COMBUSTION MODELING OF A FIXED BED DOWNDRAFT BIOMASS GASIFIER USING COMPUTATIONAL FLUID DYNAMICS DESIGN
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Date
2019-06
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Abstract
Thermochemical conversion of biomass in a gasifier for the production
of syngas provides the enabling technology for efficient biomass
resource utilization. Gasification is a complex process involving the
interactions of numerous parameters, hence CFD tool is usually utilized
to numerically optimize the design and operation of the gasifier reactor
for improved performance. The gasification of multiple biomass usually
requires a complex set of facilities for experimental set up in order to
determine the optimum operating conditions for maximum gas yield.
When this is not available, it can pose a bottle-neck to process
development and optimization. In this study, the GAMBIT and FLUENT
were used to model and simulate the gasifier reactor with emphasis on
the combustion and gasification (reduction) zones in order to maximize
the thermal output of the combustor by an optimization of biomass
fuel types. Model validation was achieved by showing a close
agreement between numerical and experimental results within the
same configuration, particularly to show the effect of temperature on
the gasification of Fixed Bed Downdraft gasifier. The fraction of initial
moisture content, air flow rate, temperature of the pyrolysis zone, and
chemical composition of the biomass were the required input data for
the model to predict the gasification temperature. Computations were
carried out for rice husk, saw dust and corn cobs as gasifier fuels,
whereby air was used as the oxidizing agent. The porosity and oxidizer
velocity were varied between 0.1 – 0.5 and 5 – 15 m/s respectively. The
predicted results compared with experimental data showed good
agreement. The simulated temperature gradient also indicated that rich
fuel combustion zone was greater for rice husk - corn cobs, an
indication that improved gasification and pyrolysis were present