Rigorous simulation and design Plate Column.pdf

7/25/2019 Rigorous simulation and design Plate Column.pdf

1/11

Comput ers & Chemi cal Engineeri ng,Vol. IO, No. 5, pp. M -515, 1986

Printed in Great

Britain. All rights reserved

0098-1354/86 3.00 + 0.00

Copyright 0 1986Pergamon Journals Ltd

RIGOROUS SIMULATION AND DESIGN OF COLUMNS

FOR GAS ABSORPTION AND CHEMICAL

REACTION-II

PLATE COLUMNS

L. DE LEYE and G. F. FROMENT

Laboratorium voor Petrochemische Techniek, Rijksuniversiteit, Gent, Belgium

(Received 22 January 1985; revisi on r eceiv ed 5 Sept ember 1985;

receiv ed for publ icat io n 20 January 1986)

1. INTRODUCTION

In Part I [l, this issue, pp. 4935041 of this paper the

mathematical modelling of absorption accompanied

by chemical reaction was developed both for simple

and complex cases and attention was focused upon

application to packed columns. Part II applies the

theory to the design or simulation of plate columns.

These are preferred to packed columns when widely

varying loadings may be expected. Also, large values

of the mass-transfer coefficients and large interfacial

areas can be achieved in traycolumns, which makes

them appropriate not only for the fast reactions

encountered in gas treating, but also, given the high

liquid hold-up, for the slow reactions encountered in

chemical-producing processes.

2. MATHEMATICALMODELLING

The various flows and compositions of the gas and

liquid in the column and on a typical plate are shown

in Fig. 1. Gas and liquid feed or withdrawal on a

plate are also included. The components in the liquid

phase are numbered in the following order: com-

ponents undergoing absorption and reaction, phys-

ically absorbed components, liquid-phase reactants,

reaction products involved in further reactions, final

reaction products and inert liquid-phase components.

When the total number of plates, the compositions,

flow rates, temperatures and pressures of the gas and

liquid feed streams and the flow rates of intermediate

gas or liquid withdrawals are given, the flow rates,

compositions, temperatures and pressures on each

plate have to be calculated. This is the simulation

problem. In the design mode the number of plates

required to achieve a specified absorption has to be

determined. This requires a number of iterations in

the column calculation.

In the model to be described, the gas is assumed to

be in plug flow, while the liquid on the plates is

completely mixed. Non-isothermal and non-isobaric

operation are considered. The equations below are

written for a fairly general example involving simulta-

neous absorption and parallel reactions (Type 1A).

The variation of, the mole fractions of the absorbing

components in the gas phase and of the total gas flow

rate on plate k are given by

F

dy i

l- yj p E?

di

I= N j l y=O

(1)

= -Njly=i AtR*

forj=l,...,nA,

and

(2)

while for non-absorbing components,

FYI constant for j = nA + 1, . . . , n,.

(3)

The boundary conditions are

for 2 = O,yj=yjpk

F=@

and

I

forj=l,...,no. (4)

for 2 = h, y,= yj,k

F = Fk

Pf and yFk are the gas flow rate and the mole

fractions in the gas entering the plate. These are

related to the quantities leaving the plate k + 1 in the

following way, accounting for side streams:

and

forj=l,...,no. (6)

The equations for the flow rate and composition of

the liquid are derived, by way of example, for the

parallel reactions (33) and (34) (Type 1A) of Part I

[l]. Since the various reactions probably have

505


2/11

506

L. DE LEVEand G. F. FROMENT

X

;j= 1 ..

.f-JL

6

1

-La

Y

;j=l,...,nG

X

, .;j

, , n

L

k-7; ,@,I,

F T

k+lk+l

Gas

Liquid

Fig. 1. Flows and compositions in the column and on a plate.

different reaction rates, the xj,k depend upon the

for the remaining absorbed components,

appropriate Hatta number.

