A crude oil distillation tower based on heat extraction in the middle section of the distillation tower and a crude oil enhanced distillation process

Abstract

The present invention relates to a crude oil distillation tower and a crude oil enhanced distillation process based on heat extraction from the middle section of the distillation tower. An in-tower gas phase condenser is provided in the distillation tower, and the rising gas phase in the distillation tower section and the feed crude oil undergo indirect contact heat exchange in the in-tower gas phase condenser. Compared with the prior art, the present invention overcomes the problem of huge liquid phase load in the tower in the conventional pump circulation area by partially condensing the gas phase, thereby reducing the full-tower pressure drop of the distillation tower. In addition, by utilizing the enhanced heat exchange method proposed in the present invention, the equipment size of the distillation tower will be reduced, or a larger processing capacity can be obtained within the existing equipment size, thereby improving the operational flexibility of the equipment. The enhanced heat exchange method proposed in the present invention circumvents the two heat exchange processes of the traditional pump circulation, completes the heat transfer through a single heat exchange process, and achieves energy saving and consumption reduction in the process. The present invention proposes an enhanced distillation tower design method, which can be used not only in the design of new towers, but also in the technical transformation of old towers.

Description

Technical Field

[0001] The present invention belongs to the field of petroleum refining and relates to a method for extracting heat from the middle section of a distillation tower by utilizing a partial gas phase condensation technology within the tower to replace a traditional pump circulation method. The method can effectively improve the mass and heat transfer efficiency of the distillation process, save energy consumption, and increase product yield. Background Art

[0002] The petroleum refining industry is one of my country's key pillar industries, providing essential energy and various chemical raw materials for the national economy. Crude oil distillation is the leading sector of the entire petroleum refining industry and holds a crucial position. Specific crude oil processing solutions exist for different crude oil properties, product types, and quality requirements, such as fuel-based, fuel-lubricant-based, and fuel-chemical-based. These solutions, in turn, have led to a variety of crude oil distillation processes, including three-stage distillation, two-stage flash distillation, three-stage distillation with pre-flash, and four-stage distillation. Three-stage distillation is the most commonly used in industrial production. The process consists of a pre-fractionation tower, an atmospheric pressure tower, and a vacuum tower. The design of the crude oil distillation tower directly determines the yield and quality of the petroleum fraction products, and thus has a decisive impact on the overall economic performance of the refinery.

[0003] Many improvement methods have been proposed at home and abroad regarding the crude oil distillation process. The Chinese patent with patent number CN108467744B discloses a method for improving the quality of the five-line product of a lubricating oil-type vacuum baffle tower. This method reduces the distillation range of the five-line by introducing baffles in the vacuum tower, thereby improving the yield of the lubricating oil base oil. The Chinese patent with patent number CN203095986U discloses an improved crude oil distillation unit top reduction non-condensable gas recovery system, which ultimately reduces the refining cost and improves economic benefits. The Chinese patent with patent number CN105602606B discloses a process and system for recovering light hydrocarbons in a crude oil distillation unit. By introducing a liquid-gas jet pump, the light hydrocarbon components in the non-condensable gas at the top of the pre-fractionation tower and the atmospheric tower are recovered. At present, most of the disclosed patents use different methods to improve the crude oil distillation process and its various petroleum product recovery systems, and do not involve improvements in the heat extraction method in the middle section of the distillation tower.

[0004] Conventional crude oil distillation processes typically utilize conventional pump circulation to extract heat from the midsection of the distillation column. This suffers from both mass and heat transfer deficiencies. From a mass transfer perspective, the pumped-circulated produced oil returns to the distillation column two to four trays above the extraction point, resulting in the top feed and bottom discharge of the pumping zone having identical compositions, reducing distillation mass transfer and separation efficiency. From a heat transfer perspective, the pumped-circulated produced oil acts as a heat exchange medium between the feed crude oil and the ascending gas phase within the column, undergoing two heat exchange processes. Because the sensible heat release per unit mass of pumped-circulated produced oil is limited, significant circulation flow rates (50-100% of the feed crude oil flow rate) and significant power consumption (to drive fluid transport) are required to meet midsection heat extraction requirements. Furthermore, the high liquid phase load in the pumping zone results in a larger column cross-sectional area and a higher pressure drop per tray, increasing equipment costs and reducing petroleum distillate product yields. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing a crude oil distillation tower and a crude oil intensification distillation process based on heat extraction from the mid-section of the distillation tower. By introducing a single-stage heat exchange and condensation method for the gas phase within the tower, replacing conventional pump circulation, the present invention overcomes the mass and heat transfer limitations of the conventional pump circulation, improves the heat exchange efficiency of the entire crude oil distillation unit, achieves process intensification of the crude oil distillation tower, and ultimately enhances the overall plant economic benefits.

