Technical Q&A on the process section

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I. Basic Knowledge 1. What is pressure? What is pressure? Pressure is the force exerted perpendicularly by a fluid on the surface of an object. The pressure exerted on a unit area of a substance is called pressure. 2. What is gauge pressure? The value indicated by a pressure gauge used in engineering, that is, the pressure measured by the gauge, is called gauge pressure. 3. What is absolute pressure? The pressure actually exerted on the equipment and materials is defined as absolute pressure. When the pressure inside a container is lower than atmospheric pressure, that portion of sub-atmospheric pressure is referred to as vacuum. Vacuum can also be expressed as a percentage; this is what we call the degree of vacuum, which is determined by the measured height of the vacuum mercury column and then converted into a percentage. P_vacuum = P_atmospheric – P_absolute. 4. What is the relationship between absolute pressure, gauge pressure, and atmospheric pressure? P absolute = P gauge + P atmospheric. 5. What is the difference between the boiling point of oils and the boiling point of simple substances? Since oils are mixtures, their boiling point is a range of temperatures known as the boiling range. The boiling point of a simple substance is a temperature value. 6. How are pressure units converted? 1 standard atmosphere = 1.033 kgf/cm2 ≈ 760 mmHg = 1.033 mH2O = 101325 paskal = 0.1 Mpa. 7. What is density? The mass of oil per unit volume is called the density of the oil. Its unit is kilograms per cubic meter. 8. What is the standard density of petroleum products? The standard density of petroleum products refers to the density of these products at a standard temperature of 20°C, denoted as d20. 9. What is specific gravity? The ratio of the mass of the oil at temperature t℃ to the mass of an equal volume of pure water at 4℃ is called the specific gravity of the oil at t℃, denoted as d4t. It can also be expressed as the ratio of the density of the oil at t°C to the density of pure water at 4°C. In the International System of Units, specific gravity is called relative density. 10. What is the relationship between the specific gravity of oil and temperature? As the temperature rises, the oil expands due to heat, its volume increases, and its specific gravity decreases. Conversely, it increases. The specific gravity of oil at different temperatures can be calculated using the following formula: d4t = d420 – r • (t – 20). Explanation: d4t: the specific gravity of the oil at temperature t°C; d420: the specific gravity of the oil at 20°C; r: the correction coefficient, also known as the temperature coefficient, which can be found in tables. 11. What is the relationship between the specific gravity of oils and their composition? The specific gravity of homologs increases as the boiling point rises. When the boiling point range is the same, the greater the amount of aromatic hydrocarbons, the higher the specific gravity; the greater the amount of alkanes, the lower the specific gravity. 12. What is traffic? Flow rate refers to the amount of fluid that passes through the effective cross-sectional area of a pipe per unit of time. It is divided into volume flow rate and mass flow rate. When fluid flows through a pipeline, the volume of fluid that passes through any cross-section of the pipeline per unit of time is called volumetric flow rate, denoted by the symbol Vt, and its unit is cubic meters per second. The weight that passes through any cross-section of a pipeline per unit of time is called weight flow rate, denoted by the symbol Gt, and its unit is kilograms per second. The relationship between the two is: Gt = Vt • r, where r is the specific gravity of the fluid under operating conditions. 13. What is flow rate? Flow rate refers to the distance that a fluid travels in a unit of time. The unit is meters per second, commonly denoted by the symbol V. The relationship between flow rate and velocity is given by: V = Vt/A, where A is the cross-sectional area of the pipe. 14. What is heat enthalpy? Enthalpy refers to the amount of heat required to heat 1 kilogram of a substance from a reference temperature to t°C. When calculating the heat enthalpy of oil products, attention must be paid to the state in which the oil products are found. 15. What is specific heat? The amount of heat required to raise the temperature of a unit weight of a substance by one degree. There are specific heat at constant pressure and specific heat at constant volume, measured in kilocalories per kilogram·degree. In the International System of Units, the unit of specific heat is joules per kilogram·liter. 16. What are heat exchange, condensation, and cooling? Heat exchange refers to the transfer of heat between two media at different temperatures. Condensation refers to the process in which a substance changes from a gaseous or liquid state to a liquid or solid state. Cooling refers to the process by which an object’s temperature gradually decreases. 17. What is viscosity? When the molecules of the oil move relative to each other, a resistive force that opposes this motion arises within the oil (also known as internal friction), and this is referred to as viscosity. 