Separation process and system for raffinate oil after decarburization 5

Abstract

The invention relates to a separation process and system for raffinate oil after decarburization 5, and the separation process comprises the following steps: the raffinate oil after decarburization 5 enters the upper part of a C7 tower, a heat source is arranged at the bottom of the C7 tower for heating, the C7 tower is controlled to operate under a rectification condition, a C7 fraction is separated from the bottom of the C7 tower, and the C7 fraction is separated from the bottom of the C7 tower. A part of hydrocarbon substances containing n-hexane and isohexane components separated from the top of the C6 tower are refluxed, and the rest of the hydrocarbon substances enter the C6 tower from the lower part of the C6 tower; the C6 tower is used for fractionating the hydrocarbon substances containing the n-hexane and the isohexane components into substances containing the n-hexane and substances containing the isohexane, the substances containing the isohexane flow out of the tower top of the C6 tower, and the substances containing the n-hexane flow out of the tower bottom of the C6 tower. By changing the separation sequence, the backmixing of the middle component n-hexane in the C7 tower is reduced, the tower bottom temperature is reduced, and a low-quality heat source such as hot water is adopted as a reboiling heat source, so that reasonable utilization of different energy grades is realized, and the energy consumption is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical industry, and in particular to a separation process and system for raffinate oil after decarbonization. Background Art

[0002] The raffinate oil after removing C5 is mainly composed of C6 (hereinafter referred to as C6) and C7 (hereinafter referred to as C7) alkanes. It is usually used as a gasoline blending component or ethylene cracking raw material. However, due to its low octane number and low ethylene conversion rate, some companies choose to produce solvents rich in normal C6 alkanes, which are well used in the vegetable oil industry. There are currently two main processes. One is to use extractive distillation, N-methyl-2-pyrrolidone (NMP) as an extractant, to achieve high-purity separation of normal hexane and methyl cyclopentane, the isomers of C6 alkanes (only 3.1°C difference) with similar boiling points, and the product concentration can reach more than 95%. The second is to use the raffinate oil after removing C5 as the raw material, first hydrogenate to remove impurities such as benzene and olefins, and then perform ordinary distillation in the order of removing light components first and then heavy components, and enter the isohexane tower and hexane tower in turn. The isohexane product and normal hexane product are obtained from the top of the two towers, and the C7 fraction is distilled from the bottom of the hexane tower. The purity of the n-hexane and isohexane products produced by this process is relatively low, so no extractive distillation is set up and a conventional plate tower is used. The isohexane products mainly include 2,2-dimethylbutane, 2-methylpentane and 3-methylpentane. The atmospheric boiling point of 3-methylpentane is close to that of n-hexane, which is 63.4℃ and 68.7℃ respectively. Therefore, the separation of isohexane tower is difficult and the energy consumption is high. There are two main problems in the sequential separation of hydrogenation products: (1) The bottom of the isohexane tower contains C7 components, so the bottom temperature is relatively high, about 90℃, and 0.5MPag steam (saturated temperature 158.8℃, superheated to 180.0℃) must be used as the heat source, which has the problem of high energy and low energy use; (2) The intermediate boiling point component, n-hexane, as the intermediate component with the largest output (accounting for about 70% of the raw material), has a low distillation efficiency due to severe backmixing during the sequential distillation process.

[0003] Therefore, how to develop a separation process for the raffinate oil after decarbonization of the fifth element, which can not only reduce the back-mixing of intermediate components, but also use low-temperature heat sources as energy sources, thereby optimizing the processing flow of the raffinate oil after decarbonization of the fifth element, improving product purity and production efficiency, and reducing energy consumption costs, is an urgent problem that needs to be solved. Summary of the invention

[0004] In view of the technical problems existing in the prior art, the first purpose of the present invention is to provide a separation process for extracting the residual oil after decarbonization of five carbons, and to change the existing separation process of "removing light components first and then heavy components" into a separation process of "removing heavy components first and then light components", and to change the separation order to reduce the backmixing of n-hexane, the intermediate component of the carbon seven tower, and to lower the bottom temperature of the tower, while using a low-quality heat source such as hot water generated by recovering waste heat as a reboiling heat source to further reduce energy consumption, so as to directly achieve the rational utilization of different energy grades.

[0005] The second object of the present invention is to provide a separation system for extracting the residual oil after decarbonization, which can achieve the purpose of energy saving and consumption reduction by lowering the bottom temperature of the tower and reducing the operating capacity of the tower so as to use a lower grade heat source for reboiling.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A separation process for raffinate oil after decarbonization, comprising the following steps: The residual oil after decarbonization of five is introduced into the upper part of the carbon seven tower, and a heat source is set at the bottom of the carbon seven tower for heating. The carbon seven tower is controlled to operate under distillation conditions, and the carbon seven fraction is separated from the bottom of the carbon seven tower. A part of the hydrocarbon substances containing normal hexane and isohexane components separated from the top of the tower is refluxed, and the rest enters from the lower part of the carbon six tower; the carbon six tower distills the hydrocarbon substances containing normal hexane and isohexane components into substances containing normal hexane and substances containing isohexane, and the substances containing isohexane flow out from the top of the carbon six tower, and the substances containing normal hexane flow out from the bottom of the carbon six tower.

[0007] Furthermore, the operating pressure of the C7 tower is atmospheric pressure-200 kPaa, the reflux ratio is 1.3-1.8, the theoretical number of plates in the C7 tower is 83-103, and the position of feeding the residual oil after decarbonization of C5 is the 20th-30th plate.

[0008] Furthermore, the gas phase at the top of the C7 tower is cooled to 42°C-50°C, and gas-liquid separation is carried out, the gas is discharged, part of the liquid is returned to the C7 tower as reflux, and the remaining liquid is introduced into the lower part of the C6 tower; the liquid phase at the bottom of the C7 tower is vaporized 15%-25% by the heat source and then returned to the C7 tower, and the remaining liquid phase is used as the C7 fraction and is cooled to 40°C-42°C by self-pressure or pumping before being sent out of the device.

