H 04 OilCharacterization

Oil Characterization

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Oil Characterization

1 © 2004 AspenTech. All Rights Reserved 1.3.4 Oil Characterization.pdf 

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Oil Characterizati Characterization on

Workshop The petroleum characterization method in HYSYS will convert laboratory analyses of condensates, crude oils, petroleum cuts and coaltar liquids into a series of discrete hypothetical components. These petroleum hypocomponents provide provide the basis for the property package to predict the remaining thermodynamic and transport properties necessary for fluid modelling. HYSYS will produce a complete set of physical and critical properties for the petroleum hypocomponents with a minimal amount of  information. However, However, the more information you can supply about the fluid, the more accurate these properties will be, and the better HYSYS  will predict the fluid's actual behaviour. In this example, the Oil Characterization option in HYSYS is used to model a crude oil. The crude is the feed stock to a Pre-heat Train, followed by the Atmospheric Crude Column, which will be modelled in a subsequent module.

Learning Objectives Once you have completed, you will be able to use the Oil Characterization option in HYSYS.

Prerequisites Before beginning this module you need to understand the basics of the Fluid Package (refer to Getting Started).

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Oil Characterization

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Building the Simulation Before you can start the actual characterization process, you will first learn how to modify the Unit Set which is very useful in a Refinery. Refinery. For 3 example, you can work with barrels/day instead of m /h. 1.

Start tart a new new case case..

Modifying the Unit Set HYSYS allows you to have your own set of units. For this case, the unit for Standard Density will be API_60 instead of kg/m3 as in the SI. 2.

From the Tools menu select Preferences, and go to the  Variables tab.

3.

Select th the SI unit set as the default.

4. You cannot cannot edit edit the default default set, but you you can make a copy copy of of it by  by  clicking the Clone button. 5. Rena Rename me the the clon cloned ed un unit it set set to to Refinery . 6. Mo Move ve the the cursor cursor to to the Stan Standar dard d Density Density cell cell.. 7.

Select API_60 from the drop-down list. Figure 1

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8. Close Close the the Pre Prefer feren ence cess view view..

Defining the Simulation Basis 1. 2.

On the Fluid Packages tab, click the Import button and select the fluid package you exported e xported in Module 1: Refinery. Refinery. Highlight th the Refinery Package and click the  View button. We are going to delete the components we do not need: C6 and C7+.

3.

Go to the Components tab and highlight n-Hexane and click the Remove button.

4.

Do the the sam same e wi with the the C7+.

5. Close Close this this wind window ow to retur return n to to the the Basis Environment . 6. Basis Environment icon

Go to the Oil Manager tab and click the Enter Oil Environment button. You You could also click the Oil Environment icon on the toolbar. toolbar. The Oil Characterization view displays.

Oil Characterization Oil Environment icon

The petroleum characterization in HYSYS accepts different types of  information about the oil. The more information you can supply about  your sample, the more accurate the representation will be. There are three steps involved in characterizing any oil in HYSYS: 1. Char Charac acte teri rize ze the the Ass Assay  ay  2. Gene Genera rate te Hypoc Hypocom ompo pone nent ntss 3. Insta Install ll the the Oil Oil in in the the Flow Flowsh shee eett The minimum amount of information that HYSYS requires to characterize an oil is:  •

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a labo labora rato tory ry dis disti till llat atio ion n curv curve e. at least least one one of tthe he ffoll ollowi owing ng b bulk ulk prop properti erties: es: Mole Molecul cular ar Weig Weight, ht, Density, or Watson K Factor.

Oil Characterization

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Characterize the Assay The assay contains all of the petroleum laboratory data, boiling point curves, light ends, property curves and bulk properties. HYSYS uses the supplied Assay data to generate internal TBP, molecular weight, density  and viscosity curves, referred to as Working Curves.

Assay Types  Accurate volatility characteristics are vital when representing a petroleum fluid in your process simulation. HYSYS accepts the following  standard laboratory analytical assay procedures. •

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•

For all the distillation curves, you are required to enter at least five data points.

