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138 Boiler Plant and Distribution System Optimization Manual
4. REPAIR LEAKING SEALS Description
ON COMBUSTION AIR PREHEATERS Turbulators are a very effective way to re-
duce stack temperatures and increase efficiency
The combustion air preheater (Figure 10.33) of fire tube boilers (Figure 10.34). In a firetube
lowers exhaust temperatures by pre heating in- boiler the hot gasses must pass through relatively
coming combustion air. The unit slowly rotates long narrow tubes where heat is given up to the
through the hot exhaust ductwork gaining heat side walls causing the gasses to contract and slow
which is then released into the incoming combus- down forming layers of colder gas along the heat
tion air. After extended use the seals need fixing exchange surfaces. This condition prevents good
because of wear. Leaking seals can introduce cold heat transfer, so turbulators are used break up
air into exhaust gases causing dew point corro- this insulating film. Turbulators are thin strips of
sion problems besides putting an additional load metal that have been bent to break up the flow of
on the combustion air fans. hot gasses in the tubes and are designed for min-
imum obstruction of the passages. They are usu-
ally installed in the last pass. By using longer tur-
5. TURBULATORS bulators in the upper tubes of the last pass, hotter
gasses are forced through lower tubes eliminating
Cost to some degree the stratification of hot gasses at
Low the end of the boiler.
Potential Savings Advantages/Disadvantages
Low Turbulators may cause condensation of flue
gasses when a boiler is first lit off. Generally, they
are a good inexpensive way to lower flue gas
temperature. They are not recommended for high
particulate loading options such as coal and re-
sidual fuel oil.
6. CHEMICALLY CLEAN INTERNAL
BOILER SCALE TO IMPROVE
HEAT TRANSFER
Impurities in boiler feedwater tend to con-
centrate in the boiler. All boiler water contains
dissolved solids. When the feedwater is heated,
it evaporates and goes off as distilled steam leav-
ing impurities behind. As more and more water is
distilled from the boiler, more feedwater is added
to replace it. As a result the amount of solids dis-
solved in the boiler water gradually increases. Af-
ter a while these highly soluble solids in solution
cause problems like scale accumulation on the
tube metal retarding heat transfer and a number
of other problems. (For further details see Chap-
Figure 10.33—Large Air Heater (Lungstrom) installa- ter 15 of this book.)
tion at an electric station
