## C6PlusHCDPmatch

**C6PlusHCDPmatch**

C6PlusHCDPmatch software provides accurate calculations of natural gas dew points in pipelines. With C6PlusHCDPmatch the gas analysis is extended mathematically so the Peng-Robinson equation of state will match the single measured dew point taken from a typical gas chromatographic analysis coupled with a dew point temperature measurement at pipeline pressure. The extended analysis with C6PlusHCDPmatch can be used with confidence of acceptable accuracy even when the flowing gas composition changes within specified tolerance limits. In addition, by using C6PlusHCDPmatch a company can avoid an expensive extended analysis chromatogram. Dew points also can be calculated using a gas analysis alone.

**The C6PlusHCDPmatch Method **

Natural gas can be characterized in the region of pipeline operations from a typical gas chromatographic analysis with lumping of hexanes plus, coupled with a single chilled mirror or other dew point temperature measurement at pipeline pressure. A key to the characterization of the natural gas is the use of an equation of state which is capable of describing the phase behavior of the natural gas. The Peng-Robinson equation of state has been tuned by Starling Associates, Inc. for natural gas dew points for use by C6PlusHCDPmatch. The resultant extended analysis can be used with confidence of acceptable accuracy even when the flowing gas composition changes within specified tolerance limits.

**C6PlusHCDPmatch Calculation Choices**

--- Input composition and pressure, output HCDP (Hydrocarbon Dew Point)**Calculate HCDP for Detailed Gas Analysis**--- Input composition, Hexanes Plus molecular weight and pressure, output HCDP (Hydrocarbon Dew Point) and Hexanes Plus estimated composition**Calculate HCDP for Gas Analysis with Lumped Hexanes Plus**--- Input Measured HCDP, composition (including Hexanes Plus mole percent) and pressure, output Hexanes Plus estimated composition which matches Measured HCDP (Hydrocarbon Dew Point)**Match Measured HCDP****Calculate HCDP using Hexanes Plus Estimated Composition at any Pressure**--- Input estimated composition and pressure, output HCDP (Hydrocarbon Dew Point)

**HOW ****C6PlusHCDPmatch**** CAN HELP YOU SOLVE PROBLEMS**

- The increase in production of natural gas since the year 2000 has led to pipeline transportation of richer gases containing increasing amounts of hydrocarbons with molecular weights greater that the molecular weight of normal hexane (86.177). C6PlusHCDPmatch calculations can be used by the pipeline operator to choose operating controls to avoid condensation resulting in two phase liquid plus gas flow in the pipeline.
- Most natural gas pipeline operations include chromatographic analyses. The addition of dew point measurements by either manual or online automatic methods allows the pipeline operator to utilize C6PlusHCDPmatch calculations to decide the maximum amounts of rich gases allowed to enter the pipeline at inlet points along the pipeline.
- C6PlusHCDPmatch calculations can be used by the pipeline operator to determine the difference between the pipeline operating temperature and the natural gas dew point at the pipeline pressure; this difference represents the safety margin to avoid liquid drop out.

**History of C6PlusHCDPmatch**

In 2000, prior to initiation of the API 14.1 program of experimental measurements of natural gas dew points at Southwest Research Institute, SAI founder Ken Starling served as a consultant in development of the research plan, a role he had previously held in 1985, prior to the dew point and liquid drop out measurements sponsored by Gasunie Research in the Netherlands.

Following the progress of both of these research projects, a need became apparent for a reliable method to accurately calculates of dew points for natural gases in operating gas pipelines. The commonly used three step method of sampling, analysis and calculation can encounter undetected errors at each step. Sampling is difficult, accurate analysis is difficult and the resultant calculations of dew point and/or condensed liquid are uncertain.

The method developed and used by the C6PlusHCDPmatch software was to combine the direct measurement of dew point and the gas analysis so that the hexanes plus portion of the gas analysis is adjusted to match the measured dew point. This adjustment of the portion of the gas analysis which has the largest uncertainty yields calculation results in the region of the dew point which have much lower uncertainty than the commonly used three step method. This method was first presented in the paper “Peng-Robinson Equation of State Natural Gas Dew Points,” by Kenneth E. Starling, AGA Operations Conference, Orlando, 2003.