Heat of Combustion: Difference between revisions

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#REDIRECTION[[Heat of combustion]]
 
The '''heat of combustion''' (ΔH<sub>c</sub><sup>0</sup>) is the [[energy]] released as [[heat]] when a compound undergoes complete [[combustion]] with [[oxygen]]. The [[chemical reaction]] for the  combustion is typically that of a [[hydrocarbon]] fuel reacting with oxygen derived from atmospheric air to form [[carbon dioxide]], [[water]] and heat. It may be quantified with these units:
 
* energy/[[mole (unit)|mole]] of fuel (such as k[[Joule|J]]/[[Mole (unit)|mol]] or [[U.S. customary units|Btu]]/[[Mole (unit)|lb-mol]])
* energy/mass of fuel (such as MJ/[[kg]] or Btu/[[U.S. customary units|lb]])
* energy/volume of fuel (such as MJ/[[Metre (unit)|m]]<sup>3</sup> or Btu/[[U.S. customary units|ft]]<sup>3</sup>)
 
The heat of combustion is traditionally measured with a [[Calorimeter#Bomb calorimeters|bomb calorimeter]]. It may also be calculated as the difference between the [[Standard enthalpy change of formation|heat of formation]] (Δ<sub>f</sub>H<sup>0</sup>) of the products and reactants.
 
== Common expressions for the heat of combustion of fuels ==
 
The heat of combustion of a [[fuel]] is commonly referred to as the '''heating value''' or the '''caloric value''' and briefly defined as the amount of heat released when a unit amount of the fuel is completely combusted. The heating value is a characteristic of each specific fuel.
 
The heating value of a fuel may be categorized as either the '''higher heating value (HHV)''' or the '''lower heating value (LHV)'''.<ref>{{cite book|author=William D. McCain|title=The Properties of Petroleum Fluids|edition=2nd Edition|publisher=Pennwell Publishing|year=1990|id=ISBN 0-8714-335-1}}</ref><ref>[http://www.princeton.edu/~humcomp/sophlab/ther_15.htm Heating values] ([[Princeton University]] website)</ref> The HHV is also known as the ''gross heating value'' (GHV) or the ''gross caloric value'' (GCV) and the LHV is also known as the ''net heating value'' (NHV) or the ''net caloric value'' (NCV).
 
More completely defined, the HHV is the amount of heat released when a unit amount of fuel at a given initial [[temperature]] (usually 20 °C or 25 °C) is completely combusted at [[stoichiomtry|stoichiometric conditions]] and constant [[pressure]] with the combustion products being cooled to the initial temperature and any water vapor produced being condensed. Condensing any water [[vapor]] produced during determination of the HHV means that the HHV includes the [[heat of vaporization]]  (ΔH<sub>v</sub><sup>0</sup> (or more simply H<sub>v</sub>) of the water produced. Stoichiometric combustion means that the combustion products do not contain any oxygen (i.e., there was no excess of combustion air during the combustion).
 
The LHV is similarly defined except that any water in the combustion products is not condensed and remains as a vapor. Thus, the LHV does not include the heat of vaporization of the water produced.
 
The relation between the HHV and the LHV may be simply expressed as:
 
:'''LHV = HHV – H<sub>v</sub>'''
 
Fuel [[gas]]es and fuel [[liquid]]s usually contain little, if any, water. However, raw solid fuels like [[coal]], [[wood]] or [[peat]]  do contain significant amounts of water. Coal, in particular, also contains significant amounts of non-combustible [[mineral]]s that form [[Coal ash|ash]] when the coal is combusted.
 
===More expressions for fuel heating values===
 
Both the HHV's and LHV's of fuels (especially coal and other solid fuels) can be be further sub-categorized and expressed as:<ref>{{cite book|author=Christopher Higman and Maarten van der Burgt|title=Gasification|edition=2nd Edition|publisher=Gulf Professional Publishing|year=2008|pages=pages 53-54|id=ISBN 0-7506-8528-X}}</ref>
 
* '''As Received (AR)''': Indicates the the fuel heating value was measured with all inherent moisture and ash forming minerals present.
 
* '''Moisture Free (MF)''' or '''Dry''': Indicates that the fuel heating value was measured after the fuel has been dried of all inherent moisture but still retained its ash forming minerals.
 
* '''Moisture and Ash Free (MAF)''' or '''Dry and Ash Free (DAF)''': Indicates that the fuel heating value has been measured in the absence of both inherent moisture and ash forming minerals.
 
