Fixed Bed Gasification of Lignocellulosic Biomass: The Cemagref Process

Abstract

The use of biomass as an energy carrier could solve some of the main energy problems especially in developing countries, and gasification of lignocellulosic material in order to produce lean gas suitable to fuel an engine seems to be one the most promising techniques.

Nevertheless, among the different technologies available (fixed bed, updraft or downdraft, fluidized bed...) none appears able to face properly the major problem related to the presence of tars in the gas produced.

CEMAGREF developped a new technology which enables the elimination of the tars produced during pyrolysis in an internal burner in order to obtain a clean gas.

An automation of the wood feeding system and the internal running of the gasifier was carried out to ensure a good gas quality even in non stationary operating of the system.

Tests results obtained on a pilot unit developed in CEMAGREF showed low tar content and good gasification efficiency in the range of 50 to 200 kg/h of dry wood chips.

A cost analysis pointed out important economy of scale achievable with this relatively complex technology and therefore commercial size will range between 500 and 5000 kg/h of dry wood.

An economic calculation proved the profitability of the technique for the production of power in developing countries even if the feed must be produced in energy plantations and oil prices remain low.

Among the various energy from biomass lines CEMAGREF identified the gasification technique as one of the most promising especially in Developing Countries.

The aim of the research described here is indeed to produce a tar free lean gas, from high or medium grain size lignocellulosic biomass. Moreover, the thermal engine fueled with lean gas must be as flexible and reliable as with an oil derived fuel. It is therefore necessary to automate the part of the line upstream from the engine (biomass feeding, control of the inner operating parameters of the gasifier according to the power level required by the engine).