155 1 100 10 Excess air 716 100 716 0016 558 6020 10 Theoretical O 2 by volume

# 155 1 100 10 excess air 716 100 716 0016 558 6020 10

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× 15.5 % 1 100 10 Excess air = × 7.16 100 7.16 0.016 5.58 60.20 = × + + +

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= 10% Theoretical O 2 % by volume 1. Fuels and Combustion Optimizing Excess Air and Combustion For complete combustion of every one kg of fuel oil 14.1 kg of air is needed. In practice, mixing is never perfect, a certain amount of excess air is needed to complete combustion and ensure that release of the entire heat contained in fuel oil. If too much air than what is required for completing combustion were allowed to enter, additional heat would be lost in heating the surplus air to the chimney temperature. This would result in increased stack losses. Less air would lead to the incomplete combustion and smoke. Hence, there is an optimum excess air level for each type of fuel. Control of Air and Analysis of Flue Gas Thus in actual practice, the amount of combustion air required will be much higher than optimally needed. Therefore some of the air gets heated in the furnace boiler and leaves through the stack without participating in the combustion Chemical analysis of the gases is an objective method that helps in achieving finer air control. By measuring carbon dioxide (CO 2 ) or oxygen (O 2 ) in flue gases by continuous recording instruments or Orsat apparatus or portable fyrite, the excess air level as well as stack losses can be estimated with the graph as shown in Figure 1.2 and Figure 1.3. The excess air to be supplied depends on the type of fuel and the firing system. For optimum combustion of fuel oil, the CO 2 or O 2 in flue gases should be maintained at 14 -15% in case of CO 2 and 2-3% in case of O 2 . 20 Bureau of Energy Efficiency Figure 1.2 Relation Between CO 2 and Excess Air for Fuel Oil 7.16 100 72.956 = × 5.58 100 100 7.5% 72.956 x = × =
1. Fuels and Combustion 21 Bureau of Energy Efficiency Oil Firing Burners The burner is the principal device for the firing of fuel. The primary function of burner is to atomise fuel to millions of small droplets so that the surface area of the fuel is increased enabling intimate contact with oxygen in air. The finer the fuel droplets are atomised, more readily will the particles come in contact with the oxygen in the air and burn. Normally, atomisation is carried out by primary air and completion of combustion is ensured by secondary air. Burners for fuel oil can be classified on the basis of the technique to prepare the fuel for burning i.e. atomisation. Figure 1.4 shows a simplified burner head. The air is brought into the head by means of a forced draft blower or fan. The fuel is metered into the head through a series of valves. In order to get proper combustion, the air molecules must be thoroughly mixed with the fuel molecules before they actually burn. The air in the center is the primary air used for atomization and the one surrounding is the secondary air which ensures complete combustion.

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• Spring '17
• Jerome Ramos

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