Scrubber on ships, with the IMO 2020 regulations mandating a global sulfur cap of 0.5% in marine fuels, shipowners and operators have turned to various solutions to comply with these emissions standards. One such solution is the installation of Exhaust Gas Cleaning Systems (EGCS), commonly known as scrubbers. Scrubbers help vessels continue using high-sulfur fuel oil (HSFO) while still meeting sulfur emission requirements. There are two main types of scrubbers: Open Loop and Closed Loop. Each system has its own advantages, disadvantages, and regulatory implications. Let’s explore the differences.
What is a Scrubber?
Scrubber on ships is an exhaust gas cleaning system that removes sulfur oxides (SOx) from a ship’s emissions before they are released into the atmosphere. The scrubber uses water to neutralize and wash out sulfur components from exhaust gases, significantly reducing air pollution. The treated wash water is then either discharged back into the sea (open loop) or treated and reused (closed loop).
Open Loop Scrubber on Ships
How It Works
An open-loop scrubber uses seawater as a scrubbing medium. The exhaust gases pass through the scrubber, where they come into contact with seawater. The seawater absorbs the sulfur oxides and converts them into sulfates before being discharged back into the ocean.
Advantages
- Lower Initial Cost: Open-loop scrubber on ships are generally cheaper to install compared to closed-loop systems.
- Lower Operational Complexity: Since they use natural seawater without requiring additional chemicals, they are relatively simple to operate.
- Lower Maintenance Requirements: Open-loop systems require less maintenance as they do not have chemical treatment units or sludge handling systems.
Disadvantages
- Environmental Concerns: The discharge of wash water containing sulfates and other residues has led to bans in certain coastal areas and ports, such as in Singapore, China, and parts of Europe.
- Regulatory Uncertainty: With growing environmental concerns, more regions may impose restrictions on open-loop scrubbers in the future, making their long-term viability uncertain.
- Limited Effectiveness in Freshwater: Open-loop scrubber on ships rely on the natural alkalinity of seawater, making them less effective in freshwater environments.
Closed Loop Scrubber on Ships
How It Works
A closed-loop scrubber operates by recirculating water within the system. Instead of using untreated seawater, it employs a chemical (typically sodium hydroxide) to neutralize sulfur oxides. The used water is treated on board, removing pollutants before being recirculated or discharged in compliance with environmental regulations.
Advantages
- Environmentally Friendly: Closed-loop systems minimize pollution as they do not discharge untreated wash water into the sea.
- Compliant with Port Restrictions: Since the system controls waste disposal, it is suitable for use in areas where open-loop scrubbers are banned.
- Works in All Water Conditions: Unlike open-loop systems, closed-loop scrubber function effectively in freshwater and low-alkalinity environments.
Disadvantages
- Higher Initial Cost: Installation of a closed-loop system is more expensive due to additional components like chemical dosing units and water treatment systems.
- Higher Operational Costs: Chemicals such as sodium hydroxide must be purchased and stored onboard.
- More Complex Maintenance: The system requires more attention, including managing sludge and chemical supplies.
| Feature | Open Loop Scrubber | Closed Loop Scrubber |
|---|---|---|
| Water Usage | Uses seawater | Uses recirculated water with chemical treatment |
| Discharge | Discharges treated water into the sea | Treats and recirculates water or discharges under strict conditions |
| Installation Cost | Lower | Higher |
| Operational Cost | Lower | Higher (due to chemicals and sludge disposal) |
| Maintenance Complexity | Lower | Higher |
| Regulatory Compliance | Restricted in some regions | More widely accepted in all waters |
| Effectiveness in Freshwater | Limited | Works in all water conditions |
Hybrid Scrubber on Ships: A Flexible Solution
A hybrid scrubber combines both open and closed-loop functionalities. Ships can operate in open-loop mode in unrestricted waters and switch to closed-loop mode in environmentally sensitive areas. This flexibility allows compliance with various regional regulations while optimizing operational costs.
Choosing the Right Scrubber
The choice between an open-loop and closed-loop scrubber depends on multiple factors:
- Operational Areas: If a ship frequently operates in regions with strict discharge regulations, a closed-loop or hybrid system may be more suitable.
- Budget Constraints: Open-loop scrubbers are more cost-effective initially but may become a liability if more ports ban them.
- Fuel Cost Considerations: Scrubber installation allows ships to continue using HSFO, which is often cheaper than low-sulfur fuel, leading to cost savings over time.
Conclusion
Both open-loop and closed-loop scrubbers on ships have their own set of advantages and limitations. While open-loop systems offer lower installation and operational costs, they face increasing regulatory scrutiny. Closed-loop systems, although costlier, provide a more environmentally sustainable and regulation-compliant solution. The decision to install a particular type of scrubber should be based on a careful evaluation of operational needs, long-term compliance requirements, and financial considerations.
