addressing uncertainty in oil and natural gas industry greenhouse

3.5 Heat Content Determination
The heating value or calorific value of a substance is the amount of heat released during the combustion
of a specified amount of the substance. The calorific value is a characteristic for each substance and is
measured in units of energy per unit of the substance, such as: kcal/kg, kJ/kg, J/mole, Btu/m³. The heat
of combustion for fuels is expressed as:
−
−
HHV – higher heating value (or gross calorific value or gross energy or upper heating value).
This value is determined by bringing all the products of combustion back to the original precombustion
temperature, and in particular condensing any water vapor produced.
LHV – lower heating value (or net calorific value) is determined by subtracting the heat of
vaporization of the water vapor from the higher heating value and treating any water formed as a
vapor. The energy required to vaporize the water therefore is not realized as heat.
In the O&G industry, the two most prevalent modes of determining heating values of gaseous fuels is
either by measuring it directly, which can be accomplished either by stoichiometric combustion or by
calorimetric techniques, or by computational methods that are based on standardized calculation
procedures using gas sample composition data. A brief summary of these two types of practices is
provided below.
3.5.1 Direct Measurements
The heating value indicates the amount of energy that can be obtained as heat by burning a unit of gas.
The heating values of a gas depend not only upon the temperature and pressure, but also upon the degree
of saturation with water vapor.
As mentioned above, general practices for determining fuel gas heating values rely on either calorimetric
techniques or stoichiometric combustion practices. Table 3-5 provides a listing and a brief description of
some selected methods for heating value determination for gaseous, liquid, and solid fossil fuels. Further
discussion of the main features of these methods can be found in Appendix C.
Pilot Version, September 2009 3-19