Seawater desalination plants produce fresh water from seawater using reverse osmosis (RO), thermal (MSF/MED), or hybrid processes. Pumps handle seawater intake, high-pressure RO feed, brine discharge, and energy recovery. This guide covers pump selection for seawater desalination plants.
Desalination Process and Pump Services
| Service | Fluid | Temp | Key Characteristic | Pump Type |
|---|---|---|---|---|
| Seawater intake | Raw seawater (3.5% TDS, with sediment, marine life) | 5–35°C | Very large flow (1000–50000 m³/h), corrosive (seawater), dirty, biological, low head | Vertical turbine or axial flow (large flow, bronze/duplex, marine, traveling screen) |
| Pre-treatment (coagulation/filtration) | Seawater + coagulant | 5–35°C | Corrosive, dirty, moderate flow, scaling, biological | 316L/duplex centrifugal (corrosion-resistant, large passage) |
| Ultrafiltration (UF) feed | Pre-treated seawater | 5–35°C | Moderate pressure (2–5 bar), fouling, biological, large flow | 316L/duplex centrifugal (large passage, open impeller, fouling-resistant) |
| RO high-pressure feed | Pre-treated seawater (filtered) | 5–35°C | Very high pressure (55–85 bar), corrosive (seawater), large flow, clean, energy-critical | Multistage centrifugal (BB3/BB5, super duplex, high pressure, high efficiency, API 610) |
| Energy recovery device (ERD) feed | RO brine (high pressure) | 5–35°C | High pressure (55–85 bar), corrosive, small flow, energy transfer | Positive displacement (piston/plunger) or integrated ERD (not standard centrifugal) |
| RO permeate (product water) | Fresh water (TDS ＜500 mg/L) | 5–35°C | Clean, large flow, low pressure, remineralization (if needed) | 316L/bronze centrifugal (clean, large flow, low head) |
| Brine discharge | RO concentrate (TDS 6–8%, 2× seawater) | 5–35°C | Very corrosive (high Cl⁻), large flow, low pressure, environmental (dilution) | Super duplex or axial flow (corrosion-resistant, large flow, low head) |
| Thermal (MSF/MED) feed | Seawater (to evaporator) | 5–120°C | Corrosive, hot, scaling, large flow, deaerated | Super duplex/duplex (hot seawater, corrosion, scaling, large flow) |
| Thermal distillate | Distilled water (pure) | 60–120°C | Clean, hot, low conductivity (corrosive to carbon steel), large flow | 316L/duplex centrifugal (clean, hot, corrosion-resistant) |
| Thermal brine (blowdown) | Concentrated brine (TDS 6–10%) | 80–120°C | Very corrosive, hot, scaling, large flow | Super duplex or PTFE lined (hot brine, corrosion, scaling) |
| Chemical dosing (antiscalant) | Antiscalant (polyacrylate, phosphonate) | Ambient | Viscous (some), precise dosing, corrosive (mild) | Diaphragm metering (precise, chemical-resistant) |
| Chemical dosing (biocide) | Sodium hypochlorite (NaOCl) or chlorine dioxide | Ambient | Corrosive (chlorine), oxidizing, toxic, precise dosing | Magnetic drive fluoroplastic or PTFE metering (zero leakage, chlorine-resistant) |
| Chemical dosing (acid pH) | H₂SO₄ (93–98%) or HCl | Ambient | Highly corrosive, precise dosing, hazardous, exothermic | PTFE diaphragm metering or magnetic drive (zero leakage, acid-resistant) |
| CIP (clean-in-place) | Citric acid (2–5%) + NaOH (1–2%) + surfactant | 25–40°C | Corrosive, intermittent, membrane cleaning, precise | 316L centrifugal or magnetic drive (corrosion-resistant, CIP-compatible) |
| Post-treatment (remineralization) | Calcium carbonate solution or CO₂ + lime | Ambient | Scaling (CaCO₃), precise dosing, corrosive (CO₂) | Diaphragm metering or 316L centrifugal (scaling-resistant, large passage) |
| Wastewater (plant effluent) | Backwash water + CIP waste | 20–40°C | Corrosive, dirty, chemical-laden, intermittent | 316L/duplex (corrosion-resistant, dirty) |
Critical: RO High-Pressure Feed (Very High Pressure + Seawater Corrosion + Energy)
The RO high-pressure pump is the most critical and energy-intensive pump in a desalination plant:
- Very high pressure: 55–85 bar (seawater RO). Use multistage centrifugal pump (BB3 axially split or BB5 radially split, API 610). 4–8 stages. Super duplex 2507 wetted parts (seawater corrosion). High-pressure mechanical seal (Plan 53A/B with barrier fluid). VFD for flow/pressure control.
