Experimental demonstration of the Ca-Cu looping process

M Martini,M Druiff,F Gallucci,M Van Sint Annaland

doi:10.1016/j.cej.2021.129505

Abstract

• A proof-of-concept of the Ca-Cu process has been carried out at larger scale. • Each process step has been studied separately for different operating pressures. • An increase in pressure negatively influences the sorption-enhanced reforming step. • H2 in the product stream higher than 90 vol% on dry basis has been obtained. In this work an experimental proof-of-concept of the Ca-Cu process has been carried out. The Ca-Cu process combines sorption-enhanced steam reforming of methane with a Ca-based sorbent with chemical looping of a Cu-based oxygen carrier to provide the energy for the sorbent regeneration. Each process step has been studied separately for different operating pressures and inlet gas compositions, and addition complete cycles (including all three consecutive process steps, viz. the sorption-enhanced reforming step, oxidation step and regeneration step) have been performed to evaluate the technical feasibility of the complete process. The pressure influences the sorption-enhanced reforming step negatively, while the steam-to-carbon ratio does not influence the average outlet H 2 (dry) fraction. When increasing the inlet O 2 concentration during the oxidation step, the amount of CO 2 released increases, whereas increasing the pressure decreases the amount of CO 2 released. In the regeneration step, increasing the H 2 fraction in the feed increases the amount of sorbent that is regenerated, reaching 70 wt% of the sorbent in the bed with 60 vol% H 2 in the feed. More than 285 complete cycles were performed, the solids were still chemically performing well, and the results were still reproducible. Simulations with a pseudo-homogeneous reactor model were performed for all the separate steps. The model does not describe the experimental data well, which was attributed to problems with the packing of the bed at the bottom of the reactor (solids maldistribution), which was confirmed after opening the reactor after the experimental campaign. The problems with the packing of the bed was caused by problems with the chemical–mechanical stability of the oxygen carrier, which became a powder after the experiments due to the high mechanical stresses it was exposed to.

Highlights

The Ca-Cu looping process is a promising pre-combustion CO2 cap ture technology which allows carrying out the energy-intensive sorbent regeneration with a moderate energy penalty and which was proposed by Abanades et al [1,2,3]
The Ca-Cu process combines sorption-enhanced steam reforming of methane with a Ca-based sorbent with chemical looping of a Cubased oxygen carrier to provide the energy for the sorbent regeneration
First each step has been studied separately, and complete cycles have been performed to prove the technical feasibility of the process

Summary

Introduction

The Ca-Cu looping process is a promising pre-combustion CO2 cap ture technology which allows carrying out the energy-intensive sorbent regeneration with a moderate energy penalty and which was proposed by Abanades et al [1,2,3]. As stated by the “Paris Agreement” adopted on 12th December 2015 [4] the carbon dioxide emissions to the atmo sphere must be reduced as soon as possible in order to limit global warming to 2 ◦C above pre-industrial levels This can be done, together with many other strategies, using Carbon Capture and Storage (CCS) technologies, using hydrogen as energy carrier together with reducing energy penalties and costs of the processes. The Ca-Cu looping process consists of the high-temperature CO2 capture during the production of hydrogen via sorption-enhanced steam-methane reforming using CaO as sorbent. This is coupled with a Cu/CuO chemical loop to supply the energy needed for the CaCO3 calcination. The calcination of CaCO3 formed during the SER step of the process occurs thanks to the energy released by the reduction of CuO, which is carried out by feeding a fuel gas containing H2, CO and/or

Methods

Results

Conclusion