Heating value describes the energy content of a specific volume of natural gas. This is important for design of gas-consuming equipment and determines the amount of gas that must be consumed to provide a specific end-use need. Heating value is also the quantity that gas pipelines and distribution companies use to convert meter reads in volume to units of energy that are then used to calculate the customer bill. Ensuring that gas flowing in a delivery system is within an acceptable heating value range is important since customer equipment will function correctly only at certain heating values.
Heating value is determined by the amount of and type of hydrocarbon and non-flammable constituents left in the gas stream during processing. If necessary, heating value can be reduced by further extracting heavier hydrocarbons or, in some cases, by injecting nitrogen into the gas stream. Heating value can be increased by leaving or injecting more natural gas liquids such as ethane into the gas stream.
Heating values are expressed in units of energy per volume. In Imperial and U.S. units the heating value is expressed in terms of Btu per cubic foot (Btu/cf). In metric units, the heating value is stated in gigajoules per cubic metre (Gj/m3). Heating values vary between regions across the US and the world depending on their sources of natural gas. Following are different typical values in different regions of the world:
Each volume of natural gas has two different heating values. The first, called high heating value or HHV, includes the heat that can be obtained by condensing the water vapor that is released during combustion. The second, called low heating value or LHV, does not include this heat. The difference between HHV and LHV is typically about 10% for natural gas. Heating values used in the gas business such as those in the table above are typically high heating values.