The effect of alkali earth metals on CuO/Al₂O₃ oxygen carrier in syngas chemical looping combustion process

• Main Author: Chang, Chia Chyi
• Other Authors: Grzegorz Lisak
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Environmental engineering
• Online Access: https://hdl.handle.net/10356/158513
• Institution: Nanyang Technological University

Chemical looping combustion (CLC) is a promising technology which could serve as a possible replacement for combustion of fossil fuel and incineration of municipal solid waste (MSW). This process involves the use of oxygen carriers to transfer oxygen from the air reactor to the fuel reactor without direct contact between the two reactors. CuO is one of the most commonly used metal oxide for oxygen carriers. However, due to the low melting points of CuO, it brings about problems of sintering and agglomeration which could defluidize the reactor. Over the years, researchers have been experimenting with different metal oxides and/or adding supports such as Al2O3 to the active phase metal oxide, in order to improve the performance of the oxygen carrier. Presently, little research has been done on the influence of sorbents in the performance of oxygen carriers for CLC. This study aims to evaluate the effect of Ba, Sr, and Ca as a sorbent for the CuO/Al2O3 oxygen carrier. The three different sorbents were mixed in 40% and 30% wt. of CuO, in order to compare their performance in CLC. In total, 11 oxygen carriers were compared in this study. A fluidised bed reactor was used to simulate the CLC process at 850°C, in order to study the differences in reactivity between the use of 3 sorbents, as well as the stability of the different oxygen carriers over 50 cycles. To further analyse the reactivity of the oxygen carriers, thermogravimetric analysis (TGA) was carried out for oxygen carriers with and without the use of sorbent, over a period of 20 and 50 cycles. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to monitor the physical characteristics of the oxygen carriers before and after CLC, analysing their effect on agglomeration. The results suggest that the addition of sorbents is an effective solution to improving the performance of oxygen carriers in CLC. In fact, Ca seemed to be the best performing sorbent in terms of reactivity, stability, and agglomeration resistance, over a period of 50 CLC cycles.