Material of Construction of Closed-Circuit cooling tower
1. Casing / Structure (The Tower’s Exterior Shell and Frame)
This provides the structural integrity and protects the internal components.
- Galvanized Steel: The most common and cost-effective material for industrial applications. It offers good strength and moderate corrosion resistance. The galvanization (zinc coating) protects the underlying steel. Best for: Standard industrial environments without highly corrosive atmospheres.
- Stainless Steel: Used for high-corrosion environments or applications requiring high hygiene standards (e.g., food, pharmaceutical, coastal plants). The most common grades are 304 SS (general corrosion resistance) and 316 SS (superior resistance, especially to chlorides, making it ideal for marine or chemical plant environments). It is more expensive but offers a much longer service life.
- Fiberglass Reinforced Plastic (FRP): Excellent corrosion resistance to a wide range of chemicals and atmospheres. It is lightweight, durable, and will not rust. It is often used for the casing and sometimes for the entire tower structure. Best for: Highly corrosive environments like chemical processing plants, paper mills, and coastal areas.
- Aluminum: Lightweight and naturally corrosion-resistant, though it can be susceptible to certain chemicals. Less common than steel or FRP for full casings but often used for internal components and louvers.
2. Cooling Coil (The Heart of the CCT)
This is the most critical component where heat exchange occurs. The material must have excellent thermal conductivity and high corrosion resistance.
- Carbon Steel: Rare and generally not recommended for the coil itself unless the process fluid is non-corrosive and the external environment is perfectly controlled. It is susceptible to corrosion from both the spray water and the atmosphere.
- Galvanized Steel: A more common choice for carbon steel coils, providing a layer of protection. However, the galvanizing can erode over time, especially with aggressive water treatment chemicals.
- Stainless Steel: The industry standard for most high-quality CCTs. 304 SS is common for general applications with clean water. 316 SS is highly preferred for its superior resistance to chlorides and other corrosive elements found in spray water and air. It ensures a long life for the core component.
- Copper: Offers the best thermal conductivity (superior to steel), which can allow for a smaller, more efficient coil. However, it is less corrosion-resistant than stainless steel in an evaporative environment and can be vulnerable to certain water chemistries and atmospheric corrosion. Its use is less common than stainless steel in modern CCTs.
3. Wet Deck Media (The “Fill”)
This is the material over which the spray water cascades to maximize its surface area for evaporation. It is constantly wet and exposed to flowing water and air.
- PVC (Polyvinyl Chloride): The most common material for fill media. It is inexpensive, lightweight, and offers excellent corrosion resistance. It is typically configured into fluted sheets (film fill) to create a large surface area for water-air contact.
- Polypropylene (PP): Similar to PVC but often used in applications requiring higher temperature resistance or specific chemical resistance.
- Stainless Steel: Sometimes used for the support structure of the media packs, but rarely for the media itself due to cost and lack of surface area compared to engineered plastic.
4. Water Distribution System (Sprays and Nozzles)
This system distributes the spray water evenly over the coil and the wet deck media.
- PVC or ABS Plastic: Commonly used for distribution pipes and troughs due to excellent corrosion resistance.
- Stainless Steel: Often used for spray nozzles themselves to prevent clogging and corrosion, ensuring a consistent spray pattern over time.
- Brass: Sometimes used for nozzles but less corrosion-resistant than stainless steel in the long term.
5. Fan and Drivetrain
- Fan Blades:
- Aluminum: Most common; good balance of strength, weight, and corrosion resistance.
- Fiberglass (FRP): Excellent corrosion resistance, especially in highly corrosive environments. They are also very durable.
- Stainless Steel: Used in the most severe environments.
- Fan Cylinder (Shroud): Typically galvanized steel or FRP.
Summary Table: Material Selection by Component
| Component | Common Material(s) | Premium/Corrosion-Resistant Material(s) | Key Consideration |
| Casing / Structure | Galvanized Steel | Stainless Steel (304/316), FRP | Environmental exposure, corrosion risk |
| Cooling Coil | Stainless Steel (304/316) (Industry Standard) | Copper (for high efficiency) | Corrosion resistance on both fluid sides, pressure |
| Wet Deck Media (Fill) | PVC | Polypropylene | Surface area, corrosion resistance, fouling |
| Spray Nozzles | Stainless Steel, Brass | PVC, PP | Clogging, corrosion, consistent spray pattern |
| Distribution System | PVC, ABS | Stainless Steel | Even water distribution, corrosion resistance |
| Fan Blades | Aluminum, FRP | Stainless Steel | Strength, corrosion resistance, balance |
| Fan Cylinder | Galvanized Steel, FRP | Stainless Steel | Containing the air flow, durability |
| Pan / Sump | Galvanized Steel (coated) | Stainless Steel (304/316), FRP | Collects water, high corrosion risk |
How to Choose: The Decision Drivers
- Environment: Is the tower located inland, on a coast (marine environment), or near a chemical plant? Coastal and industrial areas demand stainless steel (316) and FRP.
- Process Fluid: What is inside the closed loop? Standard water may allow for galvanized steel, but other fluids like glycol, oils, or chemicals may require compatibility with stainless steel.
- Spray Water Quality: Hard water leads to scaling; acidic water is corrosive. Poor water quality pushes the selection towards more inert materials like stainless steel and plastics.
- Life Cycle Cost: While a galvanized steel tower has a lower initial cost, a stainless steel or FRP tower may have a much lower total cost of ownership over 20+ years due to minimal maintenance and no replacement costs.
- Industry Standards: Food, pharmaceutical, and power generation industries often have strict codes that mandate materials like stainless steel.