Objective of the Gas Interchangeability Report
The objective of this white paper is to define acceptable ranges of natural gas characteristics that can be consumed by end users while maintaining safety, reliability, and environmental performance. It is important to recognize that this objective applies equally to imported LNG and domestic supply.
The NGC+ commissioned the Work Group on Interchangeability to examine the issues related to maintaining adequate and reliable gas supplies for consumers in a manner that will enable system integrity, operational reliability and environmental performance.
Overview of the Gas Quality Report
This report examines the occurrence of hydrocarbon liquids in natural gas, the role of gas processing, and historical measures used to control hydrocarbon liquid drop out. There are seven sections, including this Introduction. They are:
Section 2 – Liquid Hydrocarbons in Natural Gas
This section describes the sources of natural gas and shows that all gas as produced is not the same. It describes the role of treatment and processing to provide a more uniform, fungible commodity. It also describes the challenges to controlling hydrocarbon liquid drop out when faced with the influences of pressure reductions and ambient temperature.
Section 3 – Hydrocarbon Liquid Drop Out Control Measures
This section describes measures used historically to control hydrocarbon liquid drop out, including heating value (Btu/volume), and composite concentrations of heavier weight hydrocarbons (such as the mole fraction of heavier weight hydrocarbons measured as the “pentane plus” fraction, referred to as C5+ or the “hexane plus”, referred to as C6+)2. This section also provides a description of blending, a tool to provide shippers and pipeline operators some flexibility in controlling hydrocarbon liquid drop out.
Section 4 – Overview of Hydrocarbon Dew Point (HDP)
This section defines hydrocarbon dew point and describes how it can be used as a means to understand the behavior of hydrocarbons in a natural gas stream. The section provides a basic description of the thermodynamic principles governing the behavior of compounds found within natural gas. It describes the behavior of hydrocarbons as gas is processed, and as pressure and temperature change downstream in the value chain.
Section 5 – Historical Levels of Hydrocarbons and Hydrocarbon Dew Point
This section provides a summary of historical data on natural gas streams from a variety of sources, including detailed analyses of hydrocarbon constituents in gas as produced and processed. The section also provides historical levels of hydrocarbon dew points.
Section 6 – Determination of Hydrocarbon Dew Point – Measurement and
This section provides an overview of the direct determination of hydrocarbon dew point. A chilled mirror is used to measure hydrocarbon dew point directly. Alternatively, a combination of sampling, analysis and calculation using a simplified equation of state from chemical thermodynamics is used to estimate the hydrocarbon dew point. The section provides an overview of the value of each in predicting hydrocarbon liquid drop out.
Section 7 – Recommendations
This section provides a set of recommendations developed by the Natural Gas Council HDP Task Group to manage hydrocarbon liquid drop out.