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Avantis • Foxboro • SimSci-Esscor • Triconex
Molecular Level Description of Crude Oils and Complex Hydrocarbon Streams
Lanny Carr – Invensys Process System
REFINING CHINA 2006
April 24 -26
Beijing, China
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…we could remove the uncertainty about using old assay data as the basis for how we process today’s feedstocks?
…we could reduce inherent assay errors by using measurements that we can take at the plant site?
…we could make those corrections on a daily basis?
…we could produce deeper information about true compositional nature of feedstocks and other process streams?
…we could use that detailed knowledge as more accurate input to planning and optimization tools for daily operational improvements?
…what if?
What if…
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Laboratory measurements of distillation yield behavior.
A convenient way to lump crude oil into a manageable number of pseudocomponents.
Laboratory measurements of properties of these pseudocomponents.
Source of data for API correlations.
Source of data for Linear and Simulation Programs.
Assays - What they are…
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High quality assays are costly and time-consuming to produce.
Library assays go out-of-date as fields mature.
Input data used to select assays are often just bulk properties that are insensitive to distributed properties.
Blending during gathering and transportation can create compositional characteristics difficult to mimic with available assays.
Even perfect assays can fail, for fundamental reasons, to fully account for compositional differences that govern the refining outcome.
Assays - the Problems...
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Crude oil quality is difficult to measure.
Analytical measurements contain error.
Need to rely on data of unknown quality.
‘Typical’ assays are commonly used in place of ‘measured’ assays.
Bulk property correlations contain deviations and are insensitive to important compositional variations.
LP models and simulators don’t always agree with the refinery operation.
Issues when Evaluating Quality
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The Z - Based Structural Index Correlation
All compounds in crude oil are classified according to the general empirical formula:
CnH2n+zNuSvOw…– z-vectors are the classifying numbers
– ‘n’ is the primary correlating variable
[Z-BaSICtm] Method
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All crudes are made up of a few dozen classes of compounds.
Each class has a mass distribution with respect to molecular weight.
Each class and molecular weight set are comprised of multiple isomers.
In short, crude oil may be described by mass distributions with respect to 3 independent variables, ‘z’, ‘n’ and ‘i’.
Crude Oil Composition - Simplified
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Refining operations are processes to:
– alter the classes (hydrogenation, reforming, HDS, HDN, etc.)
– alter the molecular weight (FCC, HC, alkylation, coking, etc.)
– alter the isomer structure (isomerization, cat. dewaxing, etc.)
In Short, refining alters the ‘z’, ‘n’, and ‘i’ character of crude oil.
Refinery Operations - Simplified
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Correlation of Boiling Point with ‘n’ and ‘z’
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Correlation of density with ‘n’ and ‘z’
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Density
0.50.60.70.80.9
11.11.21.31.41.5
0 10 20 30 40 50Carbon number
g/c
cDensity vs Carbon Number
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'n' 'z' Pv coefficients density Weight fraction
16.00 2.0 17.07 4926 -88.0 .773 .00334 13.14 -6.0 16.70 4328 -116.9 .957 .00018 15.00 -10.0 16.12 4385 -105.5 .927 .00526 14.00 -14.0 15.64 4132 -113.0 .962 .00117 14.00 -12.0 15.84 4223 -115.9 .938 .00461 16.00 -6.0 15.91 4159 -121.5 .840 .00250 14.29 -10.0 15.42 4162 -93.5 1.051 .00358 18.00 2.0 16.11 4241 -120.5 .775 .00120 15.29 -10.0 15.56 4354 -95.4 1.035 .00048 16.00 -8.0 15.84 4167 -124.0 .900 .00094 17.00 2.0 16.15 4300 -123.4 .777 .00319
C16-C17 excerpt
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Jet A Property Variations
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Jet A Heating Value at Constant Density
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Jet A Aromatics vs. Paraffinsat Constant Density.
