Improved models for predicting bubble velocity, bubble frequency and bed expansion in a bubbling fluidized bed

• Published in: Chemical engineering research & design 2019-01, Vol.141, p.361-371
• Main Authors: Agu, Cornelius Emeka, Tokheim, Lars-Andre, Eikeland, Marianne, Moldestad, Britt M.E.
• Format: Article
• Language: English
• Subjects: Bed expansion; Bed expansions; Bubble frequency; Bubble velocity; Bubbles; Bubbling; Correlation analysis; Fluidized bed; Fluidized bed reactors; Fluidized beds; Mathematical models; Model accuracy; Predictions; Slug rise velocity; Velocity; Void fraction
• ISSN: 0263-8762; 1744-3563
• DOI: 10.1016/j.cherd.2018.11.002

[Display omitted] •Models for bubble velocity, bubble frequency and overall bed expansion ratio were proposed.•The proposed bubble velocity model gives better prediction for Geldart B and D solids.•Bed expansion ratio decreases with increasing bed diameter and particle size.•Bubble frequency attains a local maximum value at the onset of slugging regime. An efficient design and operational control of a fluidized bed reactor relies on accurate prediction of bubble properties. This paper employs measurement of bed void fraction in determining the bubble velocity in a given bed. An analytical model is developed for bubble rise velocity, which shows that the rise velocity of a single bubble is proportional to the rate of change of the bubble-projected area. Based on the model for bubble rise velocity, a correlation for bubble velocity is obtained as given by ub=φN(U0−Umf)+12.51φD(U0−Umf)0.362db0.52. Bubble frequency is also modelled and presented as fb=(0.52(dbD)1.48+mubndb)−1, and bed expansion due to bubble flow in a larger particle bed (Ar≥400) is modelled by Δe=1−0.0873U0−Umf−0.362U0D0.661−γU0Umfβ−10.66−1−1. The three models have been validated against experimental data and the results show that the bubble velocity model has a better prediction accuracy than the existing models for Geldart B and D particles with prediction errors of 15.5% and 12.0%, respectively. The results also show that the proposed bed expansion model predicts better than the existing models in the literature.