10. VISBREAKING UNIT.pdf

7/28/2019 10. VISBREAKING UNIT.pdf

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RA VIS - 00103_A_A - Rev. 1 17/01/2005

Refining-Petrochemicals-Chemicals-Engineering

PDVSA

Process Engineering Applied To Petroleum Refining

Module 8: REFINING PROCESSES (2)

VISBREAKING UNIT PERFORMANCES CHARACTERIZATION

I - UNIT DESCRIPTION................................................................................................................. 1

II - MAIN PROPERTIES OF FEED AND PRODUCTS ................................................................... 2

1 - Feed characteristics .....................................................................................................................22 - Products characteristics ...............................................................................................................2

III - UNIT PERFORMANCES CHARACTERIZATION ..................................................................... 4

1 - Material balance and yields..........................................................................................................42 - Sulphur balance ...........................................................................................................................43 - Energy consumption.....................................................................................................................54 - Conversion ...................................................................................................................................55 - Viscosity reduction .......................................................................................................................66 - Diluant or cutter saving.................................................................................................................77 - Heavy fuel oil reduction................................................................................................................8

8 - Net distillate gain..........................................................................................................................8

IV - REAL EFFECT OF VISBREAKING UNIT IN HEAVY CUTS UPGRADING .............................. 9

V - VISBREAKING CONDITIONS................................................................................................. 10

1 - Residence time...........................................................................................................................102 - Temperature profile ....................................................................................................................11

2005 ENSPM Formation Industrie - IFP Training


2/17

00103_A_A 2005 ENSPM Formation Industrie - IFP Training

1

I - UNIT DESCRIPTION

The simplified scheme of the unit is given in appendix 1, including main control loops and operating

conditions.

After preheating by the atm distillate and the visbroken vacuum resid in six exchangers, the feed is sent to thefeed drum B 101.

The heater F 101 has two radiation cells and one common convection cell.

The feed is divided into four passes and goes across:

the convection section

the radiation heating section

the radiation cracking section

The firing of each radiation section is regulated separately under control of the outlet temperature of eachsection.

A condensate injection is made at the inlet of each pass of the radiation cracking section.

At the outlet of the heater, the feed is directed to the soaker drum B 102. The soaker effluent is expanded andcooled by a distillate injection before entering the atmospheric fractionator C 101.

The temperature of the flash zone of the atmospheric fractionator is regulated by an injection of quench.

The cracked products are fractionated into five cuts: gas, naphtha, gas oil, distillate and atm visbrokenresidue. The naphtha of the overhead drum B 103 is routed most of the time to the naphtha hydrotreater.

On tray 9, the gas oil is withdrawn and steam stripped. The light vacuum gas oil is added to the atm gas oil. Apart of the gas oil blend is used as flushing oil on the equipments and instrumentation of heavy products lines.The non stripped atm distillate is routed with the vacuum gas oil to the catalytic cracking FCC. It feed also theatm fractionator pump around and the quench.

The atmospheric resid, is sent under level control, to the vacuum distillation tower C 102. The non-condensables are incinerated in the heater F 101. The top side stream: light vacuum gas oil is used as refluxto condense the overhead vapors of the vacuum unit. The blend of light vacuum gas oil and atm gas oilconstitutes the visbroken gas oil. The second side stream: vacuum gas oil is blended with the atm distillateand fed to the catalytic cracking FCC. It feeds also the second pumparound of the vacuum distillation tower.

The vacuum resid preheats the feed and generates steam. A stream of cooled vacuum resid is recycled to the

vac tower bottom to control its temperature.

Before being sent to storage, the viscosity of the visbroken vacuum residue is adjusted with a cutter.


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2

II - MAIN PROPERTIES OF FEED AND PRODUCTS

1 - FEED CHARACTERISTICS

Specific gravity 1,017

Viscosity (cSt) at 100C 1850

ASTM distillation (C)

IP

5%

10%

30%

490

530

545

cracking

Conradson Carbon Residue (% wt) 11,9

Asphaltenes (%wt)

C5 insolubles

C7 insolubles

5,9

4,6

Sulphur (%wt) 4,3

2 - PRODUCTS CHARACTERISTICS

Gas analysis

% wt

H2S 15,0

H2 0,3

C1 15,8

C2 19,3

C3 25,2

C4 16,4

C5+ 6,7

CO2+ CO + N2 2,3


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3

Other products main properties

GasolineAtmospheric

gasoilLight vacuum

gasoil

Heavyatmospheric

gasoil

Vacuumdistillate

Vacuumresidue

Specificgravity

0,696 0,807 0,849 0,899 0,920 1,045

ASTMdistillation

(C)

