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The heating value (or energy value or calorific value ) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The calorific value is the total energy released as heat when a substance undergoes complete combustion with oxygen under standard conditions. The chemical reaction is typically a hydrocarbon or other organic molecule reacting with oxygen to form carbon dioxide and water and release heat. It may be expressed with the quantities: There are two kinds of heat of combustion, called higher and lower heating value, depending on how much the products are allowed to cool and whether compounds like H 2 O are allowed to condense. The values are conventionally measured with a bomb calorimeter. They may also be calculated as the difference between the heat of formation Δ H ⦵ f of the products and reactants (though this approach is somewhat artificial since most heats of formation are calculated from ...

Higher heating value edit The quantity known as higher heating value ( HHV ) (or gross energy or upper heating value or gross calorific value ( GCV ) or higher calorific value ( HCV )) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. Such measurements often use a standard temperature of 25 °C (77 °F; 298 K) citation needed . This is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is condensed to a liquid. The higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the wa...

Gross heating value accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning.

The higher heating value is experimentally determined in a bomb calorimeter. The combustion of a stoichiometric mixture of fuel and oxidizer (e.g. two moles of hydrogen and one mole of oxygen) in a steel container at 25 °C (77 °F) is initiated by an ignition device and the reactions allowed to complete. When hydrogen and oxygen react during combustion, water vapor is produced. The vessel and its contents are then cooled to the original 25 °C and the higher heating value is determined as the heat released between identical initial and final temperatures. When the lower heating value (LHV) is determined, cooling is stopped at 150 °C and the reaction heat is only partially recovered. The limit of 150 °C is based on acid gas dew-point. Note: Higher heating value (HHV) is calculated with the product of water being in liquid form while lower heating value (LHV) is calculated with the product of water being in vapor form .

The difference between the two heating values depends on the chemical composition of the fuel. In the case of pure carbon or carbon monoxide, the two heating values are almost identical, the difference being the sensible heat content of carbon dioxide between 150 °C and 25 °C (sensible heat exchange causes a change of temperature. In contrast, latent heat is added or subtracted for phase transitions at constant temperature. Examples: heat of vaporization or heat of fusion). For hydrogen the difference is much more significant as it includes the sensible heat of water vapor between 150 °C and 100 °C, the latent heat of condensation at 100 °C, and the sensible heat of the condensed water between 100 °C and 25 °C. All in all, the higher heating value of hydrogen is 18.2% above its lower heating value (142 MJ/kg vs. 120 MJ/kg). For hydrocarbons the difference depends on the hydrogen content of the fuel. For gasoline and diesel the higher heating value exceeds the lower heating value by abo...

Engine manufacturers typically rate their engines fuel consumption by the lower heating values since the exhaust is never condensed in the engine. American consumers should be aware that the corresponding fuel-consumption figure based on the higher heating value will be somewhat higher. The difference between HHV and LHV definitions causes endless confusion when quoters do not bother to state the convention being used. since there is typically a 10% difference between the two methods for a power plant burning natural gas. For simply benchmarking part of a reaction the LHV may be appropriate, but HHV should be used for overall energy efficiency calculations if only to avoid confusion, and in any case, the value or convention should be clearly stated.

Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal: AR (as received) indicates that the fuel heating value has been measured with all moisture- and ash-forming minerals present. MF (moisture-free) or dry indicates that the fuel heating value has been measured after the fuel has been dried of all inherent moisture but still retaining its ash-forming minerals. MAF (moisture- and ash-free) or DAF (dry and ash-free) indicates that the fuel heating value has been measured in the absence of inherent moisture- and ash-forming minerals.

Higher (HHV) and lower (LHV) heating values of some common fuels at 25 °C Fuel HHV MJ/kg HHV BTU/lb HHV kJ/mol LHV MJ/kg Hydrogen 141.80 61,000 286 119.96 Methane 55.50 23,900 889 50.00 Ethane 51.90 22,400 1,560 47.62 Propane 50.35 21,700 2,220 46.35 Butane 49.50 20,900 2,877 45.75 Pentane 48.60 21,876 3,507 45.35 Paraffin wax 46.00 19,900 41.50 Kerosene 46.20 19,862 43.00 Diesel 44.80 19,300 43.4 Coal (anthracite) 32.50 14,000 Coal (lignite - USA) 15.00 6,500 Wood (MAF) 21.70 8,700 Wood fuel 21.20 9,142 17.0 Peat (dry) 15.00 6,500 Peat (damp) 6.00 2,500 Higher heating value of some less common fuels Fuel MJ/kg BTU/lb kJ/mol Methanol 22.7 9,800 726.0 Ethanol 29.7 12,800 1,300.0 1-Propanol 33.6 14,500 2,020.0 Acetylene 49.9 21,500 1,300.0 Benzene 41.8 18,000 3,270.0 Ammonia 22.5 9,690 382.6 Hydrazine 19.4 8,370 622.0 Hexamine 30.0 12,900 4,2...

