Mesoscale-Structure-Dependent EMMS Drag Model for an SCW Fluidized Bed: Formulation of Conservation Equations Based on Structures in Subphases

Abstract

Supercritical water (SCW) fluidized bed reactors release no pollutants in the gasification process of converting biomass into fuel. In this work, a mesoscale-structure-dependent (MSD) energy minimization multiscale system (EMMS) drag model for SCW fluidized beds is proposed. Experimental results and empirical correlations are applied to validate the voidage distribution and bubble hydrodynamics calculated by the MSD-EMMS model. Besides, this study presents a comparison of the properties of computed bubbles between the Gidaspow model, EMMS/bubbling model, and MSD-EMMS model. Bubble properties predicted by the MSD-EMMS model agree better with experimental results and empirical correlations than other drag models. The research work can serve as guidance for the optimization of SCW gasification technology.

3D Simulations of Bubble Hydrodynamics for the SCW Fluidized Bed Using the EMMS Model

“…Because of the huge physical difference between air and SCW, the fluidization behaviors (particle distribution and bubble hydrodynamics) of SCWFBs are inconsistent with those in gas−solid fluidized beds. The EMMS drag model of Wang and Lu 28 takes the influence of voidage distribution in emulsion 13 and drag coefficient of bubbles 14 into account, which makes the EMMS drag model suitable for fluidization in SCWFBs. The summary and key parameters of the EMMS model of Wang and Lu 28 are shown in Table S1 and Table S2 of Supporting Information.…”

“…An EMMS drag model based on mesoscale structures was developed by Wang and Lu. 28 The bubble sizes and velocities of 2D simulation results were validated by experimental results. However, the results of 2D simulations are insufficient for comprehensive understanding of the bubble hydrodynamics in SCWFBs due to the inconsistency between the 2D geometry and experimental bed column.…”

“…In this study, 3D simulations for hydrodynamics and shape properties of bubbles for SCWFBs are carried out using TFM coupled with the EMMS model 28 and the Gidaspow model. The simulated bubble sizes and velocities by the EMMS model are validated by empirical correlation and experimental results.…”

3D Simulations of Voidage Distribution in SCW Fluidized Beds Using the EMMS Model

“…The critical point of water is 22.1 MPa and 374 °C, respectively . Traditional methods, such as charge-coupled device (CCD) cameras, magnetic resonance imaging, and optical probes, fail to measure the fluidization behavior due to supercritical conditions . A concept and a design for SCWFBs were proposed by Matsumura and Minowa .…”

“…The capacitance probe method can cause interference in the flow field. Compared with experimental methods, the numerical simulation method can obtain more detailed and comprehensive two-phase flow characteristics in SCWFB . The drag on a single particle fluidized in SCW through direct numerical simulation (DNS) was studied by Wu et al A new correlation of drag coefficient for Re of 10–200 was proposed.…”