Download - Reactores con transferencia de masa
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Ceballos Cant Jos PabloCoquet Dvila Manuel
Mrquez Ramrez SofaSilva Saldivar OmarNoviembre 12, 2014
3er Parcial Ingeniera de Reactores II: Diseo de un reactor de lecho fijo
Datos naftaleno -> anhidrido ftlicoa=naftalenob=nitrgenoc=oxgenod=anhdridoe=CO2f=agua
= (*/*) = = = = = = (**) = (**) = -(*/ *) = -(*/ *) = (*/ *) = = (**) = (* - - -*) = * -(* - -*) = (*/ *) = (*/*) = (*/*) = (*/*) = (**) = (*/*) = (*/*) = (*/*) = (*/*) = (**) = (**) = (**) = - = (*/*) = = * (**) = * (**) = * * ( / )(**) - /
-
[_] = * - [_] = * - [_] = * ( / ) / ( * )
Anlisis para determinar si se puede despreciar la segunda reaccin aproximadamente = 0, porque esta muy diluido el naftaleno = - = -
= = - = - - - - =
= = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }]
[_ _] = [] * -[]*[_ _] = [] * [] * -[]* - -[]*[] - [][_ _] = [] - [ ] - [ ]
= = [ = < + ++ = [[]] = [[]] = [[[]] ][[]] = [[[]] ][[]] = [[[]] ][[]] = [[[]] ][[]] = [[[]] ][[]] = [[[]] ]]
2 3er Examen Parcial Cuevas prueba.nb
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= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->
{ } { () (/)}] = [ -> { }
{ () (/)} ] = [ -> { }
{ () (/)} ][ =] = [ ->
{ } { () (/)}] = [ -> { }
{ () (/)} ] = [ -> { }
{ () (/)} ][ =]
0.0 0.2 0.4 0.6 0.8 1.00.00000
0.00005
0.00010
0.00015
0.00020
0.00025
Tiempo (s)
Ci(mo
l/L)
T=630K
0.0 0.2 0.4 0.6 0.8 1.00.00000
0.00005
0.00010
0.00015
0.00020
Tiempo (s)
Ci(mo
l/L)
T=673K
3er Examen Parcial Cuevas prueba.nb 3
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Selectividad Puntual = dCAndCn
= -1 + k2CAnk1CN
s = CAnCN0
= k1k1+k2 (1 - XN) k2k1 - (1 - XN)
dXNdz
= -k1CN0AtFN0
(1 - XN)XN = 1- k1CN0AtFN0 zCuando el tiempo tiende a infinito
= = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [ { - }]
[_ _] = - -[]*[]** [_ _] = [][] + [] ( - [ ]) [][] - ( - [ ])
= = [ = < + ++ = [[]] = [[]] = [ [[]]][[]] = [ [[]]][[]] = [ [[]]][[]] = [ [[]]]]
4 3er Examen Parcial Cuevas prueba.nb
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= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = -> { }
() ( ) {= =} = -> { }
() ( ) {= =}
[ ]
0 50 100 1500.0
0.2
0.4
0.6
0.8
1.0
Longitud (cm)
s(CAn CN0
)
Selectividad
T=630KT=673K
Vemos que la segunda reaccin es muy lenta y que no nos va a afectar la conversin de anhdro a estas temperaturas por lo que la podemos despreciar en nuestro diseo preeliminar. (Apenas a nuestra temperatura lmite al final del reactor reacciona menos del 8% de anhidro)
a) Reactor Isotrmico de Lecho Fijo s/TM
= -
-ra = k1Ca = k1 PP0
Ca0(1 - xa)(1 + xa) = - ( - )( + ) = -
3er Examen Parcial Cuevas prueba.nb 5
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[_ _ _ _] = -[_ _ _ _] = [] * * [] ( - ) + (**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }][[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ]
6 3er Examen Parcial Cuevas prueba.nb
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
]
3er Examen Parcial Cuevas prueba.nb 7
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= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ -> { }
{ () ()} {= = = =}]
= [ -> { } { () ()} {= = = =}]
= [ -> { } { () ()} {= = = =}]
= [ -> { } { () ()} {= = = =}]
[ ] = [ ->
{ } { () } {= = = =}]
= [ -> { } { () } {= = = =}]
= [ -> { } { () } {= = = =}]
= [ -> { } { () } {= = = =}]
