Study: Carbon recycled methane can be recognized as zero-emission ship fuel

Carbon recycled methane produced by methanation technology can be recognized as zero-emission ship fuel, the Ship Carbon Recycling Working Group (WG) of Japan’s Carbon Capture & Reuse (CCR) Study Group has confirmed.

A technical paper describing the details of the calculation procedure and evaluation conducted by the WG has been published in the latest issue of the journal of the Japan Institute of Marine Engineering.

Specifically, methanation is a technology for synthesizing methane, the main component in natural gas, by causing a chemical reaction between hydrogen and CO₂ in a reactor vessel filled with a catalyst. It uses emitted CO₂ separated and captured from industrial facilities. As the CO₂ generated when combusting synthesized methane is considered to be offset by the separated and captured CO₂, it is expected that CO₂ emissions can be significantly reduced by using hydrogen generated by electrolyzing water with electricity derived from renewable energy.

Carbon recycling, which is the process of capturing and reusing emitted CO₂, is becoming increasingly important as one of the pathways to realize a carbon-neutral society.

To explore the feasibility of the concept of utilizing methanation technology for zero-emission ship fuels, the WG was formed within Japan’s CCR Study Group, and started its activity in July 2020.

Since it is a basic premise for the WG’s activity that carbon recycled methane can be recognized as zero-emission fuel, the WG firstly worked on the evaluation of its potential.

While the International Maritime Organization (IMO) has yet to develop the rules for calculating emissions from the onboard fuel combustion of carbon recycled methane (Tank to Propeller), one needs to be aware of the importance of CO₂ emissions in the fuel supply process (Well to Tank).

As informed, the WG has assumed and evaluated the following four processes as the supply chain for carbon-recycled methane fuel — CO₂ separation and capture, CO₂ transportation, methanation fuel synthesis, and methanation fuel liquefaction.

As a result, the CO₂ emission per unit calorific value of carbon-recycled methane fuel by methanation was calculated as approximately 27-gCO₂/MJ (regarded as Well to Propeller).

This figure is comparable to other alternative fuel candidates generally recognized as zero-emission fuels, confirming that carbon-recycled methane can be recognized as zero-emission ship fuel as it is a GHG with 25 times greenhouse effect of CO2, according to the WG.

In addition, further reduction to approximately 20-gCO₂/MJ is expected by improving the efficiency of the separation and capture technology and using electricity produced from renewable energy.

In order to verify the feasibility of carbon recycled methane as a ship fuel, the WG will continue to work on issues such as CO₂ transportation by large-scale liquified CO₂ carrier vessels, supply of hydrogen from renewable energy, prevention of methane slip, supply infrastructure of liquefied methanation fuel, and economic viability.