Higher heating value (HHV) is one measure of the energy content of a material. It is almost exclusively used in measuring energy content for fossil fuels and their alternatives, such as oil, coal, natural gas and biomass. HHV is the upper end of the energy content, and it includes the energy in water evaporated from the fuel as it is combusted. True HHV must be determined from experimentation, but proximate values can be calculated from a number of correlations depending on known data.
Determine the elemental composition of the material for carbon (C), hydrogen (H), sulfur (S), oxygen (O), nitrogen (N) and ash (A) in mass percentage of dry material.
Insert the values into the following equation, which was calculated to be the best fit for a variety of materials in solid, liquid or gaseous form according to Drs. Channiwala and Parikh as reported in the journal Fuel in 2002. HHV= 0.3491(C) + 1.1783(H) + 0.1005(S) + 0.1034(O) + 0.0151(N) +0.021(A).
Check your HHV against similar fuels. For example, if you are estimating HHV of an oil, compare the value to known values for crude oil, olive oil or some other similar oil.
Fixed Carbon and Volatile Matter
Determine volatile matter (VM) as mass percentage of dry material. If the material is not known, VM must be measured via experiment. Acceptable experiment standards vary, but all tests require heating the sample to about 1700 degrees F and maintaining such a temperature for several minutes to allow liberation of the VM. The difference in the mass of the sample before and at the end of this experiment represents the VM.
Determine fixed carbon (FC) as mass percent of dry material. The amount of FC in a sample is the mass of the sample before the VM was liberated minus the amount of VM.
Substitute your values into the following derived equation by Dr. Demirbas, published in the journal Fuel in 1997: HHV = 0.312(FC) + 0.1534(VM). This equation found good agreement with experimental HHV from materials with known values of FC and VM.
Determine fixed carbon (FC) as mass percent of dry material. This can be done by experimentation or by looking up the value.
Substitute the value for FC into this derived equation by Dr. Demirbas, published in the journal Fuel in 1997: HHV = 0.196(FC) + 14.119. This equation, based on regression analysis of hundreds of fuel materials with known values of FC and HHV, is the simplest one--using a multiplier and a constant--that produced results with good agreement with experimental values.
Check your value against known values of HHV. Using just one variable--FC--means you will have a wider error band than if you use more known variables.
HHV can often be looked up in a table or textbook rather than calculated. Values calculated from derived equations should be treated as rough approximations.
Jae Chapman is a sustainability enthusiast who has been writing since 2006. She writes for various websites with a focus on the environment, food, fitness, computer software and other practical topics. She holds a Master of Science in engineering from the Georgia Institute of Technology.