Chapter 2: Conversion and Reactor Sizing

Example - Use Levenspiel plots to calculate conversion from known reactor volumes

Pure A is fed at a volumetric flow rate of 1000 dm3 /h and at a concentration of 0.005 mol/dm3 to an existing CSTR, which is connected in series to an existing tubular reactor.

Diagram showing a Continuous Stirred-Tank Reactor (CSTR) with a volume of 1200 dm³ connected in series to a tubular reactor with a volume of 600 dm³. The inlet flow has a concentration C_A0 of 0.005 mol/dm³ and a volumetric flow rate v_0 of 1000 dm³/s.
If the volume of the CSTR is 1200 dm3 and the tubular reactor volume is 600 dm3 , what are the intermediate and final conversions that can be achieved with the existing system? The reciprocal rate is plotted in the figure below as a function of conversion for the conditions at which the reaction is to be carried out.

Graph showing the relationship between conversion (X) and reciprocal rate, F_A0 over -r_A, in units of dm³, for the reaction A to product. The x-axis represents conversion, ranging from 0 to 0.8, and the y-axis represents the reciprocal rate, ranging from 1000 to 4000 dm³. The curve slopes upward, indicating an increase in volume requirement with higher conversion.





Solution

By trial and error, we find that a conversion of 0.6 gives the appropriate CSTR volume of 1200 dm3

Graph showing the relationship between conversion (X) and reciprocal rate, F_A0 over -r_A, in dm³, for the reaction A to product. The x-axis represents conversion from 0 to 0.8, and the y-axis shows reciprocal rate from 1000 to 4000 dm³. A shaded region under the curve represents the volume V = 1200 dm³, indicating an intermediate conversion of X = 0.6.

Therefore, the intermediate conversion is X = 0.6






Similarly for the PFR, through trial and error, we find that a conversion of 0.8 gives the appropriate PFR volume of 600 dm3

Graph showing the relationship between conversion (X) and reciprocal rate, F_A0 over -r_A, in dm³, for the reaction A to product. The x-axis represents conversion from 0 to 0.8, and the y-axis shows reciprocal rate from 1000 to 4000 dm³. A shaded region under the curve represents the volume V = 600 dm³, indicating a final conversion of X = 0.8 for the PFR.

Therefore, the final conversion is X = 0.8




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