The gravity settling devices previously discussed make use of closely spaced internals to reduce the distance an oil droplet must rise to meet a coalescing surface. This is because within a tank or vessel there is very little turbulence to promote coalescence. The SP Pack, developed by Paragon Engineering Services and marketed by Modular Production Equipment, Houston, creates turbulent flow by forcing the water to flow through a serpentine pipe path. The path is sized to create turbulence of sufficient magnitude to cause coalescence but not so great as to shear the droplets below a specified size. The pipe path is similar in size to the inlet piping and thus is not susceptible to plugging.
As shown in Figure 7-10, the SP Pack is placed inside of any gravity settling device (skimmer, plate coalescer, etc.) and by growing a larger drop size distribution, the gravity settler is more efficient at removing oil, as shown in Figure 7-11.
Standard SP Pack sizes are shown in Table 7-2. They are designed to grow a drop size distribution curve with 1,000-micron maximum drop size. They are very efficient at removing oil when they are series staged, as shown in Figure 7-12. In such an installation, an enhanced drop size distribution is developed in the first pack, the larger drops are settled out. As the water flows through the next pack some of the remaining oil is coalesced, forming a second enhanced drop size distribution, and allowing more oil to be settled.