There are three main elements to
preventing contamination occurring
in tubular heat exchangers:
production quality, system design,
and system maintenance.
When it comes to quality, you generally get
what you pay for. If a quotation for a new heat
exchanger seems to be much lower than others,
be sure to check the specification, particularly
the materials that are being used. Not only is
the quality of materials important (such as the
use of stainless steel), but so too is the quality
of construction. Welding needs to be precise
and joints (whether rolled or welded) need to be
smooth to prevent product fouling or lodging
of product, while also being strong enough
to maintain integrity under pressure. Most
manufacturers will be happy to arrange for you
to see their production facilities and to provide
information on their fabrication processes and
standards.
The type of heat exchanger and its design
capacity will determine the number of tubes. At
some point during the design process, the tubes
will need to be supported and attached to the
body of the heat exchanger – usually at the ends.
The tube plate (sometimes known as the tube
sheet) not only supports the tubes, but usually
provides a barrier between the product and
service fluid.
In terms of design there are two main methods to
prevent cross contamination between the product
and the service medium (heating or cooling)
due to leakage in tubular heat exchangers. The
first is to maintain a positive pressure difference
between the product and the service fluid, so
that should a leak occur, the product will always
flow into the service fluid rather than vice-versa.
However, in order to be successful this pressure
differential must be maintained at all times, and
appropriate sensors and monitoring systems
must be included in the heat exchanger. It
also adds a further level of complication when
designing the operating pressures for the
equipment.
The second option is to introduce a physical
separation between two different tube plates; one
for the product and one for the service fluid. This
means that in the event of a leak from either the
service fluid or the product, the material flows into
a safety container or other vessel and no mixing
of the two materials is possible. Because this
option relies on a physical barrier, no additional
systems are required, making construction,
operation and maintenance of the heat exchanger
much simpler. For this reason, HRS Heat
Exchangers uses the double tube plate system in
food production situations where contamination
needs to be prevented, and double tube plates are
included as standard with our S and SI Series of
multitube heat exchangers, as well as the double
tube DTA Series.
The gap between the two tube plates will
depend on a number of factors, including the
food products being processed and the space
available for the installation, but can be effective
even when the distance is just 3mm. Depending
on the materials being used and the type of
situation that the heat exchanger is used in, the
gap between the two plates may be shrouded
(with appropriate drain or inspection ports) or
open.
Finally, it is important to regularly clean, inspect
and maintain heat exchanger equipment in line
with the manufacturer’s recommendations. For
example, if handling acidic or abrasive materials
(such as fruit juice) more frequent inspection and
cleaning may be required. Regular cleaning will
ensure that drain holes etc. operate correctly
in the event of a leak, while maintenance and
cleaning will reduce the risk of leaks occurring
and provide an opportunity for any repairs.
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