Abstract
Micro-fluidized bed has aroused much attention due to its low-cost, intensified-process and fast-screening properties. In this paper, a micro-fluidized bed (15 × 15 mm in cross-section) was designed and fabricated with the use of the stereolithography printing technique, for the investigation of bubbles’ hydrodynamics and comparison of the solids (3D-printed particles VS fungal pellets) fluidization characteristics. In a liquid–gas system, bubble flow regime started from mono-dispersed homogeneous regime, followed by poly-dispersed homogeneous regime, transition bubble regime and heterogeneous bubble regime with increasing gas flowrates from 3.7 mL/min to 32.7 mL/min. The impacts from operating parameters such as gas flowrate, superficial liquid velocity and gas sparger size on bubble size, velocity and volume fraction have been summarized. In liquid–solid fluidization, different solid fluidization regimes for both particles bed and pellets bed were identified. From the bed expansion results, much higher Umf of 7.8 mm/s from pellets fluidization was observed compared that of 2.3 mm/s in particles fluidization, because the hyphal structures of fungal pellets increased surface friction but also tended to agglomerate. The similar R–Z exponent n (5.7 and 5.5 for pellets and particles, respectively) between pellets and particles was explained by the same solid diameter, but much higher Ut of 436 µm/s in particles bed than that of 196 µm/s in pellets bed is a consequence of the higher density of solid particles. This paper gives insights on the development of MFB and its potential in solid processing.
Highlights
Fluidized beds use the liquid and/or gas flows instead of moving parts to improve mixing, exhibiting the advantages of sufficient multiphase contact but less energy consumption and mechanical stress [1,2,3]
A fluidized bed reaction analyzer with a 2 cm inner diameter (ID) developed by Xu and his colleagues for their thermochemical studies was regarded as micro-scale by them due to the distinguished reactor flow characteristics [22,23]
The representative images showing the gradual transitions of bubble flow regimes are presented in Figure 4 for the 100 μm gas sparger system with no liquid flow
Summary
Fluidized beds use the liquid and/or gas flows instead of moving parts to improve mixing, exhibiting the advantages of sufficient multiphase contact but less energy consumption and mechanical stress [1,2,3]. MFB has been applied to different areas such as solid processing [6,7], chemical conversions [8,9,10], CO2 capture [11], wastewater treatment [12,13], bioproduction [14,15], etc. With more novel designs and applications of MFB being reported, the hydraulic diameter of the bed column used as the defining principle is becoming broader and fuzzier. A fluidized bed reaction analyzer with a 2 cm ID developed by Xu and his colleagues for their thermochemical studies was regarded as micro-scale by them due to the distinguished reactor flow characteristics [22,23]. Gao et al [24] called a fluidized bed reactor with 7.5 cm ID as MFB when using it for pyrolysis of three Iranian waste oils.
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