[0006] The objectives of the present invention can be achieved by the following technical solution: a crude oil distillation tower based on heat extraction in the middle section of the distillation tower, an in-tower gas phase condenser is set in the distillation tower, and the rising gas phase in the distillation tower section and the feed crude oil undergo indirect contact heat exchange in the in-tower gas phase condenser.

[0007] Furthermore, the gas phase condenser in the tower is in the form of a plate heat exchanger, a shell and tube heat exchanger, a wound tube heat exchanger or any combination thereof. The heat exchange area of the gas phase condenser in the tower should have sufficient margin and the volume should meet the requirements for installation in the tower.

[0008] Furthermore, the installation position of the in-tower gas phase condenser is the pump circulation area of the existing crude oil distillation tower.

[0009] Furthermore, the feed crude oil enters through the inlet of the gas phase condenser in the tower and undergoes countercurrent heat exchange with the ascending gas phase. The preheated crude oil is extracted from the outlet of the gas phase condenser in the tower. The descending liquid phase in the distillation tower passes through the gas phase condenser in the tower, or bypasses the gas phase condenser in the tower through a bypass flow.

[0010] The invention discloses a crude oil enhanced distillation process using a crude oil distillation tower. After the feed crude oil is preheated by a heat exchange network, it is sequentially distilled through a pre-fractionation tower, an atmospheric tower, and a vacuum tower. Naphtha products are obtained from the top of the pre-fractionation tower. Naphtha, kerosene, diesel, atmospheric gas oil, and atmospheric bottom oil products are obtained through the atmospheric tower and multiple side stripping towers. Vacuum diesel, light vacuum gas oil, heavy vacuum gas oil, over-vaporized oil, and reduced bottom oil are obtained through the vacuum tower. In-tower gas phase condensers are provided in the atmospheric tower and the vacuum tower.

[0011] Furthermore, the number of theoretical plates of the pre-fractionation tower is 15 to 40; the number of theoretical plates of the atmospheric pressure tower is 30 to 70; and the number of theoretical plates of the vacuum tower is 10 to 50.

[0012] Furthermore, the atmospheric tower is connected to a plurality of side stripping towers, and each side stripping tower has 3 to 10 theoretical plates.

[0013] The internals of the pre-fractionation tower, atmospheric pressure tower and side stripping tower are mostly made of tower plates; the internals of the vacuum tower are mostly made of fillers.

[0014] Furthermore, the process specifically comprises the following steps:

[0015] The raw crude oil is desalted and dehydrated by the electric desalter and then enters the heat exchange network to be preheated to 180-230℃ before entering the pre-fractionation tower;

[0016] The bottom oil of the pre-fractionator continues to heat up to a final temperature of about 290-310°C through the heat exchange network, and then enters the atmospheric pressure furnace to continue heating to 350-380°C. The crude oil undergoes a vaporization process under the heating of the atmospheric pressure furnace and enters the atmospheric pressure tower;

[0017] In the atmospheric tower, crude oil is distilled into five petroleum fractions: naphtha, kerosene, diesel, atmospheric gas oil (AGO), and atmospheric bottom oil. The petroleum products from each side stripping column enter the corresponding side stripping column, forming a single-tower, multi-side stripping configuration. The atmospheric tower is connected to each side stripping column in a thermally coupled logistics manner, and the atmospheric tower is also equipped with multiple in-tower vapor condensers. The bottom oil discharged from the bottom of the atmospheric tower is heated to 390-420°C in a vacuum furnace before entering the vacuum tower.

[0018] The vacuum tower distills out the fraction of oil with a boiling point below 550°C at normal pressure from the normal bottom oil by reducing the pressure; the top non-condensable gas is produced from the top of the vacuum tower, and the main side products of the vacuum tower include vacuum diesel, light vacuum gas oil LVGO, heavy vacuum gas oil HVGO, over-vaporized oil and vacuum bottom oil.

[0019] Furthermore, stripping steam is injected into the bottoms of the pre-fractionation tower, atmospheric pressure tower and vacuum tower.

[0020] The gas phase streams at the top of the pre-fractionation tower and the atmospheric tower are condensed in the condenser and enter the reflux tank. After the top products are separated, they produce non-condensable gas, naphtha and oily wastewater respectively. The top products of the pre-fractionation tower and the atmospheric tower are mixed and sent to the downstream for further processing.

[0021] The vacuum tower is provided with a vacuum tower washing section on the vaporization section, wherein a tower plate and a foam breaking net are provided.

