The boiler of Example 8.1 uses 1,500,000 L of fuel oil per year. An instrumentation kit is purchased at a cost of $20,000 and is used to adjust the boiler operation so its excess of O_{2} is only 3 percent. Determine the payback of the instrumentation if the cost of fuel oil is $0.20/L.
Question 8.2: The boiler of Example 8.1 uses 1,500,000 L of fuel oil per y...
From Example 8.1, the existing boiler has excess O_{2} of 6 percent and an overall boiler thermal efficiency of about 78 percent (i.e., η_{std} = 0.78 ).
After the boiler tune-up, the excess O_{2}is 3 percent. Using the monograph of Figure 8.1, the new boiler efficiency can be determined from the flue gas temperature (343°C or 650°F) and the excess O_{2}(3 percent). It is found to be η_{eff} = 84% = 0.84 . Using Eq. (8.4), the fuel savings can be calculated:
ΔFU=\frac {η_{eff}-η_{std}}{η_{eff}}.FU_{std} (8.4)
ΔFU=\frac {0.84-0.78}{0.84}, 1,500,000=107,104L/yr
Therefore, the simple payback period for the instrumentation is:
SBP=\frac{\$20,000}{107,104L/yr *\$0.20/L}=1.0 year