In Problem 20.41, the reactor is now a fluidized bed where Dowtherm circulates through tubes in the reactor with the reaction in the shell. The Dowtherm then flows to a heat exchanger in which boiler feed water is vaporized on the shell side to high-pressure steam at 254°C. This removes the heat absorbed by the Dowtherm stream in the reactor so the Dowtherm can be recirculated to the reactor. So, the Dowtherm is in a closed loop. The resistance in the steam boiler is all on the Dowtherm side.

In the base case for the reactor, the resistance on the reactor side is four times that on the Dowtherm side. The desired increase in production can be accomplished by adding 25% more catalyst to the bed and operating at the same temperature, which is what is assumed to happen in this problem.

Write the six equations needed to model the performance of this system.

How many unknowns are there? Solve for all the unknowns.

If the temperature of the reactor is to be maintained at 510°C, determine the amount of process scale-up and all other unknowns for the following cases:

10% increase in Dowtherm flowrate

25% increase in Dowtherm flowrate

50% increase in Dowtherm flowrate

Plot the results from Parts (b) and (c) in the form of a performance curve in which the amount of process scale-up (Q₂/Q₁ on the y-axis) is plotted as a function of the increase in Dowtherm flowrate.

Problem 20.41

A reaction occurs in an S-T reactor. One type of S-T reactor is essentially a heat exchanger with catalyst packed in the tubes.

For an exothermic reaction, heat is removed by circulating a heat transfer fluid through the shell. In this situation, the reaction occurs isothermally at 510°C. The Dowtherm™ always enters the shell at 350°C. In the design (base) case, it exits at 400°C. In the base case, the heat transfer resistance on the reactor side is equal to that on the Dowtherm side. If it is required to increase throughput in the reactor by 25%, what is the required Dowtherm flowrate and the new Dowtherm exit temperature? You should assume that the reaction temperature remains at 510°C.