Cooling tower makeup water replaces water lost to evaporation, drift, and blowdown. Pumps handle raw water, treated water, and blowdown. This guide covers pump selection for cooling tower water treatment and circulation systems.
Cooling Tower Water System and Pump Services
| Service | Fluid | Temp | Key Characteristic | Pump Type |
|---|---|---|---|---|
| Circulating water (main) | Cooling tower water | 25–40°C | Very large flow (5000–50000 m³/h), open loop, scaling, biological, low head | Horizontal split case or vertical turbine (very large flow, high efficiency) |
| Makeup water (raw water) | Raw water (municipal, well, river) | Ambient | Variable quality, scaling, biological, large flow, continuous | Horizontal split case or vertical turbine (large flow, bronze fitted) |
| Makeup water (after treatment) | Treated water (filtered, softened) | Ambient | Clean, large flow, precise level control, scaling | 316L/bronze centrifugal (clean, large flow, VFD level control) |
| Blowdown (to drain) | Concentrated cooling water (high TDS) | 30–40°C | High TDS, scaling, corrosive, intermittent, small flow | 316L/duplex centrifugal (corrosion-resistant, small, intermittent) |
| Side stream filtration | Cooling water (bypass) | 30–40°C | Particulate (silt, biofilm), moderate flow, continuous, scaling | 316L centrifugal (moderate flow, clean wetted) |
| Chemical dosing (corrosion inhibitor) | Corrosion inhibitor (phosphonate, zinc) | Ambient | Corrosive, precise metering, small flow, continuous | Diaphragm metering pump (precise, chemical-resistant, PTFE) |
| Chemical dosing (biocide) | Biocide (chlorine, bromine, quaternary ammonium) | Ambient | Corrosive (chlorine), toxic, precise, hazardous | Diaphragm metering (PTFE, zero leakage, chemical-resistant) or magnetic drive |
| Chemical dosing (acid for pH) | Sulfuric acid (93–98%) or HCl | Ambient | Highly corrosive, precise, hazardous, exothermic dilution | Diaphragm metering (PTFE, zero leakage) or magnetic drive fluoroplastic |
| Chemical dosing (scale inhibitor) | Scale inhibitor (polyacrylate, phosphonate) | Ambient | Viscous (some), precise, corrosive | Diaphragm metering (precise, chemical-resistant) |
| Softener brine | NaCl brine (saturated, 26%) | Ambient | Corrosive (Cl⁻), scaling (NaCl), viscous, abrasive (salt crystals) | Duplex/super duplex or fluoroplastic (Cl⁻ corrosion, zero leakage) |
| Backwash (filters/softeners) | Water (reverse flow) | Ambient | High flow, intermittent, clean, air scour (if combined) | 316L centrifugal (high flow, intermittent, clean) |
| Condenser cleaning (on-line) | Cleaning sponge balls / water | 30–40°C | Particulate (sponge balls), intermittent, moderate flow | 316L centrifugal (large passage, intermittent) |
| Wastewater (blowdown treatment) | High-TDS blowdown + chemicals | 30–50°C | High TDS, corrosive, scaling, chemical-laden | 316L/duplex or slurry (if solids) |
Critical: Circulating Water (Very Large Flow + Open Loop + Scaling)
The main circulating water pump is the largest pump in a power plant:
- Very large flow: 5000–50000 m³/h for large plants. Use horizontal split case pump (high efficiency, easy maintenance, large flow) or vertical turbine pump (for cooling tower sumps, river intake). Multiple parallel pumps (N+1 or N+2). VFD for flow control (reduce energy at part load).
- Open loop: Cooling tower water concentrates minerals (3–5 cycles of concentration). Scaling (CaCO₃, CaSO₄), biological growth, corrosion. Water treatment (corrosion inhibitor, scale inhibitor, biocide). Bronze-fitted pumps (cast iron body, bronze impeller — resists mild corrosion). Large passage (resist clogging from biofilm/debris).
- Low head: Typically 15–30 m (condenser + piping + tower). Split case pumps are efficient at low head/large flow. High efficiency (IE3/IE4 motors) — energy cost is significant.
- Maintenance: Split case design allows access to impeller without disconnecting piping. Easy bearing/seal replacement. Strainers upstream (remove debris). Periodic cleaning (biofilm, scale).
Critical: Makeup Water (Variable Quality + Level Control)
- Water sources: Municipal (treated, low TDS), well (high hardness, iron), river (variable, sediment, biological). Pump selection depends on source — river intake needs vertical turbine with traveling screen; municipal/well uses split case.
- Level control: Cooling tower basin level controlled by makeup water valve/pump. Use VFD on makeup pump + level transmitter. Or modulating valve with constant-speed pump. Precise level (±10 mm) prevents overflow or pump cavitation.
- Pre-treatment: Makeup water may be filtered (multi-media), softened (ion exchange), or RO-treated (for high cycles). Pumps after treatment = clean water (316L/bronze). Pumps before treatment = raw water (cast iron/bronze, strainer).
