Reduced-pressure operation method of atmospheric fractionation system

Abstract

The invention discloses a reduced-pressure operation method of a normal-pressure fractionation system, and aims to overcome the defects of high consumption and investment of the fractionation system in the prior art. Comprising a fractionating tower, a tower top condenser and a tower top tank, a fractionating tower feed enters the fractionating tower for fractionating, a fractionated liquid phase is discharged from the bottom of the fractionating tower to serve as a tower bottom product, and a fractionated gas phase is discharged from the top of the fractionating tower as a tower top gas phase medium through a first process pipeline and then enters the tower top condenser to be condensed; the condensed liquid-phase medium flows downwards to a tower top tank for buffering through a second process pipeline under the action of gravity, then all or one part of the liquid-phase product in the tower top tank is pumped to other facilities, and the other part of the liquid-phase product as reflux is boosted by a tower top pump and then returns to the upper part of the fractionating tower; h1 is the vertical distance between a top gas phase outlet of the fractionating tower and a tower top condenser, and H2 is the vertical distance between the tower top condenser and a tower top tank and is 0.5 mlt; h1lt; the thickness is 150 m, 1 mlt; h21t; and the second process pipeline extends below the liquid level in the tower top tank.

Description

Technical Field

[0001] The invention relates to the field of petroleum fraction processing, and in particular to a decompression operation method for an atmospheric pressure fractionation system. Background Art

[0002] The boiling point of a liquid varies with pressure. In the petrochemical industry, different methods such as atmospheric distillation and vacuum distillation are often used to separate products. When atmospheric distillation is used, it is often equipped with equipment such as a heating furnace, and the investment and energy consumption are relatively high; vacuum distillation is carried out under reduced pressure to reduce the heat load, especially the high-temperature heat load, and can reduce or avoid adverse reactions such as oxidation, decomposition or polymerization of certain media when the temperature is too high. In order to meet the needs of vacuum distillation, vacuum pumps, steam ejectors and other measures are often used for vacuuming, which will increase the investment in corresponding vacuuming facilities and public engineering consumption.

[0003] The Chinese patent CN 215939052 U discloses a vacuum fractionation device, which includes a vacuum tower and a cooling tower; the vacuum tower is provided with a fractionation material outlet at the top, the cooling tower is provided with a fractionation material inlet, and the fractionation material outlet is connected to the fractionation material inlet; the cooling tower is provided with a condensate outlet at the bottom, the cooling tower is provided with a cooling nozzle at the top, and the condensate outlet is connected to the cooling nozzle; the cooling tower is provided with a vacuum port at the top. The vacuum fractionation device avoids the vacuum system from being directly connected to the cooler, effectively solves the problem of shutdown and maintenance of the device caused by frequent corrosion and leakage of the heat exchange core, has high cooling efficiency, and ensures the negative pressure effect of the vacuum system on the entire line fractionation system, thereby ensuring the vacuum fractionation efficiency. However, the invention adds a cooling tower system on the basis of the vacuum tower, vacuum pump and other facilities, so the system investment and consumption are further increased.

[0004] The Chinese patent CN 206035772 U discloses a water-gas separator and a vacuum system, wherein the water-gas separator comprises an outer shell (1) having an air outlet (14) at the upper end and a water outlet (15) at the lower end, wherein an inner cylinder (2) extending from the upper end of the outer shell (1) toward the lower end is arranged inside the outer shell (1), and a distance is provided between the lower end of the inner cylinder (2) and the outer shell (1); wherein a guide structure (3) extending from top to bottom in a spiral shape is arranged on the outer wall surface of the inner cylinder (2), and an air inlet (13) leading to the guide structure (3) of the inner cylinder (2) is arranged on the outer shell (1). The water-gas separator and vacuum system provided by the technology can realize the separation of gas from water and other impurities, and reduce the damage caused to the vacuum pumping facilities by the impurities. The invention is to add a water-gas separation system when the vacuum pumping facilities are configured in the vacuum tower and the vacuum system, so the system investment and consumption are further increased.

[0005] Therefore, it is necessary to provide a new fractionation operation method that can realize the decompression operation of the fractionation tower, meet the product fractionation requirements, and effectively reduce the consumption and investment of the fractionation system. Summary of the invention

[0006] The purpose of the present invention is to provide a decompression operation method for an atmospheric pressure fractionation system in view of the shortcomings of the prior art. The present invention can perform decompression operation without adding vacuum pumping facilities, thus overcoming the shortcomings of the prior art such as large consumption and investment of the fractionation system.

