Hydrocarbon Processing - April 2022 - 36

Process Optimization
TABLE 4. Calculation of butane properties from GC compositional analysis
Sphere 235
GC
Component
Propane
I-Butane
n-Butane
I-Butene
I-Pentane
n-Pentane
Results
Vol%
0.998
8.882
78.345
0.269
7.066
2.8
98.36
Tank
Flush inlet
Boundary
layer
Tank
Flush inlet
Agitator
Blend tank
Jet nozzle
Tank
RVP
188
72.6
51.7
63.3
20.4
15.6
From ASTM DS 4B
RON
101.8
100.1
93.8
97.4
92.3
61.7
MON
97.1
97.6
89.6
80.8
90.3
62.6
RVP-bbl
187.624
644.8332
4,050.44
17.0277
144.1464
43.68
RVP
51.73
Calculation per ASTM D2598
RON-bbl
101.5964
899.0882
7,348.76
26.2006
652.1918
172.76
RON
93.44
MON-bbl
96.9058
866.8832
7,019.71
21.7352
638.0598
175.28
MON
89.66
Tank homogenization. Many techniques exist for homogenizing
the contents of a tank to meet U. S. Environmental
Protection Agency (EPA) homogeneity requirements of a
maximum 6° API difference between the top third, middle and
lower third of the liquid level in a tank (FIG. 4). This requires a
95% homogeneity.
Jet nozzle mixing is quite effective, depending on the type
of nozzle-the recommended nozzle is an " eductor-type " jet
nozzle. An inline blender with a static mixer is highly effective;
however, a cheap inline static mixer requires a relatively expensive
inline blender.
The use of electric motor-driven " propeller-type " mixers
In-line static mixer
Tank circulation
In-line blending
FIG. 4. Tank mixing techniques.
r = 0.16 psi). Because it is prefabricated, it can be installed, started
up and commissioned within 2 wk-3 wk after delivery.
OTHER CONSIDERATIONS
Accuracy of gasoline, butane and naphtha properties.
The measurement of gasoline and naphtha properties can
be done directly by any competent third-party lab. The measurement
of butane properties is based on ASTM D2598 gas
chromatographic analysis of components, so it is vital to get a
representative sample of the blending butane and calculate the
properties (see TABLE 4). Using chemical handbook properties
is not recommended.
Property analyzers. It is highly recommended to acquire
table-top RVP and (possibly) multi-property analyzers that
also measure research octane number (RON), motor octane
number (MON), RVP, specific gravity (SG), etc., and allow
quick analysis of samples in minutes, whether tank samples
or pipeline samples.
It is equally important to take samples per ASTM D5842
practice to ensure sample integrity. Samples should be taken
in ASTM recommended sample bottles and stored in a cold
room/refrigerator until ready to use.
36 APRIL 2022 | HydrocarbonProcessing.com
or agitators is quite effective, but this takes a long time compared
with the other methods. If not already installed, this is
not recommended.
Tank circulation works well but requires additional expenses
in the form of two different tank lines (i.e., fill lines, suction
line), a pump and manifolding with isolation valves. Achieving
95% homogeneity requires approximately one tank turnover-
for example, a 20,000-bbl tank with a 1,000-bph pump capacity
will take approximately 20 hr (20,000 bbl/1,000 bph = 20 hr).
Project management. It is easy to fall into a trap of do-it-yourself
being less expensive than having a single point of responsibility.
Conversely, the extra 10%-15% cost is worth it to ensure
the work is accomplished on time and within budget.
The single most crucial factor is the selection of experienced
vendors/contractors that are willing to provide performance
guarantees against a 10%-15% contract value retention
until performance is demonstrated via a site acceptance test
(typically a 2-wk duration).
ELISEO CURCIO is a Chemical Engineer and CEO of Blend Tiger,
a consulting company working in the blending business and
financial modeling. He previously worked as Vice President and
CFO at Refinery Automation Institute (RAI), where he transformed
the business and increased revenue, as well as created a blending
training platform that is considered one of the best in the
business. Mr. Curcio is an optimization and modeling specialist
with more than 10 yr of experience in the areas of gasoline, diesel, crude and bunker
blending, ethanol non-linear property correlations and octane boost, and naphtha
and butane blending. He collaborates often with traders and brokers developing
custom algorithms within refineries and terminals to boost optimization. He
previously worked at Catholic University of Louvain (Belgium) in advanced modeling
and optimization in the membrane area. Mr. Curcio holds BS and MS degrees in
chemical engineering with high honors from the University of Calabria, Italy.
http://www.HydrocarbonProcessing.com
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