For the absorbed components undergoing a very

fast reaction (appropriate Hatta number > 3),

(7)

ik=O forj=l,...,nv;

for those involved in a moderately fast reaction

(appropriate Hatta number between 0.3 and 3),

forj=n,+l,...,n,. (10)

X/k(L+

Ww~)=xj,k-,L;_,

+xw,,k

WV,

+NjIy-.vL

A:Rh, - aj,jrj(l - A,y,)Rh,c,

The mole fractions of reactants, reaction products

=x,~k_,L;_,+xw,,kwk T f Q

I- I

a/,/

and inerts in the liquid on the plate are given by

X,,.k(G + WW,)

forj=n,+l,...,n,+n,; (8)

x

{(@Y - F,Y,,,) -

[x,Ow~ + 4)

for the absorbed components undergoing a very slow

reaction (Ha c 0.3)

-(G-I%-, + W,XW,,,)l~

forj=n,+l,...

,+,+nR+nP (11)

and

+y~kkFl~-Yj,kFk-Uj, jrj(l -A$,)Rh,C,

Xj,k L;+ WWt)=Xj,k-IL;-I+X~,.~Wv~

forj=nv+n,+l,...,n,+nM+n,; (9)

forj=n,+n,+n,+l,...,n,. (12)


3/11

Simulation of absorption and reaction in columns-II

507

The minus sign in equation (11) applies to the

reactants, the plus sign to the reaction products.

The absorption fluxes of the different components

are determined from

~jl,=,=kG,j Pt)k[Yj-H~ Xj.k)il

forj=l,...,nA, (13)

and from the application of Ficks law for diffusion:

du,

NjIy=o=

-

Djckdy=o

forj=l,...,n, (14)

and

N J = = -

Dj Ck

dY

YL

forj=n,+l,...,n,. (15)

For the determination of these fluxes, the concen-

tration profiles of the absorbed components, under-

going fast reactions in the liquid film, have to be

computed from the following set of second-order

differential equations:

Djdzx=%r.

or

j=

I,...

dy2 C, *

,nv+n,; (16)

and for the liquid-phase reactant participating in the

fast reactions,

Da+rFr,

/=I k

with boundary conditions

at

y=o

dx,=

Njly=o

dy

-- forj=l,...,nv+n,

DjCk

dxa

- = 0 for the liquid-phase reactant

dy

ticipating in the fast reactions

andat y=y,,

xj = 0 forj=l,...,nv

xj=xik forj=nv+l,...,nv+n,

xa = x, k for the liquid-phase reactant

ticipating in the fast reactions.

par-

(17)

par-

When the kinetic expressions of the nv very fast

and nM moderately fast reactions have the following

simple forms:

rj = kjC_?lC~R

for j = 1,

. . . , nv

(18)

and

rj =

kjC,CtR

for j = nv + 1, . . . , n, +

nM,

(19)

the interfacial fluxes of the absorbed components that

undergo the fast reactions, obtained through the

approximate solutions of Onda et al. [2],

Njly-0 =

fi

1

Hi

tanh (Ha;)

~ -

ko.j(Pt)k + kL,j(Pt)k

Hay

forj=l,...,nv, (20)

are not necessarily computed from the integrated

equations (16) and (17), but may also be obtained

through

HjXj,k

Njly-o= 1

-

cash (Ha;)

Hj

tanh(Ha;)

ko,jG,)k + kL.j(Jt)k

HaJ

forj=n,+l,...,nv+n,

and

Njly-yL=

Ha ,k ,c xj,k>i-xj,kcosh Ha~)

I

LJ k

sinh (Ha;)

forj=nv+l,...,nv+n,

with

HI = Hi(Pth

I

ck

and provided that Ha; is expressed by

(21)

(22)

Haj =

mj,,y+aj, k,C - I (xi k)?J - (xK ,+)yDj

kLJ

forj=l,...,nv (23)

and

/

kL.j

for j = nv + 1, . . . , n, + nM.

