Method for reducing the impact of polyethylene unit shutdown on olefin separation unit production

Abstract

The present invention provides a method for reducing the impact of a polyethylene unit shutdown on the production of an olefin separation unit. The method and system provided by the present invention can significantly reduce the impact of a polyethylene unit shutdown on the production of an olefin separation unit. The method comprises: when the polyethylene unit is in operation, passing liquid ethylene from the ethylene tank area through an ethylene vaporization unit to exchange heat with the propylene flow from a propylene refrigeration compressor to obtain gaseous ethylene; heating and vaporizing unqualified ethylene from the ethylene tank area through an ethylene emergency vaporizer and then feeding it to an ethylene recycling unit for recycling; passing the purge gas from the polyethylene unit to a refining stripping tower of the olefin separation unit for use as stripping gas; and when the polyethylene unit is in operation, passing the gaseous ethylene from the top of the ethylene tank area to an ethylene vaporization unit to exchange heat with the propylene flow from the propylene refrigeration compressor, and then feeding it to the ethylene recycling unit for recycling and / or feeding it to a refining stripping tower for use as stripping gas.

Description

Technical Field

[0001] The present invention relates to olefin separation and polyethylene production technology, in particular to a method and system that is beneficial for reducing the impact of polyethylene unit shutdown on the production of olefin separation units. Background Art

[0002] The raw material gaseous ethylene required for the polyethylene unit is obtained by heating and vaporizing the liquid ethylene supplied from the ethylene tank area through the ethylene vaporization unit of the olefin separation unit. For example, liquid ethylene at around -30°C is vaporized to 35°C, and the obtained gaseous ethylene is fed into the polyethylene unit as gaseous feed raw material.

[0003] Ethylene vaporization system before transformation Figure 1 As shown, the ethylene vaporization unit of the ethylene vaporization system (including heat exchangers E661A / B, E662, and E663) vaporizes ethylene for the polyethylene unit while performing heat exchange with the propylene refrigeration compressor in the olefin separation unit. Specifically, heat exchange is performed with propylene flows of different temperatures in the propylene refrigeration compressor to ensure heat balance of the propylene refrigeration compressor and normal operation of the propylene refrigeration compressor.

[0004] Figure 1 The ethylene vaporization system shown faces the following challenges when the polyethylene unit is shut down:

[0005] 1. When a polyethylene unit is shut down, there is no heat exchange between the ethylene vaporizer (such as E661A / B, E662, and E663) and the propylene refrigeration compressor system. Consequently, the propylene refrigeration compressor system cannot properly remove heat, resulting in a heat surplus state. (The heat balance of the propylene refrigeration compressor was initially designed to account for the heat exchange generated by the normal operation of the E661A / B, E662, and E663.) After the polyethylene unit is shut down, the entire heat removal task of the propylene refrigeration compressor system is transferred to the condenser of the propylene refrigeration compressor system, which uses circulating water as the cooling medium. Due to operating conditions and design limitations, even if the condenser's circulating water runs at full capacity or even if the circulating water supply temperature is lowered, it is insufficient to remove the excess heat from the propylene refrigeration compressor system. This results in a heat surplus state for the propylene refrigeration compressor system during the polyethylene unit shutdown, resulting in substandard refrigerant provided by the propylene refrigeration compressor. Propylene refrigerant users can only meet actual process requirements by increasing propylene dosage. However, if propylene users increase the amount of propylene used, the load on the propylene refrigeration compressor will increase. The propylene refrigeration compression needs to do more work, which will generate more heat. The accumulation of heat in the reciprocating circulation of the propylene refrigeration compression system will cause the propylene refrigeration compressor to enter a vicious cycle state, thereby affecting the normal operation of the distillation system in the olefin separation unit, which will at best reduce the production load and at worst affect the product quality.