•

• • •

True Boiling Point (TBP). (TBP) . Performed using a multi-stage batch fractionation apparatus operated at relatively high reflux ratios. TBP distillations conducted at atmospheric or vacuum conditions are accepted by the characterization. ASTM D86. D86. Distillation employing batch fractionation but conducted using non-refluxed Engler flasks. Generally used for light to medium petroleum fluids. HYSYS can correct for barometric pressure or cracking effects. You must provide the data on a liquid volume basis. D1160 distillation. distillation. Distillation employing batch fractionation but conducted using non-refluxed Engler flasks. Generally used for heavier petroleum fluids. Curves can be given at atmospheric pressure or corrected for vacuum conditions. You must provide the data on a liquid volume basis. D86_D1160. D86_D1160. This is a combination of the D86/D1160 distillation data types. You can correct for thermal cracking and enable vacuum distillation for sub-atmospheric conditions. You must provide data on a liquid volume basis. ASTM D2887. D2887. Simulated distillation analysis from chromatographic chromatographic data. Reported only on a weight percent basis at atmospheric conditions. Equilibrium Flash Vaporization (EFV). (EFV) . Involves a series of experiments at constant atmospheric pressure, where the total vapour is in equilibrium with the unvaporized liquid. Chromatographic Analysis. Analysis. A gas chromatograph analysis of a small sample of completely vaporized oil, analysed for paraffin, aromatic and naphthenic hydrocarbon groups from C6 to C30. Chromatographic Chromatographic analyses may be entered on a mole, mass or liquid volume basis.

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Light Ends Light Ends are defined as pure components with low boiling points. Components in the boiling range of C2 to n-C5 are most commonly of  interest. HYSYS provides three options to account for Light Ends: • •

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Ignore. Ignore. HYSYS will characterize the Light Ends portion of your sample as hypocomponents. This is the least accurate method and as such, is not recommended. Auto Calculate. Calculate. Select this when you do not have a separate Light Ends analysis but you want the low boiling portion of your assay represented by pure components. HYSYS will only use the pure components you have selected in the Fluid Package. Input Composition. Composition. Select this when you have a separate Light Ends assay and your petroleum assay was prepared with the Light Ends in the sample. HYSYS will provide a form listing the pure components you selected in the Fluid Package. Package. This is the most accurate method of representation.

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Bulk Properties Bulk Properties for the sample may also be supplied. The bulk  properties are optional if a distillation curve cur ve or chromatograph have been supplied. • • • • • •

Molecular Weight. Weight. This is the Molecular Weight of the bulk sample. It must be greater than 16. Mass Density. Density. The mass density must be between 250 and 2000 kg/m3. Watson (UOP) K Factor. Factor. This must be between 8 and 15. Bulk Viscosity. Viscosity. Given at two reference temperatures, typically 37.7°C and 98.89°C (100°F and 210°F). The units units for density density can can be mass density density,, API API or specific specific gravi gravity ty,, chosen from the drop down list in the Edit Bar The Wats Watson on K Fact Factor or is an appro approxim ximate ate inde index x of paraff paraffini inicit city y.

Physical Property Curves HYSYS accepts different types of physical property curves • • •

Molec olecul ula ar Weigh eightt Curv urve Density Cur ve Viscosity Cur ve ve

Physical property analyses are normally reported from the laboratory  using one of the following two conventions. • •

An Ind Indepe epende ndent nt assa assay y basis basis,, where where a comm common on set set of of assa assay y fractions is NOT used for both the distillation curve and the physical property curve. A Depe Depende ndent nt assa assay y basis basis,, where where a comm common on set set of of assa assay y fractions is utilized for both the distillation curve and the physical property curve.

 As you supply more information to HYSYS, the accuracy of the Petroleum Characterization increases. increases. Supplying any or all of the bulk  molecular weight, bulk density, or bulk Watson K factor will increase the accuracy of your pseudo component properties. You can also supply  laboratory curves for molecular weight, density, and/or viscosity, viscosity, which  will increase the accuracy further. further.

