Page 437 - Boiler_Operators_Handbook,_Second_Edition

422 Boiler Operator’s Handbook

started and if I drained it too far the system would shut very true for pumps, fans, etc., that are powered out of
down on low tank level… and lock out. I’ve recom- a motor control center with a common control power
mended that the designer consider simply alarming transformer or where there’s a motor area disconnect.
some of the conditions and, provided the operator ac- It’s possible for the motor starter to pull in, mak-
knowledges the alarm, let the system start when there’s ing a contact and energizing a motor running indicating
no reason not to. light, and the motor to be sitting there powerless be-
If you run into something that becomes a real pain cause the power circuit breaker or the disconnect at the
don’t hesitate to grab the engineer or technician and motor is open. I watched an operator get very frustrated,
register a complaint. Of course if all you do is complain throw tools and everything else one evening when he
they may not do anything about it. If, on the other hand, couldn’t get a boiler to fire on oil. The light at his con-
you suggest an alternative approach and explain your trol panel said the oil pump was running; it wasn’t. I
reasons they may just go along with it. do hope the obvious question came to your mind, what
about the low oil pressure switch?
Meters and other electrical devices are directional.
INSTRUMENTATION Recently some operators blew up a rather expensive
set of electrical switchgear because the phases were not
I have been in one or two boiler plants that hon- realigned after some maintenance. They thought “alter-
estly had no instrumentation. It was a violation of their nating current goes both ways so there isn’t any direc-
State law but that’s how they were. No pressure gauge, tion” but it’s important to remember that it’s different
no thermometers, nothing! Their argument was that no- for each phase and single phase power can come from a
body ever looked at them anyway so why did they need transformer on one of the other two phases so they don’t
them. One of those plants had a fuel bill equal to one parallel.
third of the prior year when I finally got them to under- Pressure gauges show pressure but a steam pres-
stand the need for instrumentation and how to use it. sure gauge that’s mounted at the operating level and has
On the other hand I’ve been in plants with all the connecting piping to a steam drum twenty feet or more
requisite instrumentation and a log book where they above the gauge also has a standing leg of water on it.
recorded many readings and discovered they gave no To properly indicate the pressure in the boiler the gauge
thought to interpreting what they had. The instruments has to be calibrated to read zero when it has that stand-
are there to provide the operator with information ing head of water.
on the status of the plant and provide a history of the Thermometers read the temperature at their bulb.
plant’s performance. The wise operator knows how to That doesn’t mean that the fluid is at the same tempera-
use those instruments. ture just a few inches away from the bulb. Use the steam
Instrumentation varies in sophistication and preci- tables in the appendix to find the temperature of the
sion from an indicating light to a fully compensated fuel steam in your boiler and compare it to the stack temper-
gas flow recorder. Some, like the indicating light, give ature. I’m always amazed when someone tries to tell me
an immediate perception of the status of the plant while the stack temperature on a boiler operating at 250 psig
others, like a flow totalizer reading, have to be subjected (406°F) is 350°F and there’s no economizer or air heater.
to study before the status is determined. One key to the Either the temperature reading is wrong or there’s a lot
use of instrumentation is—it isn’t worth anything if it of tramp air leaking into that boiler.
isn’t recorded. Many of the reasons for recording data Thermometers in the top of a pipeline can fail to in-
are explained in the section on boiler logs. The purpose dicate the temperature of the liquid flowing underneath
of this section on instrumentation is to convey some the bulb. Similarly air in the top of piping or a vessel can
points on interpreting readings and understanding the insulate the thermometer from the heat of the liquid.
effect of other conditions on the instruments. Part of using instrumentation is realizing when a read-
An indicating light provides you information on ing has to be wrong.
two states or conditions, on and off, right? Well that’s Steam flow recorders, unless compensated, are
a maybe; if the light is off it could be because the bulb calibrated for a certain operating pressure. If the header
is blown or the power is shut down to that piece of pressure is higher or lower then the recorder then the
equipment. If the light is on, well you know there’s volt- readings are wrong. I’ve encountered many a plant that
age and current at the indicating light but that doesn’t thought they had saved a lot by lowering the steam
necessarily mean the status it’s indicating exists. That’s pressure, the recorders indicated they were making