IP

5%

10%

30%

50%

70%

90%

95%FP

24

40

71

92

108

128

130

132

141

157

162

172

192

220

252

262

280

103

148

166

214

258

297

352

> 370

193

294

306

335

360

395

470

505

550

240

295

310

365

400

430

460

475

515

400

485

515

570

cracking

Sulphur (%wt) 0,92 1,4 2,1 2,6 2,9 4,7

Viscosity (cSt)

at 20C

at 50C

at 100C

at 150C

1,7

1,1

3,4

2,0 9,5

3,2

14,7

4,1 1110

91


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4

III - UNIT PERFORMANCES CHARACTERIZATION

1 - MATERIAL BALANCE AND YIELDS

Material balance and yields are given on the following table.

PRODUCTS FLOWRATE (t/h) YiELD (%wt)

Uncondensables

Gas

Overall gas

0,45

2,55

3,0 2

Gasoline 4,65 3,1

Atmospheric gasoil

Light vacuum gasoil

Total gasoil

8,4

2,4

10,8 7,3

Heavy atmospheric gasoil

Vacuum distillate

Total distillate

9,75

15,3

25,05 16,9

Vacuum residue105 70,7

TOTAL 148,5 100,0

FEED 148,5

2 - SULPHUR BALANCE

The sulphur flowrate in feed is 4,3% of the feed flowrate (148,5 t/h): 6,4 t/h

The sulphur flowrate in vacuum residue is 4,7% of the vacuum residue flowrate (105 t/h): 4,94 t/h

So, about 75% of the feed sulphur remains in vacuum residue. Only 25% of the sulphur intake can beremoved by visbroken products desulphurisation.


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5

3 - ENERGY CONSUMPTION

In the operating conditions in appendix 1, consumption or production of fuel, steam and electricity are

the followings:

- fuel consumption in the furnace: 2,5 t/h- steam production: 11,5 t/h

This production is equivalent to a fuel saving of 0,9 t/h

- electricity consumption: 1,6 kWh

This consumption is equivalent to 0,25 t/h of fuel.

As a result, fuel consumption is 2,5 0,9 + 0,25 = 1,85 t/h for a 148,5 t/h intake.

Fuel consumption is 1,25% of the feed, in the same order as for an atmospheric distillation unit.

4 - CONVERSION

Conversion can be defined either as:

- Gas + Gasoline yield

Gasoil and distillates are supposed to be incorporated in heavy fuel oil pool

Gas + Gasoline yield = 5,1 %

- Gas + Gasoline + Gasoil yield

This yield is the yield of 350+ products:

Gas + Gasoline + Gasoil yield = 12,4 %

- Gas + Gasoline + Gasoil + Distillates yield

This yield is the yield of products which can be used as 350+ products or feedstock to upgrading units:

Gas + Gasoline + Gasoil + Distillates yield = 29,3 %


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6

5 - VISCOSITY REDUCTION

Viscosity blending rule

Viscosity of a blend cannot be directly calculated by weighting the viscosities of the bases. It isnecessary to use blending indices (BI) given by formulae or tables as a function of the viscosity of thebases and can be weighted to obtain the blending index of the blend.

A table of blend indices can be found in appendix 2.

Example of use: blending of 50%wt of a 10 cSt viscosity base with 50% wt of a 90 cSt base:

Blending index corresponding to a 10 cSt viscosity base: 23,58Blending index corresponding to a 90 cSt viscosity base: 32,87Blending index of the blend: 50% x 23,58 + 50% x 32,87 = 28,22

To this blending index corresponds a 25,5 cSt value of the viscosity.

Viscosity of the 165+ products

Calculation of viscosity of the 165+ products is given in the following table

ProductFlowrate

(t/h)Viscosity (cSt)

at 100CBlending

IndexFlowrate x BI

Atmospheric gasoil

Light vacuum gasoil

Heavy atmospheric gasoil

Vacuum distillate

Vacuum residue

8,4

2,4

9,75

15,3

105

0,8

0,8

3,2

4,1

1110

0

0

15,73

17,71

39,28

0

0

153,4

271

4124,4

165+ products blend 140,85 75 32,3 4548,8

Viscosity reduction

Viscosity reduction can be expressed by the ratio between feed viscosity and products blend viscosity:

Viscosity ratio =185075

= 24,7

or by the difference between the blending indices of feed and products blend:

BI difference = 40,31 32,3 = 8


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7

6 - DILUANT OR CUTTER SAVING

Diluant saving is the difference between the quantities of diluant necessary to cut to 40 cSt the

viscosities of 100 t of feed on one hand and of the 165+

products on the other hand.