==Heating values of some common fuels==
 
{| class = "wikitable" align="center"
|+ Table 1: Higher Heating Value (HHV) Of Various Common Fuels
! Fuel!!&nbsp;Phase&nbsp;!!&nbsp;[[Molecular mass|Molecular&nbsp;<br>Weight]]!!kJ/mol!!&nbsp;MJ/kg&nbsp;!!&nbsp;MJ/m<sup>3</sup>&nbsp;!!&nbsp;Btu/lb&nbsp;!!&nbsp;Btu/ft<sup>3&nbsp;</sup>
|-
| align="center"|[[Hydrogen]] <ref name=Perry>{{cite book|author=Perry, R.H. and Green, D.W. (Editors)|title=Perry's Chemical Engineers' Handbook|edition=7th Edition|publisher=McGraw Hill|year=1997|id=ISBN ISBN 0-07-049841-5}}</ref>
| align="center"|gas
| align="center"|2.016
| align="center"|285.84
| align="center"|141.79
| align="center"|12.75
| align="center"|60,986
| align="center"|324
|-
| align="center"|[[Methane]] <ref name=Perry/><ref name=NIST>[http://webbook.nist.gov/chemistry/ National Institute of Standards and Technology's Chemistry WebBook]</ref>
| align="center"|gas
| align="center"|16.043
| align="center"|890.31
| align="center"|55.50
| align="center"|39.72
| align="center"|23,870
| align="center"|1,009
|-
| align="center"|[[Ethane]] <ref name=Perry/><ref name=NIST/>
| align="center"|gas
| align="center"|30.069
| align="center"|1,559.88
| align="center"|51.88
| align="center"|69.59
| align="center"|22,313
| align="center"|1,768
|-
| align="center"|[[Propane]] <ref name=Perry/><ref name=NIST/>
| align="center"|gas
| align="center"|44.096
| align="center"|2,220.05
| align="center"|50.35
| align="center"|99.05
| align="center"|21,654
| align="center"|2,516
|-
| align="center"|[[Butane]] <ref name=Perry/><ref name=NIST/>
| align="center"|gas
| align="center"|58.122
| align="center"|2,878.52
| align="center"|49.53
| align="center"|128.43
| align="center"|21,301
| align="center"|3,263
|-
| align="center"|[[Ethanol]] <ref name=PNL>[http://hydrogen.pnl.gov/filedownloads/hydrogen/datasheets/lower_and_higher_heating_values.xls Heating Values of Hydrogen and Fuels] [[U.S. Department of Energy]]</ref>
| align="center"|liquid
| align="center"|46.068
| align="center"|1,375.01
| align="center"|29.85
| align="center"|
| align="center"|12,837
| align="center"|
|-
| align="center"|[[Gasoline]] <ref name=PNL/>
| align="center"|liquid
| align="center"|110
| align="center"|5,013.47
| align="center"|45.58
| align="center"|
| align="center"|19,603
| align="center"|
|-
| align="center"|[[Kerosene]] <ref name=Various>Average of various sources</ref>
| align="center"|liquid
| align="center"|178
| align="center"|8,084.99
| align="center"|45.42
| align="center"|
| align="center"|19,536
| align="center"|
|-
| align="center"|[[Diesel oil]] <ref name=Various/>
| align="center"|liquid
| align="center"|225
| align="center"|10,124.99
| align="center"|45.00
| align="center"|
| align="center"|19,355
| align="center"|
|-
| align="center"|Coal <ref>There are a great many different coals. The values given here are of a single, specific [[bituminous coal]] on an "as received" basis which includes the ash and inherent moisture content of the coal.</ref>
| align="center"|solid
| align="center"|
| align="center"|
| align="center"|25.58
| align="center"|
| align="center"|11,002
| align="center"|
|-
| align="center"|Wood (dry) <ref>[http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr13.pdf Table 1: Higher heating values for wood (oven dried)] The values in this table are the average of oven-dried woods from 29 different species of trees, as listed in this publication by the [[U.S. Forest Service]]'s laboratory.</ref>
| align="center"|solid
| align="center"|
| align="center"|
| align="center"|21.14
| align="center"|
| align="center"|9,093
| align="center"|
|-
| align="center"|Peat (dry) <ref>[http://www.diva-portal.org/diva/getDocument?urn_nbn_se_kth_diva-3164-2_fulltext.pdf  Thermal and Catalytic Upgrading in a Fuel Context: Peat, Biomass and Alkenes] Thesis by Christina Hornell, Chemical Engineering Dept., [[Royal Institute of Technology]], [[Stockholm]], [[Sweden]], 2001</ref>
| align="center"|solid
| align="center"|
| align="center"|
| align="center"|22.09
| align="center"|
| align="center"|9,500
| align="center"|
|-
| colspan="8"|<small>-- The gas temperature and pressure for the values of MJ/m<sup>3</sup> are 0 °C and 101.325 k[[Pascal|Pa]].<br>-- The gas temperature and pressure for the values of Btu/ft<sup>3</sup> are 60 °F and 14.696 psia.<br>-- [[LPG]] is marketed as propane or butanes or a mixture of propane and butanes.<sup>&nbsp;</sup><br>-- [[Natural gas]], after removal of impurities and natural gas liquids (NGL), is essentially pure methane.</small>
|}
 