(24)

If one or more of the fast reactions have a more

general kinetic expression, the set of second-order

differential equations (16) has to be solved numer-

ically. The integration is performed by means of a

variable-step finite-difference method for the solution

of boundary-value problems.

The fluxes of the remaining absorbed components,

undergoing a very slow reaction or which are only

physically absorbed, are given by

Yj- HjXj*k

Njly-o= 1

Hj

ko,j(Pt)k + kL,j(Pt)k

forj=nv+n,+l,...,n,. (25)

The temperature on a plate is determined from an

enthalpy balance around the plate:


4/11

508

L. DE LEYEand G. F. FROMENT

G-IL;-, ? Xj,k-ICpL.,-Tk

Fk f yj,kCpc;.j

with

j=l

j=l

Q = (-AH,b)(Ft_YFk FkJj,k)

+ (WW, + Li) 5 Xj.kCpL,

forj=l,...,n,+ (27)

,=I

t Tk+,

[

(Fk+\- VW,+)) 2 Yj,k+lCpG.,

and

j-l

+Tvk+,l/ ,k+, j Yv,,, + I CPO., + Twt WV,

Q~k= -AH~ )~,{ ~~Y~k-F,Yj.k)

O L

-[xj,k L;+ W~,)-(~;-,~,k-,

x c xw,.kcPL.,

j=l

= Q: -, , Q;? - 5 Q; , (26)

,= I

+ WVkXW,,,I)

forj=l,...,n,. (28)

start

NO

Gas withdr.

YES

Estimate

I

ITER = 1

k=l

DETERM. PHYS. PROP.

kG kL

PLATE CHARACT.

I

Determine

Haj j = 1 . . . I-IR

YES

NO

Fig. 2(a)


5/11

Simulation of absorption and reaction in columns-11

Equation (26) is written in the following form: 3. A COMPUTER PROGRAM, A-Tray

509

Tk_,A;+TkB;+Tk+,C;=D; k=l,..., N,

The second subprogram of A-Tower, specifically

(29)

with A; = 0 and CN = 0, so that the coefficient matrix

of the set of non-linear algebraic equations (29) is

reduced to a tridiagonal matrix.

The pressure drop on a plate depends upon the

type of tray (sieve, bubble caps, valve, . . . , etc.).

Correlations are available in the literature and these

were incorporated into the program A-Tray.

Ha .

3'

j = l,n

V + M

I

dealing with plate columns is called A-Tray. It com-

prises three modules: one for physical absorption,

one for single absorption accompanied by a single

reaction, reversible or irreversible, and one for mul-

tiple absorption accompanied by a set of parallel or

consecutive reactions, with kinetic regimes ranging

from very slow to instantaneous and non-isothermal,

non-isobaric operation. It is clear from the previous

section that the calculations lead to the number of

xI

; j = l,n

j,k

V + M

I

'k

I

Determine PHYS. PROP.

Determine PHYS. PROP. 1

kG' kL

kG kL

I

Plate

charact.

RUKUGILL Num. Int.

Eqs (l),(2)

y;:k

; j = 1,nA

F;

Eq (3)

';:k

; j=n

A

+ 1,n

G

Eqs (5),(6)

Fk+l

'i,k+l'

j = l,nG

Combin.

Eqs (11),(12)

_ *

L'k

Eqs (11),(12)

'j,k'

j = nA t l,nL

Eqs (8),(9),(10)

'j,k'

j = *v t l,nA

Eqs (23),(24)

Ha :

3'

j = l.nV t nM

Calculate Ck

I

Plate chat-act.

I

RUKUGILL Num. Int.

Eqe (l),(2)

y;:k

; J = l,n

A

F;

Eq (3)

y;;k

; j = nA + l,nG

Eqs (5),(e)

Fk+l

yj,ktl'

j = 1,n

G

Num.

Integr.

2ndorder

Diff.

eqs (16)

xI.

j = 1,

J*k

V + M

dc.

