Page 135 - Boiler plant and distribution system optimization manual

120 Boiler Plant and Distribution System Optimization Manual

13. MINIMIzE MAKEUP WATER system so it won’t attack the steel piping and boil-
CONSUMPTION er components which usually shows up as severe
pitting of the metal. However, some plants have
The water leaving each steam trap is at the been found to be operating with very big steam
boiling point of 212F in the case of the atmospher- blows, sometimes hundreds of feet long which is
ic return systems. The temperature is higher in excessive, wasting a lot of steam and energy.
the case of pressurized return systems. In many
cases we have the water reaching the main plant
at much lower temperatures a case by case situ- 16. BOILERS CONVERTED FROM
ation depending on the design and condition of HEAVY FUEL OIL TO NATURAL GAS
the individual system. For the sake of example
let’s say the water is arriving back at the plant has There are still older boilers around that were
an ideal temperature of 185F. The total heat in a designed to burn heavy fuel oil with high sulfur
pound of steam is 1150 Btus and the makeup wa- content which required high exhaust tempera-
ter temperature is 50F. So we have a difference of tures to avoid acid formation on cold metal sur-
135F. faces in the exhaust system. The use of this high
sulfur fuel oil is becoming restricted by modern
Condensate return temperature 185F pollution regulations and being replaced by very
Makeup water temperature 50F low sulfur distillate heating oil and by natural gas
Total heat of atmospheric steam 1150 Btu/lb with extremely low levels of sulfur. These being
the case, much lower exhaust temperatures are
possible which the boilers were not originally de-
Formula 10-1 signed for.
There is an inherent energy loss of 11.7% For example you might come across a boiler
with each pound of condensate that doesn’t find designed for heavy fuel oil with a 400F exhaust
its way back to the condensate receiver at the temperature now burning natural gas requiring
plant under these conditions. As the condensate an exhaust temperature of only 200F. Following
is distilled from pure steam there are additional the rule of thumb that every 40 degrees you can
water consumption and chemical treatment ex- drop that temperature will improve efficiency by
penses to consider too. 1%, there is a 5% savings opportunity available.
As a bonus, the capacity of the boiler will be im-
proved by the same amount.
14. ISOLATE UNUSED HOT
STEAM PIPING SECTIONS
17. SHUT OFF STEAM COIL AHEAD
If a section of steam piping is not in use it OF AIR PREHEATER
should be isolated from the active steam sys-
tem as it still represents a significant energy loss You may sometimes find a heating coil in
whether or not it is transporting steam and con- the air intake to a boiler; this is another hangover
densate. Insulation losses remain the same. from the days when heavy residual, high sulfur
oils were burned. It served two purposes, (a) to
keep smoke levels down under cold light off con-
15. REDUCE VENTING STEAM ditions and (b) bringing the cold metal tempera-
FROM THE DEAERATOR tures up above the acid dew point temperature
quicker shortening the exposure of this section
The deareator has an open vent to allow oxy- of the boiler to acid formation during initial light
gen removed from the feedwater to escape from the off.