Page 479 - Boiler_Operators_Handbook,_Second_Edition

464 Boiler Operator’s Handbook

If used for calculating an operating efficiency you have Combustion air (c) and flue gas temperature (d) are re-
to use the stack temperature measured and adjust the corded and can be adjusted for special applications. For
excess air to match the actual operating condition. Some example, you might want to compare the performance
help in determining the excess air is obtained by using of the boiler to the performance of the boiler without
the graph in Appendix M. its economizer. You could make one worksheet up for
the boiler flue gas exit temperature and another with
Space is provided for the boiler name or number, the the economizer flue gas exit temperature to get that
date, and the fuel to separately identify each worksheet. comparison of efficiencies.
That’s because you may be considering several fuels
or have collected operating data on several boilers or For purposes of calculating efficiencies it’s simply easier,
you’re comparing the boiler’s performance to what is and produces more meaningful numbers, if you calcu-
was at another time. late the results based on therms (100,000 Btu). To deter-
mine the amount of fuel required per therm (e) divide
The excess air value (a) is the same as used in the combus- the higher heating value of the fuel into 100,000. The
tion calculation sheet. You may have run the boiler at dif- matching quantity of air (f) is determined by multiply-
ferent values of excess air when collecting operating data ing the fuel quantity (e) by the air/fuel ratio (b).
so you can compare the difference in boiler efficiency. The
air/fuel ratio (b) is the one calculated for the operating Moisture brought in with the combustion air (g) is de-
condition on the combustion calculation sheet [8]. termined by multiplying the ratio (H on the combustion

EFFICIENCY CALCULATIONS
Boiler: __________________________________ Date: _________________
Fuel: __________________________________
Excess air: _________________ % (a)

Air/fuel ratio: _______________ #/# (b)
Combustion air temperature: _______________ °F (c)
flue gas temperature: _______________ °F (d)
Quantities per therm input:

Fuel: _______________ #/Therm (e)
Air: _______________ #/Therm (f)
H O in air: _______________ #/Therm (g)
2
Wet flue gas: _______________ #/Therm (h)

H O fuel: _______________ #/Therm (i)
2
H O in flue gas: _______________ #/Therm (k)
2
Dry flue gas: _______________ #/Therm (l)
Heat losses:

Sensible heat: _______________ % (m)
H O in flue gas: _______________ % (n)
2
CO loss: _______________ % (o)
Radiation: _______________ % (p)

Total losses: _______________ % (q)
Efficiency by difference: %