Training Manual on Energy Efficiency - APO Asian Productivity ...

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Fuels and Combustion
the burner tip, possibly extinguishing the flame and reducing the flame
temperature or lengthening the flame.
1.4.4 Pre-heating of fuel oil for pumping
Pre-heating oil in storage may be needed to make it less viscous and easily
pumpable.
Heating an entire oil tank or outflow heater may be needed to heat oil
which is to be pumped away. Outflow heaters with steam or electricity are also
used often to ensure smooth pumping.
1.4.5 Pre-heating requirements for oil combustion
For pre-heating of oil, in-line heaters are to be used to raise oil temperature
from pumping to combustion temperature. In-line heaters are of either
electrical or steam tracing type. The pre-heat temperatures of oil are
determined by the viscosity of oil supplied at room temperature and the
recommended viscosity at the burner tip.
Table 1-2 Viscosity and pumping temperature
Viscosity (Centistokes) Pumping Temperature, ºC
50 60
230 104
900 121
1.4.6 Parameters for good efficiency in fuel oil combustion
• Maintain viscosity of oil of 100 Redwood sec I at burner tip by proper
setting of pre-heat temperature.
• Provide atomizing air at 1–3 kg/cm 2 (about 2% of total air requirement)
• About 14 kg of air/kg of fuel oil is required for complete combustion.
Optimum efficiency occurs with around 10% excess air.
• To control for excess air, flue gases should be continuously analyzed for
CO2 or O2.
• Acid formation occurs at around 160 ºC, and cold end corrosion should be
avoided by maintaining stack temperature at above 160 ºC.
• Slightest damage to the burner tip may increase fuel consumption by 10–
15%, and hence any wornout tips should be replaced immediately.
• Oil pressure at the burner tip for pressure jet burners should be 17–20 kg/cm 2 .
• Correct flame is normally short. Flame impingement on walls and tubes is
to be avoided since it causes carbon/soot deposits.