Mazut is a heavy oil hydrocarbon produced during the refining of crude oil, following naphtha, gasoline, and kerosene. Due to its dark color, it’s also known as “black oil.” This fuels is inexpensive and suitable for furnaces, boilers, bakery ovens, diesel engines, and certain power plants. Mazut is also referred to as heavy oil, marine oil, or mazut. It is produced as a distillation residue from crude oil refining.

In general, mazut is a liquid fuel used in boilers or furnaces to generate heat or in engines to produce power, excluding fuels with a flash point of 42°C or those used in certain burners. It is made from long-chain hydrocarbons, primarily alkanes, cycloalkanes, and aromatics. The term “gas fuel” is more strictly applied to industrial fuels derived from crude oil that are heavier than naphtha and gasoline. Lighter molecules like propane, naphtha, and gasoline are used in cars, while jet fuel, which has a lower boiling point, is obtained and separated in the early stages of distillation.

Heavy oil products like diesel and lubricating oils have lower volatility and are separated more slowly in the distillation process. Meanwhile, bunker fuel is located at the bottom of the distillation column. Heavier products like black carbon and bitumen remain as residues, which are used for road asphalt and roof insulation.

Mazut is composed of heavy oil fractions from distillation residues, adjusted with lighter fractions to modify viscosity. The composition of hydrocarbons gives it a suitable heating value, and the metal content doesn’t cause problems in the consuming systems.

Types of Mazut

Mazut comes in various types, categorized based on different characteristics. Some of the most important classifications are:

Based on Sulfur Content
The primary classification of mazut is based on its sulfur content. Sulfur can cause air pollution and equipment corrosion. Therefore, mazut with lower sulfur content is considered more refined and expensive. The types of mazut based on sulfur content are:

• Mazut with very low sulfur: Less than 0.5% sulfur
• Mazut with low sulfur: Between 0.5% and 1% sulfur
• Mazut with medium sulfur: Between 1% and 2% sulfur
• Mazut with high sulfur: Between 2% and 3.5% sulfur

Based on Viscosity
Viscosity refers to the resistance of a liquid to flow. Mazut with higher viscosity is thicker and requires heating for transport and combustion. Mazut is often classified by numbers such as 100, 180, 230, 280, and 380, indicating different levels of viscosity. For example:

• Mazut M100: Has lower viscosity and flows easily.
• Mazut M380: Has high viscosity and requires heating for use.

Applications of Mazut
Mazut is used for heating homes, commercial and industrial centers, and as fuel for trucks, ships, and certain vehicles. However, it is more polluting and expensive compared to natural gas. It is often used as a backup fuel for power plants during peak consumption periods or as a common fuel for small electricity generators, especially when natural gas is unavailable.

In Europe, diesel is primarily used for cars (40%), trucks and buses (over 99%), and SUVs (over 90%). Heating oil for homes and thermal pumps is also used, especially in regions like the northeastern U.S.

Mazut Residue
Mazut residue is less useful and very viscous, requiring a special heating system for use, and may produce high levels of pollutants such as sulfur oxides upon combustion. Despite its undesirable features, it is cheaper, as it requires substantial heating before use. In fact, it is the cheapest liquid fuel available.

Mazut residue from distillation columns cannot be used in road vehicles, boats, or small ships due to the need for complex heating systems and space constraints. However, it is practical and feasible in large power plants or ships, where the equipment required to heat the fuel can be installed.

Historical Use
In the past, mazut residue was commonly used in steam-powered locomotives, steam boilers, and ships. Today, locomotives are powered by diesel or electricity, and steamships are no longer common due to high operational costs. Many LNG carriers use steam power plants, utilizing exhaust gases from cargo to fuel their operations.

Current Usage
Today, many buildings, especially in New York, still use mazut for heating. In 2011, it was estimated that buildings using fuel numbers 4 and 6 were responsible for 86% of soot production in the city’s buildings. Due to the health impacts of fine soot particles, New York has phased out the use and production of these fuels under urban environmental programs. As a result, all buildings were required to replace fuel number 6 by the end of 2015. The use of mazut in power plants has also decreased due to price competition with natural gas and environmental restrictions.

For power plants, the cost of heating mazut, pollution control, and additional maintenance after combustion are more significant than the low cost of the fuel itself. Burning mazut, especially mazut residue, releases more carbon dioxide than natural gas.

Heavy Mazut
Heavy mazut is still used in steam boilers for the equipment needed to start up power plants that use coal as fuel. This is similar to using small wood logs to start a fire.

The main issue with using mazut residue is its high viscosity, particularly in mazut number 6, which requires an engineered combustion system for proper storage, pumping, and combustion. While lighter than water (with a specific gravity of 0.95 to 1.03), it is much thicker and heavier than mazut number 2, kerosene, or gasoline.

Mazut number 6 must be stored at 38°C and heated to 65-120°C before it can be pumped easily. At lower temperatures, it can become semi-solid and cloudy. The flashpoint of most number 6 mazut compounds is around 65°C. Attempts to pump high-viscosity mazut are the primary cause of damage to pipelines, furnaces, and related equipment, which are typically designed for low-viscosity fuels.