{| class = "wikitable" align="center"
|+ Table 2: Lower Heating Value (HHV) Of Various Common Fuels
! Fuel!!&nbsp;Phase&nbsp;!!&nbsp;Molecular&nbsp;<br>Weight!!kJ/mol!!&nbsp;MJ/kg&nbsp;!!&nbsp;MJ/m<sup>3</sup>&nbsp;!!&nbsp;Btu/lb&nbsp;!!&nbsp;Btu/ft<sup>3&nbsp;</sup>
|-
| align="center"|Hydrogen <ref name=Perry/>
| align="center"|gas
| align="center"|2.016
| align="center"|241.83
| align="center"|119.96
| align="center"|10.79
| align="center"|51,596
| align="center"|274
|-
| align="center"|Methane <ref name=Perry/>
| align="center"|gas
| align="center"|16.043
| align="center"|802.32
| align="center"|50.01
| align="center"|35.80
| align="center"|21,511
| align="center"|909
|-
| align="center"|Ethane <ref name=Perry/>
| align="center"|gas
| align="center"|30.069
| align="center"|1,427.84
| align="center"|47.49
| align="center"|63.70
| align="center"|20,424
| align="center"|1,618
|-
| align="center"|Propane <ref name=Perry/>
| align="center"|gas
| align="center"|44.096
| align="center"|2,044.00
| align="center"|46.35
| align="center"|91.19
| align="center"|19,937
| align="center"|2,317
|-
| align="center"|Butane <ref name=Perry/>
| align="center"|gas
| align="center"|58.122
| align="center"|2,658.45
| align="center"|45.74
| align="center"|118.61
| align="center"|19,673
| align="center"|3,013
|-
| align="center"|Ethanol <ref name=PNL/>
| align="center"|liquid
| align="center"|46.0684
| align="center"|1,241.66
| align="center"|26.95
| align="center"|
| align="center"|11,593
| align="center"|
|-
| align="center"|Gasoline <ref name=PNL/>
| align="center"|liquid
| align="center"|110
| align="center"|4,675.00
| align="center"|42.50
| align="center"|
| align="center"|18,280
| align="center"|
|-
| align="center"|Kerosene <ref name=Estimated>Estimated the difference between LHV and HHV</ref>
| align="center"|liquid
| align="center"|178
| align="center"|7,519.05
| align="center"|42.24
| align="center"|
| align="center"|18,169
| align="center"|
|-
| align="center"|Diesel oil <ref name=Estimated/>
| align="center"|liquid
| align="center"|225
| align="center"|9,395.99
| align="center"|41.76
| align="center"|
| align="center"|17,961
| align="center"|
|-
| align="center"|Coal <ref name=Estimated/>
| align="center"|solid
| align="center"|
| align="center"|
| align="center"|24.429
| align="center"|
| align="center"|10,507
| align="center"|
|-
| align="center"|Wood (dry) <ref name=Estimated/>
| align="center"|solid
| align="center"|
| align="center"|
| align="center"|20.09
| align="center"|
| align="center"|8,639
| align="center"|
|-
| align="center"|Peat (dry) <ref name=Estimated/>
| align="center"|solid
| align="center"|
| align="center"|
| align="center"|20.65
| align="center"|
| align="center"|8,883
| align="center"|
|-
| colspan="8"|<small>-- The gas temperature and pressure for the values of MJ/m<sup>3</sup> are 0 °C and 101.325 kPa.<br>-- The gas temperature and pressure for the values of Btu/ft<sup>3</sup> are 60 °F and 14.696 psia.<br>-- LPG is marketed as propane or butanes or a mixture of propane and butanes.<sup>&nbsp;</sup><br>-- Natural gas, after removal of impurities and natural gas liquids (NGL), is essentially pure methane.</small>
|}
 
== Sources of additional heating values ==
 
* {{cite book|author=Robert C. Weast (Editor)|title=Handbook of Chemistry and Physics|edition=56th Edition|publisher=CRC Press|year=1975|id=ISBN 0-87819-455-X}}
 
*{{cite book|author=Perry, R.H. and Green, D.W. (Editors)|title=[[Perry's Chemical Engineers' Handbook]]|edition=7th Edition|publisher=McGraw Hill|year=1997|id=ISBN ISBN 0-07-049841-5}}
 
* [http://www.nist.gov/srd/PDFfiles/jpcrd6.pdf Selected Values of Heats of Combustion and Formation of Organic Compounds Containing the Elements C, H, N, O, P and S]Eugene S. Domalski, Chemical Thermodynamics Data Center, [[National Bureau of Standards]], Washington, D.C., J. Phys. Chem. Ref. Data, Vol. 1, No. 2, 1972
 
* [http://hydrogen.pnl.gov/cocoon/morf/projects/hydrogen/datasheets/lower_and_higher_heating_values.xls Lower and Higher Heating Values of Hydrogen and Fuels] Hydrogen Analysis Resource Center, [[U.S. Department of Energy]]
 
*[http://webbook.nist.gov/chemistry/ NIST Chemistry WebBook] Website of the [[National Institute of Standards and Technology]]
 
==References==
{{reflist}}

Latest revision as of 23:52, 23 September 2008

  1. REDIRECTIONHeat of combustion
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