Crude Assay vs. Htsd

8/14/2019 Crude Assay vs. Htsd

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The Distillation Group, Inc.

Yield Correlations Between Crude Assay Distillation

And High Temperature Simulated Distillation (HTSD)

Reprint distributed with permission from the copyright holders.Copyright D.C. Villalanti, J.B. Maynard, J.C. Raia, and A.A. Arias (1997)

All rights reserved.

Not to be uploaded to any other site withoutwritten permission from the copyright

holders.

Distributed by

The Distillation Group Inc


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The Distillation Group, Inc.

Paper 51b

Yield Correlations between Crude Assay Distillation

And

High Temperature Simulated Distillation (HTSD)

Dan Villalanti , Triton Analytics Corp., 16840 Barker Springs #302, Houston, TX 77084Jim Maynard , Shell Development Co., P.O. Box 1380, Houston, TX 77001

Joe Raia , Triton Analytics Corp., 16840 Barker Springs #302, Houston, TX 77084Aaron Arias , Shell Development Co., P.O. Box 1380, Houston, TX 77001

Prepared for Presentation at

The AIChE 1997 Spring National Meeting, Houston, TX

March 9-13, 1997


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Yield Correlations between Crude Assay Distillation and

High Temperature Simulated Distillation (HTSD)

Dan Villalanti , Triton Analytics Corp., 16840 Barker Springs #302, Houston, TX 77084Jim Maynard , Shell Development Co., P.O. Box 1380, Houston, TX 77001

Joe Raia , Triton Analytics Corp., 16840 Barker Springs #302, Houston, TX 77084Aaron Arias , Shell Development Co., P.O. Box 1380, Houston, TX 77001

Prepared for Presentation at the AIChE 1997 Spring National Meeting, Houston, TX.March 9-13, 1997, Distillation Symposium, Distillation Design and Operation:

Troubleshooting, Operation, and Optimization, Paper 51b

Copyright 1997 D.C. Villalanti, J.B. Maynard, J.C. Raia, A.A. Arias.

March 1997

Summary

The ability to rapidly and accurately evaluate the variability of distillation yield curves of opportunistic crudes and crudes from currently producing fields has increasingly importanteconomic considerations in refining margins. Recent advances in the analytical laboratoryusing gas chromatography techniques have allowed the method of High Temperature


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Crude Assay Distillation

ASTM Standard Test Method D2892 for the Distillation of Crude Petroleum defines themethodology for Crude Assay Distillation. The method uses a 15 plate column operatingunder a reflux ratio of 5:1. This is known as TBP or True Boiling Point. The distillationis usually started at ambient pressure (760mm Hg) and then switched to vacuumconditions (from 100 and then to 5 mm Hg) to extend the method to about 650 FAtmospheric Equivalent Boiling Point (AEBP). At this point the remaining charge istransferred to a vacuum potstill method (ASTM D5236) where the distillation continues at0.5mm Hg, thus allowing an AEBP limit of about 1000-1050 F. Conversion tables for thevacuum conditions to AEBP are included in the method.

Although the Crude Assay Distillation (D2892 and D5236) method provides only anestimate of the yields of the fractions of various boiling ranges, the results (when properlyand skillfully obtained) are of great importance for the characterization and commercial

trading of crudes .

Several areas that contribute to the variance of the D2892 method include:

1.) Column hold up2.) Conversion to AEBP from various vacuum settings3.) Cracking Limits on the maximum distilling temperature are different for different types

of crudes.4.) Pressure drops across the column.


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Under the special conditions of HTSD, elution of materials from the GC column occurs atup to 500-600 F below their AEBP . For instance, the elution of C 110 (AEBP of 1351 F)

occurs at about 800 F column temperature. Also under these conditions, little or noevidence of cracking is normally seen in HTSD.

