ExxonMobil technical advisor John LaRese discusses the quality and stability issues that continue to affect VLSFO
In the run up to the 2020 fuel transition, the industry identified various new types of fuel and looked closely at the characteristics that were likely to be problematic after the changeover date.
One of the key issues identified was stability. Were the new fuels going to stay together and would they be compatible? “As an industry we looked at whether these new fuels could withstand being on board a ship for six or eight months of long-term storage,” explained ExxonMobil technical advisor John LaRese.
“Most VLSFOs aren’t straight run anymore, they are a blend of different components and when you put these components together, we need to know that they are going to remain together and remain compatible with each other,” he said.
Discussing the issue of fuel compatibility during a webinar hosted by Riviera Maritime Media in June, Mr LaRese noted that when talking about compatibility, the industry is referring to residual fuels made up of different components. “We are determining if there is enough solvency reserve in that fuel to ensure the asphaltenes in that fuel will stay in a state of suspension.”
If there is not enough solvency reserve, the asphaltene molecules start dropping out; that creates sediment which builds up in the tanks, blocking filters and plugging up purifiers.
The ISO limit for sediment is 0.1% and Mr LaRese explained that beyond that level, even by very small increments – just 0.2% – serious problems can materialise, where the purifiers are not able to handle the sediment levels.
“Typically, when we looked at fuels pre-IMO 2020, the sediment levels ranged at about 0.01% to 0.02%, very minimal levels,” he said. “Just prior to 2020, about 0.5% of all deliveries had experienced some sort of compatibility issue.
“Unfortunately, we are now seeing that sediment level creep up in some deliveries. We are noticing that even though the fuels are balanced or blended well, have the right components and are generally on spec, still the sediment levels are 0.06% or 0.08%. That suggests there might be something going on with the fuel.”
Mr LaRese also highlighted the issue of combustion, noting that combustion is measured by CCAI, a calculated index developed in the 1980s and based on the fuel available at that time. “Some of the fuels we have today are very different in composition to those fuels of 40 years ago,” he said.
As such, the CCAI test results – essentially a calculation based on the density/viscosity ratio and levels – may show the fuel is good, but when it arrives on board it may not burn well. “In a worst-case scenario, the engines can become seriously overloaded,” he said. “They will not fire correctly, rings will break and valves will experience problems. More commonly, combustion will suffer.”
Typically, poor combustion results in fouled turbocharger blades, nozzle rings and exhaust valves. When the exhaust valves start burning up, the efficiency of the engine plummets. “Even though the crew may not detect any visible signs of a problem, the operator will be losing money because the engine is not running efficiently,” warned Mr LaRese.
To mitigate against this, he suggested buyers ask questions of their fuel suppliers, such as, “is the combustion actually what it says it is?” He also felt it important that buyers ask if the supplier has conducted additional tasks, such as an FIA test, to determine the combustion of the fuel they developed.
It is an interesting fact that marine fuel is one of the few products that is not actually fit for use when it is on spec, said Mr LaRese. Under ISO 8217, 60 parts per million (PPM) of cat fines is permissible, “but the OEMs will often say you cannot put anything through the engine beyond 10 or 15 PPM.”
As such, the engineers on board need to make sure they are taking care of their treatment systems. “They need to regularly drain the water out to get the cat fines to settle and check the purifiers are working properly to remove the cat fines before they get into the engine,” said Mr LaRese.
And while the spec is based on the PPM, it does not focus on the size of the cat fines, which Mr LaRese stressed was of the utmost importance. “If you have very, very fine cat fines, they will be going through those fine mesh filters into your engine and working like a grinding paste in the fuel pumps and piston rings.”
These issues combined are having an impact on confidence. In a Riviera Maritime Media poll asking how confident webinar attendees were in the quality of fuels they were buying, only 7% expressed confidence in the quality of fuel purchased. Over a quarter (26%) had little confidence, but over two-thirds of respondents were in the least confident categories of ‘next-to-no confidence’ or ‘no confidence’.
However, in another poll, which offered a simple ‘yes’ or ‘no’ response, over a third of respondents (35%) admitted they do not ask their fuel suppliers for a certificate of quality or ask what steps the suppliers have taken to ensure product suitability. The responses served to underscore the importance for owners and operators of understanding as much as possible about the fuel they are buying, Mr LaRese said.
“My advice is to question your supplier; find out about the testing that has been done. If they do not want to share that information with you, then you have to ask yourself: why?”