Comprehensive CFD modeling of the ash deposition in a biomass packed bed burner

Abstract

Ash-related issues such as fouling and slagging are likely the main operational problems of most commercial solid fuel burners. To study this kind of system, a full 3D-transient bed model embedded into the commercial CFD code ANSYS-Fluent was developed to describe the main processes that occur inside the bed. The model employs several sub-models that have been validated in previous studies (e.g., drying, devolatilisation, char reaction, radiation) and were combined with an ash evaporation model that functions in conjunction with a fine-particulate ejection model for predicting typical ash-related problems. In this work, the model is applied to simulate a pilot plant where the deposition of ash on refrigerated tubes is investigated. Several operational points were tested and simulated to assess the capability of the model to explain and predict the experimental fouling rates on the tubes, using which we show the relevance of the bed thickness variation and the primary air flow in the deposition profile. The ash evaporation and fine-particulate ejection models work symbiotically with the existing packed-bed biomass combustion model. The results obtained in this work show that this is a powerful tool for improving the operation of most existing appliances and contributes to the creation of a complex ash-layer deposition model.