[0007] In order to achieve the above-mentioned object, the present invention provides a decompression operation method of an atmospheric pressure fractionation system, characterized in that: it comprises a fractionation tower, a tower top condenser and a tower top tank, the fractionation tower feed enters the fractionation tower for fractionation, the liquid phase after fractionation comes out from the bottom of the fractionation tower as a tower bottom product, the gas phase after fractionation comes out from the top of the fractionation tower as a tower top gas phase medium through a first process pipeline, and then enters the tower top condenser for condensation, the condensed liquid phase medium flows downward to the tower top tank through a second process pipeline under the action of gravity for buffering, and then the liquid phase product in the tower top tank can be completely extracted to other facilities, or part of it can be returned to the upper part of the fractionation tower as reflux after being pressurized by a tower top pump;

[0008] The operating pressure P1 of the fractionation tower is -0.099 MPa to 0 MPa (G), preferably -0.0987 to 0 MPa (G);

[0009] The operating pressure P2 of the tower top tank is 0-0.6 MPa(G), preferably 0.01-0.5 MPa(G)

[0010] The operating pressure P2 of the tower top tank is higher than the operating pressure P1 of the fractionation tower. The difference is related to the vertical height difference H2 from the tower top condenser to the tower top tank and the density of the tower top liquid phase product. Generally, P2-P1>0.01MPa. The second process pipeline penetrates below the liquid surface in the tower top tank.

[0011] The height of the gas phase outlet at the top of the fractionation tower is higher than the height of the top condenser, and the height of the top condenser is higher than the height of the top tank. H1 is the vertical distance between the gas phase outlet at the top of the fractionation tower and the top condenser, and H2 is the vertical distance between the top condenser and the top tank, 0.5m

[0012] Furthermore, a gas supply regulating valve and an exhaust regulating valve are provided on the top of the tower top tank.

[0013] The present invention is mainly applicable to atmospheric pressure fractionation systems without overhead gas phase products, such as atmospheric pressure fractionation systems of hydrogenation devices, naphtha fractionation systems, etc., and the feed of the fractionation tower is mainly mixed fraction components to be separated.

[0014] ​The advantages of the present invention compared with the prior art are as follows: 1) the height of the gas phase outlet at the top of the fractionation tower of the present invention is higher than the height of the top condenser, the height of the top condenser is higher than the height of the top tank, the second process pipeline penetrates below the liquid level in the top tank, that is, the outlet of the second process pipeline is lower than the lowest operating liquid level of the top tank, so as to ensure that the liquid phase medium after condensation flows continuously into the top tank under gravity, so a liquid column of a certain height will be formed in the second process pipeline between the top condenser and the top tank, and as the liquid phase medium flows continuously downward, the fractionation tower, the first process pipeline, the top tank and the second process pipeline are connected to each other. The pressure in the space between the condenser and the second process pipeline is reduced, that is, P1 is displayed as a negative pressure state. Due to the presence of the liquid column in the second process pipeline on the tower top tank, the tower top tank pressure P2 is higher than the distillation tower top pressure P1; the gas phase medium separated from the top of the distillation tower changes from gas phase to liquid phase after being cooled by the condenser, and the liquid phase medium flows into the tower top tank under gravity. Since the volume of the medium is significantly reduced after liquefaction, the continuous space such as the distillation tower, the tower top condenser and the connecting pipeline between the tower top tanks will naturally form a negative pressure, thereby realizing the decompression operation of the atmospheric pressure fractionation system of the present invention. 2) The present invention preferably has an air supply regulating valve and an exhaust regulating valve on the top or upper part of the tower top tank, and the tower top tank pressure P2 can be appropriately adjusted by the air supply regulating valve and the exhaust regulating valve of the tower top tank, and the tower top pressure P1 is adjusted accordingly to adjust the system vacuum degree; according to needs, no regulating valve may be provided, and the vacuum degree is not adjusted. 3) According to the properties of the product at the top of the distillation tower and the liquid injection height from the top condenser to the top tank, P2 can conventionally operate under positive pressure, so the gas in the top tank can be directly discharged to the flare system or other facilities; 4) The method of naturally forming a reduced pressure after the medium in the top system of the distillation tower is condensed does not require additional vacuum pumping facilities, let alone additional electricity, steam and other utility consumption for vacuum pumping facilities.

