1. Sample coolers are small shell and tube heat exchangers that are used to cool hot fluids or
to condense vapors such as steam to a point at which they pose no concern for personnel
safety. These are usually used to cool the fluid as it is being collect for analysis.
Sample coolers are not only used to cool samples but also
to temper the sample to the appropriate temperature for
the analysis being performed. This is important as some
analysis procedures can be affected by interferences
directly or indirectly due to the fluid temperature.
For example, when sampling steam condensate in order to
check the pH of the water, the samples should be cooled
sufficiently for safe collection and handling while avoiding
overcooling. A relatively common recommendation for
analysis of steam condensate pH is for the cooled sample
to be in the range of 100 to 105 degrees F. It is extremely
important that pH measurements be made on cooled
samples. If the sample is hot, carbon dioxide in the water
sample will be liberated from the sample and escape into
the atmosphere, which results in artificially or falsely high
pH measurements. Cooling will minimize the carbon
dioxide that will flash off from the sample. When the
carbon dioxide flashes off from the sample, it is no longer
present in the condensate sample which will result in this
measurement to be falsely high. The difference between
in-line cooled steam condensate samples and condensate
cooled at atmospheric ambient temperatures and exposed
to the atmosphere can be 2.0 pH units or more. Obviously,
this difference in pH could have implications to correctly
applying treatment to the steam condensate system and
the corrosion rates experienced.
It is sometimes also argued that over-cooled samples,
particularly if they are left exposed to the atmosphere, can
result in some atmospheric carbon dioxide and oxygen to
be absorbed into solution from the atmosphere, again
potentially resulting in false results. With regard to oxygen
for example, oxygen is more soluble in cold water than in
hot water. Therefore, it can be argued that some amount
of oxygen can potentially be absorbed in over-cooled
samples.
In applications such as described above, the practice of
local conditioning or cooling and analysis is often
exercised. This means that the sample is cooled with the
use of an in-line sample cooler relatively close to the point
of extraction from the process and the analysis is
performed at the sample cooler using a continuously
flowing sample from the cooler. This minimizes the
potential for interferences as a result of prolonged
exposure of the sample to the atmosphere when the
analysis is performed and as while the analytical
equipment acclimates to the sample and compensates for
the temperature of the sample.
Proper conditioning, collection and storage of samples
collected for remote analysis also needs to be considered.
Where samples are collected in containers so that they can
be transported to a remote location for analysis, diligence
regarding the manner in which the sample is collected is
also important. Depending on the type of analysis to be
performed, how the sample is collected can impact the
degree of interferences and the accuracy of results. Some
considerations may include but are not necessarily limited
to the following.
The correct sample temperature should be
considered for laboratory instruments and
procedures utilized.
The duration of time elapsed from when the
sample is collected to when the analysis is
performed.
Completely filling the container to the brim to
displace atmospheric gasses from the container.
Immediately capping the container to reduce
sample exposure to atmospheric conditions or
contamination.
Adequate purging of sample line is necessary to
assure a representative and “fresh” sample.
Minimize splashing, agitation and exposure to
atmosphere. Some methods for analysis
recommended that the sampling tube be long
enough to extend to the bottom of the sample
container and for the end of the sampling tube
to remain immersed in the collected sample fluid
until the required volume is obtained. This
reduces exposure to atmospheric gasses.
Another consideration for the temperature of conditioned
or cooled samples is the desired temperature of the
analytical equipment and procedures being utilized. Some
analytical equipment for instance has an optimal
temperature of 77 degrees F. The degree of deviation from
the desired temperature may affect the accuracy of the
measurement and/or the time required for the equipment
to compensate for the difference in temperature. These
factors should also be considered regarding the
appropriate temperature of samples conditioned or cooled
for analysis.
The Proper Use and Benefits of Sample
Coolers in Steam Plant Applications $

2. When purchasing or installing a sample cooler, the
conditions and application for which the cooler will be
utilized should be considered. Sample coolers are designed
and specified in various sizes and with varying rates of
heat removal. Identifying the correct sample cooler for the
application will be useful in assuring the following.
Safety of the personnel collecting samples.
The appropriate degrees of conditioning/cooling
of samples for the specific analysis to be
performed or instruments utilized.
Minimize the potential for interferences that
may result in inaccurate analysis results.
Minimizing waste from excessive amounts of
cooling water being required.
Adjustment of the cooling water flow to the sample cooler
can result in the appropriate temperature for the analysis
being performed. This can be done by installing an
additional valve which is used to throttle the flow to
achieve the desired temperature. The same may also be
accomplished by installing an orifice or flow restrictor.
Both of these methods can be employed to achieve the
desired sample temperature if the conditions, such as
temperature and pressure of the stream being sampled
and the cooling water remains stable and unchanged. This
can also minimize the variability in sample conditioning
and analytical results when tests are performed by
numerous individuals.
Additionally, diligence in understanding the importance of
employing proper sample conditioning techniques also can
reveal potential for water savings. Restricting or
controlling cooling water flows to sample coolers for the
degree of cooling required for the analysis performed can
reduce water usage. Furthermore, identifying alternative
sources of water for cooling of samples can result in even
greater water savings.
One example of an alternative cooling water source for
sample conditioning is the use of open recirculating
cooling system water. This is often available with
pressures and temperatures sufficient for sample cooling
and has the added benefit that it has been treated for
scale and corrosion inhibition that will protect the
internals of the sample cooler and result in increased
longevity of the heat exchanger for sample cooling.
Sample coolers are available in numerous sizes and
configurations depending on the application that they will
be used in. Cooling water flows can range from less than
one gallon per minute to greater than 20 gallons per
minute. It is also not uncommon for a single facility to
have multiple sample coolers used in various applications.
When one considers the amount of water potentially used
in sample cooling applications, it is easy to perceive that
there may be appreciable potential for water savings.
Recognizing the benefits of employing proper controlled
conditioning of samples is important for safe and efficient
operation of steam plants as well as numerous other
industries. System operations can be optimized resulting in
increased output, on-stream time, longevity of equipment,
personnel safety and water savings.
By Robert Jewell
Robert has 30 years of career experience in industrial utilities. He specializes in and has extensive
experience in the operation and management of steam plants, central plants, cooling and
refrigeration systems, potable (drinking) water systems, water treatment, wastewater treatment,
and facility management.
He is an advocate of water conservation, energy conservation and protecting our environment while
also incorporating those advocacies into sustainable water and energy efficiency activities and
programs that positively impact the organization and local community by finding efficiency and
savings in existing processes and procedures through creative solutions.
Connect with Robert on Linkedin at http://www.linkedin.com/pub/bob-jewell/26/810/32a