Author: Daniel G. Teleoaca – Maritime Chief Engineer
The maritime industry is under increasing pressure to reduce emissions and comply with stringent environmental regulations. One of the most effective technologies for achieving this is the Exhaust Gas Recirculation (EGR) system. This system helps reduce nitrogen oxide (NOx) emissions, a significant contributor to air pollution, by recirculating a portion of exhaust gases back into the engine’s combustion process. This article explores the components, working principle, purpose, advantages, challenges, and maintenance of EGR systems in vessels.
What is an Exhaust Gas Recirculation (EGR) system?
An Exhaust Gas Recirculation (EGR) system is an emission control technology used in internal combustion engines, including those on vessels. By redirecting a portion of exhaust gases back into the engine’s intake air, it reduces the oxygen concentration and lowers combustion temperatures. This process minimizes NOx formation during combustion, making it a vital tool for meeting International Maritime Organization (IMO) Tier III emission standards.
Key Components of an EGR System
EGR Valve
- Regulates the flow of exhaust gases into the intake manifold.
- Can be pneumatic or electronically controlled for precise operation.
EGR Cooler
- Reduces the temperature of recirculated exhaust gases before they re-enter the engine.
- Prevents engine damage and improves efficiency.
Pipes and Ducts
- Connect the exhaust manifold to the intake manifold via the cooler and valve.
Control System
- Monitors and adjusts EGR flow based on engine load and operating conditions.
Water Mist Catcher
- Removes moisture from cooled exhaust gases to prevent corrosion or damage to engine components.
Blower
- Ensures adequate pressure for recirculated gases to mix with intake air.
Sensors
- Measure parameters like temperature, pressure, and oxygen levels to optimize EGR performance.
How Does an EGR System Work?
The EGR system operates through a controlled cycle:
- Exhaust Gas Extraction: A portion of exhaust gas is diverted from the exhaust manifold.
- Cooling: The hot exhaust gas passes through an EGR cooler to lower its temperature.
- Recirculation: The cooled gas flows through pipes and ducts back into the intake manifold.
- Combustion: The diluted air-exhaust mixture enters the combustion chamber, reducing peak combustion temperatures and NOx formation.
This process ensures that NOx emissions are reduced by up to 70%, depending on system design and operating conditions.
Purpose and Benefits
- Emission Reduction: Lowers NOx emissions by reducing combustion temperatures.
- Compliance: Helps meet IMO Tier III regulations and other environmental standards.
- Fuel Efficiency: Reduces fuel consumption in some cases by improving combustion dynamics.
- Versatility: Can be used alongside other emission reduction technologies like Selective Catalytic Reduction (SCR).
Challenges and Limitations
- Complexity: Requires precise control systems for optimal operation.
- Engine Efficiency Impact: Recirculated gases reduce oxygen levels, potentially lowering engine power output.
- Maintenance Needs: Components like valves and coolers are prone to fouling from soot and deposits.
- Initial Cost: High installation costs can be a barrier for older vessels.
- Oil Contamination: Accelerates soot loading in engine oil, requiring more frequent oil changes
Common Troubles and Maintenance Practices
Frequent Issues:
- Fouling of EGR Valves: Soot deposits can block valves, reducing efficiency.
- Corrosion in Coolers: High moisture content in exhaust gases can cause corrosion over time.
- Sensor Failures: Faulty sensors can lead to incorrect EGR flow rates.
- Back-pressure Problems: Excessive back-pressure can affect engine performance negatively.
Maintenance Tips:
Proper maintenance of Exhaust Gas Recirculation (EGR) systems is critical to ensure their efficiency, reliability, and compliance with emission standards. Below is a detailed guide on best practices, recommended procedures, and maintenance frequencies to keep your EGR system in optimal condition
- Regularly clean EGR valves and coolers to remove soot buildup:
• EGR Valve: Clean the valve every 3–6 months to remove carbon deposits that can cause sticking or reduced functionality. Use a solvent or specialized cleaning solution to dissolve soot buildup.
• EGR Cooler: Inspect and clean the cooler every 6 months or during planned maintenance intervals. Clogged coolers reduce heat transfer efficiency and can lead to overheating. Use water flushing or chemical cleaning agents to remove deposits.
• Pipes and Ducts: Check for blockages or soot accumulation every 6 months. Clean these passages using brushes or compressed air to maintain a clear flow path for exhaust gases.
- Inspection of key components:
• Sensors: Inspect temperature, pressure, and oxygen sensors monthly to ensure accurate readings. Faulty sensors can disrupt EGR flow rates, leading to performance issues.
• Leak Detection: Check pipes, ducts, and cooler connections for leaks during every port stay or at least once a month. Leaks can disrupt the recirculation process and reduce system efficiency.
• Water Mist Catcher: Inspect for moisture accumulation every 3 months. Replace or clean filters as needed to prevent corrosion in downstream components.
- Functional testing. Perform functional tests of the EGR system every two weeks:
• Start the system and run it for at least two hours to prevent sticking valves, blower malfunctions, or blocked filters.
• Exercise bypass valves manually during port stays to ensure they do not seize up.
• Test the EGR water system manually by running the water recirculation loop for half an hour to flush tanks and pipes.
- Preventive Measures:
• Corrosion Control: Use high-quality materials resistant to high temperatures and moisture exposure in critical components like coolers and pipes.
• NaOH Injection Management: For systems using NaOH (sodium hydroxide) injection, monitor dosing levels regularly to prevent scaling in pipes and coolers.
• Oxygen Sensors Calibration: Oxygen sensors need to be re-calibrated frequently especially before starting up the system.
- Long term Maintenance for vessel with extended period of inactivity:
• Blank off EGR gas pipes with plates at strategic locations if the system will be out of operation for more than a year.
• Drain and store pH sensors from the water treatment system according to the manufacturer’s guidelines.
• Flush the EGR water loop with freshwater before long-term shutdowns to prevent scaling or corrosion.
- Recommended maintenance schedule must be done as per manufacturer’s instruction manual. Here below there is a general recommended maintenance schedule:
| TASK | FREQUENCY |
| Clean EGR Valve | Every 3-6 months |
| Clean EGR Cooler | Every 6 months |
| Inspect Sensors | Monthly |
| Leak Detection | Monthly |
| Functional Testing | Every 2 weeks |
| Water Mist Catcher Inspection | Every 3 months |
| Oxygen Sensor Calibration | 2 weeks |
In conclusion, the Exhaust Gas Recirculation (EGR) system is a cornerstone technology for reducing NOx emissions in vessel engines. By recirculating cooled exhaust gases into the combustion process, it effectively lowers combustion temperatures and minimizes harmful emissions. While it comes with challenges such as maintenance demands and potential impacts on engine efficiency, its benefits in terms of regulatory compliance and environmental sustainability make it indispensable for modern shipping operations.
By adopting robust maintenance practices and leveraging advanced designs, vessel operators can maximize the effectiveness of their EGR systems while meeting global emission standards efficiently.
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