Firstly, crude oil is divided into different straight-run distillate oils according to the boiling point requirements of different products, and then non-ideal components in these distillate oils are removed according to the quality standards of products;
② Through chemical reaction and transformation, the required components are generated, and then a series of qualified petroleum products are obtained.
Common technological processes in petroleum refining and chemical industry include atmospheric and vacuum distillation, catalytic cracking, delayed coking, hydrocracking, solvent deasphalting, hydrofining and catalytic reforming.
I. Atmospheric and vacuum distillation
1. Raw materials: crude oil, etc.
2. Main products: naphtha, gas oil, residual oil, asphalt and vacuum line.
3. Basic concepts
Atmospheric and vacuum distillation is a combination of atmospheric distillation and vacuum distillation, which is basically a physical process: raw oil is divided into oils with different boiling points (called fractions) in the distillation column according to its evaporation ability. Some of these oils are blended with additives in the form of products before leaving the factory, and a considerable part of them are raw materials for subsequent processing devices.
Atmospheric and vacuum distillation is the first process of petroleum processing in refineries, which is called crude oil primary processing, and includes three processes: a. crude oil desalination and dehydration; B. atmospheric distillation; Vacuum distillation.
4. Production technology
Crude oil usually contains salt and water, which will lead to corrosion of equipment. Therefore, before crude oil enters atmospheric and vacuum distillation, it must be desalted and dehydrated first, and demulsifier and water are usually added.
Crude oil passes through a flowmeter, a heat exchange part and a distillation tower to form two parts. Part of the tower top oil passes through the cooler and flowmeter, and finally enters the tank farm. This part is chemical light oil (so-called naphtha). One part forms the bottom oil, and then enters the atmospheric furnace and the atmospheric tower through the heat exchange part, forming three parts, one part is diesel oil, the other part is wax oil and the other part is bottom oil; The remaining base oil is further processed by vacuum furnace and vacuum tower to generate vacuum line, wax oil, residual oil and asphalt.
Their respective yields: naphtha (light gasoline or chemical light oil) accounts for about 1%, diesel oil accounts for about 20%, wax oil accounts for about 30%, residual oil and asphalt account for about 42%, and vacuum line accounts for about 5%.
The atmospheric and vacuum distillation process does not produce gasoline products, in which wax oil and residual oil enter the catalytic cracking process to produce refined oil such as gasoline, diesel oil and kerosene; Naphtha is directly sold to other small enterprises to produce solvent oil or enter the next step of deep processing, usually catalytic reforming to produce solvent oil or extract extracted compounds; Lubricating oil can be directly adjusted by reducing the first line.
Second, _ catalytic cracking
After atmospheric and vacuum distillation, only 10 ~ 40% of light oil products such as gasoline, kerosene and diesel oil can be obtained, and the rest are heavy distillate oil and residual oil. In order to get more light oil products, it is necessary to carry out secondary processing on heavy fractions and residual oil. Catalytic cracking is the most commonly used production process for producing gasoline and diesel, and gasoline and diesel are mainly produced by this process. This is also the most important production link of general petroleum refining and chemical enterprises.
1. Raw materials
Residue and wax oil account for about 70%. Catalytic cracking generally takes vacuum distillate oil and coker wax oil as raw materials. However, with the increase of crude oil weight and the demand for light oil, most petrochemical enterprises began to add vacuum residue to their raw materials, and even directly used atmospheric residue as refining raw materials.
2. Products
Gasoline, diesel oil, slurry oil (heavy fraction oil), liquid propylene, liquefied gas; Their respective proportions are gasoline 42%, diesel oil 2 1.5%, propylene 5.8%, liquefied gas 8% and slurry oil 12%.
3. Basic concepts
Catalytic cracking is the main process of converting heavy oil (such as residual oil) into light oil (gasoline, kerosene, diesel oil) in the presence of catalyst, and it is the main secondary processing means in oil refining. Belonging to chemical processing technology.
4. Production technology
Normal residual oil and wax oil enter the riser, settler and regenerator through the feed oil buffer tank to form oil and gas, and then enter the fractionator.
Part of the oil and gas enters the crude gasoline tower, absorption tower and air compressor, enters the condensate tank, passes through the re-absorption tower and stabilization tower, and finally is refined to produce gasoline.
Part of the oil and gas enters the diesel stripper through the fractionator, and then the diesel oil is refined to produce diesel oil. Part of the oil and gas enters the slurry circulation through the fractionator, and finally the slurry is produced.