5-l YYL

; j = nv t l,nV t M

Eqs (8),(9),(10)

'j,k'

j = nv t l,nA

Calculate Ck

d

Fig. 2(b)


6/11

510

L.

DE LEYE nd G. F.

FROMENT

real-not theoretical-trays. By way of example, the

algorithm used for the case whereby the absorption

A tray-to-tray method is used, starting at the top

plate of the column. The calculation of the successive

is accompanied by Type 1A parallel reactions,

defined in Part I [1] of this paper, is shown in Fig. 2.

estimates of the unknown variables at the top and the

various plates is reduced to the problem of solving a

NO

I

(APt)k-+.(Pt)k; k = 1 . . . N

M0

c

I

Estimate

Estimate

yj,l'

j = 1 . . . nC-1

'j,l'

j = 1 . . . nA

F1

L

I

TV

ITER = ITER t 1

I

b

(x. k)E

SSQ,

=

Z( J9

- (x. k)C 2

('j,k)E

) tZ(

(Ha" .jE - (Ha .)

-q2 t

(

(Ha j)E

('k)E - ('k)C)2

(=k)E

(Xi k)E -

(Xi,k)C 2

(x*, )E - (Xi,

SSQ, = Z(

('j,k)E

) + Z( .lgk

J,k)'

('I. )E

)2

+ (

(CkjE - (CkjC 2

)

J,k

(=k)E

(x. k)E

SSQ, = Z(

- (x. k)C 2

) +(

Cc,), -

(=k)C 2

('j,k)E

('k)E

)

Fig. 2(c)

Fig. 2(a-c). Flow chart of the algorithm for the simulation of a plate column in which absorption is

accompanied by a Type IA system of parallel reactions.


7/11

Simulation of absorption and reaction in columns---II

511

Table 1. Constructive details of the valve trays in

the H,S-DEA column

Property

Active area, n (m) 0.4225

Relative free area on plate

0.153

Weir length (m)

0.872

Weir height (m)

0.066

Valve thickness (m) 0.00188

Table 3. Commuted results for the H,S-DEA absorption column

Top

column

Bottom

column

set of non-linear algebraic equations. For this pur-

pose the program contains Wegsteins method [3] and

the generalized secant method [4]. The application of

A-Tray to a couple of important industrial processes

is illustrated in the next section.

L (kmol/h)

F (kmol/h)

YHB

xti,s

+wx-I

XHS-

;;;y

T (R)

A: (m2/m)

ko, HZ (kmollm h b)

F. ::)(mih)

F

LI

2208.8

2247.9

161.69

200.8

0.13 x lo-

0.195

0.0

0.134 x 10-J

0.41 x lo-

0.230 x IO-

0.0

0.173 x 10-l

0.0

0.173 x 10-l

7.47

7.590

318.15

321.5

535.68

292.45

0.442

0.443

0.367

0.387

0.153 0.169

0.371

0.328

No. of iterations: 4

CPU time used (Data General MV 6000): 25 s

4. EXAMPLES OF THE APPLICATION OF A-Tray

4.1. The absorption of H2S in an aqueous di-

ethanolami ne (DEA) solut ion

I n this example a DEA solution is used for the

removal of H,S from a refinery stream. The gas feed

has an average molecular weight of 24.9 kg/kmol and

contains 19.5 mol of Hz S. The flow rate, temperature

and pressure of the gas feed are 200.85 kmol/h,

318.15 K and 7.6 b, respectively. A 20 wt% DEA

solution at a temperature of 318.15 K is used as

solvent. Its flow rate is 2208.8 kmol/h. The column

has a diameter of 0.98 m and is equipped with 18

Glitsch Vl-ballast trays. The constructive details of

the plates are summarized in Table 1.

The solubility of H,S in the solution was taken

from Kent and Eisenberg [8].

The standard correlations incorporated in the pro-

gram, which are listed in Table 2, were used for the

determination of the mass-transfer coefficients and

the different plate characteristics.