[0006] 2. The stripping gas for the refining stripper in the olefin separation unit is polyethylene plant purge gas (ethylene content 96%), which is approximately 1.8 t / h. After the polyethylene plant is shut down, the refining stripper lacks stripping gas, which impairs separation efficiency. Light components such as C3 in the tower are carried to the debutanizer through the tower kettle, resulting in poor operation of the refining stripper and debutanizer, thus affecting product quality. Currently, the lack of polyethylene plant purge gas is compensated for by increasing the temperature of the refining stripper kettle and the amount of gas phase by using a reboiler in the refining stripper kettle. However, the use of a reboiler during actual operation does not guarantee stripping efficiency. Furthermore, its use causes the refining stripper kettle temperature to be too high, which can easily cause cavitation in the kettle material transfer pump and unstable operation of the refining stripper. The stripping effect of the refining stripping tower is poor, and a large amount of C3 mixed with C4 and C5+ enters the downstream debutanizer. The light components accumulate at the top of the debutanizer and cannot be condensed, causing the debutanizer to be easily over-pressurized and difficult to control, which in turn affects the debutanizer's separation effect on C4 and C5+. The debutanizer is in poor operating condition, resulting in unqualified products.

[0007] 3. After the polyethylene unit is shut down, the ethylene storage tanks in the ethylene tank area are not equipped with gas-phase refrigeration compressors. The ethylene storage tanks only receive materials but do not discharge them. The tank pressure of the ethylene storage tanks will continue to rise. The higher the ambient temperature, the more serious the overpressure phenomenon, which is particularly prominent in summer. The top of the ethylene distillation tower of the olefin separation unit is a pasteurized distillation section. The ethylene product is extracted from the side line of the seventh tray at the top of the distillation tower. The liquid-phase ethylene product is transported to the ethylene tank area by relying on the ethylene tower pressure and the height difference between the ethylene distillation tower and the ethylene storage tank. When the polyethylene unit is shut down, the increase in the tank pressure of the ethylene storage tank will affect the normal extraction of ethylene products from the ethylene distillation tower, and the propylene refrigeration compressor cannot provide standard-grade refrigerant to the condenser at the top of the ethylene distillation tower (the largest propylene refrigerant user in the propylene refrigeration compression system), resulting in overload and overpressure operation of the ethylene distillation tower. To ensure the normal operation of the ethylene distillation tower, the olefin separation unit needs to apply for load reduction, which affects the company's production capacity.

[0008] In response to the above problems, existing countermeasures include:

[0009] 1) Reduce the load of the MTO (olefin separation) unit to meet the normal operating conditions of the olefin separation distillation tower;

[0010] 2) Improving the heat exchange efficiency of the condenser at the outlet of the propylene refrigeration compressor, reducing the circulating water temperature, and increasing the amount of circulating water used, resulting in increased circulating water losses for the company;

[0011] 3) Contact the ethylene tank farm to extract approximately 3 t / h of gaseous ethylene from the top of the ethylene storage tank through the unqualified ethylene recycling pipeline and recycle it to the olefin separation unit through the ethylene emergency vaporizer E660 to reduce the ethylene tank pressure and ensure normal production of the ethylene distillation tower;

[0012] 4) Put the reboiler of the refining stripping tower into use to increase the gas phase of the refining stripping tower and make up for the lack of purge gas from the polyethylene unit.

[0013] With the existing countermeasures, the production conditions of olefin separation are subject to the frequency and duration of shutdown and maintenance of the polyethylene unit, which seriously restricts the safe, stable and long-term operation of the olefin separation unit. Summary of the Invention

[0014] In light of this, the present invention provides a method and system for reducing the impact of polyethylene plant shutdowns on olefin separation unit production. This method and system minimizes the impact of polyethylene plant shutdowns on olefin separation unit production without requiring significant adjustments to existing systems, thereby ensuring safe, stable, and long-term operation of the olefin separation unit.