Part of the oil and gas enters the liquid hydrocarbon buffer tank through a fractionator, passes through a desulfurization adsorption tank, a sand filter tower, a water washing tank, a desulfurization alcohol extraction tower, a pre-alkali washing tank, an amine liquid recoverer, a desulfurization extraction tower and a buffer tower, and finally enters the liquid hydrocarbon tank to form liquefied gas.
Part of the oil and gas enters the depropanizer, reflux tower, deethanizer, propylene refining tower and reflux tank through the liquid hydrocarbon buffer tank, and finally enters the propylene zone spherical tank to form liquid propylene. Liquid propylene is further processed in polypropylene workshop to produce polypropylene.
Third, delayed coking.
Coking (coking for short) is a deep pyrolysis process and one of the means to treat residual oil. It is the only process that can produce petroleum coke, and no other process can replace it. In particular, the special demand for high-quality petroleum coke in some industries makes coking process always occupy an important position in the oil refining industry.
1. Raw materials
Delayed coking is a decarbonization process similar to catalytic cracking to change the hydrocarbon ratio of petroleum. The raw materials for delayed coking can be heavy oil, residual oil or even asphalt, and the quality requirements for raw materials are relatively low. The main conversion processes of residual oil are delayed coking and hydrocracking.
2. Products
The main products are wax oil, diesel oil, coke, crude gasoline and some gases, and their respective proportions are: wax oil accounts for 23-33%, diesel oil accounts for 22-29%, coke 15-25%, crude gasoline 8- 16%, gas 7- 10%.
3. Basic concepts
Coking is a deep thermal cracking reaction at high temperature (400 ~ 500℃) with hydrogen-poor heavy residue (such as vacuum residue, cracked residue and asphalt) as raw materials. Through cracking reaction, a part of residual oil is converted into gaseous hydrocarbons and light oil products; Due to the condensation reaction, another part of the residual oil is converted into coke. On the one hand, because the raw materials are heavy and contain a considerable amount of aromatic hydrocarbons, on the other hand, the reaction conditions of coking are more harsh, so the condensation reaction accounts for a large proportion and produces more coke.
4. Production technology
The production process of delayed coking unit is divided into two parts: coking and decoking. Coking is a continuous operation and decoking is an intermittent operation. Because industrial plants are generally equipped with two or four coke towers, the whole production process is still continuous.
Crude oil preheating. Coking feedstock (vacuum residue) first enters the feedstock buffer tank, and then is pumped into the convection section of the heating furnace to raise the temperature to about 340~350℃.
The preheated crude oil enters the bottom of the fractionator and exchanges heat with the oil and gas produced by the coke tower in the fractionator (the bottom temperature of the tower does not exceed 400℃).
Raw oil and circulating oil are pumped from the bottom of the fractionator, pumped into the radiation section of the heating furnace by hot oil pump, heated to the temperature required for coking reaction (about 500℃), and then enter the coke tower from the lower part through the four-way valve for coking reaction.
Raw materials react in the coke tower to generate coke, which accumulates in the coke tower. Oil and gas come out from the top of the coke tower and enter the fractionator. After heat exchange with raw oil, gas, gasoline, diesel oil and wax oil are obtained by fractionation. The circulating oil at the bottom of the tower carries out coking reaction with raw materials.
Four. hydrogen cracking
The basic principle of heavy oil lightening is to change the relative molecular weight and hydrogen-carbon ratio of oil products, which are often changed at the same time. There are two ways to change the hydrogen-carbon ratio of oil products, one is decarbonization and the other is hydrogenation.
1. Raw materials: heavy oil, etc.
2. Products: light oil (gasoline, kerosene, diesel oil or raw materials for producing olefins by catalytic cracking and cracking).
3. Basic concepts
Hydrocracking belongs to the hydrogenation route of petroleum processing, which is to add hydrogen from outside in the presence of catalyst to improve the hydrogen-carbon ratio of oil products.
In essence, hydrocracking is an organic combination of hydrogenation and catalytic cracking. On the one hand, heavy oil products can be converted into light oil products such as gasoline, kerosene and diesel oil through cracking reaction, on the other hand, a large amount of coke can be avoided like catalytic cracking, and impurities such as sulfur, chlorine and oxygen compounds in raw materials can be removed through hydrogenation to saturate olefins.
4. Production process
According to the different states of the catalyst in the reactor, it can be divided into fixed bed, boiling bed and suspended bed.
(1) fixed bed hydrocracking
Fixed bed means that granular catalyst is placed in the reactor to form a static catalyst bed. Raw oil and hydrogen enter the reaction system after heating and boosting to reach the reaction conditions, and are hydrotreated to remove sulfur, nitrogen and oxygen impurities and diolefins, and then hydrocracking. After the reaction product is cooled, separated, decompressed and fractionated, the target product is sent out of the device, and the gas with high hydrogen content (80% and 90%) is separated as circulating hydrogen.