The initial estimates of temperature and pressure

on each tray were 3 18.15 K and 7.6 b. The mole

fraction of HIS at the top of the column was esti-

mated to be 1 x lo-, the convergence tolerance was

set equal to 10-j. The results of the computations are

summarized in Table 3.

The absorption of H2S in this solution is accom-

panied by the following overall reaction [5,6]:

H, S + R,NH & HS- +

RNH;

.

(30)

The variations of the mole fractions of H,S in the

gas phase, of DEA and the reaction products in the

liquid phase and of the gas and liquid flow rates along

the column are shown in Fig. 3.

Figure 4 shows the computed temperature and

pressure profiles in the column.

This reaction is instantaneous and reversible.

Data for the determination of the equilibrium

constant of the reaction, K,, were taken from the

literature [7,8].

4.2. The simul t aneous absorpti on of H,S and CO2 i n

an aqueous NaOH solut ion

Densities and viscosities of the solution and

The absorption of H2S and CO2 in an aqueous

diffusivities of the reactants in the solution were

NaOH solution is applied in the purification of the

calculated out of the experimental values [9] and

effluent resulting from the thermal cracking of naph-

literature data [lo, 111. For the determination of the

tha for the production of ethylene. The absorption is

diffusivity of the H,S in water, Wilke-Changs cor-

carried out in a plate column with two NaOH

relation was used. This diffusivity was corrected for

circuits, one with a concentrated and one with a lean

the composition of the aqueous solution according to

caustic solution. The configuration of the tower is

the Stokes-Einstein relationship.

schematically represented in Fig. 5.

Table 2. Standard correlations in

the A-Tray program for the deter-

mination of the mass-transfer

coefficients and the plate character-

istics

Property

ko

k,

A:

h,

f,

&,

h

Correlation

Stichlmair [I 21

Stichlmair [12]

Stichlmair [12]

Stichlmair (121

Stichlmair [I21

Glitsch Inc. [13]

The gas feed to the column, F,, equals

5800 kmol/h. The feed temperature and pressure are

3 13.15 K and 12.8 b. The composition of the gas feed

is given in Table 4. 2510 kmol/h of an aqueous

solution containing 4 wt% of NaOH are fed at the

top of the column. 1500 kmol/h of the liquid solution

is withdrawn from tray 15 and 2300 kmol/h of a

1 wt% NaOH solution is added on the underlying

tray.

The column, with a diameter of 2.764m, is

equipped with 30 V,-Glitsch Ballast trays. The con-

structive details of these trays are given in Table 5.


8/11

512

L. DE LEYE nd G. F.

FROMENT

Gas or liquid flaw rate kmol/h)

0

1000

2000

I

t

TOP

0

0.1 x10-

02x10-

I

0.3 x10- 0.4 x10-

l-

I

I I

I

x, mole fraction

5-

y, mole fraction

Fig. 3. Variation of the mole fractions of H,S in the gas phase, of DEA and the reaction products in

the liquid phase and of the gas and liquid flow rates along the column.

Total pressure b)

TOD

7.5 8.0

x

I _

320

330

Temperature K

1

Fig. 4. Temperature and pressure on each tray in the H,S-DEA absorption column.

The absorption of H,S in an NaOH solution is

accompanied by the following overall reaction [14]:

H,S + NaOH 2 NaHS + H20.

(31)

This reaction is instantaneous and reversible.

In strong OH solutions CO2 is undergoing the

following overall reaction [15, 161:

COz + 2NaOH - Na2 CO3 + H,O.

(32)

Since NaOH and the salt products are completely

dissociated, reactions (31) and (32) can be presented

in ionic form:

H2S + OH- & HS- + Hz0

(33)

and

CO2 + 20H- - CO:- + H,O.

Fig. 5. Schematic representation of the H,S-CO,-NaOH

(34)

column.


