Introduction to Fuel Oil Types and Factors Affecting Their Quality

Fuel oil, a fossil fuel categorized as a heavy fuel oil, is obtained from the crude oil distillation process in various separation towers. Due to its high viscosity and density, its primary application lies in large industries and power plants as an energy source. Historically, the use of this heavy oil was limited to residential heating, but today, with the utilization of specialized furnaces, it can also be converted into diesel fuel and other petroleum products.

This substance, also known as “black oil” due to its dark color, is considered the heaviest commercial fuel derived from crude oil, whether through the distillation process or as a residue of this process. Fuel oil is essentially the heavier component of crude oil that remains in the refinery after lighter compounds such as gasoline and other lighter petroleum products have been separated.

The historical use of this heavy oil in cold regions like the former Soviet Union indicates that it was initially valued as a cheap and readily available heating fuel before the widespread development of more advanced refining technologies. This also suggests a correlation between a country’s level of industrial development and its reliance on this heavy oil compared to cleaner fuels. In other words, in less industrialized regions, this heavy oil was used due to its simpler processing. With technological advancements in Europe and America, these countries moved towards cracking this heavy oil to produce more valuable products like diesel fuel. This shift reflects a trend where reliance on this heavy oil decreases with technological progress and increasing environmental concerns.

The dual perception of fuel oil as a cheap fuel source and a significant pollutant creates a challenge in its use, especially in countries with older infrastructure or limited access to cleaner alternatives like natural gas. Studies highlight both the low price and the high pollution associated with this heavy oil. This indicates a trade-off between economic considerations and environmental impacts, which likely plays a key role in decisions regarding fuel usage policies.

Review of Fuel Oil Grade Types

Fuel oil is categorized based on various characteristics, the most important of which are viscosity and sulfur content.

Classification Based on Viscosity: Common types of fuel oil include M100, M180, M230, M280, and M380 (sometimes these specific “M” designations might be less common in general English usage, but are important for technical accuracy based on the original text). The numbers used in these grade names often refer to their kinematic viscosity in centistokes at 50 degrees Celsius. Generally, higher numbers indicate greater viscosity and density, consequently requiring preheating for use. For example, M380 fuel oil is heavier than M180 fuel oil. In Iran, the commonly produced grades include M180, M280, and M380.

The viscosity-based grading system directly affects how fuel oil is handled and applied. Higher viscosity grades require more energy for pumping and combustion processes, which may offset some of the economic benefits of their lower price. Thus, higher viscosity means the liquid is thicker, and thicker liquids require more force to move. This leads to higher energy consumption for pumping and potentially the use of specialized combustion equipment, ultimately increasing the overall cost and complexity of using these grades.

Classification Based on Sulfur Content:

Another determining factor in fuel oil grading is its sulfur content. Based on this, fuel oil is divided into the following categories:

• High Sulfur Fuel Oil: Contains 2 to 3.5 percent sulfur.
• Normal Sulfur Fuel Oil: Contains 1 to 2 percent sulfur.
• Low Sulfur Fuel Oil: Contains 0.5 to 1 percent sulfur.
• Very Low Sulfur Fuel Oil: Contains less than 0.5 percent sulfur.

The sulfur content in fuel oil depends on the original source of the crude oil. Fuel oil with lower sulfur content is generally of higher quality and more expensive due to its lower environmental impact and reduced equipment corrosion. Very low sulfur fuel oil is usually produced from feedstock with minimal sulfur content, and its production volume is very low, with less being exported.

Sulfur content is a fundamental differentiating factor in fuel oil grades, representing a trade-off between cost and environmental responsibility. Higher sulfur content makes it cheaper but significantly increases pollution. In fact, sulfur produces sulfur oxides when burned, which are major air pollutants and can lead to acid rain. Reducing sulfur content requires more complex processing, which increases costs. This creates a clear division in the market based on environmental regulations and consumer priorities. The existence of different sulfur grades indicates that although fuel oil is generally considered a low-quality fuel, efforts have been made to produce cleaner versions, although these may be less economically attractive or readily available. The classification based on different sulfur levels shows the existence of qualitative variations in fuel oil, and the “very low sulfur” grade demonstrates an attempt to mitigate its negative environmental effects, implicitly acknowledging these problems.

