A simple thermodynamic tool for assessing energy requirements for carbon capture using solid or liquid sorbents. (June 2020)

• Record Type: Journal Article
• Authors: Caram, Hugo S.; Gupta, Ramesh; Thomann, Hans; Ni, Fan; Weston, Simon C.; Afeworki, Mobae
• Is Part Of: International journal of greenhouse gas control. Volume 97(2020)
• Publication Date: 2020-06
• Subjects: CO2 capture -- MEA -- Adsorption -- Solid sorbent -- Work of separation -- Free energy of separation -- Absorption regeneration -- Mof's -- TSA -- Calcium looping; Greenhouse gases -- Environmental aspects -- Periodicals; Air -- Purification -- Technological innovations -- Periodicals; Gaz à effet de serre -- Périodiques; Gaz à effet de serre -- Réduction -- Périodiques; Air -- Purification -- Technological innovations; Greenhouse gases -- Environmental aspects; Periodicals; 363.73874605
• DOI: 10.1016/j.ijggc.2020.102986
• Languages: English
• ISSNs: 1750-5836

Abstract

Graphical abstract: The minimum work requirement for carbon capture using an amine or solid sorbent -- i.e., the Gibbs free energy difference between the captured and the sorbed CO2, can be estimated simply from the CO2 sorption isotherm at ambient temperature. It does not require any other laboratory data, heat of sorption or a complex process model. Highlights: Equivalent work required for CO2 capture is better than heat of reaction to measure power lost due to capture. Minimum work of separation using sorption is simply evaluated from room temperature isotherm data. It is independent of the heat of reaction and, for most liquid sorbents, independent of the amines used. Solid gas reactions require a higher minimum work. For TSA, high sorbent capacity and heat recovery are most important and yield good estimates of overall work requirements. Abstract: Carbon capture and sequestration is known to be energy intensive and will result in 20–30 % reduction in net output of a power plant. However, a simple thermodynamic tool is currently unavailable for assessing the work of CO2 separation using a given solid or liquid sorbent. This paper provides rigorous yet simple framework of equivalent work to assess the energy requirement for CO2 capture using liquid amines or solid adsorbents. First, the theoretical minimum work is determined by assuming that each step in the sorption - desorption cycle is thermodynamically reversible. Then, irreversible heat transfer losses are added to calculate total work for the actual process. The model provides useful insights into the sorbent and process selection. The minimum work for reversible separation can be calculated merely from CO2 sorption equilibria at ambient temperature without requiring laborious data or complex models. A sorbent with low ab/adsorption heat does require less thermal energy, but this thermal energy is required at a higher temperature. Thus, contrary to conventional thinking, the equivalent work is not reduced. The irreversible heat transfer losses for the amines are mostly dictated by the amine's circulation rate which will be minimized by using amines with the highest CO2 capacity. On an energy requirement basis, the solid adsorbent based processes cannot compete with amines because practical methods of heat recuperation from the hot regenerated adsorbent are unavailable. Without heat recuperation, the solid adsorbent processes will be attractive only if their capital advantage outweighs their higher energy use.