Title : Syngas cleaning by chemical looping conversion of tars from hazelnut shells pyrolysis and gasification
Abstract:
The depletion of fossil fuel reserves, exacerbated by the climate crisis, is driving scientific research towards innovative and more sustainable methods to supply feedstocks for the energy and chemical industries. Chemical looping biomass gasification (CLBG) emerges as a promising alternative to conventional gasification processes, offering several advantages: a) no nitrogen dilution of the syngas, b) no external heat required to drive endothermic gasification reactions, and c) reduced tar generation. This technique involves the circulation of a solid material between two reactors: the fuel reactor and the air reactor. In the fuel reactor, biomass undergoes sequential pyrolysis and gasification, while the oxygen carrier interacts with char through solid-solid and gas-solid reactions, facilitating the reduction of volatiles. In the air reactor, an exothermic reaction restores the oxygen carrier to its original phase. Iron oxide (Fe2O3) is the most developed material for this purpose, being environmentally benign, readily available, and resistant to attrition.
This study employs an iron-based oxygen carrier to chemically loop gasify biomass waste, such as hazelnut shells. The investigation focuses on the impact of adding alkaline earth metals and/or transition metals to iron oxides on the composition of the resultant syngas. The synergistic effects of combining two or more metal oxides for chemical looping applications, including the use of waste materials as oxygen carriers, are also examined. A parametric analysis is conducted in a lab-scale fixed bed reactor, considering variables such as steam-to-biomass ratio, biomass-to-oxygen carrier ratio, reaction temperature, tar release, and gas space hourly velocity. Optimizing these parameters aims to enhance syngas output, lower heating value, improve biomass conversion, and increase carbon capture efficiency.
The performance comparison with an inert bed is discussed. Finally, material characterization before and after the reaction is carried out to assess: a) changes in material morphology (Scanning Electron Microscopy), surface area (Brunauer, Emmett, Teller analysis), and crystalline phase (X-Ray Diffraction) at each reaction step; b) the reaction pathway at different temperatures (Temperature Programmed Reduction); and c) the presence of deposits on the particle surface. This comprehensive characterization contributes to defining the proposed material's suitability for high energy density syngas production through chemical looping gasification.
Audience Take Away Notes
- Understanding the basic principles and advantages of CLBG compared to traditional gasification methods.
- The role of the oxygen carrier in the gasification process and its circulation between the fuel reactor and air reactor. Key parameters affecting CLBG performance: steam to biomass ratio, biomass to oxygen carrier ratio, reaction temperature, tar release, and gas space hourly velocity.
- How optimizing these parameters can enhance syngas output, reduce heating value, improve biomass conversion, and increase carbon capture efficiency?
