Multiple Reactors

Question 1

Draw the 1/r_A against conversion graph and mark how the volume would be distributed for 3 PFRs in series.

Answer 1

Question 2

Draw the 1/r_A against conversion graph for multiple CSTRs in serires.

Answer 2

Question 3

How do we find the minimum size of two CSTRs in series?

Answer 3

Find the intermediate conversion values by maximising the area of the rectangle KLMN shown in the curve of 1/r_A against conversion. This is achieved when the diagonal of the rectangle is equal to the tangent of the curve.

Question 4

State the equation for the intermediate concentration between two CSTRs of minimised volume.

Answer 4

Where f(X) is given by the X-containing term from the reciprocal of the rate equation (the equation of the line).

Question 5

How does the order of two CSTRs change depending on the order of the reaction?

Answer 5

1st order: equal size reactors are best

positive order: the smaller reactor should come first

negative order: the larger reactor should come first

Question 6

Is the minimum-size or equal size system better when considering 2 CSTRs in series?

Answer 6

The advantages of the minimum-size system rarely outweigh the equal-size system when considering the economics of the process.

Question 7

What is an alternative to the Simpson’s rule for solving a PFR integral?

Answer 7

Treating the integral as multiple CSTRs (2 is usually enough).

Question 8

Why are reactors used in parallel and how does the design equation change?

Answer 8

They are used in parallel to scale up the reaction, the equation does not change apart from the throughput is multiplied by the number of reactors.