Ship’s Exhaust Scrubber System: An Essential Guide to Types, Operation, Maintenance, and Troubleshooting

In the maritime industry, environmental regulations and sustainability have become critical concerns. To comply with these regulations and minimize its environmental impact, the shipping industry has turned to innovative technologies, one of which is the ship’s exhaust scrubber system. These systems help vessels reduce harmful emissions, especially sulfur oxides (SOx), and enhance air quality. In this comprehensive guide, we will dive into the different types of scrubbers, their operation modes, maintenance requirements, and troubleshooting tips.

Types of Scrubbers

    • Open Loop Scrubbers:

      These scrubbers use seawater as the scrubbing medium to remove pollutants from the exhaust gas before it is released into the atmosphere. Open loop scrubbers are one of the most common and cost-effective solutions for complying with environmental regulations, such as the International Maritime Organization’s (IMO) sulfur emissions limits.. The sulfur in the exhaust reacts with the alkaline seawater, forming sulfuric acid. The acidified seawater is then discharged back into the sea, subject to strict environmental regulations in certain regions.

    • Closed Loop Scrubbers:

      Closed loop scrubbers circulate a specific amount of water within a closed loop system. The process neutralizes the sulfuric acid formed during the scrubbing process using an alkaline substance, usually caustic soda (sodium hydroxide). This allows the scrubber to comply with stricter discharge regulations, as no acidified water is released into the ocean.

    • Hybrid Scrubbers: A hybrid scrubber system is an advanced exhaust gas cleaning system used in ships to reduce harmful emissions, particularly sulfur oxides (SOx), from the vessel’s exhaust gases. As the name suggests, a hybrid scrubber combines the features of both open loop and closed loop scrubbers, offering greater flexibility and adaptability to comply with varying environmental regulations in different regions.

Scrubber System Operation Mode

Open Loop System Operation

Here’s how open loop scrubbers work:

    • Seawater Intake: Open loop scrubbers draw in seawater from the ocean through an intake located on the ship’s hull (sea chest). This water is used as the scrubbing medium for cleaning the exhaust gases.

    • Scrubbing Process: The exhaust gas from the ship’s engines is directed through the scrubber tower. As the gases rise through the tower, they come into contact with the downward flow of seawater.

    • Acid-Base Reaction: In the scrubber tower, the sulfur dioxide (SO2) and other acidic components present in the exhaust gas react with the alkaline seawater. This reaction results in the formation of sulfuric acid (H2SO4), a water-soluble and less harmful compound compared to SO2.

    • Neutralization: As the sulfuric acid is formed, it dissolves in the seawater, causing the water to become acidified. However, the seawater’s alkaline nature naturally neutralizes the acid, reducing its overall impact on the marine environment.

    • Discharge: The now acidified seawater is discharged overboard, subject to strict environmental regulations in specific areas. The discharged water must comply with the applicable limits for pH levels and other pollutants, which are usually determined by local or international regulations.

Open loop scrubbers are popular due to their simplicity, lower installation costs, and ease of operation. However, their usage is subject to regional restrictions, as some countries and regions have banned the use of open loop scrubbers within their territorial waters due to concerns about the environmental impact of discharging acidified water into the ocean.

To address these concerns, some ship operators may opt for closed loop scrubbers or hybrid scrubber systems, which offer more flexibility and compliance with stringent regulations by treating and reusing the scrubbing water within a closed system, rather than discharging it directly into the sea.

Closed Loop System Operation

Here’s how closed loop scrubbers work:

    • Freshwater Intake: Unlike open loop scrubbers that use seawater, closed loop scrubbers use freshwater as the scrubbing medium. The freshwater is typically stored in onboard tanks.

    • Scrubbing Process: The exhaust gas from the ship’s engines is directed through the scrubber tower, where it comes into contact with the circulating freshwater.

    • Acid-Base Reaction: Similar to open loop scrubbers, the acidic components, including sulfur dioxide (SO2), in the exhaust gas react with the alkaline freshwater. This reaction results in the formation of sulfuric acid (H2SO4), just as in the open loop process.

    • Neutralization: After the scrubbing process, the acidified freshwater is collected and pumped to a neutralization unit. In this unit, an alkaline substance, usually caustic soda (sodium hydroxide – NaOH), is added to the acidified water. The alkaline substance neutralizes the sulfuric acid, transforming it into harmless salts, such as sodium sulfate (Na2SO4).

    • Recirculation: The neutralized freshwater is then re-circulated back into the scrubber tower to continue the scrubbing process. This closed-loop system ensures that no acidified water is discharged into the sea.

Closed loop scrubbers provide the advantage of reducing the environmental impact by avoiding the direct discharge of acidified water into marine ecosystems. However, they require additional infrastructure and chemical handling for the neutralization process, making them slightly more complex than open loop scrubbers.

