Combined Flue Gas Cleanup Process for Simultaneous Removal of SO_x, NO_x, and CO₂ - A Techno-Economic Analysis

Flue gas cleanup often requires the removal of SO_x, NO_x, and CO₂ in separate units before being emitted into the atmosphere. This stepwise treatment process incurs significant cost and energy penalty to the electricity production. A combined adsorption process based on pressure swing adsorption (PSA) by which these impurities are removed is envisioned as an efficient means of flue gas cleanup that can be applied relatively easily. In this study, the technological and economic feasibilities of a combined separation process in which SO_x, NO_x, and CO₂ are simultaneously removed from flue gas streams are assessed. Capital and operating costs are estimated based on sizing the equipment items and utilities needed, and the potentials for increased energy efficiency are determined in relation to the required PSA performance. The energy saving potential for the adoption of 2-bed and 4-bed PSA cycles is compared with conventional FGD, SCR, and amine scrubbing units needed to clean up flue gas in a stepwise fashion. The results show that energy savings can be expected when the PSA removal efficiency is greater than 90%. In the case of a 550 MW coal-fired power plant, the proposed system will impose an energy penalty of 24% to the cost of electricity, which is lower than that of current individual treatment units associated with SO_x, NO_x, and CO₂ removal. This energy penalty corresponds to a cleanup cost of $57/ton of all impurities captured for a 2-bed, four-step PSA process with a cycle time of 400 s, adsorption and desorption pressures of 10 and 1 bar, respectively, and a purge flow rate of 100 mol/s. This techno-economic assessment shows that the integrated combined system can be an attractive technology compared to multi-step systems for the removal of flue gas impurities.