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Lecture 2 Kjemisk reaksjonsteknikk Chemical Reaction Engineering

Lecture 2 Kjemisk reaksjonsteknikk Chemical Reaction Engineering. Review of Lecture 1 Definition of Conversion, X Design Equations in Terms of X Size CSTRs and PFRs given –r A = f(X) Conversion for Reactors in Series. General Mole Balance. General Mole Balance on System Volume V.

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Lecture 2 Kjemisk reaksjonsteknikk Chemical Reaction Engineering

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  1. Lecture 2 Kjemisk reaksjonsteknikk Chemical Reaction Engineering • Review of Lecture 1 • Definition of Conversion, X • Design Equations in Terms of X • Size CSTRs and PFRs given –rA= f(X) • Conversion for Reactors in Series

  2. General Mole Balance General Mole Balance on System Volume V System Volume, V FA0 FA GA 2

  3. Reactor Mole Balance Summary NA FA V t Batch CSTR PFR 3

  4. Consider the generic reaction 4

  5. Batch 5

  6. Reactor Mole Balances in terms of conversion X Batch t X CSTR W PFR PBR 6

  7. Batch reactor

  8. Continuous stirred tank reactor (CSTR)

  9. Continuous stirred tank reactor (CSTR)

  10. Plug flow reactor (PFR)

  11. Plug flow reactor (PFR)

  12. Levenspiel Plots Reactor Sizing Given –rA as a function of conversion, -rA= f(X), one can size any type of reactor. We do this by constructing a Levenspiel plot. Here we plot either (FA0/-rA) or (1/-rA) as a function of X. For (FA0/-rA) vs. X, the volume of a CSTR and the volume of a PFR can be represented as the shaded areas in the Levenspiel Plots shown as: 12

  13. Levenspiel Plots 13

  14. Numerical Evaluations of Integrals The integral to calculate the PFR volume can be evaluated using method as Simpson’s One-Third Rule: (See Appendix A.4) Other numerical methods are: Trapezoidal Rule (uses two data points) Simpson’s Three-Eight’s Rule (uses four data points) Five-Point Quadrature Formula 14

  15. Reactors in Series Given: rA as a function of conversion, one can also design any sequence of reactors: Only valid if there are no side streams. Molecule Flow rate of species A at point i: 15

  16. Reactors in Series 16

  17. Reactors in Series Reactor 1: V1 17

  18. Reactors in Series Reactor 2: V2 18

  19. Reactors in Series Reactor 3: V3 19

  20. Reactors in Series 20

  21. Important Definitions Space time is the time necessary to process one reactor volume of fluid at entrance conditions. Space velocity: SV = v0/V (s-1)=1/  Space velocity is normally given at the standard conditions (STP). Liquid hourly space velocity (LHSV= v0,liquid/V) Gas hourly space velocity (GHSV) = v0,gas/V S-1

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