeled results while 328 kg CO2 equivalent with PTC provided sustainably sourced energy. The proposed method is expected to be applicable not only for CO2 capture systems but also for plasma or electrochemical synthesis/separation of NH3, as well as provide a much better sustainability description to any green synthesis processes that involve dynamic externalities, such as solar energy supply, feed flow, and composition.