PureSOx Scrubber

CE Delft study on CO2 emissions and MARPOL Annex VI compliance options

It’s been a long while since my last blog post, in which I promised to dive further into PAH and how it relates to marine environmental impact. I’m sorry for that, and I’ll have to ask for your continued patience. It’s still work in progress.

In the meantime, I’d like to look at a report issued by CE Delft this past August. The report details a new study named “Comparison of CO2 emissions of MARPOL Annex VI compliance options in 2020”, which I will nickname the “WtW study” in reference to its well-to-wake scope. Alfa Laval, Wärtsilä and Yara were all involved in funding this study, but the technical evaluation was done solely by CE Delft in order to ensure its scientific independence.

We know that it takes less energy to wash the sulphur out after its oxidation (combustion) than it does to remove it as an element from the fuel itself. But just how much less energy does it take, and what does that mean for CO2 footprint? The answers depend on what you consider to be the likely refinery processing strategy, knowing that not all refineries will use the same process. This is what the WtW study reflects when considering the “compliant fuel” scenario. For the increase in CO2 footprint associated with compliant fuels, the study gives a range from 1% to 25%.  That span seems ridiculous at first glance, so let’s examine it a little.

The least energy-intensive way to make a compliant fuel is to treat a straight-run fuel. Such treatment requires only an additional amount of hydrogen for the hydrodesulphurization (HDS) process. For 0.5% and 0.1% sulphur fuels, this will lead to a CO2 footprint increase of 0.9%[1] and 1.2% respectively.

The most energy-intensive way to achieve a compliant fuel is to further treat an HFO. This requires more coking, hydrocracking, catalytic cracking or other processing compared with a straight-run fuel. The additional processes involve breaking up the carbon chain length, which means a loss of energy. For 0.5% and 0.1% sulphur fuels, the resulting increase in CO2 footprint will be 20.3% and 26.2% respectively.

Of course, the results above are based on model refineries that don’t exist in reality. They represent two theoretical extremes of energy expenditure – one yield for this process, one yield for that process – that real refineries won’t likely mirror. The span doesn’t reflect how individual refineries are operated in practice, nor does it reflect the increased expenditure on a global level in conjunction with IMO 2015/2020.[2]

Due to IMO 2015/2020, more low-sulphur fuels are needed.[3] Assuming that there was previously a reasonable balance between market demand and supply, this requires the balance to shift. Several resulting strategies can be utilized from the refinery’s side, and I’m no expert in this area. However, the following would seem natural to me: if you don’t want to change your refinery and you have the ability to increase throughput, you would opt for processing more crude to create a larger amount of compliant fuel. On a global level, this would entail increased amounts of extracted crude and an increased amount of residual fuel as well.

If, on the other hand, it’s difficult for you as a refiner to sell the last and/or increased remainder of the barrel, or if you don’t have the capacity for more throughput, you might need to invest in new/additional processing equipment. That will also be associated with increased CO2 footprint, at least if you’re making a fair comparison between compliant fuel and the option of an EGCS.

Considering these effects is of course a very complicated task, because it’s difficult to assess which changes are caused by IMO 2015/2020 alone – or even to determine for which product stream the related “outside” costs and CO2 footprint should be adjusted. For that reason, the really big holistic view and assessment still include unanswered questions.

The refinery industry itself (Concawe) reports that IMO 2015/2020 will lead to an increase in CO2 footprint of approximately 10%, without any consideration of installation-related footprint.[4] The supplemental IMO fuel availability study[5] assesses the increase at 4.4%, based on the assumption that a specific number of ships would be operated with an ECGS on board – an assumption the Concawe study doesn’t share.

Considering the numbers from the WtW study and the numbers from the additional studies mentioned above, it’s reasonable to assume that the increase in CO2 footprint if all ships used compliant fuel only would be more than 4.4%, given that Concawe’s own figures put it at approximately 10%. It’s also reasonable to assume that the number is unlikely to go as high as the approximately 25% at the upper extreme of the WtW study, because this would represent too costly an investment for the refineries. However, one needs to realize that the scarcer crude oil as a resource becomes, the stronger the tendency towards desulphurizing HFO will grow, so long as the process remains competitive with net-zero-carbon/zero-carbon fuel alternatives and GHG market-based measures.

The initial IMO GHG strategy[6] speaks of “peaking GHG emissions as soon as possible”, taking into account the forecast of increased shipping business. Promoting EGCS use would help in minimizing the peak and would make perfect sense, since net-zero-carbon and zero-carbon fuel alternatives won’t become available at scale and on a global level within the next 5–10 years.

But let’s get back to the WtW study. By now it should be clear that the study should be read in this way: the process of desulphurizing straight-run fuel is less energy-consuming than the desulphurization of an HFO. In this regard, the study doesn’t consider the impact on a global level if all refineries worldwide were to use straight-run fuels as a resource. Nonetheless, it’s unlikely that all refineries would upgrade their plants to solely desulphurize HFO. Therefore, if you’re looking to find out which impact IMO 2015/2020 would have on the global CO2 footprint if all ships operated on compliant fuel, you won’t find the answer in this study. What you will find, however, is an answer to how much the CO2 footprint would increase globally due to IMO 2015/2020 if all ships were fitted with an EGCS.



[1] The WtW study states 0.7%. However, review shows that using the numbers in the study produces a result of 0.9%.

[2] MARPOL Annex VI regulation 14 – Sulphur emission control areas and global sulphur cap.

[3] Delft (2016). Assessment of Fuel Oil Availability – Final Report. MEPC 70/INF.6 IMO fuel availability study. July.

[4] Concawe (2018). Environmental Impacts of Marine SO2 Emissions. Report 1/18.

[5] EnSys Energy with Navigistics Consulting (2016). Supplemental Fuel Availability Study – Final Report. MEPC 70/INF.9 IMO fuel availability study. 15 July.

[6] Resolution MEPC.304(72) – Initial IMO strategy on reduction of GHG emissions from ships. Adopted 13 April 2018.