Unconverted oil (called tail oil) can be partially recycled, completely recycled or not recycled at one time.
(2) boiling bed hydrocracking
Boiling bed (also called expanded bed) process is to drive the catalyst with a certain particle size to move by means of fluid velocity to form a gas, liquid and solid three-phase bed, so that hydrogen, raw oil and catalyst can fully contact and complete the hydrogenation reaction process.
Fluidized bed process can treat raw materials with high metal content and carbon residue value (such as vacuum residue) and can deeply convert heavy oil; But the reaction temperature is higher, generally in the range of 400~450℃.
This process is complicated and has not been industrialized in China.
(3) Suspension bed (slurry bed) hydrogenation process
Suspended bed process is a kind of hydrogenation process that attracts much attention in order to adapt to very inferior raw materials. Its principle is similar to that of boiling bed. The basic process is that the fine powder catalyst is premixed with raw materials, and then flows into the reactor from bottom to top with hydrogen. The catalyst is suspended in the liquid phase for hydrocracking reaction, and the catalyst flows out from the top of the reactor together with the reaction products.
The device can process all kinds of heavy crude oil and common crude oil residue, but the investment of the device is large. At present, this technology is still in the research and development stage in China.
V _ solvent deasphalting
Solvent deasphalting is the pretreatment process of inferior residual oil. A petroleum product refining process in which gum and pitch are removed from vacuum residue (sometimes atmospheric residue) obtained from crude oil distillation by extraction to prepare deasphalted oil and produce petroleum pitch.
1. Raw material: heavy oil such as vacuum residue or atmospheric residue.
2. Products: deasphalted oil, etc.
3. Basic concepts
Solvent deasphalting is a petroleum refining process for processing heavy oil. The process takes heavy oil such as vacuum residue as raw material and hydrocarbons such as propane and butane as solvents for extraction. The extracted deasphalted oil can be used as heavy lubricating oil raw material or cracking raw material, and the deasphalted raffinate oil can be used as road asphalt or other purposes.
4. Production process
Include extraction and solvent recovery. The extraction part generally adopts primary extraction process or secondary extraction process.
Propane in asphalt and heavy deasphalted oil solution is less, so propane is recovered by one-time evaporation stripping, while propane in light deasphalted oil solution is more, so propane is recovered by multi-effect evaporation stripping or critical recovery stripping, which reduces energy consumption.
In the critical recovery process, the light deasphalted oil and most propane are separated in the critical tower by using the property that the solubility of propane in oil is close to the minimum and the density is close to the minimum under the conditions of near critical temperature and slightly higher critical pressure (the critical temperature of propane is 96.8℃ and the critical pressure is 4.2MPa), thus avoiding the evaporation and condensation process of propane, thus reducing energy consumption to a greater extent.
Domestic solvent deasphalting processes mainly include settling two-stage deasphalting process, critical recovery deasphalting process and supercritical extraction solvent deasphalting process.
(1) Two-stage Deasphalting Process by Settling Method
Two-stage deasphalting by sedimentation method is developed on the basis of conventional one-stage deasphalting. On the basis of studying the unique properties of Daqing vacuum residue, it is pointed out that conventional propane deasphalting can not make full use of this resource, and a new deasphalting process is developed.
(2) Critical recovery deasphalting process
With the increase of temperature, the solubility of solvent in oil decreases. When the temperature and pressure are close to critical conditions, the solubility of solvent in oil drops to a very low level. At this time, the propane solvent can be directly recovered after cooling without evaporation.
(3) Deasphalting process of supercritical extraction solvent
Supercritical fluid extraction (SFE) is a technology that utilizes the abnormal phase equilibrium and thermodynamic properties of the extraction system near the critical zone, and changes the parameters such as temperature and pressure to drastically change the mutual solubility of the components in the system, thus realizing the separation of components.
Six, hydrofining
Hydrorefining generally refers to the reprocessing of some petroleum products that can not meet the requirements of use through hydrogenation process, so that they can reach the specified performance indicators.
1. Refining raw materials: gasoline, diesel oil, kerosene, lubricating oil, petroleum wax, etc. Contains more harmful impurities, such as sulfur, oxygen and nitrogen.
2. Refined products: refined and upgraded gasoline, diesel, kerosene, lubricating oil, petroleum wax and other products.
3. Basic concepts
Hydrorefining process is a general term for catalytic upgrading of various oils under hydrogen pressure. It means that various non-hydrocarbon compounds in oil products undergo hydrogenolysis reaction at a certain temperature and pressure in the presence of catalyst and hydrogen, and then are removed from oil products to achieve the purpose of refining oil products.