[0015] To achieve its purpose, the present invention provides the following technical solutions:

[0016] In one aspect, the present invention provides a method for reducing the impact of a polyethylene unit shutdown on the production of an olefin separation unit, the method comprising:

[0017] When the polyethylene unit is in operation, liquid ethylene in the ethylene tank area is passed through an ethylene vaporization unit to exchange heat with a propylene stream from a propylene refrigeration compressor in an upstream olefin separation unit to obtain a gaseous ethylene feed for input to the polyethylene unit; unqualified ethylene in the ethylene tank area is heated and vaporized in an ethylene emergency vaporizer and then fed to an ethylene recycling unit of the olefin separation unit for recycling; and purge gas from the polyethylene unit is passed into a refining stripping tower of the olefin separation unit for use as stripping gas;

[0018] When the polyethylene unit is shut down, the gaseous ethylene at the top of the ethylene tank area is sent to the ethylene vaporization unit to exchange heat with the propylene flow of the propylene refrigeration compressor, and then sent to the ethylene recycling unit for recycling and / or sent to the refining stripping tower for use as stripping gas.

[0019] Furthermore, the ethylene vaporization unit includes a first heat exchanger, a second heat exchanger, and a third heat exchanger, and the propylene stream of the propylene refrigeration compressor includes a first propylene stream, a second propylene stream, and a third propylene stream having different temperatures;

[0020] When the polyethylene unit is in operation, the liquid ethylene flows through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence, and exchanges heat with the first propylene stream, the second propylene stream, and the third propylene stream in sequence;

[0021] When the polyethylene unit is shut down, the gaseous ethylene at the top of the ethylene tank area flows through the first heat exchanger, the second heat exchanger and the third heat exchanger in sequence, and exchanges heat with the first propylene flow, the second propylene flow and the third propylene flow in sequence.

[0022] Furthermore, when the polyethylene device is shut down, nitrogen replacement of the pipeline is first performed, and then the gaseous ethylene at the top of the ethylene tank area passes through the ethylene vaporization unit to exchange heat with the propylene flow of the propylene refrigeration compressor.

[0023] Furthermore, the ethylene recycling device includes a depropanizer and / or a compression device.

[0024] Furthermore, when the ethylene vaporization unit is stopped while the polyethylene device is in operation, the liquid ethylene in the ethylene tank area is fed into the ethylene emergency vaporizer for vaporization to obtain gaseous ethylene feed for input into the polyethylene device.

[0025] The present invention also provides a system for implementing the above-mentioned method, which comprises an ethylene tank farm, a polyethylene device, an ethylene vaporization unit, an ethylene emergency vaporizer, and an olefin separation device; the olefin separation device comprises a propylene refrigeration compressor, a refining stripping tower, and an ethylene recycling device; and is characterized in that:

[0026] The ethylene tank farm is connected to the ethylene vaporization unit via a pipeline, so that the liquid ethylene output from the ethylene tank farm undergoes heat exchange with the propylene stream from the propylene refrigeration compressor in the ethylene vaporization unit to obtain a gaseous ethylene feed for input to the polyethylene device; the ethylene vaporization unit and the polyethylene device are connected via a pipeline for transporting the gaseous ethylene feed to the polyethylene device;

[0027] The ethylene tank farm is connected to a recycle line for unqualified ethylene, which is in communication with the ethylene emergency vaporizer via a pipeline for feeding unqualified ethylene from the ethylene tank farm into the ethylene emergency vaporizer for heating and vaporization. The recycle line for unqualified ethylene is also in communication with the ethylene vaporization unit via a jumper line for feeding gaseous ethylene from the tank top of the ethylene tank farm into the ethylene vaporization unit for heat exchange with the propylene flow from the propylene refrigeration compressor.

[0028] The ethylene emergency vaporizer is connected to the ethylene recycling device via a pipeline so as to feed the unqualified ethylene heated and vaporized by the ethylene emergency vaporizer into the ethylene recycling device;

[0029] The ethylene vaporization unit is connected to the ethylene recycling device via a pipeline so that at least a portion of the gaseous ethylene from the tank top of the ethylene tank farm, after being processed by the ethylene vaporization unit, can be fed into the ethylene recycling device;

[0030] The polyethylene device is connected to the refining stripping tower via a pipeline to transport the purge gas in the polyethylene device to the refining stripping tower for use as stripping gas;

[0031] The ethylene vaporization unit is connected to the refining stripping tower via a pipeline so that at least a portion of the gaseous ethylene from the top of the ethylene tank area after being treated by the ethylene vaporization unit can be fed into the refining stripping tower for use as stripping gas;

[0032] Each pipeline is provided with a valve for controlling the on-off of the pipeline.