[ ]
8 3er Examen Parcial Cuevas prueba.nb
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0 50 100 1500
5
10
15
20
25
z (cm)
P(psia
)Presin
T=630KT=640KT=650KT=660K
0 50 100 1500.0
0.2
0.4
0.6
0.8
1.0
z (cm)
X
Conversin
T=630KT=640KT=650KT=660K
Resultados : No es posible alcanzar una x=0.99 por la cada de presin para T=630K y T=640K T = 630 K Xmax = 0.9394 z = 188 cm T = 640 K Xmax = 0.9887 z = 188 cm T = 650 K X = 0.99 z = 78.21 cm P = 14.61 psi T = 660 K X = 0.99 z = 45.87 cm P = 18.91 psi
b) Reactor Adiabtico de Lecho Fijo s/TM
T (x) = T0 + (xf - x0) = - ()
= (( * ) / ) * ( / ) * * * * (*/*)
= - * *
3er Examen Parcial Cuevas prueba.nb 9
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= - ( - )( + ) = - =
[_ _ _ _ _] = -[_ _ _ _ _] = [] * * [] ( - ) + [_ _ _ _ _] = * [ ]
10 3er Examen Parcial Cuevas prueba.nb
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(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /
]
3er Examen Parcial Cuevas prueba.nb 11
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= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->
{ } { () } {=} ]
= [ -> { } { () ()} {=} ]
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
z (cm)
X
Conversin
T=630K
0.0 0.5 1.0 1.5 2.0
650
700
750
800
850
900
950
1000
z (cm)
Tempe
ratura
(K)
Temperatura
T=630K
Vemos que un reactor adiabtico sin enfriamiento no nos sirve ya que se descontrola por que la temper-atura crece exponencialmente y explota. De hecho nos sale una longitud de solamente 2.1 cm antes de descontrolarse y esto se debe a que la reaccin es altamente exotrmica.
c) Transferencia de Calor con Medio de Enfriamiento
= - ( - )( + )
12 3er Examen Parcial Cuevas prueba.nb
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= - = - ([ ] - )
[_ _ _ _ _] = -[_ _ _ _ _] = [] * * [] ( - ) + [_ _ _ _ _] = [ ] * - * * * * ( - ) *
3er Examen Parcial Cuevas prueba.nb 13
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(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /
]
14 3er Examen Parcial Cuevas prueba.nb
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(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /
]
3er Examen Parcial Cuevas prueba.nb 15
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(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /
]
16 3er Examen Parcial Cuevas prueba.nb
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= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->
{ } { () } {= = =} ]
= [ -> { } { () } {= = =} ]
= [ -> { } { () } {= = =} ]
[ ] = [ -> { }
{ () ()} {= = =} ]
= [ -> { } { () ()} {= = =} ]
= [ -> { } { () ()} {= = =} ]
[ ]
0 50 100 1500.0
0.2
0.4
0.6
0.8
1.0
z (cm)
X
Conversin
T=630KT=640KT=650K
3er Examen Parcial Cuevas prueba.nb 17
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0 50 100 150630
640
650
660
670
680
z (cm)
Tempe
ratura
(K)Temperatura
T=630KT=640KT=650K
Al agregar el enfriamiento podemos ver este comportamiento, donde la temperatura aumenta pero la sal de enfriamiento la controla (arriba de 650C se descontrola ya que el calentamiento es mayor a lo que se enfria el reactor por las paredes ). Considerando nuestra Tmax = 673 K, el caso ideal sera tener las sales a una temperatura de T=648 K.
Tambin vemos que a la temperatura de 630 K alcanzamos una conversin mxima de 0.951 ya que nuestra cada de presin no permite una conversin mayor.
