Computational fluid dynamics (CFD) modeling for biomass and wate to energy production

Abstract

Solid fuel particles are usually modeled as point particles in simulations using the Eulerian-Lagrangian approach. The particles and gas phases can be resolved on vastly different scales. Since the particles are treated as zero dimensional in the gas phase’s modeling description, the details of the flow near the particle surface are therefore not fully resolved. When the particles are larger than the computational cell size, the coupling between the two phases is no longer straightforward and requires special attention. In this thesis, the coupling between the Eulerian gas phase model and the Lagrangian particle model is studied comprehensively under the scenario of combustion of solid fuel particles. The state-of-the-art Eulerian-Lagrangian modeling for biomass and waste fixed combustion is introduced. The detailed modeling framework and the coupling algorithms are overviewed. The advantages and disadvantages of the commonly used and newly proposed coupling strategies are compared and summarized. In order to improve the model’s accuracy and the computational efficiency, new coupling strategies are also proposed, and their performances are as expected in the applications. Based on the modeling description, the numerical tools are developed using the open-source software OpenFOAM. The new CFD models are validated through both the simulation of the single particle reactor and the lab-scale fixed bed combustor. The coupling effects are discussed in detail. The interplay between the heat transfer mechanisms inside the fixed bed and the coupling scheme is thoroughly analyzed.