Page 147 - Boiler_Operators_Handbook,_Second_Edition

132 Boiler Operator’s Handbook

side of a fluid heater is critical to detecting a buildup of growth of a leak also becomes a factor to consider. The
carbon in the tubes. Monitoring is not as simple as read- fluid has to be circulated long enough to allow the heater
ing the gauges at the inlet and outlet then subtracting to cool until it will not carburize the fluid left standing in
the difference. Since viscosity changes with temperature it. It also has to be cooled enough so it will not spontane-
you need to have a record of pressure drop at different ously ignite when exposed to air, then the fluid must be
average temperatures so you have relative pressure drained from the system back to storage until the level
drops for comparison. You want to be as precise as is below the point of the leak. Some facilities don’t have
possible with your measurements because you want to sufficient storage to completely drain their systems and
catch the carbon formation the instant it starts. require a supplier’s empty truck, on rental, to hold the
Even a very thin coating of carbon is so rough it fluid as it’s drained.
can produce a significantly rough surface on the inside Organic fluid heaters and the occasional vaporizer
of the tubes so the pressure drop increases significantly. make some chemical processes possible only because
That’s usually not a problem because the circulating they can produce high temperatures at low pressure. A
pumps are normally positive displacement types that common application is in the asphalt industry where the
will continue to force the designed flow of fluid through product must be heated to high temperatures so it can
the heater. When carbon builds up failure tends to be flow readily. All the rules for high pressure boilers apply
instantaneous because the increased pressure drop is and every plant will have unique and special provisions
handled until the pump motor is overloaded and trips that the operator should know. Among all plants these
out. Systems with centrifugal circulating pumps are un- are the ones where the SOPs must be memorized be-
common because the viscosity variation with tempera- cause lack of rapid and proper response to an upsetting
ture has a significant effect on the flow in the system and condition can lead to hazardous conditions or long-term
the performance of the pump. shutdown of the facility.
I did have one customer that solved his problem
temporarily by installing a larger motor on the pump. It
was nearly impossible to tell what was going on in the SERVICE WATER HEATING
system because none of the pressure gauges worked.
When they finally got some gages in place a high pres- Service water is the term currently used by
sure drop was detected across the heater and they had to ASHRAE to describe what I always called domestic hot
shut the whole plant down to retube it. water heating. Heating of water for cooking, showers,
Any organic fluid system should be checked baths, washing, etc., is not the same as heating water for
throughout its entire length at least once a shift with closed hydronic building heating systems so we’ll use
special attention paid to any signs of leakage. The in- the term “service water” to describe it.
sulation is typically calcium silicate in order to handle Service water heating systems are frequently ig-
the high temperatures, and it’s also very thick, so a slow nored. I didn’t think about it much at my home because
leak can penetrate a lot of insulation (store a lot of fuel) I have an electric hot water heater and it managed to
before it’s detected. System leaks are dangerously close operate trouble free for thirty years. Finally, the plastic
to becoming fires and they must be caught before they dip tube failed, disintegrating into thousands of little
become a fire; there is no steam quenching on the piping pieces that fouled every faucet and toilet tank float valve
like there is in the furnace. until I was so frustrated I called the water company to
Since most organic fluid systems are used in pet- complain about the junk they put in the water. It was a
rochemical and similar industrial production plants little embarrassing to have them tell me it was probably
immediate shutdown to repair a leak could result in the dip tube then discover that was the case. Anyway, I
thousands of dollars of production loss so you may be figure my new electric hot water heater and it’s dip tube
compelled to simply monitor a minor leak and be pre- will outlive me.
pared to extinguish any fire that results until the entire I wish you were all that lucky. It won’t happen very
facility can be economically shut down. It’s one of those often. Service water heaters do not enjoy the presence of
situations where the operator has to consider multiple chemically treated water to prevent scale and corrosion
risks and the cost of each; any leak that can’t be made and most of them have such problems. I remember one
up, or becomes extensive to the degree it’s a dramatic area where the well water contained so much calcium
hazard, requires a shut down. sulphate that it would form heavy scale if the water tem-
Shutting down a fluid system takes time so the perature was increased by 6°F. There’s nothing you can