The cutter used is supposed to have a viscosity of 2 cSt at 50C and of 1,05 cSt at 100C. Thecorresponding value of blending index is: 3,91.

The blending index corresponding to 40 cSt is 30,03.

Diluant D1 necessary to cut the viscosity of 100 t feed

Weight Viscosity at 100C Blending Index

Feed

Diluant

100

D1

1850

1,05

40,31

3,91

Blend 100 + D1 40 30,03

The viscosity blending rule gives:

100 x 40,31 + D1 x 3,91 = (100 + D1 ) x 30,03

D1 = 39,4 t

Diluant D2necessary to cut the viscosity of the 165+ products

With 100 t feed, the 165+

products are 94,9 t since the Gas + Gasoline yield is 5,1 % and have a 75cSt viscosity.

Weight Viscosity at 100C Blending Index

165+

products

Diluant

94,9

D2

75

1,05

32,3

3,91

Blend 94,9 + D2 40 30,03

The viscosity blending rule gives:

94,9 x 32,3 + D2 x 3,91 = (94,9 + D2 ) x 30,03

D2 = 8,25 t


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8

Diluant saving

Diluant saving is the difference between D1

and D2.

D1 - D2 = 39,4 8,25 =31,15 t for 100 t feed

7 - HEAVY FUEL OIL REDUCTION

Heavy fuel oil reduction is the difference between the heavy fuel oil production from 100 t of feed and

from the 165+ products.

Heavy fuel oil production from 100 t feed

As shown above, 39,4 t of diluant are necessary to cut the viscosity of 100 t feed. Due to this blending,the heavy fuel oil production from 100 t feed is:

Heavy fuel oil production from 100 t feed = 100 + 39,4 = 139,4 t

Heavy fuel oil production from the165+

products

From 100 t feed, the 165+

products are 94,9 t and the diluant is 8,25 t. The heavy fuel oil production is:

Heavy fuel oil production from the165+

products = 94,9 + 8,25 = 103,15 t

Heavy fuel oil reduction

The heavy fuel oil production from 100 t feed is reduced of:

Heavy fuel oil reduction = 139,4 103,15 = 36,25 t for 100 t feed

The heavy fuel oil reduction is the sum of the 165+ conversion and of the diluant saving.

8 - NET DISTILLATE GAIN

The Net Distillate Gain is the sum of valuable distillates produced by the visbreaking unit.

Liquefied Petroleum Gas

LPG are about 40% of the produced gas. For 100 t feed, LPG are 0,8 t.

Gasoline

Gasoline yield is 3,1 %.

Diluant saving

Diluant saving is 31,15 t for 100 t feed.

Net Distillate Gain

Net Distillate Gain = 0,8 + 3,1 + 31,15 = 35,05 t for 100 t feed


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9

IV - REAL EFFECT OF VISBREAKING UNIT IN HEAVY CUTS UPGRADING

A simpli fied refining scheme of the visbroken products is given in appendix 3. The real effect of the

visbreaking unit in refinery appears as a result of the material balance shown on the following table.

For 100 t feed Without visbreaker With visbreaker Gain

Gas 0 6 6

Gasoline 0 10,1 10,1

Light fuel oil - 39,4 10,7 25 = - 14,3 25,1

Heavy fuel oil 139,4 97,4 42

Total 100 99,2( 0,8 t coke )

These results show:

- gas and gasoline production much higher than visbreaker conversion- light fuel oil production due to diluant saving (major effect in value)- heavy fuel oil reduction (major effect in volume)


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10

V - VISBREAKING CONDITIONS

1 - RESIDENCE TIME

Definition

Residence time definition is:

Residence time (hour) =Equipment volume (m3)

Feed flowrate (m3/h)

The volume flowrate changes along the equipment parts due to volume expansion by heating and tolight cracked products in vapor phase.

By convention residence time is calculated assuming the flowrate for feed at 15C.