[0033] Further, the ethylene vaporization unit comprises a first heat exchanger, a second heat exchanger and a third heat exchanger connected in series;

[0034] The propylene flow of the propylene refrigeration compressor includes a first propylene flow, a second propylene flow and a third propylene flow at different temperatures;

[0035] By switching the valves, the liquid ethylene or the gaseous ethylene transported from the top of the ethylene tank area through the jumper line flows through the first heat exchanger, the second heat exchanger and the third heat exchanger in sequence and exchanges heat with the first propylene flow, the second propylene flow and the third propylene flow in sequence.

[0036] Furthermore, the unqualified ethylene recycling pipeline is also connected to a nitrogen input pipeline for introducing nitrogen for replacement, and a valve is provided on the nitrogen input pipeline.

[0037] Furthermore, the ethylene recycling device includes a depropanizer and / or a compression device.

[0038] Furthermore, the ethylene tank farm is connected to the ethylene emergency vaporizer via a pipeline, for vaporizing the liquid ethylene output from the ethylene tank farm in the ethylene emergency vaporizer to obtain a gaseous ethylene feed for input to the polyethylene device; the ethylene emergency vaporizer is connected to the polyethylene device via a pipeline, for feeding the gaseous ethylene feed into the polyethylene device;

[0039] Each pipeline is provided with a valve for controlling the on-off of the pipeline.

[0040] The technical solution provided by the present invention has the following beneficial effects:

[0041] The solution provided by the present invention eliminates the need for significant modifications to the existing production system. When a polyethylene unit is shut down, the gaseous ethylene at the top of the ethylene tank farm is exported through a recycle pipeline for unqualified ethylene and sent via a jumper line to an ethylene vaporization unit for heat exchange with the propylene flow from the propylene refrigeration compressor. The treated gaseous ethylene is then sent to the refining stripper instead of the purge gas from the polyethylene unit. This not only alleviates the excess heat in the propylene refrigeration compressor but also ensures the stripping effect of the refining stripper. Furthermore, it reduces the storage tank pressure in the ethylene tank farm, ensures the normal production of products from the upstream ethylene distillation tower, and facilitates the normal operation of the refining stripper, debutanizer, and other components in the olefin separation unit. The solution of the present invention can significantly reduce the impact of the polyethylene unit shutdown on the production of the olefin separation unit, thereby ensuring the safe, stable, and long-term operation of the olefin separation unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the flow diagram of the ethylene vaporization system before transformation;

[0043] Figure 2 A schematic diagram of a system provided in one embodiment of the present invention after modification. DETAILED DESCRIPTION

[0044] In order to facilitate understanding of the present invention, the present invention will be further described below in conjunction with the accompanying drawings. It should be understood that the following description is only for a better understanding of the present invention and does not mean that the present invention is limited to the following embodiments.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the related listed items. In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connected" may refer to direct connection or indirect connection through an intermediary.

[0046] The present invention is based on the modification of the ethylene vaporization system in the existing methanol to olefins process system to propose a method and system that is beneficial to reducing the impact of the shutdown of the polyethylene unit on the production of the olefin separation unit. The specific structure of the olefin separation unit is known in the art, specifically a device for separating the various components of the product gas in the methanol to olefins technology, which includes a product gas compression system, a distillation system, a propylene refrigeration compression system (or called a propylene refrigeration compressor), a refining stripping tower and an ethylene recycling device, etc.; wherein the propylene refrigeration compressor is used to provide propylene refrigerant of different temperatures for different links of the methanol to olefins process; the refining stripping tower is used to remove the C4 and C5 components in the product gas; the ethylene recycling device is used to send unqualified gas-phase ethylene to the depropanizer and / or compression device for treatment, and then enter the distillation system for further separation and treatment. The propylene refrigeration compressor, the refining stripping tower, the ethylene recycling device and other devices are all conventional devices in the field of methanol to olefins, and will not be described in detail.

