Page 165 - Boiler plant and distribution system optimization manual

150 Boiler Plant and Distribution System Optimization Manual

lot of fuel is expended to keep the boiler hot when to swell up, causing priming or excessive carry-
it has no real load comparable to its rated capacity over. Priming is the introduction of slugs of water
especially during off-hours. into the steam piping, moving over 100 miles per
hour or more. When these high velocity masses of
water slam into a sharp turn they can burst pip-
3. REPLACE OVERSIzED BOILERS TO ing. In the case of excessive carryover, the boiler
MATCH ExISTING LOADS. water contains a lot dissolved solids which can
contaminate steam piping and cause blockages.
There are many reasons for finding oversized This dirty boiler water which gets into the
boilers. The first question that must be answered steam system can foul heat exchange surfaces and
is how you would even know it was oversized. mess up heat exchange equipment in general.
This would take some instrumentation to mea-
sure steam demand or even length of on cycles
verses off cycles with attention to the fact of a cer- 6. INSTALL A STEAM SEPARATOR TO
tain investment of Btus just to keep the system MAINTAIN CLEAN DRY STEAM
operating. Without adequate instrumentation
and information this condition is hard to detect. One way to keep boiler water and carryover
Consider that in the original design the de- out of the steam piping is to install a steam sep-
mands for steam were not know so a large safety arator (Figure 10.43) near the boiler outlets. They
factor went into the original design. Then an ad- have proven to be 99.9% efficient at eliminating
ditional safety margin was built into the facility priming and carryover, so they have a vital func-
beyond what its highest demands might be. Then tion to perform keeping heat exchange equipment
add efficiency improvements over the years and clean and functioning.
other possible load reductions and oversizing
becomes a real possibility. This is not normally
checked for and more or less guessed at. 7. HEAT PUMPS

Cost
Moderate
4. REPLACE THE ExISTING FEEDWATER
HEATER OR DE-AERATOR WITH A Savings
NEW MORE EFFICIENT DEAERATOR Moderate

Earlier units were not insulated and often Description
insulation has been stripped away for inspection Heat pumps have high efficiencies when mea-
and repairs. If oxygen pitting of pipes and boil- sured against engines, boilers and turbines (Figure
er tubing is showing up, then the effectiveness of 10.44). In the example below the Heat Pump can
the deareator is slipping. In any case it should be bring the apparent efficiency of a boiler up to 128%
checked out. using waste heat or low pressure steam available
in a boiler plant or they can be used to augment old
5. INSTALL A BACK PRESSURE CONTROL steam systems with air source heat pumps. (Figure
VALVE TO REDUCE CARRYOVER 10.45) Heat Pumps can raise efficiencies signifi-
DURING ExTREME LOAD CONDITIONS cantly when combined with low grade waste heat
from engines, boilers and turbines.
When steam demands exceed plant capaci- Waste heat can be put to work at a higher
ty there is a tendency to reduce boiler pressures temperature by the use of heat pumps. One sys-
caused by lower pressures in the distribution pip- tem design circulated 150°F water from a waste
ing. This will cause the water levels in the boilers heat recovery system throughout a plant using