ΕΘΝΙΚΟ ΜΕΤΣΟΒΙΟ ΠΟΛΥΤΕΧΝΕΙΟ

parallel, a reduced amount of the produced char is observed and consequently a
reduction of available produced heat in the char combustor.
Elemental oxygen and hydrogen mass balance closure objectives show that steam
decomposition is mandatory revealing thus its participation in the chemically reactive
system, especially at high gasification temperatures.
A thermodynamic consideration of the gasification process is applied demonstrating the
composition of the produced synthesis gas as a function of the gasification temperature
in chemical equilibrium state.
This work also studies the gasification of different type of biomass feedstock like
agricultural residues, energy crops and dry sewage. The mathematical modeling of their
gasification process is attainable, if the elemental analysis of the biomass feedstock is
comparable to that of hybrid poplar, e.g. bagasse or switchgrass. If the elemental carbon
or/and hydrogen content of biomass feedstock is quite low, then the simulation
“collapses”, inasmuch as, mass balance closure fails for these elements, as is the case of
dry sewage.
The comparison of the simulation results versus the experimental data from indirect
gasification processes of pilot or industrial scale units using similar woody feedstock is
found satisfactory. However, the results of this simulation significantly differ from those
of other bibliographical mathematical models due to the fact that those models use a
chemical reactive system in equilibrium. As a consequence these mathematical models
ignore mass and heat transfer limitations due to various resistances, while the empirical
correlations of this work encapsulated similar limitations during the experimental data
regression process.
Preliminary economic analysis shows that synthesis gas production from hybrid poplar
as a biomass feedstock is a profitable entrepreneurial venture. The annual profit is
derived subtracting the cost of annual biomass feedstock demand from the value of the
yearly produced synthesis gas tonnage. Further technical and economic ratifications are
required before such a gasification technology is opt for commercialization targeting
small and medium scale installations, more appropriate for small rural communities.
Main issues governing biomass gasification are tar formation and correction of the
hydrogen to carbon monoxide ratio. Future research will focus on the catalytic
gasification process, whereas the catalyst will also serve as the heat transfer medium
between the gasifier and the char combustor. On the other hand, future simulation
should be based further on the fluidmechanical aspects of the reactor scheme. Such a
simulation of the gasification reactor will provide a more precise description and a better
insight and understanding of the real process. Thus, knowledge will be gained in relation
with the intricacy and peculiarities of the involved mechanisms of mass, heat transfer
along with the intrinsic chemical reaction scheme.
Keywords: biomass, syngas, gasification, olivine, Aspen, simulation, mathematical
model, hybrid poplar, forest products, agricultural residues, energy crops
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