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

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 u(b) = phi(N) (U-0 - U-mf) + 12.51(phi D) (U-0 - U-mf)(0.362) d(b)(0.52). Bubble frequency is also modelled and presented as f(b) = (0.52(d(b)/D)(1.48) + mu(b)(u)d(b))(-1), and bed expansion due to bubble flow in a larger particle bed (Ar >= 400) is modelled by Delta e = [1 - 0.0873(U-0 - U-mf)(-0.362) (U-0/D)(0.66) (1 - gamma(U-0/U-mf)(beta-1))(0.66)](-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. (C) 2018 The Author(s). Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.