Etude de la combustion de gaz de synthèse issus d'un processus de ...

Conclusions
CHAPTER 7
CONCLUSIONS
7.1 Summary of present work and principal findings
In the currently reported work, three typical syngas mixtures of H 2 , CO, CH 4 , CO 2 and
N 2 have been considered as representative of the producer gas coming from forest
biomass gasification, and its combustion characterization is made in order to improve
current knowledge and provide reference data for modeling and simulation with the
objective of its application in stationary energy production systems based on internal
combustion engines.
tel-00623090, version 1 - 13 Sep 2011
A detailed bibliographic study was performed concerning two fundamental topics
evolving this work - gasification and combustion. First, in its widest sense the term
gasification covers the conversion of any carbonaceous fuel to a gaseous product with
an useable heating value. The result of the gasification is a fuel gas - the so-called
syngas - consisting mainly of CO, H 2 , CO 2 , H 2 O, CH 4 , N 2 , some hydrocarbons in very
low quantity and contaminants, such as carbon particles, tar and ash. Key parameters
for successful gasification are the feedstock properties (moisture, ash, alkalis and
volatiles) and feedstock pre-treatment (drying, particle size, fractionation and leaching).
The main advantage of gasification over direct combustion of biomass is the improved
balance of carbon dioxide, nitrogen oxides and sulphur in the atmosphere. The main
attraction of this technology is the production of a fuel gas, which can be used into an
engine or turbine for power production. This is remarkable important if one considerer
that biomass power plants today operate on a steam-Rankine cycle with low
efficiencies due to modest steam conditions. Gasification is being used to improve the
efficiency and to reduce investment costs of biomass electricity generation through the
use of gas turbines and combined cycles where efficiencies of 50% are obtained.
Gasifiers are of two main types, fixed bed and fluidized bed, with variations within each
type and specific characteristics which determine the need for and extent of feedstock
preparation/pre-treatment. For use in gas engines gas produced from a fixed bed,
downdraft gasifier provides a low tar gas, with a high particulates loading: as tar is a
major contaminant for engine operation and particulates can be relatively easily
removed, this system is considered best for fuelling gas engines. There is a significant
discrepancy in the final composition of the syngas, even considering the same type of
biomass and type of gasifier. This highlights the strong dependence of the syngas
194