Predicting Melt Formation and Agglomeration in Fluidized Bed Combustors by Equilibrium Calculations

• Published in: Waste and biomass valorization 2014-10, Vol.5 (5), p.879-892
• Main Authors: Billen, P., Van Caneghem, J., Vandecasteele, C.
• Format: Article
• Language: English
• Subjects: Engineering; Environment; Environmental Engineering/Biotechnology; Industrial Pollution Prevention; Renewable and Green Energy; Review; Waste Management/Waste Technology
• ISSN: 1877-2641; 1877-265X
• DOI: 10.1007/s12649-013-9285-0

Thermal valorization of biomass or waste in a fluidized bed combustor may result in agglomeration of the bed material, coated with ash, potentially causing defluidization. In this paper, the causes of agglomeration for various fuels are critically reviewed, based on thermodynamic grounds. It is shown that even for phosphorus rich biomass types, in most cases the largest melt phase consists of alkali silicates: Ca phosphates are formed instead of Ca silicates, leading to lower melting points in the CaO–K 2 O–SiO 2 system. Although thermodynamic optimization of the four main ash forming elements (K, Ca, Si and P) only provides an estimate of the amount of melt phase, it is shown that for various fuels the agglomeration behavior can be explained consistent with experimental findings from literature. As a consequence, for most biomass and waste types a similar thermodynamic estimation can be made to predict agglomeration problems and incorporate countermeasures in the design and operation of the fluidized bed combustor.