A gas phase replacement method for a spherical tank

Abstract

The present invention provides a method for gas-phase replacement of a spherical tank. By using the method of the present invention for gas-phase replacement of an ethylene spherical tank or a propylene spherical tank, the gas-phase materials in the spherical tank to be overhauled or modified can be fully utilized without being discharged to the flare for treatment, which can not only reduce material losses, but also is simple, safe and highly efficient in operation. The gas-phase replacement method includes the following steps: 1) sending the gas-phase materials in the first spherical tank that has completed the material emptying operation into the second spherical tank that has been replaced with nitrogen by using the pressure difference to replace the nitrogen in the second spherical tank; 2) connecting the third spherical tank in the state of receiving liquid-phase materials to the second spherical tank, and making the gas-phase materials in the third spherical tank flow into the second spherical tank by using the pressure difference, so that the second spherical tank reaches the preset pressure required to enter the state of receiving materials.

Description

Technical Field

[0001] The present invention relates to the technical field of gas-phase replacement of ethylene spherical tanks and propylene spherical tanks, and particularly relates to a method for gas-phase replacement of spherical tanks. Background Art

[0002] When an ethylene spherical tank (or a propylene spherical tank) is put into use, nitrogen replacement is first carried out, and then gas-phase ethylene is used to replace nitrogen. At present, the common spherical tank replacement method in most domestic chemical enterprises is to first empty the spherical tank and discharge it to the flare, and then carry out nitrogen replacement. Before putting into use, the spherical tank after qualified nitrogen replacement is subjected to actual gas pressure boosting replacement, and after passing the inspection, it is pressurized and charged with materials; or, the spherical tank is filled with nitrogen to the operating pressure and then charged with materials, and the flare is continuously discharged during the charging process to replace all the nitrogen in the tank to the flare. If there are a large number of spherical tanks to be inspected or renovated and the volume is large, if the process replacement and disposal are carried out according to the traditional method, not only a large amount of ethylene or propylene will be wasted. At the same time, since the temperature of the spherical tank after nitrogen replacement is normal temperature, it is also necessary to use a liquid-phase heat exchange medium to pre-cool it to the required temperature before putting into use. Not only does the pre-cooling take a long time, affecting the entire replacement progress, but also safety risks such as pipeline cold brittleness are likely to occur. Summary of the Invention

[0003] In view of this, the present invention provides a method for gas-phase replacement of spherical tanks. By using the method of the present invention for gas-phase replacement of ethylene spherical tanks or propylene spherical tanks, the gas-phase materials in the spherical tanks that need to be overhauled or renovated can be fully utilized, and there is no need to discharge and treat the flare, which can not only reduce material losses, but also be simple, safe and efficient in operation.

[0004] The present invention provides the following technical solutions to achieve its purpose:

[0005] The present invention provides a method for gas-phase replacement of spherical tanks, the spherical tank being an ethylene spherical tank or a propylene spherical tank, and the gas-phase replacement method comprising the following steps:

[0006] 1) Sending the gas-phase material in the first spherical tank that has completed the material emptying operation into the second spherical tank that has been subjected to nitrogen replacement by using the pressure difference to replace the nitrogen in the second spherical tank;

[0007] 2) Connecting the third spherical tank in the material receiving state of receiving liquid-phase materials with the second spherical tank, and using the pressure difference to make the gas-phase material in the third spherical tank flow into the second spherical tank, and making the second spherical tank reach the preset pressure required to enter the material receiving state.

[0008] In some embodiments, in step 1), the first spherical tank is a spherical tank that needs to be overhauled or renovated.

[0009] In some embodiments, in step 1), the operation of emptying the material includes: feeding the liquid-phase material and the gas-phase material in the first spherical tank into the production device for use as reaction raw materials, and the pressure of the first spherical tank that has completed the operation of emptying the material is higher than the pressure of the second spherical tank that has been purged with nitrogen.

