Hydrocarbon Processing - October 2021 - 32

Plant Safety and Environment
heat section. A preliminary version of the
study with a commercial rigorous simulation
model showed valuable improvement
possibilities, so a pinch analysis in
the unit was executed to determine the
VR to tanks
Lube oil feed
Feed-PA
heat exchangers (4 Shells)
Feed
Feed-VR
new heat
exchanger
Feed-VR
Feed-HV Distillate-1
Heat Exchanger
FIG. 2. Revised preheat train after Case 1.
VR to tanks
Lube oil feed
Feed-PA
heat exchangers (4 Shells)
Feed
Feed-VR
Feed-LT distillate
heat exchanger
Feed-VR
heat exchanger
(modified)
FIG. 3. Revised preheat train after Case 2.
VR to tanks
Lube oil feed
Feed-LT distillate
heat exchanger
Feed
Feed-PA
heat exchangers
(4 Shells)
Feed-VR
new heat
exchanger
FIG. 4. Revised preheat train after Case 3.
VR
Feed-LT distillate
heat exchanger
Feed
Feed-VR
Feed-PA
heat exchangers
(4 Shells)
Lube oil feed
Lube oil
HEX
VR to tanks
FIG. 5. Revised preheat train after Case 4.
32 OCTOBER 2021 | HydrocarbonProcessing.com
Lube oil
process
Lube oil unit
fired heater
Feed-HV distillate-2
heat exchanger
heat exchangers
(4 Shells)
Feed-HV distillate-1
heat exchanger
Fired heater
Vacuum
distillation
column
Feed-HV distillate-2
heat exchanger
Lube oil
HEX
Feed-HV distillate-1
heat exchanger
Feed-VR
heat exchangers
(4 Shells)
Lube oil unit
fired heater
Lube oil
process
VR
Fired heater
Vacuum
distillation
column
Heat Exchangers
(4 Shells)
Feed-HV distillate
heat exchanger
Lube oil
HEX
VR
Lube oil unit
fired heater
Lube oil
process
Fired heater
Vacuum
distillation
Heat Exchangers
(4 Shells)
Lube oil
HEX
Feed-LT Distillate
Heat Exchanger
Lube oil unit
fired heater
Lube oil
process
VR
Feed-HV Distillate-2
Heat Exchanger
Fired heater
Vacuum
distillation
column
optimum energy efficient application for
the pre-heat section.
VDU simulation and validation. A
commercial rigorous simulation program
was used to model the VDU with the goal
of optimizing the heat exchanger network
and the fired heater. The appropriate thermodynamic
fluid package for this simulation
was Peng Robinson. For characterization
of the streams (AR, spindle, light and
heavy distillate and VR), an oil manager
was used. The unit model was configured
by using field data (distillation, flowrates,
operational data, etc.) and equipment
process data sheets. The main focus was
optimizing the heat network, which is
why the rigorous models were considered
for exchangers. For the analysis, the exchangers
were modeled in both cases for
SOR as clean and also for EOR as dirty.
The main hydraulic and thermal checks
were crucial steps in the study and were
the main assumptions before validation.
VR from the VDU and LOP feed were
integrated via a heat exchanger and the
lube oil plant feed entered the fired heater
after this heat exchanger, as shown in
FIG. 1. Both fuel consumption effects for
the VDU and the LOP fired heater should
be considered before performing a heat integration
study. The fired heaters efficiencies
were assumed as 90% and 80%, based
on the design for the VDU fired heater
and lube oil unit fired heater, respectively.
For the first step of validation, the
base model of the system was created.
Heat and material balance were checked
on the selected data set for this model.
This model was then analyzed based on
simulation outputs according to predetermined
verification limits. In each step
of validation, the exchangers design data
were considered for detailed comparison
with the datasheet values for duties, hydraulics
and fouling factors. The acceptable
criteria were ± 5% based on possible
measurement errors and general refinery
applications.
The base model. The base model of the
system is shown in FIG. 1. The scope of
this pinch analysis only covered the atmospheric
straight-run fuel oil (ASRFO) heat
network; the remaining sections of the
unit were not modeled in this study. All
alternative cases were based on the model
discussed below.
CASE STUDY
Pinch studies were conducted for five
different cases and the numbers of shells
for new heat exchangers in EOR and SOR
were changed. As previously stated, 38 dif
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