Seawater refrigeration systems are widely used in coastal industrial facilities, marine vessels, coastal data centers, and petrochemical plants due to their excellent heat exchange performance and abundant seawater resources. However, seawater contains high concentrations of chloride ions, microorganisms (bacteria, algae, fungi), and suspended solids, which easily cause severe problems such as equipment corrosion, biofilm fouling, and pipeline blockage in the refrigeration loop. Traditional seawater treatment methods, such as adding commercial sodium hypochlorite or chlorine gas, have limitations including unstable dosing concentration, high transportation and storage costs, and potential safety hazards. Electrolytic chlorination systems, which produce chlorine-based disinfectants on-site using raw seawater, have become the preferred solution for seawater refrigeration system water treatment. This article explores the application value, working principles, and key implementation points of electrolytic chlorination systems in seawater refrigeration scenarios.
1. Core Advantages of Electrolytic Chlorination Systems for Seawater Refrigeration
Compared with traditional chemical dosing methods, electrolytic chlorination systems are highly compatible with the operating characteristics of seawater refrigeration systems, with the following irreplaceable advantages:
- On-Site Production, No Secondary Hazards: Electrolytic chlorination systems use seawater (rich in chloride ions) as the raw material, and produce hypochlorous acid, sodium hypochlorite, and other efficient disinfectants through electrolysis without adding additional chemicals. This eliminates the transportation, storage, and leakage risks of toxic and harmful chemicals such as chlorine gas and concentrated sodium hypochlorite, which is particularly critical for coastal facilities and marine vessels with strict safety requirements.
- Stable Dosing, Efficient Fouling Control: The system can automatically adjust the electrolysis intensity according to the seawater flow rate, temperature, and microbial content in the refrigeration loop, ensuring stable output of disinfectant with controllable concentration (usually 0.5-2.0 ppm free chlorine). This effectively inhibits the growth of algae and bacteria in the heat exchanger, condenser, and pipelines, prevents biofilm formation and slime fouling, and maintains the heat exchange efficiency of the refrigeration system.
- Corrosion Mitigation, Extending Equipment Lifespan: Seawater’s high chloride ions easily cause pitting corrosion and crevice corrosion of carbon steel, copper alloy, and stainless steel equipment in refrigeration systems. The trace chlorine produced by electrolysis forms a thin, dense passivation film on the metal surface, which inhibits the anodic dissolution of the metal and reduces corrosion rates by 60%-80% compared to untreated seawater. This significantly extends the service life of condensers, heat exchangers, and pipelines, reducing maintenance and replacement costs.
- Low Operating Costs, Energy Conservation and Emission Reduction: The system only consumes electricity and seawater during operation, with no need to purchase commercial disinfectants. For a seawater refrigeration system with a daily processing capacity of 10,000 m³, the annual operating cost of an electrolytic chlorination system is 30%-40% lower than that of adding commercial sodium hypochlorite. At the same time, the system has a compact structure, small footprint, and low energy consumption, which is in line with the development trend of green and energy-saving industrial water treatment.
2. Working Principle and Application Process in Seawater Refrigeration Systems
2.1 Core Working Principle
Electrolytic chlorination systems for seawater refrigeration mainly consist of electrolytic cells, power supplies, seawater pre-treatment units (filters), dosing pumps, and automatic control systems. The core principle is based on the electrolysis reaction of seawater: when seawater passes through the electrolytic cell, under the action of a direct current electric field, chloride ions (Cl⁻) in the seawater are oxidized at the anode to generate chlorine gas (Cl₂), which then reacts with water to form hypochlorous acid (HOCl) and hypochlorite ions (OCl⁻)—collectively known as free available chlorine (FAC), which has strong broad-spectrum disinfection and sterilization capabilities. The cathode generates hydrogen gas (H₂), which is safely discharged or burned after collection.
Key reaction equations:
Anode: 2Cl⁻ - 2e⁻ → Cl₂↑
Cl₂ + H₂O → HOCl + H⁺ + Cl⁻
Cathode: 2H₂O + 2e⁻ → H₂↑ + 2OH⁻
2.2 Typical Application Process in Seawater Refrigeration Systems
The integration of electrolytic chlorination systems into seawater refrigeration systems follows a streamlined process to ensure treatment efficiency and system safety:
- Seawater Intake and Pre-Treatment: Raw seawater is extracted from the ocean and passed through a pre-filtration system (usually 50-100 μm cartridge filters) to remove suspended solids, sand, and large particles. This prevents clogging of the electrolytic cell’s electrode plates and ensures stable electrolysis efficiency.