9/11

Simulation of absorption and reaction in columns-11 513

Table 4. Composition of gas feed

for the H,S-CO,-NaOH absorp-

tion column

Component

Mole fraction

KS

0.00079

CO,

0.00055

CH,

0.28612

GH,

0.31337

C,H,

0.07493

C,H,

0.10218

C,H,

0.0442

C,H,s

0.0171

H,

0.16076

Table 5. Constructive details of the ballast trays in

the H,S-CO,-NaOH absorntion column

Prooertv

Active area, C2(m*) 5.072

Relative free area on plate 0.1869

Weir length (m) 2.259

Weir height (m) 0.05

Valve thickness (m)

0.00188

Density material (kg/m) 8169

The equilibrium constant K, of the first reaction is

W-1

K1 = (HrS)(OH-)

The kinetic expression of the reaction with CO2 has

the following form:

r =

kCco,

CoH

For the determination of the equilibrium constant

K, , data of Edwards et al. [17] were used. The

reaction rate coefficient

k

in equation (36), as a

function of temperature and ionic strength of the

Table 6. Compositions, flow rate and temperature

of the intermediate liquid withdrawal (W,,,) and

liquid feed (WV,,) in the H,S-CO,-NaOH absorp

tion column

W (kmol/h)

XHlS

xcol

hOH

%w-IS

%&go,

T

(K)

Stream Wwll Stream IV,,,

1500

2300

0.123 x lo-

0.0

0.0

0.0

0.183 x lo-

0.4529 x IO-

0.602 x 10-J

0.0

0.710 x lo-*

0.0

314.63

313.15

Table 7. Computed results for the H -CD-NaOH absorption

column

L (kmol/h)

F (kmol/h)

YH2.s

Y,Z

+s

xcol

+&OH

+WiS

XN.EO,

P, b)

T (K)

A ; (m2/m)

IC0.u2skmollm2 h b)

ko.,,, (kmol/m h b)

k,n,, (m/h)

k,, co1 (m/h)

hF (m)

el.

Haco2

Top

Bottom

column

column

2510 3314.6

5792.2 5800

0.103 x 10-r

0.792 x 10-s

0.132 x 10-s

0.551 x lo-

0.0 0.903 x 10-s

0.0 0.0

0.1842 x 10-l

0.551 x 10-Z

0.0

0.138 x 1O-2

0.0 0.930 x 10-a

12.569 12.79

314.11 313.78

525.7 523.1

0.401 0.381

0.392 0.378

0.390 0.313

0.429 0.410

0.159 0.170

0.225 0.226

76.1 39.3

No. of iterations: 8

CPU time used: 242 s

Flow rote (kmol/h)

0

2500

5000

b

0. 1 x10 1

I

I

x, mole fraction

5

-

NoOH

10

25

Bottom

0

0.1 x10-3

0.5 x10-3

01 x10-z

02x10-4

I

*

F

y, mole fraction

Fig. 6. Variations of the mole fractions of the different components in the gas and liquid phases and of

the gas and liquid flow rates along the H,S-CO,-NaOH absorption column.


10/11

514

L. E LEYEand G. F. FROMENT

TOP 12 0

,

1

Total pressure (b)

12 5 130

30

ottom >\:

3,0

315 320

5

0): 15

T

10

Temp mtermed

is

laquld feed

i

4

f;

a

20

T

25

Temperature

1

K)

Fig. 7. H -CO, absorption in NaOH. Temperatures and

pressures along the column.

solution, is given by Hikita et al. [16] and Pinsent et

al. [18].

The simultaneous absorption of H,S and CO2 in

the NaOH solution is accompanied by a Type 1B

system of parallel reactions.

The diffusion coefficients of H,S and CO, in Hz0

were determined from experimental data [9, 191.

These coefficients were corrected for the composition

of the liquid using the Stokes-Einstein relationship.

For the determination of the diffusion coefficients of

the ionic species the correlation of Nernst-Haskell

[20] was used.