[0009] Furthermore, the operating pressure of the C6 tower is atmospheric pressure-200 kPaa, the reflux ratio is 7.7-9.9, the number of theoretical plates in the C6 tower is 90-100, and the position for feeding the hydrocarbon material containing n-hexane and isohexane components is the 60th-70th plate.

[0010] Furthermore, the gas phase at the top of the C6 tower is cooled to 42°C, and gas-liquid separation is carried out, the gas is discharged, part of the liquid is returned to the C6 tower as reflux, and the remaining liquid is cooled to 40°C-42°C by self-pressure or pumping as an isohexane product and sent out of the device; the liquid phase at the bottom of the C6 tower is vaporized 15%-25% by the heat source and then returned to the C6 tower, and the remaining liquid is cooled to 40°C-42°C by self-pressure or pumping as a normal-hexane product and sent out of the device.

[0011] Furthermore, the substance containing n-hexane flowing out of the bottom of the C6 tower is heat exchanged with the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower through a heat exchanger, and the temperature of the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower is heated from 42°C to 50°C.

[0012] Furthermore, the arithmetic mean heat transfer temperature difference of the heat exchanger is ≥10°C, the flow rate on the hot logistics side is 13t / h, the temperature after heat exchange is 60°C-65°C, the flow rate on the cold logistics side is 16-18t / h, and the temperature after heat exchange is 45°C-50°C.

[0013] Furthermore, the heat source comes from a reboiler, the reboiler heat source at the bottom of the C7 tower is 0.5-1.0 MPag steam, and the reboiler heat source at the bottom of the C6 tower is 95°C-105°C hot water.

[0014] Furthermore, the arithmetic mean heat transfer temperature difference of the steam reboiler at the bottom of the C7 tower is ≥20°C, the flow rate on the hot logistics side is 200-350t / h, the temperature after heat exchange is 159°C, the flow rate on the cold logistics side is 200-250t / h, and the return tower temperature is 96°C-105°C; the arithmetic mean heat transfer temperature difference of the hot water reboiler at the bottom of the C6 tower is ≥15°C, the flow rate on the hot logistics side is 150-300t / h, the temperature after heat exchange is 86°C-88°C, the flow rate on the cold logistics side is 190-260t / h, and the return tower temperature is 75°C-80°C.

[0015] A separation system for raffinate oil after decarbonization of five carbons comprises a C7 tower and a C6 tower arranged in series, wherein an inlet pipeline for raffinate oil after decarbonization of five carbons is arranged at the upper part of the C7 tower, an outflow pipeline and a reflux pipeline for hydrocarbon substances containing normal hexane and isohexane components are arranged at the top of the C7 tower, a reboiler and a C7 fraction outflow pipeline are arranged at the bottom of the C7 tower, an outflow pipeline and a reflux pipeline for substances containing isohexane are arranged at the top of the C6 tower, a reboiler and a outflow pipeline for substances containing normal hexane are arranged at the bottom of the C6 tower, and the outflow pipeline for hydrocarbon substances containing normal hexane and isohexane components is connected to the lower part of the C6 tower.

[0016] The present invention has the following advantages: 1. The present invention provides a separation process for removing the residual oil after C5 removal, which changes the current separation process of "first removing light components and then removing heavy components" into a separation process of "first removing heavy components and then removing light components", that is, the original isohexane tower is changed into a C7 tower, and the hexane tower is changed into a C6 tower. First, the heaviest C7 component is separated from the bottom of the C7 tower, and the mixture of n-hexane and isohexane is distilled from the top of the tower. This can reduce the backmixing of the intermediate component n-hexane (backmixing refers to the concentration of the intermediate component n-hexane in the original isohexane tower first increasing and then decreasing, forming a concentration peak in the tower), while reducing the difficulty of system separation and energy consumption, and reducing the number of tower plates, saving investment costs; the mixture of n-hexane and isohexane enters the C6 tower, and the isohexane product rich in 2,2-dimethylbutane, 2-methylpentane and 3-methylpentane is separated from the top of the tower, and the n-hexane product is distilled from the bottom of the tower. In this way, the system components become lighter, the bottom temperature of the tower is reduced, and low-grade heat sources such as 95°C hot water can replace high-grade 0.5MPag steam as a reboiling heat source, solving the problem of high energy and low utilization of the device, realizing the rational utilization of energy, and further reducing energy consumption.

[0017] 2. The C7 fraction of the present invention is separated in advance, avoiding repeated distillation in subsequent towers, thereby reducing the processing volume in the separation process of the difficult-to-separate systems n-hexane and 3-methylpentane, and improving the overall separation efficiency. At the same time, the functional transformation of the original isohexane tower changes the top product from isohexane to mixed C6, reducing the difficulty of separation, not only reducing the consumption of reboiled steam at the bottom of the tower, but also reducing the number of tower plates and equipment investment. After the original hexane tower is transformed into a C6 tower, the bottom product is transformed from the C7 fraction to n-hexane, the bottom temperature is reduced, and 95°C hot water can be used instead of 0.5MPag steam as a reboiled heat source.

[0018] 3. The present invention realizes heat exchange between the inlet and outlet of the C6 tower by configuring a heat exchanger. The material containing n-hexane flowing out of the bottom of the C6 tower and the hydrocarbon material containing n-hexane and isohexane components entering the C6 tower are heat exchanged through the heat exchanger, realizing the preheating of the feed, thus reducing both the reboil load at the bottom of the tower and the cooling load of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the process flow of Example 1 and Example 2 of the separation process of the present invention for the residual oil after decarbonization.

[0020] Figure 2 It is a schematic diagram of the process flow of Example 3 of the separation process of the present invention for the residual oil after decarbonization.

[0021] Figure 3 It is a process flow diagram of comparative example 1 of the existing process for sequential separation of raffinate oil after decarbonization.

