Page 372 - Boiler_Operators_Handbook,_Second_Edition

Plants and Equipment 357

were evaluated that I couldn’t justify the power genera- When capable of tri-generation you can identify
tion. Further investigation revealed the reason: the facil- and develop SOPs for spring and fall operation to bal-
ity’s accountants charged all electrical maintenance in ance wasted energy, by heating and cooling at the same
the plant to plant generated power. That produced a cost time, to optimize your operating cost by generating
of generated power, on the books, that was only 80% of more electricity and reducing demand when you nor-
the cost of purchased power despite the fact the actual mally don’t have the loads at the generator exhaust. It
cost was only about 25%. The accountants ruled and the requires knowledge of the electrical contract and how
project reverted to a new saturated steam boiler operat- to manipulate it and good records on power generation
ing at the turbine exhaust pressure. The operators in the and system loads. Many of you will gladly allow an
plant were not happy, nor was I, but fiscal stupidity won engineer or consultant to help you develop the program
that argument because I didn’t have enough gray hairs for such operations because it does get complicated. In
at the time to get anyone to believe me. I know an opera- time you’ll probably find that it will take a computer
tor can’t do anything directly about such stupidity but to guide you in the decision making process because
maintaining good quality records of power generation electricity costs will vary hourly. There are already situ-
and its cost would have allowed me to beat that argu- ations where the cost of electricity varies with each hour
ment back then. You got it! The old document or disaster of the day. An example was one in North Carolina where
rule repeats itself. electricity cost as little as 2¢ per kW at night and 26¢ in
The key to cogeneration is to use the energy that’s the early afternoon with hourly variations in between.
left over after generating electric power. One company You’re limited with controlling power usage to avoid
is promoting tri-generation where the plant produces the higher costs but cogeneration gives you the ability
power, heat, and chilled water for refrigeration or air to really save your employer some money on power.
conditioning. The heat of the generator exhaust is used I do hope that any plant that allows a computer to
in absorption chillers in the summertime to produce do the controlling also has an operator to make certain
chilled water. That allows plants that only need heat in the computer is doing what it’s supposed to.
the winter to become cogenerators (or, if you will, tri- There are several options for generating power
generators) although they can’t do much in the spring with exhaust heat to be used for steam, hot water, ser-
and fall. Of course that depends on your electrical con- vice water and absorption chillers. They include steam
tracts and fuel costs. In some cases it pays to generate turbines and engines that have a long history in that
electricity and waste some of the exhaust heat that you service; turbines require substantially less maintenance
can’t use in order to avoid standby charges (although and operator attention than engines.
they will give them a different name) and related ex- Generating steam or hot water with exhaust from
penses. You may also be expected to operate the genera- diesel generators, including those fired on natural gas,
tor to minimize demand charges. also have a long history but, like engines, the generators
Somewhere in this book I have suggested operat- require a considerable amount of maintenance. Modern
ing practices to minimize demand charges but operating engines have improved on that maintenance require-
a generator to minimize them, when possible, can also ment to the degree that they are being used. Modern
be the responsibility of a boiler plant operator. With co- devices include gas turbines and fuel cells. Let’s discuss
generation you can produce additional power, even if it them just a little so you know what they’re like. Once
isn’t efficient to do so, to reduce a peak load and lower again, the instruction manual and other documentation
those demand charges. The degree you go to is depen- is necessary for you to learn all that’s required for op-
dent on the length of time a peak load is endured and erating them because they aren’t a common element of
the inefficiency associated with producing that extra today’s boiler plant.
power. If the peak is substantial and only occurs during
a short period of time (like half an hour a week) it may Steam Engines and Turbines
pay to dump steam to atmosphere, as mentioned earlier, Take a good look at the photograph of Figure 10-
just to eliminate that peak. You have to look at the cost 99, it’s a steam engine driven air compressor and it’s
to generate the power for that period of time and how probably one of the few that are still operating today.
much you save overall on demand charges. Now you Specific problems with steam engines have almost elimi-
know why operation of an emergency generator can be a nated their use today. Lubrication oil getting into the
small cogeneration activity like what I explained under boilers has just about been eliminated with provision of
reducing demand charges. better materials that can seal the piston and shaft of a