Abstract
As part of the strive for a carbon neutral energy production, biomass combustion has been widely implemented in retrofitted coal burners. Modeling aids substantially in prediction of biomass flame behavior and thus in boiler chamber conditions. In this work, a simple model for devolatilization of biomass at conditions relevant for suspension firing is presented. It employs Arrhenius parameters in a single first order (SFOR) devolatilization reaction, where the effects of kinetics and heat transfer limitations are lumped together. In this way, a biomass particle can be modeled as a zero dimensional, isothermal particle, facilitating computational fluid dynamic calculations of boiler chambers. The zero dimensional model includes the effects of particle aspect ratio, particle density, maximum gas temperature, and particle radius. It is developed using the multivariate data analysis method, partial least squares regression, and is validated against a more rigorous semi-2D devolatilization model. The model has the capability to predict devolatilization time for conditions in the parameter ranges; radius (39–1569 μμm), density (700–1300 kg/m3), gas temperature (1300–1900 K), aspect ratio (1.01–8). Results show that the particle radius and gas phase temperature have a large influence on the devolatilization rate, and the aspect ratio has a comparatively smaller effect, which, however, cannot be neglected. The impact of aspect ratio levels off as it increases. The model is suitable for use as stand alone or as a submodel for biomass particle devolatilization in CFD models.
Highlights
An increased awareness of the need for a carbon neutral energy production has led to a corresponding increase in biomass combustion
To compromise between the need for a simple devolatilization model and the need for describing the complicated phenomenon of biomass particle pyrolysis, this paper introduces lumped Arrhenius kinetic parameters for a single first order global pyrolysis model
They have been determined for T = 1600 K, and plotted with these A and E values for a short temperature interval to illustrate the effects of the different parameters
Summary
An increased awareness of the need for a carbon neutral energy production has led to a corresponding increase in biomass combustion. Combustion of biomass can be regarded as a carbon neutral source for energy [2]. Byutilizing suspension firing technology in existing coal power plants rebuilt to combust biomass particles, a decrease in carbon emissions can be obtained, which enables the European Union’s Green deal of no net emission of green house gasses by 2050. In combined heat and power plants, up to 90% of the energy stored in woody biomass can be recovered as heat and electricity [2]. With this aim, the interest in retrofitting suspension firing units to combust biomass instead of coal has increased over the past decades.
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