As a compliant alternative fuel to deal with the IMO 2020 sulfur limitation regulations, the impact of LNG on decarbonization has been controversial. According to SINTEF, the use of liquefied natural gas (LNG) as a fuel may in some cases increase greenhouse gas emissions in the atmosphere.
Dr Elizabeth lindstad, chief scientist of SINTEF ocean as, told shipowners that the full life cycle greenhouse gas emissions of dual fuel engines powered by low-pressure LNG are higher than those of heavy fuel engines powered by scrubbers.
In an eight year long scientific research project, SINTEF compares the differences in the application of low-pressure and high-pressure LNG technologies on two-stroke and four stroke engines, and takes the emission of marine light diesel oil (MgO) as the baseline, i.e. 100% emission level. The results show that the emission of two-stroke engine using low-pressure LNG as fuel is 137% of that of marine light diesel, while the emission of low-pressure LNG powered dual fuel four stroke engine is 106%. If low-pressure LNG is used as fuel, the carbon emission of four stroke engine is almost the same as that of marine light diesel. However, the carbon emission of heavy fuel equipped with washing tower is only 97%.
According to Elizabeth lindstad, the energy efficiency design index (EEDI) can only measure carbon dioxide emissions, while the low-pressure LNG system is at least one option of capital expenditure required to meet the requirements of the third phase of EEDI. If shipowners adopt the cheapest scheme in succession, the temperature chamber gas emissions will continue to rise.
Looking at this situation, Elizabeth lindstad asked, "what do you think will happen? The business of such manufacturers is booming, but we are unable to achieve the goal of dealing with climate change. We are on a completely wrong track. "
The application of high pressure LNG system in two stroke engine can burn LNG more effectively, so it can also reduce the phenomenon of methane slippage. This efficiency will also be reflected in the emission level. In this case, the carbon emission is equivalent to 93% of the emission of marine light diesel, which is slightly better than the heavy fuel emission reduction effect of using the scrubber.
SINTEF's study debunked the idea that LNG can be used as a transitional fuel to help the marine industry achieve its decarbonization goals, and Elizabeth lindstad firmly criticized the efforts of some organizations to promote the use of LNG as a transitional fuel.
In comparison with the research on carbon emission in LNG production stage, Elizabeth lindstad mentioned the 2013 concove study, which calculated that each megajoule energy produced by LNG would emit 21.1g carbon dioxide equivalent. Two years later, veerbeek did the same calculation, resulting in a figure of 19g. In 2018, another industry organization made a similar calculation, and found that in the LNG production stage, only 10.7g CO2 equivalent was emitted for each megajoule of energy generated.
According to Elizabeth lindstad, the last agency's data came from veerbeek's 2013 study, after which veerbeek admitted that his calculations were wrong and the data was corrected. Elizabeth lindstad explained that it was not surprising that LNG performed so well in the last agency's study, but they were naval architects, after all, with limited knowledge of LNG or refineries. However, the data they choose has a great impact on the calculation results, so they will find that after using such low data, even taking serious methane slippage into account, the greenhouse gas emission of LNG is still only 90% of that of marine light diesel.
The high-pressure LNG system can reduce carbon dioxide emissions by 35%, optimize ship design and improve ship energy efficiency, while the heavy fuel oil using the scrubber can only reduce greenhouse gas emissions by 20%, but the low-pressure LNG system will aggravate global warming, said Elizabeth lindstad.
Some experts also pointed out that LNG application related technology has made great progress, the current two-stroke engine has been able to solve the problem of methane slippage to a large extent, and the performance of the next generation engine will be better. In view of the existing technical means to deal with methane slippage, the problem of LNG emission reduction is actually cost rather than technology. Engines that can significantly reduce greenhouse gas emissions are not without them, but are expensive.