[0022] Among them, 1 is a C7 tower, 1a is an inlet pipeline for the residual oil after decarbonization of C5, 1b is an outflow pipeline for hydrocarbon substances containing normal hexane and isohexane components, 1c is a reflux pipeline for hydrocarbon substances containing normal hexane and isohexane components, 1d is an outflow pipeline for C7 fraction, 101 is an air cooler, 102 is a circulating water cooler, 103 is a gas-liquid separation tank, 104 is a reflux pump, 105 is a reboiler, 106 is a transfer pump, 107 is a circulating water cooler, 2 is a C6 tower, 2a is an outflow pipeline for substances containing isohexane, 2b is a reflux pipeline for substances containing isohexane, 2c is an outflow pipeline for substances containing normal hexane, and 20 1 is an air cooler, 202 is a circulating water cooler, 203 is a gas-liquid separation tank, 204 is a reflux pump, 205 is a reboiler, 206 is a delivery pump, 207 is a circulating water cooler, 208 is a heat exchanger, 3 is an isohexane tower, 301 is an air cooler, 302 is a circulating water cooler, 303 is a gas-liquid separation tank, 304 is a reflux pump, 305 is a reboiler, 306 is a delivery pump, 4 is a hexane tower, 401 is an air cooler, 402 is a circulating water cooler, 403 is a gas-liquid separation tank, 404 is a reflux pump, 405 is a reboiler, 406 is a delivery pump, and 407 is a circulating water cooler. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0024] like Figure 1 and Figure 2 As shown, a separation process for raffinate oil after decarbonization of five carbons comprises the following steps: the raffinate oil after decarbonization of five carbons enters the upper part of the carbon seven tower 1, and a heat source is set at the bottom of the carbon seven tower 1 for heating, the carbon seven tower 1 is controlled to operate under distillation conditions, and the carbon seven fraction is separated from the bottom of the carbon seven tower 1, and a part of the hydrocarbon substances containing normal hexane and isohexane components separated from the top of the tower is refluxed, and the rest enters from the lower part of the carbon six tower 2; the carbon six tower 2 fractionates the hydrocarbon substances containing normal hexane and isohexane components into substances containing normal hexane and substances containing isohexane, and the substances containing isohexane flow out from the top of the carbon six tower 2, and the substances containing normal hexane flow out from the bottom of the carbon six tower 2. Among them, the raffinate oil after decarbonization of five carbons is a product formed by hydrogenation to remove impurities from a continuous reforming unit and after decarbonization of five carbons.

[0025] like Figure 1 and Figure 2As shown, the operating pressure of the C7 tower 1 is normal pressure-200kPaa, and the range of the operating pressure is set relatively wide, and the low-pressure environment can be used to reduce the energy consumption of the device. The reflux ratio is 1.3-1.8, wherein the reflux ratio is a mass ratio, i.e., the ratio of the reflux amount to the distillate amount. The reflux ratio should be determined according to the operating pressure and product quality. It should not be too large, which will cause the device to over-operate and increase energy consumption. The present invention reduces the reflux amount, which can reduce the separation capacity of the entire tower, and increases the extraction amount of the top product, so that the intermediate product n-hexane that was originally suppressed by high reflux can be extracted from the top of the tower. The number of theoretical plates in the C7 tower 1 is 83-103, and multiple tower plates are arranged at a certain interval along the vertical direction of the tower body. Due to the reduced separation difficulty, only C6 and C7 need to be separated, so the number of theoretical plates is reduced compared to the original number of plates, and the original number of sequentially separated tower plates is 123. The C7 tower 1 can adjust the tower pressure, extraction amount, reflux amount and other parameters according to the product quality requirements of the C7 fraction to achieve the separation requirements. The feeding position of the residual oil after decarbonization is the 20th-30th plate. Specifically, the feeding position is located at the upper part of the C7 tower 1, and the feed is fed from the 20th-30th plate. Among them, the bottom of the tower needs to obtain a C7 fraction (C6 ≤5%) that meets a certain product quality, so the number of plates needs to be increased in the distillation section at the bottom of the tower. The number of plates in the distillation section will affect the quality of the bottom product. The more plates there are, the better the separation effect is, and the less the content of light components in the bottom product is.

[0026] like Figure 1 and Figure 2As shown, the gas phase at the top of the C7 tower 1 is partially cooled to 42°C-50°C, and gas-liquid separation is performed, the gas is discharged, part of the liquid is returned to the C7 tower 1 as reflux, and the remaining liquid is introduced into the lower part of the C6 tower 2. Specifically, the gas phase at the top of the C7 tower 1 first passes through the air cooler 101, and then is cooled to 42°C-50°C by the circulating water cooler 102, and then enters the gas-liquid separation tank 103 for gas-liquid separation. In the gas-liquid separation tank 103, a small amount of gas with C5 and C6 is separated from the tank top and enters the fuel gas system, while part of the liquid phase is returned to the C7 tower 1 through the reflux pump 104 as reflux, and the remaining liquid is sent out of the C7 tower 1 as a mixed hydrocarbon of normal and isohexane, and is sent to the C6 tower 2 by self-pressure or by pumping. Among them, by controlling the cooling amount of the air cooler 101 and the circulating water cooler 102, the temperature of the tower top gas after cooling can be controlled, so that the temperature of the tower top gas after air cooling and water cooling is 42°C-50°C. The liquid phase at the bottom of C7 Tower 1 is vaporized by 15%-25% through a heat source and then returns to C7 Tower 1. The remaining liquid phase is used as a C7 fraction and is pumped by self-pressure or a delivery pump 106 to be cooled to 40°C-42°C before being sent out of the device. Specifically, the liquid phase at the bottom of C7 Tower 1 passes through a reboiler 105, vaporized by 15%-25%, and then returns to C7 Tower 1. The remaining liquid phase is used as a C7 fraction and is cooled by self-pressure or a delivery pump 106 through a circulating water cooler 107 to be cooled to 40°C-42°C before being sent out of the system. Since the circulating water temperature is higher in summer, it is sufficient to ensure a minimum temperature of 42°C to maintain stable operation. In winter, the circulating water temperature is lower, and the operating temperature of the gas-liquid separation tank 103 can be appropriately reduced to about 38°C. Among them, the air cooler 101, circulating water cooler 102 and gas-liquid separation tank 103 at the top of the tower, and the reboiler 105 and circulating water cooler 107 at the bottom of the tower can all utilize existing equipment. Among them, the circulating water cooler 107 at the bottom of the tower can use the circulating water cooler 407 of the C7 fraction product at the bottom of the second hexane tower, which does not require new equipment and reduces equipment investment costs.

