Why Do Ocean-going Ships Use Closed-loop Dry Cooling Systems?

Why Do Ocean-going Ships Use Closed-loop Dry Cooling Systems?

On ocean-going vessels, although seawater is abundant, its direct use as a cooling medium (i.e., open-loop circulation) presents a series of challenges:

Corrosion and Blockage: Seawater is highly corrosive and contains significant amounts of microorganisms, sediment, and marine organisms. Direct flow through the intricate piping systems of precision generator sets causes severe corrosion, scaling, and blockage.

Maintenance Challenges: Cleaning and repairing piping systems corroded or clogged by seawater is extremely difficult and costly.

Temperature Dependency: Seawater temperature varies by region. In tropical waters, excessively high temperatures can reduce cooling efficiency.

Consequently, modern vessels universally employ centralized cooling systems, where dry coolers (also known as air coolers or air-cooled radiators) serve as a critical component.

When vessels are in port or sensitive waters: To avoid discharging warm seawater into harbor basins (which may violate environmental regulations or impact ecosystems), seawater pumps are shut off, relying entirely on dry coolers to cool the high-temperature freshwater in the primary circuit.

During operation in cold waters: When seawater temperatures are too low, dry coolers provide better control over generator set operating temperatures, preventing overcooling.

As the primary cooling method: On certain specialized vessels or offshore platforms (e.g., drilling rigs, LNG carriers), where system reliability is paramount and long-term stationary operation is common, dry coolers are designed as the primary cooling solution, completely eliminating seawater usage.

The dry cooler operates as follows:

High-temperature freshwater from the primary circuit is pumped into the dry cooler's extensive heat dissipation finned tubes. High-power axial fans force ambient air through these finned tubes. The air contacts the hot tubes, transferring heat via convection and conduction to cool the freshwater. The cooled freshwater is then returned to the generator set, completing the cycle.