Fuel oil is a kind of refined oil, which is widely used in power plant power generation, ship boiler fuel, heating furnace fuel, metallurgical furnace and other industrial furnace fuels. Fuel oil is mainly composed of petroleum pyrolysis residue and straight-run residue, which is characterized by high viscosity and contains many non-hydrocarbon compounds, resins and asphaltenes.
(1) viscosity
Viscosity is the most important performance index of fuel oil and the main basis for classifying fuel oil grades. It is a measure of fluidity impedance, and its size indicates the fluidity, pumpability and atomization performance of fuel. For high viscosity fuel oil, it is generally necessary to preheat to reduce the viscosity to a certain extent, and then enter the burner to facilitate spray atomization at the nozzle. There are many methods to measure viscosity. Redwood viscosity is commonly used in Britain, Cyberport viscosity is commonly used in the United States, and engler viscosity is commonly used in continental Europe. The kinematic viscosity is more widely used in various countries because of its higher determination accuracy than the above methods, less sample consumption and rapid determination. The conversion between various viscosities can usually be approximated by a pre-made conversion table.
At present, 40°C kinematic viscosity (distillate fuel oil) and100 C kinematic viscosity (residual fuel oil) are commonly used in China. In the past, engler viscosity (80 C,100 C) was used as the quality control index in China's fuel oil industry standard, and brands were classified by 80 C kinematic viscosity. The kinematic viscosity of oil is the ratio of dynamic viscosity to density of oil. The unit of kinematic viscosity is Stokes, or Stokes for short. When the dynamic viscosity of the fluid is 1 poise and the density is 1g/cm3, the kinematic viscosity is 1 stokes. CST is the abbreviation of Centistokes, which means Liz, that is, 1 stokes 1%.
(2) Sulfur content
Excessive sulfur content in fuel oil will cause corrosion of metal equipment and environmental pollution. According to the sulfur content, fuel oil can be divided into high sulfur, medium sulfur and low sulfur fuel oil. Besides carbon and hydrogen, sulfur is the third main component of petroleum. Although it is much lower than the first two, its content is still an important index. According to the sulfur content, fuel oil is generally divided into low sulfur (LSFO) and high sulfur (HSFO). The sulfur content of the former is below 1%, while the latter usually reaches 3.5% or even 4.5%. There is also low wax oil (LSWR), which has high wax content and high pour point (such as 40 ~ 50℃). High sulfur fuel oil (HSFO) is traded in Shanghai Futures Exchange.
(3) Density
It is the mass ratio of petroleum products to specific products. Common units-gram/cubic centimeter, kilogram/cubic meter or kilogram/cubic meter, etc. Because volume changes with temperature, density cannot exist independently without temperature. For comparison, the density at15 C is defined as the standard density of western petroleum.
(4) Flash point
It is an indicator of oil security. Petroleum products are heated to a certain temperature under certain standard conditions, so the steam escaping from their surfaces is just enough to form a combustible mixture with the surrounding air. When it comes into contact with the standard test fire source, it will cause instantaneous flash, and the temperature of the oil is defined as its flash point. Its characteristic is that the flame is extinguished instantly, and the oil reaching the flash point temperature cannot provide enough flammable vapor to maintain continuous combustion. Only when it is heated again and reaches another higher temperature, once it encounters a fire source, it will constitute continuous combustion, and the temperature at this time is called ignition point or ignition point. Even so, the flash point is enough to characterize the danger degree of an oil product, and it is customary to classify dangerous goods according to the flash point. Obviously, the lower the flash point, the more dangerous it is, and the higher it is, the safer it is.
(5) Moisture
The existence of water will affect the freezing point of fuel, and with the increase of water content, the freezing point of fuel will gradually increase. In addition, moisture will also affect the combustion performance of fuel machinery, which may cause accidents such as flameout and shutdown.
(6) Ash content
Ash is the residual non-combustible part after combustion, especially after FCC circulating oil and slurry oil penetrate into fuel oil, the silica-alumina catalyst powder will accelerate the wear of pumps and valves. In addition, ash will cover the heating surface of the boiler and make the heat transfer worse.
(7) Mechanical impurities
Mechanical impurities will block the filter screen, resulting in oil pump wear and nozzle blockage, affecting normal combustion.