Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The effect of fluidizing gas relative humidity RH, and the role of electrostatics, on bed characteristics of cracking catalyst were investigated at velocities up to 650 mm/s.;The minimum bubbling velocity U{dollar}\sb{lcub}\rm mb{rcub}{dollar} rose with RH (1{dollar}-{dollar} to 95+%) in a 0.190 m ID plastic column, while the bed density {dollar}\rho\sb{lcub}\rm bed{rcub}{dollar} curve fell for velocities up to 100 mm/s and remained the same for velocities above. The minimum fluidization velocity U{dollar}\sb{lcub}\rm mf{rcub}{dollar} did not change with RH. Using a method developed here, bed voltage in a 0.123 m ID plastic column was found to generally decrease with increasing RH or ammonia addition; both are known to decrease electrostatics. Finally, in a 0.209 m ID metal column, the {dollar}\rho\sb{lcub}\rm bed{rcub}{dollar} curve and U{dollar}\sb{lcub}\rm mf{rcub}{dollar} fell with rising temperature (20 to 200{dollar}\sp\circ{dollar}C), another means, cited in the literature, for decreasing electrostatics.;Although any modifications with RH and temperature in U{dollar}\sb{lcub}\rm mf{rcub}{dollar}, at which velocity the bed voltage for all RH's was nil, could be explained by changes in the gas and particle physical properties, this was not possible for U{dollar}\sb{lcub}\rm mb{rcub}{dollar} and the {dollar}\rho\sb{lcub}\rm bed{rcub}{dollar} curve. Nor could an increase in particle cohesivity with RH be demonstrated using the Hausner Ratio test. A decrease in electrostatic charging however, effected by high relative humidity (60+ %), increased temperature (150+ {dollar}\sp\circ{dollar}C) or ammonia (50+ ppm), accompanied these changes in bed characteristics and is therefore proposed as being responsible for them; this decrease in charging resulted in decreased interparticle forces, allowing greater bed expansion. Thus, in order to reduce scatter in data and to obtain bed characteristics in cold units that are representative of high temperature systems, reduction of electrostatics must be considered.;The bed deaeration characteristics, by contrast, were not found to be a function of RH for velocities above 20 mm/s. They depended strongly, though, on which deaeration procedure was employed, certain procedures from the literature resulting in deaeration parameters that were inconsistent with bed parameters under fluidization. A new, valid, procedure was proposed, in which the bed was maintained at its pressure of previous fluidization; the deaeration parameters so obtained were then consistent.



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