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Adding Assay Data On the Assay  tab of the Oil Characterization view, select the  Add button to display the Input Data tab of the Assay view. view. 2. In the the Name Name cell, cell, chang change e the assay assay name name to Crude. 1.

3. We will use use three three types types of data data here. here. Use Use the drop-d drop-down own lists to select the following in the Assay Definition group box. For this option...

Select...

Bulk Properties

Used

Assay Data Type

TBP

Light Ends

Input Composition

4.

Select th the Distillation radio button in the Input Data group box.

5.

Select tth he Assay Basis as Liquid Volume (use the drop-down menu). Click the Edit Assay  button; this will allow you to enter the assay  information below.

Assay Percent

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Temperature

0.0000

-12°C -12°C (10.4° (10 .4°F) F)

4.000

32°C (90°F)

9.000

74°C (165°F)

14.00

116°C (241°F)

20.00

154°C (310°F)

30.00

224°C (435°F)

40.00

273°C (523°F)

50.00

327°C (620°F)

60.00

393°C (740°F)

70.00

450°C (842°F)

76.00

490°C (914°F)

80.00

516°C (961°F)

Oil Characterization

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Select th the Light Ends radio button and enter the data given below:

Light Ends

Composition

Methane

0.0065

Ethane

0.0225

Propane

0.3200

i-Butane

0.2400

n-Butane

1.7500

i-Pentane

1.6500

n-Pentane

2.2500

 You  You need to enter the light components in the Fluid Package for them t hem to be available to the Oil Manager. Manager. 7.

Bulk information . Select th the Bulk Props radio button to enter the Bulk information

8. In the Standar Standard d Density Density cell, enter an API API Gravity Gravity of 29 for the crude. 9. Once Once you have have enter entered ed all all of the the data, data, click click the the Calculate button. The status message at the bottom of the Assay view will display   Assay Was Calculated. Once the Assay is calculated, the working curves are displayed on the Plots and Working tabs. The working curves are regressed and extrapolated from the Assay input. From the user-supplied data, HYSYS generates curves for NBP, molecular weight, mass density, and viscosity. These working curves are used in determining the properties of the hypocomponents generated in the Blend step. 10. Close the view and return to the Oil Characterization view. view. You You should still be on the  Assay  tab of the view. Notice that all of the buttons on the view are now accessible.

Hypocomponent Generation/Blending Generation/Blending the Oil The Cut/Blend characterization in HYSYS splits the internal working  curves for one or more assays into hypocomponents. The Blend tab of  the Oil Characterization view provides two functions, Cutting the Oil into Hypocomponents and Blending two or more Assays into one set of  hypocomponents.

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Cut Ranges  You  You have three choices for the Cut Option Selection: •

Auto Cut. Cut. HYSYS cuts the assay based on internal values

Range

Cuts

37.7 37.78 8 - 425° 425°C (10 (100 0 - 797° 797°F)

28 (4 per per 37. 37.78 78° °C/10 C/100° 0°F)

425 425 - 650° 650°C(79 C(797 7 - 1202 1202° °F)

8 (2 per per 37. 37.78 78° °C/10 C/100° 0°F)

650 650 - 871° 871°C(12 C(1202 02 - 160 1600° 0°F)

4 ((1 1 per per 37.7 37.78° 8°C/10 C/100° 0°F)

•

User Points. Points. You specify the number of hypocomponents required. HYSYS proportions the cuts according to an internal weighting scheme.

Cutpoint Range

Internal Weighting

IBP - 42 425°C(IBP - 797°F)

4 per 37.78° 78°C/100°F

425 425 - 650° 650°C(797 (797 - 120 1202° 2°F)

2 per per 37. 37.78° 78°C/100° 100°F

650° 650°C - FBP FBP(1 (120 202° 2°F - FBP FBP))

1 per per 37. 37.78 78° °C/10 C/100° 0°F

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User Ranges. Ranges. You specify the boiling point ranges and the number of cuts per range.

