Fuel and Combustion Data

The type of fuel and its heating value should be specified, preferably at the lower heating value, in Btu per pound of fuel. Even for gas fuel, this provides a better relationship than heating value per cubic foot, as it must eventually be put in terms of mass to make the computations of air-fuel ratio. 

For fuel oil, the ultimate analysis in terms of hydrogen, carbon, sulfur and any other component should be given — as well as the specific gravity (or API gravity). Viscosity at two temperatures should also be given. This is needed to determine the temperature to which the fuel must be heated for good atomization. 

For gas, in addition to the heating value (preferably the lower heating value in Btu per pound), an ultimate analysis is also useful although certain available correlations of heating value and specific gravity (referred to air) can be used in many instances. 

The percent of sulfur by weight should be included unless it can be given as the mole fraction of H2S. In some natural gases there may be appreciable fractions of carbon dioxide or nitrogen or both. It is important to note this, because it affects not only the combustion characteristics and heating value but also the operation of the CO2 recorder that will be provided to control the amount of air for combustion. 

Modem fired heaters absorb by radiation 60 to 70% of the total heat absorbed in the heater although this percentage is influenced by the temperature at which the oil enters the heater. The combustion gases are still quite hot (1,500 to 1,800°F). Usually a convection section is added to recover as much additional heat as is economical. 

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