Diseño de Procesos Clase 7

JORGE LUIS PIÑERES

PROGRAMA DE INGENIERIA QUIMICA

UNIVERSIDAD DEL ATLANTICO

BIENVENIDOS A DISEÑO Y ANALISIS DE PROCESOS

Diseño del reactor: Conversión del producto deseado (selectividad) Tipo de reacción: Exotérmica o Endotérmica Selección de la temperatura apropiada Selección y diseño apropiado del reactor o reactores (serie – paralelo)

SINTESIS DE DISEÑO DE REACTORES

Modelos de Reactores: Generalmente para Procesos en Continuo Múltiples fases: vapor, liquido, solidos, con catalizadores solidos Diversas geometrías: Tanque agitado, Reactor tubular, Boquillas, Flujo en espiral, entre otros Transferencia de masa y calor Flujo viscoso, flujo turbulento, conducción, radiación, difusión, dispersión.


Diversas simulaciones proveen cuatro clases de modelos de reactores: • Modelo estequiometrico que permite las especificaciones de

conversión • Modelo de múltiples fases (vapor, liquido, solido) en equilibrio

químico, donde el equilibrio para reacciones individuales pueda ser especificada


Diversas simulaciones proveen cuatro clases de modelos de reactores: • Modelo cinético para un CSTR continuo, que se asume

perfectamente mezclado en fase homogénea (liquido o vapor) • Modelo cinético para un PFR en fase homogénea (liquido o

vapor) asumiendo que no hay retromezclado Estos modelos ideales son usado en las primeras etapas del proceso (requerimientos de las corrientes y de calor)


El modelo del reactor ideal es reemplazado por el modelo real que se ajusta al proceso. Datos cinéticos del laboratorio o en planta piloto son requeridos.



Reaction stoichiometry



Equilibrium


Equilibrium


Equilibrium


Equilibrium


Equilibrium


Equilibrium


Equilibrium


Equilibrium

Kinetics


Kinetics


Kinetics


Kinetics


CSTR

PFR


PFR



CONFIGURATIONS

STIRRED-TANK REACTOR SELECTION

The operating mode of a stirred-tank reactor may be either continuous or batch. A STR consists of a vessel to contain the reactants, a heat exchanger, a mixer, and baffles to prevent vortex formation and to increase turbulence, enhancing mixing. To evaluate and select a STR, consider the following factors: 1. mixing 2. heat transfer 3. jacket pressure drop 4. cleaning


The factors that influence the selection of a heat exchanger are: 1. heat-transfer coefficients 2. jacket pressure 3. reactor pressure 4. jacket pressure drop 5. cleanliness 6. Cost The jacket pressure and reactor pressure also influences jacket selection. If the jacket pressure is large the reactor wall thickness becomes large, reducing heat transfer. Markovitz has given the following rules for selecting the jacket type:


for < 500 gal (1.89 m3) use the simple jacket for > 500 gal (1.89 m3) use the dimple or half-pipe coil if the reactor pressure is greater than twice the jacket pressure use the simple jacket for a jacket pressure < 300 psi (20.7 bar) use the dimple for a jacket pressure > 300 psi (20.7 bar) use the half-pipe coil jacket but < 1000 psi (68.9 bar) use the half-pipe coil jacket for steam the pressure is < 750 psi (51.7 bar) use the half-pipe coil jacket


Dimple Half-pipe

https://www.google.com.co/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRxqFQoTCP-N8_6HrMgCFdG4HgodkloGSQ&url=http%3A%2F%2Fwww.ras-inc.com%2Fhtml%2Freactors.html&psig=AFQjCNHjl5as4pm0Cr5p_VvA08plohOOTg&ust=1444159465430110

CONTINUOUS STIRRED-TANK REACTOR SIZING

For each reactor in the series, we assume:

Perfect mixing

Constant volume

Constant temperature

Constant density

Constant heat capacities

Equal mixer power for each reactor


First Subscript: entering stream or CSTR number: n, leaving stream: n + 1, reactant: A Mole Balance: mn.A = mn+1,A + (xn+l,A – xn,A)mn,A Energy Equation: (ΔHn)mn + (ΔH°R) (xn+1,A - xn,A)mn,A = Qn+ (ΔHn+1) mn+1

Rate Equation: -rA = KCA VR = f(Vr) QJ = UJ AJ (TJ -TR)


TJ = (TJ1+ TJ2)/2, AJ = f(Vr)

If Qn < QJ ; then AR = AJ

If Qn > QJ ; then calculate Qc

Qc = UcAc(Tc - TR)

Tc = (TC1 + TC2)/2, Ac = 4.6 Vr

2/3

If Qn < Qc ; then AR = Ac

If Qn > Qc and Qn < QJ + Qc ; then AR = AJ + Ac

If Qn > QJ + Qc ; then AR = AE


This problem is an adaptation of a problem taken from Fogler. Propylene glycol is produced by hydrating propylene oxide using a solution of 0.1 % sulfuric acid in water as a catalyst. The reaction is

CH2-O-CH-CH3 + H2O → CH2-OH-CH-OH-CH3 An equi-volumetric solution of methanol and propylene oxide flows into a CSTR. At the same time, a 0.1% sulfuric acid solution also flows into the CSTR at a rate of 2.5 times the combined flow rate of propylene oxide and methanol. The coolant is chilled water. Size the reactor, determine the heat exchanger type and area, and calculate the mixer power.


Data: Methanol volumetric flow rate: 800ft3/h(22.7m3/h) Propylene oxide volumetric flow rate: 800 ft3/h (22.7 m3/h) Acid solution volumetric flow rate: 4000ft3/h(l 13 m3/h) Feed inlet temperature: 75°F(23.9°C) Reaction temperature: 100°F(37.8°C) Chilled water inlet temperature: 5°C(41°F) Chilled water exit temperature: 15°C(59°F) Required propylene oxide conversion: 0.37


Thermodynamic properties are summarized in Table, and reaction properties are given below. Fogler estimated the heat capacity for propylene glycol using a rale-of-thumb. The rule states that the majority of low-molecular weight, oxygen-containing organic liquids have a heat capacity of 0.6 cal/g °F ± 15% (35Btu/lbmol°F). Reaction Properties Pre-exponential factor, A = 16.96 x1012 h-1

Activation energy, E = 32,400 Btu/lbmol (75,330 kJ/kgmol)


Documents

Diseño de Procesos Clase 7