Sanatatea Optima de-a lungul vietii. Vol. 4 Sanatatea adultului, cap. Nutritia
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P14Q03. V4
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Visbreaker Background The purpose of the visbreaker is to take the resid, or pitch, from other units in a refinery and run mild thermal cracking to reduce the viscosity. Visbreakers generally reduce the amount of resid by about 20-30% and produce middle distillate products and light ends. The products are separated in a fractionator after the reactor. A portion of the bottoms is circulated to mix with the fractionator feeds.
Learning Objectives Create a Visbreaker model in Petro-SIM Create and converge a Distop column Add and converge a Recycle Create a case study for the Visbreaker to examine the key input and resulting properties
V4 Rev 1 Oct 2010
Exercise - Visbreaker with Column and Recycle
1. Open up Petro-SIM and select new case prebuilt template. 2. Click on the unit preferences icon RefineryMetric units.
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from the toolbar to access the
and select either RefineryField or
Defining the Feed Stream 1. If not visible, click the PFD palette icon and rename it VB feed.
Add a stream
to the PFD
2. On the Conditions view enter a stream temperature of 280 C (536 F) a pressure of 25 bar_g (363 psig) and a mass flow of 150000 kg/h (330700 lb/h.) 3. Select the Select Assay button Plant Data
and select the option Synthesize from
4. Add the properties from the table below and select OK. Fill in the data values from the table. Asphaltenes content [wt %] Conradson carbon content [wt %] Distillation ASTM D1160_1 vol % Distillation ASTM D1160_5 vol % Distillation ASTM D1160_10 vol % Distillation ASTM D1160_30 vol % Distillation ASTM D1160_50 vol % Distillation ASTM D1160_70 vol % Distillation ASTM D1160_90 vol % Specific gravity Sulphur content [wt %] Viscosity (Kinematic)_80 C (176 F) [cSt] Viscosity (Kinematic)_100 C (212 F) [cSt] Wax content [wt %]
5.58 14.1 554 C 560 C 568 C 587 C 639 C 665 C 781 C 1.0035 3.17 2041 cSt 568 cSt 8.9
5.58 14.1 1026 F 1039 F 1058 F 1086 F 1178 F 1227 F 1449 F 1.0035 3.17 2041 cSt 568 cSt 8.9
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Creating the Visbreaker 1. From the option palette first attach a valve to the VB feed stream. Label the product stream Furnace inlet. Do not set a pressure drop or enter an outlet pressure; this will be back-calculated by the Visbreaker.
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2. From the object palette select a visbreaker unit . Add Furnace Inlet as the Feed and enter VB steam as the Injection steam. Enter VB effluent as the Product stream. Enter 53 for the Number of Tubes.
3. Go to the Operating Data tab, Operations page. Check the box next to Simulate Furnace, indicating it will be solved in detail. Enter a Severity of 90%. Enter Outlet Temperature of 430 C (806 F) and Outlet Pressure of 10 bar_g (145 psig). Enter the value, 7.0, for the Max Conversion to set the limit on visbreaker (Note: the default 7.0 is not activated for visbreaker unless an user input is provided)
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4. Return to the Design Tab and go to the Tube Data page. Enter the specifications for the tubes below. Note: you only need to enter tube information into the first tube for each section. # of tubes Soaker Transfer Radiant Cross-over Convection
5. Return to the Operating Data tab and go to the Tube Data page. Select the option Specify tube by tube heat fractions and enter the specifications from the table below: Tube Number 1 3 Visbreaker Page 6
Temperature 430 C 806 F
Pressure 10 bar_g 145 psig
Heat Fraction 0.0 0.7
33 34 53
0.0 0.3 280 C 536 F
16 bar_g 232 psig
6. Go to the Steam Injectors page and enter the following information: Tube Number Mass Percent Temperature Pressure
53 0.5 380 C 28 bar_g
53 0.5 716 F 406 psig
All streams should now be calculated. Check to see that all streams are dark blue. 7. Save your case as VB.ksc Installing the Distillation Column
1. Add a mixer to the VB Effluent stream. This will be used later to connect a recycle stream. Label the product stream Quenched Effluent. 2. Create two new steam feeds for the stripping column. Rename the first stream GO steam and enter the information as shown: Temperature Pressure Composition H20
350 C 28 bar_g 1.0 mole fraction
662 F 400 psig 1.0 mole fraction Visbreaker Page 7
Rename the second stream Bottom steam and enter the information as shown: Temperature Pressure Composition H20
350 C 28 bar_g 1.0 mole fraction
662 F 400 psig 1.0 mole fraction
Note: The stream flow rates will be calculated by DISTOP.
