Page 138 - Boiler_Operators_Handbook,_Second_Edition

Chapter 4

Special Systems

A working knowledge of steam systems makes it
possible to understand the use of special and unique
systems and heat exchange materials because all the
rules of heat and flow don’t change with a system or the
fluids used as the heat exchange medium. This section
provides a little insight into some of the special systems
that a boiler operator can encounter and may be called
upon to operate.

SPECIAL SYSTEMS

You can always read the instruction manual but
just in case you happen to encounter one of the special
systems found in some boiler plants I thought I would Figure 4-1. Vacuum pumps for condensate system
touch on them here. You may never encounter one but if
you do, at least you’ll have an idea what you’re dealing is air leakage which is impossible to locate during nor-
with before you open the instruction manual. mal operation and even when you can pressurize the
system they don’t show up because a drop of water or
piece of scale can prevent water leaking out but will al-
VACUUM SYSTEMS low air to leak in. Once air leaks start they tend to get
worse because the air dries out the joint sealing com-
In the chapter on energy we touched on what hap- pounds. Technology could probably provide us with a
pens in steam systems with temperatures below 212°F joint compound that could maintain a seal in a vacuum
but there are systems that are designed to operate with a system but the horse has already escaped the barn.
vacuum. Vacuum pumps (Figure 4-1) intentionally pro- Another problem I encounter regularly with vac-
duce a vacuum by removing air from the piping system, uum systems is someone works on the system with no
both the original air on start-up and air that manages to knowledge that there’s a vacuum pump back at the boil-
leak in. Condensate flows to the vacuum system which er plant and they put in a vent. Now you’re assured of
is operating as the lowest pressure in the system and is a leak because someone created it and it looks perfectly
pumped out to the boiler feed tank or deaerator. The normal. I find open vented condensate return units on
system shown in Figure 4-1 is a common one that pro- vacuum systems regularly. If someone does this to you
duces a vacuum by pumping water through a water jet the simple solution is to connect the vent to the steam
that acts as an ejector to pump the air out of the system. line instead of atmosphere when the tank can take the
The vacuum system allows users of the heat to operate steam pressure. You’ll also have to install a valve so you
at lower temperatures, maybe a necessity in some situ- can service the unit and put a liquid trap in the overflow
ations where there’s a concern for someone touching a line to block it. The water in the trap tends to dry out so
radiator and the problem is solved by operating at 25 you have to have a way to refresh it as well.
inches of mercury where the steam temperature would Since there’s so few of these systems around I’ll just
be 134°F. suggest you use the manufacturer’s instruction manual
You won’t run into many vacuum systems because as a guide and other information in this book that should
they’ve been declared unworkable by many engineers help you understand what’s happening with them and
and boiler operators. A singular big problem with them how your SOPs, etc., should address them.

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