Page 127 - Boiler_Operators_Handbook,_Second_Edition

112 Boiler Operator’s Handbook

loads where it was the most efficient. should never associate the number of pumps in opera-
Once Boiler three was installed, a necessity to tion with the number of boilers. They deserve their own
match increased plant load, the Operators chose to fire it set of rules, established by experience and observation.
alternating with a combination of Boilers one and two. Many operators don’t realize that there’s a lower
The significant discrepancy between those two operat- limit to efficient operation of water softeners. Once the
ing setups was obvious to the plant engineers and an flow in a softener, or any ion exchange bed for that mat-
investigation was conducted to determine what to do ter, drops below a set value (usually 3 gpm per square
about it. It was determined that the principal reason for foot of flow area) they begin channeling. The water
the difference was that Boiler three was equipped with tends to bypass much of the resin and its capacity isn’t
an economizer. Due to the age of the first two boilers used. Operators can allow a lot of scale forming hard-
a decision was made to purchase another new boiler ness to sneak through their softeners if they run too
with an economizer rather than installing economizers many of them in parallel.
on the older boilers. Part of the investigation included If everyone in your plant is doing their best to con-
generation of the graphs. Now the Operators know that serve that valuable condensate you will have reduced
for certain periods of operation including the Christmas the demand for makeup water and may have reduced it
shutdown it’s advisable to operate the oldest boiler be- to the point that your softeners start channeling. You’ll
cause it’s the most efficient for low steam loads. have to watch the softeners closer if you’re down to one
Evaluation of the plant’s steam loads later led to because it might start regenerating automatically when
the decision to abandon, dismantle, and scrap Boiler two you’re not looking. That will shut off your supply of
because plant operations almost never produced steam makeup.
loads that were best served by that boiler and mainte- Some plants are constantly having trouble with
nance of it wasn’t economical. condensate loss. It’s either due to contamination indi-
This example should serve to prove to you that cations or leaks. In those cases it’s better to have the
knowing your load and knowing your equipment can technician that services those softeners modify the
make a significant difference in the cost of operation of programming to limit the softeners on line unless the
your boiler plant and a graphing your data helps make pressure drop through them gets too high. It’s a mat-
it evident. Decisions to simply alternate firing boilers ter of adding a differential pressure switch so another
without regard to load performance cost that manufac- softener will come on line when needed. He should also
turer hundreds of thousands of dollars. add a bypass switch that permits you to manually put a
Now that you know your plant and know your softener in service.
load you will make decisions that reduce the impact Whenever I visit a plant and find more than one
on operating costs. Frequently operators will decide piece of equipment operating I do a quick check of the
to put another boiler on line whenever the load on one loads to see if the loads and equipment match. I should
approaches 70%. That immediately converts operating note that this also applies to chillers and devices other
conditions from one boiler operating at its maximum than boiler systems. It is always a cheap way to give a
efficiency to two boilers operating near minimum effi- customer a return on his investment in my time because
ciency at 35% load. Radiation losses are doubled with no I can usually show a considerable savings for doing
change in load and all losses associated with lower fir- nothing but shutting off some of the operating equip-
ing rates are encountered. Knowing the load, being able ment.
to forecast its changes, and knowing what your boiler In mid summer of 2001 I visited a plant where the
can do will frequently prevent putting that other boiler gas booster was running constantly when the gas sup-
on the line until the load will exceed 100% of what is ply pressure was more than adequate to serve the boiler
on line. Establish values based on experience and don’t load. The owner had his operators shut the booster
hesitate to experiment to see what the best matches are. down and bypass it. Of course they had to check it when
Matching equipment to load isn’t restricted to the the temperatures got colder to determine when they
boilers. I don’t know how many plants I visit where might need it. I encouraged them to establish an SOP to
the scheme is to operate one boiler feed pump for each check it out by running it temporarily every fall so they
boiler on the line. Since feed pumps have to be capable would be capable of putting it in service should they
of delivering water at the boiler safety valve pressure need it in the winter but, to the best of my knowledge,
it’s not uncommon for them to have significant capacity it hasn’t run since. That wasn’t just a case of matching
relative to normal operating pressures. As a result you load, it was a case of recognizing there was no load.