HTSD Precision

The Quality Control (QC) and Quality Assurance (QA) procedures in the lab to assure theintegrity of HTSD must be followed rigorously to ensure statistically meaningful results. 1

The initial QC involved the analysis of a reference oil (F igur e 3) that has been physicallydistilled by ASTM D2892 (TBP). This material (with FBP


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The crudes included in this study have a widely varying content of pitch of Pitch, Sulfur, Nickel, Vanadium, Conradison Carbon or Microcarbon Residue, and Asphaltene.

Comparison of Crude Assay and HTSD

The comparisons of the yield curves (expressed in %weight) of Crude Assay (ASTMD2892) to HTSD are presented for five typical crudes spanning the range of light,intermediate, and heavy API gravities. (F igu res 4, 5, 6, 7, & 8). Each crude is comparedat the following ten distillation cutpoints:

Cutpoint Number Cutpoint Temperature F

1 682 1553 265

4 3505 4006 5007 6008 7509 90010 1000

In the next series of comparisons, the % weight at each of the ten cutpoints as determined by HTSD was subtracted from the % weight from Crude Assay Distillation. The average


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contribute most of the difference when compared to HTSD, which has no pressure-relatedcrossover effects.

The precision of HTSD cutpoints up to 1000 F is better than 0.5%wt. The estimated precision of the correlation between Crude Assay Distillation and HTSD yield at eachcutpoint result in a standard deviations of


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Figure 1 Summary of ASTM Physical and Simulated Distillation

HT 750

D2887E

D2887

D3710

BP

D86

D1160

D2892

D5236

C 60

C 44

C 15

125 C 250 C 375 C 500 C 625 C 750 C

257 F 482 F 707 F 932 F 1157 F 1382 F

C 120

C 14

C 25

C 26

C 44


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FIGURE 4

ASSAY AND HTSD YIELDSLIGHT CRUDE - API GRAVITY = 50.4

60

80

100

Y E I L D , W T %

ASSAY HTSD


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FIGURE 5

ASSAY AND HTSD YIELDSLIGHT CRUDE - API GRAVITY = 34.2

60

80

100

Y E I L D , W

T %

ASSAY HTSD


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FIGURE 6

ASSAY AND HTSD YIELDSINTERMEDIATE CRUDE - API GRAV = 24.2

60

80

100

Y E I L D , W

T %

ASSAY HTSD


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FIGURE 7

ASSAY AND HTSD YIELDSHEAVY CRUDE - API GRAVITY = 16.8

60

80

100

Y E I L D , W T %

ASSAY HTSD


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FIGURE 8

ASSAY AND HTSD YIELDSHEAVY CRUDE - API GRAVITY = 9.7

60

80

100

Y E I L D , W T %

ASSAY HTSD


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FIGURE 9

CRUDES GROUPED BY API GRAVITIES

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ASSAY -HTSD

AVG DIFF AND STD DEV AT EACH CUT POINT

-8

-6

-4

-2

0

2

4

68 155 265 350 400 500 600 650 750 900 1000CUT BP DEG F

W T %

API >20 AVG DIFF API >20 STD DEV


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FIGURE 10


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ASSAY- HTSD AVG DIFF AND STD DEV AT EACH CUT POINT

-8

-6

-4

-2

0

2

4

68 155 265 350 400 500 600 650 750 900 1000CUT BP DEG F

W T %

API 20-30 AVG DIFF API 20-30 STD DEV


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FIGURE 11


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ASSAY -HTSD AVG DIFF AND STD DEV AT EACH CUT POINT

-8

-6

-4

-2

0

2

4

68 155 265 350 400 500 600 650 750 900 1000CUT BP DEG F

W T %

API


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FIGURE 12


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ASSAY -HTSDWT% DIFF AT EACH CUT POINT

-8

-6

-4

-2

0

2

4

68 155 265 350 400 500 600 650 750 900 1000CUT BP DEG F

W T %

API >30 AVG DIFF API 20-30 AVG DIFF API


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FIGURE 13


20

ASSAY -HTSDWT% DIFF AT EACH CUT POINT

0

1

2

3

68 155 265 350 400 500 600 650 750 900 1000CUT BP DEG F

W T %

API >30 STD DEV API 20-30 STD DEV API

Crude Assay vs. Htsd

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