1. Aspen Plus does not generate distillation curves for a stream containing 4 pseudo-components. Why?
To generate a distillation curve, a stream must contain at least 5 pseudo-components of non-zero flow to generate distinctive data points at 10%, 30%, 50%, 70, 90%.
2. For streams with significant amount of light components, the calculated Reid vapor pressure is usually off. Why is that? Are there any guidelines for using Reid vapor pressure?
Reid vapor pressure is the absolute pressure exerted by a mixture (in pounds per square inch)
determined at 100 F and at a vapor-to-liquid volume ratio of 4 (ASTM Method D 323. RVP is intended for
characterizing the volatility of gasoline and crude oil, with a typical range of 1 to 20 psia. Out of this range,
the accuracy may be poor. Therefore, RDV should not be applied to very light or very heavy streams.
3. How is the Reid vapor pressure calculated in ASPEN PLUS?
The Reid vapor pressure is vapor pressure of liquid at 100 F, as measured according to ASTM D-323procedures. Aspen Plus simulates these procedures by a series of flash as follows:
i. Check if N2 or O2 is present; if so, determine their index values.
ii. Setup to the ideal gas option-set (sysop0).
iii. Calculate volume for AIR at 32 and 100 Degree F, 1 atm.
iv. Determine bubble point pressure of the liquid stream at 100 F.
v. Saturate the liquid with air at 32 degree F.
vi. Mix liquid with 4 vol% equivalent of air and flash at 100 F under constant volume.
vii. If calculated Reid vapor pres. is greater than 26 psi repeat w/o air saturation.
The Reid vapor pressure as measured by the ASTM D-323 differs from the true vapor pressure of the sample due to some small sample vaporization and the presence of water vapor and air. Reid vapor pressure is often used to determine the appropriate type of storage tank (cone roof or floating roof) for petroleum stocks with undefined components.
4. What is the difference between Prop-Set REIDVP, RVP-ASTM, and RVP?
The Prop-sets REIDVP and RVP-ASTM are identical. Both are kept for upward compatibility, and can be requested like any other Prop-set. RVP, however, is available only if you define a petroleum property curve for the Reid vapor pressure in the ASSAY.PROP-Curve form, by providing a table of Mid-Percent distilled vs. Reid vapor pressure values.
5. Aspen calculated API gravity is quite different from that of PRO II in some cases. What is the
method used in Aspen Plus and what are the assumptions/limitations?
The API Liquid Volume model implemented in Aspen Plus uses the following eqution:
Vm = Xp Vp + Xr Vr
Where
V = liquid molar volume
X = liquid mole fraction
m = mixture
p = pseudocomponents
r = real components
Vp (for pseudocomponent liquid mixture) is calculated using a correlation based on API Figure
6A3.5 (API Technical Data Book, 4th edition).
Vr (for real component liquid mixture) is caculated by the mixture Rachett model.
The variations in petroleum liquid density results are often caused by the number of cuts generated.
Increasing the number of cuts or reducing the cut temperature intervals may improve the accuracy. Refer to Solution 103736 for more details.
When multiple assays are present, the way they are blended could also affect the liquid density
calculation. The choices include generating:
one common pseudocomponent set for all assays
one pseudocomponent set for each assay
some combinations of assays and blends
Refer to Solution 103921 for more about one versus multiple pseudocomponent sets.
6. How is assay broken into pseudo-components?
Assay is broken into pseudo-components based on the number of cuts on the True Boiling Point (TBP) curve. The middle point of each cut is used as the boiling point of that cut.By default, Aspen Plus generates 40 pseudo-components using the following cut temperatures:
TBP Range (F) No. of Cuts Increments (F)
100 - 800 28 25
800 - 1200 8 50
1200 - 1600 4 100
User can change the default settings under Components, ADA Characterization, Generation.
7. Can users access Aspen Plus generated pseudo-components like real components? Users would like to access pseudo-component properties, such as Tc, Pc, Vc, API gravity, SG, and MW. Currently they are listed in the external report file.
No. Only a limited number of pseudo-component property parameters are reported as results in GUI.
User cannot alter what to report. To access and change pseudo-component property parameters, use user property model subroutines.
8. How does Aspen handle petroleum properties among pseudo-components? For example, if only bulk sulfur content is given, how does Aspen distribute it to pseudo-components?