Hydrorefining is mainly used for refining products, and its main purpose is to improve the performance of oil products through refining.
4. Production process
Hydrorefining process generally includes three parts: reaction system, heat exchange of generated oil, cooling, separation system and circulating hydrogen system.
reaction system
Raw oil is mixed with fresh hydrogen and circulating hydrogen, and after exchanging heat with reaction products, it enters the heating furnace in a gas-liquid mixed state (this way is called mixed hydrogen in front of the furnace), and enters the reactor after being heated to the reaction temperature.
The reactor feed can be gas phase (when refining gasoline) or gas-liquid mixed phase (when refining diesel oil or petroleum products heavier than diesel oil). The catalyst in the reactor is usually packed in layers to facilitate the injection of cold hydrogen to control the reaction temperature. The mixture of circulating hydrogen and oil material is hydrogenated through each catalyst bed.
Heat exchange cooling separation system for generated oil
The reaction products come out from the bottom of the reactor and enter the high pressure separator after heat exchange and cooling.
Before the cooler, high-pressure washing water should be injected into the product to dissolve ammonia and part of hydrogen sulfide produced by the reaction.
The reaction product is subjected to oil-gas separation in a high-pressure separator, and the separated gas is circulating hydrogen, in which there are a small amount of gaseous hydrocarbons (non-condensable gas) and water-insoluble hydrogen sulfide besides the main component hydrogen; The separated liquid product is hydrogenated oil, in which a small amount of gaseous hydrocarbons and hydrogen sulfide are dissolved;
After depressurization, the generated oil enters a low-pressure separator to further separate out gaseous hydrocarbons and other components, and the product is separated into qualified products by a fractionation system.
Circulating hydrogen system
After the circulating hydrogen separated from the high-pressure separator passes through the storage tank and the circulating hydrogen compressor, a small part (about 30%) directly enters the reactor as cold hydrogen, and most of the rest is distributed and mixed with raw oil for recycling in the device. In order to ensure the purity of circulating hydrogen and avoid the accumulation of hydrogen sulfide in the system, hydrogen sulfide recovery system is usually adopted. Generally, ethanolamine is used to absorb and remove hydrogen sulfide, and the rich liquid (absorption liquid) is regenerated and recycled. The desorbed hydrogen sulfide is sent to a sulfur production unit to recover sulfur, and the purified hydrogen is recycled.
Seven, catalytic reforming
1. Main raw materials
Naphtha (light gasoline, chemical light oil, stable light oil) is generally produced in refineries, and sometimes it can also be produced in stable stations of oil production plants. Good quality naphtha has a low sulfur content and a color close to colorless.
2. Main products
High octane gasoline, benzene, toluene, xylene and other products (these products are the main raw materials for the production of synthetic plastics, synthetic rubber, synthetic fibers and so on. ) and a large number of by-products of hydrogen.
3. Basic concepts
Reforming: The rearrangement of hydrocarbon molecules into a new molecular structure.
Catalytic reforming unit: using straight-run gasoline (naphtha) or mixed oil of secondary processing gasoline as raw material, under the action of catalyst (platinum or multi-metal), hydrocarbon molecules are rearranged into new molecular structures through dehydrocyclization, hydrocracking and isomerization, with the main purpose of producing C6-C9 aromatic products or high octane gasoline, and hydrogen is used as the by-product of reforming to delay the secondary processing thermal cracking and hydrofining of coking gasoline or diesel oil.
4. Production process
According to the basic principle of catalytic reforming, a complete industrial reforming unit mainly includes two parts: raw material pretreatment and catalytic reforming. The reformer for producing aromatic hydrocarbons also includes two parts: aromatic hydrocarbon extraction and aromatic hydrocarbon rectification.
Raw material pretreatment
Cut raw materials into distillation ranges suitable for reforming requirements, and remove impurities harmful to the catalyst.
Pretreatment includes pre-arsenic removal, pre-fractionation and pre-hydrogenation.
catforming
Catalytic reforming is the main reaction of dehydrogenation, aromatization and isomerization of cycloalkane by using multi-metal (Pt-Re, Pt-Ir, Pt-Sn) catalysts under certain temperature and pressure conditions. To increase the octane number of aromatic hydrocarbons or gasoline.
The reaction system processes widely used in industrial reforming units can be divided into two categories: semi-regeneration process of fixed bed reactor and continuous regeneration process of moving bed reactor.