Resultados : T = 630 K Xmax = 0.951 z = 188 cm P = 0 psi Tmax = 636.321 T = 640 K X = 0.99 z = 141.53 cm P = 6.20 psi Tmax = 651.799 T = 648 K X = 0.99 z = 71.63 cm P = 15.48 psi Tmax = 671.676 T = 650 K X = 0.99 z = 61.21 cm P = 18.87 psi Tmax = 681.535
d) Adiabtico con Transferencia de Masa
Calculo externoCalculo de la difusividad combinada
Daire-naftaleno = 0.0018583 T
3
2 1Maire
+ 1Mnaftaleno
12Ptotal ab2 abaire = 3.617
Vb naftalento = 10C + 8H - 30 (correccin)Vb naftalento = 10(14.8) + 8(3.7) - 30 =147.6
naftalento = 1.18 Vb 13=6.236ab = a +b
2=4.9265
kb
aire = 97K
18 3er Examen Parcial Cuevas prueba.nb
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Tc = 748.4 K
kbT =1.3 TTc kb naftaleno = 575.69Kabkb
= (575.69) (97) = 236.31KDe ahi sacamos kbTab =2.67ab=0.9876
= = [_] = * / *
+
( / ) * * []
[_] = * ( / ) * * (*/*) = * ( - ) *
[_] = * * [_] = []-
Suponiendo am/at = 1
[_] = [] [] [_] = [][]/ [_] = [] [] [_] = []
[] * * * * [_] = + []
3er Examen Parcial Cuevas prueba.nb 19
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[_] = - * [] []Gradiente de temperaturas causado por la transferencia de masa externa
[_] = [] * [] * [] [] [] []
Vemos que la temperatura no cambia mucho por razones de transferencia de masa externa (0.66C) por lo que decidimos despreciarlo
Calculo interno = * * (**)
Difusividad
[_] = * * * ( / )Calculamos la difusividad combinada despreciando alfa ya que la fraccin de a es mnima
[_] = [] + []
[_] = [] * [_] = [] * [] [_] = [] [ []] - [] []
[_] = - * [] * * [] + [] []
Vemos que la temperatura cambia a lo mucho 0.005C por razones de transferencia de masa interna
20 3er Examen Parcial Cuevas prueba.nb
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por lo que decidimos despreciarlo
Diseo del Reactor
= - ( - )( + ) = - = - ([ ] - )
[_ _ _ _ _] = -[_ _ _ _ _] = [] * [] * [] * * [] ( - ) + [_ _ _ _ _] = [ ] * - * * * * ( - ) *
3er Examen Parcial Cuevas prueba.nb 21
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(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /
]
22 3er Examen Parcial Cuevas prueba.nb
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(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]]
[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *
[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /
]
3er Examen Parcial Cuevas prueba.nb 23
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= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->
{ } { () } {= = =} ]
= [ -> { } { () } {= = =} ]
[ ] = [ -> { }
{ () ()} {= = =} ]
= [ -> { } { () ()} {= = =} ]
0 50 100 1500.000
0.005
0.010
0.015
0.020
z (cm)
X
Conversin
T=630KT=650K
24 3er Examen Parcial Cuevas prueba.nb
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0 50 100 150630.000
630.005
630.010
630.015
630.020
630.025
630.030
630.035
630.040
z (cm)
Tempe
ratura
(K)Temperatura
T=630K
0 50 100 150650.000
650.005
650.010
650.015
650.020
650.025
650.030
650.035
650.040
z (cm)
Tempe
ratura
(K)
Temperatura
T=650K
Vemos que al incluir los problemas de transferencia de masa externa e interna, nuestro diseo de reactor ya no funciona ya que no podemos pasar a una conversin mayor a 0.02. De hecho vemos que al aumentar la temperatura se perjudica la conversin por lo que tenemos que usar otros mtodos para abatir los problemas de transferencia de masa.
Para la externa podemos aumentar el dimetro del pellet para incrementar la am (esto puede afectar la transferencia de masa interna) disminuir el flujo.
Para la interna podemos disminuir el dimetro de particula.
Para ambas podemos cambiar la geometra del pellet cuidando la resistencia mecnica, disminuir la temperatura de operacin y aumentar la presin.
Ejemplo: A 650K alcanzamos una conversin del 0.0126A 630K alcanzamos una conversin del 0.0183A 610K alcanzamos una conversin del 0.0256
3er Examen Parcial Cuevas prueba.nb 25