The job of a production facility is to separate the well stream into three components, typically called “phases” (oil, gas, and water), and process these phases into some marketable product(s) or dispose of them in an environmentally acceptable manner. In mechanical devices called “separators” gas is flashed from the liquids and “free water” is separated from the oil. These steps remove enough light hydrocarbons to produce a stable crude oil with the volatility (vapor pressure) to meet sales criteria. Figures 1-1 and 1-2 show typical separators used to separate gas from liquid or water from oil. Separators can be either horizontal or vertical in configuration. The gas that is separated must be compressed and treated for sales. Compression is typically done by engine-driven reciprocating compressors, Figure 1-3. In large facilities or in booster service, turbine-driven centrifugal compressors, such as that shown in Figure 1-4, are used. Large integral reciprocating compressors are also used, Figure 1-5. Usually, the separated gas is saturated with water vapor and must be dehydrated to an acceptable level (normally less than 7 Ib/MMscf). Usually this is done in a glycol dehydrator, such as that shown in Figure 1-6.
Dry glycol is pumped to the large vertical contact tower where it strips the gas of its water vapor. The wet glycol then flows through a separator to the large horizontal reboiler where it is heated and the water boiled off as steam. In some locations it may be necessary to remove the heavier hydrocarbons to lower the hydrocarbon dew point. Contaminants such as H2S and CO2 may be present at levels higher than those acceptable to the gas purchaser. If this is the case, then additional equipment will be necessary to “sweeten” the gas.
