Characterization of the reactive system involved in the high temperature treatment of tar and gas coming from biomass pyrolysis

Abstract

This work contributes to the on going emergence of new technologies for energy production. It deals with the use of lignocellulosic biomasses to produce syngas that can be transformed into synthetic fuel by the Fischer Tropsch process. A two-stage process is studied performing first the biomass pyrolysis then the catalytic treatment of the produced gas at 1000°C. The objective of this study is to better understand the physical and chemical phenomena involved during the high temperature gas treatment stage through a coupled experimental and modelling approach. A particular attention is paid to the removal of tar produced during the first stage, and to the opportunity of using the char produced during the biomass pyrolysis as catalyst in the second stage. A phenomenological model describing the system (geometry, heat transfer, mass transfer between the different phases (gas, tar, char) and throughout the bed) has to be developed. The tar and the char compositions and potential interactions are particularly complex. Indeed, the tar is a lump of a hundred compounds and in addition, the reaction network is rather complex: decomposition reactions (steam and dry reforming, cracking), polymerisations, soot formation and interactions between the compounds. So some “model compounds” illustrating some of the characteristics of the whole group or the limit of these characteristics (i.e. the steam reforming reactivity, the thermal stability…) have been selected to simplify the reaction network. In order to establish the basis of the phenomenological model, some preliminary experiments are carried out on the Biocarb facility to study the behaviour of the first stage and the destruction of tar on different loads.