October 2016 • Volume 23, Number 10
Extending
the Life
of Your
HEAT
TRANSFER
FLUID
By Heather Bateman,
Radco Industries Inc.
Follow us on:
Heat Transfer Fluids
It is important to manage the life of
your heat transfer fluid through a
fluid sample analysis program using
a qualified laboratory.
Extending
the Life of Your
HEAT
TRANSFER FLUID
Follow these guidelines to manage and extend the life of your heat transfer fluid.
By Heather Bateman,
Radco Industries Inc.
H
eat transfer fluid heating systems often are a critical aspect
of many manufacturing processes. If the heat transfer fluid
running through these systems is not
properly operated, monitored and maintained, fluid replacement may be required
before the expected fluid lifetime. Fluid
replacement can be costly and result in
production downtime. It is important,
therefore, to ensure that the heat transfer
fluid remains healthy and operational.
Consider these guidelines for extending
the life of your heat transfer fluid.
2 Operating, Monitoring
and Maintaining Heat
Transfer Fluids in
Industrial Processes
Heat transfer fluid maintenance begins by
ensuring that the system was properly designed, and the initial fluid selection was
appropriate for the particular application
and operating temperature range. Given
that, it is expected that most heat transfer fluids will provide good performance
for many years before fluid replacement is
necessary. However, the manner in which
a heat transfer fluid heating system is operated and maintained will impact this
expected fluid lifetime. If a system is not
properly operated, monitored and main-
tained, fluid replacement may be required
much earlier than expected.
The following operational and maintenance practices play a significant role in
achieving long heat transfer fluid life.
Minimize Degradation. During
normal operation, heat transfer fluids can
degrade due to thermal stress or oxidation. All heat transfer fluids experience
degradation as a result of thermal stress
or molecular cracking when subjected to
high temperatures. Degradation from oxidation takes place when hot heat transfer
fluid comes into contact with oxygen. Oxidation is accelerated when temperatures
are above 300°F (149°C).
The extent to which a heat transfer fluid
Heat Transfer Fluids exhibits the effects of degradation while
in operation depends upon the particular
fluid properties and the level of degradation products in solution. When the products of degradation in solution reach the
fluid’s solubility limit, the formation of
solids will occur.
Excessive degradation and the resulting buildup of byproducts lead to potential mechanical and operational issues.
These include sludge, fouling and coking
of piping and equipment as well as decreased heat transfer efficiency.
To minimize fluid degradation, operate
the fluid below the manufacturer’s recommended maximum bulk operating temperature. The maximum bulk operating
temperature is the highest temperature
at which the fluid can be used and still
have acceptable thermal stability as recommended by the manufacturer. Longer
fluid life can be achieved when the system is operated at temperatures below the
maximum bulk operating temperature. It
is best to operate the fluid temperature of
the process near the middle of the operating range of the heat transfer fluid for
minimal degradation.
Fluid thermal degradation rates are
closely related to temperature. Keep in
mind that continuous use above the manufacturer’s recommended maximum bulk
operating temperature will increase degradation rates exponentially. Additionally, fluid can be protected by ensuring
that fluid flow through the heat transfer
system is sufficient to maintain turbulent
flow in the bulk region. Monitor heat
transfer fluid flow throughout the system,
especially in the heater section.
Degradation can be minimized as well
through the proper use of an expansion
tank. This allows for a reservoir of fluid
that is at a much lower temperature than
the fluid running through the circulation
loop. By using the expansion tank only for
fluid expansion and not as part of the fluid
flow through, minimal fluid degradation
occurs for this portion of your fluid. Furthermore, keeping a clean inert-gas blanket on the expansion tank will protect
fluid from oxidation.
Eliminate Contamination. Contaminated heat transfer fluid can result in
It is important to ensure that the heat transfer fluid remains healthy and
operational, as seen in this sample of new heat transfer fluid.
unplanned downtime and can be a costly
fluid changeout. Contamination from the
process can cause fluid degradation and
lead to operational issues as well as present a potential safety risk.
