Hydrocarbon Processing - January 2021 - 52

Heat Transfer
second fluid mentioned herec has the lowest line pressure drop and lowest cost per
year, which minimizes the operating costs
of pumping. Even though the third fluidd
has the highest heat transfer coefficient, it
is not preferred due to the higher pumping
related operating cost. The cost of these
fluids per barrel is very high compared
with the base oila and ULSD. The second
thermic fluidc was chosen for the project
due to its stability at very high temperature and lowest pumping cost compared
with the other two fluids discussed hereb,d.
The base oila and ULSD are unsuitable for
an operating temperature above 600°F.
Over a 10-yr-20-yr cycle, a hot oil system has exchanger leaks, flange leaks, sol-

ids building up in the system, etc., which
can amount to substantial volume loss.
Also, de-inventorying the system for 10yr vessel inspections typically results in
some fairly high system losses as some
will ultimately get pushed to the flare, regardless of how well the plant minimize
the losses. Large systems are harder to
manage in a refinery system. Due to the
sheer volume of the hot oil system, and
the fact that the refinery frequently contaminates and purges high volumes of hot
oil material (especially during an outage),
the price-rendered specialized heat transfer fluidsb,c,d are infeasible. For this reason,
the refinery went with a superheated 450#
steam on another new project. If a hot oil

TABLE 1. Fluid properties of hot oils at 680°F (360°C) and vapor pressures
at 680°F and 551°F (288°C)
Thermic fluids

Density, Viscosity,
Cp,
lb/ft3
cP
Btu/lb-°F

k, Btu/hrft-°F

Vapor pressure, Vapor pressure,
psia at 680°F
psia at 551°F

100Na

40.19

0.2

0.746

0.02756

37.8

15.16

ULSD

35.13

0.1

0.762

0.02358

133.9

50.85

45.94

0.15

0.608

0.0487

90.4

27.51

Dowtherm G

49.1

0.21

0.651

0.05404

48.8

14.35

Therminol 72d

48.1

0.16

0.591

0.0568

Dowtherm Ab
c

TABLE 2. Estimated mass and volumetric flowrates of different hot oils
Thermic fluids

Absorbed heater duty required, MMBtu/hr

m, lb/hr

VF, gpm

48.1

499,823

1,551

ULSD

48.1

489,328

1,737

Dowtherm Ab

48.1

613,270

1,664

Dowtherm Gc

48.1

572,762

1,454

Therminol 72

48.1

631,911

1,635

100N

TABLE 3. Hydraulic performance of different hot oils
Thermic fluids
a

100N

ULSD

HH, hp

AH, hp

24.01

21.7

36.2

13,312

26.2

26.5

44.2

16,257

ΔP/100ft

ΔP for 2,000 ft

0.0186

1.2

0.0185

1.31

$/yr

Dowtherm Ab

0.0185

1.57

31.46

30.6

18,772

Dowtherm Gc

0.0186

1.29

25.78

21.9

36.5

13,435

Therminol 72d

0.0185

1.59

31.81

30.4

50.7

18,649

TABLE 4. Thermal performance of different hot oils
V, ft/sec

ΔH%

9.9

1.95E + 06

0.003703

316

ULSD

11.1

4.06E + 06

0.002075

386

Dowtherm Ab

10.7

3.24E + 06

0.001258

545

Dowtherm G

9.3

2.16E + 06

0.0017

493

10.5

3.13E + 06

0.00112

589

Thermic fluids
100Na

Therminol 72

52 JANUARY 2021 | HydrocarbonProcessing.com

system loses appreciable volumes of material, or simply needs a fresh load, it is going to take at least a month for the thermic
fluidsb,c,d to generate and supply the necessary volumes. The refinery still uses hot
oil systems such as the base oila and ULSD
for operating temperatures below 600°F.
Through trial and error in the refinery, the
plant noticed that if the existing system is
operated near 575°F, virtually no thermal
degradation occurs, making the base oila
and ULSD thermally stable below 575°F,
ideally. Although, the base oila and ULSD
are economically very attractive, these can
only be used when the system operating
temperatures are below 575°F.
This research can be utilized in any revamp, new grassroot refinery or a chemical project where hot oil fluids require
comparison. It is vital to look for temperature range of processes, and vapor pressure is a critical parameter in selecting
an appropriate hot oil fluid for a system.
With the presented calculation approach,
defining heat transfer and hydraulics process parameters can be estimated to properly select a hot oil type. Additionally, it is
important to note that a single parameter
is insufficient; analysis of many parameters provides a bigger picture of the system. Refinery experience with operation
of a particular hot oil fluid and the cost of
hot oil play critical roles in choosing a hot
oil for new projects.
NOTES
a Ergon 100-N oil by Ergon North & South America
b Dowtherm A Heat Transfer Fluid by Dow
c Dowtherm G Heat Transfer Fluid by Dow
d Therminol 72c Heat Transfer Fluid by Eastman
e ASPEN HYSYS
LITERATURE CITED
Complete Literature Cited available online at
www.HydrocarbonProcessing.com
AVINASHKUMAR KARRE is a
Process Engineer with Worley
Group in Baton Rouge, Louisiana.
He has 13 yr of experience in the
refining and chemical industries, as
well as extensive experience in oil
refinery revamp operations,
catalysis and water treatment areas.
KALLIAT T. VALSARAJ is the
Charles and Hilda Roddey
Distinguished Professor of Chemical
Engineering at Louisiana State
University in Baton Rouge,
Louisiana. Dr. Valsaraj received his
B.Sc degree from Calicut University,
India; an M.Sc degree from the Indian Institute of
Technology, Madras; and his PhD from Vanderbilt
University in Nashville, Tennessee. He is a fellow of
AIChE, AAAS, NAI and RSC.

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