[0010] In some embodiments, the pressure of the second spherical tank that has been purged with nitrogen is less than or equal to 0.03 MPa (G); the pressure of the first spherical tank that has completed the operation of emptying the material is less than or equal to 1.5 MPa and higher than the pressure of the second spherical tank that has been purged with nitrogen.

[0011] In some embodiments, the spherical tank is an ethylene spherical tank;

[0012] Multiple spherical tanks are respectively connected to the gas-phase flare main pipe, and a switching valve is respectively provided on the connecting pipeline between each spherical tank and the gas-phase flare main pipe; when performing step 1), the first spherical tank and the second spherical tank are connected to each other through the gas-phase flare main pipe, so that the gas-phase material in the first spherical tank is fed into the second spherical tank that has been purged with nitrogen by using the pressure difference.

[0013] In some embodiments, multiple spherical tanks are respectively connected to the gas-phase balance pipeline to achieve pressure balance between the spherical tanks in the receiving state;

[0014] When performing step 1), the first spherical tank and the second spherical tank are not connected to the third spherical tank in the receiving state; when performing step 2), the third spherical tank and the second spherical tank are connected through the gas-phase balance pipeline, so that the gas-phase material in the third spherical tank is introduced into the second spherical tank.

[0015] In some embodiments, for the first spherical tank after completing step 1), before it is about to enter the receiving state, the first spherical tank is purged with nitrogen, so that the first spherical tank is converted into the second spherical tank that has been purged with nitrogen, and then the nitrogen in it is replaced according to the operation of step 1), and the preset pressure required to enter the receiving state is reached according to the operation of step 2).

[0016] In some embodiments, the nitrogen content in the second spherical tank that has been purged with nitrogen is greater than or equal to 99.8%.

[0017] In some embodiments, the temperature of the second spherical tank that reaches the preset pressure in step 2) is adjusted so that its temperature reaches the preset temperature required for the receiving state.

[0018] In some embodiments, the preset temperature is ≥ -30 °C; the preset pressure is ≥ 1.65 MPa (G).

[0019] The technical solution provided by the present invention has the following beneficial effects:

[0020] Through the gas phase replacement method provided by the present invention, for a spherical tank that needs to be overhauled or renovated, after the material is emptied, all the remaining gas phase materials in it do not need to be discharged to the flare for combustion, but these gas phase materials can be utilized for the actual gas pressure boosting after nitrogen replacement, which can reduce raw material waste, improve the replacement progress, shorten the gas phase replacement time of the spherical tank, improve production efficiency, and reduce operation risks. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the connection relationship between every two adjacent spherical tanks. Detailed Embodiments

[0022] For the convenience of understanding the present invention, the present invention will be further described below in conjunction with embodiments. It should be understood that the following embodiments are only for better understanding of the present invention, and do not mean that the present invention is only limited to the following embodiments.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The term "and / or" as used herein may include any and all combinations of one or more of the related listed items. For those parts in the embodiments where specific experimental steps or conditions are not indicated, the operations or conditions of the corresponding conventional experimental steps in the technical field of the present invention can be followed. The terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] The present invention improves the gas phase replacement method of spherical tanks in the existing spherical tank storage system, and provides a new gas phase replacement method for spherical tanks. The spherical tank can be an ethylene spherical tank or a propylene spherical tank, that is, a spherical tank for storing liquid propylene or liquid ethylene. As is well known to those skilled in the art, during the storage of materials in the spherical tank, due to factors such as environmental temperature changes, a part of the liquid materials in the spherical tank will turn into gas phase materials, that is, there are two forms of liquid phase materials and gas phase materials. As is well known to those skilled in the art, during the use of the spherical tank, it needs to be overhauled regularly or repaired and renovated according to actual production needs. When the spherical tank needs to be overhauled or renovated, the traditional method is to empty the materials in it and discharge the gas phase materials to the flare for combustion; this method has a large amount of raw material waste, a long operation cycle, affects production efficiency, and has high safety risks. Based on the existing spherical tank storage system, the present invention provides a new gas phase replacement method for spherical tanks. The gas phase replacement method provided by the present invention mainly includes the following steps:

[0025] 1) Send the gaseous material in the first spherical tank that has completed the material emptying operation into the second spherical tank that has been purged with nitrogen by using the pressure difference to displace the nitrogen in the second spherical tank;

[0026] 2) Connect the third spherical tank in the material receiving state for receiving liquid-phase material to the second spherical tank, and use the pressure difference to make the gaseous material in the third spherical tank flow into the second spherical tank, and make the second spherical tank reach the preset pressure required to enter the material receiving state.

