Hysys Blend Oil Crude
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Transcript of Hysys Blend Oil Crude
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OPTIMIZATION OF A
REFINERY CRUDE
DISTILLATION UNIT IN THE
CONTEXT OF TOTAL ENERGY
REQUIREMENT
E. O. Okeke & A. A. Osakwe-Akofe
NNPC R&D Division, Port Harcour t,
Nigeria
APACT03, York, 2830, April, 2003
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INTRODUCTION
The Nigerian National Petroleum Corporation,has 4 refineries, in its downstream operations,
The primary goal of this refiner is to achieve and
maintain high gasoline production,Hence, the main objective of this study is tooptimize gasoline production in all the refineries,
The strategy being to first target the CDUs in
these refineries. Maximizing the yield of gasolineand its intermediates will directly impactpositively on total pool gasoline production,
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PROGRAMME FOR MAXIM IZING
GASOLINE PRODUCTION
Maximizing gasoline and itsintermediates production from therefinries has been planned to beaccomplished in phases, viz-
Phase ICDU 1 (the first refinerys CDU)
Phase I ICDU 2,3,4, 5 (the other 3 ref iner ies),
Phase I I ICatalytic plants - CRU, FCC & HF Alky
Phase Ibegan with CDU 1 as a basis toascertain plant suitability to process differentcrude oil.
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CDU 1 FEED & MAIN
COLUMN SUBSYSTEM
The CDU 1of the first of these refineries,
the object of our presentation, was
installed in the 1960s to processnaphthenic crude of API 40.3 at first and
another of API 35.4 afterward,
It has a main fractionator with 44 traysand 4 side strippers, and a stabilizer
column.
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CDU 1 DISTI LLATES
The intermediate distillates are as inconventional CDUs,
Unstabilized gasoline from the main
fractionator is further processed in thestabilizer column,
Straight run naphtha and other distillates fromthe main fractionator are routed further
downstream for processing and upgrading,Stabilizer produces an intermediate gasoline asbottoms and LPG as overhead
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CDU 1 MAIN DESIGN & HARDWARE
FEATURES
Licensed by SHELL and designed as aconventional crude distillation unit,
Crude oil characteristics and productrequirements as applicable inestablishing hardware design,
Hardware performance evaluation,
maintenance and upgrading of facilityundertaken periodically.
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MAIN FOCUS AREAS TO ACHIEVE
MAXIMUM GASOLINE IN CDU 1
Main areas are:
efficient operation of the CDU,review of configuration of CDU
to determine opportunity for
further increase in gasoline yield,
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GENERAL I ZED STRUCTURE
OF THE CDU 1
The CDU can be decomposed in stages as
follows:
Stage 1, the main f ractionator producingfeed for Stage 2 (i .e. the stabi l izer)
Achievement and sustenance of increase
yield must be progressivefrom Stage 1through Stage 2
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METHODOLOGYSTEADY STATE
SIMULATION TO OPTIM IZATION
The main stages are as follows:
Compare the crude assays for the twonaphthenic crudes,
Configure, specification and steady statesimulation of the CDU using HYSYS.Plant,
Match HYSYS.Plantsimulation results withoriginal design requirements,
Carry out optimization of the CDU
Results obtained showed good opportunity.
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COMPARISION OF THE TWO
CRUDESLight ends Crude properties
BL TNP
LV% LV% BL TNP
Methan, C1 0 0 Density, Kg/m3 847 823.6
Ethane, C2 0.02 0 API Gravity 35.4 40.3
Propane, C3 0.24 0.6 Barrel/Tonne 7.426
iso-butane, 0.36 0.7 Kinematic viscosity at 40 3.34
n-butane 0.75 1.4 Kinematic viscosity at 60 2.24 3.418
iso-pentane 1.01 1.6 Sulphur content (wt %) 0.14 0.06
n-pentane 0.77 1.6 Pour Point C 12cyclopentane 0.16 0.2
n-hexanes 0.72
other C6 2.47
Benzene 0.12
6.62 6.1
Heavy Ends ASTM D86 Properties
BL TNP BL TNP
IBP vac 363 IBP 57 39
5 400 391 5 100 91
10 404 393 10 125 114
30 418 406 30 215 188
50 439 421 50 280 259
70 463 438 70 334
90 503 460 90 446
EBP 564 482 EBP 529
Parameters
ParametersParameters
Parameters
Total
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COMPARISION OF PRODUCTS
DERIVED FROM ON THE TWO CRUDES
1.00E-06
1.00E-02
1.00E+02
1.00E+06
Crude LPG Gasoline Kerosene LGO HGO AR
Products
F
lowrates(kg
per
hour)
Design
HYSYS
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I NCREASING GASOLINE YIELD
For a given CDU, yield of gasoline derivatives
depends on,
Feed characteristics,Process requirements/operating conditions.