Petroleum properties are treated as component attributes and attached to pseudo-components. When a property curve is given, the distribution of the property is based on the curve. When only a bulk property
is given, it is evenly distributed among all pseudo-components.
9. How does Aspen Plus calculate motor and research octane number?
Octane number is calculated from the Octane curve entered with the assay. There are four (4)property-sets for Octane number:
i. MOC-NO - Motor octane number
ii. MOCNCRC - Motor octane number curve
iii. ROC-NO - Research octane number
iv. ROCNCRV - Research octane number curve
10. What is the difference between match and not-match light ends?
Light-ends (gases) are typically analyzed separately from the liquid fractions. The distillation curves from
the lab normally exclude the light-ends. To generate a distillation curve reflecting the full distillation range of an assay, you need to use Match Light-ends. Match light-ends uses the boiling points of the light-ends components to determine the curve in the range from 0 to lt% where lt% is the percentage of the light-ends in the assay. The default is not match light-ends.
11. How does Aspen Plus match light ends?
When Match Light-ends is selected, the TBP curve, from the light-end fraction and blow, will be represented by the boiling points and concentrations of the light-end components. For example, given the light-end fraction = 0.05, the boiling point of the heaviest lights = 64 F, the original TBP curve at 0.05 = 68 F. After matching light-ends, the final TBP curve will be 64 F at 0.05. And, from 0 to 0.05, the curve will be calculated from the light-ends. The original TBP curve in the range from 0 to 0.05 is not used.
12. When using match light ends, sometime I receive a warning message saying the temperature
difference is too large. Under what conditions will Aspen Plus not perform matching light ends?
Match light-ends works only when the boiling point of the heaviest component in the light-ends falls within
10 F on the TBP curve at the light-end fraction. In the above example, if the original TBP curve at 0.05 is below 54 F or above 74 F, Aspen Plus will give an error message and not perform matching light-ends.
To avoid this error, user has to make sure that the light-ends analysis is accurate and the fraction of light-ends in the assay is accurate. To force matching light-ends when the temperature difference is > 10F, you can：
a. Add or remove the heavy components in the light-end analysis.
b. Change light-end fraction.
13. Can one enter viscosity data for a stream? For heavy petroleum fractions, the API methods do not cope well. If two viscosity points are available, 2800 cp @275 F and 600 cp @325 F can they be used in the simulation?
You cannot enter the data directly either in Assay input or stream input. The current procedure is to substitute MUL2USR for the mixture viscosity model. Write a Fortran subroutine for doing interpolation
based on these two points. The subroutine fits a model of the type:
ln(mulmx) = aa + bb/T
14. How is pseudo-component specific gravity calculated?
Liquid molar volume is based on the Rackett or Cavett model. The default is Rackett. Refer to the Aspen Plus on-line help.
15. How is pseudo-component MW calculated?
There are nine (9) models for calculating pseudo-component molecular weight. Refer to the Aspen Plus on-line help.
16. How is gross/net heating value calculated for a petroleum stream? Is the method the same for pure components and pseudo-components?
Heating value is also called heat of combustion. The heat of combustion of a substance is the change in enthalpy when that substance is converted to its final oxidation products by means of molecular oxygen. The beginning and ending states are:
standard heat of combustion: 77 F and 1 atm
gross heat of combustion: 60 F and 1 atm
The normal state for the water formed by the reaction is liquid in both cases. Since the sensible heat of water from 60 to 77 F is usually negligible in comparison with the heat of combustion, the gross and standard heats of combustion are approximately equal. The net heat of combustion is the heat evolved in combustion beginning and ending at 60 F with product water in gaseous phase. Therefore, the net heat of combustion is less than the gross heat of combustion by the heat of vaporization of the water product.
Net/Gross heating value can be reported in Dry/Wet basis for a stream:
Dry basis - excludes water already present in the stream before combustion,
Wet basis - includes water already present in the stream before combustion.
The methods for calculating pure component and petroleum fractions heating value are different.
Petroleum Fractions: The method is based on API Procedure 14A1.3, 4th Edition (1983). The heating value is a function of API gravity corrected for impurity concentrations of H2O, S and other inert. Pure components Net Heating Value = -HCOM from pure component databank
17. How does ASPEN PLUS extrapolate values between 0% and the first distillation point and between the end point and 100% point for the True Boiling Point curve?