- Seawater corrosion: Seawater (3.5% NaCl, 19000 mg/L Cl⁻) is highly corrosive. Use super duplex 2507 (PREN ＞40) for wetted parts. NO 316L (pitting in warm seawater). NO duplex 2205 (PREN ~35, marginal for warm seawater). Cupronickel (CuNi 90/10) for piping. Sacrificial anodes. Epoxy coating. Flush with fresh water after shutdown.
- Energy critical: High-pressure pump consumes 3–5 kWh/m³ of product water — 30–50% of plant energy. Use high-efficiency pump (＞85%) + energy recovery device (ERD, isobaric or turbocharger). ERD recovers 30–50% of brine energy. VFD. IE4/IE5 motor. Pump selection must match ERD. Our multistage range includes high-efficiency designs.
- Large flow: Large plants use multiple parallel high-pressure pumps (N+1 or N+2). Each pump 500–3000 m³/h. Modular design. Common header. Isolation valves. Performance monitoring.
Critical: Seawater Intake (Very Large Flow + Dirty + Marine)
- Very large flow: 1000–50000 m³/h (2× product flow + brine). Use vertical turbine pump (for shoreline intake, deep well) or axial flow pump (for open intake, very large flow/low head). Multiple parallel pumps. Bronze (Ni-Al bronze) or super duplex wetted. Traveling screen (remove marine life, debris). Fish-friendly design (low velocity intake).
- Marine growth: Barnacles, mussels, algae grow on intake and pump. Use biocide dosing (continuous chlorination or intermittent shock). Copper-nickel piping (natural antifouling). Epoxy coating. Periodic cleaning. Large passage (resist clogging). Strainer.
- Sediment: Seawater contains sand, silt. Use sand separator or settling basin. Wear-resistant impeller (bronze, Ni-hard). Larger passage. Monitor sediment. Our vertical turbine/axial flow range handles seawater intake.
Critical: Brine Discharge (Very Corrosive + Large Flow + Environmental)
- Very corrosive: RO brine is 2× seawater TDS (6–8%, 38000 mg/L Cl⁻). Use super duplex 2507 or PTFE lined. NO 316L/duplex 2205 (pitting at high Cl⁻). PTFE/FFKM seals. Flush with fresh water. Large passage (scaling from concentrated salts).
- Environmental: Brine discharge must be diluted (＜10% above ambient salinity) to avoid marine impact. Use axial flow pump (large flow, low head) for outfall. Diffuser design (multi-port, rapid dilution). Mixing zone monitoring. Brine temperature (thermal plants) also controlled.
Material Compatibility
| Material | Seawater (25°C, 3.5% NaCl) | RO brine (25°C, 7% NaCl) | Hot seawater (90°C, thermal) | NaOCl biocide (ambient, chlorine) |
|---|---|---|---|---|
| Bronze (Ni-Al bronze) | Excellent (standard marine) | Fair (high Cl⁻) | Fair (hot) | NOT (chlorine attack) |
| CuNi 90/10 | Excellent (piping, antifouling) | Fair | Fair | NOT |
| 316L SS | Fair (pitting in warm seawater) | NOT | NOT | NOT (chlorine pitting) |
| Duplex 2205 | Good (cold seawater) | Fair (high Cl⁻) | Fair (hot) | NOT |
| Super duplex 2507 | Excellent (standard for RO) | Good | Good (hot seawater) | Fair (chlorine) |
| PTFE/PFA lined | Excellent | Excellent (standard for brine) | Good (＜150°C) | Excellent (standard for chlorine) |
| Hastelloy C-276 | Excellent | Excellent | Excellent | Excellent (expensive) |
| EPDM seals | Good | Good | Fair (hot) | NOT (chlorine attacks EPDM) |
| PTFE/FFKM seals | Excellent | Excellent | Excellent | Excellent |
| FKM (Viton) seals | Good | Good | Good | Fair (chlorine) |
Critical: Seawater (cold) = bronze/duplex 2205/super duplex. RO high-pressure = super duplex 2507 (NO 316L/2205). Brine = super duplex/PTFE (NO 316L/2205). Hot seawater (thermal) = super duplex/Hastelloy. Chlorine/biocide = PTFE lined/magnetic drive + FFKM (NO EPDM, NO 316L). All seawater = flush with fresh water + sacrificial anodes + biocide.
