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 Some inherent errors exist due to the assumptions used. This method is
idea l for continuous monitoring if automatic recording devices a re used and
is particularly helpful when blending oils of nearly equal speci fic
gravities.
3.7 VISCOSITY CONTROL. Waste oil added to regular fuel affects the
viscosity of. the blend and,. hence, the fuel flow rate and nozzle spray
.
characteristics.
To minimize the requirements for burner adjustments the
firing temperature of a blend should be controlled so that its viscosity is
nearly the same as that of the regular fuel oil at its normal firing
temperature. The viscosity variation with the temperature of typical fuel
oils may be estimated by using the viscosity-temperature charts for liquid
petroleum products `in Schmidt's Fuel Oil Manual. A working chart for
determining the approximate operating temperature of fuel oil blends is
shown in Figure 3-4. The one on the left is used to determine the
viscosity of a blend of two oils of different viscosities (all in SUS* at
lOOoF), and the one on the right shows the temperature variation of
viscosity for oils whose viscosities at 100F are known. The use of these
graphs is illustrated in the following example:
A burner is designed for burning heavy fuel oil with a viscosity of
1,000 SUS at 100F. This oil is heated to 180F to achieve
satisfactory firing. A light waste oil with a viscosity of 50 SUS
at 100F will be blended into the heavy fuel oil to supplement the
boiler fuel. To fully utilize this light waste oil, its
concentration in the blend is determined to be 30 percent. What is
the satisfactory operating temperature of this blend?
From the right-hand graph of Figure 3-4, along the diagonal line
labeled 1,000 SUS, we find that the viscosity of this oil at 180F
is 125 SUS. This is also the viscosity of the blend needed in
order to achieve the desired performance. From the left-hand
graph, a line is drawn connecting 1,000 SUS for the high viscosity
component and 50 SUS for the low viscosity component to determine
the viscosity of a 30 percent waste oil blend which is slightly
less than 300 SUS. Again on the ri ght-hand side of the graph,
along the line labeled 300 SUS, we find that to attain 125 SUS the
oil should be heated to 140F. Th is is shown in the graphical
construction.
3.8 BURNER MODIFICATIONS. Minor adjustments are sometimes necessary to
correct unstable combustion and smoke emission similar to the routine
adjustments for firing clean fuel.
*Saybolt Universal Seconds.
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