Hybrid Scrubber System Operation

The hybrid scrubber system can operate in three different modes:

    • Open Loop Mode: In the open loop mode, the scrubber system uses seawater as the scrubbing medium, just like a traditional open loop scrubber. The exhaust gas comes into contact with the seawater, and the sulfur dioxide (SO2) in the gas reacts with the alkaline seawater to form sulfuric acid. The acidified seawater is then discharged overboard, subject to compliance with local regulations.
    • Closed Loop Mode: In the closed loop mode, the scrubber system uses freshwater as the scrubbing medium, similar to a closed loop scrubber. The exhaust gas is scrubbed with the freshwater, and the resulting acidified water is collected and pumped to a neutralization unit. In the neutralization unit, an alkaline substance, usually caustic soda (sodium hydroxide – NaOH), is added to neutralize the sulfuric acid, transforming it into harmless salts. The neutralized water is then recirculated back into the scrubber tower to continue the scrubbing process.
    • Hybrid Mode: In the hybrid mode, the scrubber system combines the features of both open loop and closed loop modes. The system can switch between using seawater and freshwater as the scrubbing medium, depending on the vessel’s location and the applicable environmental regulations.

The hybrid scrubber system provides several advantages:

    • Compliance Flexibility: The ability to operate in multiple modes allows ship operators to comply with different environmental regulations in various regions. When sailing in areas where open loop scrubbers are allowed, the system can use seawater, and when entering regions with stricter regulations, it can switch to closed loop mode.

    • Environmental Benefits: Like closed loop scrubbers, the hybrid system prevents the direct discharge of acidified water into the sea, reducing the potential environmental impact on marine ecosystems.

    • Cost-Efficiency: The hybrid scrubber system provides cost savings by enabling the use of seawater when permitted, which eliminates the need for additional infrastructure and chemicals for neutralization.

The hybrid scrubber system has gained popularity in the maritime industry as it strikes a balance between compliance with environmental regulations and cost-effective operations, making it a viable solution for shipowners aiming to reduce their environmental footprint.

Scrubber System Maintenance

    • Regular Inspections: Conduct routine inspections of the scrubber system, including the tower, nozzles, pumps, and pipes, to identify any signs of wear, corrosion, or blockages. This helps to prevent clogging, corrosion, erosion, leakage, and fouling that can affect the efficiency and reliability of the scrubber system.
    • Cleaning: Clean the nozzles and scrubber tower regularly to prevent the accumulation of deposits and ensure efficient operation. Inspection and cleaning intervals may vary depending on the type of scrubber, the quality of the scrubbing material, and the operational conditions of the vessel.
    • Replacing and replenishing the consumables and spare parts of the scrubber system, such as the scrubbing material, filters, seals, gaskets, electrodes, and catalysts. This helps to maintain the functionality and durability of the scrubber system. Replacing and replenishing intervals may depend on the availability, cost, and environmental impact of the consumables and spare parts.
    • Filter Replacement: Replace filters in closed-loop scrubbers as per the manufacturer’s recommendations to maintain water quality and optimal performance.

To optimize vessel scrubber system maintenance, it is advisable to follow the maintenance guidelines and recommendations provided by the scrubber manufacturer or supplier. Additionally, it is beneficial to adopt a proactive and preventive maintenance strategy that uses data-driven digital services to monitor, analyze, predict, and optimize the condition and performance of the scrubber system. This can help to reduce maintenance costs, increase operational efficiency, enhance environmental compliance, and extend the service life of the scrubber system.

Scrubber System Troubleshooting

The common issues and troubleshooting of the vessel scrubber system are:

    • Reduced Scrubbing Efficiency: Over time, vessel scrubber systems might experience reduced efficiency in removing pollutants. This can be due to factors such as fouling, corrosion, or malfunctioning components.
      • Solution: Regular maintenance and inspections are essential. Fouling and corrosion should be addressed promptly, and components should be cleaned or replaced as needed. Analyzing the scrubber’s performance data can also help identify underlying issues.
    • Corrosion and Leaks: Corrosion and leaks in the scrubber system can lead to environmental contamination and reduced efficiency. Inspect the system for visible leaks and pressure anomalies. Tighten connections and replace faulty components as necessary.
      • Solution: Utilize materials that are resistant to corrosion, and apply protective coatings where necessary. Regular inspection and maintenance can help catch corrosion early and prevent extensive damage.
    • Chemical Imbalance: In closed-loop scrubbers, monitor the chemical levels regularly and ensure they are within the recommended range to maintain the system’s effectiveness.
    • Alarm Indications and Error Codes: Familiarize the crew with the scrubber’s alarm system to quickly identify and address any operational issues. Scrubber systems are equipped with monitoring and control systems that generate alarms or error codes when anomalies are detected. These alarms can range from issues with pump flow rates to pH imbalances.
      • Solution: Consult the system manual and diagnostic tools to interpret error codes correctly. Address the root cause of the alarms, which might involve checking sensors, valves, or other system components.
    • Sludge Build Up: The scrubbing process generates sludge as a byproduct, which can accumulate in tanks and pipes, leading to clogs and reduced efficiency.
      • Solution: Implement a regular maintenance schedule for sludge removal. Ensuring proper waste disposal procedures and following manufacturer guidelines for sludge management are crucial.

In conclusion, the ship’s exhaust scrubber system plays a crucial role in mitigating the environmental impact of maritime operations by reducing harmful emissions. By understanding the different types of scrubbers, their operation modes, maintenance requirements, and troubleshooting techniques, shipowners and crews can ensure the efficient and compliant operation of these systems. As the industry continues to embrace sustainable practices, exhaust scrubbers will remain a vital tool in safeguarding our oceans and the environment for generations to come.

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