Attrition in a fluidized bed

Author

Andrew Joseph Welter, New Jersey Institute of Technology

Document Type

Thesis

Date of Award

6-30-1961

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering

First Advisor

Peter L. Silveston

Second Advisor

Jerome J. Salamone

Third Advisor

George C. Keeffe

Abstract

The object of this thesis is to study attrition in a fluidized bed in an attempt to find a reliable method for predicting attrition rate when fluid flow rates and particle sizes are varied.

The system studied consisted of air as the fluidizing median with bauxite and fuller's earth as the solids in suspension. Fluid flow rates were changed while all other variables were held constant. Systems with both large and small particles were studied for each material.

It was found that the attrition rate of the material when the bed is maintained at a constant mass flow rate is greatest at the beginning of the fluidization operation and that it progressively decreases with time until a point is reached at which very little particle size reduction takes place with further operation. Attrition appears to be a logarithmic function of the elapsed time according to the equation:

log_e(1-(D₂/D₁)³) = A log_e T

Two distinct attrition stages are evident. The initial stage has a high attrition rate and exhibits a large value for constant A. The second stage in which very little attrition coccurs has an A which is quite low.

The instantaneous attrition rate is given by the relation:

d(1-(D₂/D₁)³)/dT = A(1-(D₂/D₁)³)/T

Here it is shown that this rate is proportional to the size reduction which has already taken place and inversely proportional to the elapsed time of fluidization of the material in the bed. The term (1-D₂/D₁)³/T is the average attrition rate over the period T. This average rate appears to be a logarithmic function of the mass flow rate G/G_mf. The constant A is directly proportional to a pseudo momentum term (dbD³G/G_mf).

Although the proper data for a general correlation was not obtained in this study, the correlations developed indicate that thee is a good chance of finding a general correlation which will permit calculation of attrition rate or for predicting attrition for a given operating time using only the simple parameters of bulk density, average particle size, superficial fluidizing velocity and an unknown physical property or group of properties of the material.

Recommended Citation

Welter, Andrew Joseph, "Attrition in a fluidized bed" (1961). Theses. 3238.
https://digitalcommons.njit.edu/theses/3238