Stoichiometric Reactor Module

Transcription

1 Reactor Analysis

2 Types of Reactors

3 Stoichiometric Reactor Module

4 Stoichiometric Reactors (1)

5 Stoichiometric Reactors (2)

6 Stoichiometric Reactors (3)

7 Equilibrium Reactors

8 Gibbs Reactor

9 RGibbs Module

10 Equilibrium Reactor

11 REquil Module

12 Equilibrium Reactor Calculations

13 Results of Equilibrium Calculations (1)

14 Results of Equilibrium Calaulations (2)

15 Comments on Equilibrium Reactors

16 Kinetic Reactors

17 RPLUG Module

18 PFTR Reactors (1)

19 PFTR Reactor (2)

20 CSTR Reactors

21 RCSTR Module

22 CSTR (1)

23 CSTR (2)

24 ChemCAD Reactor Simulation

25 ChemCAD Reactors Types of Reactors General Considerations and Phase Key Stoichiometric Reactor Equilibrium Reactor Kinetic Reactor Gibbs Reactor

26 Types of Reactor Stoichiometric Reactor Kinetic Reactor Equilibrium Reactor Gibbs Reactor

27 ChemCAD Reactors General Considerations Heat of reaction calculated or specified Reactor thermal mode: - Adiabatic -Isothermal - Heat Load - Fixed Temp. profile - Utility Stream Phase Consideration

28 Stoichiometric Reactor General One Reaction Only Conversion must be specified Heat of reaction calculated or specified Typical Uses Early of "Budget" process analysis Component switching - Changing properties Complete reactions or known conditions

29 Workshop Reactor1 : Stoichiometric Reactor Benzene + 3 H 2 ---> Cyclohexane Adiabatic Conversion of 1 mole of benzene to cyclohexane using excess of hydrogen Change reactor type to isothermal at 600 F. Note cooling load required Highly exothermic reactions will usually require quenching, cooling or multiple reactors. Cyclohexane is normally produced in multiple reactors with intercooling.

30 Kinetic Reactor Reactor Type CSTR Plug Flow Calc Mode Volume specified Conversion specified Phase Liquid (Default) Vapor Mixed phase, reaction occurs in the liquid phase Mixed phase, reaction occurs in the vapor phase

31 Kinetic Reactor r i = nrx j j /( kj k/( RT) Ej RT) a N + ij* Aj * e * ( Ckj) *(1 j= 1 k= 1 k= 1 n n φ kj* e e * C b kj kj ) β Rate of reaction = (kinetic term) * (driving forces) (resistence terms) r i = Rate of formation for component I, mole/volume-time i = Subscript for component i k = Subscript for reactant k j = Subscript for reaction j N i = Stoichiometric coefficient for component i A = Frequency factor (Arrhenius parameter) E = Activation energy R = Universal gas constant T = Absolute temperature C k = Concentration of reactant k, mole/volume or the partial pressure of reactant k a kj = Exponential factor for reactant k in reaction j n = Number of reactants nrx = Number of reaction Φ kj = Absorption frequency factor for component k k = Absorption energy factor for component k β i = Power factor for absorption sites term for reaction, j = Product of all reaction concentration terms Σ = Sum of absorption factor for each reactant b kj = Exponential factor for reactant k in reaction j

32 Workshop Reactor2: Kinetic Reactor Adiabatic kinetic reaction of a lbmole each of acetic acid and ethanol, fed at it's bubble point to a 1 liter reactor. Kinetics of the forward and reverse reactions are considered. Mixed phase, reaction occurs in the liquid phase. Acetic Acid + Ethanol <==> Ethyl Acetate + H 2 O r 1 =K 1 [AA][EtOH]=k 10 e -E1/RT [AA][EtOH] r 2 =K 2 [EA][H 2 O]=k 20 e -E2/RT [EA][H 2 O] Concentration flag : moles/volume Time Unit : Min. k 10 =29000, E1=7150 Volume Unit : Liters k 20 =7130, E2=7150 Activation Energy : Cal Simulate this reactor This reaction is endothermic. Molar Flow Unit : Gm-mole Change reactor type to isothermal at 100 C. The conversion decreases. Why?

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34 Equilibrium Reactor ln( K eq ) = ln ( P ( R ) ) 1 1 x1 y1 ( P ( R 2 2 ) ) x 2 y ( P ( R i i ) ) xi yi = A + B / T Where, P i R i X i Y i A,B T : Parial pressure or mole fraction of product component i : Parial pressure or mole fraction of reactant component i : Power coefficient of the product component i generally equal to stoichiometric coefficient : Power coefficient of the reactant component i generally equal to stoichiometric coefficient : Arrhenius coefficients : temperature, absolute degrees

35 Equilibrium Reactor Equilibrium Reactor Type General equilibrium reactor Shift reactor Methanation reactor Specify calculation mode Conversion specified Approach temperature. ( T = T reactor + DT) Approach fractional conversion (eq).

36 Workshop Reactor3: Equilibrium Reactor 1/2 N 2 + 3/2 H 2 ---> NH 3 Fractional conversion of 1 mole of N 2 to ammonia using excess of H 2 Adiabatic, P=200 atm, T=1450 R, H 2 /N 2 = 3:1 ( mole ratio) in feed. Equilibrium data developed from figure, next page The equation: from figure A= B = Simulate this reactor ln (Keq) = A + B/T Keq = R Keq = R

37 Equilibrium Constant Estimation

38 Workshop Reactor4: Equilibrium Reactor Change reactor type to isotherml at 1534 R and approach fraction of 1.0. rerun ( at 200 atm) and check the Keq against the attached data. Conclusion 1. Keq and its correction constants(a and B) are dependent on the stoichiometric equation. The stoichiometric coefficients used in the data input must be consistent with those used to derive the A and B coefficients of the Keq equation. 2. ChemCAD uses the mole fractions or partial pressures to define Keq. The thermodynamically correct form for Keq uses activities, which are unimportant for liquids. For gases it means that the Keq equation must be known or correlated at the reactor pressure.

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40 GIBBS Reactor Based on free energy minimization Similar form to equilibrium reactor Species derived from component list; inerts may be defined User components need thermo, atom data Approach temperature allowed

41 Workshop Reactor4 : GIBBS Reactor Adiabatic equilibrium conversion of 1 mole of nitrogen to ammonia using an excess of hydrogen. Conversion is based on free energy minimization. P=200 atm Simulate this reactor Change reactor type to isothermal at 1534 R. Rerun and check results against equilibrium reactor results. The Gibbs reactor is particularly useful where no experimental exists on equilibrium or kinetics. data

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