Cutting the Assay Once the Assay has been calculated, you can cut the Assay into individual hypocomponents. 1.

Move to the Cut/Blend tab of the Oil Characterization view. Select the Add button to create a new Blend.

2.

In the Name cell, change the name from the default, Blend-1 to Crude.

 Available Assays A ssays (there should only be one), select 3. From rom the the list list of  Available Crude and click the  Add button. This will add the Assay to the Oil Flow Information table and a Blend (Cut) will automatically be calculated. The Blend is calculated using the default Cut Option,  Auto Cut.

4. Inst Instea ead d of usin using g the the defa defaul ultt Auto Cut option, change the Cut Option Selection to User Ranges. Select 20 cuts for a Cut Point temperature of 425°C (800°F), 5 cuts at 620°C (1150°F), and 2 cuts for the range up to 720°C (1328°F).

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Oil Characterization

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Click th the Submit button to accept the ranges and cut the oil. Figure 2

The results of the calculation can be viewed on the Tables tab of the Blend view. Go to the composite plot tab to verify the calculated curve matches the input one.

Installing the Oil in the Flowsheet The final step of the characterization is to transfer the hypocomponent information into the Flowsheet. 1. Close Close the the Blend Blend view view, and and mov move e to the Install Oil tab of the Oil Characterization view. view. 2. The Bl Blend, Crude, appears in the Oil Install Information group. group.

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3. In the the Str Stream eam Na Name me colu column mn,, enter enter the the name name Raw Crude to which the oil composition will be transferred. Figure 3

HYSYS will assign the composition of your calculated Oil and Light Ends into this stream, completing the characterization process. Return to the Basis Environment by clicking the Return to Basis Environment button.  When you return to the Basis Environment, the hypocomponents that  you have generated in the Oil Characterization are placed in the current fluid package. You You can view the fluid package and examine the individual hypothetical components which make up your oil. Hypotheticals are named according to the blend group to which they  belong and to their normal boiling point. For example, a component named NBP[0]118* was generated by the first blend in the case and has a boiling point of 118°F.

Save your case!

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 Answer the following questions: What are the two lowest boiling points for the hypocomponents? _________ What are the Ideal Liquid Density for those hypocomponents? ___________

Exploring the Simulation Exercise 1 HYSYS allows you to introduce a Sulphur Curve as a User Property. Property. This is done in the Oil Environment. Go to the User Property tab of the Oil Characterization and click the Add button. All the default options will be used in this case except for the Mixing Basis fields. Sulphur is quoted on a weight basis, so select Mass Fraction from the drop-down list. Click on the Edit component user property values button located at the bottom of the User Property view. view. The User Property Value appears. Enter a value of 0 in the User Property Value cell for all the light products (C1, C2, C3, i-C4, n-C4, i-C5, and n-C5). Click  Submit when finished.  You  You can also provide a descriptive Name for the property, property, such as Sulphur.

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Now that you have created it, you can return to the Assay Property view, view, User Curves tab, and add it to your Assay. The view displayed should look like this: Figure 4

Click the Edit button to enter the sulphur curve data. Assay (%)

Sulphur Value

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0.083

27

0.212

36

1.122

52

2.786

64

2.806

72

3.481

85

4.984

90

5.646

Click the Calculate button on the Assay view. You can now print the new  plots, especially that of the sulphur, to analyse them. Tip: Go to the Blend tab, and then to the Composite Plot. Plot.

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Save your case!

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Exploring the Simulation Exercise 2: Heavy Oils Characterization Characterization Heavy oils are traditionally defined as those whose specific gravity is lower than 20 API and viscosity is higher than 1000 cP. In the past, commercialization and transportation of heavy oils has not been ver y  profitable, but recently developed technologies are now making them much more attractive. One of the inherent practical difficulties of heavy oils is their high viscosities. Transportation Transportation of heavy oil for instance is difficult due to the high energy losses and pressure drops generated by the large friction effects.

