Page 41 - Boiler Operator’s Handbook

26 Boiler Operator’s Handbook

ing pure oxygen in the capsules, a small electrical fire Carbon, in complete combustion, combines with
provided enough heat to get things started and, without the oxygen in the air to make carbon dioxide, CO for
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the nitrogen to moderate the rate of combustion, the short. We say “C-oh-two” basically reading off the let-
inside of the capsule was consumed by fire in seconds. ters and number. That’s one atom of carbon and two
We do have flames that burn fuel with pure oxygen, the atoms of oxygen. You’ll probably recall that it’s the
space shuttle’s engines do it and the typical metalwork- fizz in soda pop and what we breathe out. Actually
er’s cutting torch uses it, but those applications have a our bodies convert hydrocarbons to water and car-
limit on their burning imposed by consumption of all bon dioxide. We just do it slower and at much lower
the fuel and the moderating effect of the nitrogen in air temperatures than in a boiler furnace. Since carbon is
surrounding those operations. Keeping those cutting the major element in fuel, we make lots of carbon di-
torch oxygen tanks properly strapped down in the boiler oxide in a boiler. Next in quantity is water. Now, that
plant is important because they’re a source of pure oxy- brings up an interesting point, if we’re making carbon
gen that could produce a rapid, essentially explosive, dioxide and water, both common substances that we
fire in the plant where we aren’t prepared for it. consume, then what’s the problem with boilers and
The appropriate title for this part should be com- the environment? We’ll get to that but, for the most
bustion chemistry but I know what would happen. part, firing a boiler is natural and it produces mostly
Mention the word “chemistry” and a boiler operator’s CO and H O which aren’t harmful.
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eyes glaze over and they look for a route of escape. Hey, Notice that I had to say “in complete combus-
if we wanted to be an engineer or chemist maybe we tion” in the lead sentence of that last paragraph. If we
would study chemistry, we’re not engineers or chemists have incomplete combustion, the carbon will not burn
so don’t bother us with that stuff. Okay, I understand completely. Instead of forming CO it forms CO, carbon
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the feelings and I remember them but you have to un- monoxide. That’s the colorless, odorless gas that kills.
derstand what’s happening in that fire to know how to The person deciding to commit suicide by sitting in his
operate a boiler properly. I’m not going to present any- running car in a closed garage dies because the car en-
thing that’s far out, no confusing calculations or any of gine generates CO and he breathes it. That CO is trying
that stuff, it’s really quite simple and you’ll find you can to find another oxygen atom to become CO and it will
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understand it and use that understanding to become a strip it from our bodies if it can. That’s what happens, it
wiser operator. robs us of our oxygen and we die of asphyxiation.
Any fossil fuel has only three elements in it that The last flammable (stuff that burns) constituent
will combine with the oxygen in the air and release heat. in fuel is sulfur. Sulfur combines with the oxygen in the
All of a sudden combustion chemistry is not so complex air to form SO , sulfur dioxide. There isn’t a lot of sul-
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is it? Actually there are only four reactions that you need fur in fuel but what’s there burns. And, that’s it! Three
to know. (Combining of materials to produce different elements, Carbon, Hydrogen, and Sulfur combine with
materials is a reaction). Let’s start with the easy one first; oxygen to produce CO , water, and SO and heat is gen-
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hydrogen in the fuel combines with oxygen in the air erated in the process. Now, hopefully, I can show you
to produce di-hydrogen oxide (H O). Yes, you’re right, the chemical combustion formulas and they’ll all make
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that’s really what we call H-two-O and it’s water. sense. When we use numbers in subscript (small and
Of course the heat generated by the process pro- slightly below normal) that indicates the numbers of
duces water so hot that it’s steam so we don’t see liquid atoms (represented by the letter just in front of the num-
water dripping from a fire. I like to say hydrogen is like ber) in a molecule. Numbers in normal case indicate the
the best looking girl at the dance. She always gets a number of molecules. Atoms, represented by the letters,
partner. Hydrogen will mug one of the other products combine to form molecules. Many gases, oxygen is one
of combustion if necessary to get its oxygen. To date no- of them, are what we call diatomic; that means it takes
body has been able to find any hydrogen left over from two atoms to make a molecule of that gas. All fuels are
a combustion process because it always gets its oxygen made up of atoms of hydrogen and carbon, it’s the mix
to make water. You’re assured that all the hydrogen in of atoms to form the molecules of the fuel that produces
the fuel will burn to water if combustion is complete. the different fuels we’re used to. In other words, it’s
If it isn’t complete, the hydrogen will still be combined the combination and number of hydrogen and carbon
with some carbon atoms to produce a hydrocarbon, molecules that determines if the fuel is a gas, an oil, or a
sometimes it isn’t any of the hydrocarbons that the fuel solid material like coal. Here’s the list of basic combus-
started out as, it can be an entirely different one. tion chemistry equations.