Common Problems and Solutions
Problem 1: RO high-pressure pump corrodes (seawater). 316L/duplex 2205 pump pits in warm seawater. Solution: use super duplex 2507 multistage pump. Cupronickel piping. Sacrificial anodes. Flush with fresh water after shutdown. Epoxy coating. Biocide (control marine growth). Our super duplex multistage range handles seawater RO.
Problem 2: Intake pump clogs (marine life/debris). Jellyfish, seaweed, fish clog intake pump. Solution: traveling screen (continuous cleaning). Vertical turbine with large passage. Fish-friendly intake (low velocity). Biocide (chlorination) to prevent mussel/barnacle growth. Periodic cleaning. Our vertical turbine range handles seawater intake.
Problem 3: Brine pump pits (high chloride). 316L pump pits with RO brine (7% NaCl). Solution: use PTFE/PFA lined pump or super duplex 2507. Flush with fresh water. Large passage (scaling). Velocity ＜3 m/s. Our fluoroplastic/super duplex range handles brine.
Problem 4: Biocide pump fails (chlorine attack). EPDM seal/316SS pump fails with NaOCl. Solution: use magnetic drive fluoroplastic pump (zero leakage, PTFE wetted). PTFE/FFKM seals (NO EPDM). Flush with water. Gas detection (Cl₂). Closed system. Our magnetic drive range handles chlorine biocide.
Problem 5: High energy cost (RO pump). High-pressure pump consumes too much energy. Solution: use high-efficiency pump (＞85%) + ERD (energy recovery device, 30–50% savings). VFD. IE4/IE5 motor. Optimize operating pressure (match membrane). Our multistage range includes high-efficiency designs compatible with ERD.
Selection Summary
- Seawater intake: Vertical turbine or axial flow (very large flow, bronze/super duplex, traveling screen, biocide, fish-friendly)
- Pre-treatment/UF feed: 316L/duplex centrifugal (large passage, fouling-resistant, moderate pressure)
- RO high-pressure feed: Multistage centrifugal (55–85 bar, super duplex 2507, API 610, high efficiency, ERD-compatible, VFD)
- RO permeate: 316L/bronze centrifugal (clean, large flow, low head)
- Brine discharge: Super duplex or axial flow (very corrosive, large flow, low head, dilution)
- Thermal feed: Super duplex/duplex (hot seawater 5–120°C, corrosion, scaling)
- Thermal distillate: 316L/duplex centrifugal (clean, hot 60–120°C, NO carbon steel)
- Thermal brine blowdown: Super duplex or PTFE lined (hot brine 80–120°C, very corrosive, scaling)
- Antiscalant: Diaphragm metering (precise, chemical-resistant)
- Biocide (NaOCl): Magnetic drive fluoroplastic or PTFE metering (zero leakage, chlorine-resistant, NO EPDM/316L)
- Acid pH: PTFE diaphragm metering or magnetic drive (zero leakage, H₂SO₄/HCl)
- CIP: 316L centrifugal or magnetic drive (citric acid + NaOH, intermittent, membrane cleaning)
- Critical: RO HP = super duplex 2507 + multistage + ERD + high efficiency (NO 316L/2205), seawater = bronze/super duplex + flush + biocide + anodes, brine = super duplex/PTFE (NO 316L), chlorine = PTFE/magnetic drive + FFKM (NO EPDM), thermal = super duplex + jacketed + scaling control, all = flush with fresh water after shutdown
- Our multistage super duplex covers RO HP; vertical turbine covers intake; fluoroplastic covers brine/chlorine; metering covers chemicals. For desalination pump selection, talk to our water treatment engineers with your capacity, feed water quality, and process (RO vs. thermal).