Cooling tower water treatment at a Gulf Coast refinery required the help of an outside firm to efficiently handle the cleaning project in a tight time frame. The supplier was Rain for Rent, headquartered in Bakersfield, Calif.

After assessing the situation, Rain for Rent recommended a water filtration system consisting of a 48-2 sand-media filter, Spillguard portable spill-containment berm and dewatering box to capture the backwash from the sand-media system. A diffuser made of Schedule 80 PVC pipe with 1" holes in a single line down the length of the pipe was used to spray the discharge evenly into a solids/liquid separating dewatering box.

According to Rain for Rent, the system worked well during cooling tower recirculation, achieving the necessary water clarity. However, after bringing one of the production units back on line, a significant quantity of insoluble iron was stirred up and circulated throughout the system. Suddenly the sand media was unable to reduce the nephelometric turbidity units (NTUs) to an acceptable level.

Rain for Rent's Baton Rouge team and regional filtration specialist ran a series of vacuum filtration tests on samples captured from the inlet line. With the plant representatives observing, the team determined that the particle sizes contained within the additional circulation volume were in the 1 to 3 µm range. The particles were being transported through the sand-media bed because the filtration capability was limited to capturing 20 µm and larger particles.

The team added a PF-400 particulate filter with 1 µm media to polish the sand-media effluent and reduce the NTUs to an acceptable level. The method was chosen over a biopolymer flocculant because plant managers did not want to introduce any polymers into the cooling tower system.