(276f) Process Flow Sheet Optimization and Techno-Economic Assessment of Post-Combustion CO2 Capture Using Heat Integrated, Sub-Ambient PSA

Solid sorbents are a promising low-energy approach to post-combustion CO2 capture. However, the relatively low swing capacities (i.e., ~ 1 mmol CO2/g) of most solid sorbent systems drives up both capital and operating costs. These challenges can be overcome by an unorthodox approach: flue gas cooling and compression matched with sorbent materials that have large isotherm steps. These two factors enable high swing capacity (>10 mmol CO2/g) sorbent that can drive down capital costs relative to other state-of-the-art sorbent systems by many folds. Further, the sorbents are embedded within hollow fiber modules that have been shown to be 3-5x more capital and energy efficient than traditional pellet-packed fixed beds. Critically, the energy associated with flue gas cooling and compression system is largely recouped by employing sub-ambient heat exchange and power recovery from the clean N2 exhaust. The goal of this study is to show the viability of this heat exchange/power recovery approach for our sub ambient pressure swing adsorption (PSA) system.

Flue gas compression and cooling is major cost elements and tradeoffs between the capital cost of the heat exchangers and compressor train and utility use are explored. In the optimization model, the major components are considered including the gas-gas heat exchanger to recover the cold utility from the CO2 stripped flue gas and the work recovery from the stream for gas compression. The optimization problem is solved by considering a superstructure that embeds the different options of multistage compression and cooling. Some optimal designs are considered as case studies to perform high-level technoeconomic analysis. After the technoeconomic analysis, the optimization models discussed earlier are refined and updated, thus making the entire effort iterative. To estimate the capital cost, only major components are considered such as fiber modules, compressors, turbines, and heat exchangers utilizing the existing models. The specifications given by NETL for a 550MW (net) power plant is used and our initial studies show the CO₂ capture cost to be below $25.0/ton.