Another way to transport heavy oil would be to operate at elevated temperatures however this can have adverse effects like increasing the solubility of the water in the crude oil, as well, some materials may lose mechanical strength at elevated temperatures.

In order to facilitate their transport, an attractive option could be to mix  the heavy oil with a lighter one––often termed a “diluent” “diluent”. This way the resulting mixture’ mixture’s density and viscosity could become much more appropriate for the transportation and further commercialisation of the oil. If we have a good representation of both the heavy oil and the diluent(s) in our simulation it is possible to model different scenarios and quickly  evaluate them. HYSYS can thus be an invaluable tool in helping us to make the best decision! In this example, we will use our existing crude from the previous exercise (Raw Crude) as a diluent and mix it with a heavy oil of 15 API, in order to see what the new calculated properties of the resulting mixture are. In characterizing the heavy heavy oil, we have its bulk density (15 API), a TBP curve, and will also use viscosity curves provided by the lab.

Remember: API density is inversely proportional to Specific Gravity so the lower it is, the higher the density value.

  API API gravity gravity ( degrees degrees)

141.5 =

- –

Specific Gravity at 

131.5

60

---

60 F 

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How HYSYS Calculates Oil Viscosity

Adapted from HYSYS 3.2 Simulation Basis Guide Appendix A.5 Physical and Transport Properties.

HYSYS automatically selects the model best suited for predicting the phase viscosities of the system under study. study. The model selected is from one of the three available in HYSYS: a modification of the NBS method (Ely and Hanley) for vapours and light hydrocarbons, Twu's Twu's model for fo r heavy hydrocarbons, or a modification of the Letsou-Stiel correlation for non-ideal liquids.  When supplied viscosity assays are used to regress the parameters used in the viscosity correlations. correlations. The parameters (known as shape factors) are specific to each hypothetical component.  Average  Average crude oils (including ( including water and acid gases) gase s) are well represented by the modified NBS method, however the Twu Twu method is found to do a better job of predicting the viscosities of heavier hydrocarbons (NBP>155oF). The method used for the mixed oil stream will depend on its composition (NBP).

Exercise For a proper characterization of a heavy oil it is crucial to know its bulk  density and its viscosity at two different temperatures; providing providing the  Watson  Watson K factor facto r is also recommended. Physical Property curves can improve the accuracy of your oil characterization, particularly when combined with bulk property data. The hypothetical component physical properties will be correlated so that the property curves are matched. If the user does not supply  property curves HYSYS Oil Manager must generate its own internal curves for density and viscosity using API recommended correlations and known bulk property data.

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Physical Property Curves Physical property curves are normally reported from the laboratory  using one of the following two conventions: Adapted from HYSYS 3.2 Simulation Basis Guide Characterization Assays

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An Inde Indepen penden dentt assay assay basi basis, s, w wher here e diff differe erent nt sampl sample e assay assays s are done––one for the distillation curve, and a different one for each of the physical property curves. The assay fractions will likely be different for each curve. A Depe Depende ndent nt assa assay y basis basis,, where where a comm common on set set of of assa assay y fractions is used for both the distillation curve and the physical property curves.

Calculated hypothetical component physical properties are average values for the given boiling point range, and hence are midpoint values. Distillation data reports the temperature when the last drop of liquid boils off for a given assay range and therefore distillation is an endpoint property. property. Since all dependent input property curves are reported on the same endpoint basis as the distillation curve, they are converted by  HYSYS to a midpoint basis. Independent property curves are not altered in any manner as they are already defined on a midpoint basis.  As with distillation curves, there is no limit to the number of data points  you provide. The order in which you input the points is not important, as HYSYS sorts the input data. A minimum of five data points is required to define a property curve in HYSYS. It is not necessary that each property curve point have a corresponding distillation value. Using bulk properties. If a bulk molecular weight or mass de nsity is going to be supplied, then the corresponding Molecular Weight Weight or Density working curve generated from your input is smoothed to ensure a match with the bulk property. If you do not enter bulk properties, then they are calculated from the unsmoothed working curves. 1. En Enter ter the Assay Assay data data for the Heavy Heavy Oil. Oil. From the existing case, go to the Oil Environment and add a new Assay   with the following data: • • • •