Residence time on cold feed

With a specific gravity equal to 1,017 and a148,5 t/h mass flowrate, the volume flowrate is 146 m3/ h.

According to the volumes of equipment parts given in the following table, the residence time in eachpart is calculated.

Volume (m3) Residence time (h) Residence time (mn)

Heater convection zone 7 0,05 3

Heating cell 10,8 0,075 4,5

Cracking cell 10,8 0,075 4,5

Soaker 56 0,383 23

C 101 bottom 6 0,1 3

The major part of the residence time is obviously in the soaker.

Effect of steam or condensate injection

In fact, residence time is reduced by steam or water condensate injection at the entrance of thecracking cell coil.

The water condensate flowrate in the visbreaking unit operating conditions is 400 kg/h.

The steam specific gravity in the average temperature and pressure conditions can be read on thediagram given in appendix 4.

Average operating conditions in cracking coil and soaker:

Pressure: 9 bar abs.Temperature: 450C

Steam specific gravity: 2,6 kg/m3


12/17


11

The steam volume flowrate is 400 / 2,6 = 154 m3/ h.

The steam volume flowrate being slightly equal to the feed volume flowrate, the steam injection leadsto a division of residence time by a factor 2.

2 - TEMPERATURE PROFILE

The temperature profile is given in appendix 5.

On this diagram, the vertical scale graduated in temperature is in fact proportional to chemical reactionvelocity. As a consequence, the area under the temperature profile is proportional to chemical reactionrate. Obviously, chemical reactions begins in the cracking coil of the heater but the major part occurs inthe soaker where temperature decreases due to endothermic effect.


13/17


14/17

2005 ENSPM Formation Industrie - IFP Training

VISCOSITY BLENDING INDEX (weighting by mass fraction)

Appendix 2

V(

cSt)

BI

D

V(

cSt)

BI

D

V(

cSt)

BI

D

V(

cSt)

BI

D

V(

cSt)