[0027] like Figure 1 and Figure 2As shown, the operating pressure of C6 Tower 2 is normal pressure-200kPaa, and the range of operating pressure is set wider, because the lower the operating pressure, the lower the energy consumption of the device. The reflux ratio is 7.7-9.9, wherein the reflux ratio is a mass ratio, i.e., the ratio of the reflux amount to the distillate amount. The reflux ratio should be determined according to the operating pressure and product quality. It should not be too large, which will lead to over-operation of the device and increased energy consumption. The number of theoretical plates in C6 Tower 2 is 90-100, preferably 96, and the position of the hydrocarbon material feed containing normal hexane and isohexane components is the 60th-70th block, and the preferred feed position is the 64th block, and the feed position is located at the lower part of C6 Tower 2. Among them, the number of theoretical plates and the feed position of C6 Tower 2 are the same as before, so the original equipment can be used, and there is no need to build new equipment, reducing the equipment investment cost. C6 Tower 2 adjusts the parameters such as tower pressure, extraction amount, reflux amount, etc. according to the product quality requirements of isohexane and normal hexane to meet the separation requirements.

[0028] like Figure 1 and Figure 2 As shown, the gas phase at the top of the C6 tower 2 is partially cooled to 42°C, and gas-liquid separation is performed, the gas is discharged, and part of the liquid is returned to the C6 tower 2 as reflux, and the remaining liquid is first cooled to 40°C-42°C as an isohexane product by self-pressure or pumping before being sent out of the device. Specifically, the gas phase at the top of the C6 tower 2 first passes through the air cooler 201, and then passes through the circulating water cooler 202 to be cooled to 42°C, and enters the gas-liquid separation tank 203. Because the feed is the lightest material system in the system, a small amount of gas is also carried in the isohexane and separated from the tank top, and part of the liquid is returned to the C6 separation tower as reflux through the reflux pump 204, and the remaining liquid is first cooled to 40°C~42°C as an isohexane product by self-pressure or pumping through the circulating water cooler 202 before being sent out of the C6 tower 2. The liquid phase at the bottom of C6 Tower 2 is vaporized by 15%-25% through a heat source and then returns to C6 Tower 2. The remaining liquid phase is cooled to 40℃-42℃ as a n-hexane product by self-pressure or pumping before being sent out of the device. The liquid phase at the bottom of C6 Tower 2 passes through a reboiler 205, vaporized by 15%-25%, and then returns to C6 Tower 2. The remaining liquid phase is cooled to 40℃-42℃ as a n-hexane product by self-pressure or by a delivery pump 206 through a circulating water cooler 207 before being sent out of the system. Among them, the air cooler 201, circulating water cooler 202 and gas-liquid separation tank 203 at the top of the tower, as well as the reboiler 205 at the bottom of the tower can all use the original equipment, and only one circulating water cooler 207 needs to be added at the bottom of the tower.

[0029] like Figure 2As shown, the substance containing n-hexane flowing out of the bottom of the C6 tower 2 is heat exchanged with the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower 2 through the heat exchanger 208, and the temperature of the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower 2 is heated from 42°C to 50°C, effectively reducing the reboiling load at the bottom of the C6 tower 2, and at the same time reducing the cooling load of the n-hexane product circulating water cooler 207. The arithmetic mean heat transfer temperature difference of the heat exchanger 208 is ≥10°C, the flow rate on the hot logistics side is 13t / h, and the temperature after heat exchange is 60°C-65°C, the flow rate on the cold logistics side is 16-18t / h, and the temperature after heat exchange is 45°C-50°C. The heat exchange of the logistics in the C6 tower 2 can reduce energy consumption and reduce the reboiling load. The calculation formula of the arithmetic mean heat transfer temperature difference is ((hot logistics inlet temperature - cold logistics outlet temperature) + (hot logistics outlet temperature - cold logistics inlet temperature)) / 2. The heat transfer area of ​​the heat exchanger cannot be too large, otherwise it cannot be realized in practical applications. However, the gas-liquid temperature difference is large, and the arithmetic mean heat transfer temperature difference can reach 20°C, which has a large heat transfer driving force.

[0030] like Figure 1 and Figure 2 As shown, the heat source comes from the reboiler. The heat source of the reboiler 105 at the bottom of the C7 tower 1 is 0.5-1.0MPag steam. The steam at the temperature of 0.5MPag is generally obtained by reducing the pressure of 1.0MPag steam. In actual devices, only 1.0MPag steam is generally produced. Although the steam temperature of 0.5MPag is more consistent with the bottom product of the C7 tower 1, if there is no 0.5MPag steam in actual production, 1.0MPag steam can also be used instead. The reboiler heat source at the bottom of the C6 tower 2 is 95℃-105℃ hot water. The reboiler heat source of the C6 tower 2 is changed from steam to hot water, because the bottom product changes from C7 fraction to n-hexane, the system becomes lighter, and the corresponding temperature also decreases. There is no need to use the original higher temperature heat source, and hot water can be used as the reboiler heat source to achieve high energy and high use, low energy and low use, and rational use of energy at different energy levels. The arithmetic mean heat transfer temperature difference of the steam reboiler 105 at the bottom of the C7 Tower 1 is ≥20°C, the flow rate on the hot logistics side is 200-350t / h, the temperature after heat exchange is 159°C, the flow rate on the cold logistics side is 200-250t / h, and the return tower temperature is 96°C-105°C; the arithmetic mean heat transfer temperature difference of the hot water reboiler 205 at the bottom of the C6 Tower 2 is ≥15°C, the flow rate on the hot logistics side is 150-300t / h, the temperature after heat exchange is 86°C-88°C, the flow rate on the cold logistics side is 190-260t / h, and the return tower temperature is 75°C-80°C.

