Page 438 - Boiler_Operators_Handbook,_Second_Edition

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more steam per gallon of oil or hundred cubic feet of gas chance of being stung for a major cleanup cost. The oil
than they used to. They called me in to help them find in the tanks should match a calculation of what you had
out why they weren’t saving any fuel because, for some plus what was delivered less what you burned. If it’s a
strange reason, their steam consumption had increased. little less or more you simply show an inventory adjust-
I hope you got it, their steam consumption hadn’t in- ment, you must have burned it or not burned it depend-
creased, they just introduced a recorder error by lower- ing on which way you’re off. If the calculation says you
ing the pressure and had saved almost nothing. should have a lot more than what’s in the tanks you’ve
If the steam pressure varies at the recorder (more got a leak or an oil thief. If it’s a leak you have to call the
than plus or minus two or three psi) and you want it to local Coast Guard office and inform them, that’s federal
be accurate it needs to be compensated. Compensated law.
recorders for steam use a steam pressure and/or tem- Fuel oil or gas is measured by the supplier and the
perature input that allows calculation of the density user has to pay for what they measured. The plant meter
of the steam at the orifice for accurate measurement. readings, values from your instrumentation, should be
Superheated steam flow recorders need both pressure corrected to match the supplier’s numbers so your data
and temperature inputs to determine the density of the are considered accurate. Divide the combined fuel meter
steam, saturated steam only needs one of them. readings for all boilers by the fuel supplier’s number to
Fuel gas flow recorders are subject to the same produce a correction factor then multiply that result by
errors from pressure and temperature fluctuations as your meter readings at each boiler to get the actual fuel
steam flow recorders. By maintaining the pressure con- consumed in the each boiler. Keep track of the correction
stant there’s usually little variation between actual and factor and ask yourself “why?” if it changes significant-
recorded flow so it’s suitable to use a simple recorder. ly. When firing oil you would use the oil drawn from a
Normally fuel gas flow is recorded at each boiler because particular tank as the supplier’s number since you nor-
we have the flow instruments to provide a control signal mally verify each delivery with a sounding.
for the firing rate controls and it doesn’t cost much more What’s a sounding? It’s a measurement of the
to add the recorder. For purposes of control we can live depth of liquid in a tank. The term comes from taking an
with little errors in the gas flow recordings. Besides, we ullage reading. (Just like those darn engineers, use one
have a way of correcting them to the purchased values. confusing word to define another)… I’ll clarify. When
We do? Yes, you do. If you don’t compare the read- we measure the depth of heavy fuel oil in a tank we
ings of your fuel gas recorders with the gas company’s don’t like to drop a tape all the way to the bottom then
meter you’re missing a real bet. You’ll also have some clean it off. We use a probe at the end of a tape that looks
smart ass engineer like me come into the plant and dem- like a brass rod with an upside down cup on the end.
onstrate to your boss that you don’t know what’s going When we lower that into the tank it makes a plop sound
on. On the one hand you can catch problems with your when it hits the surface of the oil. Using the tape mea-
metering. On the other, well, I could tell you about two surement from the top of the pipe and subtracting the
jobs where customers were being billed for far more gas depth of the tank from the reading gives us the depth
than they were actually using. of the oil. Since the process involves making a sound
You should also track your inventory and man- (the probe going “plop” when it hits the oil we called it
age it. When I was operating we burned heavy fuel oil. sounding the tank. The actual measurement is called an
Since it had to be heated we always burned more oil “ullage” when it’s the distance down to the top of the
than we had. Now that I have you confused I’ll explain oil.
why. We knew how much oil we had by sounding the The sounding of light oil storage tanks doesn’t
fuel oil tanks. The oil in the tanks was maintained at a require wiping off a lot of black sticky oil so we usually
temperature much lower than the temperature at which take soundings where the probe is simply a pointed
we burned the oil. The oil we burned was measured by brass rod or wood stick that drops to the bottom of the
a fluid meter after the oil was heated for firing. The oil tank. We read the level where the liquid coats the rod or
expanded as it was heated so a gallon of fuel burned stick and wipe the thin coat of oil off the rest of it. That
was always less mass than the gallon in the tank and less stick you drop into the oil tank is an instrument too.
mass than the gallon of oil that was delivered. The tip can be torn off (there’s usually a brass button on
You have to correct for temperature to keep a good the bottom) or, as in one case I encountered, someone
accounting of your oil inventory. If you aren’t watch- can need a piece of wood about that size and cut a few
ing your oil inventory then your employer has a good inches off. Also, just like the meter readings, you can