[0022] To address the mass and heat transfer deficiencies of conventional pump circulation designs, the present invention proposes an enhanced heat exchange method based on partial vapor phase condensation within the distillation tower. This method can increase the final heat exchange temperature of the feed crude oil, reduce the pressure drop in the distillation tower, and achieve energy savings and consumption reductions during the process, as well as increased yields of petroleum distillate products. Unlike the direct gas-liquid contact heat exchange within the conventional pump circulation area, the enhanced heat exchange method proposed in the present invention utilizes indirect contact heat exchange between the ascending vapor phase within the distillation tower section and the feed crude oil within the tower's vapor phase condenser. Specifically, the feed crude oil undergoes countercurrent heat exchange with the ascending vapor phase at the heat exchanger inlet, and the preheated crude oil is withdrawn from the heat exchanger outlet. The descending liquid phase within the distillation tower does not participate in the heat exchange process due to the smaller temperature difference between the descending liquid phase and the ascending vapor phase. The descending liquid phase can flow through the vapor phase condenser within the tower or bypass it through a circumferential flow. The vapor phase condenser within the tower can be plate-type, shell-and-tube-type, wound-tube-type, or any combination thereof.

[0023] Compared with the conventional pump circulation mid-section heat extraction method, the enhanced heat exchange method proposed in the present invention overcomes the mass transfer and heat transfer defects of the pump circulation area. In terms of mass transfer, the partial condensation structure of the gas phase in the tower proposed in the present invention is equivalent to a theoretical tower plate in the distillation principle; while the pump circulation design loses the mass transfer separation effect due to the "back mixing effect"; in addition, the conventional pump circulation area needs to introduce two to four tower plates to receive the circulating oil, which causes a large pressure drop in the tower; in the present invention, the pressure drop in the heat exchange process can be effectively reduced by rationally designing the condenser structure, thereby improving the yield of some petroleum fraction products. In terms of heat transfer, the indirect contact heat exchange between the feed crude oil (1) and the rising gas phase (29) only undergoes one heat exchange process, that is, the latent heat contained in the rising gas phase (29) is directly used to preheat the feed crude oil (1) through phase change. The phase change heat exchange method can increase the heat transfer film coefficient, thereby effectively reducing the heat exchange area. Compared with the two heat exchange processes of the pump circulation, the one heat exchange process can effectively reduce heat loss, so that the energy of the logistics in the distillation tower can be utilized to a greater extent. The enhanced heat exchange method proposed in this invention can effectively increase the final heat exchange temperature of the feed crude oil, reduce atmospheric furnace load and associated carbon dioxide emissions, and enhance the overall economic benefits of oil refining. Furthermore, the enhanced heat exchange method proposed in this invention avoids the large produced oil circulation flow rate problem in conventional designs, thereby effectively reducing the liquid phase load within the tower and the associated equipment size. It can also achieve a larger feed rate within the existing equipment size, improving equipment operational flexibility.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention effectively overcomes the existing mass and heat transfer deficiencies, resulting in a more energy-efficient crude oil distillation unit. By utilizing partial vapor condensation within the tower and synthesizing a corresponding optimal heat exchange network, it maximizes energy recovery and significantly reduces energy consumption. Furthermore, the invention overcomes the high pressure drop in the pump circulation area, improving the yield while maintaining the quality of the petroleum distillate product. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the process flow of the enhanced crude oil distillation tower in Example 1;

[0027] Figure 2 This is a schematic diagram of the flow chart of the gas phase condenser in the tower of Example 1;

[0028] Figure 3 This is a schematic diagram of the process flow of crude oil distillation in Comparative Example 1;

[0029] Figure 4 This is a schematic diagram of the process flow of conventional pump circulation for mid-stage heat extraction in Comparative Example 1;

[0030] Figure 5 This is a comparison chart of the gas-liquid phase load in the tower of Example 1 and Comparative Example 1;

[0031] Figure 6 This is a comparison chart of the distillation ranges of the products of Example 1 and Comparative Example 1;

[0032] Figure 7 This is a comparison chart of product mass flow rates between Example 1 and Comparative Example 1;

[0033] Figure 8 1 is a comparison chart of the cold and hot flow synthesis curves of Example 1 and Comparative Example 1.

[0034] The serial numbers are as follows: 1 - feed crude oil; 2 - heat exchange network; 3 - pre-fractionator; 4 - stripping steam; 5 - condenser; 6 - reflux drum; 7 - overhead non-condensable gas; 8 - naphtha; 9 - oily wastewater; 10 - atmospheric furnace; 11 - atmospheric tower; 12 - pump circulation; 13 - side stripper; 14 - thermally coupled flow; 15 - kerosene; 16 - diesel; 17 - atmospheric gas oil (AGO); 18 - atmospheric bottom oil; 19 - vacuum furnace; 20 - vacuum tower ; 21-top non-condensable gas; 22-vacuum diesel; 23-light vacuum gas oil LVGO; 24-heavy vacuum gas oil HVGO; 25-overvaporized oil; 26-bottom oil; 27-vacuum tower washing section; 28-distillation tower section; 29-ascending gas phase; 30-descending liquid phase; 31-tower plate; 32-produced circulating oil; 33-heat exchanger; 34-subcooled circulating oil, 35-heat exchanger inlet; 37-heat exchanger outlet, 38-gas phase condenser in the tower. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0036] Example 1