[0047] See also Figure 2 The system provided herein, which helps reduce the impact of polyethylene plant shutdowns on olefin separation unit production, includes: an ethylene tank farm 1, a polyethylene unit 2, an ethylene vaporization unit, an ethylene emergency vaporizer E660, and an olefin separation unit. The olefin separation unit includes a propylene refrigeration compressor (not shown), a refining stripping column T401, and an ethylene recycling unit. The olefin separation unit in methanol-to-olefins technology also has other components, such as a product gas compressor and a distillation system, which are not described in detail here.

[0048] In the system of the present invention, ethylene tank farm 1 is used to store liquid ethylene obtained from olefin separation and distillation. Ethylene tank farm 1 is connected to an ethylene vaporization unit via pipeline 13. This allows the liquid ethylene output from ethylene tank farm 1 to undergo heat exchange with the propylene stream from the propylene refrigeration compressor in the ethylene vaporization unit, thereby obtaining vapor-phase ethylene feed for feeding into polyethylene unit 2. The ethylene vaporization unit and polyethylene unit 2 are connected by pipeline 11, which transports the vapor-phase ethylene feed obtained by vaporization in the ethylene vaporization unit to polyethylene unit 2.

[0049] Ethylene tank farm 1 is also connected to a reject ethylene recycle pipeline 5 for discharging reject ethylene from ethylene tank farm 1. Reject ethylene recycle pipeline 5 is connected to ethylene emergency vaporizer E660 via pipeline 7, allowing it to be heated and vaporized there. Reject ethylene recycle pipeline 5 is also connected to the ethylene vaporization unit via a jumper line 8, allowing gaseous ethylene from the top of ethylene tank farm 1 to be fed into the ethylene vaporization unit for heat exchange with the propylene stream from the propylene refrigeration compressor.

[0050] The ethylene emergency vaporizer E660 is connected to the ethylene recycling unit via pipeline 6, so that unqualified ethylene from the ethylene tank area 1 can be heated and vaporized by the ethylene emergency vaporizer E660 and then sent to the ethylene recycling unit for recycling.

[0051] The ethylene vaporization unit and the ethylene recycling device are connected by pipeline 6, so that the gaseous ethylene from the top of the tank in the ethylene tank area 1 can enter the ethylene vaporization unit through the jumper pipeline 8 for heat exchange, and at least part of the gaseous ethylene can be sent to the recycling device.

[0052] The polyethylene device 2 is connected to the refining stripping tower T401 via a pipeline (not shown in the figure), so that the purge gas in the polyethylene device 2 can be transported to the refining stripping tower T401 for use as stripping gas.

[0053] The ethylene vaporization unit and the refining stripping tower T401 are connected by pipeline 10, so that the gaseous ethylene from the top of the tank in the ethylene tank area 1 can enter the ethylene vaporization unit through the jumper pipeline 8 for heat exchange, and at least part of the gaseous ethylene can be sent to the refining stripping tower T401 for use as stripping gas.

[0054] Each of the above pipelines is provided with a valve for controlling the on / off of each pipeline, such as Figure 2 As shown, valves V1, V2, V3, V4, V5, V6, V7, XV-6060, XV-6059, HC-6067, etc. are respectively provided.

[0055] Specifically, the ethylene vaporization unit includes a first heat exchanger E661A / B, a second heat exchanger E662, and a third heat exchanger E663 connected in series. The first, second, and third heat exchangers are heat exchangers from the propylene refrigeration compressor, acting on three propylene streams of different temperatures from the propylene refrigeration compressor, respectively. Specifically, for example, the first, second, and third propylene streams from the propylene refrigeration compressor are sequentially acting on the first, second, and third propylene streams of different temperatures. In some specific embodiments, the temperature of the first propylene stream is 6°C, the temperature of the second propylene stream is 2°C, and the temperature of the third propylene stream is 32°C. Through valve switching, liquid ethylene from ethylene tank farm 1 or gaseous ethylene from the top of ethylene tank farm 1 (transported via unqualified ethylene recycling line 5 and jumper line 8) flows through the first heat exchanger E661A / B, the second heat exchanger E662, and the third heat exchanger E663, and exchanges heat with the first, second, and third propylene streams, respectively. In some embodiments, the temperature of the propylene stream obtained after the first propylene stream passes through the first heat exchanger E661A / B is -10°C, the temperature of the propylene stream obtained after the second propylene stream passes through the second heat exchanger E662 is -22°C, and the temperature of the propylene material obtained after the third propylene stream passes through the third heat exchanger E663 is 22°C.

