2026-10-29
Seawater Reverse Osmosis (SWRO) desalination systems are highly vulnerable to marine bio-fouling, silt, algae blooms, and suspended solids. A major coastal petrochemical refinery in South America was experiencing rapid fouling of its SWRO membranes due to seasonal red tides and high turbidity in raw seawater intake.
LEFILTER deployed a multi-stage primary filtration architecture comprising LF-BS Series Automatic Multi-Basket Self-Cleaning Strainers combined with heavy-duty Duplex Stainless Steel housings. The system successfully handles a continuous seawater intake flow of 4,500 m³/h, capturing algae, marine debris, and sand down to 150 µm without interrupting raw water delivery. The installation extended downstream ultrafiltration (UF) and RO membrane lifespan by 300%, reduced chemical cleaning frequency from bi-weekly to bi-monthly, and delivered a complete capital payback within 11 months.
Located on the Pacific coast of South America, the integrated petrochemical refining complex relies heavily on a 100,000 m³/day SWRO desalination facility to generate high-purity process water, cooling tower makeup water, and boiler feed water. Raw seawater is pumped directly from an open ocean intake channel into the desalination pretreatment building.
Seawater along this coastline contains high concentrations of fine suspended sand, organic debris, shellfish larvae, and seasonal toxic dinoflagellate algae blooms (red tides). The plant’s original intake pretreatment section featured passive manual dual-basket strainers rated at 500 µm.
During seasonal weather shifts and red tide events, raw water Silt Density Index ($SDI_{15}$) spiked dramatically from 3.5 to over 6.8, overwhelming the plant:
Rapid Strainer Blindness & Cavitation: Heavy loading of organic algae and marine silt clogged the manual basket strainers within 15 to 30 minutes during peak bloom periods. Manual switching and cleaning of dirty baskets required constant operator presence, causing pump suction starvation, pressure fluctuations, and severe pump cavitation.
Severe Downstream UF/RO Membrane Damage: Microscopic algae cells and fine sand bypassed the coarse 500 µm baskets and directly impacted downstream Ultrafiltration (UF) modules and high-pressure SWRO membranes. Fine sand abraded membrane surfaces, while organic mucilage formed an irreversible bio-film on RO spacers.
Excessive Chemical Cleanings & Plant Shutdowns: To recover flux, the refinery was forced to perform Clean-In-Place (CIP) chemical washes on its RO trains every 12 to 14 days. Frequent exposure to harsh acid/alkaline CIP chemicals degraded membrane polymers, shortening RO membrane design life from 5 years to under 18 months and causing frequent refinery-wide water rationing.
Seeking an industrial-grade, corrosion-proof, and fully automated primary seawater filtration system, the refinery’s chief utility engineer partnered with LEFILTER for a complete system overhaul.
Recognizing the hyper-corrosive marine environment and the dynamic challenge of seasonal red tides, LEFILTER’s marine engineering department custom-built a 4-vessel parallel system utilizing LF-BS Series Heavy-Duty Automatic Multi-Basket Self-Cleaning Strainers.
Because raw seawater contains high chloride concentrations ($>19,000\text{ mg/L}\text{ Cl}^-$) under warm tropical temperatures, conventional 316L stainless steel suffers from pitting and crevice corrosion. LEFILTER fabricated all pressure vessels, internal shaft components, and strainers using Super Duplex Stainless Steel UNS S32750 (2507). This material offers a Pitting Resistance Equivalent Number ($PREN$) exceeding 42, guaranteeing zero localized corrosion over a 20-year design life.
Each LF-BS vessel houses four independently operating wedge wire screen baskets rated at 150 µm.
Wedge Wire Advantage: Smooth, V-shaped slot profiles ensure that particulates make contact at only two points, preventing wedging or permanent trapping of fibrous algae and sand grains.
Low Differential Pressure: The multi-basket geometry expands the total filtration area to 14.2 m² per vessel, keeping initial pressure drop below 0.015 MPa under full 1,125 m³/h design flow per unit.
The LF-BS strainer utilizes an internal rotating suction scanner mechanism driven by a heavy-duty electric motor.
Differential Pressure & Timer Dual Logic: When algae loading raises internal $\Delta P$ to 0.05 MPa (or when a timer interval elapses), a motor rotates the suction arm directly under each individual basket while opening a flush valve to atmosphere.
Localized Reverse Flow: The pressure differential between internal seawater and atmospheric exhaust forces clean seawater backward through the wedge wire slots, blasting away sticky organic film and sand into the drain header.
Zero Interruption: Only one basket is backwashed at a time for 15 seconds; the remaining three baskets continue filtering at 100% capacity, ensuring an uninterrupted raw water flow to UF/RO units.
Since commissioning over 22 months ago, the LEFILTER LF-BS Seawater Self-Cleaning Filtration Architecture has successfully defended the desalination plant through two severe seasonal red tide cycles:
Complete Automation & Zero Labor Intervention: The system eliminated all manual strainer cleaning operations. The automatic backwash cycle executes seamlessly in 45 seconds per vessel without operator intervention or flow disruption.
Dramatic Protection of Downstream UF & RO Membranes: By capturing organic mucilage, shellfish larvae, and sand at 150 µm, raw water $SDI_{15}$ downstream of pretreatment dropped from >6.0 to a stable <2.8. RO membrane chemical CIP frequency decreased from every 14 days to once every 75 days.
Massive Maintenance & Membrane Replacement Savings: Reduced chemical CIP cycles saved over $85,000 annually in cleaning chemicals and neutralizer handling. SWRO membrane replacement cycles reverted to their full 5-year design lifespan, saving the refinery an estimated $210,000 in premature membrane replacement capital.
Zero Unplanned Downtime: The refinery’s process water supply achieved 100% uptime, eliminating costly production curtailments across ethylene and aromatics production units.
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