[0031] like Figure 1 and Figure 2As shown, a separation system for the raffinate oil after decarbonization of five carbons comprises a C7 tower 1 and a C6 tower 2 arranged in series, the upper part of the C7 tower 1 is provided with an inlet pipeline 1a for the raffinate oil after decarbonization of five carbons, the top of the C7 tower 1 is provided with an outflow pipeline 1b for hydrocarbon substances containing normal hexane and isohexane components and a reflux pipeline 1c, the bottom of the C7 tower 1 is provided with a reboiler 105 and a C7 fraction outflow pipeline 1d, the top of the C6 tower 2 is provided with an outflow pipeline 2a for substances containing isohexane and a reflux pipeline 2b, the bottom of the C6 tower 2 is provided with a reboiler 205 and a outflow pipeline 2c for substances containing normal hexane, and the outflow pipeline 1b for hydrocarbon substances containing normal hexane and isohexane components is connected to the lower part of the C6 tower 2.

[0032] Example 1 The principle process of the embodiment of the present invention is as follows Figure 1 As shown, the raw material is the residual oil extracted from the continuous reforming unit after pre-hydrogenation and decarbonization. The difference from Comparative Example 1 is that the separation process of "first decarbonization and then decarbonization" is adopted, that is, the first tower is C7 tower 1, the second tower is C6 tower 2, the heaviest component C7 is obtained from the bottom of C7 tower 1, and the product isohexane and product normal hexane are obtained from the top and bottom of C6 tower 2 respectively. The specific process is as follows.

[0033] The raffinate oil after pre-hydrogenation and decarbonization of the raw material is fed from the upper part of the plate tower C7 tower 1. The top gas of the C7 tower 1 is cooled by the top air cooler 101 and the top circulating water cooler 102 in turn, and then enters the top gas-liquid separation tank 103 of the C7 tower 1. The separated liquid phase is pressurized by the top product of the C7 tower 1 and the reflux pump 104, and then returns to the top of the C7 tower 1 through the reflux pipeline 1c as cold reflux, and returns to the top of the C7 tower 1 through the outflow pipeline 1b as n-hexane. A mixed hydrocarbon of hexanes and isohexane is produced, and a small amount of gas is produced from the gas-liquid separation tank 103 and enters the fuel gas system; the C7 fraction is distilled from the bottom of the C7 tower 1, a part of it returns to the tower through the bottom reboiler 105, and the other part is pressurized by the transfer pump 106 through the C7 fraction outflow pipeline 1d, and then cooled to about 40°C through the C7 fraction product circulating water cooler 107 for production, wherein the bottom reboiler 105 of the C7 tower 1 uses 0.5MPag steam as the heat source.

[0034] The mixed hydrocarbons of normal hexane and isohexane distilled from the top of C7 tower 1 are fed into the lower part of C6 tower 2 of the plate tower. The top gas of C6 tower 2 is cooled by top air cooler 201 and top circulating water cooler 202 in turn, and then enters into gas-liquid separation tank 203 at the top of C6 tower 2. The separated liquid phase (isohexane) is pressurized by top product of C6 tower 2 and reflux pump 204, and then returns to the top of C6 tower 2 as cold reflux through reflux pipeline 2b, and then returns to the top of C6 tower 2 through outflow pipeline 2a. It is sent out as the isohexane product, and a small amount of gas is extracted from the gas-liquid separation tank 203 and enters the fuel gas system; the n-hexane product is distilled out from the bottom of the C6 tower 2, a part of it returns to the tower through the bottom reboiler 205, and the other part is pressurized by the bottom delivery pump 206 of the C6 tower 2 through the material outflow pipeline 2c containing n-hexane, and then cooled to about 40°C through the n-hexane product circulating water cooler 207 for extraction, wherein the bottom reboiler 205 of the C6 tower 2 uses 95°C hot water as the heat source.

[0035] The difference between this embodiment and comparative example 1 is that: the isohexane tower 3 in comparative example 1 is replaced by a C7 tower 1, and normal hexane and isohexane are produced from the top of the C7 tower 1, and the C7 fraction is produced from the bottom; the hexane tower 4 in comparative example 1 is replaced by a C6 tower 2, and the normal hexane and isohexane from the top of the C7 tower 1 enter the lower part of the C6 tower 2, and the isohexane product is distilled from the top after separation, and the normal hexane product is distilled from the bottom.

[0036] This embodiment adjusts the component separation order based on comparative example 1. The bottom component of C6 tower 2 is changed from the original C7 fraction to n-hexane, the component becomes lighter, and the bottom temperature is reduced, so the reboiling heat source can be changed from the original 0.5MPag steam of hexane tower 4 to 95℃ hot water.

[0037] The new separation process of "first removing the heavy oil and then removing the light oil" of the raffinate oil after decarbonization of this embodiment is adopted, and the products obtained are shown in Table 1.

[0038] Table 1 Composition of the product of Example 1 process.

[0039] As shown in Table 1, the product flow rates are: isohexane 3222.0kg / h, n-hexane 13400.0kg / h, C7 fraction 2229.4kg / h, 18851.4kg / h. The corresponding product concentrations are: isohexane 81.20%wt, C7 fraction ≤C6 content 4.94%wt, and n-hexane distillation range 64.7℃-81.7℃, all meeting the requirements.

[0040] The operating parameters and tower parameters of C7 Tower 1 and C6 Tower 2 are shown in Table 2.

[0041] Table 2 Main operating parameters and tower parameters of C7 tower and C6 tower.

