Syngas Cleaning by Chemical Looping Conversion of Tars from Hazelnut Shells Pyrolysis/gasification

Abstract

Syngas tars are responsible for clogging and corrosion of pipelines and equipments due to their high condensation temperatures. At the same time, considering their energy content they cause a reduction in the energy efficiency of the conversion process. To overcome these drawbacks, the addition of a downstream reactor to perform hot catalytic gas cleaning has been proposed. However, the occurrence of significant carbon deposition and sulphide formation on the catalytically active surfaces can easily lead to early deactivation of the catalyst. Chemical looping tar reforming is based on a solid material, known as oxygen carrier, that undergoes two reactions steps: (1) reduction by interaction with the gas and tar streams; (2) regeneration by oxidation with ambient air, which also involves the combustion of any deposits on the particle surface. In this work, the first reaction step of the process is investigated in an integrated setup involving the pyrolysis or the gasification of hazelnut shells and the reaction with the oxygen carrier for tar abatement. Two reactor configurations have been considered: (1) single reactor, where the biomass and the oxygen carrier beds are loaded in series into the same reactor; (2) two reactors, where the two beds are loaded into different reactors in series. Blank tests for pyrolysis and gasification are also carried out for comparison. The results indicate that the two beds configuration enables higher tar conversion (89% wt for pyrolysis and 75% wt for steam gasification), though the presence of the oxygen carrier causes a reduction in the energy content of the syngas, especially in terms of H2 concentration, which is reduced from around 34% to 21% mol for pyrolysis and from 28% to 21% mol for steam gasification.