[0015] The present invention will be further described in detail below with the accompanying drawings and specific embodiments, but the scope of the present invention is not limited thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a simple flow chart of a decompression operation method of a normal pressure fractionation system.

[0017] The reference numerals shown in the figures are:

[0018] 1-distillation tower; 2-tower top condenser; 3-tower top tank; 4-tower top pump; 5-air supply regulating valve; 6-exhaust regulating valve; 7-first process pipeline; 8-second process pipeline; 9-distillation tower feed; 10-tower bottom product; 11-tower top product. DETAILED DESCRIPTION

[0019] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited by the specific implementation modes.

[0020] like Figure 1As shown, a decompression operation method of an atmospheric pressure fractionation system comprises a fractionation tower 1, a tower top condenser 2 and a tower top tank 3, a fractionation tower feed 9 enters the fractionation tower 1 for fractionation, a liquid phase after fractionation comes out from the bottom of the fractionation tower as a tower bottom product 10, a gas phase after fractionation comes out from the top of the fractionation tower as a tower top gas phase medium through a first process pipeline 7, and then enters the tower top condenser 2 for condensation, a liquid phase medium after condensation in the tower top condenser 2 flows downward to the tower top tank 3 through a second process pipeline 8 under the action of gravity for buffering, and then the liquid phase in the tower top tank 3 can be completely extracted as a tower top product 11, or part of it can be extracted as a tower top product 11 and the other part can be returned to the upper part of the fractionation tower 1 as reflux after being pressurized by a tower top pump;

[0021] The operating pressure P1 of the fractionation tower is -0.099 MPa to 0 MPa (G), preferably -0.0987 to 0 MPa (G);

[0022] The operating pressure P2 of the tower top tank is 0-0.6 MPa(G), preferably 0.01-0.5 MPa(G)

[0023] The operating pressure P2 of the tower top tank is higher than the operating pressure P1 of the fractionation tower. The difference is related to the vertical height difference H2 from the tower top condenser to the tower top tank and the density of the tower top liquid phase product. Generally, P2-P1>0.01MPa. The second process pipeline penetrates below the liquid surface in the tower top tank.

[0024] The height of the gas phase outlet at the top of the fractionation tower is higher than the height of the top condenser, and the height of the top condenser is higher than the height of the top tank. H1 is the vertical distance between the gas phase outlet at the top of the fractionation tower and the top condenser, and H2 is the vertical distance between the top condenser and the top tank, 0.5m

[0025] The top or upper part of the tower top tank is provided with an air supply regulating valve and an exhaust regulating valve.

[0026] The liquid medium condensed by the top condenser 2 flows downward to the top tank 3 through the second process pipeline 8 under the action of gravity, and forms a liquid column of a certain height in the second process pipeline between the top condenser 2 and the top tank 3. As the liquid medium continuously flows downward, a vacuum is formed in the spaces including the distillation tower 1, the first process pipeline, the top condenser 2 and the second process pipeline, that is, P1 is displayed as a negative pressure state; due to the existence of the liquid column in the second process pipeline on the top tank 3, the pressure P2 of the top tank 3 is higher than the tower top pressure P1.

[0027] ​The pressure difference between P2 and P1 described in the present invention corresponds to the height difference (H2) of the process pipeline from the top condenser to the top tank and the density of the liquid phase product at the top of the tower. The pressure P2 of the top tank can be appropriately adjusted through the gas replenishment regulating valve 5 and the exhaust regulating valve 6 of the top tank, and the pressure P1 of the top of the tower is adjusted accordingly. According to the properties of the top product of the fractionation tower and the liquid injection height from the top condenser to the top tank, P2 can conventionally be operated under positive pressure. Therefore, when adjusting the pressure of the fractionation tower system, the gas in the top tank can be directly discharged to the flare system or other facilities through the exhaust regulating valve 6.

[0028] Example

[0029] Example 1

[0030] A diesel hydrotreating unit: The distillation system of the unit is configured in the form of a distillation tower + reboiler. The top product is refined naphtha, and the bottom product is refined diesel. The top of the distillation tower is 22 meters higher than the top condenser, and the top condenser is 6 meters higher than the top tank. In order to save energy and reduce consumption, the heating furnace is gradually stopped during the operation of the distillation part of the unit, and the operating pressure of the distillation tower 1 is successively reduced to 0, -20KPa, -35KPa, etc. At this time, the pressure of the top tank 3 is displayed as ~40KPa, ~20KPa, and ~5KPa, respectively, and the differential pressure with the top of the distillation tower is maintained in the range of ~40KPa. When the heating furnace is stopped and the distillation tower system is actually operated using the decompression operation method, the separation accuracy of the refined naphtha product at the top of the distillation tower and the refined diesel product at the bottom of the distillation tower meets the requirements, and the operating pressure of the distillation tower system is flexible.

