In the process of reducing pressure, some of the heavier components may drop out, particularly if the pressure reduction is done in the retrograde region. To do an analysis using a field GC, the pressure has to be regulated down to close to atmospheric pressure. The first source of error is the sampling error.The theoretical methods using GC analysis suffer from four sources of error: The Peng–Robinson and Kwong–Redlich–Soave equations of state are the most commonly used for determining the HCDP in the natural gas industry. The theoretical methods use the component analysis of the gas mixture (usually via gas chromatography, GC) and then use an equation of state (EOS) to calculate what the dew point of the mixture should be at a given pressure. One category involves "theoretical" methods, and the other involves "experimental" methods. There are primarily two categories of HCDP determination. Furthermore, GPM and HCDP are not interchangeable and one should be careful not to confuse what each one exactly means. Ĭare must be taken not to confuse the two different definitions of the term GPM.Īlthough GPM is an additional parameter of some value, most pipeline operators and others who process, transport, distribute or use natural gas are primarily interested in the actual HCDP, rather than GPM. Similarly, when characterized as being propane or higher molecular weight components, they are reported as GPM (C3+). In such cases, when the liquefiable hydrocarbons in the raw natural gas are characterized as being ethane or higher molecular weight components, they are reported as GPM (C2+). However, the quality of raw produced natural gas is also often characterized by the term GPM meaning the gallons of liquefiable hydrocarbons contained in 1,000 cubic feet (28 m 3) of the raw natural gas. When the liquefiable hydrocarbons are characterized as being hexane or higher molecular weight components, they are reported as GPM (C6+). In the United States, the hydrocarbon dew point of processed, pipelined natural gas is related to and characterized by the term GPM which is the gallons of liquefiable hydrocarbons contained in 1,000 cubic feet (28 m 3) of natural gas at a stated temperature and pressure. The hydrocarbon dew point of a gas is a different concept from the water dew point, the latter being the temperature (at a given pressure) at which water vapor present in a gas mixture will condense out of the gas.
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 chain, from producers through processing, transmission and distribution companies to final end users.
The hydrocarbon dew point is a function of the gas composition as well as the pressure. The maximum temperature at which such condensation takes place is called the cricondentherm. It is often also referred to as the HDP or the HCDP. 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 condense out of the gaseous phase. For the meteorological dew point, see Dew point.
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