Mean residence time general expression

Table 8.1 summarizes the fundamental design relationships for the various types of ideal reactors in terms of equations for reactor space times and mean residence times. The equations are given in terms of both the general rate expression and nth-order kinetics. 

The mean residence time of a phase, which is most important for the degree of conversion in multiphase reactors, is directly related to one of these parameters, i.e. the phase holdup, but in addition, pressure drop and catalyst wetting are also related to holdup. In general, hold-up is expressed either as fractional bed volume C or as fractional void volume p. 

The extent of axial mixing can be expressed by the distribution in residence times. Small distributions in residence times will lead to a uniform product and is generally considered to be favorable. However, the associated small axial mixing makes it nessecary to assure a very constant feed flow. An important parameter in the analysis of the residence time distribution is the mean residence time 7, which can easily be obtained from... 

For a given raw material, the composition of the reaction effluents is obviously related to the variables of temperature, residence time, pressure, and steam dilution rate. At the industrial level, the individual optimization of these parameters normally leads to contradictory requirements hence the solution adopted is generally the result of a compromise in the choice of furnace design on the one hand, and operating conditions on the other. However, an attempt is made to express the overall influence of these factors on the performance of the reaction section by means of a representative value that can indicate the degree of severity of the treatment. 

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