Suppose that the first point is at 10% and the last at 90%. Aspen Plus extrapolates between 0 - 10% and 90 - 100% using two methods: Probabilistic and Quadratic. The default is Probabilistic, which assumes a normal distribution of boiling points and uses the last point provided to extrapolate to the initial and end point. Quadratic was introduced in Aspen Plus Release 9.1-3
18. What is the difference between Probabilistic and Quadratic methods?
19. How does initial (default = 0.5%) and final (default = 99%) boiling points setting affect extrapolation?
The setting determines at what percentage the end points are reported. For example, with final point set at 0.99%, the temperature corresponding to 99% in the extrapolation is reported as the 100% temperatures. They may be adjusted to match end points.
20. For viscosity the API formula is limited to temperatures of below 400 C (750 F) and component MW of not greater than 7000. How does the program handle very heavy crudes or residues beyond these limits?
The procedure uses linear extrapolation for Watson K and API based the chart on 11-31 API Data Book, Fourth Edition.
21. How can Aspen Plus cope with downstream refinery products that are higher in olefinic components than the original crude does? For flosheets with reactors, there should be 2 sets of pseudo-components, one set for the streams before the reactor block and another set after the reactor. Each set of pseudo-components should have its own ssay data characterization. The reactor model will need to determine the flows of each pseudo-component for the reactor effluent.
22. How to use a SEP block to separate pseudo-components?
SEP block can only access pseudo-components entered in the Component.Main form or generated with Naming Option = LIST. It cannot access pseudo-components generated with the default Naming Option (NBP). You can set the Naming Option in pseudo-component Generation form to LIST. The steps are:
Run the simulation once to obtain the pseudo-component break-down.
Go to the pseudo-component Generation (PC-Calc) form and change the naming option from
NBP to LIST. Enter the names of all the pseudo-components in the LIST fields.
Now the pseudo-components become accessible in the SEP block.
23. What is the procedure of using pseudo-component components in a reactor model (eg. RYIELD)?
To do this, it is necessary to associate pseudo-components that are generated during an ADA/PCS run with components on the Components.Main form. These components can then be used in a reactor
model.
Steps:
Perform an ADA/PCS run.
Create a component id for each ADA/PCS fraction that you want to include in the reactor.
Go to 'Components.Main' form
Enter a user-specified Comp Id of type 'Pseudo' for each component.
Enter the required properties for each of the above components.
The component IDS now can be accessed in the reactor model.
24. If pseudo-components are used in RSTOIC, would atom balance be a problem since
pseudo-component MW's are estimated from correlation?
25. What is the difference of the five Naming Options in Pseudo-Component Generation?
NBP - use the normal boiling points to name each cut
LIST - use the IDs in the ID-LIST fields to name the cuts
NUMBERED - use integer numbers to name the cuts
ROUND-UP - use the upper temperature of the cut as its name
ROUND-DOWN - use the lower temperature of the cut as its name
For example, if a cut has an average T=215.4 F and the cut temperature specification is 200, 250, . . . F,
the cut will be named as
Naming Option Cut Name (ID)
BNP PC215F
ROUND-DOWN PC200F
ROUND-UP PC250F
25. Can I generate cuts at specified normal boiling temperatures?
No. You cannot specify a set of normal boiling temperatures (NBP) to generate cuts. What you can specify is the cut temperatures, such as 200, 225, 250, 275, 300, ... Aspen Plus will generate cuts at these temperatures and calculate the normal boiling point for each cut. With Naming Option = BNP, the cut names in the results or report file will not match the cut temperatures in the specification, although the
actual cuts are generated at the temperatures specified by user. Cut temperature and cut name are not to be confused. The specified cut temperatures are used to generate cuts at specific temperature points, and the cut name is as component ID for a pseudo-component. In the ADA/PCS.PC-Calc form, you can specify both
1. Cut Temperatures - used to generate the cuts.
2. Naming Option - used to name the cuts.
The specified cut temperatures overwrite the default values (see online HELP). There are five ways to name the cuts: NBP, LIST, NUMBERED, ROUND-UP and ROUND-DOWN.