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total sulfur distribution
0
1
2
3
4
5
500 600 700 800 900 1000 1100endpoint in F
% s
ulfu
rSpeciation with Molecular Modeling
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Percent Distilled0 20.0 40.0 60.0 80.0 100.0
Te
mp
era
ture
(C
)
-100.0
100.0
300.0
500.0
700.0
900.0
Assay Processing for Stream QTL-CRUDE
Input TBP data
Fitted TBP Curve
Component Cuts
ROMeoNon Linear Planner
Old System
Cut-Point Base
(Pseudo Component)
51 Pure-components
39 High Fidelity Pseudo-
Components
0 10 20 30 40 50 60 70 80 90 100
0200400600800
1,0001,2001,4001,6001,800
Liquid Volume Percent, LV%
TB
P T
emp
erat
ure
, d
eg.
F
Lig
ht
Na
ph
tha
He
avy
Na
ph
tha
LGO RCHGOKERO
LPG
LN
HN
KERO
LGO
HGO
RC
LPG
LN
HN
KERO
LGO
HGO
RC
NL Planner System (Assay)
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ZKQ density vs SimDis
0.5
0.6
0.7
0.8
0.9
1
1.1
-100 400 900 1400
Grouping of Hi Fidelity Pseudocomponents
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composition of HN, dens =.7306, bp 80-150
0
10
20
30
40
50
60
13.8% 14.0% 14.2% 14.4% 14.6% 14.8% 15.0% 15.2% 15.4%
H content
n-paraffins
i-paraffins
mononaphthenes
dinaphthenes
monoaromatics
Heavy Naphtha Cut at Constant Density
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ComponentEstimation
C4 C12
Assay
Blend Crudes & generate pure components & high fidelity
pseudo-components
Crude Assay
Library
ROMeo Online Model
Z-Basic
Update individualcrude ASSAYS from
online measurements & lab
data
Data ReconciliationPerformance Monitoring
Crude Assay Data Compensation Method
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Z-BaSIC™ Information Logic
Preparation of original 'cp' files
'cp' file adjuster Z-BaSIC Applications
Physical Crude Oils and Intermediate
Process Streams
Laboratory and on-line monitored property data Composition and
Property Reports
Z-Assays(reconciled)
Model, Simulator and Optimizer Input files
First-Principal Simulators
Library Assays
LP Input files
HTSD, light gas analysis
Density
Elemental analysis -C, H, S, N, O & metals
GC-MSanalysis
Optional - NMR, viscosity, RVP, MW, etc.
NMR provides additional information for the Z-BaSIC convergence
• Total Hydrogen
• A, O, S Hydrogen
• Sulfur
Data Inputs & Outputs
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Conventional
Assays
Pseudocomponents
________________
LP Sim Opt
Crude Oil or Monitors
Reference file
Pure components
+ Hi Fidelity Pseudocomponents
___________________
Props, Comp, Sim, Opt
Interface with Conventional Systems
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Weight % Species+
Properties
Pseudo ComponentsPlus Distinct Species
Weight % HC minus Species+
Properties
Each Pseudo-Component
NL Planner/ROMeo
Reconciled Assay
Speciated Stream Preparation and Analysis
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SimulatedUnit
Yield2 & Properties+
Components
Yield3 & Properties+
Components
Yield5 & Properties+
Components
Yield4 & Properties+
Components
Yield1 & Properties+
Components
…What can we do with Speciation?
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Role Activity Technology
Process UnitTargets with
Refinery Wide Representation
Operator Set Operating Limits
APC Targets
Set Process Unit Detailed Targets
RefineryScheduler
Schedule Refinery
Approved Targets
Process UnitDetailed Targets
Set points
Schedule
RefineryPlanner
Refinery NLP or LPUpdate qualities
Develop Operating
Plan
Daily Targets with Refinery Wide
Representation
Daily Crude Mix
Daily Liftings Prices
ConstraintsOperationsManager
LostOpportunity
Price & Constraint Visibility
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Overcomes limitations of existing crude oil assay technology
Enables crude oil analysis on a fundamental molecular level
Potential benefits in excess of $0.30/bbl
Moves technology to a more scientific basis for component speciation
Molecular Modeling - Advantages
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