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Abstract
The subject of this work is the mathematical modelling of a counter-current moving-bed gasifier fuelled by wood-pellets. Two versions of the model have been developed: the one-dimensional (1D) version-solving a set of Ordinary Differential Equations along the gasifier height-and the three-dimensional (3D) version where the balanced equations are solved using Computational Fluid Dynamics. Unique procedures have been developed to provide unconditionally stable solutions and remove difficulties occurring by using conventional numerical methods for modelling counter-current reactors.The procedures reduce the uncertainties introduced by other mathematical approaches, and they open up the possibility of straightforward application to more complex software, including commercial CFD packages. Previous models of Hobbs et al., Di Blasi and Mandl et al. used a correction factor to tune calculated temperatures to measured values. In this work, the factor is not required. Using the 1D model, the Mandl et al. 16.6 kW gasifier was scaled to 9.5 MW input; the 89% cold-gas efficiency, observed at 16.6 kW input, decreases only slightly to 84% at the 9.5 MW scale.
Highlights
Introduction and ObjectivesCombustion and gasification of biomass has become considerably important in the current energy scenario due to both resource protection and climate precaution (CO2 neutrality)
It is perhaps fair to say that the CFD-modelling approach, initially developed for grate-fired stockers and waste-incinerators [26,27], has nowadays become widely applied to biomass gasification in fixed-beds
Most of the mathematical modelling work has been concerned with performance predictions of co-current gasifiers where a biomass and a gasifying agent are supplied at the top and both move downwards
Summary
Combustion and gasification of biomass has become considerably important in the current energy scenario due to both resource protection and climate precaution (CO2 neutrality). Biomass importance strongly varies from country to country depending on the financial incentives instituted. Co-firing of coals with biomass [1,2,3] became commonplace in the Nordic countries, in the UK and in the Netherlands, while it is hardly used in Germany. Denmark is certainly the leading country in producing electricity in full-scale boilers fired with biomass [4,5,6,7]. Biomass gasification is typically carried out in fluidized-beds, entrained-flow reactors or in fixed- or moving-beds. Gomez-Barea and Leckner [10] reviewed the fluidized-bed technology, Higman [11] reviewed the entrained-flow gasifiers, while Chopra and Jain [12]
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