For most multi-well situations horizontal treaters are normally required. Figure 6-10 shows a typical design of a horizontal treater.
Flow enters the front section of the treater where gas is flashed. The liquid falls around the outside to the vicinity of the oil-water interface where the liquid is “water washed” and the free water is separated. Oil and emulsion rise past the fire tubes and are skimmed into the oil surge chamber. The oil-water interface in the inlet section of the vessel is controlled by an interface level controller, which operates a dump valve for the free water.
The oil and emulsion flow through a spreader into the back or coalescing section of the vessel, which is fluid packed. The spreader distributes the flow evenly throughout the length of this section. Treated oil is collected at the top through a collection device sized to maintain uniform vertical flow of the oil. Coalescing water droplets fall countercurrent to the rising oil continuous phase. The oil-water interface is maintained by a level controller and dump valve for this section of the vessel.
A level control in the oil surge chamber operates a dump valve on the oil outlet line regulating the flow of oil out the top of the vessel to maintain a fluid packed condition.
The inlet section must be sized to handle settling of the free water and heating of the oil. The coalescing section must be sized to provide adequate retention time for coalescence to occur and to allow the coalescing water droplets to settle downward counter current to the upward flow of the oil.