Temperature change from isenthalpic expansion of aqueous triethylene glycol mixtures for natural gas dehydration

In natural gas dehydration units, rich TEG solutions are decompressed before the TEG regeneration stage and the direction of the temperature change during the decompression has been debated. The temperature change from an isenthalpic expansion from (7000 kPa to 440 kPa was measured for the following aqueous mixtures: pure water, 99% pure triethylene glycol (TEG), aqueous TEG (99 wt% TEG + 1% water), aqueous TEG saturated with methane, aqueous TEG saturated with n-pentane, and aqueous TEG saturated with n-heptane. In all cases, the temperature increased upon expansion with the magnitude of the temperature change ranging from 1.4 K for pure water to 2.4 K for TEG. A simple equation of state model predicted the correct direction for the temperature change and the predicted values were within ±1 K of the experimental data.

► Measurement of Joule–Thomson temperature change across a valve from 7000 kPa down to 440 kPa.
► Triethylene glycol/water vapour–liquid equilibrium.
► Triethylene glycol/water enthalpy prediction using simple cubic equation of state.
► Triethylene glycol/water isobaric heat capacity prediction using simple cubic equation of state.
► Validation of process simulator predictions for natural gas dehydration plants.