Ash related issues

Analysis of ash formation and behaviour in biomass combustion plants

In order to allow a fundamental analysis of ash related issues in biomass fired boilers, a comprehensive CFD model for fine dust and deposit formation and as well as high temperature corrosion has been developed in several research projects. This model is capable of considering the condensation of ash vapours (direct wall condensation and fine dust formation), the deposition of fine dust, coarse salt-rich and silica-rich fly ash particles as well as the erosion of the deposit layer by non-sticky coarse fly ash particles. Moreover, two CFD-based models for high temperature corrosion in biomass fired boilers have been developed (a fast empirical model and a detailed model considering transport processes and chemical reactions). Ongoing research in this field is focusing on the implementation of a detailed gas phase sulphation kinetic mechanism into the existing model. Furthermore, the catalytic effects of certain species, e.g. the iron oxide layer, on the sulphation rate of already deposited chlorides are part of ongoing research.

Total fine particle concentration (mg/Nm³ dry flue gas, 13% O₂) (left) and chemical composition of the fine particles (right) in a 70 kW pellet boiler [Schulze et al. 2010]