Reactors
A. The rate of reaction must be established in the laboratory and the residence time or space velocity
will eventually have to be determined in a pilot plant.B. Catalyst particle sizes: 0.10 mm for fluidized beds, 1 mm in slurry beds, and 2-5 mm in fixed beds.C. For homogeneous stirred tank reactions, the agitor power input should be about
0.5-1.5 hp/1000 gal (0.1-0.3 kW/m3), however, if heat is to be transferred,
the agitation should be about three times these amounts.
D. Ideal CSTR behavior is usually reached when the mean residence time is 5-10 times
the length needed to achieve homogeneity. Homogeneity is typically reached with
500-2000 revolutions of a properly designed stirrer.
E. Relatively slow reactions between liquids or slurries are usually conducted most
economically in a battery of 3-5 CSTR's in series.
F. Tubular flow reactors are typically used for high productions rates and when the
residence times are short. Tubular reactors are also a good choice when significant
heat transfer to or from the reactor is necessary.
G. For conversion under 95% of equilibrium, the reaction performance of a 5 stages
CSTR approaches that of a plug flow reactor.
H. Typically the chemical reaction rate will double for a 18 °F (10 °C) increase in
temperature.
I. The reaction rate in a heterogeneous reaction is often controlled more by the rate of
heat or mass transfer than by chemical kinetics.
J. Sometimes, catalysts usefulness is in improving selectivity rather than increasing
the rate of the reaction.
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