August 19th, 2009
Hand ndliling ng As Assays says in PRO/II Mike Donahue NA Technical Support
Outline Background •
What they are
•
Why they’re used
•
Pseudo-components
Laboratory Methods •
TBP
•
D86
•
D1160
•
D2887 et al
Pro/II Data Data Entry Entr y •
Stream
•
Characterization
•
Cut-points
As A s s ay Pr Pro o c es ess sing •
Steps
•
Light Ends
•
Blending
Common Pitfalls
Hand ndliling ng As Assays says in i n Pro Pro//II Background
Petr trol ole eum Ass A ssa ay Back Backgr grou ound nd What they are:
• The chemical evaluation of crude oil feedstocks by petroleum testing laboratories. The test consists of the recording the temperature and corresponding volume or weight % recovered.
T
% Dist Distilled illed
Petr trol ole eum Ass A ssa ay Back Backgr grou ound nd Why we use them
• API Project 6 – Isolated over 16,000 distinct hydrocarbon compounds from a single sample of Oklahoma crude. – C40 has 62,491,178,805,831 isomers
Petroleum assays were utilized to reduce the dimensionality of the calculations.
Crude Oil Assay Data • There is a large amount of crude assay data available for crude oils of the world • Some are proprietary / some are available in open literature • Typically the data contained in a crude assay includes: – Yields generated from the physical or simulated distillation – Specific gravity – Gas chromatographic components – Sulfur – Nitrogen – Viscosity – Cold flow (pour point, cloud point, freeze point) – Heavy Metals
Petroleum Assay Background Developing Petroleum Pseudo‐components
• Pseudo-components are developed to represent the unknown components in the stream • Petroleum assay is divided into predetermined cut-point ranges • Each pseudo-component corresponds to several unknown actual components • Doing this introduces a degree of uncertainty Pseudo-component Properties (FCC Gasoline) •
Cut-point range on TBP
150-175 F
•
Average NBP
164F
•
Average API
63.4
•
Average MW
84.4
Component
Class
NBP
API
MW
Octane
Hexane
paraffin
155.7
81.6
86.2
24.8
2,2 dimethylpentane
paraffin
174.6
77.1
100.2
92.8
MCP
naphtene
161.3
56.2
84.2
91.3
Hexene
olefin
146.3
72.2
84.2
83.0
1-M-cyclopentene
olefin
158.4
48.7
82.1
>100
4-M-cyclopentene
olefin
167.4
48.8
82.1
>100
Petroleum Assay Background
Handling Assays in Pro/II Laboratory Methods
Laboratory Methods - TBP True Boiling Point (TBP)
– The best representation of the true composition of the petroleum stream – Unfortunately, time (minimum of 8 hours) and expense usually limit its use to crude samples – Fractionating still with reflux – There is no standard (ASTM‐2892 15 trays & 5:1 reflux ratio) – Separates component by component (sharp cuts) – Upper limit is approximately 650°F or 900‐950°F NBP – Typically the pressure is reduced to 40 mmHg – 950°F
TBP Equipment
ASTM D86 • The D86 is a non‐fractionating test run at room temperature and pressure • Condenser is cooled with ice water specified to be between 32 and 40F • Most common laboratory distillation • Most widely used for finished product specifications • Reproducibility is reported to be +/‐ 6 degrees • Care should be taken to insure data is corrected for lab pressure
Distillations ASTM D1160 • Designed for high boiling point samples (heavy heating oil, gas oils, residual oils)
• Commonly conducted at 10 mmHg • Upper limit is approximately 1000°F • Most labs apply pressure corrections and report at 760 mm Hg
• Initial point is higher than TBP, from 50% to end point test is nearly identical to TBP distillation
• The pressure conversion back to 1 ATM is prescribed by the ASTM method
ASTM D2887 • G.C. simulated distillation approximates TBP distillation
ASTM D‐2887
• There are four standard tests ASTM D‐3710
ASTM D‐5307
ASTM D‐6352
ASTM D‐6417
• Replacing TBP distillations (time and cost are much less) • Aromatic limitations – aromatic compounds have lower retention times than normal paraffins
ASTM D‐7096
ASTM D‐7169
ASTM D2887 • Highly reproducible
REFERENCE RUN 1 0.5% (IBP) 115 112 5% 151 148 10% 176 173 15% 201 197 20% 224 221 25% 243 241 30% 259 255 35% 275 271 40% 289 287 45% 302 298 50% 312 309 55% 321 318 60% 332 329 65% 343 339 70% 354 350 75% 365 362 80% 378 374 85% 391 388 90% 407 404 95% 428 426 99.5% 475 474
RUN 2 112 147 175 198 220 240 256 272 288 299 308 318 330 340 352 363 376 387 404 425 475
Handling Assays in Pro/II Assay Data Entry / Characterization / Cutpoints
Distillation Data Entry in Pro/II
Distillation Data Entry in Pro/II
Distillation Data Entry in Pro/II
Characterization Options
Characterization Options
Property Generation All the characterization methods except Heavyoil apply predominantly to paraffinic fluids having API gravities greater than 20 and Watson K factors in the 12.5 to 13.5 range. They are progressively less accurate as the API gravity drops to 10 or less, and as the Watson K factor approaches 9 or 10.