The solubilities of H,S and CO, in H,O were

computed from data by Edwards et al. [17]. They

were corrected for the ionic strength of the solution.

Again, the standard correlations (see Table 2) in

the program were used for the determination of the

mass-transfer coefficients and plate characteristics.

The initial estimates of temperature and pressure

on each tray were 313.15 K and 12.8 b. The mole

fractions of H,S and CO2 at the top of the column

were estimated to be 1 x lOen and 1 x 10m6. The

convergence tolerance was set equal to lo-. The

computed results are summarized in Tables 6 and 7.

The reaction with CO2 is in the very fast regime.

The variations of the mole fractions of the different

components in the gas and liquid phases and of the

gas and liquid flow rates along the column are shown

in Fig. 6. Fig. 7 shows the computed temperatures

and pressures along the column.

NOMENCLATURE

A, = Absorbed component j

a = Stoichiometric coefficient

A, = Gas-liquid interfacial area per unit liquid

A: = Gas-liquid interfacial area per m3 froth on the

volume (m2/m3)

plate (m2/m3)

a; = Interfacial area per unit of packed column

(mlm)

C, = Molar concentration of component A

(kmol/m)

C, = Total molar concentration in the liquid on

plate k (kmol/m)

cP= Specific heat (kJ/kmol K)

D = Molecular diffusivity (m2/h)

dk = Column diameter (m)

F =

Total molar gas flow (kmol/h)

F, = Enhancement factor

Fk = Molar gas flow rate leaving plate k (kmol/h)

Hj =

Henrys coefficient for absorbed component j

(b m3/kmol)

Ha, Ha = Hatta number, modified Hatta number

-AH, = Heat of absorption of component j (kJ/kmol)

-AH? =

Heat of reaction of reaction i (kJ/kmol)

& = Froth height on plate (m) .

Ki =

Equilibrium constant of reaction j

k

kj = Reaction-rate coefficient of reaction j

o, A, = Gas-side

mass-transfer

coefficient for

k

absorbed component A, (kmol/m2 h b)

, *. =

Liquid-side mass-transfer coefficient of

-_I absorbed component A, (m/h)

L = Volumetric liquid flow rate (m3/h)

L = Molar liquid kow rate (kmoljhj

L& = Molar flow rate of liquid feed to column

(kmol/h)

L; = Molar flow rate of liquid stream leaving plate

k (kmol/h)

mj,, = Reaction order with respect to component j

in reaction I

h4 = Molecular weight (kg/kmol)

m = Reaction order

Njl,-0

= Interfacial flux of component j per unit

gas-liquid interfacial area (kmol/m2 h)

n, = Number of absorbing components

n, = Number of reactions in the liquid phase

no = Total number of components in gas phase

nL = Total number of components in liquid phase

nM = Number of gas-phase components involved in

moderately fast reactions

np = Number of reaction products in the liquid

phase

na = Number of reactants in liquid phase

n, = Number of gas-phase components involved in

very slow reactions

nv = Number of gas-phase components involved in

very fast reactions

p = Partial pressure (b)

pt =

Total pressure (b)

P, = Product j

r = Reaction rate (kmol/m h)

Rj = Liquid-phase reactant j

Q = Total heat of absorption of component j on

plate k (kJ/h)

QF = ;f;;;,heat of cooling taken away from plate

QTk = T )heat of reaction of reaction j on plate k

Tk =

Temperature on plate

k

(K)

T,, = Temperature of intermediate gas feed to plate

k (K)

T,, =

Temperature of intermediate liquid feed to

plate k (K)

V,, = Flow rate of intermediate gas withdrawal

from plate k (kmol/h)

X, = Mole fraction of component j in the liquid

bulk

V,, = Flow rate of intermediate gas feed to plate k

(kmol/h)