The International Energy Agency reports the following typical higher heating values: The lower heating value of natural gas is normally about 90 percent of its higher heating value.

The higher heating value is experimentally determined in a bomb calorimeter. The combustion of a stoichiometric mixture of fuel and oxidizer (e.g. two moles of hydrogen and one mole of oxygen) in a steel container at 25 °C (77 °F) is initiated by an ignition device and the reactions allowed to complete. When hydrogen and oxygen react during combustion, water vapor is produced. The vessel and its contents are then cooled to the original 25 °C and the higher heating value is determined as the heat released between identical initial and final temperatures. When the lower heating value (LHV) is determined, cooling is stopped at 150 °C and the reaction heat is only partially recovered. The limit of 150 °C is based on acid gas dew-point. Note: Higher heating value (HHV) is calculated with the product of water being in liquid form while lower heating value (LHV) is calculated with the product of water being in vapor form .

The difference between the two heating values depends on the chemical composition of the fuel. In the case of pure carbon or carbon monoxide, the two heating values are almost identical, the difference being the sensible heat content of carbon dioxide between 150 °C and 25 °C (sensible heat exchange causes a change of temperature. In contrast, latent heat is added or subtracted for phase transitions at constant temperature. Examples: heat of vaporization or heat of fusion). For hydrogen the difference is much more significant as it includes the sensible heat of water vapor between 150 °C and 100 °C, the latent heat of condensation at 100 °C, and the sensible heat of the condensed water between 100 °C and 25 °C. All in all, the higher heating value of hydrogen is 18.2% above its lower heating value (142 MJ/kg vs. 120 MJ/kg). For hydrocarbons the difference depends on the hydrogen content of the fuel. For gasoline and diesel the higher heating value exceeds the lower heating value by abo...

Engine manufacturers typically rate their engines fuel consumption by the lower heating values since the exhaust is never condensed in the engine. American consumers should be aware that the corresponding fuel-consumption figure based on the higher heating value will be somewhat higher. The difference between HHV and LHV definitions causes endless confusion when quoters do not bother to state the convention being used. since there is typically a 10% difference between the two methods for a power plant burning natural gas. For simply benchmarking part of a reaction the LHV may be appropriate, but HHV should be used for overall energy efficiency calculations if only to avoid confusion, and in any case, the value or convention should be clearly stated.

Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal: AR (as received) indicates that the fuel heating value has been measured with all moisture- and ash-forming minerals present. MF (moisture-free) or dry indicates that the fuel heating value has been measured after the fuel has been dried of all inherent moisture but still retaining its ash-forming minerals. MAF (moisture- and ash-free) or DAF (dry and ash-free) indicates that the fuel heating value has been measured in the absence of inherent moisture- and ash-forming minerals.

Higher (HHV) and lower (LHV) heating values of some common fuels at 25 °C Fuel HHV MJ/kg HHV BTU/lb HHV kJ/mol LHV MJ/kg Hydrogen 141.80 61,000 286 119.96 Methane 55.50 23,900 889 50.00 Ethane 51.90 22,400 1,560 47.62 Propane 50.35 21,700 2,220 46.35 Butane 49.50 20,900 2,877 45.75 Pentane 48.60 21,876 3,507 45.35 Paraffin wax 46.00 19,900 41.50 Kerosene 46.20 19,862 43.00 Diesel 44.80 19,300 43.4 Coal (anthracite) 32.50 14,000 Coal (lignite - USA) 15.00 6,500 Wood (MAF) 21.70 8,700 Wood fuel 21.20 9,142 17.0 Peat (dry) 15.00 6,500 Peat (damp) 6.00 2,500 Higher heating value of some less common fuels Fuel MJ/kg BTU/lb kJ/mol Methanol 22.7 9,800 726.0 Ethanol 29.7 12,800 1,300.0 1-Propanol 33.6 14,500 2,020.0 Acetylene 49.9 21,500 1,300.0 Benzene 41.8 18,000 3,270.0 Ammonia 22.5 9,690 382.6 Hydrazine 19.4 8,370 622.0 Hexamine 30.0 12,900 4,2...

The International Energy Agency reports the following typical higher heating values: The lower heating value of natural gas is normally about 90 percent of its higher heating value.