Postcombustion CO₂ Capture from Wet Flue Gas by Temperature Swing Adsorption

Abstract

We present an analysis of a novel temperature swing adsorption (TSA) process with condensers capable of treating wet flue gas reaching 90% CO2 recovery and 95% purity (on a dry basis). In the first part, the characterization of the binary CO2/water vapor adsorption equilibrium on zeolite 13X is presented, quantifying residual CO2 adsorption at different levels of water adsorption. On this basis, we propose an empirical and analytical isotherm model able to capture the competition between CO2 and water vapor. In the second part, the isotherm model is used in a process simulator to assess the performance of the proposed TSA process in detail. The strict specifications on the CO2 product could be reached by employing a layered-bed configuration, where a portion of the zeolite 13X bed is replaced by activated alumina. Further, the process is optimized by parametric analysis with respect to productivity and energy consumption while using the specifications as constraints. It is shown that reasonable performance can be obtained, comparable to the scenario where a drying step precedes the cyclic adsorption process but achieving this in a single process step. Moreover, the critical effect of the significant mass transfer resistance of water vapor on zeolite 13X is quantified. Due to a spread of reported mass transfer coefficients of water vapor on zeolite 13X, the process is assessed for three representative values, showing that comparable performance can be obtained for all cases considered by varying the length of the guard layer. The robustness of the process is further underlined by the reasonable performance for varying concentrations of water vapor in the feed.

Analysis of direct capture of $${\hbox {CO}}_{2}$$ from ambient air via steam-assisted temperature–vacuum swing adsorption

“…Although the relation holds for some data points, it fails to describe the behavior of others. Similar to a recent work (Hefti and Mazzotti 2018), a new isotherm model, accounting for the dependence on the water loading, is proposed in this work to describe CO 2 uptake in binary conditions. Using the Toth isotherm as a basis, the new isotherm model proposed in the following equation accounts for the water uptake dependence in the maximum uptake term, n s , and in the affinity coefficient, b:…”

The impact of binary water-CO2 isotherm models on the optimal performance of sorbent-based direct air capture processes.

“…Adsorption of water onto solid species is an interesting field of study itself and is essential for CO2 capture applications. The work by Hefti et al, [15][16][17][18] provides a very relevant body of knowledge. Water adsorption on Lewatit® VP OC 1065 follows a typical Type III isotherm, with hysteresis loops of Type H3, according to the IUPAC classification.…”

Post-combustion CO2 Capture: A Comparison Between Commercially Ready Technologies

“…As regards the adsorbent, a conservative choice has been made in considering zeolite 13X, a very well known CO 2 sorbent, suitable for this type of separations and still believed to be a competitive alternative to more expensive, tailor-made materials [21,22,23]. Due to the high selectivity of zeolites towards water [24], a relevant implication of the use of this sorbent is the need for the pre-dehydration of the flue gas ahead of the separation, as previously mentioned. In this study, the flue gas is dried down to a water content of 100 ppm by means of a simple two-step TSA process, where water is adsorbed on silica gel.…”