Page 133 - Boiler_Operators_Handbook,_Second_Edition

118 Boiler Operator’s Handbook

three times as much energy in fuel as it delivers to the ated by the gallons of oil or therms of gas burned to get
facility. Now consider the fact that so many boilers are it. Don’t, as one plant in Missouri did, simply put 122
outsized so they’re running at those low loads most of the in the column on the log for evaporation rate because
time and that cycling efficiency becomes meaningful. that’s what it is. In that instance, and in many others, I
Uh oh! Used another word that isn’t in the diction- found the operators put a value in the log that the chief
ary. Outsized means the boiler is no longer the right wanted so everyone was happy. It wasn’t anywhere
size for the facility. With added insulation, sealing up near the actual value which could be calculated from the
air leaks, adding double glazing, and other activities to other entries in the log.
conserve energy we have decreased the load so much In the case of the Missouri plant I upset everyone
that the boiler is now too big for it. It got outsized! I can’t because I did the math and showed the actual value was
guarantee that it wasn’t too big to begin with because around 108 pounds of steam per gallon of oil and that
that’s usually a fact, but calling it outsized doesn’t raise two of the three operators managed to run the plant so
the hackles of engineers like telling them they oversized their value was 105 while one managed to maintain 114.
it does. Once the other two were clued in as to what they were
When a modulating heating boiler is cycling at doing wrong, and settled down, the average went to 114.
temperatures that are halfway between the winter There were sound reasons why the plant couldn’t man-
design low and 65°F cycling efficiency has to be deter- age an evaporation rate of 122 but, since the manager
mined because it’s so low that replacing that boiler with wouldn’t accept anything less, the operators put what
one that’s the right size (perhaps you’ve heard of right- he wanted in the log book.
sizing, it’s been the rage) fuel savings will pay for it in Evaporation rate can be used to compare boilers
one or two heating seasons. Use that half the load and to each other and to performance at other loads and at
cycling determination to identify boilers that are cycling other times. It’s comparable to a boiler efficiency as far
excessively and get an engineer to do an evaluation to as variations is concerned. A change in evaporation rate
determine if the boiler should be replaced. should be relative to a change in combustion efficiency.
Perhaps the boss won’t go to the expense of hir- Of course that doesn’t come close to monitoring
ing an engineering firm to do it but you might suggest plant efficiency. For that you have to compare the de-
he contact an ESCO (Energy Service Company) and livery rate, how many pounds of steam you deliver to
invite them to look into it. ESCO’s install modifications the facility divided by the amount of fuel burned in the
to plants to reduce energy consumption and get their same time frame.
money back from the savings with no money layout by The actual value of the number itself isn’t im-
the owner. portant. The object of calculating these rates is to see if
they’ve changed and, if so, did they change for the better.
Whatever you use it should be treated as a flexible num-
PERFORMANCE MONITORING ber with a goal of increasing or decreasing it depending
on how you calculate it. The concept is exactly the same
Calculating boiler efficiency may not be consid- as monitoring your gas mileage on your car where the
ered part of the duties of a boiler operator. Monitoring miles per gallon dropping off indicates there’s something
and optimizing plant performance is. To make it simple wrong or you just did a lot of city driving you normally
we use values that are less complicated to determine, don’t do. Changes in the rate can be an indication of im-
and easier to understand and work with. Of course you proved performance or changes in the load.
have to understand how they’re calculated, and whether Evaporation rate provides a value very consistent
you want the results to be higher or lower to indicate an with boiler operating efficiency and delivery rate is con-
improvement in performance or they’re a waste of time. sistent with plant efficiency so they are good parameters
If you want to work in terms of efficiency the pre- to measure, log, and compare to monitor your perfor-
vious section provides guidelines to do just that. Don’t mance and the performance of the plant.
be surprised if you get numbers that seem out of place Evaporation rate can indicate problems that can’t be
but don’t accept them as true either. It’s simply unrealis- determined by combustion analysis or other methods of
tic to believe something can operate at more than 100% monitoring boiler efficiency because the latter are instan-
efficiency, even if the calculations are accurate. taneous readings. Frequently combustion analysis are
The best method for evaluating steam boilers is performed while the boiler controls are in manual and the
evaporation rate. Divide the quantity of steam gener- service technician has adjusted them to optimum. That