Innospec: Common HSFO Issues and the Case for Additives

by Joshua Townley, Market Specialist Marine, Innospec
Friday February 5, 2021

This article addresses the common issues faced by vessels using SOx scrubbers and other post combustion systems.

Each section presents and explains how topics such as exhaust emissions, fuel economy and quality are vital to vessel performance, and how small changes today will impact your long-term success.

The shipping industry has embraced the move towards a more sustainable future, adapting quickly to objectives set out by the IMO to reduce emissions hazardous to both human health and the environment as a whole. We are on the path to success thanks to the adoption of systems such as Exhaust Gas Cleaning Systems (EGCS/ Scrubbers), Selective Catalytic Reduction (SCR), Exhaust Gas Recirculation (EGR) and alternative fuels such as VLSFO (Very Low Sulphur Fuel <0.5%) or Biofuels.

While VLSFO and Biofuels have had some well reported issues, this article will focus on the engineering solutions being used to control emissions from vessels, and the challenges faced when doing so.

Reduced emissions from traditional fuels will ultimately need to come from better performance, reduced fuel consumption and reduced margins for error. This is where the unpredictable quality of residual marine fuels such as HSFO has proven to be problematic. Post combustion systems such as EGCS, EGR and SCR are sensitive to deposits caused by poor quality fuels or incomplete combustion, the same mechanisms that cause fouling, after-burn and black smoke in exhaust gases and/or high levels of PAH and turbidity in wash water systems.

Emissions / Black Smoke

HSFOs are notorious for producing soot and black smoke as they contain high levels of residual aromatics such as asphaltenes (approximately 15% m/m) which burn poorly if unstable i.e. grow into larger structures that settle out as sludge in tanks or contribute to poor combustion. If a fuel is kept stable, asphaltenes remain small enough to burn completely, releasing the large amount of chemical energy they contain during combustion without causing after-burn and excessive particulates.

Otherwise if unstable, they will form excessive deposits, impinge on liner walls or burn away Cylinder Lube Oil (CLO), damaging liners or creating harmful emissions and post-combustion fouling.

Incomplete and poor combustion is the primary cause of black carbon, soot and PAH in exhaust gases. The process starts in the gas phase after combustion where unburnt fuel grows into larger structures that either foul turbochargers, economisers and scrubbers, or leave the stack as black smoke or PAH in scrubber wash water.

PAH and Scrubber Wash Water

Polycyclic Aromatic Hydrocarbons (PAH) are organic hydrocarbons that exist in large numbers within residual marine fuels. The primary source of PAH in the environment is incomplete combustion and unburnt fuel which normally would be expelled into the atmosphere, but are also captured by the wash water from SOx scrubbers.

PAH levels are closely monitored in scrubber wash water due to the damage they can cause to human health and the marine environment, and for this reason the IMO stipulates that the PAH content of wash water shall not exceed 50 μg/L. The poorer the combustion and fouling characteristics of HSFO the higher the PAH levels.

The introduction of a powerful combustion and soot catalyst like Innospec's Octamar Complete has the potential to address PAH by improving combustion and reducing Particulate Matter (PM) and therefore PAH particulates by 60%.

Fouling, back pressure and fuel efficiency

Even small changes in back pressure have been shown to increase fuel consumption and reduce gas flow, and is affected through two primary mechanisms:

  • Lower turbocharger efficiency (lower temperature drop across the turbine) and therefore lower scavenge pressure.
  • Lower scavenge efficiency i.e. a reduction in the fresh air caused by reduced gas flow through the engine.

The installation of additional equipment downstream is known to increase back pressure and without the proper precautions (by re-matching turbochargers or nozzle rings), has a significant negative effect on engine performance.

This is why MAN B&W strongly recommends that a scrubber installation does not increase the back pressure of an engine by more than 305 mmWc (MAN B&W, MUN2017-06-21).

However, the increase in post combustion complexities is also a cause of increased fouling as exhaust gases are slowed or forced to change direction with particulates in the exhaust gas dropping out to foul machinery surfaces.

Octamar Complete acts to prevent and remove the build-up of post-combustion fouling, ensuring expensive exhaust systems work efficiently and vital machinery assets are protected.

Fuel Quality -- The Changing Landscape

Octamar Complete containsInnospec's unique combustion catalyst that significantly improves the combustion of marine residuals, including all HSFO. Independently verified studies have proven how the combustion catalyst in Octamar Complete reliably reduces Ignition Delay (ID) and the end of Main Combustion Delay (MCD), while increasing the Estimated Cetane Number (ECN) to improve Specific Fuel Oil Consumption (SFOC) by as much as 2.2%.

Those using Octamar Complete enjoy all the benefits of a higher-quality fuel for a fraction of the cost differential. Every Innospec product is designed to maximise the output and operability of fuel to ensure consistent optimum performance.

Small changes in ECN, MCD and EMC provided by Octamar Complete give huge benefits to both reducing emissions and post combustion fouling, which is the primary failure mode for more post-combustion systems.

A 3.9% reduction in EMC has shown to reduce particulate mass in emissions by more than 60%. Smaller particles (less than 0.03 μm) from incomplete combustion, which is responsible for PAH in exhaust gas and therefore scrubber wash water, are reduced by 73%.

A cleaner combustion means cleaner exhaust gases, producing less PM, PAH and black smoke to protect your post-combustion assets – so you can meet the challenges of tomorrow.

Fuel efficiency starts in the storage tank

Almost 2% of all HSFO bunkered globally is lost as sludge due to fuel instability, and this represents a significant loss of energy and contributes towards the cost of shipping as a whole. This does not include the associated costs related to handling and treating unstable fuels.

This is why we believe fleet efficiency starts in the storage tank, a principle that has driven us to continually develop the best technology to ensure that fuel remains stable, so that more of it makes it to the combustion chamber, creating less problems on the way and burning more effectively when there, resulting in increased fleet performance and reduced costs.

Octamar Complete has been used in millions of tonnes of bunkers globally to improve the quality of HSFO and mitigate the risks of using residual fuels. We take an evidence based approach to our work, and the trial below (one of many) demonstrates how selective chemical treatment gives real world benefits, reducing sludge on-board by over 60%, a fact that saves not only money, but makes life easier on board for our hard working seafarers.

Energy efficiency

If you consider fuel simply in terms of energy, it becomes clear that any improvement to fuel reliability and quality will quickly translate to an overall improvement in fleet performance. By reducing the volume of fuel wasted as sludge, keeping asphaltenes small and able to burn more completely, boosting the ECN of a fuel to reduce SFOC, and preventing post combustion deposits so that high performance machinery will run more efficiently and with less issues.

Ultimately you gain all the benefits of a higher-quality fuel, for a fraction of the investment when using our targeted chemistry.