A journey into the energy-efficient aspect of CO2 adsorption technologies: Thermodynamic analysis based on carbon pump cycle

In the present work, the development of high-efficiency adsorbents and optimization of engineering processes are the main research objects for CO2 adsorption technologies. However, there is still no consensus guideline on how to analysis and optimization of CO2 adsorption system for energy-efficient improvement. Considering that Thermodynamic Carbon Pump (TCP) has been proposed for CO2 capture technologies in recent years, thermodynamic could be applied to analyse CO2 adsorption system and the concept of “cycle” in thermodynamic can be applied to analyse the energy-efficient performance of CO2 adsorption technology with different adsorbents and engineering processes. In such kind of generalized thermodynamic cycle, the adsorbed phase could be considered as “working fluid” for energy-efficient analysis. In this paper, a 4-step TSA cycle is established based on TCP cycle, which regards the adsorbed CO2 as working fluid. The thermodynamic properties including isosteric heat of adsorption, specific heat capacity and entropy of adsorbed phase, estimated from the measured adsorption isotherms data of CO2. The experimental data of CO2 adsorption isotherms were modelled using Dubinin-Astakhow (D-A) isotherm model. The Clausius-Clapeyron equation is applied to evaluate isosteric heat of adsorption. With the decoupling of thermodynamic processes in the TCP cycle, the entropy analysis on the heat transfer and mass transfer steps can be obtained. The results show that the entropy contribution of heat transfer accounts for nearly 71%, which means that the heat recovery or optimization of adsorbent properties would be effective to reduce the energy consumption of adsorbent regeneration, however, the entropy generation of heat transfer accounts for only 41% to the total entropy generation of the whole energy consumption process, while these two ratios increase with the desorption temperature increasing. By these methods, energy-saving strategies of CO2 adsorption technologies can be obtained.