Critical: Chemical Dosing (Precise + Corrosive + Hazardous)
Cooling water treatment requires precise chemical dosing:
- Corrosion/scale inhibitor: Phosphonate, polyacrylate, zinc. Use diaphragm metering pump (precise ±1%, PTFE wetted, 316L body). Continuous dosing proportional to makeup flow (flow-paced).
- Biocide: Chlorine (gas or bleach), bromine, quaternary ammonium. Chlorine is corrosive and toxic — use magnetic drive fluoroplastic or PTFE metering pump (zero leakage). Gas detection. Closed system. Shock dosing (intermittent) vs. continuous.
- Acid (pH control): H₂SO₄ (93–98%) or HCl. Highly corrosive — use magnetic drive fluoroplastic or PTFE metering. Dilution injection point (exothermic). Secondary containment. Acid-resistant piping (PVDF/CPVC).
- Multiple pumps: Each chemical has dedicated pump (no cross-contamination). Backup pump for critical chemicals. Calibration columns for verification.
Material Compatibility
| Material | Circulating water (35°C, open loop, scaling) | Raw makeup (ambient, variable) | Concentrated H₂SO₄ (ambient) | NaCl brine (26%, ambient) |
|---|---|---|---|---|
| Cast iron/bronze fitted | Good (standard, with treatment) | Good (standard) | NOT (acid) | NOT (Cl⁻ pitting) |
| 316L SS | Good (better corrosion resistance) | Good | Fair (concentrated acid passivation) but risky | Fair (Cl⁻ pitting risk) |
| Duplex 2205 | Excellent | Excellent | Good | Good (Cl⁻ resistant) |
| Super duplex 2507 | Excellent | Excellent | Good | Excellent (high Cl⁻) |
| PTFE/PFA lined | — | — | Excellent (standard for acid) | Excellent |
Critical: Circulating/makeup = cast iron/bronze fitted or 316L (with water treatment). Acid = PTFE lined/magnetic drive (NO metal). Brine = duplex/super duplex or PTFE (NO 316L for high Cl⁻). Dosing = diaphragm metering (PTFE, precise).
Common Problems and Solutions
Problem 1: Circulating pump efficiency drops (scaling/biofilm). CaCO₃ scale and biofilm reduce flow and efficiency. Solution: water treatment (scale inhibitor + biocide). Large passage pump. Periodic acid wash (5% HCl). Strainer. Use split case (easy access for cleaning). High-efficiency motor. Our split case range handles cooling water.
Problem 2: Makeup pump cavitates (low basin level). Cooling tower basin level drops — pump suction vortexes/cavitates. Solution: level control (VFD + level transmitter). Minimum level alarm. Submerged bell inlet. Anti-vortex plate. NPSH margin. Our vertical turbine/split case range includes anti-vortex designs.
Problem 3: Acid dosing pump leaks (safety hazard). Mechanical seal fails on H₂SO₄ — acid spray, corrosion, injury. Solution: use magnetic drive fluoroplastic or PTFE diaphragm metering (zero leakage). Secondary containment. Acid-resistant piping. Dilution injection. Leak detection. Our magnetic drive/metering range handles acid safely.
Problem 4: Biocide pump fails (chlorine corrosion). Chlorine/bleach attacks 316SS and elastomers. Solution: use PTFE metering pump or magnetic drive fluoroplastic. PTFE/FFKM seals. Flush with water after use. Gas detection (Cl₂). Our fluoroplastic range handles chlorine/biocide.
Problem 5: Brine pump corrodes (NaCl pitting). Saturated NaCl brine (26%) pits 316SS. Solution: use duplex/super duplex or fluoroplastic PTFE lined. Large passage (salt crystals). Flush with water. Our duplex/fluoroplastic range handles brine.
Selection Summary
- Circulating water: Horizontal split case or vertical turbine (very large flow, bronze/316L, N+1, VFD, high efficiency)
- Makeup water (raw): Split case or vertical turbine (large flow, strainer, level control)
- Makeup water (treated): 316L/bronze centrifugal (clean, VFD level control)
- Blowdown: 316L/duplex centrifugal (high TDS, corrosion-resistant, intermittent)
- Side stream filtration: 316L centrifugal (moderate flow, clean)
- Corrosion/scale inhibitor: Diaphragm metering (PTFE, precise, flow-paced)
- Biocide (chlorine/bromine): PTFE metering or magnetic drive fluoroplastic (zero leakage, toxic)
- Acid (pH control): Magnetic drive fluoroplastic or PTFE metering (zero leakage, secondary containment)
- Softener brine: Duplex/super duplex or fluoroplastic (Cl⁻ resistant, large passage)
- Backwash: 316L centrifugal (high flow, intermittent)
- Critical: circulating = large split case/turbine + water treatment, makeup = level control + VFD, acid/biocide = zero leakage (magnetic drive/metering), brine = duplex/PTFE (NO 316L), scaling = large passage + periodic cleaning, energy = high-efficiency motor + VFD
- Our split case and vertical turbine cover circulating/makeup; metering and magnetic drive cover chemicals; fluoroplastic covers acid/brine. For cooling tower pump selection, talk to our water treatment engineers with your flow, cycles of concentration, and water source.