10. visbreaking unit.pdf
TRANSCRIPT
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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
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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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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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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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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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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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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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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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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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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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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
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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.
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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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