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Seawater is used worldwide for offshore cooling and fire protection systems. Unfortunately, the practice comes with one problem: biofouling. Biofouling is the buildup of microorganisms on submerged surfaces, and it creates time- and money-intensive maintenance. Seawater electrochlorination (SWEC) can solve the issue.
The oil and gas industry is increasingly concerned with environmental awareness and safety, yet no current regulations cover SWEC for offshore applications. Following the global trend, the water industry is innovating to protect the environment. However, the impacts of SWEC on the oceans have not been addressed. Environmentally responsible companies lead the way, designing sustainable, reliable and efficient SWEC systems.
SWEC works by electrolyzing seawater to create sodium hypochlorite (NaClO). The only inputs are seawater and electricity; the only byproduct is hydrogen gas.
Salt + Water + Energy 🡪 Sodium Hypochlorite + Hydrogen
NaCl + H2O + 2e- 🡪 NaClO + H2
Any industrial process that uses seawater for cooling and fire protection can develop unwanted biofouling, requiring extra maintenance and labor to maintain optimal conditions. Sodium Hypochlorite (hypo) is an effective biocide and disinfectant for various applications, including marine, offshore and industrial markets. SWEC is a safe, efficient and cost-effective solution for onsite hypochlorite generation that removes the need for bulk-hypochlorite from expensive commercial sources.
Although SWEC technology provides many benefits to the offshore oil and gas industries, the potentially harmful environmental impacts should not be overlooked.
SWEC produces sodium hypochlorite as equivalent chlorine, a highly electronegative and reactive halogen. Chlorine forms acids when combined with hydrogen and readily combines with metals to create salts. Even at low concentrations, chlorine can be toxic to aquatic life, decreasing reproduction rates, increasing mortality and altering habitats. In addition, low levels can induce stress in marine species, making them vulnerable to disease and changing behavior patterns.
Fortunately, because of its highly reactive nature, chlorine does not persist for long in the environment. Due to its low and monitored concentrations, SWEC does not cause these direct effects.
However, sodium hypochlorite byproducts last much longer and with more significant environmental consequences, primarily when high concentration chlorine is used in bulk systems. This is because chlorine reacts with the bromine and other naturally occurring chemicals in seawater to produce a range of oxidants. Reactions between the oxidants and natural organic matter lead to toxic halogenated organic compounds such as trihalomethanes, haloacetic acids, haloacetonitriles and halophenols (Abdel-Wahab et al., 2010).
The addition of any chemical to the ocean can potentially harm marine life with more detrimental effects at higher concentrations. Further research into these effects is required, but companies can minimize their impact now.
New electrochlorination system
De Nora has more than 400 installations in 60 countries, producing more than 65% of the world capacity. Designing systems with the future in mind, De Nora sets environmentally safe standards ahead of regulations.
De Nora's new SANILEC TRP electrochlorination system features a self-cleaning cell and still combines seawater and electricity to generate sodium hypochlorite. The SANILEC system is automation: it allows continuous and unattended operation, requiring minimal monitoring. The system reacts to variable conditions, automatically adjusting NaClO production to ensure minimal chlorine impact on the oceans.
Leveraging its self-cleaning technology for other marine applications, De Nora has developed continuous hypochlorite production using reverse polarity. Normal production applies a full current on electrodes in forward bias – cathode (-) to anode (+). The self-cleaning function is activated by applying a smaller current to the electrodes on the reverser bias – anode (+) to cathode (-). Any deposit buildup is dissolved from the electrode surface and flushed through the system. The function occurs daily for less than 10 minutes per continuous cycle with a negligible operational impact.
The new self-cleaning technology is safe and effective while eliminating the need to purchase, store and handle hazardous chemicals for electrode maintenance.
Offshore facilities require disinfection to control biofouling in cooling and fire protection systems.
For offshore facilities using seawater for cooling, marine growth reduces the efficiency and equipment lifespan while increasing maintenance frequency. De Nora's SANILEC TRP systems receive seawater at a fixed flow rate, producing NaClO for direct injection at any point within the rig. Adjusting the applied current varies concentrations.
For offshore facilities using seawater for firewater systems, biofouling control ensures no compromises in vital safety equipment performance. The SANILEC TRP system produces NaClO for continuous dosing of jockey pump caissons and intermittent shock dosing of firewater pump caissons. Shock dosing keeps the firewater pump caissons clean and free from fouling while ensuring the firewater main loop is algae and slime-free.
The SANILEC SWEC system was designed to account for the future needs of the industry, addressing environmental standards and worker safety while optimizing cost-effectiveness and efficiency.
With its low chlorine concentration, the system mitigates the harmful impact of chlorine on the marine ecosystem. Onsite hypochlorite generation is much safer than 12% bulk hypochlorite, producing a non-hazardous 0.08% NaClO solution. For context, household bleach is 5% to 6% NaClO. Also, onsite generated hypochlorite does not present a threat to public safety and does not require personal protective equipment for handling or containment provisions in case of leaks.
Compared to a bulk solution, the low-strength hypo produced by an onsite SWEC system decomposes at a much slower rate. It is also typically used as soon as it is produced, significantly reducing harmful chlorine byproducts. Due to long storage time, high storage temperature and exposure to UV light, the high concentrations of bulk NaClO decompose rapidly, causing the formation of chlorine byproducts with significant impacts on the environment.
Finally, the self-cleaning SANILEC TRP system eliminates the need for frequent acid cleaning using hazardous chemicals, increasing worker safety.
Currently, no international body creates regulations for chlorine discharge into the ocean by SWEC systems in offshore applications. De Nora implements its own standards, leading the way to environmentally safe SWEC practices and showing what it means to be sustainable.
Abdel-Wahab, A., Khodary, A., Bensalah, N. 2010. Formation of Trihalomethanes during seawater chlorination. Journal of Environmental Protection 1 456-465.
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