low-temperature separation[′lō ‚tem·prə·chər ‚sep·ə′rā·shən]
a process of producer treatment of natural gas to extract gas condensate and remove moisture from it to the dew point, which would preclude hydrate formation during transportation to consumers. The process consists in condensation of water vapor and heavy hydrocarbons dissolved in the gas at temperatures of 0° to —15°C. The gas is cooled by the Joule-Thomson effect (gas throttling).
In the simplest low-temperature separation unit, gas from wells passes at pressures considerably exceeding the working pressure in the pipeline into a separator-entrainment trap, where part of the liquid is removed from the gas stream. The gas is then cooled to 5°-15°C in a recuperative heat exchanger and throttled to the working pressure in the main pipeline. The temperature of the gas usually drops to minus 5°-10°C during throttling. To preclude hydrate formation, inhibitors (usually alcohols) are added to the gas before cooling. The gas is then passed into the separator, where the condensate and aqueous solution of the inhibitor are removed from it, and the dried gas flows through the heat exchanger, where it cools the stream of raw gas and passes into the pipeline.
As the gas is removed, the formation pressure decreases and finally becomes insufficient for attainment of the desired dew point; this impairs the process of treatment of the gas. This is the main shortcoming of production treatment of gas by means of low-temperature separation, since at this point more than 50 percent of the total reserves of gas still remains underground. To prolong the usefulness of a low-temperature separation unit, the gas is precooled in water and air heat exchangers or refrigeration machines. Work is in progress on the improvement of low-temperature separation through the design of small, high-speed turbine cooling devices. A process of gas treatment involving the introduction and regeneration of a sorbent, which removes the moisture, has been adopted at the Shebelinka gas field (Ukrainian SSR).
REFERENCESKorchazhkin, M. T. “Tekhnologicheskaia skhema separatsii vysokonapornogo kondensatnogo gaza.” In Dobycha gaza. Moscow, 1961.
Bazlov, M. N. , A. I. Zhukov, and T. S. Alekseev. Podgotovka prirodnogo gaza i kondensata k transportu. Moscow, 1968.
B. V. DEGTIAREV