BI

D

0.8

0

0.8

5

0.9

0

0.9

5

1.0

0

1.0

5

1.1

0

1.1

5

1.2

0

1.2

5

1.3

0

1.3

5

1.4

0

1.4

5

1.5

0

1.5

5

1.6

0

1.6

5

1.7

0

1.7

5

1.8

0

1.8

5

1.9

0

1.9

5

2.0

0

2.12.22.32.42.52.62.72.82.93.03.13.23.33.43.5

0.0

0

0.9

2

1.7

6

2.5

4

3.2

5

3.9

1

4.5

3

5.1

1

5.6

5

6.1

6

6.6

4

7.0

9

7.5

2

7.9

3

8.3

2

8.6

9

9.0

4

9.3

8

9.7

1

10.0

2

10.3

2

10.6

0

10.8

8

11.1

5

11.4

0

11.8

9

12.3

4

12.7

7

13.1

7

13.5

5

13.9

1

14.2

5

14.5

8

14.8

8

15.1

8

15.4

6

15.7

3

15.9

8

16.2

3

16.4

6

0.9

2

0.8

4

0.7

8

0.7

1

0.6

6

0.6

2

0.5

8

0.5

4

0.5

1

0.4

8

0.4

5

0.4

3

0.4

1

0.3

9

0.3

7

0.3

5

0.3

4

0.3

3

0.3

1

0.3

0

0.2

8

0.2

8

0.2

7

0.2

5

0.4

9

0.4

5

0.4

3

0.4

0

0.3

8

0.3

6

0.3

4

0.3

3

0.3

0

0.3

0

0.2

8

0.2

7

0.2

5

0.2

5

0.2

3

3.53.63.73.83.94.04.24.44.64.85.05.25.45.65.86.06.26.46.66.87.07.58.08.59.09.5

10.0

10

11

12

13

14

15

16

17

18

19

20

16.4

6

16.6

9

16.9

1

17.1

2

17.3

3

17.5

2

17.9

0

18.2

5

18.5

7

18.8

8

19.1

8

19.4

6

19.7

2

19.9

7

20.2

1

20.4

4

20.6

5

20.8

6

21.0

6

21.2

6

21.4

4

21.8

7

22.2

7

22.6

4

22.9

7

23.2

9

23.5

8

23.5

8

24.1

1

24.5

8

25.0

0

25.3

9

25.7

3

26.0

5

26.3

5

26.6

2

26.8

8

27.1

1

0.2

3

0.2

2

0.2

1

0.2

1

0.1

9

0.3

8

0.3

5

0.3

2

0.3

1

0.3

0

0.2

8

0.2

6

0.2

5

0.2

4

0.2

3

0.2

1

0.2

1

0.2

0

0.2

0

0.1

8

0.4

3

0.4

0

0.3

7

0.3

3

0.3

2

0.2

9

0.0

0

0.5

3

0.4

7

0.4

2

0.3

9

0.3

4

0.3

2

0.3

0

0.2

7

0.2

6

0.2

3

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

55

60

65

70

75

80

85

90

95

100

110

120

130

140

150

160

170

180

190

200

27.1

1

27.5

5

27.9

3

28.2

8

28.5

9

28.8

8

29.1

5

29.3

9

29.6

2

29.8

3

30.0

3

30.2

1

30.3

9

30.5

6

30.7

1

30.8

6

31.2

1

31.5

1

31.7

9

32.0

4

32.2

7

32.4

9

32.6

8

32.8

7

33.0

4

33.2

0

33.4

9

33.7

6

34.0

0

34.2

2

34.4

2

34.6

0

34.7

7

34.9

3

35.0

8

35.2

2

0.4

4

0.3

8

0.3

5

0.3

1

0.2

9

0.2

7

0.2

4

0.2

3

0.2

1

0.2

0

0.1

8

0.1

8

0.1

7

0.1

5

0.1

5

0.3

5

0.3

0

0.2

8

0.2

5

0.2

3

0.2

2

0.1

9

0.1

9

0.1

7

0.1

6

0.2

9

0.2

7

0.2

4

0.2

2

0.2

0

0.1

8

0.1

7

0.1

6

0.1

5

0.1

4

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

600

700

800

900

1000

1200

1400

1600

1800

2000

2500

3000

3500

4000

4500

5000

6000

7000

8000

9000

10000

35.2

2

35.4

8

35.7

1

35.9

2

36.1

1

36.2

9

36.4

5

36.6

1

36.7

5

36.8

8

37.0

0

37.1

2

37.2

3

37.3

4

37.4

4

37.5

3

37.9

5

38.3

0

38.5

9

38.8

5

39.0

7

39.4

5

39.7

6

40.0

3

40.2

6

40.4

6

40.8

8

41.2

1

41.4

9

41.7

3

41.9

3

42.1

1

42.4

2

42.6

7

42.8

9

43.0

8

43.2

5

0.2

6

0.2

3

0.2

1

0.1

9

0.1

8

0.1

6

0.1

6

0.1

4

0.1

3

0.1

2

0.1

2

0.1

1

0.1

1

0.1

0

0.0

9

0.4

2

0.3

5

0.2

9

0.2

6

0.2

2

0.3

8

0.3

1

0.2

7

0.2

3

0.2

0

0.4

2

0.3

3

0.2

8

0.2

4

0.2

0

0.1

8

0.3

1

0.2

5

0.2

2

0.1

9

0.1

7

10000

12000

14000

16000

18000

20000

25000

30000

35000

40000

50000

60000

70000

80000

90000

100000

150000

200000

250000

300000

400000

500000

600000

700000

800000

900000

1000000

1500000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

9000000

10000000

15000000

20000000

43.2

5

43.5

3

43.7

7

43.9

7

44.1

5

44.3

0

44.6

3

44.8

9

45.1

0

45.2

9

45.5

9

45.8

3

46.0

3

46.2

1

46.3

6

46.4

9

46.9

9

47.3

4

47.6

0

47.8

2

48.1

4

48.3

9

48.5

9

48.7

6

48.9

0

49.0

3

49.1

4

49.5

6

49.8

5

50.2

5

50.5

3

50.7

4

50.9

1

51.0

6

51.1

8

51.2

9

51.3

8

51.7

4

51.9

9

0.2

8

0.2

4

0.2

0

0.1

8

0.1

5

0.3

3

0.2

6

0.2

1

0.1

9

0.3

0

0.2

4

0.2

0

0.1

8

0.1

5

0.1

3

0.5

0

0.3

5

0.2

6

0.2

2

0.3

2

0.2

5

0.2

0

0.1

7

0.1

4

0.1

3

0.1

1

0.4

2

0.2

9

0.4

0

0.2

8

0.2

1

0.1

7

0.1

5

0.1

2

0.1

1

0.0

9

0.3

6

0.2

5


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10. VISBREAKING UNIT.pdf