26. How is the Pour Point calculated in Aspen Plus?
When a liquid petroleum product is cooled a point can be reached at which the oil ceases to flow in a standard test. The pour point is defined as the temperature 5 F above that point.
The user can input a pour point curve by supplying temperature values for the pour point at different mid-percent distilled points. Four such data points are required to define a property curve.
The value of pour point may be accessed by two different prop-set properties. Prop-set property 'POURPT' calculates the pour point of a stream based on the pour point property curve entered with the
assay. Prop-set property 'PRPT-API' calculates the pour point based on API procedure 2B8.1, a function of molecular weight, specific gravity and kinematic viscosity.
27. Does Aspen Plus estimate DHFORM and DGFORM for pseudo-components?
Yes. Both are by the Edmister method. Refer to the online help.
28. What are the limitations of the COSTALD method for calculating mole-volume? Can it be
applied to pseudo-components of high MW? How does it compare to API or Rackett?
Costald is an empirical correlation that computes mole-volume from Tb, MW and SG. For very heavy components, the calculated liquid density may be abnormally high. This method should not be used for pseudo components of high MW. For example, set up a system that has 1 pseudo component. MW = 980, GRAV=0.894 NBP=750.
COSTALD: density = 2790 kg/m3
API or Racket: density = 890 kg/m3
29. For a single component stream, the purecomp and mixture densities differ much.
RHO prop-set uses DNLDIP(DIPPR model)and that RHOMX uses the Rackett model even if the ThermoSwitch is set to use DIPPR. Aspen Plus uses DIPPR model for pure component and Rachett model for mixture. VL2RKT (mixture model) does not calculate mixture volume by mole-fraction average of pure component volume. It is a corresponding-state method in which the parameters are mixed (there are mixing rules for TC, RKTZRA, etc.). The pure-component model, on the other hand allows both the Rackett and the DIPPR model.
30. Why is the end point of a D86 curve higher than the boiling point of the heaviest component in a mixture?
The end point (100%) is extrapolated from the last percentage point (such as 95%). Therefore, it can be higher than the boiling point of the heaviest component.
31. Why does the distillation curve reported for an assay sometimes differ from the input curve?
This may be due to the presence of light-ends or curve fitting.
32. What value does Aspen Plus use for the endpoint and IBP of an assay? SimSci uses the 98% point as the endpoint and the 2% as the IBP, by default.
By default Aspen Plus use 0.5% and 99% for the initial and end points, respectively. The setting can be modified by user.
33. How can I change the number of pseudo-components generated?
This is under Components, Petro Characterization, Generation, Cuts.
33. Should I enter my light-end analysis in the stream input form or in the assay input form? Which is better?
In general light-end analysis is entered with assay in the assay input form. In that form, you can also enter specific gravity and molecular weight for each component. To enter light-end analysis in the stream
input form, the flow rate of each light-end component must be entered according to its concentration in the assay feed.
34. How many pseudo components should I generate for a given assay? The Getting Started
Guide shows how to do this but does not explain how to set the numbers.
As a Rule-of-Thumb, you should generate smaller (more) cuts at lower temperatures and larger (less)
cuts at higher temperatures. The idea is to generate more cuts in the temperature range of high interest
and less cuts in the temperature range of low interest. Cut temperature smaller than 5 F likely will not have much effect and larger than 25 F should be used with reason. The default cut setting is good for most applications.
35. How is the "Weight Factor" used in pseudo-component generation (PC-Calc)?
The Weight-Factor determines how pseudo-component parameters (Tc, Pc, ...) are linearly averaged of the assays/blends. The default is 1.0. For example, given a cut of 100 - 120 C
Assay-1 Assay-2
Weight-factor 0.4 0.6
Tc, C 500 550
Average Tc = 0.4 x 500 + 0.6 x 550 = 530 C
36. How are pseudo-components generated when multi assays/blends are entered?
Generation under Components, Petro Characterization (PC-Calc in R9) controls pseudo-component set generation.
When Generation is not specified (default), Aspen Plus will generate one common set of pseudo-components for all assays and blends, averaged with Weight Factor = 1.0. All assays/blends will be accessible in the feed stream input form. When Generation is specified, Aspen Plus will generate one set of pseudo-components for each ID created under Generation, where one ID may contain several assays, blends or combination of both. In this case only assays/blends included in Generation will show in the feed stream form. Those not included will be treated as not used in simulation and, therefore, become not accessible in the feed input form.