[0027] In the present invention, the "first spherical tank", "second spherical tank", and "third spherical tank" are only for facilitating the distinction of spherical tanks in different operation stages or different states, and do not mean to limit the number or order of spherical tanks.

[0028] In some embodiments, in step 1), the first spherical tank is a spherical tank that needs to be overhauled or reformed. Such a spherical tank needs to empty the material in the spherical tank first due to the need for overhaul (for example, it needs to be overhauled when reaching the inspection period) or reform (for example, it needs to be repaired and reformed). Specifically, in step 1), the operation of emptying the material in the spherical tank includes: sending the liquid-phase material and gaseous material in the first spherical tank into the production device as reaction raw materials for use, that is, for recycling; and the pressure of the first spherical tank that has completed the material emptying operation is higher than the pressure of the second spherical tank that has been purged with nitrogen. Specifically, in actual production, when emptying the material in the spherical tank and sending it into the production device for recycling, for example, it is first treated by an olefin separation caustic scrubber tower before entering the production device, and then enters the downstream production device as a reaction raw material. When the pressure of the spherical tank is close to the pressure of the olefin separation caustic scrubber tower, the recycling is stopped. At this time, there is still residual gaseous material in the spherical tank, and the pressure is, for example, less than or equal to 1.5 MPa, for example, about 1.2 MPa, or about 0.9 MPa.

[0029] In some embodiments, the pressure of the second spherical tank that has been purged with nitrogen is less than or equal to 0.03 MPa (G); in actual production, after purging the spherical tank with nitrogen, it also includes an operation of depressurizing to a slightly positive pressure. For example, the pressure after depressurization is less than or equal to 0.03 MPa (G), and this pressure is lower than the pressure of the first spherical tank that has completed the material emptying operation. The pressure of the first spherical tank that has completed the material emptying operation is less than or equal to 1.5 MPa and higher than the pressure of the second spherical tank that has been purged with nitrogen.

[0030] In some embodiments, the spherical tank is specifically an ethylene spherical tank. The gas phase replacement method of the present invention can be implemented based on the existing pipeline structure of the existing ethylene spherical tank storage system. The existing ethylene spherical tank storage system usually includes multiple spherical tanks, for example, including more than three spherical tanks. See Figure 1, which shows the pipeline structure between every two adjacent spherical tanks A and B; this figure is shown taking the adjacent spherical tanks A and B as an example, and the connection relationships between other spherical tanks with adjacent relationships can be referred to Figure 1 , and will not be elaborated one by one. Among them, each spherical tank is provided with a nitrogen inlet, and the nitrogen inlet is communicated with the nitrogen inlet pipe 5. Medium-pressure nitrogen can be introduced through the nitrogen inlet pipe 5 during nitrogen replacement to perform nitrogen replacement on the spherical tank; each spherical tank is provided with an emission flare port, and the emission flare port is communicated with the emission flare pipeline 3, which is used to send the emission gas in the spherical tank into the flare for combustion. The ethylene spherical tank storage system includes a gas-phase flare main pipe 1, and each spherical tank is respectively communicated with the gas-phase flare main pipe 1, and a shut-off valve is respectively arranged on the connecting gas paths between each spherical tank and the gas-phase flare main pipe 1. During the normal charging process, the spherical tank and the gas-phase flare main pipe 1 are in a non-connected state. Usually, only when the spherical tank has an overpressure risk or other emergency conditions exist in the working condition, the spherical tank and the gas-phase flare main pipe 1 are connected. The ethylene spherical tank storage system includes a gas-phase balance pipeline 2, and multiple spherical tanks are respectively communicated with the gas-phase balance pipeline 2, and a shut-off valve is arranged on the connecting gas paths between each spherical tank and the gas-phase balance pipeline 2. Through the opening and closing operation of the shut-off valve, the pressure balance between the spherical tanks in the charging state can be achieved. In the gas-phase replacement method of the present invention, when performing the step 1), the first spherical tank and the second spherical tank are connected to each other through the gas-phase flare main pipe 1, so that the gas-phase material in the first spherical tank is sent into the second spherical tank that has undergone nitrogen replacement by using the pressure difference; that is, when performing the step 1) of the present invention, through the operation of the shut-off valve, the first spherical tank and the second spherical tank are connected to each other through the pipe section of the gas-phase flare main pipe 1 located between them, so that the gas-phase material (such as gas-phase ethylene) in the first spherical tank can be pressed into the second spherical tank, replacing the nitrogen in the second spherical tank and realizing the pressure increase; in the specific operation, the main valve 7 of the gas-phase flare main pipe is closed to prevent the gas-phase materials in the first spherical tank and the second spherical tank from being discharged from the outlet of the gas-phase flare main pipe.