- Electrolysis and Disinfectant Generation: Pre-treated seawater enters the electrolytic cell, where the system adjusts the current and voltage according to the real-time seawater flow rate and free chlorine demand. The electrolytic cell produces a disinfectant solution containing free chlorine, which is directly injected into the seawater refrigeration loop through a dosing pump.
- Disinfection and Heat Exchange Cycle: The disinfectant-containing seawater flows through the condenser, evaporator, and pipeline network of the refrigeration system. It inhibits microbial growth and biofilm formation during the heat exchange process, while the passivation film formed on the metal surface prevents corrosion. After heat exchange, the seawater is either discharged back to the ocean (meeting environmental discharge standards) or recycled (after secondary treatment).
- Real-Time Monitoring and Automatic Regulation: The system is equipped with online free chlorine detectors, pH meters, and flow meters. The automatic control system adjusts the electrolysis parameters in real time based on the monitoring data to ensure that the free chlorine concentration in the refrigeration loop is maintained at the optimal range (0.5-2.0 ppm). If the concentration exceeds or is lower than the set value, the system will automatically alarm and adjust.
3. Key Implementation Considerations and Practical Cases
3.1 Critical Application Considerations
To ensure the stable and efficient operation of electrolytic chlorination systems in seawater refrigeration scenarios, the following key points must be noted:
- Electrode Plate Maintenance: Seawater contains calcium, magnesium, and other ions that may cause scaling on the electrode plates during electrolysis. Regular cleaning (chemical cleaning or physical cleaning) of the electrode plates is required to avoid reducing electrolysis efficiency and increasing energy consumption. It is recommended to clean the electrodes once every 1-3 months according to water quality conditions.
- pH Value Control: The optimal pH range for the disinfection effect of free chlorine in seawater is 7.0-8.5. If the seawater pH is too high (above 8.5), the free chlorine will be converted into hypochlorite ions (OCl⁻), reducing disinfection efficiency; if the pH is too low (below 7.0), the corrosion risk of the system will increase. Appropriate pH adjusters can be added if necessary.
- Compatibility with Other Treatments: If the seawater refrigeration system uses corrosion inhibitors or scale inhibitors, it is necessary to ensure compatibility with the electrolytic chlorination system. Avoid using chemicals that react with free chlorine (such as ammonia-based corrosion inhibitors) to prevent reducing the efficacy of both.
- Environmental Compliance: The treated seawater discharged back to the ocean must meet local environmental standards for residual chlorine concentration (usually ≤0.2 ppm). A dechlorination unit (such as sodium bisulfite dosing) can be installed at the discharge port if necessary to ensure compliance.
3.2 Practical Application Case
Background: A coastal data center in Southeast Asia adopted a seawater refrigeration system with a daily seawater processing capacity of 15,000 m³. Previously, the center used commercial sodium hypochlorite for seawater disinfection, but faced problems such as unstable dosing concentration, frequent biofilm fouling on condensers (resulting in a 20% reduction in heat exchange efficiency), and high transportation costs. In addition, the corrosion rate of the copper alloy condenser tubes exceeded the standard, requiring annual tube replacement.
Implementation: The data center installed a modular electrolytic chlorination system with a daily chlorine production capacity of 50 kg. The system was integrated with the existing seawater intake and refrigeration loop, with pre-filtration units added to remove suspended solids. The free chlorine concentration was set to 1.0-1.5 ppm, and the system was equipped with automatic pH adjustment and online monitoring functions.
Results: After 6 months of operation, the biofilm fouling on the condensers was completely controlled, and the heat exchange efficiency of the refrigeration system recovered to the design level. The corrosion rate of the copper alloy condenser tubes decreased by 75%, extending the expected service life from 1 year to 4-5 years. The annual operating cost was reduced by 38% compared to using commercial sodium hypochlorite, and the system operated stably with no safety incidents such as chemical leakage. The discharged seawater fully met local environmental standards for residual chlorine.
4. Conclusion
Electrolytic chlorination systems have become a core water treatment solution for seawater refrigeration systems due to their on-site production, stable efficacy, corrosion mitigation, and cost-saving advantages. They effectively solve the key problems of microbial fouling and equipment corrosion in seawater refrigeration loops, ensuring the stable, efficient, and safe operation of coastal industrial facilities, marine vessels, and other applications. With the continuous promotion of green and low-carbon development in the industrial sector, electrolytic chlorination systems will be more widely used in seawater refrigeration and other marine-related water treatment fields, providing reliable technical support for the sustainable development of coastal industries.