Industries 
LNG
Historically, gas quality issues were rare. However, the quality of natural gas in today's energy markets can vary and present problems to gas pipelines, distributors, appliance manufacturers and consumers. This can be due to several factors:
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| Gas Interchangeability |
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LNG Interchangeability Issue
Imported LNG may have different physical characteristics from domestically produced gas. The ability to substitute one gas supply for another is known as interchangeability. Interchangeability is often measured by Wobbe Index of the gas which is derivative of the higher heat content and specific gravity of the gas. The differing characteristics of imported LNG may appear to present operational issues for transmission systems and end-use equipment, although the extent to which these cause any real problems is addressed in the independent report on gas quality and interchangeability prepared by the Department of Energy's National Energy Technology Laboratory.
Hydrocarbon Dew Point (HDP) Issue
Natural gas is primarily methane, but in some regions where it's produced, it contains heavier liquid hydrocarbons (pentanes, hexanes, etc.). The quantity of these liquids in a natural gas stream depends on whether or not natural gas producers extract the liquids. The temperature when liquids suspended in the natural gas stream separate and drop out is called the hydrocarbon dew point.
When market economics favor the sales of liquid hydrocarbons, gas producers will process the gas to extract the liquids. When produced, these liquids create safety, reliability and integrity problems for pipelines and downstream customers. Some natural gas transactions for pipelines have specific tariff provisions and set an HDP limit to control the quality of the gas. The HDP issue relates to specific cases such as Toca/Southern, Natural, and ANR.
Other Gas Quality Issues
Today, there is very little consistency on natural gas quality specs among pipeline tariffs, even within corporate pipeline families. Even gas quality specs in tariffs vary in degrees of specificity. There have been some protests to several pipeline tariff filings proposing changes in gas quality specifications.
The natural gas industry and FERC are exploring other natural gas quality specifications other than Btu and HDP in pipeline tariffs. Some of the limitations are for carbon dioxide, oxygen, nitrogen, water vapor, hydrogen sulfides, sulfur, temperature, PCB, microbiological agents, objectionable materials (odors, dust, impurities), among others.
Resolution of Gas Quality Issues
Natural gas quality is a complex and highly technical issue. The Commission has set some cases for technical conferences; some for hearing, and has issued proposed regulations on natural gas quality and interchangeability. FERC's expressed preference is that the natural gas industry reach a consensus with gas quality stakeholders.
