The measurement and control of contaminants in natural gas pipeline systems are crucial to maintaining safe, reliable transport and consistent quality final product. Contaminants that require continuous analysis include total sulfurs (primarily hydrogen sulfide, or hLS), water vapour, carbon dioxide (C02) and heavier hydrocarbons (as hydrocarbon dew point temperature).
The water connection
Natural gas at the wellhead is typically saturated with water under natural conditions. Water, in combination with other impurities and the hydrocarbons present in the gas stream, has the potential to severely damage a natural gas processing and delivery system. A major source of trouble in natural gas pipelines is the formation of a gas hydrate. A hydrate is a physical combination of water and other small molecules to produce a solid that has an 'ice like' appearance but possesses a different structure to ice. Figure 1 shows a nearly fully obstructed pipeline as a result of hydrate formation.
Excess water vapour content reduces the combustion quality of the gas and may lead to corrosion of components used to transport the natural gas when combined with any of the acid gases present in the natural gas.
Removal of the water is achieved using a variety of liquid or solid desiccants to strict specifications. Examples of water content (or dew point temperature) specifications are provided in Table 1.