[0031] In the gas-phase replacement method of the present invention, when performing the step 1), the first spherical tank and the second spherical tank are not connected to the third spherical tank in the charging state, that is, the first and second spherical tanks are not connected to each spherical tank in the charging state, and only the first spherical tank and the second spherical tank are connected. When performing the step 2), the third spherical tank and the second spherical tank are connected through the gas-phase balance pipeline 2, so that the gas-phase material in the third spherical tank is introduced into the second spherical tank, that is, the gas-phase material in the third spherical tank during normal charging is introduced into the second spherical tank that has completed the step 1) through the gas-phase balance pipeline 2, so that the pressure in the second spherical tank rises and the preset pressure required for entering the charging state is obtained.

[0032] Further, after the first spherical tank has completed step 1) and after subsequent maintenance or renovation operations, before it is to be put into use for receiving materials (for example, for receiving liquid-phase ethylene), the first spherical tank is purged with nitrogen to convert it into the second spherical tank that has been purged with nitrogen, and the nitrogen in it is displaced according to the operation of the aforementioned step 1), and the pressure is increased according to the operation of step 2) to reach the preset pressure required to enter the material receiving state. For example, the preset pressure ≥ 1.65 MPa (G).

[0033] In some embodiments, the nitrogen content in the second spherical tank that has been purged with nitrogen is greater than or equal to 99.8%. When this requirement is met, it is considered that the nitrogen purging is qualified.

[0034] In some embodiments, the temperature of the second spherical tank that has reached the preset pressure in step 2) is adjusted so that its temperature reaches the preset temperature required for the material receiving state. For example, the preset temperature is ≥ -30 °C, and the preset temperature is, for example, below 0 °C, such as -25 °C; the means for adjusting the temperature of the spherical tank are conventional in the art, and an existing spherical tank with a temperature control function can be used to achieve this.