18. How many ways are there to express viscosity? What is the unit? (1) Dynamic viscosity: It is the resistance generated when two liquid layers separated by 1 centimeter, with an area of 1 square centimeter, move relative to each other at a speed of 1 centimeter per second. It is also known as absolute viscosity. The unit is grams per centimeter•second. (2) Kinematic viscosity: The ratio of a liquid’s dynamic viscosity to its density. The unit is cm2/second. (3) Engler viscosity: At a certain temperature, it is the ratio of the time required for 200 milliliters of oil to flow through an Engler viscometer to the time required for the same volume of distilled water to flow at 20°C. Viscosity is an indicator used to evaluate the fluidity of oils. 19. What is the relationship between viscosity and temperature? Temperature has a significant impact on the viscosity of oils; as temperature rises, viscosity decreases. Conversely, the viscosity increases; when the temperature exceeds a certain value, the viscosity of the oil tends to stabilize at a constant level. 20. What are the reasons why oils lose their fluidity at low temperatures? (1) As the temperature drops, its viscosity increases, causing it to lose its fluidity. (2) Since the oil contains wax, as the temperature drops, the wax crystallizes and precipitates. The resulting wax forms a network-like structure that encloses the liquid oil, preventing it from being fluid. 21. What is the cloud point? The cloud point is the highest temperature at which, under test conditions, microparaffin crystals or ice crystals begin to form, causing the oil to become cloudy. 22. What is the freezing point? In the same instrument, after the cloud point is determined, cooling is continued until visible crystals begin to form in the oil; this temperature is known as the freezing point. 23. What is the freezing point? The freezing point of petroleum products is defined under specified test conditions: when the oil is cooled to a certain temperature in a test tube, and the tube is tilted at 45 degrees, if no movement of the liquid is observed after one minute, this phenomenon is known as freezing. The highest temperature at which this phenomenon occurs is referred to as the freezing point of the oil. 24. What is vaporization? The phenomenon in which a substance changes from a liquid state to a gaseous state is called vaporization. 25. What is evaporation? Evaporation is a phenomenon in which liquid molecules gradually turn into gas molecules at the surface of the liquid. 26. What is Enneberg distillation? Enneberg distillation is a process of gradual vaporization; it involves using an Enneberg flask to heat and evaporate the oil, followed by condensation, in order to separate out various fractions with different temperature ranges. 27. What is boiling? Boiling is a vaporization phenomenon that occurs on and within the surface of a liquid. 28. What is single vaporization? When a liquid mixture is heated, the vapor generated and the liquid remain in close contact. Once the temperature reaches a certain level, the vapor and liquid phases separate at once; this separation process is known as primary vaporization, or equilibrium evaporation. 29. What is gradual vaporization? In the absence of reflux, during the vaporization process, the vaporized gas is continuously removed for separation at all times. 30. What is the boiling point? The temperature at which a liquid begins to boil under certain conditions. The boiling point of a pure substance changes with external pressure; as the external pressure increases, the boiling point rises. The boiling point decreases as external pressure drops. 31. What is the relationship between the boiling point of a mixture and pressure? For liquid mixtures, boiling begins when the sum of the partial pressures of their components equals the external pressure. Since the partial pressures of each component vary depending on their concentration in the liquid phase, such mixtures do not have a fixed boiling point. They remain in a boiling state over the entire temperature range from the bubble point to the dew point, and the compositions of the vapor and liquid phases differ at different temperatures. 32. What is the dew point of a gas solution? At a certain system pressure, the temperature at which a liquid solution is heated until it just vaporizes completely, or a gas is cooled until the first droplets of liquid appear, and equilibrium is reached, is known as the dew point of that gas solution. 33. What is the bubble point of a gas solution? The temperature at which a liquid solution is heated, under a certain system pressure, to the point where the first bubble appears and equilibrium is reached, is known as the bubble point of that gas solution. 34. What is saturated vapor pressure? At a certain temperature, the pressure exerted by the vapor when the liquid is in equilibrium with its vapor above the surface is called the saturated vapor pressure, or simply vapor pressure. 35. What is the relationship between vapor pressure and temperature? The vapor pressure of a liquid with the same composition increases as the temperature rises. 36. What is the relationship between vapor pressure and composition? At a certain temperature, the heavier the oil fraction, the greater its vapor pressure. 37. What is superheated steam? Steam with a temperature higher than its saturation vapor temperature is called superheated steam. 38. What is the initial boiling point? The temperature of the vapor phase at the moment the first drop of liquid flows out during the heating and distillation of oil in an Enneberg distillation apparatus is called the initial boiling point. 