For example, if there are four assays A1, A2, A3 and A4. Under Generation, two Ids are created:
G-1, contains A1 and A2 with Weight Factor = 1.0 G-2, contains A3 only
Aspen will generate the first set of pseudo-components for G-1 and the second set for G-2. A1, A2 and
A3 will show in the feed input. No pseudo-component will be generated for A4, and it will not show in the
feed input form.
37. How are the following petroleum properties calculated?
ANIL-API
CETANENO
FLPT-API
MABP-API
PHYDRATE
THYDRATE
38. Do we have a correlation for calculating Cloudpt?
No.
39. What is the difference between the Harwell spline fitting method and the Hermite method?
When should I use the new method?
40. There are a number of different distillation curve conversion methods. Which one should I use?
The question applies to both the ASTM D2287 and ASTM D86 conversions.
API94 is the latest and recommended. The default is Edmister for D86 and API87 for D2287.
41. When should I change the Blend Options for a property?
If you have an in-house blending correlation and you know that gives better results.
42. Which option of SOLU-WATER should be used?
Option 3 is recommended for most applications. Option 2 is the default for petroleum applications when Free-Water = YES.
43. What is the plan for future versions with the crude library? (update or expansion)
Currently there is no plan to update/expand the assay library. Aspen Plus does have an interface to the Phillips Petroleum Assay Library which contains up to 500 assays.
44. How can we use in-house correlation for properties like assay viscosity?
Substitute user subroutines for assay parameter models under Components, Petro Characterization, Property.
45. Are there plans to improve the petroleum properties as REIDVP, hydrate formation temperature and pressure.
No. There is no such plan.
46. What does "Apply cracking correction" do when the distillation curve type is ASTM D86?
ASTM D86 distillation is carried out at atmospheric pressure. When heated sufficiently hot, heavy fractions undergo thermal cracking before vaporization. The amount and severity of thermal cracking
increases with increasing boiling point, contact time, pressure and temperature. Early editions of API included a correction for cracking for observed ASTM D86 temperatures above 475 F. No correction for cracking is now recommended.
47. Is D2887 on volume or weight basis?
D2887 is always on weight basis.
48. The final boiling points (TBP, D86 and other curves) generated by Aspen Plus for the bottom product and the feed differ up to 70 C. I would expect that the final boiling points be close together because they contain about the same amount of heavies.
The discrepancy is caused by end point extrapolation. Many users think that the initial and end points should be corresponding to the boiling points of the lightest and the heaviest component or pseudocomponent in the assay. That is NOT true. As a matter of
fact, TBPs of an assay are a function of component distribution. For two streams containing the same components but with different distribution, their TBP curves will differ. TBPs are defined by the "cumulative mid-point mass fractions" and the boiling temperature of components (pure or pseudo) in the mixture. The cumulative mid-point mass fraction is the sum of all the mass fractions of the components lighter than the component plus 1/2 of the mass fraction of the component.
Example:
Fraction Cumulative Frac
Pseudo Feed Residue Feed Residue Tb,C
PC242C 0.004045 4.97E-06 0.002023 2.48E-06 242
PC253C 0.007435 1.08E-05 0.007763 1.04E-05 253
PC267C 0.008231 1.5E-05 0.015596 2.33E-05 267
PC281C 0.00921 2.12E-05 0.024316 4.14E-05 281
PC295C 0.010555 3.11E-05 0.034199 6.76E-05 295
PC309C 0.012675 4.83E-05 0.045813 0.000107 309
PC323C 0.018611 8.98E-05 0.061456 0.000176 323
PC336C 0.023724 0.000148 0.082624 0.000295 336
PC351C 0.025983 0.000215 0.107478 0.000477 351
PC365C 0.036273 0.0004 0.138605 0.000784 365
PC379C 0.057014 0.000845 0.185249 0.001406 379
PC392C 0.067484 0.001328 0.247497 0.002493 392
PC406C 0.058821 0.001595 0.31065 0.003954 406
PC420C 0.067442 0.002511 0.373781 0.006008 420
PC440C 0.134319 0.008157 0.474662 0.011342 440
PC468C 0.125365 0.014943 0.604504 0.022892 468
PC496C 0.087523 0.021416 0.710947 0.041071 496
PC524C 0.085013 0.044097 0.797215 0.073828 524
PC548C 0.059187 0.058576 0.869315 0.125164 548
PC579C 0.016588 0.037357 0.907203 0.173131 579
PC607C 0.015729 0.068538 0.923362 0.226078 607
PC635C 0.01623 0.118288 0.939341 0.319491 635
PC677C 0.033627 0.375979 0.964269 0.566625 677
PC720C 0.018917 0.245386 0.990541 0.877307 720
If Tb vs cumulative fraction is plotted for the two streams, the curve will look differently.