Contaminants can be introduced into
the system from process fluid leaks that
are a result of failed equipment or piping. Another source of contamination is
through the addition of an incorrect product or fluid during routine maintenance
such as top-off activities. Additionally, if
the expansion tank experiences a leak due
to corrosion, external contaminants could
enter the system at that point.
Heat transfer fluid contamination is
eliminated through proper design and
maintenance. The heat transfer system
should be included in a preventive maintenance program that routinely monitors
and inspects equipment to ensure sources
of contamination are eliminated.
Manage Heat Transfer
Fluid Life Through Fluid
Sample Analysis
It is important to manage the life of your
heat transfer fluid through a fluid sample
analysis program using a qualified laboratory. Many heat transfer fluid suppliers
offer this service free of charge. Monitoring your heat transfer fluid plays a significant role in maintaining production
rates, minimizing unscheduled fluid-related downtime and reducing overall heat
transfer fluid costs.
Proper preventive maintenance analysis
starts by taking a fluid sample at predetermined time intervals. This time interval
may be determined based upon past ex 3
Heat Transfer Fluids
perience with the system. In the case of
no experience or a new system startup,
samples should be taken quarterly. The
sampling time interval then can be adjusted based on an interpretation of the data,
with the first sample serving as a baseline.
Once the sample is analyzed, the data
is provided to the user. Often, the heat
transfer fluid supplier will interpret the
sample result in a report. In some cases,
the interpretation is left to the user. In
cases where the results of the sample analysis are outside the used fluid limit (determined by experience), the heat transfer
fluid supplier will provide heat transfer
system recommendations. In other cases,
where the fluid sample results are within
the used fluid limits, the fluid is satisfactory for continued use.
Extending the Life of
Heat Transfer Fluids in
Industrial Processes
When degradation and contamination
lead to a significant decrease in heat transfer fluid efficiency and production time,
and costs have significantly increased, options for fluid replacement are evaluated.
In many cases, a full fluid changeout may
be required to restore system performance.
Many times, however, the cost-effective
alternatives listed below can extend fluid
life and maximize system performance.
Partial Fluid Changeout. Replacement of a percentage of the initial
fluid charge with new fluid can improve
performance by diluting degradation byproducts or contaminates to within acceptable limits. Often, the off-spec fluid
that was removed from the system can
be returned to the fluid manufacturer for
credit, or the fluid can be reprocessed, returned and kept on-site for future makeup
requirements.
Fluid Filtration. The formation of
hard carbon or coke particles can lead to
the fouling of heat transfer surfaces. By
using portable filtration units brought on
site, a service team from a fluid manufacturer can remove these particles either
while the system is in operation or during a shutdown. On-site filtration saves
transportation costs and fluid drainage
time and expense.
4 During normal operation, heat transfer fluids can degrade due to thermal stress
or oxidation, as seen in this sample of degraded heat transfer fluid.
Fluid Reprocessing. Degraded or
contaminated fluid is removed from the
system and sent to the fluid manufacturer
for reprocessing. Low boilers and high
boilers are separated by distillation, and
the recovered heat transfer fluid is sent
back to the original user. Reprocessed
fluid usually will meet new fluid specifications. Partial fluid volumes can be
drained from the system and sent in for
reprocessing, allowing continuous operation and eliminating a system shutdown.
Reprocessing costs are based on the total
quantity shipped and offer savings over
the purchase of a new charge.
In conclusion, heat transfer fluid users can achieve long fluid life if steps are
taken to properly operate and maintain
© of Process Heating 2016
these systems. Eliminating degradation
and contamination is key to extending
fluid life. It also is important to monitor
and maintain heat transfer fluids through
a sample analysis program. When heat
transfer fluids reach a point where fluid
replacement is necessary, options other
than total system changeout can be evaluated. Considering these guidelines can result in improved system performance and
an overall lower heat transfer fluid cost.
Heather Bateman is a sales and applications
engineer for heat transfer fluids with
Radco Industries Inc. The Batavia, Ill.-based
company can be reached at 630-232-7966
or visit the company’s website at www.radcoinc.com.