Page 371 - Boiler_Operators_Handbook,_Second_Edition

356 Boiler Operator’s Handbook

lubricated and are typically used for low values of com- where electric power is generated by many smaller
pression, producing air pressures in the range of thirty operations. When a boiler plant passes all the steam it
to fifty psig. generates through a steam turbine to produce electric
I used one rotary compressor as a gas booster on a power with a generator then uses all the steam in the
job in the 1980’s and was hoping to get capacity control facility the thermal efficiency is much higher than a
later by converting the drive to variable speed. That power company that normally runs at 40% (60% of the
never worked out because the oil lubrication would be energy they consume in fuel goes up the stack and out
lost if the compressor was slowed down. the cooling tower). Understanding steam turbines and
I have to elaborate a little on gas boosters here their operation is going to become more important for
because they are frequently found in a boiler plant. the wise boiler operator.
They are either the rotary or centrifugal type and can’t The principal reason most plants have not gener-
be turned down significantly so the gas has to be recir- ated power is the utility’s standby charges. The utilities
culated through the booster to reduce output to match argued, with a certain degree of justification, that they
the requirements of the boiler’s burner when it’s modu- had to provide generating capacity to replace any gener-
lating. If the boiler shuts down the booster must also ator someone else owned to ensure an adequate power
shut down. During certain periods of boiler operation supply. In other words, they needed additional capacity
the booster must run to produce pressure while the to replace the power normally produced in one of their
burner isn’t firing (to prove fuel pressure available) so customer’s plants in the event the customer’s genera-
full recirculating mode exists for a period of time. To tor failed. The charge was almost always large enough
prevent overheating the gas as it continues to recirculate that the customer abandoned any thoughts of power
in the booster some means is required to cool it. An air generation. Despite that and other disincentives some of
cooled heat exchanger is recommended. Water cooled my customers are cogenerators. With deregulation a lot
heat exchangers can waste a lot of good water and need more are going to be.
so much that it all can’t be used for makeup. If you do It really isn’t a new thing. Cogeneration was the
use a water cooled heat exchanger, and it’s using city way of the world early in the twentieth century. Power
water, allow the water to get up to at least 140°F before companies had not strung lines everywhere and new
discharging it so you waste as little as possible and use facilities didn’t have a source of reliable power so they
whatever you can for makeup. generated their own. Buried deep in the bowels, and
Don’t run a booster you don’t need either. I visited sometimes under the concrete, of many old industrial
one plant where the booster was running but the service and institutional facilities throughout the country are
supply pressure was more than adequate. I suggested old cogeneration plants which generated power with
they try operating with the booster shut down and by- steam engines and used the exhaust to supply the
passed. They did, and it worked fine. I’m told they went process. Many industrial museums are popping up to-
through the winter without needing the booster. I would day with the remnants of many of those old plants as
love to have all the money they saved on electricity with showcases. A visit to one is always worthwhile. I know
that one suggestion. because I learn something new with every one I visit.
So, unless you have a plant where your load is very
small or very inconsistent you’re going to be exposed
COGENERATION to a change that involves cogeneration sometime in
the near future. It’s simply energy sense and, since the
There’s no question that the de-regulation of elec- utilities don’t have a monopoly on power generation
tricity has changed the scene of electric power genera- any more, it’s also economic sense. Of course econom-
tion. Without their monopolistic position utilities have ics doesn’t always make sense. I know many a boiler
been compelled to produce power more efficiently. The operator that complained about the accounting practices
ability of the ordinary steam boiler plant to convert fos- of their employer and I’ve seen many examples of fiscal
sil fuel energy at an 80% efficiency has allowed many stupidity that converted an obvious economic advan-
facilities to incorporate power generation, what we call tage to a loss.
cogeneration (the generation of both heat and electric I remember a project many years ago where I had
power), into conventional plants with a lower overall the opportunity to install a new boiler and back pressure
operating cost. turbine generator in a plant that was already a cogenera-
The new buzzword is ‘distributed generation’ tor but discovered when the economics of the project