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Lecture 19 Tuesday 3/18/08 Gas Phase Reactions Trends and Optimuns

Lecture 19 Tuesday 3/18/08 Gas Phase Reactions Trends and Optimuns. User Friendly Equations Relate T and X or F i. User Friendly Equations Relate T and X or F i. Heat Exchange. Elementary liquid phase reaction carried out in a PFR

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Lecture 19 Tuesday 3/18/08 Gas Phase Reactions Trends and Optimuns

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  1. Lecture 19 Tuesday 3/18/08Gas Phase ReactionsTrends and Optimuns

  2. User Friendly Equations Relate T and X or Fi

  3. User Friendly Equations Relate T and X or Fi

  4. Heat Exchange Elementary liquid phase reaction carried out in a PFR The feed consists of both inerts I and Species A with the ratio of inerts to the species A being 2 to 1.

  5. Heat Exchange Elementary gas phase reaction carried out in a PBR The feed consists of both inerts I and Species A with the ratio of inerts to the species A being 2 to 1. (a) Adiabatic. Plot X, Xe, T and the rate of disappearance as a function of V up to V=40 dm3. (b)Constant Ta. Plot X, Xe, T, Ta and Rate of disappearance of A when there is a heat loss to the coolant and the coolant temperature is constant at 300 K for V = 40 dm3. How do these curves differ from the adiabatic case? Variable Ta Co-Current. Plot X, Xe, T, Ta and Rate of disappearance of A when there is a heat loss to the coolant and the coolant temperature varies along the length of the reactor for V = 40 dm3. The coolant enters at 300 K. How do these curves differ from those in the adiabatic case and part (a) and (b)? (d) Variable Ta Counter Current. Plot X, Xe, T, Ta and Rate of disappearance of A when there is a heat loss to the coolant and the coolant temperature varies along the length of the reactor for V = 20 dm3. The coolant enters at 300 K. How do these curves differ from those in the adiabatic case and part (a) and (b)?

  6. Mole Balance (1) Rate Law (2) (3) (4)

  7. Stoichiometry (5) (6) Parameters (7) – (15)

  8. Energy Balance Adiabatic and CP = 0 (16A) Additional Parameters (17A)&(17B) Heat Exchange (16B)

  9. (16B) A. Constant Ta (17B) Ta = 300 Additional Parameters (18B – (20B): Ta, , Ua, B. Variable Ta Co-Current (17C) C. Variable Ta Counter Current (18C) Guess Ta at V = 0 to match Ta = Tao at exit, i.e., V = Vf

  10. Adiabatic Exothermic Endothermic

  11. Heat Exchange Exothermic Endothermic

  12. Gas phase heat effects Example: PBR A ↔ B • Mole balance: • Rates: • Stoich (gas):

  13. Exothermic Case: Endothermic Case: ~1 kC Xe kC Xe T T T T 4) Heat effects 5) Parameters…. - for adiabatic: Ua = 0 - constant Ta: - co-current: equations as is - counter-current: Co-current, (Ta-T) for counter-current

  14. exothermic endothermic X X Adiabatic: Adiabatic T and Xe X T T T0 T0 As T0 decreases the conversion X will increase, however the reaction will progress slower to equilibrium conversion and may not make it in the volume of reactor that you have. Therefore, for exothermic reactions there is an optimum inlet temperature, where X reaches Xeq right at the end of V. However, for endothermic reactions there is no temperature maximum and the X will continue to increase as T increases. As inert flow increases the conversion will increase. However as inerts increase, reactant concentration decreases, slowing down the reaction. Therefore there is an optimal inert flow rate to maximize X. T V1 V2 X T X T optimum T0

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