Other Classifications: Some classifications are based on density, with light (940-970 kg/m³) and heavy (970-985 kg/m³) categories. Historically, there were also classifications like No. 1, 2, 3, 4, 5, and 6, which often related to boiling point range and carbon chain length. Higher numbers generally corresponded to greater viscosity and lower prices. It is worth noting that No. 6 is essentially a type of heavy fuel oil. In marine applications, there are also bunker fuel classifications (Bunker A, B, C), with Bunker C often referring to heavy fuel oil.

Factors Affecting Fuel Oil Quality

The quality of fuel oil is influenced by several factors, the most important of which are:

Sulfur Content:

As mentioned earlier, sulfur content is a primary indicator of fuel oil quality. Lower sulfur content is more desirable due to reduced pollutants and equipment corrosion. The high sulfur content in Iranian-produced fuel oil (around 3.5 percent) is significantly higher than international standards for ship fuel in open waters (less than 0.5 percent), posing challenges for exports.

The discrepancy between the sulfur content of Iranian fuel oil and international standards indicates a potential competitive disadvantage in the global market and highlights the need for sulfur reduction technologies in Iranian refineries. Thus, if Iranian fuel oil does not meet international standards, its export potential to countries with stricter regulations or those equipped to further refine it is limited. This suggests a need for investment in desulfurization processes.

Viscosity:

Viscosity indicates a liquid’s resistance to flow. Higher viscosity requires preheating for handling and combustion. This property is measured in centistokes (cSt) at a specific temperature (usually 50 degrees Celsius). Viscosity affects the ease of pumping and the type of equipment needed to use fuel oil.

Viscosity is not only a grading factor but also a crucial operational consideration. Consumers must have the appropriate equipment and facilities to handle the specific viscosity grade of fuel oil they intend to use. Indeed, different viscosities require different pumping systems and combustion technologies, and choosing the wrong grade can lead to operational problems and equipment damage.

Density:

Density, defined as mass per unit volume, affects the amount of energy per unit volume and handling considerations. The density of fuel oil typically ranges from 940 to 985 kg/m³.

Flash Point:

The flash point is the lowest temperature at which the fuel vapor can form an ignitable mixture in air. For heavier grades, the flash point is usually around 65 degrees Celsius.

Pour Point:

The pour point is the lowest temperature at which the fuel can flow. Higher pour points can cause handling problems in cold weather.

Carbon Residue:

The amount of carbon residue after fuel evaporation and combustion indicates its tendency to form coke deposits.

Ash Content:

Non-combustible materials remaining after combustion, which can affect equipment performance and maintenance.

Heating Value:

The heating value is the amount of heat released during the combustion of a specific amount of fuel and indicates its energy content. For fuel oil, this value typically ranges from 38 to 42 megajoules per kilogram.

While fuel oil has a high heating value, making it energy-efficient, its other quality parameters, especially sulfur content, often outweigh this advantage in terms of environmental impact and operational costs. Indeed, the high heating value makes it attractive for power generation, but the environmental and equipment-related issues arising from its impurities mean that overall “quality” must consider more than just energy output.

The Place of Fuel Oil Among Petroleum Products

Fuel oil is obtained as a heavy cut in the crude oil refining process. After lighter petroleum products such as gases, naphtha, gasoline, and jet fuel (a type of kerosene) are separated, fuel oil remains. It is at the heavy end of the petroleum product spectrum, with only bitumen being a more condensed residue.

Fuel oil’s position in the crude oil distillation process explains its properties – as a residue, it naturally contains higher concentrations of heavier hydrocarbons and impurities like sulfur. Thus, the distillation process separates components based on boiling points, and fuel oil, due to its high boiling point, remains at the bottom, accumulating less volatile and often undesirable compounds.

Lighter cuts like kerosene and diesel fuel are distilled before fuel oil. Additionally, fuel oil can be further processed (cracked) to produce lighter and more valuable products like diesel fuel. Bitumen is the heaviest residue remaining after fuel oil extraction. In the refining process, after the removal of lighter fractions including fuel oil, the remaining substance is primarily bitumen, used for road paving and sealing. Some bitumen production methods also involve processing fuel oil.

