Liquefied Natural Gas (LNG), is a clean fuel compared to fuel oils, causing low levels of emissions of sulphur dioxide, particles and soot. Also, CO2 emissions per energy unit is relatively low from LNG combustion due to more chemically bound energy per carbon content in natural gas than in fuel oil. But recently, a debate has started about the methane slip of LNG engines. Although the liquefied natural gas produces about 25 percent lower carbon dioxide emissions than conventional ship fuels, many engines, especially older ones, leak methane during operation. Since methane is a potent greenhouse gas that captures 86 times more heat in the atmosphere than carbon dioxide over a 20-year period, the "climate benefit" of LNG is quickly eaten up.
- For ships that have LNG engines with a large methane slip, it may be better
from a climate point of view to run on gas oil than on LNG, but at the same time it should be pointed out that LNG has significantly better performance when it comes to sulfur, nitrogen oxides, soot and other pollutants that affect locally, says Hulda Winnes at IVL, one of the researchers behind the pre-study.
The pre-study has therefore examined whether there are sustainable, technically suitable and economically feasible after-treatment methods that can be applied to existing LNG vessels.
- The results show that catalysts work but make demands on fuel and regeneration processes. You use catalysts on gas engines in trucks, but in shipping it gets a little trickier because you often use engines with dual fuel technology where each combustion cycle is started with a little gas oil injected. The sulfur content in it poisons the catalysts quite quickly and therefore you have to switch to a lower sulfur fuel.
In the project, Daphne Technology has also performed lab tests with its new plasma technology Non Thermal Plasma (NTP). The result was promising, but the technology is a bit behind the catalysts in development.
But technology is not the big challenge. A case study carried out on one of Furetank's vessels showed that the installation and operation of an oxidation catalyst is an expensive affair. The installation costs were estimated at SEK 4.5 million and the annual operating costs at SEK 1.1 million.
- These costs must be borne by someone and at present there are no requirements for shipping to keep methane emissions down. The next step will therefore be to look at policies and possible financial incentives that can facilitate the development and introduction of technologies.
According to the report a full-scale demonstration of methane oxidation catalysts on ships is needed and should be technically possible. Before any demonstration, further guidance on operational practices should be developed and be accurately addressed for the specific case.
- When it comes to plasma technology, we also hope for development in new projects. We applied for EU funding to take this technology to the next step, says Hulda Winnes.
The pre-study was carried out by Hulda Winnes and Erik Fridell (IVL), Joanne Ellis and Björn Forsman (SSPA), William Ramsay and Henrik Westermark (Daphne Technology) in collaboration with Clas Gustafsson at Furetank Rederi.