Minimum Fluidization Velocity and Gas Holdup in Fluidized Beds With Side Port Air Injection

Abstract

Fluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 cm and 15.2 cm diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum fluidization velocity is determined through pressure drop measurements. Time-averaged local and global gas holdup are recorded using X-ray computed tomography imaging. Results show that by varying the side port air flow rate as a percentage of the minimum fluidization flow rate, partial and complete fluidization is observed in both fluidized beds. Local gas holdup trends are also similar in both fluidized beds. These results will be used in future studies to validate computational fluid dynamics models of fluidized beds.Keywords fluidized bed, gasification, minimum fluidization velocity, particle injection, x-ray computed tomography ABSTRACTFluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. Knowing how the fluidized bed hydrodynamics vary as reactor dimensions are scaled up is vital for improving reactor efficiency. This study utilizes 10.2 em and 15.2 em diameter fluidized beds with added side port air injection to investigate column diameter effects on fluidized bed hydrodynamics. Both inert (glass beads) and biomass (ground walnut shell and ground corncob) bed materials are used and the hydrodynamic differences with side port air injection are recorded. Minimum fluidization velocity is determined through pressure drop measurements. Timeaveraged local and global gas holdup are recorded using X-ray computed tomography imaging. Results show that by varying the side port air flow rate as a percentage of the minimum fluidization flow rate, partial and complete fluidization is observed in both fluidized beds. Local gas holdup trends are also similar in both fluidized beds. These results will be used in future studies to validate computational fluid dynamics models of fluidized beds.

Approximating a Three-Dimensional Fluidized Bed With Two-Dimensional Simulations

“…2, comparing the experimental measurements to that predicted using MFIX. Once the bed is fluidized at~"/= 21.7 cm/s [10], the measured pressure drop is approxi- …”

“…Thus, investigations arc now pursued to determine the fluidization hydrodynamics of gas-solid flows for a geometry with a single side port. Franka et al [10] have experimentally studied a I 0.2 em diameter reactor using glass beads and various materials to represent biomass. The efforts of this paper are to begin with a study using glass beads as the medium and validate new CFD predictions with the experiments.…”

“…Heindel et al [7] have reviewed the state-of-the-art methods for noninvasive monitoring techniques for internal flows. Their recent work [9,10] used X-ray computed tomography (CT) and radiography to analyze fluidized bed media such as melamine, walnut and corncob. The choice of bed media was prompted by using particle sizes and densities according to Geldart type B particles, a classification identifying particles that will satisfactorily fluidize [II] .…”

“…Franka ct al. [9,10] found minimum fluidization velocities using pressure drop measuremente; and provided time-averaged local and global gas holdup based on X-ray CT imaging. The quantitative data obtained has been beneficial with validating computational models used in numerical simulations by Deza ct al.…”

“…The experiments were accomplished using X-ray CT and radiography [10]. The simulations will be performed using the software Multiphase Flow with Interphase eXchanges (MFIX) [14].…”