Heavy fuel oil (HFO)

Heavy fuel oil (HFO) is a fuel with high viscosity and density that is used both in shipping and in energy production. It is produced as a residual oil during the distillation of crude oil and is often mixed with lighter fuels.

Definition
Heavy fuel oil is a collective term for fuels that are characterized by high viscosity and density. According to the MARPOL Convention, heavy fuel oil is defined as an oil with a density of more than 900 kg/m³ at 15°C or more than 180 mm²/s viscosity at 50°C and contains mainly heavy molecules such as long-chain hydrocarbons.

Background / Origin
Heavy oil is obtained as residual oil during crude oil distillation. The quality of the residual oil depends on the crude oil used. In order to achieve certain specifications, heavy fuel oil is often blended with lighter fuels such as marine gas oil or marine diesel. These blends are classified as Intermediate Fuel Oils (IFO) or Marine Diesel, with common types being IFO 180 and IFO 380 with viscosities of 180 mm²/s and 380 mm²/s respectively.

The international standard ISO 8217 categorizes marine fuels into distillate fuels and residual oils, whereby residual oils are referred to as heavy fuel oils. One exception is the quality grade RMA 10, which is no longer considered heavy fuel oil with a low heavy fuel oil content. According to ISO 8217, used oils and lubricating oils are not permitted as residue oils.

The sulphur content is an important aspect of heavy fuel oils, as it varies depending on the category. A maximum of 3.5 % sulphur content is permitted according to ISO 8217 in order to minimize environmental damage. The classes are High Sulfur Fuel Oil (HSFO), Low Sulfur Fuel Oil (LSFO) and Ultra Low Sulfur Fuel Oil (ULSFO).

Properties
The physical properties of heavy fuel oil include high viscosity and density. Heavy fuel oil is not pumpable at 20°C and must be heated to at least 40°C before use. At 15°C, HFO has a bitumen-like consistency.

The chemical composition consists mainly of heavier molecules. The main components are long-chain hydrocarbons and aromatics with branched side chains. Differences in quality result in particular from the sulphur content:

- High Sulfur Fuel Oil (HSFO): max. 3.5 % sulfur
- Low Sulfur Fuel Oil (LSFO): max. 1.0 % sulfur
- Ultra Low Sulfur Fuel Oil (ULSFO): max. 0.1 % sulfur

Application and importance in the market
Heavy fuel oil is primarily used as a marine fuel, especially in medium and low-speed diesel engines. Older steam locomotives and oil-fired power stations also use heavy fuel oil to generate energy.

The regulation of sulphur content in Emission Control Areas (ECA) has influenced the use of heavy fuel oil-based fuels. Since 2015, ships in these areas have only been allowed to emit emissions with a maximum sulphur content of 0.1 %. As a result, the importance of ULSFO has increased in these protected areas, while LSFO has become less important.

In regions where the use of heavier sulphur oils is required, scrubber technologies are used to reduce emissions, but allow the use of HSFO.

Differentiation from similar terms
- High Sulfur Fuel Oil (HSFO): Heavy fuel oils with a maximum sulphur content of 3.5%.
- Low Sulfur Fuel Oil (LSFO): Heavy fuel oils with less than 1% sulphur.
- Ultra Low Sulfur Fuel Oil (ULSFO): Heavy fuel oil with a sulphur content of less than 0.1%, often from marine gas oil.

Summary
Heavy fuel oil (HFO) is a highly viscous and dense fuel that is primarily used as a marine fuel. It is produced as a residual oil during crude oil distillation and can be prepared with lighter substances. The use of heavy fuel oil is increasingly influenced by legal regulations regarding sulphur content, which promote the use of ULSFO in Emission Control Areas. Heavy fuel oil is an important source of energy, but the different quality levels require careful attention to properties and standards.