Page 200 - Boiler plant and distribution system optimization manual

Boiler Plant Calculations 185

2. What will the fuel savings be with the same 7. A tune-up has reduced the oxygen level in
excess air reduction with a stack tempera- the combustion gases of a wood (40% mois-
ture of 300F [149C] instead of 600F [316C]? ture) fired boiler from 14% to 5% with the net
stack temperature remaining at 400F [204C].
As found efficiency 83.3% What is the change in stack loss? See Table
Net stack temperature 11-10.
300F-80F [149-27C] 220F [104C] (Ans .: Losses from 31 .8% to 20 .8%; a 11 .0%
CO 5.9% change)
2

Efficiency with reduced 8. The measured oxygen level in the flue gas-
excess air 86.2% es of a boiler firing bituminous coal has in-
Net stack temperature creased from 2.5% to 14% with the net stack
300F-80F [149-27C] 220F [104C] temperature remaining at 600F [316C]. What
CO 10% is the change in stack loss? See Table 11-4.
2
(Ans .: losses from 16 .5% to 36 .4%; a 19 .9% in-
Fuel savings _____% crease)
(Ans.: 3.4%)
9. The measured oxygen level in the flue gas-
3. What conclusion can you draw from these es of a boiler firing number 6 fuel oil has in-
examples? ________ creased from 6% to 15% with the net stack
(Ans .: There is 5%greater opportunity for fuel temperature remaining at 700F [371C]. What
savings at the higher temperature) is the change in stack loss? See Table 11-6.
(Ans .: losses from 22 .1% to 46 .9%; a 24 .8% in-
4. A tuneup has reduced the excess air for a crease)
natural gas fired boiler from 60% to 12% with
the net stack temperature remaining at 600F 10. The measured oxygen level in the flue gases of
[316C]. What is the change in Stack Loss? See a boiler firing number 2 fuel oil has increased
the Table 11-1. from 2% to 9% with the net stack tempera-
(Ans .: Losses from 25 .8% to 20 .7%; a 5 .1% ture remaining at 500F [260C]. What is the
change) change in efficiency? See Table 11-13.
(Ans .: losses from 16% to 21 .4%; a 5 .4% in-
5. A tune-up has reduced the excess air for a crease)
natural gas fired boiler from 60% to 12% with
a net stack temperature remaining at 300F
[149C]. What is the change in stack loss? See AIR INFILTRATION
Table 11-9.
(Ans .: losses from 17 .7% to 15 .2%; a 2 .5% The infiltration of cold air into a boiler or fur-
change) nace can represent a serious energy loss. This usu-
ally occurs in negative draft boilers and furnaces
6. A tune-up has reduced the oxygen level in where dampers, doors and inspection ports are
the combustion gases of a wood (40% mois- inadvertently left open or no longer form a tight
ture) fired boiler from 14% to 5% with the net seal after years of use. Because these boilers are
stack temperature remaining at 750F [399C]. usually constructed of brick and are often quite
What is the change in stack loss? See Table old, cracks from thermal expansion and other rea-
11-10. sons allow cold air to be pulled into the boiler to
(Ans .: Losses from 49 .5% to 28 .8%; a 20 .7% mix with the hot combustion gases.
change)