Notice the ends at the cumulative mid-point mass fraction of the heaviest component. It is 0.99 for Feed and 0.877 for Residue. This means that points above 88%wt (90%, 95% and end point) for for Residue have to be extrapolated. The extrapolation may well generate an end point higher than the boiling temperature of the heaviest component. The fact that the highest mass fraction for Feed is 99% explains why its TBPCRV end point is much closer to the boiling temperature of the heaviest component. The extent of extrapolation is controlled by the Assay Procedure in R10:I
Initial boiling point =
Final boiling point =
The specified values determine at what percentage the 0% and 100% points are reported. To improve
end point calculation:
a. Increase the number of cuts.
b. Change the initial/final boiling points settings.
c. Use a different extrapolation method.
49. How to apply user correlation for assay physical property parameter (MW, Tc, Pc, . . .)
calculation in Aspen Plus.
Aspen has a suite of user routines for these property parameters. Currently they are not documented but can be obtained from Aspen Customer Support on an as-needed basis and used as templates for writing user models. Aspen plans to document and deliver these user models in future product release.
50. How is D86 curve converted to TBP curve? Aspen Plus and Pro II give different end points.
There are three (3) procedures for converting D86 data to TBP:
i. Edmister
ii. Edmister-Okamoto
iii. API procedure 3A1.1 Vol 1. 1994
As far as the end-point difference from Aspen Plus and Pro II, it has to do with the difference in curving fitting technique, which is standardized by API.
Test results from Release 9.3 are given below for conversion of D86 TO TBP - D86 data taken from API 5th Edition (1992):
%Dist D86 (F) API94 (F) ED-OK (F) EDMISTER (F)
0 303.404785 241.655090 248.901810 236.724243
5 336.359467 295.528229 302.408966 290.206329
10 350.000000 316.537140 325.531799 313.357819
30 380.000000 372.577423 376.742188 365.252502
50 404.000000 411.190308 415.087708 404.005188
70 433.000000 451.185425 456.328430 445.771851
90 469.000000 496.695404 501.794098 491.966125
95 486.264587 511.385498 521.353027 510.775635
100 503.529144 538.973938 540.911987 529.585205
Conversion by API94 matches exactly the example in API 5th Edition (1992).
51. How can I obtain the results of pumparound flows and side-stripper stage flows in PetroFrac?
In PetroFrac Pumparounds and Sidestripers have their own psuedostream forms. You can attach pseudo-streams to pumparound and side-strippers. For pumparounds, you can specify whether the
pseudo-stream is connected to the inlet or outlet. For side-strippers, you can specify the stage and phase of the pseudo-stream.
52. MultiFrac and PetroFrac report the liquid flow rates around the condenser with their own convention ( different from RADFRAC ) that may cause confusion for users. For instance, column profile seems to indicate that the liquid flow coming off the top stage is higher than the column liquid product rate, and reported RR seems to be inconsistent with the reported flow rates. What is the convention?
The source of the confusion is the way that the liquid flow rates around the top of the tower are reported:
The liquid product rate reported in column profiles includes the free water (it is wet) The top stage liquid flow rate is water free. The subcooled liquid flow rate includes hydrocarbon liquid product.
