May 2013

Special Report: Maintenance/Reliability

Prevent methane hydrate formation in natural gas valves

The discussion here focuses on the thermodynamics involved and on the requirements for a successful natural gas valve application in which the incidences of hydrate formation and icing of the valve are reduced.

Glaun, A., Shahda, J., GE Oil & Gas

Gas flow across a control valve is considered a classic “throttling” process that is defined by energy not being added or extracted from the process gas as it traverses the valve. Therefore, total enthalpy is preserved, entropy increases and the process is thermodynamically irreversible. The consequences of this process are that many real gases experience a drop in temperature while following the constant enthalpy line as the pressure drops across the valve. This effect was first described by William Thomson and James Joule, and it now bears their names. The Joule-Thomson effect is leveraged in the production of cryogenic fluids such as liquid oxygen, nitrogen and argon, and it is

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