Reactores con transferencia de masa

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

= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->

{ } { () (/)}] = [ -> { }

{ () (/)} ] = [ -> { }

{ () (/)} ][ =] = [ ->

{ } { () (/)}] = [ -> { }

{ () (/)} ] = [ -> { }

{ () (/)} ][ =]

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

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

= = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [ { - }]

[_ _] = - -[]*[]** [_ _] = [][] + [] ( - [ ]) [][] - ( - [ ])

= = [ = < + ++ = [[]] = [[]] = [ [[]]][[]] = [ [[]]][[]] = [ [[]]][[]] = [ [[]]]]


= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = -> { }

() ( ) {= =} = -> { }

() ( ) {= =}

[ ]

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) = - ( - )( + ) = -


[_ _ _ _] = -[_ _ _ _] = [] * * [] ( - ) + (**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }] = [ { - }][[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] [[]] [[]]] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ] = [[[]] + [[]] + * * [[]] + * * ]


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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) = - ()

= (( * ) / ) * ( / ) * * * * (*/*)

= - * *


= - ( - )( + ) = - =

[_ _ _ _ _] = -[_ _ _ _ _] = [] * * [] ( - ) + [_ _ _ _ _] = * [ ]


(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]

[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]]

[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /

]


= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->

{ } { () } {=} ]

= [ -> { } { () ()} {=} ]

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

= - ( - )( + )


= - = - ([ ] - )

[_ _ _ _ _] = -[_ _ _ _ _] = [] * * [] ( - ) + [_ _ _ _ _] = [ ] * - * * * * ( - ) *


(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]

[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]]

[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /

]


= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->

{ } { () } {= = =} ]

= [ -> { } { () } {= = =} ]

= [ -> { } { () } {= = =} ]

[ ] = [ -> { }

{ () ()} {= = =} ]

= [ -> { } { () ()} {= = =} ]

= [ -> { } { () ()} {= = =} ]

[ ]

0 50 100 1500.0

0.2

0.4

0.6

0.8

1.0

z (cm)

X

Conversin

T=630KT=640KT=650K


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


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

[_] = [] [] [_] = [][]/ [_] = [] [] [_] = []

[] * * * * [_] = + []


[_] = - * [] []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


por lo que decidimos despreciarlo

Diseo del Reactor

= - ( - )( + ) = - = - ([ ] - )

[_ _ _ _ _] = -[_ _ _ _ _] = [] * [] * [] * * [] ( - ) + [_ _ _ _ _] = [ ] * - * * * * ( - ) *


(**) = = (* *) = [ { - }] (* *) = [ { - }] = [ { - }] = [ { - }] = [[]] = [[]] = [[]] = [[]] = [ = < ++ = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] [[]] [[]] [[]] [[]]] = [[[]] + [[]]

[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]]

[[]] + * * [[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * *

[[]] + * * [[]] + * * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ] = [[[]] + [[]] [[]] + * [[]] + * [[]] + * ](* *)[[ + ]] = [[]] + [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * / [[ + ]] = [[]] + ( + + + ) * /

]


= [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [{[[]] [[]]} { }] = [ ->

{ } { () } {= = =} ]

= [ -> { } { () } {= = =} ]

[ ] = [ -> { }

{ () ()} {= = =} ]

= [ -> { } { () ()} {= = =} ]

0 50 100 1500.000

0.005

0.010

0.015

0.020

z (cm)

X

Conversin

T=630KT=650K


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


Reactores con transferencia de masa

Documents

Transcript of Reactores con transferencia de masa