Page 380 - Boiler_Operators_Handbook,_Second_Edition

Chapter 11

Controls

There was a time when the operator was the only than fight it. Controls are simply one of the things that
controlling influence on the operation of a boiler plant. help you do a better job and you should know how to
Today controls are an extension of the operator’s eyes, use them.
ears, hands and feet that help the operator keep the There are two basic types of control, on-off and
plant running in a safe and efficient manner. There’s modulating. On-off control isn’t as simple as you might
no question that less manpower is needed in a plant think and I’ll cover some of the unique conditions you
equipped with controls but, unlike a human, they can’t should be aware of within the discussion of specific ap-
always let someone know when they aren’t working plications which follow. The following few paragraphs
correctly. address the general elements of modulating controls
The modern boiler plant operator uses the latest which a boiler plant of any reasonable size will have.
controls made available to manage the ever increasing If you recall the section on flow you know that con-
cost of operating a boiler plant. With these tools the op- trols change the rate of flow in order to maintain a desir-
erator can easily manage to reduce operating costs by as able condition such as pressure, level or temperature.
much as 15%. Despite the fact that we can’t really control pressure,
level or temperature we identify a control loop using
those parameters. Just keep in mind the fact that you
CONTROLS aren’t controlling anything but flow.
Just like an engineer, right? Using big words like
“Controls! What controls?” The fireman walked parameter! Parameter is one of those words that we use
away shaking his head and muttering something about to mean several things and it’s not that complicated a
those dumb young engineers fresh out of the academy. I concept. We use it because controls aren’t selective; the
would discover later that what I thought were controls controller doesn’t know if it’s controlling to maintain a
were considered a simple obstacle to walk around on pressure or a level, that information isn’t even important
that ship. They were Bailey Standard Line controls and to the controller. We say parameter and we mean level,
the honest truth was that none of them were working. pressure, temperature, pH, or anything else we choose
It didn’t deter me because I had seen them working to maintain with a controller. The controller does the
on ships when I was a cadet three years earlier. After a same thing regardless so we give it one generic name,
couple of weeks of tightening connections, adjusting set- parameter.
tings, and replacing most of the diaphragms that sense There are a number of words used by the control
air and flue gas pressures I managed to show that fire- designer and technician that you should know. Why?
man that the controls could maintain the steam pressure Because they only know about controls and use words
as well as he could and all he had to do was sit back and specific to their controls that don’t differentiate among
watch them do it. the hundreds or even thousands of different systems
I believe the attitude that controls would put that can use those controls. A controller can be used for
everyone out of work are gone and most operators so many different applications that assigning names that
consider them just another tool that only they have the are independent of the process being controlled was es-
skill to use. The last plant I was in where the controls sential. Once you know what they are and what they
were not allowed to do their job now operates automati- represent you’ll have a better understanding of controls.
cally, without any operator in attendance. Because the Despite a tendency of some people to award a level
controls do a better job? Nope, because the operators of intelligence to controls they are really quite limited.
simply refused to allow them to work at all. A concern They don’t know what they’re controlling nor what pa-
for keeping their jobs led to them losing all of them. I rameters they are maintaining, they respond to control
won’t argue the fact that people have been replaced by signals and produce control signals. The signals are air
technology, but I do know that it’s better to embrace it pressure, fluid pressure, electrical voltage, electrical cur-
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