CFD modeling of biomass combustion and gasification in fluidized bed reactors using a distribution kernel method

Miao Yang,Jingyuan Zhang,Shenghui Zhong,Tian Li,Terese Løvås,Hesammedin Fatehi,Xue-Song Bai

doi:10.1016/j.combustflame.2021.111744

Miao Yang, Jingyuan Zhang + Show 5 more

Open Access

https://doi.org/10.1016/j.combustflame.2021.111744

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Abstract

A three-dimensional reactive multi-phase particle-in-cell (MP-PIC) model is employed to investigate biomass combustion and gasification in fluidized bed furnaces. The MP-PIC model considered here is based on a coarse grain method (CGM) which clusters fuel and sand particles into parcels. CGM is computationally efficient, however, it can cause numerical instability if the clustered parcels are passing through small computational cells, resulting in over-loading of solid particles in the cells. To overcome this problem, in this study, a distribution kernel method (DKM) is proposed and implemented in an open-source CFD code, OpenFOAM. In DKM, a redistribution procedure is employed to spread the solid volume and source terms of the particles in the parcel to the domain in which the particles are clustered. The numerical stiffness problem caused by the CGM clustering can be remedied by this method. Validation of the model was performed using data from different lab-scale reactors. The model was shown to be able to capture the transient heat transfer process in a lab-scale bubbling fluidized bed reactor under varying fluidization velocities and loads of sand. Then, the model was used to study the combustion/gasification process in a bubbling fluidized bed reactor under varying ambient temperatures, equivalent air ratios, and steam-to-biomass ratios. The performance of DKM was shown to improve the accuracy and the robustness of the model.

Highlights

Biomass is considered a promising energy source because of its worldwide availability, ease of access, and renewable generation within a short period [1,2]
A three-dimensional multi-phase particle-in-cell (MP-PIC) model was developed for numerical simulation of heat transfer and biomass combustion/gasification process in fluidized bed reactors
The conventional MP-PIC method is based on the particle centriod method (PCM) and coarse grain method (CGM), which is computationally efficient but suffers from local over-loading if the computational fluid dynamic (CFD) cell is fine or if locally small-size cells are used

Summary

Introduction

Biomass is considered a promising energy source because of its worldwide availability, ease of access, and renewable generation within a short period [1,2]. Biomass can be used in different applications, such as heat or power generation, chemical synthesis, and production of nanomaterials. Biomass can be transformed into liquid, gaseous, and solid fuels through different chemical, physical, and biological conversion processes [3]. As an alternative to fossil fuel for power generation and heating, biomass energy can contribute significantly towards the objectives of the UN’s Paris Agreement in reducing greenhouse gas emissions. Multi-scale and multi-physicochemical processes, such as complex hydrodynamics of dense gas-solid flow, particle collision, heat and mass transfer, radiation, homogeneous and heterogeneous chemical reactions, and turbulent combustion, occur simultaneously in a FB furnace [5]. The computational fluid dynamic (CFD) approach is considered as an efficient method for investigation of the complex gas-solid two-phase flow and combustion process [8]

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