Carbon recycled methane can be recognised as zero emission ship fuel

THE Ship Carbon Recycling Working Group of Japan’s Carbon Capture & Reuse Study Group has confirmed that carbon recycled methane produced by methanation technology can be recognised as zero emission ship fuel.

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

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

Methanation is a technology for synthesising 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 synthesised 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 electrolysing water with electricity derived from renewable energy.

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

While the International Maritime Organization has yet to develop the rules for calculating emissions from the onboard fuel combustion of carbon recycled methane (tank to propeller), the importance to be cognisant of CO₂ emissions in the fuel supply process (well to tank) has been noted.

The working group has assumed and evaluated the following four processes as the supply chain for carbon-recycled methane fuel:

(1) CO₂ separation and capture

(2) CO₂ transportation

(3) methanation fuel synthesis

(4) 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 recognised as zero-emission fuels.

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 working group 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.