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The '''hydrocarbon dew point''' is the [[temperature]] (at a given  [[pressure]]) at which the [[hydrocarbon]] components of any hydrocarbon-rich gas mixture, such as [[natural gas]], will start to [[Condensation|condense]] out of the gaseous phase. It is often also referred to as the '''HDP''' or the '''HCDP'''. The maximum temperature and the pressure at which such [[condensation]] takes place is called the ''cricondentherm''.<ref>[http://www.effectech.co.uk/images/hydrocarbon.PDF Hydrocarbon Dew Point]</ref> The hydrocarbon dew point is a function of the gas composition as well as the pressure.


The hydrocarbon dew point of a gas is a different concept from the water dewpoint, the latter being the temperature (at a given pressure) at which water vapor present in a gas mixture will condense out of the gas.
==Importance of the hydrocarbon dewpoint==
If the hydrocarbon dew point of the pipelined gas is too high, liquids may condense out in the gas pipeline. This not only degrades the heating value of the remaining gas, it increases the potential for problems in the [[pipeline transmission]] systems and causes problems for the end users of the gas such as industrial combustion equipment and household gas appliances.
Therefore, the hydrocarbon dew point is universally used in the natural gas industry as an important quality parameter, stipulated in contractual specifications and enforced throughout the natural gas supply train, from producers through [[natural gas processing|processing]], transmission and distribution companies to the final end users.
==Relation of the term GPM to the hydrocarbon dew point==
In the [[United States]], the hydrocarbon dewpoint of [[Natural gas processing|''processed, pipelined natural gas'']] is related to and characterized by the term "GPM" which is the gallons of liquifiable hydrocarbons contained in 1,000,000 cubic feet of natural gas at a stated temperature and pressure. When the liquifiable hydrocarbons are characterized as being [[hexane]] or higher [[molecular weight]] components, they are reported as "GPM (C6+)" meaning hydrocarbons with 6 carbon atoms or more.<ref name=NGC>[http://www.naesb.org/pdf/update011905w9.pdf White Paper on Liquid Hydrocarbon Drop Out in Natural Gas Infrastructure] (NGC+ Liquid Hydrocarbon Dropout Task Group, October 15, 2004)</ref><ref name=NGC2>[http://www.beg.utexas.edu/energyecon/lng/documents/NGC_HDP_Paper.pdf White Paper on Liquid Hydrocarbon Drop Out in Natural Gas Infrastructure] (NGC+ Liquid Hydrocarbon Dropout Task Group, September 28, 2005)</ref>
However, it should be noted that the quality of ''raw produced natural gas'' (before it is purified by processing) is also often characterized by the term "GPM" meaning the gallons of liquifiable hydrocarbons contained in 1,000 cubic feet of the raw natural gas. In such cases, when the liquifiable hydrocarbons in the raw natural gas are characterized as being [[ethane]] or higher molecular weight components, they are reported as "GPM (C2+)". Similarly, when characterized as being [[propane]] or higher molecular weight components, they are reported as "GPM (C3+)".<ref name=NGC/><ref name=NGC2/>
Care must be taken not to confuse the two different definitions of the term GPM.
=== Liquifiable hydrocarbons terminology im metric countries ===
The natural gas industry in countries using the metric system probably use similar terminology (for characterizing liquifiable hydrocarbons in pipelined gas) expressed in metric units rather than the above units used in the [[United States]]. [[British Petroleum]]'s Miller Gas System delivering gas from the ([[North Sea]] to [[Scotland]]), for example, uses m³ of liquid per 1,000 m³ of gas to characterize liquifiable hydrocarbons in their pipeline gas.<ref>[http://www.bpnsi.com/index.asp?id=7369643D312669643D313133 Miller Gas System]</ref>
==References==
{{reflist}}
==External links==
*[http://www.eia.doe.gov/pub/oil_gas/natural_gas/feature_articles/2006/ngprocess/ngprocess.pdf Natural Gas Processing: The Crucial Link Between Natural Gas Production and Its Transportation]
*[http://www.iceweb.com.au/Analyzer/MoistMeas/Hydrocarbon%20Dew%20Point%20article%20-%20Oct%202004.doc Hydrocarbon Dew-point – A Key Natural Gas Quality Parameter]
*[http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=32874&ICS1=75&ICS2=60&ICS3=&scopelist=ALL (ISO 6570:2001) Natural gas -- Determination of potential hydrocarbon liquid content]
==Bibliography==
*{{cite book|author=A.J. Kidnay and William Parish|title=Fundamentals of Natural Gas Processing|edition=1st Edition|publisher=CRC Press|year=2006|id=ISBN 0-8493-3406-3}}
*{{cite book|author=Francis S. Manning and Richard E. Thompson|title=Oilfield Processing of Petroleum|edition=|publisher=Pennwell Books|year=1991|id=ISBN 0-87814-343-2}}

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