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3. Add a Refluxed Absorber . Set the number of stages to 25. Feed Bottom Steam to the Bottom stage inlet and feed stream Quenched Effluent to stage 20. Enter the remaining stream names: Cond Q, Ovhd Gas, Unstable Naphtha, Overhead Water, and VBU residue.
4. Click the Next button and enter the column pressure profile: Condenser Condenser DeltaP Bottom Stage
2.8 bar_g 0.2 bar 3.4 bar_g
41 psig 5 psi 49 psig
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5. Click the Next button and enter the column temperature profile: Condenser Bottom Stage
40 C 360 C
104 F 680 F
6. Click the Next button and then the Done button. 7. Go to the Side Ops tab. On the Side Strippers page install a sidestripper drawing at stage 10 and returning at stage 7. Change the configuration to Steam Stripped. Select the Steam Feed to be GO steam. Name the product stream VBU Gasoil. Click the Install button.
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8. Go to the Pump Arounds page and add a pumparound drawing at stage 10 and returning at stage 7. Click the Install button.
9. Go to the Parameters tab, Solver page and the change the solver type to Distop.
10. Go to the DISTOP tab. On the Efficiencies page, enter the following values:
VBU Gasoil VBU Residue
Section Efficiency 65 50
Stripper Efficiency 60 60
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11. On the Pumparounds page enter the following information Vol Flow Draw T Return T
80 m3/h 260 C 200 C
12000 BPD 500 F 392 F
12. On the Product Specs page enter the following information for stripping steam ratio, in mass flow of steam per volume flow of stripped product: VBU Gasoil VBU residue
12 kg steam/m3 15 kg steam/m3
0.1 lb steam/gal 0.125 lb steam/gal
13. Enter the following information for TBP Cutpoints (note no entry is required for the gas) Unstable Naphtha SS1_Prod VBU residue
0C 190 C 350 C
32 F 374 F 662 F
14. Click the Run button to converge the column using the DISTOP solver. 15. Save your case.
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Creating the Recycle to the VBU residue stream, and enter as outlet streams VBU 1. Add a Tee Residue product and Residue Quench.
2. Specify the flow of the Residue Quench stream 50 m3/h (7500 BPD) under Conditions in the Worksheet tab
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3. Add a cooler to the Residue Quench and name the outlet stream Cooled Residue and the energy stream Quench-Q.
4. On the Parameters page, enter 0 for the pressure drop 5. Specify an outlet stream temperature of 250 C (482 F). . For the inlet stream select Cooled Residue and 6. Add a recycle stream for the Outlet stream enter Residue Recycle.
7.
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8. Connect Residue Recycle to MIX 100.
The recycle unit operation should converge. 9. Save the case when complete.
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Case Study: Severity vs. Viscosity and COT In this section, we will look at the effect of the visbreaker severity on product properties and coil outlet temperature.
1. Go to the VBU Residue stream, Properties page, and select the Viscosity at 100C Right-click on the value and select Send To… Databook.
2. Go to the Visbreaker unit operation, Operating Data tab. Highlight the input value for Severity. Right-click on this value and select Send To… then select Databook. Go to the section with results, highlight the calculated outlet T value and send that value to the Databook as well. 3. If you closed the view, go to the Tools menu option and select Databook. The Variables tab will display the variables that were sent from the Visbreaker and streams.
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4. Go to the Case Study Tab. Click the Add button to create a Case Study. Check the box under Independent variable for the Severity and Dependent for the other variables.
5. Click the View button. Enter a Severity range of 20-90% with a step size of 10.
6. Run the Case study and examine the results, in both table and graph form.