S. Joaquin Crude Stand tandar ard d de densit nsity y 15 15.3 API API Viscosity @ 70 F 2040 c cS St Viscosity @ 100 F 337 c cS St

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TBP

T (C)

%LV %L V 0.446

70

0.854

100

2.444

150

4.824

190

10.004

235

15.814

280

24.904

343

65.304

565

Kinematic Viscosity @ 100 F

Kinematic Viscosity @ 210 F

0.408

0.447

0.446

0.326

1.59

0.631

0.854

0.343

2.38

1.03

2.444

0.430

5.18

1.85

4.824

0.592

5.81

3.89

10.004

0.860

9.09

9.01

15.814

1.340

4 0 .4

144

24.904

2.250

65.304

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2. Creat Create e a new blend blend for the heavy heavy oil. oil. There are two methods for blending oils in HYSYS: • •

If the the 2 oils oils are blend blended ed with within in Oil Oil Mana Manager ger only only 1 set set of hypo hypo components is created, representing the blended mixture. Howe Ho weve verr, when when diffe differen rentt crudes crudes are comi coming ng from from very very diff differe erent nt sources, it is a good idea to blend them separately (creating two different blends) and mix them in the Simulation Environment instead. The reason for this is that in blending the crudes within Oil Manager, HYSYS must generate a set of common hypocomponents hypocomponents that can well predict the properties both of the source oils––not necessarily a reasonable expectation expectation for very different crudes.

The S Joaquin Crude in this case differs greatly from the "Raw Crude" we created earlier in this module (both in NBP and in physical properties). For this reason the user is encouraged to create another blend, instead of creating a common set of hypocomponents from the two crudes.

Optional Exercise Test this out yourself––after completing this exercise in full, create a new  blend in the Oil Manager that is a mix of both assays. Then compare the properties of this blend with the those of the mixed stream created in Step #6 below.

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3. Validat alidate e the generat generated ed pseudo/ pseudo/hyp hypo o compone components nts::  After you've created the blend, go to the Composite Plot tab and compare the generated curves with the input data. (You can change the scale of the graph in order to have a better view of the viscosity by right clicking on the plot). 4.

Install th the S Joaquin oil in the PFD. Go to the Install tab of the Oil Manager and enter the stream name "S Joaquin".

5. Enter Enter the Simul Simulation ation Environme Environment nt and and view the the S Joaquin Joaquin stream. stream. What is the current API density of the SJoaquin stream at1 bar and 60 F?  ____________________________________________________________________

 You  You can see the importance of using the bulk density in the characterization of the oil: go back to the Oil Environment and delete the value that is entered there. Go back to the Simulation Environment. Environment. What is the calculated SJoaquin density? _______________________________  And the Raw Crude one? ______________________________________________

Restore the value 15 API for the bulk density of the heavy oil assay in the Oil Environment before continuing. 6. Mix Mix the the Hea Heavy vy Oil Oil and and Dil Dilue uent nt::  As mentioned, to make a crude lighter for transporting by pipeline, Heavy Oil is mixed with a diluent such as naphtha or a lighter crude oil.  We  We want to transport 600000 Kg/h of San Joaquin Crude but in this example our transportation system will only accept crudes star ting from 21 API. We have studied several scenarios and the best one seems to be mixing the heavy Oil with another one, the Raw Crude. What is the minimum quantity of Raw Crude we need to add? (Hint: Use an   Adjust) _____________________________________________________________ Is the viscosity of the mixed stream better for transportation now? _______

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Save this case for your records and load the one we created prior to the Exploring the Simulation exercise. The rest of the course materials are built using the lighter "Raw Crude" stream as the oil source.

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