From the above therefore, since feed is
constant, optimizing gasoline yield will
depend on process requirements/operating
conditions.
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FRONT-END CDU 1 EVALUATION
FOR HYSYS IMPLEMENTATION
The evaluation of the CDU is as follows:
Establish a reliable CDU configuration, determine
process conditions using HYSYS and match these
with the original plant design basis andrequirements,
Properly decompose the structure of the CDU and
determine boundary conditions for optimization,
Achieve a reliable process optimization in the
context of total energy requirements.
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OPTIM IZATION PARAMETERS
The parameters for optimization are derived fromprocess/hardware environments, viz,
The main fractionator and the stabilizer are
linked together: stabilizer feed comes from themain fractionator,
The other gasoline blending stock, SRN, aderivative from the main fractionator is routed
for further processing,Four side strippers in the main fractionator,
The stabilizer has a condenser and a reboiler
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PLANT ARRANGEMENT FOR
OPTIMIZATION
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HEAT LOAD DISTRIBUTION
CDU has an integrated heat exchangernetwork for heat recovery which sharesloads, viz, Q1,,Q7, where Q4 and Q5 are
utilities,
Heat loads in the network are assumed tobe efficiently shared,
Heat supplied through the crude chargeand for the various steam strippingsupplies are constant.
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HYSYS FLOWSHETET
CONFIGURATIONOveral l CDU
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HYSYS FLOWSHEET CONF IGURATION
Main Column Subsystem
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MODELLING PROCEDURE
Stage-wise approach was adopted, viz,
Evaluate CDU configuration and steady state simulation
data to determine opportunity for optimization,
Based on the structure of CDU process and hardwarerequirements, evolve an optimization algorithm and define
boundary conditions to be solved by HYSYS.Plant,
Define steady state parameters from HYSYS.Plant
simulation as first level data, and referenced as baseor
designvalues,
Optimize the overall gasoline yield in the context of total
energy requirement.
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OPPORTUNITI ES FOR
OPTIM IZING GASOLINE YIELD
We observed the following:
The columns are linked in sequential arrangement,
Possibility of enhanced recoveries of gasoline in the
nearest distillates below and above SRG, ie SRK andLPG, and in the stabilizer overhead,
To maintain high quality gasoline to meet baseor
designspecification, the path to solution must be
constrained,Problem is non-linear.
Based on these conditions an algorithm was developed
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THE ALGORITHMHeat Loads
Heat load differential at steady state
Qibase = Q1base + Q2base+ + Q7base 1Heat load at any level of optimizationQiopt = Q1opt + Q2opt+ + Q7opt 2And the differential
Qdifferential = Qiopt - Qibase 3
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THE ALGORITHMGasoline Yields
Gasoline yield at steady state
yibase = y1base + y2base+ + y7base 4Gasoline yield at any level ofoptimization
yiopt = y1opt + y2opt+ + y7opt 5And the differentialydifferential = yiopt + yibase 6
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THE ALGORITHMObjective Function
Incorporating the various energy and gasoline costs, theresultant differential becomes,
INB = y*differential - Q*differential 7 The objective function becomes
Max [f(X1,X2,X3) = y*differential-Q*differential] 8Where,
y*differential & Q*differential are gasoline and energy costs,X1, main column naphtha stripper reboiler return temp,
X2, main column kero stripper reboiler return temp,X3, stabilizer reboiler return temp,
Subject to RON and RVP of gasoline being within baseordesignvalues.