[0042] By comparing Table 2 and Table 8, it can be seen that after the original hexane tower 4 is changed to the C6 tower 2 in Example 1, the reboiler flow returning to the C6 tower 2 is 79.5°C, so 95°C hot water can be used to replace 0.5MPag steam as the reboiler heat source.

[0043] As can be seen from Table 2, the total cooling load of the two towers in Example 1 is 7777kW, and the total reboiler load is 7724kW. Example 1 consumes 755.1t / h of circulating water, and the cost is 1.586 million yuan / year; the 0.5MPag steam heating load is 4164kW, and the 0.5MPag steam consumption is 6717.7kg / h, and the cost is 12.414 million yuan / year; the 95℃ hot water heating load is 3681kW, the hot water consumption is 300.8 t / h, and the cost is 1.808 million yuan / year. Based on the above results, the total energy consumption cost of Example 1 is 15.808 million yuan / year, which is 9.536 million yuan / year lower than the total energy consumption cost of Comparative Example 1, a decrease of 37.6%.

[0044] Example 2 The principle process of the embodiment of the present invention is as follows Figure 1 As shown, this embodiment is an operation improvement based on the embodiment 1, the original cold reflux at the top of the carbon seven tower 1 is changed to hot reflux, and the reflux temperature is increased from the original 42°C to 50°C. The other processes not described are the same as those in the embodiment 1, and no further description is given here. That is, the top circulating water cooler 102 of the carbon seven tower 1 in the embodiment 1 originally condensed the top gas to 42°C and fed it into the top gas-liquid separation tank 103 of the carbon seven tower 1. In the embodiment 2, the top circulating water cooler 102 of the carbon seven tower 1 condensed the top gas to 50°C and then fed it into the top gas-liquid separation tank 103 of the carbon seven tower 1. In this way, the top condensation load of the carbon seven tower 1 can be reduced, while the feed temperature of the carbon six tower 2 can be increased, the heat load of the bottom reboiler 205 of the carbon six tower 2 can be reduced, the amount of hot water can be reduced, and the energy utilization efficiency can be improved.

[0045] The products obtained by adopting the separation process of "first removing the heavy and then removing the light" of the hot reflux raffinate oil of this embodiment are shown in Table 3.

[0046] Table 3 Composition of the process product of Example 2.

[0047] It can be seen from Table 3 that the product composition and flow rate of Example 2 are basically consistent with those of Comparative Example 1.

[0048] The operating parameters and tower parameters of C7 Tower 1 and C6 Tower 2 are shown in Table 4.

[0049] Table 4 Operating parameters and tower parameters of C7 tower and C6 tower.

[0050] As can be seen from Table 4, the total cooling load of the two towers in Example 2 is 7556kW, and the total reboiler load is 7613kW. Example 2 consumes 733.7t / h of circulating water, and the cost is 1.541 million yuan / year; the 0.5MPag steam heating load is 4051kW, and the 0.5MPag steam consumption is 6535.0kg / h, and the cost is 12.077 million yuan / year; the 95℃ hot water heating load is 3562kW, the hot water consumption is 294.0 t / h, and the cost is 1.750 million yuan / year. Based on the above results, the total energy consumption cost of Example 2 is 15.368 million yuan / year, which is 9.975 million yuan / year lower than the total energy consumption cost of Comparative Example 1, a decrease of 39.4%.

[0051] Example 3 The principle process of the embodiment of the present invention is as follows Figure 2 As shown, this embodiment is based on the embodiment 1 and the operation is improved. A feed heat exchanger 208 for C6 tower 2 is newly added. The rest of the processes not described are the same as those in embodiment 1 and will not be described in detail here. In this embodiment, the n-hexane product of the bottom product of C6 tower 2 is pressurized by the bottom delivery pump 206 of C6 tower 2, and then heat exchange is performed with the substance containing n-hexane flowing out of the bottom of C6 tower 2 and the hydrocarbon substance containing n-hexane and isohexane components entering C6 tower 2 through the heat exchanger 208. After the heat exchange, the substance is cooled to about 40°C through the circulating water cooler 207 for the n-hexane product before extraction. In this way, through the heat exchange between the raw material and the product, the characteristics of the large flow rate and high temperature of the n-hexane product are effectively utilized to realize the heat recovery of the logistics in the tower, effectively reduce the reboiling load of C6 tower 2 and the cooling load of the n-hexane product cooler, and further improve the energy utilization efficiency.

[0052] The products of the separation process of "first removing the heavy and then removing the light" of the raffinate oil by recovering the heat of the tower logistics of this embodiment are shown in Table 5.

[0053] Table 5 Composition of the process product of Example 3.

[0054] It can be seen from Table 5 that the product composition and flow rate of Example 3 are basically consistent with those of Comparative Example 1.

[0055] The operating parameters and tower parameters of C7 Tower 1 and C6 Tower 2 are shown in Table 6.

[0056] Table 6 Operating parameters and tower parameters of C7 tower and C6 tower.

[0057] The total cooling load of the two towers in Example 3 is 7832kW, and the total reboiler load is 7752kW. Example 3 consumes 760.5t / h of circulating water, and the cost is 1.597 million yuan / year; the heating load of 0.5MPag steam is 4164kW, and the consumption of 0.5MPag steam is 6717.7kg / h, and the cost is 12.414 million yuan / year; the heating load of 95℃ hot water is 3588kW, the hot water consumption is 296.7 t / h, and the cost is 1.763 million yuan / year. Based on the above results, the total energy consumption cost of Example 3 is 15.774 million yuan / year, which is 9.569 million yuan lower than the total energy consumption cost of Comparative Example 1, a decrease of 37.8%.

