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Monday, September 22, 2014

Heating value

Posted by Krzysztof Lis on March 17, 2008

Heating value is the amount of heat released during a combustion of some fuel. It is sometimes called a calorific value. There are two ways to describe this amount of heat.

Higher Heating Value (HHV)

Higher Heating Value is calculated when we assume that all the combustion products (combustion gasses, like carbon dioxide CO2 and water vapor H2O) are cooled to the temperature on which the fuel was fed to the combustor. It is also said that any water vapor in combustion gasses will be condensed which will result in some additional heat delivered to the heated object.

Lower Heating Value (LHV)

Lower Heating Value is used when we know that water vapor in flue gasses will not be condensed. It means that some heat will be lost with the combustion gasses, since that water wasn’t condensed. LHV is used also when determining thermal efficiency of any device, e.g. internal combustion engine. This efficiency is a ratio between energy taken from such an engine (in engine case this would be mechanical power delivered on transmission) to energy introduced to the engine (mass of fuel multiplied by LHV of this fuel).

There are some additional conditions used then calculating or measuring LHV and HHV.

As received (AR) means that the heating value is measured for the given fuel, including all the moisture and ash (all the material that isn’t combustible).
Dry or moisture free (MF) means that the fuel is first dried until it contains no moisture, and then the heating value is measured. This is important for fuels of various moisture, like wood and all biomass materials.
Dry and ash free (DAF) or moisture and ash free (MAF) is measured when fuel is heated and all ash is removed.

Below is a short list of some fuels with their heating values.

Fuel HHV in MJ/kg HHV in BTU/lb LHV in MJ/kg
Hydrogen 141.8 61,100  
Methane 55.5 23,900  
Ethane 51.9 22,400  
Propane 50.35 21,700  
Butane 49.5 20,900  
Gasoline 47.3 20,400 44.4
Diesel 44.8 19,300 42.5
Kerosene 46.2   43.0
Methanol 22.7 9,800  
Ethanol 29.7 12,800  
Propanol 33.6 14,500  
Isobutanol 33.0    
Carbon 33.8 14,100 33.8
Coal 15 – 27 8,000 – 14,000  
Peat 6 – 15 2,500 – 6,500  
Wood 15 6,500  

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