[0037] Crude oil enhanced distillation process such as Figure 1 As shown:

[0038] After desalting and dehydrating in the electric desalter, feed crude oil 1 enters heat exchange network 2, where it is preheated to 180-230°C before entering pre-fractionation tower 3. Stripping steam 4 is injected into the bottom of pre-fractionation tower 3, and the overhead vapor stream is condensed in condenser 5 before entering reflux drum 6. The overhead products undergo phase separation to produce non-condensable gas 7, naphtha 8, and oily wastewater 9. The oil at the bottom of pre-fractionation tower 3 continues to heat exchange in heat exchange network 2 to a final temperature of approximately 290-310°C. It then enters atmospheric pressure furnace 10, where it continues to be heated to 350-380°C. Heated in atmospheric pressure furnace 10, the crude oil undergoes a primary vaporization process before entering atmospheric pressure tower 11.

[0039] Similar to the pre-fractionation tower 3, stripping steam 4 is injected into the bottom of the atmospheric tower 11, and the gas phase flow at the top of the tower is condensed by the condenser 5 and enters the reflux tank 6. After phase separation, the products produce the top non-condensable gas 7, naphtha 8 and oily wastewater 9 respectively. After the top products of the pre-fractionation tower 3 and the atmospheric tower 11 are mixed, they go to the downstream for further processing. In the atmospheric tower 11, crude oil is distilled and cut into five petroleum distillate products: naphtha 8, kerosene 15, diesel 16, atmospheric gas oil AGO17 and atmospheric bottom oil 18. These products are often at a higher temperature and can be used to preheat the feed crude oil 1, forming part of the heat exchange network 2. In order to achieve clear separation between the various distillation products, the petroleum products cut from each side line of the atmospheric tower 11 enter the corresponding side line stripping tower 13, forming a single-tower multi-side line configuration. A small amount of stripping steam 4 is injected into the bottom of each side stripper 13 to reduce the oil and gas partial pressure of the side product. The steam dosage (mass fraction) is approximately 2-5% of the feed crude oil. This allows the lighter fractions mixed into the product to vaporize and return to the atmospheric column 11. The atmospheric column 11 is connected to each side stripper 13 via a thermally coupled flow system 14. The feed point of the side stripper 13 and the side stripper extraction point of the atmospheric column 11 are positioned at a certain level, ranging from 0.5 to 2 meters, to ensure that the side liquid flows naturally out of the atmospheric column 11 and that the vapor phase in the side stripper 13 can be smoothly returned to the atmospheric column 11. Furthermore, the atmospheric column 11 is equipped with multiple in-tower vapor condensers 38 (three in this embodiment) for mid-stage reflux heat extraction. This is to mitigate operational anomalies such as flooding and leakage caused by uneven distribution of vapor and liquid loads within the distillation column.

[0040] The basic structure of the gas phase condenser 38 in the tower is as follows Figure 2 As shown, within the distillation tower section 28 of the atmospheric tower 11, the ascending vapor phase 29 within the distillation tower section 28 and the feed crude oil 1 undergo indirect contact heat exchange in the tower vapor phase condenser 38. Specifically, the feed crude oil 1 undergoes countercurrent heat exchange with the ascending vapor phase 29 through the heat exchanger inlet 35, and the preheated crude oil is withdrawn from the heat exchanger outlet 37. The descending liquid phase 30 within the atmospheric tower 11 does not participate in the heat exchange process due to the smaller heat exchange temperature difference with the ascending vapor phase 29. The descending liquid phase 30 can flow through the tower vapor phase condenser 38 or bypass the heat exchanger. In this embodiment, the descending liquid phase 30 passes through the tower vapor phase condenser 38.

