Techno-economic optimization and cycle schedule analysis of poly-bed VPSA process for CO2 capture from natural gas combustion emissions using parallel Bayesian optimization with ANN ensembles

초록

Vacuum pressure swing adsorption (VPSA) processes stand out among CO2 capture technologies for their low energy requirement, environmental sustainability, and operational flexibility. Most existing VPSA-based CO2 capture studies have focused on coal-fired flue gas (similar to 15% CO2). However, the ongoing shift toward natural gas-fired power plants, which emit flue gas with lower CO2 concentrations (< 10% CO2), highlights the need for systems optimized for dilute CO2 streams. Moreover, previous studies have largely been limited to small-scale systems with simplified cycle configurations, restricting their industrial applicability. This study optimizes the operating conditions and cycle configurations of industrial-scale poly-bed VPSA processes for CO2 capture by introducing a novel parallel batch multi-objective Bayesian optimization framework utilizing artificial neural network ensembles. The optimization considered three objectives of CO2 purity, recovery, and total annualized cost (TAC), with a focus on the role of pressure equalization (PE) steps in minimizing energy consumption during desorption. A pronounced trade-off was found: adding PE steps enhances CO2 purity and recovery and lowers energy consumption, but raises TAC. Notably, the optimization results indicated that incorporating three or more PE steps was essential for achieving optimal performance. Global sensitivity and techno-economic analyses were conducted to identify key variables and to examine the effects of PE steps, CO2 emission penalties, and electricity prices. To rationalize the need for PE steps, a net CO2 recovery was introduced to consider both process-level CO2 recovery and indirect CO2 emissions associated with energy consumption. This study provides a comprehensive optimization framework that balances energy efficiency, cost, and separation performance, contributing to the sustainable design of next-generation VPSA systems for low-concentration CO2 flue gas.

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