The goal of this project is to investigate innovative materials in the Calcium-Copper looping process combining both copper and calcium phases in the same particle. The objective is to favor heat transfer from the exothermic CuO reduction to the endothermic CaCO3 calcination reaction, reducing the amount of inert phase in the solid inventory, lowering the final reactor volume and increasing thermal efficiency.
Sorption Enhanced Reforming combines reforming of methane and CO2 capture by a CaO-based sorbent at mild temperature (650-700 °C) to produce a highly concentrated H2 stream (>99.5 %). The CO2 sorbent needs to be further regenerated in a separate reactor (or process step) by rising the temperature (to 850-900 °C), with the potential of producing a pure CO2 stream available for sequestration. Chemical Looping Combustion (CLC) technology, on the other hand, involves cyclic oxidization (by air) and reduction (by a hydrocarbon fuel or syngas) of solid oxides to produce heat and power with inherent CO2 capture. The calcium-copper looping process integrates both Sorption Enhanced Reforming (SER) and Chemical Looping Combustion (CLC) technologies to produce heat/power and H2 with simultaneous CO2 capture.
By coupling calcium and copper looping, the heat for CaCO3 regeneration at high temperature, which is the energy demanding step of the SER technology, is supplied by in-situ CuO reduction with H2, CO and/or CH4. In this way, the sorbent regeneration step is carried out by oxidation of gaseous fuels in a N2 free environment, producing a pure CO2 stream without the need of an expensive Air Separation Unit (ASU).
Materials were first synthesized in powder form. CaO/Ca12Al14O33, CaO/Al2O3 and CaO/CaZrO3 were selected as CO2 sorbents and supports for CuO introduction. Activity screening was carried out using process relevant TGA multi-cycle tests, where cyclic CO2 capture/release and O2 capacity were measured. SEM, XRD, ICP-MS and BET analysis were used to thoroughly characterize the materials. The best performing material powders (based on mayenite) were granulated using a high shear granulator to produce particles in the optimal size range (0.5 ? 0.8 mm diameter) for further tests in a fixed bed reactor validation at laboratory scale (75 g of materials total). These tests were carried out successfully at Instituto de Carboquímica (ICB) in Zaragoza, Spain, September through November 2018.
Mathematical modelling has resulted in a pseudohomogeneous reactor model for the calcination process and a Changing Grain Size Model (CGSM) for combined particles. The CGSM model has indicated that mass transport can be a potential bottle neck for the process if the particle porosity is low. At low porosity the CO2 concentration inside the porous particle can reach the equilibrium pressure of over the CaO/CaCO3 solid. This effect can stop calcination while copper reduction is continuing, leading to intraparticle hot spots (> 900°C).
The thermal properties of developed materials have been investigated using a combination of CGSM modelling and measurements of effective thermal conductivity through a transient plane source (TPS) method. The collected TPS data were used to select a best-fit mathematical effective transport equation for the CGSM model from literature. The CGSM model was also run using other sub-optimal thermal relations in order to evaluate the model sensitivity. Indications are that the thermal properties of the combined particles are more dependent on the gas phase and its composition than to the solid phase composition and state given a material porosity around 30 ? 55%. In terms of thermal properties there does not seem to be significant differences between combined and segregated calcium-copper materials. The CGSM model is moderately sensitive to the choice of effective transport equation, and for a given material the selection of effective thermal transport equation should be supported by experimental measurements.
A paper on combined CaZrO3-based calcium-copper materials was accepted December 2019 and is available in the ?International Journal of Greenhouse Gas Control? early 2020. The data presented in the article shows that the CuO/CaO ratio is tunable for the developed material in a Ca-Cu Looping relevant ratio range > 2.0 [wt/wt] with an optimal CuO loading likely in the range [40, 50) wt%, similar to the results found for the previously developed combined mayenite materials.
The project achieved the experimental validation of newly synthesized multi-functional calcium-copper particles adapted to the calcium-copper looping. Better heat transfer due to the intimate contact between Ca and Cu species during calcination, and lower inert content in the reactor can be achieved making use of the developed materials versus conventional "segregated" particles - which can result in increased materials stability and process efficiency. Achieved results in both modelling activities and experimental tests have ensured a strong interdisciplinary approach and a robust proof of concept of the combined calcium-copper CO2 sorbent and oxygen carrier materials. This shows that it is possible to boost process intensification concepts from the perspective of (multifunctional) materials development. International collaborations with universities and research centers in Spain, Italy and Netherlands were created.
The Calcium-Copper technology (CaCu) is an emerging technology for pre-combustion CO2 capture. This technology was proposed in 2012 by two Spanish Research Council institutes (ICB and INCAR) for the reforming of natural gas with integrated CO2-capture. It is based on the catalytic Sorption-Enhanced Reforming reaction using a CaO-based sorbent, combined with the exothermic redox reactions of copper. The CaO captures the CO2, shifting the reforming reaction towards higher hydrogen yield. The reduction of CuO by natural gas provides the heat necessary to release the CO2 at another stage. This process does not require pure oxygen streams at any stage, avoiding the costly and energy demanding air separation unit used in alternative CO2 capture technologies. The operation of each of the 4 process steps is controlled by pressure and temperature swing, and requires highly efficient and durable materials, containing CaO, Cu and a reforming catalyst. The CaCu process is under development in a running FP7-European project (ASCENT). In that project, IFE has synthesized for the first time integrated materials that combine the functions of Cu and CaO over the same support, in opposition to separate pellets for each material and function. This approach has the potential to improve heat transfer efficiency and diminish the total amount of inert fraction in the reactor beds. This translates into an increase of energy efficiency and lower investment and operation costs. The proposed 6Cs project will be performed in parallel to the ASCENT project, to study and optimize the heat transfer mechanisms and the materials production methods. The focus will be to study the fundamentals of the materials performance with experimental and modelling tools, to optimize the synthesis methods accordingly - by promoting the use of low-cost raw materials - and to quantify the technical, economic and environmental impacts of using these integrated materials in the CaCu process.