Page 262 - Boiler_Operators_Handbook,_Second_Edition

Water Treatment 247

the exact same results. I remember one customer calling there’s less of a chance of error if the tester reads directly
me up in a panic and requesting a boilermaker crew as in ppm instead of micro-mho.
soon as possible. It seems an operator decided that the You’re luckier than I was. When I was testing for
two boilers always tested the same so he saved himself hardness we only had one method, soap. I’m sure you
some time by copying the values for one to the log for know that hard water causes problems in the laundry.
the other. They rotated shifts each week and the next It’s because the ions that cause hardness, calcium, mag-
operator to come on that watch tested both boilers to nesium and iron have to be captured by the soap before
find the one had very excessive levels of chealant. When it can foam. We call water “hard” when it’s hard to get
the boilermakers pulled the baffles out of the drum they a foam with soap and soft when the soap lathers easily.
looked like Muenster cheese, full of holes. In another You don’t have to worry about lather factor and main-
few days the boiler would have failed dramatically. Test- taining the soap solution.
ing is one of the most important things you do and you Modern titration or colorimetric methods for hard-
shouldn’t take it lightly. ness testing are much easier to use and provide a better
Some operators are color blind. It’s not a signifi- determination of the amount of hardness ions in water
cant problem except for colorimetric testing and it’s not than our obscure method with so many drops of stan-
something you need to be ashamed of. If you’re color dard soap solution.
blind make sure the boss knows it and sees to it that the Testing for acidity is a lot easier too. Now all you
chemical consultant provides a test method that you can have to do is stick the instrument in the water sample
use accurately. Some operators also have vision prob- and read the pH on the little screen on the instrument.
lems and trouble reading the little numbers on the bu- We had complicated probes that were always a problem.
rettes. That’s okay, there are magnifying glasses for that. Testing for alkalinity hasn’t really changed much
It’s better to admit you have trouble reading those little from my day and still depends on titration testing with
numbers (I do) than to guess at what you’re reading and phenopthalein for partial alkalinity. Acid is added to
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destroying a boiler. neutralize all the OH ions from the caustic soda added
If you’re still using one of those testers that pro- to the water, half the alkalinity produced by carbonate
vides a conductivity reading for the water suggest dissolved in the water and one third of the alkalinity
purchasing a new one. Conductivity is measured in mi- produced by phosphates dissolved in the water. The
cro-mho where a mho is “ohm,” the label for resistance result is rather simple and straightforward, the water is
to electricity, spelled backwards. What you end up do- either pink or it isn’t. The color changes at a pH of ap-
ing with one of those meters is looking up the matching proximately 8.3.
TDS level on a chart. It’s a lot easier to have a meter that Testing for total alkalinity uses the same sample.
is simply labeled with values for TDS. Using methyl orange or methyl purple indicator you
Oh, you’re one of those guys or gals that’s inter- add more acid until the color changes. The acid removes
ested in operating boilers but doesn’t know what TDS is. the remaining half of the alkalinity due to dissolved car-
Mentioned earlier… it stands for total dissolved solids, bonates and the other two thirds produced by dissolved
a measure of the amount of solid material that’s dis- phosphate. The color changes at a pH of approximately
solved in the water. Those solids include what the water 4.3. Good results is another matter because the color
managed to dissolve as it hung around as droplets in change is very subjective. You add acid until the yellow
a cloud, including gases from the atmosphere and fine turns pink or the green turns purple. I seemed to always
particles of dust, what it picked up as a raindrop falling get on ships that used methyl purple and had a lot of
from that cloud, from the dirt and rocks it ran over going trouble deciding when green turned to purple.
down the stream or river or as it trickled down through Those tests can be problematic because you never
the earth to the well, and everything it managed to get know how much of what you’re looking at is carbonate
from the piping until it entered the boiler plant plus the alkalinity and how much is phosphate alkalinity. We
chemicals we added to it. don’t use sodium carbonate for water treatment any-
TDS is measured in ppm. Steam boiler water more so you can count on most of it being due to the
should have the highest value of TDS and condensate phosphate you added to the water. Some carbonate is
the lowest with makeup and boiler feedwater falling dissolved in the makeup water with the amount varying
in between so it’s a value that’s useful in determining depending on the location of your plant and your source
percentage makeup and condensate as well as providing of water. It’s really not important how much of each is
values for blowdown control (described later). Anyway, in there, only that you realize that changes in results of