[0058] Based on the above embodiments 1-3, it can be known that the present invention makes the following improvements on the basis of the original isohexane tower 3 and hexane tower 4 sequential separation: the original isohexane tower 3 is changed to C7 tower 1, and the original hexane tower 4 is changed to C6 tower 2, that is, the "first light removal, then heavy removal" process is changed to "first heavy removal, then light removal" process. Among them, the heaviest C7 fraction is distilled from the bottom of C7 tower 1, normal and isohexane are distilled from the top of C7 tower 1 into C6 tower 2, isohexane products are distilled from the top of C6 tower 2, and normal hexane products are distilled from the bottom of C6 tower 2, thereby overcoming the back mixing of the intermediate component normal hexane and improving the distillation efficiency; and the second tower is used to separate normal hexane and isohexane, the components become lighter, the bottom temperature of the tower is reduced, and 95°C hot water can be used instead of 0.5MPag steam as a heat source; at the same time, the first tower is changed from the original separation of similar boiling point systems to the separation of non-boiling point similar systems, which greatly reduces the difficulty of separation, not only reduces energy consumption, but also reduces the number of plates and investment.

[0059] Comparative Example 1 Comparative Example 1 is an existing sequential separation process for the raffinate oil after decarbonization of a continuous reforming unit in a refinery. The feed is 19047 kg / h, and it is necessary to separate the n-hexane product with an Engler distillation range of 64°C-82°C, the isohexane product with an isohexane concentration of ≥80%wt, and the C7 fraction product with a C6 concentration of ≤5%wt. The principle process is shown in the figure below. Figure 3 As shown, the specific process is as follows.

[0060] The raffinate oil after pre-hydrogenation and decarbonization is fed from the lower middle of the plate tower isohexane tower 3. The top gas of the isohexane tower 3 is cooled by the top air cooler 301 and the top circulating water cooler 302 of the isohexane tower 3 in turn, and then enters the top gas-liquid separation tank 303 of the isohexane tower 3. The separated liquid phase is pressurized by the top product of the isohexane tower 3 and the reflux pump 304, and part of it returns to the top of the isohexane tower 3 as cold reflux, and part of it is produced as the isohexane product. A small amount of top gas is discharged from the gas-liquid separation tank 303, wherein the bottom reboiler 305 of the isohexane tower 3 uses 0.5MPag steam as a heat source.

[0061] The mixed hydrocarbons of normal hexane and carbon seven fraction distilled from the bottom of isohexane tower 3 are sent to hexane tower 4 after being pressurized by the bottom delivery pump 306 of isohexane tower 3. The top gas of hexane tower 4 is cooled by the top air cooler 401 of hexane tower 4 and the top circulating water cooler 402 of hexane tower 4 in turn, and then enters the top gas-liquid separation tank 403 of hexane tower 4. The separated liquid phase is pressurized by the top product of hexane tower 4 and the reflux pump 404, and part of it is returned to the top of hexane tower 4 as cold reflux, and part of it is extracted as normal hexane product, and the top of hexane tower 4 does not extract the gas phase; wherein, the reboiler 405 at the bottom of hexane tower 4 uses 0.5MPag steam as a heat source, and part of the carbon seven fraction at the bottom of hexane tower 4 is returned to the tower through the reboiler 405, and the other part is discharged from the device through the delivery pump 406 and the circulating water cooler 407. That is, comparative example 1 is a "light removal first, heavy removal later" sequential separation process.

[0062] The composition of the process product of Comparative Example 1 is shown in Table 7.

[0063] Table 7 Composition of the product of comparative example 1.

[0064] As shown in Table 7, the product volume isohexane 3219.6kg / h, normal hexane 13400.0kg / h, C7 fraction 2229.4kg / h, totaling 18849.0t / h. The product concentration isohexane 82.25%wt, C7 fraction ≤C6 content 3.42%wt, and normal hexane distillation range 64.7℃-81.8℃, all meeting the requirements.

[0065] The main operating parameters and tower parameters of isohexane tower 3 and hexane tower 4 are shown in Table 8.

[0066] Table 8 Main operating parameters and tower parameters of isohexane tower and hexane tower.

[0067] As can be seen from Table 8, the total cooling load of Comparative Example 1 is 8195kW and the total reboiler load is 7942kW. The circulating water supply is 25℃, the return water is 32℃, and the unit price is 0.25 yuan / t; the unit price of 0.5MPag steam is 220 yuan / t; the hot water supply is 105℃, the return water is 88℃, and the unit price is 0.68 yuan / 10 4 kcal; the unit is operated for 8400 hours per year. For Example 1, the circulating water is converted to 795.7t / h, with a cost of 1.671 million yuan / year; the consumption of 0.5MPag steam is 13.4t / h, with a cost of 24.672 million yuan / year; the total energy consumption cost is 25.343 million yuan / year.

[0068] In general, the separation process of the present invention for removing carbon five and then extracting the residual oil changes the current separation process of "removing light components first and then heavy components" into a separation process of "removing heavy components first and then light components", that is, the original process of the isohexane tower is changed into a carbon seven tower, and the hexane tower is changed into a carbon six tower. First, the heaviest C7 component is separated from the bottom of the C7 tower, and the mixture of n-hexane and isohexane is distilled from the top of the tower. This can reduce the backmixing of the intermediate component n-hexane (backmixing refers to the concentration of the intermediate component n-hexane in the original isohexane tower first increasing and then decreasing, forming a concentration peak in the tower), while reducing the difficulty of system separation and energy consumption, and reducing the number of tower plates, saving investment costs; the mixture of n-hexane and isohexane enters the C6 tower, and the isohexane product rich in 2,2-dimethylbutane, 2-methylpentane and 3-methylpentane is separated from the top of the tower, and the n-hexane product is distilled from the bottom of the tower. In this way, the system components become lighter, the bottom temperature of the tower is reduced, and low-grade heat sources such as 95°C hot water can replace high-grade 0.5MPag steam as a reboiling heat source, solving the problem of high energy and low utilization of the device, realizing the rational utilization of energy, and further reducing energy consumption. The C7 fraction of the present invention is separated in advance, which avoids repeated distillation in the subsequent tower, thereby reducing the processing amount in the separation process of the difficult-to-separate system n-hexane and 3-methylpentane, and improving the overall separation efficiency. At the same time, the functional transformation of the original isohexane tower changes the top product from isohexane to mixed C6, which reduces the difficulty of separation, not only reduces the consumption of reboiling steam at the bottom of the tower, but also reduces the number of tower plates and equipment investment. After the original hexane tower is converted into a C6 tower, the bottom product is converted from the C7 fraction to n-hexane, the bottom temperature of the tower is reduced, and 95°C hot water can be used instead of 0.5MPag steam as a reboiling heat source. The present invention realizes heat exchange between the inlet and outlet of the C6 tower by configuring a heat exchanger. The substance containing n-hexane flowing out of the bottom of the C6 tower and the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower are heat exchanged through a heat exchanger, and the feed is preheated, which reduces both the reboiling load at the bottom of the tower and the cooling load of the product.

