carbon Carbon burned to CO 2 will produce more heat per pound of fuel than when

Carbon carbon burned to co 2 will produce more heat

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carbon) Carbon burned to CO 2 will produce more heat per pound of fuel than when CO or smoke are produced. 1. Fuels and Combustion 15 Bureau of Energy Efficiency C + O 2 CO 2 + 8084 kCals/kg of Carbon 2C + O 2 2 CO + 2430 kCals/kg of Carbon 2H 2 + O 2 2H 2 O + 28,922 kCals/kg of Hydrogen S + O 2 SO 2 + 2,224 kCals/kg of Sulphur Each kilogram of CO formed means a loss of 5654 kCal of heat.(8084-2430). 3 T’s of Combustion The objective of good combustion is to release all of the heat in the fuel. This is accomplished by controlling the “three T’s” of combustion which are (1) Temperature high enough to ignite and maintain ignition of the fuel, (2) Turbulence or intimate mixing of the fuel and oxygen, and (3) Time sufficient for complete combustion. Commonly used fuels like natural gas and propane generally consist of carbon and hydrogen. Water vapor is a by-product of burning hydrogen. This robs heat from the flue gases, which would otherwise be available for more heat transfer. Natural gas contains more hydrogen and less carbon per kg than fuel oils and as such produces more water vapor. Consequently, more heat will be carried away by exhaust while firing natural gas.
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Too much, or too little fuel with the available combustion air may potentially result in unburned fuel and carbon monoxide generation. A very specific amount of O 2 is needed for perfect combustion and some additional (excess) air is required for ensuring complete combus- tion. However, too much excess air will result in heat and efficiency losses. 1. Fuels and Combustion 16 Bureau of Energy Efficiency Not all of the heat in the fuel are converted to heat and absorbed by the steam generation equip- ment. Usually all of the hydrogen in the fuel is burned and most boiler fuels, allowable with today’s air pollution standards, contain little or no sulfur. So the main challenge in combustion efficiency is directed toward unburned carbon (in the ash or incompletely burned gas), which forms CO instead of CO 2 . 1.7 Combustion of Oil Heating Oil to Correct Viscosity When atomizing oil, it is necessary to heat it enough to get the desired viscosity. This temper- ature varies slightly for each grade of oil. The lighter oils do not usually require pre-heating. Typical viscosity at the burner tip ( for LAP, MAP & HAP burners) for furnace oil should be 100 Redwood seconds-1 which would require heating the oil to about 105°C. Stoichiometric Combustion The efficiency of a boiler or furnace depends on efficiency of the combustion system. The amount of air required for complete combustion of the fuel depends on the elemental constituents of the fuel that is Carbon, Hydrogen, and Sulphur etc. This amount of air is called stoichiometric air. For ideal combustion process for burning one kg of a typical fuel oil containing 86% Carbon, 12% Hydrogen, 2% Sulphur, theoretically required quantity of air is 14.1 kg. This is the minimum air that would be required if mix- ing of fuel and air by the burner and combustion is perfect. The combustion products are primarily Carbon Dioxide (CO 2 ), water vapor (H 2
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  • Spring '17
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