Cleaner alternatives to heavy fuel oil

Industries are waking up to the reality of climate change, and oil-in-water emulsion fuels stand out as an immediate transition solution.

Jack Williams

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Article Summary

Often portrayed by its critics as the world’s dirtiest liquid fuel, heavy fuel oil (HFO or bunker fuel) is central to the environmental challenges faced by the global marine sector and regional power and industrial sectors. Widely available as leftovers from the oil refinery, this highly viscous, tar-like substance is so thick that it requires preheating to more than 100°C prior to combustion. Once combusted, HFO releases high levels of CO2, NOx, SO2, and particulate emissions.

When an HFO spill occurs, it requires toxic dispersants to dissipate and naturally solidifies to form difficult-to-remove tar balls, prolonging its impact on marine ecosystems and local economies. Despite the damaging effects on the environment, the IEA World Energy Outlook 2022 estimates that even if all aspirational climate targets announced by governments are met on time and in full, global HFO demand will remain significant at a projected 2.5 million barrels per day (b/d) by 2050 (IEA, 2022).

Why is HFO so fundamental to powering these sectors? HFO mostly comprises heavy refinery residue, such as vacuum residue, blended with lighter distillates to reduce viscosity and increase product value.  Nevertheless, the high sulphur variety sells at a discount to the crude oil used to produce it, and its attractive selling price is enough to ensure its continued utilisation.

One potential alternative to HFO is liquified natural gas (LNG); however, implementation of this fuel requires extensive infrastructural changes. The risk of methane slip and wild price fluctuations caused by external market factors such as the Ukraine War have highlighted its vulnerability as a long-term investment and solution to decarbonise.

Medium- and long-term solutions like green methanol, ammonia, and hydrogen show promise but are untested at large scale and have significant safety concerns. Questions remain over the supply of green variants of these fuels, which is a requirement for significant carbon reduction.

The marine, power, and industrial sectors require an immediate and proven alternative to HFO. Ideally, this solution must use existing infrastructure, be quick and safe to implement, and offer substantial CO2 and emission savings at a cost-competitive price. With oil-in-water (OIW) emulsions fuels, there is such a solution.

What are oil-in-water emulsion fuels?
As the name suggests, an OIW emulsion fuel combines two notoriously immiscible phases, oil and water, to create a stable fuel blend using a small amount of surfactants. Quadrise’s MSAR emulsion fuel combines 70% of the same heavy residues used to blend HFO with a 30% water phase (water and surfactant mixture), enhancing viscosity reduction while eliminating the need for valuable distillates, which can be sold by the refinery at a premium. For the end consumer, on an energy equivalent basis, it is a much cheaper fuel than HFO.

The manufacture of OIW emulsion fuels is simple. Heavy residue is taken from the refinery and blended in a high-shear colloid mill with a water phase stream. This process pre-atomises the heavy residue into 5-10 µm droplets and suspends them within the water phase. The pre-atomised droplets are far smaller than HFO droplets atomised within an engine (around 80 µm), which results in enhanced engine efficiency of up to 5% and a significant  reduction in black soot emission when burning the fuel, as the pre-atomised droplets combust almost completely, proportionately reducing fuel consumption and CO2 emissions.

The presence of water in the fuel reduces the temperature of combustion, decreasing NOx emissions by around 30%. Its lower viscosity also reduces the heating requirements for fuel storage and handling compared to HFO. If a high-discharge event were to occur, the fuel readily disperses in water, causing minimal damage to marine life.

A typical MSAR manufacturing unit (MMU) produces 1,000 million t/d of emulsion fuel and is supplied to a refinery in a modular 40 ft container. A previous MMU installation at a refinery in Spain (see Figure 1) took only nine months from design sign-off to production of fuel. Based on average ARA bunker prices from 2022, installation of a 1,000 million t/d MMU can save approximately $40 million/y from the liberation of valuable distillates, which can be shared between the refinery and the consumer, providing rapid payback time for the refinery and a cheaper fuel. By burning MSAR instead of HFO, the end user could save an estimated 37,000 million t/y of CO2 from engine efficiency benefits.

Quadrise has further developed the technology with its bioMSAR fuel, incorporating a renewable biocomponent within the emulsion fuel blend – waste-based glycerine. This is a non-toxic, biodegradable byproduct from the manufacture of biodiesel that is miscible with water. It is manufactured using the same emulsification technology as MSAR and comprises 50% residue or HFO, 40% glycerine, and 10% water with additives.

bioMSAR offers environmental benefits of more than  20% CO2 savings on a well-to-wake basis vs HFO, improved engine efficiency due to pre-atomisation of the oil phase, lower NOx and particulate emissions, and a significantly reduced risk from spillage as it is readily soluble in water. Similar to MSAR, it can be handled at ambient temperature (circa 20-30°C), reducing energy consumption, as HFO is typically heated to much higher temperatures to pump freely.

On a per-unit energy basis, bioMSAR is cheaper than LNG (see Figure 2) and provides superior well-to-wake CO2 reduction due to its high glycerine content. It requires little to no additional operational changes to burn in a diesel engine, unlike the high investment cost required to burn LNG. Finally, there is no concern for ‘methane slip’ as methane is not present within the fuel.

bioMSAR is also an effective alternative to used cooking oil methyl ester (UCOME)-based biodiesel blends such as B30. A CO2 equivalent bioMSAR blend is cheaper on a cost-per-unit energy basis, and testing has demonstrated no concern for microbial growth, which is a notable issue with biodiesel storage. Moreover, it qualifies for renewable credits in the EU, as crude glycerine is featured as an advanced renewable feedstock on the RED II Annex 9A list.

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