Filters and Relaxation Tanks

FIQURE 5-3.5. Schematic charge density variation in tanker loading circuit. (Adapted from API RP 2003.) 

Mesh strainers finer than 100 mesh/inch ( 150 /rm) should be treated as microfilters. Coarser strainers up to 50 mesh/inch (300 /rm) may generate significant static when fouled with accumulated debris, so should be treated as microfilters except in cases where fouling is not expected or may be rapidly identified by either periodic inspection or monitored pressure drop. Clean strainers should nevertheless be placed as far upstream as practical for nonconductive liquid service. A theoretical model for the charging process in strainers (screens) is given in [119-120]. Viscous nonconductive liquids (5-2.5.4) may produce unusually high charging currents in strainers. 

---

Filters, strainers, pumps, and other devices can produce static charges through normal flow turbulence with a number of nonconductive flammable liquids. Loading system pipe run lengths from such potential static-generating elements should be so located to allow a minimum of 30 seconds relaxation time prior to discharging into the vessel s tank compartment (NFPA 30 and NFPA 77). 

U.S. Filter Microfiber membranes with 0.4-pm pore size. The membranes were arranged in a vertical position in an off-line tank. The membranes relaxed and back-pulsing. 

---