39. What is the final boiling point? (The dry part) The highest temperature of the vapor phase reached at the end of the heating and distillation of oil in an Enneberg distillation apparatus is called the final boiling point. 40. What is the boiling range of petroleum products? In an Enneberg distillation apparatus, the temperature range of a petroleum product from its initial boiling point to its final boiling point is referred to as the boiling range of that petroleum product. 41. What is a fraction? The oil distilled within a certain temperature range is called a fraction. 42. What is distillate composition? The relationship between the distillation temperature and the amount of distillate (by volume) is called the fraction composition. 43. What is a characteristic factor? The characteristic factor (K) is an index that indicates the chemical properties of petroleum or petroleum products, and it is calculated using the following formula: K=1.216T1/3/d15.615.6. Where: K—is the characteristic factor of the petroleum or product. T—cube root average boiling point of oil or product (K). d—Proportion of oil or petroleum products. Characteristic factors can be used for the classification and evaluation of crude oil, as well as for determining other physical properties of oils, such as viscosity, latent heat of vaporization, and enthalpy. 44. What is octane rating? Octane number is a relative standard for measuring anti-knock performance, with the octane number of pure heptane set at zero and that of pure isooctane (2,2,4-trimethylpentane) set at 100. 45. What is MON? What is RON? What is the blast resistance index? The anti-knock property of gasoline is expressed by the octane rating. There are two methods for determining octane rating: the Motor Method (MON) and the Research Method (RON). The engine speeds used for these tests are 900 revolutions per minute and 600 revolutions per minute, respectively. The Motor Method octane rating indicates the anti-knock properties of gasoline at high engine speeds, while the Research Method octane rating indicates such properties at low engine speeds. Sometimes, the anti-knock index, which is the average of the values obtained from both the Research Method and Motor Method octane ratings, is used to represent the anti-knock performance. 46. What is residual carbon? The oil is placed in a carbon residue tester and heated in the absence of air; the polycyclic aromatic hydrocarbons, gum resins, and other substances present in the oil evaporate, decompose, and condense as a result of the heat. The scale-like black residue that remains after the combustion gases are expelled is known as carbon residue. It is often expressed as a weight percentage. The amount of residue mainly depends on the chemical composition of the oil. A high amount of residue indicates that the oil is prone to oxidation, leading to gum formation or carbon deposition. 47. What is saturated steam? The vapor on the surface of the liquid in a container, at a certain temperature, when there is gas-liquid equilibrium between the liquid and the gas above its surface. At this point, the number of molecules that evaporate from the liquid per unit time is equal to the number of molecules that return from the gas to the liquid surface; in other words, the number of molecules in the gas no longer increases, nor does the number of molecules in the liquid decrease. 48. What is crude oil? Natural petroleum is also known as crude oil. In terms of appearance, it is a flowing or semi-flowing viscous liquid ranging in color from light yellow to dark green, dark brown, and black; in terms of its elemental composition, it is a complex mixture made up of an extremely large number of compounds. 49. In terms of chemical composition, what elements are crude oil made up of? Crude oil is primarily composed of two elements: carbon (C) and hydrogen (H), forming a complex mixture mainly of hydrocarbon compounds, with carbon accounting for 83-87% and hydrogen accounting for 11-14% ； Secondly, there are sulfur-, nitrogen-, and oxygen-containing compounds formed by sulfur (S), nitrogen (N), and oxygen (O), as well as gelatinous asphalt-like substances ； They are composed of non-hydrocarbon compounds, with sulfur, nitrogen, and oxygen together accounting for 1–4% ； There are also trace amounts of heavy metal elements such as vanadium V, nickel Ni, sodium Na, copper Cu, iron Fe, and lead Pb, with concentrations in the PPM range; as well as trace amounts of non-metallic elements such as arsenic As, phosphorus P, and chlorine Cl, whose concentrations are also in the PPM or ppb range. 50. What are the patterns of hydrocarbon distribution in petroleum fractions? Gasoline fractions (at temperatures below 200°C) contain n-paraffins and isoparaffins with carbon chains of C5–C11, as well as monocyclic naphthenes and monocyclic aromatics. Diesel fractions (at temperatures of 200–350°C) contain n-paraffins and isoparaffins with carbon chains of C11–C20, along with monocyclic naphthenes and bicyclic serta tricyclic naphthenes ； as well as monocyclic, bicyclic, and tricyclic aromatic hydrocarbons ； The paraffin oil fraction (350–520°C) contains n-paraffins and isoparaffins with carbon numbers around C20–C36, as well as cycloparaffins with one, two, or more rings, and aromatic hydrocarbons.