Page 150 - Boiler plant and distribution system optimization manual

Over 100 Ways to Improve Efficiency 135

viscosity. Viscosity is the relative ease or difficul- 23. INTERMITTENT IGNITION DEVICES
ty with which oil flows or is pumped. Viscosity
affects the quality of atomization and the smoke Cost
point which determines the minimum excess air Low
possible. Because of this, the viscosity of fuel oil
must be closely controlled at all times. Since oil Savings
is obtained on the open market, its source of ori- Moderate
gin can be uncertain. Therefore, the properties of
one batch will not likely be the same as those of Description
another batch. Oil viscosity is controlled by tem- It doesn’t make any sense to keep a flame lit
perature, the oil temperature necessary at the in a furnace or boiler if heat isn’t needed; it wastes
atomizer depends on the particular fuel. Some energy. Especially with gas fired equipment, there
heavy fuels are very fluid and require little or are many smaller sized boilers and furnaces with
no heating. A viscosity of 180 to 200 Saybolt Sec- continuous pilot flames. On a 24-hour-a-day ba-
onds Universal (SSU) often gives best results for sis, year after year, these small flames can use a
atomization and if the oil at ordinary tempera- lot of Btus. Intermittent ignition technology has
ture is of higher viscosity, it must be heated to a been proven to be reliable and safe, so these older
temperature which will reduce viscosity to this continuous pilot lights should be replaced with
point. Intermittent Ignition Devices.
The temperature control of the fuel oil heat-
er is a key element in controlling atomization and Advantages/Disadvantages
smoke point for excess-air control. Fuel batches Intermittent ignition devices are proven, re-
should be sampled to determine the temperature liable equipment. They have been designed to ret-
set point. If the heater does not maintain an ac- rofit on most boilers and furnaces and are not ex-
curate set point, close excess-air tolerances may pensive. Their payback period is relatively short
not be possible. Automatic viscosity controllers
will feed back information on viscosity to the
heater and maintain a proper temperature. 24. PREVENT HEAT
TRANSFER SURFACE FOULING
Advantages/Disadvantages
In general, the lowest fuel temperature per- Cost
mitting good furnace conditions and low ex- Low
cess-air is most desirable. Too high a tempera-
ture may cause carbonization of fuel oil heaters Savings
and atomizer tips, sparking in the furnace and a Moderate
tendency for the flame to become unsteady and
blow off the tip. Description
Burner performance controls the minimum With the increased use of natural gas, com-
possible excess-air levels which can be held bustion source fouling has become much less of
consistently. The burner depends for its perfor- a problem, however with distillate fuels, heavy
mance on oil being at the proper viscosity. Poor fuel oils and coals heat exchange surface fouling
viscosity (temperature) control can prevent is still a constant threat which requires diligence
high efficiency. A properly working and main- to keep under control. Inadequate air supply to
tained fuel oil heater and good viscosity control the burner or localized poor air fuel mixing can
either through regular tests on oil batches or cause small smoke sources that over time foul
with an automatic controller is the key to low heat exchange surfaces raising exhaust tempera-
excess-air. tures. This can take just a few minutes or occur