Abstract
The EU FP7-funded HiPerCap project aims to develop novel post-combustion CO2 capture technologies and processes which are environmentally benign and have high potential to lead to breakthroughs in energy consumption and overall cost. Three different separation technologies are being evaluated on a fair basis: absorption, membranes and adsorption. In this work, some of the results related to the development of adsorption-based fixed bed systems are presented. The design and optimization of a multibed adsorption-based separation process requires the use of powerful simulators that can describe the non-steady state process. However, prior to use a mathematical model for process design this should be validated against experimental data. A VTSA experiment has been carried out in order to provide information on the cyclic performance of a microporous biochar. The working capacity of the adsorbent is reduced due to incomplete regeneration during cyclic operation, although it stabilizes at 0.5 mol CO2 kg-1 and 0.4 mol H2O kg-1 once cyclic steady state is reached. A non-isothermal non-adiabatic dynamic model of the VTSA cycle was built in Aspen Adsorption, which makes use of the Ideal Adsorbed Solution theory to account for competitive adsorption between N2, CO2 and H2O. The model satisfactorily describes the history of the temperature of the adsorbent, the pressure, the total mass flow rate of the effluent, and the working capacity at cyclic steady state of the VTSA experiment. The validated model will be used as a starting point for process development.
Highlights
Up to date, only one post-combustion CO2 capture (PCC) unit is operating at commercial scale in the power sector [1]
During the VTSA experiment, regeneration is not completed, which means that part of the H2O and CO2 remain in the adsorbed phase, reducing the amount adsorbed in the subsequent cycle
A VTSA cycle consisting of four steps has been carried out experimentally: (i) adsorption of a synthetic flue gas mixture with 84% N2, 14% CO2 and 2% H2O at 50 °C and 1.4 bar; (ii) heating to 70 °C and evacuation to 0.02 bar; (iii) cooling to 50 °C; (iv) repressurization to 1.4 bar and purge with N2 at 50 °C
Summary
Only one post-combustion CO2 capture (PCC) unit is operating at commercial scale in the power sector [1]. Large scale adsorptive separation systems can be divided into two broad classes: cyclic multibed processes, in which a series of stationary adsorbent beds are synchronously saturated and regenerated in order to provide continuous feed treatment, and steady-state processes that involve countercurrent contact between the feed gas and the solid adsorbent (likewise to the absorption case, except that the liquid solvent is replaced by the solid adsorbent). Both types of processes are being evaluated within HiPerCap project. Some of the results related to the development of adsorption-based fixed bed processes are presented
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