Poor atomization may result in the formation of carbon deposits on the burner tips or on thewalls. Therefore pre-heating is necessary for proper atomization.Flash PointThe flash point of a fuel is the lowest temperature at which the fuel can be heated so that thevapour gives off flashes momentarily when an open flame is passed over it. Flash point for furnace oil is 66°C.Pour PointThe pour point of a fuel is the lowest temperature at which it will pour or flow when cooledunder prescribed conditions. It is a very rough indication of the lowest temperature at whichfuel oil is readily pumpable.Specific HeatSpecific heat is the amount of kCals needed to raise the temperature of 1 kg of oil by 1°C. The unit of specific heat is kCal/kg°C. It varies from 0.22 to 0.28 depending on the oil specif-ic gravity. The specific heat determines how much steam or electrical energy it takes to heat oilto a desired temperature. Light oils have a low specific heat, whereas heavier oils have a high-er specific heat.Calorific ValueThe calorific value is the measurement of heat or energy produced, and is measured either asgross calorific value or net calorific value. The difference being the latent heat of condensationof the water vapour produced during the combustion process. Gross calorific value (GCV)assumes all vapour produced during the combustion process is fully condensed. Net calorificvalue (NCV) assumes the water leaves with the combustion products without fully being condensed. Fuels should be compared based on the net calorific value.The calorific value of coal varies considerably depending on the ash, moisture content andthe type of coal while calorific value of fuel oils are much more consistent. The typical GrossCalorific Values of some of the commonly used liquid fuels are given below:1.Fuels and Combustion2Bureau of Energy Efficiency
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Fuel OilGross Calorific Value (kCal/kg)Kerosene- 11,100 Diesel Oil - 10,800 L.D.O- 10,700 Furnace Oil- 10,500 LSHS- 10,600 SulphurThe amount of sulphur in the fuel oil depends mainly on the source of the crude oil and to alesser extent on the refining process. The normal sulfur content for the residual fuel oil (furnaceoil) is in the order of 2-4 %.Typical figures are:Fuel oilPercentage of SulphurKerosene0.05 – 0.2Diesel Oil0.05 – 0.25L.D.O0.5 – 1.8Furnace Oil2.0 – 4.0LSHS< 0.5The main disadvantage of sulphur is the risk of corrosion by sulphuric acid formed during andafter combustion, and condensing in cool parts of the chimney or stack, air pre heater andeconomiser. Ash ContentThe ash value is related to the inorganic material in the fuel oil. The ash levels of distillate fuelsare negligible. Residual fuels have more of the ash-forming constituents. These salts may becompounds of sodium, vanadium, calcium, magnesium, silicon, iron, aluminum, nickel, etc.
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