Gas Is Not Enough for Clean Transport: Report

A report Can Natural Gas Reduce Emissions from Transport? published January 28 by the Sustainable Gas Institute (SGI) at London's Imperial College, concludes that gas has the potential to reduce greenhouse gas emissions in trucks by 16% and in ships by about 10% on a full life-cycle basis, compared against the lowest estimates for diesel trucks and heavy fuel oil-fired ships.

However, the SGI warns "natural gas fuelled trucks and ships at worst may have lifecycle emissions exceeding current incumbent diesel trucks and heavy fuel oil ships". The worst case examples refer to dual fuel trucks in urban environments or vessels using low pressure dual fuel or lean burn engines.

The SGI finds that nitrogen oxide emissions from trucks using natural gas engines may be reduced by up to 80%, but that NOx emissions from dual fuel engines may be higher than diesel vehicles. Particulate matter emissions can be reduced by 18% relative to diesel trucks, the SGI says.

In shipping, NOx emissions can be reduced by about 90%, SOx emissions by 90% and particulates by up to 98% against average heavy oil fuel ships, findings which are in line with standard industry claims. The report says: "the emissions benefit of natural gas in shipping is notable due to the significant reduction in air pollution."

Climate change targets

The report says that natural gas use in shipping, combined with ambitious energy efficiency improvements, could potentially reduce GHG emissions by 35% relative to 2008 levels by 2050, but that it would be insufficient to hit a 50% reduction without deeper decarbonisation measures.

Based on International Energy Agency data for 2015, road freight accounts for 7% of global CO2 emissions and shipping 2.6%. The IEA forecasts that road freight emissions will grow by a third by 2050, the reports says, and that the International Maritime Organisation estimates shipping emissions could rise between 50% and 250% by 2050, largely through increased demand for movement of goods.

Although the report focuses on average emissions reductions for natural gas against the lowest cases for diesel trucks and heavy oil ships, the range of potential outcomes is very wide, depending on the nature of the natural gas or LNG supply chain, as well as engine type and use.

"Deeper decarbonisation appears possible if a lower emissions ship technology such as hydrogen fuel cell ships becomes available from 2040 to 2050," the report says, although it notes that the emissions from hydrogen production depend heavily on how the hydrogen is produced.