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HYSYS OPTM IZER
Primary variables (X1, X2, X3) are manipulated to
maximizeINB. Primary variables must have
upper & lower limits, and these are used to
normalize the primary variables, viz,
Xinorm= [(XiXilower)/(XiupperXilower)] . Where Xi= X1,
X2, X3
Objective functionas defined by INB
,
Constraints as defined for RON & RVP,
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OPTIM IZATION BY SEQUENTI AL
QUADRATIC PROGRAMMING
Sequential Quadratic Programming (SQP) was
applied for solution.
SQP minimizes a quadratic approximation of
the Lagrangian function subject to linear
approximations of the constraints. The second
derivative matrix of the Lagrangian function is
estimated automatically. A line searchprocedure utilizing the watchdog technique
(Chamberlain & Powel) is used.
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PROBLEM SOLUTION
Sequential quadratic programming
was found to be ideal for solution,
Solution was found for all casesstudied,
General increase in yield of stabilizer
feed and SRN from the main column,
Gasoline yield was increased by 8 %
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BASE & OPTIM IZED VALUES
Base Optimi zed Dif ference
NAPHTHA Side Stripper Reboiler Temperature, C, X1 174 176 2
KERO Side Stripper Reboiler Temperature, C, X2
245 260 15
STABILIZER Reboiler Temperature, C, X3 155 153.05 -1.95
STABLIZER Feed, m3/hr 45 47.97 2.97
Straight Run NAPHTHA product, m3/hr, y1 63.57 64.27 0.7
GASOLINE, m3/hr, y2 41.3 44.24 2.94
Total Gasoline (Straight-run Naphtha+Gasoline) 104.87 108.51 3.64
HYSYS Resul t
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TESTING ALGORITHM ROBUSTNESS &
RELATIONSHIP OF KEY PARAMETERS
Some optimization test runs were done using sameHYSYS.Plantto
Test the robustness and reliability of the algorithm
at achieving early convergence,Determine the variation of key parameters, thatimpact on the structure of the CDU and theinteraction of the main fractionator and thestabilizer. These parameters are the naphthastr ipper reboi ler return temp, the kero str ipper
reboiler return temp, and the stabil izer gasoline.
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VARIATION OF GASOLINE WITH NAPHTHA
STRIPPER REBOILER RETURN TEMP
174
176
178
180
182
184
43.52
43.88
44.15
44.4
44.45
44.72
45.02
Gasoline (m3/hr)
Naphthas
tripper
reboilerreturn
Tempera
tureC
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VARIATION OF GASOLINE WITH KERO
STRIPPER REBOILER RETRUN TEMP
235
240245
250
255
43.52
43.88
44.15
44.4
44.45
44.72
45.02
Gasoline (m3/hr)
Kerostrippe
rreboiler
returnTemp
eratureC
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VARIATION OF GASOLINE WITH
STABI L I ZER REBOILER RETRUN TEMP
146
148150
152
154
156
43.52
43.88
44.15
44.4
44.45
44.72
45.02
Gasoline (m3/hr)
Stabilizer
reboiler
returnTemp
eratureC
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OBSERVATIONS FROM THE
OPTIMIZATION
The optimization based on this algorithmachieves earlyconvergence,
As expected, the naphtha stripper (X1) and
kero stripper reboiler (X2) temperatures haveindirect impact on the stabilizer gasoline, whilethe stabilizer reboiler (X3) temperature has adirect impact on the same gasoline yield,
The 3 parametersX1, X2 & X3 aremanipulated as appropriate to optimize thegasoline produced.
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CONCLUSION
Sequential quadratic programme technique ideal for
solution,
Solution ofthe algor ithm isreliable, achieving early
convergence in the cases studied,Objective of obtaining increased gasoline yield in the
context of reduced energy requirement achieved,
Since the configuration of the refinery CDUs are
similar, this algorithmcan be applied to optimize theCDU 2,3,4,5in the other 3 refineries
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