Chemical-looping Utilization Of Biomass With Copper-based Oxygen Carrier

Chemical-looping combustion(CLC) is an innovative breakthrough that has the potential to solve the problem of energy and environment. Compared with the traditional combustion technology, CLC technology has many advantages such as inherent CO2 separation, low reaction temperature, inhibition of thermal NOX formation, and two-stage reactions to improve system efficiency. Chemical-looping with oxygen uncoupling(CLOU) is another new-type combustion technology based CLC. The difference is the specific oxygen carrier(OC) CLOU adopted which can release gaseous oxygen when the surrounding oxygen pressure is below its equilibrium partial pressure. The slow gasification process of solid fuels is avoided and the overall reaction rate is improved greatly since the gaseous oxygen is available. Chemical-looping reforming(CLR) is a novel technique to generate synthesis gas utilizing similar principles as CLC. The difference lies in that the product of CLR desired is not heat but synthesis gas, a mix of H2 and CO. Biomass is a renewable new energy which is considered as carbon neutral, because the amount of carbon it can release is equivalent to the amount it absorbed during its life time. Much attention has been paid to its utilization patterns. Combining chemical-looping technology and biomass utilization, Chemical-looping utilization of biomass with Cu-based OC experimental research was carried out from several aspects. The feasibility is discussed, as well as the effect of different experimental conditions.Firstly, using CuO/CuAl2O4 prepared by sol-gel method as OC and sawdust as fuel, the feasibility of biomass CLOU was investigated in a fluidized bed. The influence of reaction temperature was discussed. For further research, sawdust was blended with anthracite as fuel to investigate the synergistic effect between the two kinds of fuel. Then, the feasibility of biomass CLR using Cu-based OC was investigated. The effects of OC and reactor temperature on the syngas composition distribution, gas yield, carbon conversion efficiency, lower heating value and gasification efficiency as well as tar content were examined. At last, steam was introduced to explore the infulence of operation conditions such as the ratio of oxygen and biomass, OC, steam to biomass ratio and temperature, on biomass CLR process. The results illustrate that the reacting temperature has a great influence on the carbon conversion of biomass direct CLOU. With the rise of temperature, the carbon conversion rate was accelerated. Using sawdust as fuel resulted in lower CO2 capture efficiency. However, the efficiency of biomass direct CLOU could be improved when the sawdust was mixed with anthracite. With regard to biomass CLR, it was found that when using Cu-based OCs, the gas yield and carbon conversion efficiency increased significantly, but the gasification efficiency and low heating value decreased accordingly. The presence of Cu-based OCs helps reduce C2 Hm and tar in syngas. It is hard to give a conclusion that copper based oxygen carrier is better than or worse than iron based oxygen carrier for a biomass CLR at present. The disadvantage of using copper based OC is the decrease of gasification efficiency and LHV at the expense for maintaining heat balance in the CLR process. The disadvantage of using iron based OC is the low reactivity as well as the low carbon conversion efficiency. In addition, the selection of copper or iron based OC also depends on the purpose of the CLR and the downstream gas processing. If less tar and light hydrocarbon are expected for the downstream gas processing, copper based oxygen carrier may be a better choice. In the tar composition analysis, it was found that the macromolecular compounds content reduced, the small molecule compounds content and species increased while using Cu and Fe-based OCs. It can be explained that the existence of OC makes the decomposition of macromolecular compounds in the tar take place in a certain degree.