[0056] Furthermore, the unqualified ethylene recycling pipeline 5 is also connected to a nitrogen input pipeline 3 for introducing nitrogen for replacement, and a valve is provided on the nitrogen input pipeline 3.

[0057] More specifically, the ethylene recycling unit includes, for example, a depropanizer T501 and / or a compression unit E405, and the compression unit is, for example, a product gas compressor in a methanol to olefins system.

[0058] Furthermore, ethylene tank farm 1 is connected to ethylene emergency vaporizer E660 via pipeline 12. When the ethylene vaporization unit is deactivated, liquid ethylene output from ethylene tank farm 1 is vaporized in ethylene emergency vaporizer E660 to produce gaseous ethylene feed for polyethylene unit 2. Ethylene emergency vaporizer E660 is connected to polyethylene unit 2 via pipeline 14, which feeds the gaseous ethylene vaporized from ethylene emergency vaporizer E660 into polyethylene unit 2. When the ethylene vaporization unit is deactivated, ethylene emergency vaporizer E660 can be used to vaporize liquid ethylene.

[0059] In the system of the present invention, each pipeline is provided with a valve for controlling the on-off of the pipeline.

[0060] The present invention also provides a method for utilizing the above-described system to reduce the impact of the shutdown of the polyethylene unit 2 on the production of the olefin separation unit. Specifically, the method comprises the following steps:

[0061] When polyethylene unit 2 is in operation, liquid ethylene from ethylene tank farm 1 is passed through the ethylene vaporization unit to exchange heat with the propylene stream from the propylene refrigeration compressor in the olefin separation unit, thereby obtaining gaseous ethylene for input to polyethylene unit 2. Unqualified ethylene from ethylene tank farm 1 is re-vaporized through the ethylene emergency vaporizer E660 and then fed to the ethylene recycling unit of the olefin separation unit for recycling. The purge gas from polyethylene unit 2 is passed into the refining stripping tower T401 of the olefin separation unit for use as stripping gas.

[0062] When the polyethylene unit 2 is shut down, the gaseous ethylene at the top of the tank in the ethylene tank area 1 is passed through the ethylene vaporization unit to exchange heat with the propylene flow of the propylene refrigeration compressor, and then sent to the ethylene recycling unit of the olefin separation unit for recycling and / or sent to the refining stripping tower T401 for use as stripping gas.

[0063] In some embodiments, the ethylene vaporization unit comprises a first heat exchanger E661A / B, a second heat exchanger E6612, and a third heat exchanger E663. The propylene stream from the propylene refrigeration compressor includes a first propylene stream, a second propylene stream, and a third propylene stream at different temperatures. When polyethylene unit 2 is in operation, liquid ethylene output from ethylene tank farm 1 flows sequentially through the first, second, and third heat exchangers, exchanging heat with the first, second, and third propylene streams, thereby vaporizing the liquid ethylene to produce gaseous ethylene, which serves as the gaseous ethylene feed for polyethylene unit 2. When polyethylene unit 2 is shut down, gaseous ethylene from the top of ethylene tank farm 1 is output via unqualified ethylene recycling line 5 and enters jumper line 8. It then flows sequentially through the first, second, and third heat exchangers, exchanging heat with the first, second, and third propylene streams, respectively. The first, second, and third heat exchangers are propylene heat exchangers included in the propylene refrigeration compressor.

[0064] Furthermore, when the polyethylene unit 2 is stopped, nitrogen replacement of the pipeline is first performed, and then the gaseous ethylene at the top of the tank in the ethylene tank area 1 is passed through the ethylene vaporization unit to exchange heat with the propylene flow of the propylene refrigeration compressor.

[0065] Furthermore, the ethylene recycling unit may specifically include a depropanizer T501 and / or a compression unit E405. The ethylene material recycled by the ethylene recycling unit is subsequently sent to a distillation unit for further separation.

