XYLENES PURIFICATION USING A SUPER-FRACTIONATOR

Description

This example describes a section of a complex xylene separation plant with the aim to show results of the simulation of a column of over 300 theoretical trays.

Plant feed stream S1 is at 50°C and 3 bar, its composition is defined as follows:

No	Components	Weight flow rate, kg/h
1	ISOHEXANE	0.020
2	BENZENE	0.0
3	TOLUENE	1077.480
4	ETHYLBENZENE	4997.940
5	P-XYLENE	7689.970
6	M-XYLENE	0.0
7	O-XYLENE	5019.990

In this simulation m-xylene is considered already separated by an extraction stage with HF+BF3.

The Formex block separates the small isohexane feed content.

The first column AS503 separates toluene from the other components.

The superfractionator AF901 separates ethylbenzene as overhead product with a minimum molar composition equal to 99.3%. This column has 303 theoretical trays, a total condenser and a reboiler. The feed S6 in inserted over the 256^th tray.

The text file that describes the complete simulation input is presented hereunder.

As usual for hydrocarbon systems, the Soave-Redlich-Kwong (SRK) is used for vapor-liquid equilibrium and the Lee-Kesler (LK) for enthalpy, entropy and density calculations.

Results of the column simulation for the AF901 column are summarized hereunder.

*** UNIT 4 - 'AF901 ' - ' DISTILLATION COLUMN ' ***

--- Feed Streams --- - Product Streams -

from unit 3 - AS503 'S6 ' 'S7 '

'S9 '

1) * OPERATING CONDITIONS *

*** OUTLET LIQUID *** *** OUTLET VAPOR ***

* Tray * Temperature * Pressure * -Molar Rate- -Weight Rate- -Molar Rate- -Weight Rate-

°C bar kmol/h kg/h kmol/h kg/h

CON 183.18 3.10 3225.6 342365. 0.0000 0.00000

1 183.82 3.14 3207.8 340521. 3225.6 342365.

2 183.94 3.15 3208.7 340636. 3238.8 343811.

3 184.06 3.15 3209.5 340737. 3239.7 343926.

. . . . . . . . . . . . . . . . . . .

254 208.15 4.91 3366.3 357397. 3397.4 360704.

255 208.28 4.92 3366.1 357379. 3397.3 360687.

256 208.42 4.92 3596.6 381845. 3397.1 360670.

257 208.50 4.93 3597.3 381924. 3469.5 368355.

258 208.59 4.94 3598.0 382002. 3470.2 368434.

. . . . . . . . . . . . . . . . . . .

302 213.57 5.25 3608.0 383059. 3482.3 369720.

303 213.81 5.25 3606.4 382893. 3480.9 369570.

REB 214.06 5.26 127.06 13489.7 3479.4 369403.

- HEATER/COOLERS -

1 - Condenser -24876.311 Mcal/h

2 - Reboiler 25383.947 Mcal/h

- PRODUCT STREAMS -

Stream 'S7 ', LIQUID draw-off from condenser

Flow rate, molar 31.000 kmol/h - weight 3290.358 kg/h

Stream 'S9 ', LIQUID draw-off from reboiler

Flow rate, molar 127.058 kmol/h - weight 13489.749 kg/h

- FEED STREAMS -

Stream 'S6 ', Feed on tray 256

Flow rate, molar 158.058 kmol/h - weight 16780.110 kg/h

- REFLUX DATA -

Molar rate 3194.580 kmol/h Weight rate 339074.578 kg/h

Ratios with respect to OVERHEAD product(s)

Molar 103.0510 Weight 103.0510

Ratios with respect to TOTAL FEED

Molar 20.2114 Weight 20.2069

2) * PRODUCT STREAMS *

* Stream 'S7 ', LIQUID draw-off from condenser

- Temperature 183.179 °C - Pressure 3.1000 bar

* No * Component * -Molar Rate- -Mol Fr- - Weight Rate- -Wt Fr-

3 TOLUENE 0.065 0.002096 5.988 0.001820

4 ETHYLBENZENE 30.757 0.992156 3265.452 0.992431

5 P-XYLENE 0.178 0.005748 18.918 0.005750

7 O-XYLENE 0.000 0.000000 0.000 0.000000

---------------------------------------------------------------------------------

