Page 373 - Boiler_Operators_Handbook,_Second_Edition

358 Boiler Operator’s Handbook

Figure 10-99. Steam powered air compressor

steam engine but the need for skilled workers to main- lower pressure in a manner that converts the static pres-
tain and rebuild them and the high initial cost and cost sure in the steam to velocity pressure. Once the steam is
of maintenance has pretty much priced them out of exis- moving at a high velocity the mechanical energy is in the
tence. It’s not that they cost more than a motor over their steam and the turbine has to transfer the energy in the
lifetime, it’s just that they cost more to begin with and steam to rotation of the shaft. Turbines use two methods
their maintenance isn’t understood. Direct conversion to transfer the energy to the rotating shaft, either im-
of steam to power should more than cover the mainte- pulse or reaction. An impulse turbine works the same as
nance costs but most owners are not willing to invest in a pinwheel, when you blow on a pinwheel the air strikes
these very efficient devices. Let’s see if another revision the surface of the pinwheel, giving up it’s velocity pres-
of this book reflects change in that attitude. sure to the blades of the pinwheel.
Steam turbines have also seen a decline in use, A reaction turbine works more like a loose garden
mostly because electric power has become so reliable and hose. I’m sure you have turned the water on a garden
there is such a low demand for steam turbines that they hose at some occasion when the nozzle was open and
are only found in medium to large boiler plants which the hose twisted around splashing all over the place.
are willing to invest in them. There has been no argument The hose reacted to the water spraying out the nozzle.
for having turbines to ensure continued operation in the Figure 10-100 shows the two types of turbine stages
event of an electric power interruption because of power graphically and includes what is called a velocity com-
reliability and the ability to operate a generator to run pounded stage where the back splash from an impulse
motors so you don’t need dual drives. I can remember stage is re-directed to a second set of turbine blades to
many installations that had boiler fans and feed pumps increase the performance. All steam turbines have a
with dual drives, a motor on one end of the piece of least one impulse stage because the steam is initially
equipment and a turbine on the other. Auxiliary turbines, supplied through a set of stationary nozzles in the tur-
(see earlier discussion) which exhaust steam to the de- bine casing. Moving blocks are shown in black, nozzles
aerator are just about the only surviving application. and satationary blades in dark gray, and steam flow in
Steam turbines convert the heat energy in steam light gray.
to mechanical energy. It’s a simple matter of passing Multiple stages just like pumps? Yes, by dropping
the steam through a nozzle from a higher pressure to a the pressure in stages we get better efficiency. Utility