A steady, one-dimensional model of the biomass gasification
process has been developed. The model considers the main
processes that are relevant for the thermochemical transformation
of biomass in a gaseous fuel that can be used in
reciprocating internal combustion engines.
The model has been validated with biomass of different size
and varying the air superficial velocity. A reasonable agreement
between the experimental and calculated results has been
achieved. The developedmodel thus simulates satisfactorily the
main sub-processes of the biomass gasification process.
The gasification model allows evaluating the effect of the
physical, chemical and energy properties of biomass (size,
density, proximate and ultimate analysis, and heating value)
on the gasification process. Moreover, it enables the study of
the gasifier geometry, the heat exchange and the different
injection points of the gasifying agent.
The producer gas composition calculated by the model can
be used to predict the performance and pollutant emissions of
an engine that is fuelled with the gas.
The main energy fluxes in the gasification process have
been analyzed by the model, and the most important flux is
the heat transfer by radiation in the solid phase, which
facilitates the drying and devolatilization processes, thus
opening the way to the combustion stage.
The model can be used as a design tool for downdraft
gasifiers; it gives the thermal power generated, the flow and
the composition of the producer gas, the global efficiency of
the process, and others.
The different stages of the gasification process and the heat
transfer mechanisms in the bed (hard to measure by conventional
techniques) have been recognized and analysed, and it
is proposed a possible sustainable auto thermal mechanism of
the flame front in downdraft fixed bed gasifiers.