The HEAVY extension of the SIMSCI method exhibits better extrapolation qualities for heavier, more naphthenic and aromatic materials typically present in heavy oils and bitumens.
Characterization Options
Assay Curve Fitting Procedures The curve fitting procedures are used to extrapolate and interpolate the distillation data supplied for an assay.
Cubic Spline (default or SPLINE method) This method usually results in the best possible fit for Property nearly allGeneration laboratory curves. Curves with step functions may cause fitting problems and should this occur the All the characterization methods except Heavyoil apply validity of the data should be checked. predominantly to paraffinic fluids having API gravities greater than 20 and Watson K factors in the 12.5 to 13.5 range. Quadratic Polynomials They are progressively less accurate as the API gravity This method is not as elegant as the Cubic Spline method, drops to 10 or less, and as the Watson K factor but does exhibit more stability for curves with step approaches 9 or 10. functions. The HEAVY extension of the SIMSCI method exhibits Probability Density Function (PDF) better extrapolation qualities for heavier, more naphthenic and aromatic materialsdensity typically present in is PDF is a least squares probability function which heavy oilspoints and bitumens. fit to all on the curve that are supplied. This method is recommended when errors are suspected in the distillation data.
Alternate Cubic Spline In certain situations, when partitioning an assay, the SPLINE option selects an integration block that is inappropriately large, resulting in inaccurate cut ranges.
Characterization Options
Distillation Curve Interconversions
API 1994 Developed by Daubert, T.E.. This method uses an approach similiar to that of the API 1963 procedure, which always produces a monotonic D86 curve.
API 1987 Developed by Riazi and Daubert. This method is reputed to be more accurate than older methods by statistical comparisons. Be careful of narrow boilers – a non‐monotonic curve may result.
API 1963 Procedure developed by W.C. Edmister, et.al. This method was used exclusively in the SimSci Process program and always produces a monotonic D86 curve.
Edmister‐Okamoto This is an earlier version of the API 1963 method. Application is identical to that described above for API 1963.
Characterization Options Curve Fit VER6 Selects the traditional PRO/II method (default prior to ver 7.0) Generates a quadratic using the first 3 (for IP) or last 3 (for EP) supplied data points. It uses the slope of this curve to linearly extrapolate to the appropriate end point (0%) or 100%). This may artificially introduce an inflection point in the data curve.
VER8 (Improved 7.0‐8.1) Uses a quadratic spline for locating the end points. This first appeared in PRO/II v7.0, and became the default starting with v8.0.
CURRENT Same method as the VER8 option, but now ignores all components having zero flow rates. Adding a component to the component list without changing composition of a stream could change the assay curve fit performed using VER8. This is because the VER8 curve fitting algorithm attempts to fit the midpoint of all components, even components having a zero rate. Starting with version 8.2, PRO/II no longer supports a default method for CURVEFIT.
