Page 179 - Boiler plant and distribution system optimization manual

164 Boiler Plant and Distribution System Optimization Manual

Description Advantages/Disadvantages
Installing pressure reducing valves near the It is a more complex system to manage but
point-of-use can reduce flash steam losses. Also, produces electric power much cheaper than com-
high pressure steam has a higher temperature, mercial power.
lower specific volume and is economical to dis-
tribute through steam mains requiring smaller
sized piping. As a general rule, steam is most eco- 13. HAVE A STEAM SYSTEM SURVEY
nomically distributed at high pressure and if re- DONE BY A PROFESSIONAL
duced to the lowest pressure that will satisfy the CONTRACTOR
temperature requirements at the point-of-use, the
least amount of energy will be lost. Steam system surveys can be quite informa-
Advantages come with lowering steam pres- tive and useful but requiring special skills, judg-
sure; a 600 psig system will have a 30% flash ment and background. Their usual product is a
steam rate, at 175 psi this reduces to a 17% flash map of your steam system with all traps iden-
and at 50 psi its 4%. This represents a consider- tified as to type and manufacturer, quite useful
able amount of energy because every pound of for ordering parts and replacements. The traps
steam flashed contains about 1,100 Btus where are given identification tags and you also get a
the condensate contains only 180 Btus per pound condition report on each trap with misapplication
a difference in energy levels of about 6. information and such. It’s a good way to identify
any problems with your steam system as a start to
Advantages/Disadvantages putting it right and a successful energy conserva-
The cost of installing and maintaining pres- tion program.
sure reducing valves and possible replacement of
steam traps will have to be balanced against pre- Advantages/Disadvantages
dicted savings. It might seem a little expensive or unusual
but it is a good way to find out exactly what is
going on with your steam distribution system.
12. UTILIzE BACKPRESSURE TURBINE Good reports and successful energy savings are
FOR STEAM PRESSURE REDUCTION the usual case concerning these special surveys.

Description
The use of turbogenerators as an option for 14. INSTALL PRESSURE PUMP RETURNS
reducing steam pressures in large plants instead ELIMINATING ELECTRIC PUMPS
of pressure reducing valves is an efficient way to
generate electricity. It starts with relatively high Electrical pumps have a number of draw-
pressure steam boilers on the high pressure end of backs. Being electrical in a wet environment
the steam system. The steam pressure is reduced sometimes gets unhealthy for the electrical end
to intermediate and low pressure steam systems of things. They have centrifugal impellers that
through the turbines before it enters the plant’s can form a partial vacuum at the water inlet with
steam distribution system. This is a very efficient the water near the boiling point. This can cause
way to generate electricity at 80% efficiency rath- steam flashing and the loss of suction and effec-
er than efficiencies in the 33% range by electrical tiveness and of course there is the electrical load
generating plants which have no way to utilize and the need to have electricians prowling your
their turbine exhausts. The usual design is 50 steam system’s tunnels vaults and confined spac-
KW and up with a minimum steam flow of 3,000 es checking on things and making repairs.
pounds per hour. The industry has come up with an alterna-
tive pump (Figure 10.60) without these draw-