Articles about thermal fluid systems often start with a variation of the statement that “thermal fluid systems typically require little ongoing maintenance for the first few years of operation” and then go on to extol the various advantages of indirect thermal-fluid process heating over competitive heating methods, such as direct heat, steam and so on. The corollary to that statement, however, is that by the time there is a problem, the operating personnel that were trained on the system have moved on, been excessed or promoted. As a result, when things do go wrong, the guessing begins. And, unless there is an obvious cause like a geyser from the expansion-tank vent or a pump that sounds like it’s moving ball bearings, someone will likely blame the thermal fluid for the problem. There are several problems that seem to occur with some frequency. This article reviews a number of real examples and describes how the symptoms can be misinterpreted. The suspected fluid properties and the testing procedures necessary to determine which of the fluid properties (if any) is responsible for the problem are examined. Finally, recommended corrective actions are proposed.
Reduced throughput in a convection oven
The following is an example, Illustrate Fluid can not be real culprit to reduce throughput in a continuous convection oven.
EXAMPLE: A poultry processor was
experiencing reduced throughput in
a continuous convection oven. The
heater and pumps were checked for
problems, and all temperature and
pressure sensors were replaced. Someone suggested cleaning the heat-transfer fluid system. Since the fluid had
been in service for a number of years,
it was assumed to have degraded and
formed blockages in the coils because
the temperature drop across the heat
exchanger was much lower than when
the unit was new. The fact that the
fluid had been tested routinely and
found to be in good condition was totally ignored in the evaluation. Management personnel wanted to clean
the system and then change the heat
transfer fluid. A lube-oil additivetype cleaner was added to the system
with the expectation that the problem
would be solved. When there was no
progress, a thermal-fluid sample kit
was requested along with a request
to estimate the cost of replacement
fluid. Once again the viscosity of the
sample was found to be well within
the normal range. The plant manager
was very disappointed with the results showing that the fluid was not
the problem, because he had to send
the maintenance staff back in to keep
looking for the real culprit. Eventually
it was discovered that an air damper
inside the oven had a broken weld
that allowed it to flip up into the air
stream, effectively blocking the coils.
Throughput was reduced because insufficient heat was getting to that section of the oven.
Author Jim Oetinger is the director of technology at Paratherm Corp. (4 Portland Rd., West Conshohocken, PA 19428; Phone: 800-222-3611, Fax: 610-941-9191; Website: www. paratherm.com). He has over 30 years experience in the chemical and plastics indus- tries. He has been involved with a wide range of products and processes including pig- ments, refrigerants, consumer plastic recycling, polymer compounding, process instrumentation and spray dried polymers. In addition, Oetinger has over 20 years experience in sales, marketing, and technical support of thermal fluids. He has authored articles on thermal fluid and system troubleshooting for this and other publications. A member of the Delaware Valley Chapter of the AIChE, he holds a B.S.Ch.E. from Clarkson University and a Masters of Management degree from Northwestern University. Oetinger and his family reside in a suburb of Philadelphia, Pa.
content and image courtesy:www.paratherm.com