Characterization Options
Kinematic Viscosity Reconciliation (KVRECONCILE) Selects a method for adjusting supplied kinematic viscosity data to agree with supplied average KVIS value. This option applies only when calculating kinematic viscosity using an index method for a stream containing assay components. It applies when KVIS calculations are requested, but the supplied kinematic viscosity data are incomplete and do not include values above the 95% distillation cut.
TAIL The default option (and the only option available in PRO/II prior to version 8.1). It extrapolates the kinematic viscosity curve to match the calculated average kinematic viscosity to the supplied average KVIS value (required input data on the KVIS statement).
CURVE First available in PRO/II version 8.1. Instead of extrapolating the KVIS curve, it shifts the entire curve until the average calculated value matches the supplied average KVIS value.
Assay Cutpoints
Handling Assays in Pro/II Assay Processing • Steps taken in Pro/II • Light Ends • Blending
Assay Processing Steps
Distillation Distillation Data Data
Process ProcessLight LightEnds Ends
Convert ConvertData DatatotoEquivalent Equivalent TBP Curve @ 760mm TBP Curv e @ 760mmHg Hg
Determine Determi neAv Average erageNBP, NBP, SPGR SPGRand andMW MWfor for Pseudocomponents Pseudocomponents
Characterize CharacterizeOther Other Thermop hysic al Properties Thermop hysic al Properties for forPseudocomponents Pseudocomponents
Distribu DistributeteAssay AssayCurve Curve into intoCuts Cuts
Determine Determi neMoles, Moles,Mass Massand and Volume for Each Volume for EachCut Cut
Light LightEnds Ends ininStr Stream eam
Set of Petroleum Components
Light Ends
Light Ends Matching TBP Data
Match Lightends to TBP Curve
F º e r u t a r e p m e T
0 2 1 P B N
4 C i
5 C i 4 C n
0
10
2 7 3 8 1 3 6 8 2 1 1 1 5 P P P P C B n B B B N N N N
20
30
0 7 3 2 P B N
2 6 2 P B N
40
Volume % Distilled
7 8 2 P B N
50
60
70
Assay Blending • A “ blend” is a set of cutpoints (petrocomponents) •
The properties of a given cut are “ averaged” from every assay containing that cut:
•
The blend prop erties are used everywhere in the simu lation for that component
NBP Specific Gravityblend
Volum NBP
cut weighti cut volumei i
Molecular Weight blend cut weight i
i
cut mol
Assay Blending TBP
Feed 1, Rate=150
Feed 2, Rate=400
Feed 3, Rate=100
215º 205º
% Distilled NBP = 212º SPGR = 0.85 Sulfur wt% = 0.012 Rate = 30
NBP = 211º SPGR = 0.83 Sulfur wt% = 0.010 Rate = 60
Blending NBP = 211.5º SPGR = 0.838 Sulfur wt% = 0.0107
NBP = 213º SPGR = 0.85 Sulfur wt% = 0.011 Rate = 10
Assay Blending Overhead Light Oil
Property Differentiation
Low Sulfur Assay
High Sulfur Assay
LSFO
HSFO
Economic Analysis Assay 1 Assay 2
Processing
Product A (X$/BBL) Product B (Y$/BBL)
Assay Blending •
Multiple blends: – Use to preserve stream differences (e.g. Virgin & Cracked stocks) – Any number of assays can be combined into a blend – Any number of blends can be defined – Default: Combine all streams that use the same cutpoint set
•
XBLEND (exclude from blending): – Use when you wish to characterize a stream using a certain blend but do not want the properties of that stream to be included in the blending operation
Handling Assays in Pro/II Common Pitfalls
Common Pitfalls Accuracy Cut-Point ranges
Heavy Product
e r u t a r e p m e T
Light Product Overlapping Components Needed
TBP Percent Distilled
Common Pitfalls Accuracy Cut-Point ranges 500
450
Only 2 pseudo-components Only two petrocomponents ininoverlap region overlap region
400
) 350 F ( e r u t a 300 r e p m e T 250
NBP-288 NBP-311
NBP-262 200
150
100 0
10
20
30
40
50
60
Percent Distilled
70
80
90
100
Common Pitfalls Accuracy 500
450
petrocomponents Many Many pseudocomponents in overlap region in overlap region
400
) 350 F ( e r u t a 300 r e p m e T 250
200
150
100 0
10
20
30
40
50
60