The close relationship between fuel oil and bitumen suggests that the profitability of fuel oil as a fuel may be influenced by the demand and pricing of bitumen, especially if refineries have the flexibility to shift production based on market conditions. Thus, if bitumen prices are high, refineries may prefer to direct more of the heavier fractions towards bitumen production, potentially reducing the supply or increasing the price of fuel oil.

Base oil is another important petroleum product used in the production of lubricants. Base oil is typically extracted through more specialized refining processes than fuel oil, often involving solvent extraction or hydroprocessing. While both originate from crude oil, they serve different primary purposes.

Applications of Fuel Oil in Various Industries

Due to its specific characteristics, fuel oil has diverse applications in various industries:

Electricity Generation:

Fuel oil is widely used in thermal power plants for electricity generation. Its high heating value and relatively low price make it an attractive option for large-scale energy production. This application is particularly common in countries like Iran for heating boilers in power plants. However, burning fuel oil in power plants releases significant amounts of toxic substances into the air, contributing to air pollution.

The heavy reliance on fuel oil for electricity generation in some regions like Iran poses a significant environmental challenge, especially in urban areas where air quality is already a concern. This dependence is often due to economic factors and the availability of alternatives. Thus, news sources frequently mention the use of fuel oil in Iranian power plants and its contribution to air pollution, particularly in the winter season. This indicates a systemic problem where cleaner alternatives may be either too expensive or not available in sufficient quantities.

Steam Boilers and Industrial Furnaces:

Fuel oil is used as fuel in steam boilers and industrial furnaces to generate heat and steam for various manufacturing processes. It is also used in furnaces in industries such as cement and steel.

Marine Fuel (Bunker Fuel):

Due to its lower price compared to other marine fuels, fuel oil is a common fuel for ships. The term “bunker fuel” originates from coal bunkers where fuel was originally stored on ships.

Heating:

In the past, fuel oil was used for residential heating. Today, it is still used in some regions for heating buildings and in oil heating systems.

Petrochemical Industry:

Fuel oil can be used as a feedstock in the production of other petrochemical products.

Supply and Procurement of Petroleum Products in Iran

Overview of Petroleum Product Supply: Iran is a significant producer of various petroleum products, including liquefied gas, fuel oil, sulfur, coke, soot, lube cut, diesel fuel, kerosene, gasoline, and naphtha. The Ministry of Petroleum oversees the oil and gas sector, and several key companies are involved in production, refining, and distribution. These companies include the National Iranian Oil Company, the National Iranian Gas Company, the National Petrochemical Company of Iran, and the National Iranian Oil Refining and Distribution Company. The National Iranian Oil Refining and Distribution Company (NIORDC) manages the country’s refineries and the distribution of petroleum products within Iran. Iran aims to increase its refining capacity and the production of higher value-added petroleum products. The supply chain involves production by the National Iranian Oil Company, refining by private and semi-private companies, and transportation by the National Iranian Oil Refining and Distribution Company.

The structure of Iran’s oil and gas industry, with a strong government presence and a mix of state and private entities across different parts of the supply chain, likely influences the availability and pricing of fuel oil and other petroleum products. Thus, government policies, production quotas, and the efficiency of the distribution network all play a role in how easily and affordably fuel oil and related products can be procured.

Conclusion: Understanding Fuel Oil in the Energy Sector

Fuel oil, as a heavy and viscous fuel with a high heating value but significant sulfur content, plays an important role in the energy sector. Its primary applications are in electricity generation, industrial processes, and marine transportation. However, the combustion of fuel oil poses significant environmental concerns, particularly due to sulfur emissions that contribute to air pollution. In Iran, fuel oil has a specific place among petroleum products and has close ties to bitumen, kerosene, diesel fuel, and base oil. Despite the global trend towards cleaner energy sources, fuel oil remains important in regions with existing infrastructure and economic considerations, particularly in Iran. Understanding the characteristics, types, and factors affecting the quality of fuel oil is essential for energy industry stakeholders and policymakers in this field.