[0041] Atmospheric bottom oil 18 discharged from the bottom of atmospheric tower 11 is heated to approximately 390-420°C in a vacuum furnace 19 before entering vacuum tower 20. Vacuum tower 20 reduces the pressure to distill the fraction of the atmospheric bottom oil 18 that boils below 550°C at atmospheric pressure. A large amount of stripping steam 4 is injected into the bottom of vacuum tower 20, with the steam dosage (mass fraction) being approximately 2-5% of the feed crude oil, to reduce the oil and gas partial pressure in the vaporization section. At the top of vacuum tower 20, non-condensable gas 21, primarily diesel and water, is produced. This non-condensable gas 21 is connected to a vacuum pumping system to maintain the vacuum level within the tower. The main side products of vacuum tower 20 include vacuum diesel 22, light vacuum gas oil (LVGO) 23, heavy vacuum gas oil (HVGO) 24, over-vaporized oil 25, and bottom oil 26. To reduce the carbon residue and heavy metal content of the distillate, a vacuum tower scrubber section 27 equipped with trays and a defoamer is installed above the vaporization section. To ensure a sufficient reflux flow below the lowest sideline extraction plate, a degree of supervaporization of 1-2% is typically set, meaning a certain amount of supervaporized oil 25 is produced. Similarly, multiple in-tower vapor phase condensers 38 (two in this embodiment) are installed on the sidelines of vacuum tower 20. Each in-tower vapor phase condenser 38 is located above the vacuum tower scrubber section 27. A pump 12 is provided at the bottom of vacuum tower 20 to return a portion of the bottom oil 26 to vacuum tower 20.

[0042] In this embodiment, the feed crude oil processed is 3 million tons / year, the feed temperature is 45°C, the specific gravity is 0.95, and the actual boiling point distillation data is as follows: Figure 1 shown.

[0043] Table 1 Actual boiling point distillation data of feed crude oil in the embodiment

[0044]

[0045]

[0046] The conventional crude oil distillation process was used as a benchmark for comparison with the enhanced crude oil distillation process proposed in this invention. The main design parameters for the benchmark process and the comparative process proposed in this invention are as follows:

[0047] In this example, the design parameters for pre-fractionator 3 are as follows: the total number of theoretical stages is 23, with crude oil feed entering the pre-fractionator on the 22nd stage; stripping steam is injected into the tower on the 23rd stage; the overhead vapor phase of the pre-fractionator is condensed in a condenser (equivalent to the 1st stage) and subjected to gas-liquid-liquid separation in a reflux drum, before the naphtha fraction is returned to the tower on the 2nd stage. The outlet temperatures of the atmospheric and vacuum furnaces are kept consistent, at 367°C and 399°C, respectively.

[0048] The design parameters of the atmospheric tower 11 in this embodiment are as follows: a total of 53 theoretical stages, with the feed crude oil entering the atmospheric tower from the 48th stage; stripping steam is injected into the tower from the 53rd stage; the atmospheric tower overhead gas phase is condensed in a condenser (equivalent to the 1st stage) and subjected to gas-liquid-liquid separation in a reflux tank, after which the naphtha fraction is returned to the tower from the 2nd stage; the tower is provided with three pump circulation areas for mid-stage heat extraction, with their extraction stage / return stage ratios being 6 / 3, 22 / 19, and 32 / 29, respectively; the tower is provided with three side strippers for producing kerosene, diesel, and atmospheric gas oil, respectively; each side stripper is provided with 6 stages, with stripping steam injected from the bottom of the side stripper; and the three side strippers are connected to the atmospheric tower in a thermally coupled logistics manner, at stages 14, 28, and 44, respectively.

[0049] The design parameters of the vacuum tower 20 in this embodiment are as follows: a total of 32 theoretical plates, with the feed crude oil entering the vacuum tower from the 25th plate; stripping steam is injected into the tower from the 32nd plate; the non-condensable gas at the top of the vacuum tower enters the vacuum pumping system; the tower is provided with four pump circulation areas for mid-section heat extraction, with their extraction plate / return plate ratios being 5 / 1, 15 / 11, 20 / 16, and 32 / 32, respectively; the tower is provided with a washing zone between plates 20-24; the vacuum tower produces diesel, light vacuum gas oil, heavy vacuum gas oil, over-vaporized oil, and reduced bottom oil, with their extraction plates being the 5th, 15th, 20th, 24th, and 32nd plates, respectively.

[0050] Comparative Example

[0051] Crude oil distillation process Figure 3 As shown:

[0052] After desalting and dehydrating in an electric desalter, crude oil 1 enters heat exchange network 2, where it is preheated to 180-230°C before entering pre-fractionation tower 3. Stripping steam 4 is injected into the bottom of the pre-fractionation tower. The overhead vapor stream is condensed in condenser 5 and enters reflux drum 6. The overhead products undergo phase separation to produce non-condensable gas 7, naphtha 8, and oily wastewater 9. The crude oil at the bottom of the pre-fractionation tower continues to heat exchange in heat exchange network 2 to a final temperature of approximately 290-310°C before entering atmospheric furnace 10 for further heating to 350-380°C. Heated in the atmospheric furnace, the crude oil undergoes a primary vaporization process before entering atmospheric tower 11.

