AMF #20, Plasma-Catalytic Technology for Methane Slip Reduction: A Technical Overview

1- Introduction

Methane slip is the release of unburned methane from natural gas-fired engines, remains a critical challenge in reducing greenhouse gas emissions. To tackle this issue, an advanced plasma-catalytic exhaust treatment system has been developed, offering a solution for the maritime, oil & gas, and land-based industries.

This technology combines non-thermal plasma (NTP) and a methane oxidation catalyst (MOC) to convert methane into carbon dioxide (CO?) and water (H?O), significantly reducing its environmental impact. The system is installed at the exhaust gas outlet of natural gas-fueled engines, directly addressing methane slip before it is released into the atmosphere.

The core of the system relies on a wavelet pulse power (WPP) supply, which generates non-thermal plasma (cold plasma). Unlike conventional thermal processes, NTP operates at lower temperatures, where energy is primarily stored in electrons rather than heating the gas itself. This ensures efficient methane conversion while maintaining system durability and low operational costs.

This innovative plasma-catalytic technology offers a promising pathway to minimize methane slip emissions, helping industries transition toward cleaner and more sustainable operations.

2- Plasma-Catalytic Reaction Process

The plasma-catalytic process enhances methane conversion by combining NTP-generated reactive species with catalytic oxidation, ensuring efficient methane removal even at lower exhaust temperatures. The process follows these key steps:

1. Electron Interaction: Energetic electrons from NTP collide with exhaust gas molecules, generating highly reactive species such as hydroxyl radicals (OH), atomic oxygen (O), and excited nitrogen species. These species play a crucial role in initiating methane oxidation.
2. Methane Oxidation: The OH radicals and other reactive species break CH? bonds, enabling its oxidation in the presence of O? and the MOC. This step enhances methane decomposition beyond conventional catalytic oxidation methods.
3. Catalytic Enhancement: The presence of NTP lowers the activation energy required for MOC to oxidize methane, allowing for effective conversion at exhaust temperatures where traditional catalytic systems are less efficient. This improves methane removal efficiency while reducing energy consumption.
4. By-product Formation & Emission Reduction: The oxidation process leads to the formation of CO? and H?O, replacing methane, a far more potent greenhouse gas with a significantly less impactful emission profile. This reduces overall GHG emissions while maintaining compatibility with existing exhaust treatment systems.

This plasma-catalytic technology provides an efficient, scalable approach to reducing methane emissions in natural gas-powered applications.

3- Key Technological Advantages

This plasma-catalytic system offers several advantages over conventional methane reduction technologies, making it an efficient and scalable solution for reducing methane slip in gas-fueled engines.

1. Low-Temperature Operation: Effectively reduces methane slip at exhaust temperatures as low as 380°C, aligning with the typical operating conditions of marine and stationary gas engines.
2. Energy Efficiency: Optimized plasma-catalytic interaction reduces plasma power consumption, making it more efficient than plasma-only systems while maintaining high methane conversion rates.
3. High Methane Reduction: Achieves greater methane slip reductions at lower exhaust temperatures compared to catalyst-only solutions, improving performance in variable operating conditions.
4. Innovative Technology: The synergistic combination of plasma and catalysis significantly enhances methane oxidation efficiency, setting it apart from conventional exhaust after-treatment systems.
5. Integration with Real-Time Emission Monitoring: Seamlessly integrates with GHG quantification and monitoring systems, enabling real-time tracking of methane reduction performance and ensuring regulatory compliance.

This advanced technology provides a scalable, energy-efficient, and highly effective solution for methane slip reduction, supporting decarbonization efforts in gas-powered applications.

4- Performance Metrics and Testing

The plasma-catalytic methane reduction system has undergone rigorous testing to evaluate its efficiency and real-world applicability. The key results from testing include:

1. Test Engine: Evaluated on a 746 kW lean-burn spark-ignited engine under controlled conditions
2. Operational Duration: The system completed nearly 100 hours of continuous operation, demonstrating durability and stability in a marine engine environment.
3. Methane Removal Efficiency: Achieved a 62% reduction in methane slip, removing 4.0 g/kWh of CH? at 75% engine load, significantly improving emission control.
4. Exhaust Temperature Performance: Operated effectively at temperatures as low as 380°C, confirming its suitability for marine and stationary gas engines that run at moderate exhaust temperatures.

These results validate the high efficiency, reliability, and scalability of this plasma-catalytic solution, reinforcing its potential for widespread adoption in decarbonization strategies for gas-fueled applications.

5- Regulatory Context and Importance of Methane Slip Reduction

The International Maritime Organization (IMO) has intensified its focus on methane slip reduction, recognizing its significant contribution to greenhouse gas (GHG) emissions. The Marine Environment Protection Committee (MEPC) 81st session emphasized the growing urgency of this issue, given that methane has a global warming potential (GWP) 28 times greater than CO? over a 100-year period, increasing to 86 times over a 20-year period.

IMO Discussions on Methane Emissions

1. Tank-to-Wake (TtW) Emissions: The Working Group on Air Pollution and Energy Efficiency has been tasked with developing a framework for measuring and verifying TtW emissions of methane (CH?), nitrous oxide (N?O), and other GHGs from ships.
2. Engine Certification: Future engine certification standards will incorporate methane slip considerations, aligning with Life Cycle Assessment (LCA) Guidelines to provide a more comprehensive evaluation of emissions.
3. Methodologies and Accuracy: MEPC 81 reviewed various quantification methods for ship-level methane slip, assessing their accuracy and reliability in real-world applications.
4. Certification Options: The committee discussed potential certification frameworks for CH? and N?O emissions, as well as Cslip (methane slip coefficient) for different engine and energy conversion technologies.

Importance of Addressing Methane Slip

1. Climate Impact: With a GWP significantly higher than CO?, methane reduction is a high-priority climate action to mitigate near-term warming effects.
2. LNG as a Transition Fuel: As the industry expands its reliance on LNG as a low-carbon alternative, controlling methane slip is essential to maximizing its environmental benefits.
3. Technological Solutions: Advanced methane abatement technologies will be key enablers in meeting emerging regulatory requirements and industry GHG reduction targets.
4. Data Collection and Reporting: MEPC’s push for standardized measurement and verification reinforces the need for accurate emissions tracking and integrated mitigation solutions across the shipping sector.

As regulatory concerns on methane slip increases, innovative exhaust treatment and emissions management technologies may play a important role in achieving the industry’s decarbonization goals.

6- Final Thoughts

Methane slip reduction is becoming an essential part of the maritime industry’s decarbonization journey, as regulatory frameworks evolve to address its climate impact. With IMO's increasing focus on methane emissions, industry stakeholders must proactively seek practical and scalable solutions to minimize methane slip and improve overall emission efficiency.

While LNG remains a key transition fuel, its full potential as a cleaner alternative depends on how effectively methane slip is controlled. Technologies such as plasma-catalytic oxidation offer promising pathways to significantly reduce methane emissions, ensuring that LNG-powered vessels contribute meaningfully to climate goals.

Addressing methane slip is not just about meeting regulations; it is about ensuring that the industry moves forward with a responsible and long-term approach to emissions reduction.

Disclaimer: This article reflects the author's personal views and does not represent ABS in any way. It is not official communication from ABS, and the information here should not be taken as professional or legal advice.