[0035] Through the gas phase replacement method provided by the present invention, for spherical tanks that need to be maintained or renovated, after the material emptying operation, all the remaining gas phase materials in them do not need to be discharged to the flare for combustion, but these gas phase materials can be utilized for the actual gas pressure boosting after nitrogen replacement, which can reduce raw material waste. Moreover, the temperature of the second spherical tank that has been purged with nitrogen often reaches room temperature. According to the traditional method, it needs to be pre-cooled to the operating temperature by a liquid-phase heat exchange medium before being put into use; however, in the present invention, by sending the remaining gas phase of the first spherical tank (whose temperature is about -25 °C) into the second spherical tank that has been purged with nitrogen, while displacing the nitrogen in it, it also plays a role in cooling the second spherical tank, which can significantly shorten the time for the second spherical tank to reach the preset temperature required to enter the material receiving state. Moreover, using the remaining gas phase of the first spherical tank to pre-cool the second spherical tank is more stable and controllable than the traditional liquid-phase heat exchange medium pre-cooling, can reduce the risk of cold embrittlement of the pipeline, and can reduce the operation links, improve the overall gas phase replacement progress, shorten the gas phase replacement time of the spherical tank, improve production efficiency, and reduce operation risks. In some embodiments, taking an ethylene spherical tank as an example, when using the gas phase replacement method of the present invention, the ethylene spherical tank (the first spherical tank) after the material emptying operation can reduce the ethylene emission by up to 10 t, and the second spherical tank can recover up to 10 t of ethylene. At the same time, the remaining gas phase of the first spherical tank can be used to pre-cool the second spherical tank, which can shorten the time required for the second spherical tank to cool down, reduce the risk of cold embrittlement, keep the temperature drop of the spherical tank within a controllable range, is easy to operate and implement, saves material losses, and reduces safety risks.

[0036] The specific structure of the spherical tank storage system and the specific operation of the spherical tank storage belong to the conventional technologies in this field. Those skilled in the art can understand or know based on the mastered conventional technical means and common general knowledge, and will not be elaborated one by one here.

[0037] The gas phase replacement method of the present invention will be exemplarily described below through specific application examples:

[0038] See Figure 1 , in a certain working condition of the ethylene spherical tank storage system for storing liquid-phase ethylene, the ethylene spherical tank A needs to be overhauled. The material in the ethylene spherical tank A is emptied. Specifically, the liquid-phase ethylene in the ethylene spherical tank A is output through the ethylene discharge pipeline 4, and after being treated by the olefin separation caustic scrubber tower, it enters the production device as a reaction raw material. The gas-phase ethylene in the ethylene spherical tank A is output through the pipeline 6, and after being treated by the olefin separation caustic scrubber tower, it enters the production device as a reaction raw material, that is, it is recycled. When the pressure of the ethylene spherical tank A is close to the pressure of the olefin separation caustic scrubber tower and reaches 1.2 MPa (G), the recycling is stopped. At this time, the temperature of the ethylene spherical tank A is the ambient temperature, and the mass of the gas-phase ethylene in it is 30 t. The material emptying operation of the ethylene spherical tank A is completed. The ethylene spherical tank A that has completed the material emptying operation is the first spherical tank.

[0039] In this working condition, the ethylene spherical tank B has been overhauled and nitrogen replacement has been carried out. As the second spherical tank, the pressure of the ethylene spherical tank B is 0.03 MPa (G) at this time. The main valve 7 of the gas-phase flare header 1 is closed, and the switch valves on the connecting gas paths connecting the aforementioned ethylene spherical tank A that has completed the material emptying operation and the ethylene spherical tank B to the gas-phase flare header 1 are opened, so that the ethylene spherical tank A and the ethylene spherical tank B are connected through the gas-phase flare header 1. The residual gas-phase ethylene in the ethylene spherical tank A is pressed into the ethylene spherical tank B under the action of the pressure difference, and the ethylene spherical tank B is pressurized. During this process, the nitrogen in the ethylene spherical tank B is replaced and sent to the flare through the discharge flare pipeline 3. When the pressure of the ethylene spherical tank B no longer rises, the switch valve on the discharge flare pipeline 3 of the ethylene spherical tank B is closed, and the switch valves on the connecting gas paths connecting the ethylene spherical tank A and the ethylene spherical tank B to the gas-phase flare header are closed.

[0040] Then, the switch valve on the connecting gas path between the ethylene spherical tank B and the gas-phase balance pipeline 2 is opened, and the ethylene spherical tank B and other ethylene spherical tanks (i.e., the third spherical tank, not shown in the figure) in the receiving state of receiving liquid-phase ethylene are connected through the gas-phase balance pipeline 2, so that the gas-phase ethylene in the third spherical tank is filled into the ethylene spherical tank B, and the pressure of the ethylene spherical tank B rises above 1.65 MPa (G), reaching the pressure requirement for entering the receiving state.