[0053] Similar to the pre-fractionation tower 3, stripping steam 4 is injected into the bottom of the atmospheric tower 11, and the gaseous phase flow at the top of the tower is condensed by the condenser 5 and enters the reflux tank 6. After phase separation, the products produce the top non-condensable gas 7, naphtha 8 and oily wastewater 9 respectively. After the top products of the pre-fractionation tower 3 and the atmospheric tower 11 are mixed, they go downstream for further processing. In the atmospheric tower 11, crude oil is distilled and cut into five petroleum distillate products: naphtha 8, kerosene 15, diesel 16, atmospheric gas oil AGO17 and atmospheric bottom oil 18. These products are often at a higher temperature and can be used to preheat the feed crude oil 1, forming part of the heat exchange network 2. In order to achieve clear separation between the various distillation products, the petroleum products cut by each side line of the atmospheric tower 11 enter the corresponding side line stripping tower 13, forming a single-tower multi-side line configuration. A small amount of stripping steam 4 is injected into the bottom of each side stripper 13 to reduce the oil and gas partial pressure of the side product, allowing the lighter fractions mixed in the product to vaporize and return to the atmospheric tower 11. The atmospheric tower 11 is connected to each side stripper 13 via a thermally coupled flow system 14. The feed point of the side stripper 13 is offset from the side stripper extraction point of the atmospheric tower 11 to ensure that the side liquid flows naturally out of the atmospheric tower 11 and that the vapor phase in the side stripper 13 can smoothly return to the atmospheric tower 11. Furthermore, the atmospheric tower 11 is typically equipped with multiple pump circuits 12 for mid-stage reflux heat extraction. This is to mitigate operational anomalies such as flooding and leakage caused by uneven distribution of gas and liquid loads within the distillation tower.

[0054] The basic structure of the pump cycle 12 is as follows Figure 4 As shown, within the pumped-circulation distillation column section 28, circulating oil 32 is side-drawn from tray 31 to preheat the feed crude oil 1. The higher-temperature produced circulating oil 32 exchanges heat with the lower-temperature feed crude oil 1 in heat exchanger 33, forming part of the heat exchange network 2. This heat exchange cools the produced circulating oil 32 to a subcooled state, forming subcooled circulating oil 34 that is returned to the distillation column. Within distillation column section 28, the ascending vapor phase 29 and descending liquid phase 30 engage in direct contact heat exchange, completing the mid-stage heat extraction process.

[0055] The bottom oil 18 discharged from the bottom of the atmospheric tower 11 is heated to approximately 390-420°C in a vacuum furnace 19 before entering the vacuum tower 20. The vacuum tower 20 reduces the pressure to distill the fraction of the atmospheric bottom oil 18 that boils below 550°C at atmospheric pressure. A large amount of stripping steam 4 is injected into the bottom of the vacuum tower 20 to reduce the oil and gas partial pressure in the vaporization section. The top of the vacuum tower 20 produces a non-condensable gas 21, primarily diesel and water. This non-condensable gas 21 is connected to a vacuum pumping system to maintain the vacuum level within the tower. The main products from the vacuum tower side stream include vacuum diesel 22, light vacuum gas oil (LVGO) 23, heavy vacuum gas oil (HVGO) 24, over-vaporized oil 25, and bottom oil 26. To reduce the carbon residue and heavy metal content of the distillate, a vacuum tower scrubber 27 equipped with trays and a defoamer is installed above the vaporization section. To ensure a sufficient reflux flow below the lowest side draw plate, a degree of supervaporization of 1-2% is typically set, producing a certain amount of supervaporized oil 25. Similarly, a pump loop 12 is provided between the side draw and the bottom of vacuum tower 20 to extract heat mid-section. This extracted heat is used to preheat the feed crude oil 1, forming part of the heat exchange network 2.

[0056] The design parameters of the pre-fractionation tower 3 in Comparative Example 1 are consistent with those in Example 1.

[0057] The design parameters of the atmospheric tower 11 in Comparative Example 1 are as follows: a total of 46 theoretical stages, the feed crude oil enters the atmospheric tower from the 40th stage; stripping steam is injected into the tower from the 46th stage; the atmospheric tower overhead gas phase is condensed in a condenser (equivalent to the 1st stage), and after gas-liquid-liquid separation in a reflux tank, the naphtha fraction is returned to the tower from the 2nd stage; the tower is provided with three in-tower gas phase condensers, located on the 3rd, 16th, and 24th stages, respectively; the tower is provided with three side strippers for producing kerosene, diesel, and atmospheric gas oil, respectively; each side stripper is provided with 6 stages, wherein the stripping steam is injected from the bottom of the side stripper; and the three side strippers are connected to the atmospheric tower in the form of thermally coupled logistics, with the connection positions being the 11th, 22nd, and 35th stages, respectively.

