RTD and scaleup problems

RTD data from a small-scale apparatus cannot be used for larger-scale units. Ross86 has shown this for hydrodesulfurization in a trickle-bed reactor wherein the prevailing flow regimes in small- and large-scale reactors may be different. 

Flow maldistribution of the phases can render the evaluation of RTD data very difficult. In some cases, maldistribution may exist in small units but it may not exist in large-scale units (e g., trickle-bed reactors). While in some other cases, such as three-phase fluidized-bed reactors, nonuniform gas distribution in large-scale units may cause undesirable recirculation and dead zones. Uniform gas distribution can usually be achieved in the small-scale fluidized-bed reactor. 

In large-size mechanically-agitated multistage contactors, the speed of the agitator is kept at a relatively low level and horizontal baffles are provided. Here, RTD in the gas and liquid phases may show different behavior compared to a small-scale unit. 

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