[0031] Example 2

[0032] Table 1 shows a naphtha fractionation tower of a certain device, the top product of the tower is light naphtha, and the bottom product is heavy naphtha. On the basis of the same product separation accuracy, the heat exchange of the fractionation tower operated at normal pressure and the fractionation tower operated at reduced pressure of the present invention are compared.

[0033] Table 1 Comparison of heat exchange of naphtha fractionator

[0034]

[0035] As can be seen from Table 1, the cooling load of the distillation tower and the load of the bottom reboiler are significantly reduced when the decompression operation is adopted. In addition, according to the operating temperature of the bottom reboiler, taking steam as the heat source of the reboiler as an example, it can be seen that the atmospheric pressure naphtha distillation tower needs to use steam with a pressure level of 1.0MPa or above as the heat source of the bottom reboiler; after the decompression operation is adopted, the bottom reboiler of the naphtha distillation tower can use 0.5MPa steam as the heat source, and at this time, the steam energy consumption required by the reboiler alone will be reduced by ~32.4%.

[0036] Example 3

[0037] Table 2 shows a 2.6 million tons / year residue oil hydrotreating fractionator system. The top of the fractionator separates refined naphtha, the side line extracts refined diesel, and the bottom product is hydrotreating residue oil. On the basis of the same product separation accuracy, the main equipment of the fractionator system using a fractionator feed heating furnace + atmospheric pressure fractionator + diesel side stripper and the system using a reduced pressure fractionator + diesel side stripper is compared.

[0038] Table 2 Comparison of main equipment of distillation tower system

[0039]

[0040] It can be estimated from Table 2 that the 2.6 million tons / year residue oil hydrotreating unit adopts a self-vacuum distillation tower system and does not need to set up a distillation tower feed heating furnace. The one-time equipment investment alone will save more than 5 million yuan compared with the atmospheric pressure distillation tower + heating furnace process.

Claims

1. A method for operating a decompression system of an atmospheric pressure fractionation system, comprising a fractionation tower, a tower top condenser and a tower top tank, wherein a feed of the fractionation tower enters the fractionation tower for fractionation, a liquid phase medium at the bottom of the tower comes out from the bottom of the fractionation tower as a bottom product, and a gas phase medium at the top of the tower exits the fractionation tower, characterized in that: The gas-phase medium at the top of the tower exits from the top of the fractionating tower through the first process pipeline, and then enters the top condenser for condensation. The condensed liquid-phase medium flows downward through the second process pipeline under the action of gravity to the top tank. The liquid phase in the top tank is completely withdrawn as the top product, or part of it is withdrawn as the top product and the other part is returned as reflux to the upper part of the fractionating tower; The operating pressure P1 of the fractionating tower is -0.099 MPa to 0 MPa (G), and the operating pressure P2 of the top tank is 0 to 0.6 MPa (G). The operating pressure P2 of the top tank is higher than the operating pressure P1 of the fractionating tower; The second process pipeline extends below the liquid level in the top tank; The height of the gas-phase outlet at the top of the fractionating tower is higher than the height of the top condenser, and the height of the top condenser is higher than the height of the top tank.

2. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 1, characterized in that: The vertical distance between the gas-phase outlet at the top of the fractionating tower and the top condenser is H1, 0.5 m < H1 < 150 m, and the vertical distance between the top condenser and the top tank is H2, 1 m < H2 < 150 m.

3. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 1 or 2, characterized in that: The top of the top tank is provided with a gas replenishing regulating valve and an exhaust regulating valve.

4. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 1, characterized in that: The operating pressure P1 of the fractionating tower is -0.0987 to 0 MPa.

5. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 1, characterized in that: The operating pressure P2 of the top tank is 0.01 to 0.5 MPa.

6. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 1, characterized in that: P2 - P1 > 0.01 MPa.

7. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 2, characterized in that: 0.5 m < H1 < 100 m.

8. The method for operating a decompression system of an atmospheric pressure fractionation system according to claim 2, characterized in that: 1 m < H2 < 100 m.

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