Computational modeling of fluidized bed behavior with agglomerates.

Abstract

The transition towards the use of more renewable energy is an essential subject for the imminent climate crisis. Biomass can be converted into syngas in a gasification process. The formation of agglomerates in a Bubbling Fluidized Bed (BFB) gasifier is a major problem when gasifying biomass to syngas. An agglomerated bed may lead to instability in the fluidization process. These instabilities are incomplete fluidization, fluid channeling, and defluidized zones in the gasifier. In the worst cases, agglomeration may lead to complete defluidization of the bed. The objective of this thesis is to develop a Computational Particle Fluid Dynamic (CPFD) model to simulate the flow behavior in a hot BFB with agglomerates. The CPFD model is created using the commercial software Barracuda Virtual Reactor 17.4.1 and validated with experiments performed in both cold and hot models of BFB. The models showed promising accuracy when compared with the experimental data. The cold and hot BFB had an average deviation of 6 %, and a deviation of 3 %, respectively. The minimum fluidization velocity for the cold and hot model was 6 % and 12 %, respectively. The hot BFB geometry was scaled up from lab-scale to pilot-scale using Glicksman’s scaling rules. The pilot-scaled bed needed additional agglomerates corresponding to 20% of the bed volume to affect the flow behavior. The agglomerated bed simulation gave promising results. The simulation showed similarities in the flow behavior with experimental data found in the literature. The overall pressure gradient over the bed decreased, and the minimum fluidization velocity increased. The CPFD model is capable of predicting the fluidization process in a BFB gasifier with agglomerates.