.x~,~ Mole fraction of component j in the bulk of

the liquid stream leaving plate k

x~,,~ = Mole fraction of component j in the inter-

mediate liquid feed to plate k

y = Coordinate perpendicular to the gas-liquid

interface (m)


11/11

Simulation of absorption and reaction in columns-II

515

yr, = Location of reaction front of reaction j (m)

yo = Gas-film thickness (m)

y, = Mole fraction of component j in the bulk of

the gas phase

yik = Mole fraction of component j in the bulk of

the gas stream leaving plate k

y, = Liquid-film thickness (m)

J+,,~ = Molar fraction of component j in the inter-

mediate gas feed to plate k

z = Axial coordinate in the froth on the plate (m)

Greek symbols

eL = Liquid hold-up of packing or fraction of

liquid in the froth

pL = Liquid density (kg/m3)

R = Cross-section of tower (m2)

R, =

Active area of plate (m)

Subscripts

A, = With respect to absorbed component j

b = In the bulk of the gas or liquid phase

Cj = With respect to the consecutive component j

G=Gas

i = At gas-liquid interface

j = Co&one& index

k = Plate number

14.

5.

6.

7.

8.

9.

10.

11.

12.

13.

L = Liquid

Pj= With respect to product j

RI= With respect to reactant j

15.

16,

Superscripts

G = In gas phase

L = In liquid phase

in = At inlet

out = At outlet

eq = Equilibrium value

abs = Absorption

R = Reaction

C = Cooling

17.

18.

19.

20.

REFERENCES

L. De Leye and G. F. Froment, Comput. them. Engng

10, 493 (1986).

K. Onda, E. Sada, T. Kobayashi and M. Fujine, Chem.

Engng Sci.

25, 1023 (1970).

J. H. Wegstein, Communs Ass. comput. M ach. 1, 9

(1958).

A. W. Westerberg, H. P. Hutchison, R. L. Motard and

P. Winter, Process F lowsheeting, pp. 54-65. Cambridge

Univ. Press, Cambs. (1979).

C. Ouwerkerk, Hydrocarbon Process. 57 4), 89 1978).

A. E. Cornelissen, Trans. I nst. them. Engrs 58, 242

1980).

Handbook of Physical Constants, revised edn; Geol. Sot.

Am. Mem. 97, Sect.18 (1966).

R. L. Kent and B. Eisenberg, Hydrocarbon Process.

55 2), 87 1976).

W. J. Thomas and I. A. Furzer, Chem. Engng Sci. 17,

115 1962).

Y. M. Tseng and A. R. Thompson, J. them. Engng Data

9(2), 264 (l-964).

J. A. Riddick and W. B. Bunger, Organic Solvents, 3rd

edn. Wiley Interscience, New York (1970).

J. Stichlmair, Grundlagen der Dimensioni erung des

GaslFlussiakeit-Kontaktapparates.

Bodenkolonne.

Verlag Chemie, Weinheim-(1978).

Glitsch Inc.. Ballast Tray Design Manual, Bull. NO.

4900. Dallas, Tex. (1978): -

G. Astarita, Mass Transfer with Chemical Reaction.

Elsevier, Amsterdam (1967).

P. V. Danckwerts, Gas-Liquid Reactions. McGraw-

Hill, New York (1970).

H. Hikita, S. Asai and T. Takatsuka, Chem. Engng J.

11, 131 (1976).

T. J. Edwards, J. Newman and J. M. Prausnitx, AIChE

JI 21(2), 248 (1977).

B. R. W. Pinsent, L. Pearson and F. J. W. Roughton,

Trans. Farad. Sot. 52, 1512 1956).

R. H. Perrv and C. H. Chilton, Chemical Engineers

Handbook, Chap. 3, 5th edn. McGraw-Hill, New York

(1973).

R. C. Reid, J. M. Prausnitz and T. K. Sherwood, The

Properties of Gases and L iqui ds. McGraw-Hill, New

York (1977).

Documents

Rigorous simulation and design Plate Column.pdf