Hydrocarbon Processing - June 2021 - 41

Process Optimization
The Ethyl model1,2
A2
) 2.2(
considers the aromatics and olefin contents
of the blend stocks (Eqs. 28-31):
( ) = 0.33(
)2 + 0.67(
( ) - A2 = 5,947 - 63.8(
( ) = 0.33(
A2
O2
O2
) 0.9(
( ) - O2 = 0.509 - 0.7(
The Ethyl model1,2
) 2.5(
RJ = 0.33(
) 63.7(
) + 0.67(
) 2.5(
) 2.5(
) 94.2(
)2 + 0.67(
) 0.6(
)2
)2 = 0.02
and MON of the blend stocks (Eqs. 32-36):
J = 0.33(
) 8.9(
RJ - R × J = 704.3 - 94.3(
MJ = 0.33(
) 61.2(
) = 6.79
) + 0.67(
) 6.79(
) + 0.67(
MJ - M × J = 649.2 - 87.5(
)(109.3) 8.9(
) = 64.5
) 6.79(
) = 704.3
)(100.4) 8.9(
) = 55.5
) = 649.2
)2
)2 = 1,871
= 0.509
= 5,947
(28)
(29)
(30)
(31)
considers the spread between the RON
60
(32)
(33)
(34)
(35)
(36)
Using the Ethyl model based on 135 blends, the RON and
MON are (Eqs. 37 and 38):
R = 94.25 + 0.03324) 64.5(
(
M= 87.5 + 0.04285) 55.5(
2
(
( 0.00632)
1,871
100
) + 0.00085) 0.020) = 96.4 (37)
(
(
= 87.6
(
1
) + 0.00066) 0.020)
(
(38)
Average of R and M = (96.4 + 87.6)/2 = 92.0
Severity, J = 96.4 - 87.6 = 8.8
The model shows that the gasoline will meet the premium
octane specification, and the Excel spreadsheet shows the calculations
of the Ethyl model. FIG. 3 shows a screenshot of the
Excel program. FIG. 4 shows the relationship between octane
number vs. fraction of light straight-run naphtha for an Ethyl
135 blend model.
Takeaway. Petroleum blending of refinery products is a
rather complex mixture of hydrocarbons with components
that frequently vary widely in properties. The final blended
products must meet certain specifications, and optimization
techniques can be employed to achieve the desired parameters;
otherwise, a trial-and-error procedure can prove costly in
time and materials.
Furthermore, due to the complexity of the blending problem,
many blends can be used to meet the required specifications.
Such a problem becomes more complicated as refiners
resort to a linear program to optimize their blends, especially
in the case of gasoline.
Refiners still blend products batch-wise; however, most facilities
apply continuous or inline blending with much-improved
analyzers for octane and volatility by applying optimization
2
10
20
30
40
50
60
Fraction light straight-run, vol%
FIG. 4. Octane number vs. fraction light straight-run gasoline
for Ethyl 135 blend model.
techniques. Refiners can confidently blend directly to tankers
and pipelines at considerable savings over batch blending.
Part 2 of this article will appear in the July issue and further
explores the optimization technique in Microsoft Excel and
the LINGO program with the application of a case study.
LITERATURE CITED
Maples, R. E., Petroleum refinery process economics, 2nd Ed., PennWell Corp.,
January 2000.
Healy Jr., W. C., C. W. Maasen and R. T. Peterson, " Predicting octane numbers of
multi-component blends, " Report number RT-70, Ethyl Corp., Detroit, Michigan,
April 1959.
A. KAYODE COKER is an Engineering Consultant for AKC
Technology and has been a chartered chemical engineer
for more than 30 yr. Dr. Coker is an Honorary Research
Fellow at the University of Wolverhampton, U.K., a former
Engineering Coordinator at Saudi Aramco Shell Refinery
Company (SASREF) and Chairman of the department of
Chemical Engineering Technology at Jubail Industrial College,
Saudi Arabia. He is a Fellow of the Institution of Chemical Engineers, U.K.
(C. Eng., FIChemE), and a senior member of the American Institute of Chemical
Engineers (AIChE). He holds a BS (honors) degree in chemical engineering,
an MS degree in process analysis and development and a PhD in chemical
engineering, all from Aston University, Birmingham, U.K., as well as a Teacher's
Certificate in education at the University of London, U.K. He has directed and
conducted short courses extensively throughout the world and has been a
lecturer at the university level. His articles have been published in several
international journals. Dr. Coker is an author of six books in chemical
engineering, a contributor to the Encyclopedia of Chemical Processing and
Design, Vol. 61, and a certified trainer and mentor. He is a Technical Report
Assessor and Interviewer for Chartered Chemical Engineers (IChemE) in the
U.K. as well as a member of the International Biographical Centre in
Cambridge, U.K. (IBC) as " Leading Engineers of the World " for 2008.
ABDULRAHMAN S. ALSUHAIBANI is a PhD candidate in the
Chemical Engineering Department at Texas A&M University.
His research is in sustainable design of industrial systems
with a specific focus on developing a novel collaborative
approach between process systems engineering and
catalysis to efficiently accelerate the development of
process design and optimization. He has focused his
research applications on important contemporary issues for sustainability,
including CO2 utilization and hydrogen economy. Prior to pursuing his
PhD, Mr. Alsuhaibani worked for Saudi Aramco R&DC.
Hydrocarbon Processing | JUNE 2021 41
70
80
90
100
120
110
100
90
80
70
RON-Ethyl 135 blend model
(R+M)/2
MON-Ethyl 135 blend model
" Linear blend "
Octane number
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