Page 151 - Boiler plant and distribution system optimization manual

136 Boiler Plant and Distribution System Optimization Manual

over months; the stack temperature will tell the 26. REDUCE RADIATION LOSSES
story. The possible causes are many and varied
Cost
and may take a detailed investigation once the
Low
higher exhaust temperatures become apparent,
especially when firing at Maximum Rated Capac- Savings
ity. Moderate

Advantages/Disadvantages Description
Keeping heat exchange surfaces clean pre- Hot surfaces can waste a lot of energy by means
vents wasted fuel, increased pollution and un- of radiation. Radiation is a very effective heat trans-
necessary carbon emissions. It is a matter of being fer medium. Unlike convection and conduction ra-
able to spot this condition when it is developing. diation losses may not be obvious because it does
not heat up the local area but may transfer its ener-
gy to surfaces quite a distance away and because of
25. INSTALL AIR PREHEAT OR OTHER the much greater surface areas affected at a distance
HEAT RECOVERY EQUIPMENT this way the actual energy transfer can be great-
ly under estimated. Some older boilers have large
Cost metal doors that radiate heat like this, flame on one
Varies side and a much cooler plant on the other side with
rather forceful blowers cooling things down with
Savings people moving around in their shirt sleeves on very
Moderate cold days; its radiation just like the sun. The real
problem can often be picked up with infrared scans
Description or surface thermometers.
This option comes under the general heading
Advantages/Disadvantages
of what to do when other options don’t appear to
This is not an obvious problem and a condi-
be workable or cost effective. There are two wide-
tion commonly taken for granted in boiler plants;
ly used choices to improve efficiency effective-
their hot! It may be awkward and challenging
ly; put excess heat into an economizer or into a
to correct this situation or even convince some
combustion air preheater. Let’s say the fuel is the
people this represents a significant loss of ener-
problem and frequent cleaning is not possible, a
gy especially at low firing rates as this condition
combustion air pre heater might be the solution.
becomes a much larger percentage in the losses
The rule of thumb for this option is that every 40F
column. Good insulating materials are available
you bring the exhaust temperature down rais-
with experts that know how to apply them.
es efficiency by 1% and every 11F the feedwater
is raised improves efficiency by 1%. So in some
cases you may find this to be the most workable
solution to investigate. In some cases it might be Section 10-3
cost effective to put the energy from high exhaust Boiler Improvements
losses through an older inactive boiler as a hot
water source.
CHECkLIST - 3
Advantages/Disadvantages Boiler Improvements
This comes under the heading of initiatives,
1. Replace binding or worn control system
a fall back position if fuel becomes very expensive
linkages
or scarce or if regulatory constraints block other
2. Conduct infrared scans of boiler shell to
conventional options like installing new boilers.
identify poor refractory and insulation