Percent Dist illed
70
80
90
100
Pseudo Components • Do you have enough? • Crude Distillation Example
Common Pitfalls Assays change over time • Production • Wells on line
The general rule of thumb is to be wary of assays more than 2 years old for simulation work
Feed Characterization •
When product data is available – Supply the product and back blend together to produce the feed for: • Crude and Vacuum Units • FCC Main Fractionators • Coker Fractionators
– Be careful to enter the data as a mid-point /cumulative basis
Feed Characterization 1700
s d n E t h g i L
1500 1300 ) 1100 F º ( e r 900 u t a r e 700 p m e T 500
a h t h p a N y v a e H
a h t h p a N t h g i L
12.7% 8%
l i O s a G t h g i L
e n e l s e o s r i e e K D
10%
9.3%
100
l i O s a G y v a e H
90
s m o t t o B
70 60
15.3% 7.2%
80
24% 13.5%
50 40 30
300
Enter Gravity at Midpoi nt of Product Cut
100
20 10
-100
0 0
10
20
30
40
50
60
Percent Distilled
70
80
90
100
y t i v a r G I P A
Common Pitfalls Average Gravity 3
• Average Gravity assumes a constant (or nearly constant) UOP K. • The slope tends to be too flat.
e r u t a r e p m e T
s d n E t h g i L
First, Integrate to Get NBP’s . . . .
t t u u C C t d s n 1 2
t u C d r 3
Percent Distilled
y t i v a r G I P A
. . . Then Use Watson K Factor to Compute Gravity
Volume % Disti lled
"K" =
NBP SPGR
Common Pitfalls Molecular weight is the most difficult property to predict •
Molecular weight is the most difficult property to predict accurately, especially for cracked stocks such as FCC and coker cycle oils, FCC slurry, etc. Therefore, this property should always be supplied when possible for the most accurate characterization of a petroleum component.
•
Correlations biased towards paraffins
Common Pitfalls ASTM D86 Distillations Interconversion
• API 1987 Interconversion by Riazi and Daubert (default for Pro/II 7.0 - 8.1) – TBP curves with narrow boiling range or flat sections in curve can result in negative slopes when converted back to D86. PRO/II will generate “Non-monotonic curve” message.
• API 1994 is more widely recognized
Cracking Correction
• Recent versions of the API data book no longer include this correction • Pro/II still provides this functionality • Better results from adjusting the cracking portion of the curve with probability paper
Assay Conversion - Tips Crude Oil Data Crude Oil E.P. = 1600ºF FCC Slurry E.P. = 1200ºF
1500
ºF
900 800 700 20
50
80
Percent Distilled
99.9
Common Pitfalls D2887 (SimDist) • Applicable to fractions with a final boiling point of 1000F or less. • API 1987 Interconversion uses a two‐step process and is not recommended • API 1994 corrected this to a single conversion where the 50% points are equal • API 1994 had strict limitations on the boiling point gaps and is not recommended for broad boiling
mixtures such as crude units. For example, the limit for D2887(100) – D2887(95) is 30 F. Because of the exponential form of the conversion, broader boiling high‐ends results in wild TBP(100) points.
Suggestions
• Per ASTM: Boiling range distributions obtained by this test method are essentially equivalent to those obtained by true boiling point (TBP) distillation.
• For broad boiling mixtures it’s best to enter the D2887 as a TBP wt basis • Modify the TBP to account for the aromatics – Aromatic boiling point correction estimated through comparison with a physical distillation – Probability paper • Use discretion – there is no single solution
Assay Blending – Pro/II’s default is to blend all assays into one cutpoint set – Use XBlend to limit this data averaging – Use multiple cutpoint sets to preserve assay data
SimSci Technical Support • Manuals: – C:\SimSci\ProII83\Manuals • Help while running program – Searchable – Content sensitive • Technical Support – Phone: (800) SIMSCI-1 (746-7241) – E-mail:
[email protected] • Training – Public – Private • Seminars/Webinars