[0041] After the residual gaseous ethylene in the ethylene spherical tank A is pressed into the ethylene spherical tank B under the action of the pressure difference, the remaining gas phase in the ethylene spherical tank A is sent into the flare through the discharge flare pipeline 3 for safe combustion, and then the maintenance operation is carried out; when the maintenance operation is completed and before it is ready to be put into use, the spherical tank is pre-purged with nitrogen in advance. After it has been purged with nitrogen, it can be used as the second spherical tank, and the nitrogen is replaced and the pressure is increased with reference to the foregoing operations.

[0042] It is easy to understand that the above embodiments are only examples for clear illustration, and do not mean that the present invention is limited thereto. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to enumerate all the embodiments here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for gas phase replacement of a spherical tank, wherein the spherical tank is an ethylene spherical tank, characterized in that, The gas phase replacement method includes the following steps: 1) Sending the gas phase material in the first spherical tank that has completed the material emptying operation into the second spherical tank that has been replaced with nitrogen by using the pressure difference to replace the nitrogen in the second spherical tank; the first spherical tank is the spherical tank that needs to be overhauled or reformed; 2) Connecting the third spherical tank in the state of receiving liquid phase material to the second spherical tank, and using the pressure difference to make the gas phase material in the third spherical tank flow into the second spherical tank, and making the second spherical tank reach the preset pressure required to enter the state of receiving material; Multiple spherical tanks are respectively connected to the gas phase flare main pipe, and a switch valve is respectively arranged on the connecting pipeline between each spherical tank and the gas phase flare main pipe; when performing step 1), the first spherical tank and the second spherical tank are connected to each other through the gas phase flare main pipe, so that the gas phase material in the first spherical tank is sent into the second spherical tank that has been replaced with nitrogen by using the pressure difference; Multiple spherical tanks are respectively connected to the gas phase balance pipeline to realize the pressure balance between the spherical tanks in the state of receiving material; When performing step 1), the first spherical tank and the second spherical tank are not connected to the third spherical tank in the state of receiving material; when performing step 2), the third spherical tank and the second spherical tank are connected through the gas phase balance pipeline, so that the gas phase material in the third spherical tank flows into the second spherical tank.

2. The gas phase replacement method of the spherical tank according to claim 1, characterized in that, In step 1), the material emptying operation includes: sending the liquid phase material and the gas phase material in the first spherical tank into the production device for use as reaction raw materials, and the pressure of the first spherical tank that has completed the material emptying operation is higher than the pressure of the second spherical tank that has been replaced with nitrogen.

3. The gas phase replacement method of the spherical tank according to claim 2, characterized in that, The pressure of the second spherical tank that has been replaced with nitrogen is less than or equal to 0.03 MPa (G); the pressure of the first spherical tank that has completed the material emptying operation is less than or equal to 1.5 MPa and higher than the pressure of the second spherical tank that has been replaced with nitrogen.

4. The gas-phase replacement method of the spherical tank according to any one of claims 1 to 3, characterized in that, After the first spherical tank completes step 1), before it is about to enter the state of receiving material, the first spherical tank is replaced with nitrogen to convert the first spherical tank into the second spherical tank that has been replaced with nitrogen, and then the nitrogen in it is replaced according to the operation of step 1), and the preset pressure required to enter the state of receiving material is reached according to the operation of step 2).

5. The gas phase replacement method of the spherical tank according to any one of claims 1-3, characterized in that, The nitrogen content in the second spherical tank that has been replaced with nitrogen is greater than or equal to 99.8%.

6. The gas phase replacement method for a spherical tank according to any one of claims 1-3, characterized in that, Adjust the temperature of the second spherical tank that reaches the preset pressure in step 2) to make its temperature reach the preset temperature required for the state of receiving material.

7. The gas phase replacement method of the spherical tank according to claim 6, characterized in that, The preset temperature is ≥ -30°C; The preset pressure ≥ 1.65 MPa (G).

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