Page 272 - Boiler_Operators_Handbook,_Second_Edition

Water Treatment 257

gree and type of chemical treatment. See the discussion It’s like having a boiler inspector, always better to have
on water as a consumable. some other, somewhat disinterested, party looking at
the chemistry. It’s really best if the consultant doesn’t get
to sell you the chemicals.
CHEMICAL TREATMENT A water treatment program only has two goals,
prevent corrosion and prevent scale formation, it’s that
If there’s any time for you to make a bad decision simple. The causes of corrosion and scale formation
regarding reading this book it’s right here. I know that have to be understood to prevent them and knowing
many times chemical treatment of water is treated like how the chemicals prevent (or enhance) those condi-
a black art but hopefully you have had no trouble un- tions must be understood to maintain proper chemical
derstanding any other part of this book and this section water treatment. The process of obtaining representative
should be no exception. water samples and properly testing them for chemical
I will admit that chemical treatment suppliers content has been covered and how to use that informa-
have, and will continue to, make it difficult to under- tion to achieve the goals of the program is described in
stand what their product is doing by using obscure the paragraphs that follow.
names and numbers to label what are really common Recording everything that happens, every test run
chemicals. The first rule in understanding your chemi- and follow-up actions is important to understanding
cal treatment program is knowing what’s in the con- what’s happening and the result of your actions. Don’t
tainer. There aren’t that many compounds for water limit the record to the space provided on the log sup-
treatment and they do the same thing regardless of the plied by the chemical treatment supplier. I’ve already
name or number on the barrel so you can understand mentioned a few incidents that can occur and alter water
the purpose and function of the chemical if you know chemistry but there are many others and I’m counting
what’s in it. on you knowing enough about it to determine when
If your supplier will not tell you my suggestion something has altered the chemistry and logging it in
is to go find one that will. Given the true title of the ac- addition to correcting for it.
tive chemical and the following paragraphs you should Your boiler or water system has boundaries and
know enough to properly maintain chemical treatment contains a certain volume of water. That volume or
of your plant’s water. weight of water contents can be determined from manu-
I’ve said it before and I will repeat it; the only facturer’s instruction manuals and estimates using
person that can effectively operate a water treatment actual measurements and the data in the pipe tables in
program is the educated boiler operator. Those chemi- the appendix to calculate the volume and determine
cal treatment consultants that arrive at the plant every the weights. Once you have an initial volume or weight
month or two have no idea what has transpired between determined you know what the weight of the water in
visits. They can’t possibly know that the boiler was shut the system or boiler will be when it’s cold, at 70°F where
down, drained and refilled, left sitting idle or operated water weighs 62.27 pounds per cubic foot. Freezing
continuously. They might if they bothered to look at the (32°F) water weighs 62.4.
operator’s log but I don’t recall ever seeing one do that. Once the system is up to operating temperature the
They may not know that there was an upset in the level weight will be lower and you may want to adjust your
controls and the operator used the bottom blowoff to re- data for the effect of thermal expansion. Determine the
store water level several times dramatically reducing the ratio of cold to operating by dividing the specific vol-
chemical levels. All too often I’ve noticed that a water ume of water at 70°F (0.016025) by the specific volume of
treatment consultant has changed a program due to an water at the operating temperature using the data from
upset condition with resulting over-treatment. the steam tables and multiplying it by the weight of the
You and your fellow operators are able to commu- water when it’s cold. That’s the weight of the water in
nicate so you’re aware of all the variables that affect the the system when it’s operating. Move the decimal place
chemical concentrations in your boiler water and can of that result six places to the left or, if you’re using a
make sound decisions about changes in the treatment calculator then divide by one million, to know how
program much better than a consultant. Knowing this, I many million pounds of water are in your system. Un-
trust you’ll be able to explain the activities that changed less it’s a very big system the number will be small but
the water content to your consultant so you get better you will know how many million pounds of water you
service. Note that I didn’t say get rid of that consultant. have so the results of chemical tests in parts per million