Fluidization Behaviors for Coating Cohesive Particles

2008

Ind. Eng. Chem. Res.

The fluidization behaviors of binary mixtures of biomass and quartz sand were investigated in an acoustic bubbling fluidized bed. Two kinds of biomass particles, sawdust and wheat stalk, were employed in this test. The experiments indicated that the addition of quartz sand can improve the fluidization quality of biomass. The minimum fluidization velocity of the mixtures increased with increasing biomass content in the mixtures. A new correlation was developed for predicting the minimum fluidization velocity of different binary mixtures. The minimum fluidization velocity decreased with increasing sound pressure level and had a minimum value over the sound frequency range of 100−200 Hz. Such an acoustic fluidized bed operated in a stable or unstable fluidization regime depending on the operating conditions. According to the slope of a plot of standard deviations, unstable fluidization can be expected if the slope is greater than 50, and stable fluidization can be expected if the value is less than or equal to 50.

Section: Resultsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Fluidization Characteristics of Binary Mixtures of Biomass and Quartz Sand in an Acoustic Fluidized Bed

Chen

2008

Ind. Eng. Chem. Res.

“…It has been demonstrated [1,2] that ultrafine particle fluidization is a promising technology for a number of applications of ultrafine particles. Up to now, ultrafine particles have been fluidized, forming agglomerates at the superficial gas velocity, exceeding the minimum fluidization velocity of primary particles.…”

Section: Introductionmentioning

confidence: 99%

Fluidization Characteristics of SiO₂ Nanoparticles in an Acoustic Fluidized

Wang

et al. 2006

Chem Eng & Technol

Self Cite

Under the action of an acoustic field, the fluidization behavior of 5-10 nm SiO 2 nanoparticles, with and without surface modification, was investigated. In a packed bed, the sound wave energy has a significant influence on the compact ratio of the bed. Experimental results indicated that the bed of nanoparticle agglomerates can be fluidized smoothly with the assistance of an acoustic field, and the minimum fluidization velocity is initially reduced dramatically with increasing sound frequency and then rises with increasing sound frequency. Under the same experimental conditions, the minimum fluidization velocity of 5-10 nm SiO 2 nanoparticles is greater than that of 5-10 nm SiO 2 nanoparticles with surface modification. The collapse of the bed demonstrates that SiO 2 nanoparticles, surface modified using organic compound, have longer minimum collapse times than SiO 2 nanoparticles.

“…As the superficial gas velocity u is increased from 0.0237±0.0775 m/s, stable channels are formed in the static bed which is charaterized by a low pressure drop 1) . Because of channeling and cracking, the fluidization behaviors of the bed are very unstable, indicating that no reproducible results are obtained by repetition of the experiment [9].…”

Section: Fluidization Behaviors Of 30 Nm Tio 2 Particlesmentioning

confidence: 97%

Fluidization of Ultrafine Particles in a Bubbling Fluidized Bed with Sound Assistance

Wang

et al. 2005

Chem. Eng. Technol.

Self Cite

CommunicationsHowever, the bubbling up vapor flows just through the downcomer bottom-orifices. The vapor occupies the part the of orifice area, so the orifice area for liquid descending is reduced and the downcomer liquid height increases which causes a premature downcomer flood as well. Moreover, the orifice area for liquid descending will be reduced further because bridging occurs, accompanied by vapor bubbling, with the area ratio of bridging being 0.4±1.8 of the area ratio of vapor bubbling. Therefore, the bubbling vapor rate and also the ratio of bridging are restricted for the sealed hangingdowncomer. ConclusionsThere are three states of (liquid descending, bridging, and vapor bubbling) at hanging downcomer bottom-orifices. Momentary variations in P i cause the occurrence of the three states. The three states are affected by superficial F-factor and liquid rate. The time and area ratios of bridging and vapor bubbling increase with increasing F-factor, and decrease with increasing liquid rate. Bridging really exists and is not negligible. The ratio of bridging is 0.4±1.8 of the ratio of vapor bubbling. Moreover, due to bridging, the bubbling vapor rate and also the ratio of bridging is restricted for the sealed hanging-downcomer. AcknowledgmentsThe authors thank the staff at the Institute of Chemical Engineering Design and Research in Zhejiang University of Technology (China) for assistance in the experimental work. Symbols usedarea of downcomer bottom-orifices C 0G [±] vapor flow coefficient ______________________ Fluidization of Ultrafine Particles in a Bubbling Fluidized Bed with Sound AssistanceBy Qingjie Guo*, Minghua Wang, Yan Li, and Chaohe YangThe fluidization behaviors of various nanometer and micron particles, including SiO 2 , TiO 2 , and cornstarch particles with primary particle sizes of 5 nm±10.69 lm, were investigated in a fluidized bed with inside diameter 56 mm under different sound pressure levels and sound frequencies. It has been demonstrated that the relatively uniform ultrafine particle agglomerates reach homogeneous fluidization with sound assistance at low sound frequencies due to the sound Communications field disrupting large size agglomerates. Furthermore, slugging and channeling of the bed was eliminated, accompanied by negligible elutriation. For each of the nanometer and micron particles examined, the minimum fluidization velocity decreased with increasing sound frequency, and then increased with sound frequency at a given sound pressure level. There is a minimum value in the curve of minimum fluidization velocity versus sound frequency, the critical sound frequency, at which the bed fluidized smoothly. Varying the sound pressure level can significantly improve the fluidization quality of the bed.