What is the difference between #1 and #2 fuel oil?

Heavy fuel oil (HFO), also known as fuel oil, is the residual heavy oil left after gasoline and diesel are extracted from crude oil. It is a dark black liquid characterized by large molecular weight, high viscosity, and low volatility. Its main components are hydrocarbons, and it also contains 0.1% to 4% sulfur as well as trace amounts of nitrogen, oxygen, and inorganic compounds, with a calorific value of approximately 10,000-11,000 kcal/kg (or 40,000-42,000 kJ/kg). Heavy fuel oil is usually blended from raw materials such as atmospheric residue, vacuum residue, and cracked residue in the crude oil refining process. Some heavy oils with a specific gravity exceeding 0.91 have extremely high viscosity, contain large amounts of nitrogen, sulfur, wax, and metals, and are essentially non-flowable. During extraction, heat injection (such as steam or hot water) or solvents are required to increase their fluidity. It was once widely used in large steam turbine boilers, medium- and large-sized ship engines, as well as blast furnace injection and heating furnace ignition roasting in steel plants. Due to its high combustion temperature and strong radiation capacity, it is a high-quality industrial fuel. However, with increasingly stringent environmental requirements and technological advancements, heavy oil boilers have been gradually phased out. Currently, it is mostly used as ignition fuel for modern large-scale coal-fired boilers or processed into other chemical raw materials. The global recoverable reserves of heavy oil and oil sands are about 400 billion tons, which is 2.7 times that of conventional crude oil, indicating significant resource potential. However, its processing is challenging and inefficient, requiring specialized technologies to remove impurities and enhance economic value.

Light fuel oil is an oil product with a low boiling point (usually below 200°C), low density (e.g., naphtha at 0.65-0.75 g/cm³), low viscosity, good fluidity, and high volatility. It primarily consists of low-molecular-weight hydrocarbons (5-12 carbon atoms) and has low impurity content (e.g., low sulfur). Common types include gasoline, diesel, kerosene, and naphtha. Gasoline is mainly used in automobile internal combustion engines, diesel is suitable for truck and bus diesel engines, while naphtha serves as an important chemical feedstock for producing ethylene, fertilizers, or blended gasoline products. Heavy fuel oil is the residual heavy oil remaining after light oil extraction from crude oil. It has a high boiling point (typically above 200°C, sometimes exceeding 350°C), high density (0.82-0.95 g/cm³), high viscosity, poor fluidity, and low volatility. Composed mainly of high-molecular-weight hydrocarbons (over 20 carbon atoms), it contains more impurities such as sulfur. Common types include residual oil and fuel oil, primarily used in power plant boilers, industrial furnaces, and marine medium/low-speed engines. Some high-viscosity heavy oils require preheating to improve fluidity before use. Regarding processing, crude oil undergoes distillation to separate light oil first, with heavy oil further processed through methods like catalytic cracking to extract additional light oil products. Environmentally, light oil combustion generates fewer pollutants, whereas heavy oil combustion produces relatively higher emissions. However, environmentally compliant products like low-sulfur heavy oil are now available.

Examples of heavy oil include fuel oils blended from feedstocks such as vacuum residue, cracked residue, cracked diesel, catalytic diesel, etc., as well as heavy oils with a specific gravity exceeding 0.91, bituminous sands, and the like. Heavy oil is characterized by large molecular weight and high viscosity, with abundant combustible components: it contains 86% to 89% carbon and 10% to 12% hydrogen, and its calorific value can reach 40,000 to 42,000 kilojoules per kilogram. It has a high combustion temperature and strong flame radiation capacity, making it commonly used as a high-quality fuel in steel production, and it can also serve as fuel for heavy low-speed diesel engines in power applications such as shipping and power generation.

Heavy grade oil is a type of lubricating oil product with a relatively high viscosity grade and excellent oil film strength, typically formulated with highly refined base oils and additives that possess thermal stability and anti-emulsification properties. This type of oil offers outstanding anti-wear performance, rust and corrosion protection (including resistance to saltwater corrosion), as well as a high viscosity index. It maintains stable oil film thickness across varying temperatures while reducing power loss during equipment startup. With broad application scope, it is suitable for industrial circulation systems such as steam and hydraulic turbines, as well as mechanical components requiring general or intermittent lubrication, including enclosed gears, sliding and anti-friction bearings. It effectively withstands demanding operating conditions like high loads and elevated temperatures, extending equipment service life and lowering maintenance costs. Additionally, heavy grade oil exhibits excellent air release and water separation characteristics, preventing operational issues caused by oil emulsification or air entrainment, making it an optimal choice for lubricating industrial equipment and certain heavy machinery.

Fuel oil can mainly be divided into three types: light fuel oil, heavy fuel oil, and marine fuel oil. Light fuel oil has low viscosity and good fluidity, making it suitable for light-load mechanical equipment and small generator sets, and it is also widely used in automobiles, aviation and other fields. Heavy fuel oil has high calorific value and high viscosity, and is often used in heavy-load machinery and large-scale power generation equipment; some can also be used as raw materials for refining and processing. Marine fuel oil is fuel specially designed for ships, which needs to meet the requirements of engines with different speeds. For example, low-speed diesel engines are compatible with high-viscosity fuel oil, and with the advancement of environmental protection policies, the market share of low-sulfur marine fuel oil is gradually increasing. These types of fuel oil are classified according to standards such as physical properties and uses, and each plays a different role in the energy supply system, providing power support for transportation, industrial production and other fields.