The following definitions should resolve the confusions:
a. Distillate liquid product (DL) in stream report:
o DL = total liquid product - water decant
b. Stage-1 liquid flow rate (L1) in the column profile:
o L1 = vapor from stage-2 (V2) - vapor product (V1)
c. Liquid return to the column (LR):
o LR = stage-1 liquid flow (L1) - DL
d. Reflux Ratio (RR):
o RR = LR / ( DL + DV )
53. How is the Flash Point calculated in Aspen Plus?
Flash Point is a measure of the volatility and the inflammability of liquid petroleum mixtures. It is the lowest temperature at which a liquid will give off enough vapor to form an flammable mixture with air. The value of the flash point may be accessed by prop-set properties:
FLPT-API, the API method for determining flash point (ASTM-D86)
FLPT-PM, the Pensky-Martens method (ASTM-D93)
FLPT-TAG, the Tag method (ASTM-D56)
FLASHPT and FLASHCRV, user specified assay property data for petroleum mixtures
For more information see Solution 115183.
54. If a stream contains significant amount of light components (vapor fraction), distillation curves, such as D86 curve will not be generated. What is the upper limit of vapor fraction above
which distillation curves are not generated?
1. D86T is not calculated if the related stream contains less than four(4) components of significant mole fraction (i.e., a mole fraction of greater than 1.D-2).
2. D86T is not calculated for streams that contain a lot of light end (>0.8) or are hydrogen rich(>0.01).
These limits were set to ensure the quality of simulation results.
55. What is free-water?
Free water is a term used in 3-phase (VLL) separation, referring to liquid that contains mainly water and little hydrocarbon. In such a case, the amount of hydrocarbon in the phase is so low that it is insignificant to simulation. Free-water assumption is often used in petroleum separation.
56. How is water solubility calculated and how to select water solubility option codes in 3-phase calculation?
There are several models for calculating water solubility in the organic phase in a 3-phase (VLL) equilibrium system. The water solubility option codes (0, 1, 2 and 3) determine which model to use for the simulation. The default:
Solu-water=2, Free-water=YES for petroleum application, Solu-water=3, Free-water=NO for all other applications.
When Free-water=NO, solu-water=3 is internally selected and what entered in the GUI is ignored. Choosing a water solubility option code is similar to selecting a property option set. It depends on the
system. In the past, codes 0 and 1 were widely used in refining applications with free-water = YES. However, code 3 is the most rigorous approach in dealing with 3-phase. Code 2 is somewhere between 1 and 3.
Aspen Plus calculates water k-value as follows:
k = gamma *(water fugacity coeff in organic phase)/(water fugacity coeff in vapor phase)
where, Water fugacity coeff in organic: free water option set (solu-water = 0,1,2,3)
Water fugacity coeff in vapor: the primary option set (solu-water = 1,2,3) and free water option set (solu-water = 0)
Gamma: 1/(mole fraction of water saturated in organic) (solu-water = 0,1)
ln (gamma) = G(1 - x)^2 (solu-water = 2): primary option set (solu-water = 3)
Mole fraction of water saturated in organic = calc from databank parameters A,B,C
ln (x) = A + B/T + CT
G is determined from gamma = 1/(mole frac of water saturated in organic)
1. Solu-water = 0 and 1 works OK when free water is ALWAYS present. When water is not saturated in organic, the results will be off.
2. Solu-water = 2 and 3 give more accurate results.
3. Solu-water = 3 is rigorous and recommended.
Water solubility increases exponentially with temperature. A saturated system at normal temperatures may well become unsaturated at higher temperatures.
57. I have the distillation curves of the products but not the curve of the feed. How can I set up my simulation?
Enter the product distillation curves as assay input and the gas products as light-ends. Blend them to create the feed.
58. What is the definition of "mid-percent distilled" in assay property input?
Mid-percent-distilled refers to a cut. A cut between 5% - 10% has a mid-percent-distilled point of 7.5%. The property entered should be the property of the cut, not the accumulative of the distilled or the heavy left in the pot.
59. What is the furnace feed convention in Petrofrac?
Stage duty on feed stage: similar to "on-stage" feed convention, specified furnace duty added to the feed stage. Single stage flash: similar to "above-stage" feed convention. Single state flash with liquid runback: similar to "above-stage" feed convention with the liquid runback from the stage above the feed stage sent to the furnace instead of the feed stage.
60. What is "liquid runback" in Petrofrac?
Liquid runback is the liquid flow from one stage to the stage below. Runback differs from stage liquid flow that includes side- draws (products or pumparounds). The RunbackSpec is usually used to set column liquid flow rates and prevent dry stage