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CONTROLS FOR LARGE BOILERS are addressed
in this issue of WLEtter. "Large" in this instance means over 10 million
Btu of fuel per hour (200 boiler horsepower or greater). They are common in the central energy plants of hospitals, industrial
plants, and university and other institutional campuses.
In a discussion of control systems, the terms
architecture and strategy occur, most often when the process to be controlled is industrial. In this context,
"architecture" refers to the type of controls used and how the pieces are connected. "Strategy" refers to the
manner in which the measured parameters are
manipulated to effect the control of the final process. In process control in general, and especially in boiler
control, the strategy used dictates the system control architecture. Generally there are two boiler control
functions: combustion controls which produce constant steam pressure (or water temperature), and Burner
Management Systems which maintain safety of the firing boiler, also known as "Flame Safeguard Systems".
BOILER CONTROL SYSTEMS
Here it comes, the meeting without end. Someone has -- maybe correctly -- decided that your
facility's boilers need controls upgrades. At this moment you wish they were "their" boilers.
You know a lot about these large devices. They use more than 100 therms of gas per hour, you
have several of them, and although the mechanical and chemical upkeep of the beasts is generally well
in hand, you and your staff are at the mercy of the
outside maintenance contractor when it comes to the controls. And you can't even communicate
with these guys face to face because they use terms like "high low select" and "lead lag". Geeks.
In the meeting, someone says, "Parts for your control system are no longer available." How can
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WLEtter is a bimonthly publication for the clients and other friends of Wieland Lindgren Engineers. It is intended to help facility managers and architects with the design, construction, operation and maintenance of the many complex electromechanical systems included in modern buildings.
that be? You have some difficulty getting 54 Dodge parts from Shucks, but...
In addition, you have gotten several quotations for a controls upgrade, all unsolicited. They range
from $689.00 to $257,000.00 per boiler. How do you get a handle on that ? Your company makes
software, or paper, or test equipment, but not steam, at least not as its prime business.
There are some guidelines that can be used. Boiler controls, and their types, or architectures, can be
categorized by the boiler size and the operational concerns of the facility. First let's discuss the two
main categories of controls associated with large boilers.
Figure 1. Boiler Controls.
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