* TOTAL * 31.000 1.000000 3290.358 1.000000

kmol/h kg/h

* Stream 'S9 ', LIQUID draw-off from reboiler

- Temperature 214.061 °C - Pressure 5.2610 bar

* No * Component * -Molar Rate- -Mol Fr- - Weight Rate- -Wt Fr-

3 TOLUENE 0.000 0.000000 0.000 0.000000

4 ETHYLBENZENE 13.789 0.108527 1464.000 0.108527

5 P-XYLENE 68.398 0.538320 7261.806 0.538320

7 O-XYLENE 44.871 0.353153 4763.942 0.353153

---------------------------------------------------------------------------------

* TOTAL * 127.058 1.000000 13489.749 1.000000

kmol/h kg/h

Generated Keyword Input File

<XPSIM> ...generated by XpsimWin v.1.06 ...

RUN ID=SUFRA CUSTOMER='XYL PROD CO' PROJECT='XYLENES RECOVERY'

DESC XYLENE REVAMPING

DESC COLUMN AS503 and AF-901

DESC ethylbenzene - xylenes separation

DIMENSION INPUT MET PRES=BAR

System Data

CHEMCOMP 2MPT / BNZN / TOLU TOLUENE / EBZN / PXYL P-XYLENE / MXYL +

M-XYLENE / OXYL O-XYLENE / NC9 / 135Z

THERMSET UID=M1

METHODS K=SRK HS=LK CP=LK D=LK TRAN=IDEAL SURT=IDEAL

Flowsheet Data

STREAM=S1 TEMP=50 PRES=3 XBASIS=W

COMP 2MPT:0.02 / BNZN:0 / TOLU:1077.48 / EBZN:4997.94 / PXYL:7689.97 +

/ MXYL:0.0 / OXYL:5019.99 / NC9:0 / 135Z:0

COMPSEP IN S1 OUT S2 S3 UID=FORMEX

OVHD STR=S3 DP=0 DT=0

BTMS STR=S2 DP=0 DT=0

BTMFLOW COMP=2MPT RATIO=0

BTMFLOW COMP=NC9 RATIO=0

OVHFLOW COMP=BNZN,OXYL RATIO=0.05

OVHFLOW COMP=135Z RATIO=0.05

HEATEXCH IN S2 OUT S4 UID=E1

COLD OUT=S4 FEED=S2 TEMP=101 DP=0

COLUMN IN S4 OUT S6 S5 UID=AS503

PARA TRAY=35 CON REB NITER=40

FEED STR=S4 TRAY=13

DRAWOFF STR=S5 TRAY=0 PHASE=LIQ RATE(FIX)=11.5

DRAWOFF STR=S6 TRAY=36 PHASE=LIQ

PROFILE TRAY=0 LIQ=80 TEMP=100 PRES=1.02 / TRAY=1 TEMP=105 PRES=1.07 +

/ TRAY=36 TEMP=158 PRES=1.44

SPEC RRATIO=17

HEAT TRAY=0 VAR

HEAT TRAY=36 VAR

PRINT TRACE=PART STREAM=1 RECOVERY

COLOPT LKEY=TOLU HKEY=EBZN

SPEC RATE(M)=7 OVERHEAD

SPEC FRAC(M)=0.0002 LIGHT BOTTOM

CALC MRMIN=1.01,1.1 POINTS=5

</DISABLE>

COLUMN IN S6 OUT S7 S9 UID=AF901

PARA TRAY=303 CON REB NITER=20

FEED STR=S6 TRAY=256

DRAWOFF STR=S7 TRAY=0 PHASE=LIQ RATE(FIX)=31

DRAWOFF STR=S9 TRAY=304 PHASE=LIQ

PROFILE TRAY=0 LIQ=5000 TEMP=185 / TRAY=304 TEMP=215

HEAT TRAY=0 DUTY(VAR)=0

HEAT TRAY=304 DUTY(VAR)=0

PSPEC PTOP=3.10 TRAY=0 DP=0.04 / TRAY=1 DP=0.007

SPEC RRATIO=82

</DISABLE>

SPEC FRAC(M)=0.993 MINI STR=S7 COMP=EBZN

PRINT TRACE=PART STREAM=1

NAME S9 'AF-901 BOTTOM' / S7 'AF-902 TOP'

END