[0058] The design parameters of the vacuum tower 20 in Comparative Example 1 are as follows: a total of 20 theoretical plates, the feed crude oil enters the vacuum tower from the 13th plate; stripping steam is injected into the tower from the 20th plate; the non-condensable gas at the top of the vacuum tower enters the vacuum pumping system; the tower is provided with three in-tower vapor phase condensers, located on the 1st, 7th, and 8th plates, respectively; in addition, the tower is provided with a pump circulation at the bottom of the tower for heat extraction, consistent with the benchmark process; the tower is provided with a washing zone between the 8th and 12th plates; the vacuum tower produces diesel, light vacuum gas oil, heavy vacuum gas oil, overvaporized oil, and reduced bottom oil, and their extraction plates are the 2nd, 7th, 8th, 12th, and 20th plates, respectively.

[0059] The enhanced crude oil distillation tower design method proposed in Example 1 of the present invention is employed, and the process flow is essentially the same as that of Comparative Example 1. The differences are that the pump recirculation area 12 of the atmospheric tower 11 is replaced by an in-tower vapor-phase condenser 38, and the pump recirculation area 12 above the scrubbing zone 27 of the vacuum tower 20 is replaced by an in-tower vapor-phase condenser 38. The pump recirculation area 12 on the bottom oil stream 26 is not replaced because this stream is liquid, not vapor.

[0060] The basic design parameters of the atmospheric tower and vacuum tower of Example 1 and Comparative Example 1 are the same. In Example 1, the trays / packings occupied by the pump circulation area in Comparative Example 1 are removed and replaced with a vapor phase condenser in the tower, while the remaining trays / packings used for distillation are retained.

[0061] Figure 5 The following figure compares the gas-liquid loads within the two process towers: Example 1 shows the improved atmospheric and vacuum towers, while Comparative Example 1 shows the conventional atmospheric and vacuum towers. It can be seen that the gas-liquid loads in the atmospheric and vacuum towers in Comparative Example 1 are greater than those in Example 1. This means that the distillation tower in Comparative Example 1 must have a larger diameter to accommodate the large flow rate of oil and gas. In contrast, in Example 1, the liquid load within the distillation tower is relatively low, which helps reduce the pressure drop within the tower and improve product yield.

[0062] Figure 6 The figure is a comparison chart of the distillation ranges of the products of the two processes. Comparing the ASTM D86 temperatures of the atmospheric tower products in the two processes, it can be seen that the petroleum product fractions obtained by the two processes have very similar distillation curves. The naphtha, kerosene and diesel fractions are clearly separated, that is, the final distillation points of the lighter products (naphtha, kerosene) are very close to the initial distillation points of their adjacent heavier products (kerosene, diesel). The corresponding temperature for the 95% distillation volume fraction of diesel is 357°C, and the corresponding temperature for the 5% distillation volume fraction of atmospheric gas oil is 344°C, with only 13°C overlapping between the two. Comparing the ASTM D1160 temperatures of the vacuum tower products in the two processes, it can be seen that the corresponding temperature for the 5% distillation volume of the light / heavy vacuum gas oil in Example 1 is slightly lower than that in Comparative Example 1. This is because a portion of the vacuum diesel is mixed into the vacuum gas oil, and this deviation can be processed in the downstream process.

[0063] Figure 7 The following chart compares the product mass flow rates of the two processes. As can be seen, the mass flow rates of the main products are very similar. Excluding over-vaporized oil and reduced base oil, the petroleum fraction yield in Comparative Example 1 is 65.30%, while that in Example 1 is 66.04%. These results show that Example 1 can increase the yield by approximately 0.74%. Under an annual plant operating condition of 8,000 hours, the increased product flow rate reaches approximately 22,000 tons / year.

[0064] Figure 8The comparison of the cold and hot flow synthesis curves of the two processes is shown in FIG. It can be seen that the process proposed in Example 1 of the present invention has a higher pinch point temperature and a larger temperature range below the pinch point, which is beneficial to energy recovery. When the minimum heat exchange temperature difference ΔT of 20°C is adopted min The maximum recoverable energy for Comparative Example 1 and Example 1 was 70,778 kW and 74,477 kW, respectively, with corresponding minimum utility energy consumption of 31,415 kW and 27,683 kW. Therefore, Example 1 achieved an 11.88% energy saving compared to Comparative Example 1. If heat were not squeezed across the pinch point, the final heat exchange temperature in Example 1 could reach as high as 347.6°C, far exceeding the theoretical value of 320.4°C for the baseline design.

[0065] It’s important to note that the above process intensification methods can be used for both new plant design and retrofitting of existing plants. When retrofitting existing plants, the trays or packing in the pump circulation area should be replaced with a suitable heat exchanger configuration, and the associated heat exchange network should be modified.