[0069] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A separation process for raffinate oil after decarbonization, characterized in that: The following steps are involved: The raffinate oil after decarbonization is fed into the upper part of the C7 tower, and a heat source is set at the bottom of the C7 tower for heating, and the C7 tower is controlled to operate under distillation conditions, and a C7 fraction is separated from the bottom of the C7 tower, and a part of the hydrocarbon substances containing normal hexane and isohexane components separated from the top of the tower is refluxed, and the rest enters from the lower part of the C6 tower; The C6 tower fractionates the hydrocarbon material containing normal hexane and isohexane components into normal hexane-containing material and isohexane-containing material. The isohexane-containing material flows out from the top of the C6 tower, and the normal hexane-containing material flows out from the bottom of the C6 tower.

2. A separation process for raffinate oil after decarbonization according to claim 1, characterized in that: The operating pressure of the C7 tower is normal pressure-200 kPaa, the reflux ratio is 1.3-1.8, the theoretical number of plates in the C7 tower is 83-103, and the position of feeding the residual oil after decarbonization of C5 is the 20th-30th plate.

3. A separation process for raffinate oil after decarbonization according to claim 1, characterized in that: The gas phase at the top of the C7 tower is cooled to 42°C-50°C, and gas-liquid separation is carried out. The gas is discharged, and part of the liquid is returned to the C7 tower as reflux, and the remaining liquid is introduced into the lower part of the C6 tower; the liquid phase at the bottom of the C7 tower is vaporized 15%-25% by the heat source and then returned to the C7 tower, and the remaining liquid phase is used as the C7 fraction by self-pressure or pumping to be cooled to 40°C-42°C before being sent out of the device.

4. A separation process for raffinate oil after decarbonization according to claim 1, characterized in that: The operating pressure of the C6 tower is atmospheric pressure-200 kPaa, the reflux ratio is 7.7-9.9, the number of theoretical plates in the C6 tower is 90-100, and the position for feeding the hydrocarbon material containing normal hexane and isohexane components is the 60th-70th block.

5. A separation process for raffinate oil after decarbonization according to claim 1, characterized in that: The gas phase at the top of the C6 tower is cooled to 42°C, and gas-liquid separation is carried out. The gas is discharged, and part of the liquid is returned to the C6 tower as reflux, and the remaining liquid is cooled to 40°C-42°C by self-pressure or pumping as an isohexane product and then sent out of the device; the liquid phase at the bottom of the C6 tower is vaporized 15%-25% by the heat source and then returned to the C6 tower, and the remaining liquid is cooled to 40°C-42°C by self-pressure or pumping as a normal hexane product and then sent out of the device.

6. A separation process for raffinate oil after decarbonization according to claim 1, characterized in that: The substance containing n-hexane flowing out of the bottom of the C6 tower is heat exchanged with the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower through a heat exchanger, and the temperature of the hydrocarbon substance containing n-hexane and isohexane components entering the C6 tower is heated from 42°C to 50°C.

7. A separation process for raffinate oil after decarbonization according to claim 6, characterized in that: The arithmetic mean heat transfer temperature difference of the heat exchanger is ≥10°C, the flow rate on the hot logistics side is 13t / h, the temperature after heat exchange is 60°C-65°C, the flow rate on the cold logistics side is 16-18t / h, and the temperature after heat exchange is 45°C-50°C.

8. A separation process for raffinate oil after decarbonization according to claim 1, characterized in that: The heat source comes from the reboiler. The reboiler heat source at the bottom of the C7 tower is 0.5-1.0 MPag steam, and the reboiler heat source at the bottom of the C6 tower is 95°C-105°C hot water.

9. A separation process for raffinate oil after decarbonization according to claim 8, characterized in that: The arithmetic mean heat transfer temperature difference of the steam reboiler at the bottom of the C7 tower is ≥20°C, the flow rate on the hot logistics side is 200-350t / h, the temperature after heat exchange is 159°C, the flow rate on the cold logistics side is 200-250t / h, and the return tower temperature is 96°C-105°C; the arithmetic mean heat transfer temperature difference of the hot water reboiler at the bottom of the C6 tower is ≥15°C, the flow rate on the hot logistics side is 150-300t / h, the temperature after heat exchange is 86°C-88°C, the flow rate on the cold logistics side is 190-260t / h, and the return tower temperature is 75°C-80°C.

10. A separation system for raffinate oil after decarbonization, characterized in that: The invention comprises a C7 tower and a C6 tower which are arranged in series, wherein the upper part of the C7 tower is provided with an inlet pipeline for the residual oil extracted after decarbonization of C5, the top of the C7 tower is provided with an outflow pipeline and a reflux pipeline for hydrocarbon substances containing normal hexane and isohexane components, the bottom of the C7 tower is provided with a reboiler and an outflow pipeline for the C7 fraction, the top of the C6 tower is provided with an outflow pipeline and a reflux pipeline for substances containing isohexane, the bottom of the C6 tower is provided with a reboiler and an outflow pipeline for substances containing normal hexane, and the outflow pipeline for hydrocarbon substances containing normal hexane and isohexane components is connected to the lower part of the C6 tower.

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