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Net Heating Value Calculation

The Net Heating Value of a fuel is defined as the amount of energy released by the combustion (burning) process of a unit amount of that fuel with these assumptions:

The combustion products are cooled to the initial fuel-air temperature.

The water produced by the process remains a vapor.

Net Heating Values are needed to perform energy balances or to estimate the energy content of a certain amount of fuel. Typically, fuels are a mixture of other fuels with known Net Heating Values.

Net Heating Values are reported in different units of measure and bases. The bases are the following:

  • Energy per unit of liquid volume
  • Energy per unit of standard gas volume
  • Energy per unit of mole
  • Energy unit per unit of mass

The Net Heating Value of a mixture is calculated with the following equation:

Where:

NHVm = the Net Heating Value of the mixture

xi = the component fraction

NHVi = the Net Heating Value of each component

Each xi and NHVi must have a compatible basis. Example groups of compatible bases are the following:

xi is volume fraction and NHVi has units of energy per standard volume.

xi is volume fraction and NHVi has units of energy per liquid volume.

xi is mass fraction and NHVi has units of energy per mass

xi is a mol fraction and NHVi has units of energy per mole.

Here are examples of incompatible bases:

xi is mass fraction and NHVi has units of energy per standard volume.

xi is mol fraction and NHVi has units of energy per liquid volume.

xi is volume fraction and NHVi has units of energy per mass.

xi is a mass fraction and NHVi has units of energy per mole.

ClosedEXAMPLE: Net Heating Value Calculation

A gas stream is composed of 30% and 70% mass for methane and ethane, respectively. Determine the Net Heating Value (NHV) per unit of mass for the mixture. Consider a NHV of 11,946 kcal/kg for methane and 11,350 kcal/kg for ethane.

NHV1 = NHV for methane = 11,946

NHV2 = NHV for ethane = 11,350

x1 = component fraction for methane = 0.3

x2 = component fraction for ethane = 0.7

NHVm = 0.3 × 11,946 + 0.7 × 11,350 = 11,528

The Net Heating Value is 11,528 kcal/kg for this gas mixture.