Page 263 - Boiler_Operators_Handbook,_Second_Edition

248 Boiler Operator’s Handbook

alkalinity testing can be due to the phosphate you added guy on the second shift should get the same reading as
to the boiler water. the gal on the first shift and the third shift should concur.
The main reason for looking for the difference If everyone gets different results one or more of you are
between partial alkalinity and total alkalinity was the doing something wrong or the test is no good.
determination of how much scale treatment (carbonate Any trainee should be allowed to test water with
or phosphate) was in the water. Keeping up the spread the operator repeating the test to see if the results are
between partial and total alkalinity was, at one time, the identical. If the results don’t make sense there’s always
only way to tell. a possibility that you missed a step or upset the sample
I always disliked the chloride test because it used and the best thing to do is draw another sample and
silver nitrate solution which made your skin brown and repeat the test to see if you get the same results. I dis-
I just never managed to keep from getting it on me. My covered long ago that I had to ignore everyone when
hands were always blotchy from that stuff. Chloride I was doing a water test or I had to put it down and
tests are very handy however. The chloride ion doesn’t walk away. If I stood there talking to someone I had a
really react with anything once it’s in the water so chlo- tendency to let the sample bottle tilt to dump a little and
ride measurements provide an excellent means of de- blow my results out of the water.
termining the mixture of different waters. For example, Sampling and testing water is the first step in a
you can figure out your percent makeup by testing the good treatment program. If you know how to measure
makeup water and the boiler feed water. The condensate the quality of the water and how to determine what is
should have zero chlorides in it (it is, after all, distilled in it, both desirable and undesirable, you’re that one
water) so all you need do is divide the feedwater ppm step closer to ensuring the boiler plant remains intact.
by the makeup ppm and multiply by 100 to get percent Keep in mind that carelessness and inattention to detail
makeup. can result in major, sometimes catastrophic failure of a
Of course that doesn’t work when there’s some boiler, and you’re the closest one to it.
leakage into the condensate at hot water heaters and the
like—which is best caught by testing for chlorides. We
used to use chlorides as a measure of dissolved solids PRETREATMENT
on ships but that was a given since our major source of
contamination was salty sea water. Pretreatment is the conditioning of water to pre-
In addition to checking for ratios of mixtures of pare it for use in the boilers. It is less expensive and
water, chloride tests can indicate the performance of a easier to alter the conditions of the water before it gets
dealkalizer, where chloride ions are exchanged for other into the boiler because we can do it at lower pressures
anions (ions with a negative charge). It also allows a de- and temperatures. Only the more common pretreatment
termination of the concentration of the boiler water, pro- methods are described in this book. There are other
vided there’s no carryover because they’re concentrated resources, with the best being your water treatment sup-
as the steam leaves. Of course they’re used to check for plier, for descriptions of other methods.
carryover because otherwise there’s no reason for them Filtering is the most common form of pretreatment
to be in steam line condensate. but it’s seldom done at the boiler plant. If you use well
Despite getting brown finger spots you should water you should filter it. City water is normally filtered
make judicious use of the chloride test to answer your by the city and is adequate for boiler makeup water.
own questions about what’s happening with your water. Filters vary from a simple cartridge filter to large sand
As far as I know you still test for phosphates like I filters that are tanks filled with sand that does the filter-
used to. Mixing some boiler water with an indicator and ing. Sand filters are back-washed at regular intervals
filling another sample tube with plain boiler water then or when the pressure drop through them increases to
comparing the color. Those color comparitor tests were a predetermined value. A back-wash removes the ac-
always subjective, and I’m not color blind. Similar tests cumulated material by pumping filtered water through
are available for chelants and I don’t know of any for the filter in the opposite direction of normal flow. The
polymers. water used to back wash is sent to a sewer as waste and
Whatever ion you’re looking for, or the test method can, at least in the first few minutes of back-washing,
used, you should read the instruction manual and care- contain a large amount of solid material. Back-washing
fully follow the instructions if you want to get reliable, also serves to fluff up the sand so the water will flow
repeatable results. When I say repeatable I mean that the through it at a lower pressure drop. Some other pretreat-