Claims

1. A crude oil distillation tower based on heat extraction in the middle section of the distillation tower, characterized in that: An internal gas phase condenser is provided in the distillation tower, and the rising gas phase in the distillation tower section and the feed crude oil undergo indirect contact heat exchange in the internal gas phase condenser; The gas phase condenser in the tower is in the form of a plate heat exchanger, a shell and tube heat exchanger, a wound tube heat exchanger or any combination of one or more; The installation position of the gas phase condenser in the tower is the pump circulation area of the existing crude oil distillation tower; The feed crude oil enters through the inlet of the gas phase condenser in the tower and undergoes countercurrent heat exchange with the ascending gas phase. The preheated crude oil is extracted from the outlet of the gas phase condenser in the tower. The descending liquid phase in the distillation tower passes through the gas phase condenser in the tower, or bypasses the gas phase condenser in the tower through a bypass flow.

2. A crude oil intensified distillation process using the crude oil distillation tower according to claim 1, wherein the feed crude oil (1) is preheated by the heat exchange network (2), and then distilled in a pre-fractionation tower (3), an atmospheric tower (11), and a vacuum tower (20) in sequence, wherein: A naphtha product is obtained at the top of the pre-fractionation tower (3); naphtha, kerosene, diesel, atmospheric gas oil and atmospheric bottom oil products are obtained through an atmospheric tower (11) and a plurality of side stripping towers; and vacuum diesel, light vacuum gas oil, heavy vacuum gas oil, over-vaporized oil and reduced bottom oil are obtained through a vacuum tower (20). The invention is characterized in that an in-tower gas phase condenser is provided in the atmospheric tower (11) and the vacuum tower (20).

3. The crude oil enhanced distillation process according to claim 2, characterized in that: The number of theoretical plates of the pre-fractionation tower (3) is 15 to 40; the number of theoretical plates of the atmospheric pressure tower (11) is 30 to 70; and the number of theoretical plates of the vacuum tower (20) is 10 to 50.

4. The crude oil enhanced distillation process according to claim 2, characterized in that: The atmospheric tower (11) is connected to a plurality of side stripping towers (13), and each side stripping tower (13) has 3 to 10 theoretical plates.

5. The crude oil enhanced distillation process according to claim 4, characterized in that: The internals of the pre-fractionation tower (3), atmospheric tower (11) and side stripping tower (13) are tower plates; the internals of the vacuum tower (20) are packings.

6. The crude oil enhanced distillation process according to claim 2, characterized in that: The process specifically comprises the following steps: The crude oil (1) is desalted and dehydrated by the electric desalter and then enters the heat exchange network (2) where it is preheated to 180-230°C before entering the pre-fractionation tower (3). The oil at the bottom of the pre-fractionation tower (3) is further heated to a final temperature of 290-310°C by the heat exchange network (2), and then enters the atmospheric pressure furnace (10) to continue heating to 350-380°C. The crude oil undergoes a primary vaporization process under the heating action of the atmospheric pressure furnace (10) and enters the atmospheric pressure tower (11); In the atmospheric tower (11), crude oil is distilled and cut into five petroleum fraction products: naphtha (8), kerosene (15), diesel (16), atmospheric gas oil (AGO) (17), and atmospheric bottom oil (18); the petroleum products cut from each side line enter the corresponding side line stripping tower (13), forming a single tower multi-side line configuration, the atmospheric tower (11) and each side line stripping tower (13) are connected in the form of thermal coupling flow (14), and the atmospheric tower (11) is also equipped with multiple in-tower gas phase condensers; the atmospheric bottom oil (18) discharged from the bottom of the atmospheric tower (11) is heated to 390~420℃ in a pressure reducing furnace (19) and enters the pressure reducing tower (20); The vacuum tower (20) distills out the fraction of the oil with a boiling point below 550°C at normal pressure from the bottom oil (18) by reducing the pressure; the top non-condensable gas is produced from the top of the vacuum tower (20); the main side products of the vacuum tower (20) include vacuum diesel (22), light vacuum gas oil (LVGO) (23), heavy vacuum gas oil (HVGO) (24), over-vaporized oil (25) and bottom oil (26).

7. The crude oil enhanced distillation process according to claim 6, characterized in that: Stripping steam (4) is injected into the bottoms of the pre-fractionation tower (3), the atmospheric pressure tower (11) and the vacuum tower (20). The gaseous streams at the top of the pre-fractionation tower (3) and the atmospheric tower (11) are condensed by the condenser (5) and then enter the reflux tank (6). After the top products are separated, they respectively produce the top non-condensable gas (7), naphtha (8) and oily wastewater (9). The top products of the pre-fractionation tower (3) and the atmospheric tower (11) are mixed and sent to the downstream for further processing. The vacuum tower (20) is provided with a vacuum tower washing section (27) on the vaporization section, wherein a tower plate and a foam breaking net are provided.

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