[0066] Furthermore, when the ethylene vaporization unit is shut down while the polyethylene device 2 is in operation, the liquid ethylene in the ethylene tank area 1 is fed into the ethylene emergency vaporizer E660 for vaporization, thereby obtaining gaseous ethylene feed for input into the polyethylene device 2.

[0067] The switching of different processing flow directions in the above-mentioned starting state and stopping state of the polyethylene device 2 can be achieved by switching the valves provided on each pipeline.

[0068] The following is an example of how to implement the above method using the system of the present invention:

[0069] Step S1: When the polyethylene unit 2 is in operation, valves V1 and V4 are opened, and valves V2, V3, V5, V6, and V7 are closed.

[0070] Liquid ethylene from ethylene tank farm 1 flows sequentially through the first heat exchanger E661A / B, the second heat exchanger E662, and the third heat exchanger E663 to exchange heat with three propylene streams (the first propylene stream, the second propylene stream, and the third propylene stream) of different temperatures from the propylene refrigeration compressor, thereby vaporizing the liquid ethylene to obtain gaseous ethylene feed for polyethylene unit 2. This gaseous ethylene is then fed into polyethylene unit 2 as a gaseous raw material.

[0071] The unqualified ethylene from the ethylene tank farm 1 is sent to the ethylene emergency vaporizer E660 through the unqualified ethylene recycling pipeline 5 and pipeline 7 for vaporization, and then sent to the depropanizer T501 and / or the compression unit E405 for further recycling;

[0072] The purge gas generated in the polyethylene unit 2 is sent to the refining stripping tower T401 through a pipeline for use as stripping gas.

[0073] Step S2: When the polyethylene unit 2 is stopped, close valves V1, V4, XV-6060, XV-6059, and HC-6067, and slowly open valves V2, V3, V5, and V6 until valves V2, V3, V5, and V6 are fully open.

[0074] Step S3: Open the valve on the nitrogen input pipeline 3 and introduce nitrogen for replacement to achieve nitrogen replacement.

[0075] Step S4: Open valves HC-6067 and XV-6059 to allow the gaseous ethylene at the top of the tank in ethylene tank farm 1 to undergo heat exchange with three propylene streams (the first, second, and third propylene streams) at different temperatures from the propylene refrigeration compressor via the first heat exchanger E661A / B, the second heat exchanger E662, and the third heat exchanger E663. The ethylene is then fed to the depropanizer T501 and / or the compression unit E405 via pipeline 6. The amount of gaseous ethylene recycled is controlled by HC-6067.

[0076] Open valve V7 and send the gaseous ethylene from the top of the ethylene tank area after being heated in the first, second and third heat exchangers to the refining stripping tower T401 to be used as the stripping gas of the refining stripping tower T401.

[0077] Step S6: When the polyethylene device 2 is overhauled and started up again, valves V2, V3, V5, V6, and V7 are closed, and valves V1 and V4 are opened; and the operation flow of the polyethylene device 2 in the started-up state is restored.

[0078] By applying the technical solution of the present invention, the impact of the shutdown of the polyethylene unit 2 on the production of the olefin separation unit can be minimized, thereby changing the passive production situation of the olefin separation unit.

[0079] The technical solution provided by the present invention can achieve the following technical effects:

[0080] By applying the technical solution of the present invention, it is ensured that during the shutdown and maintenance of a polyethylene device, propylene refrigerant users such as the propylene refrigeration compressor, ethylene distillation tower, refining stripping tower, and debutanizer tower of the olefin separation device are less affected, thereby ensuring qualified product quality; production units do not need to deliberately lower the circulating water temperature of the propylene refrigeration compressor, thereby reducing the energy consumption of the circulating water; there is no need to reduce the production load, thereby ensuring normal production tasks; the technical solution of the present invention can improve the ability of the olefin separation device to resist external interference factors, thereby ensuring the safe, stable, long-term, full, and excellent operation of the olefin separation device.

[0081] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for reducing the impact of polyethylene plant shutdown on olefin separation unit production, characterized in that: The method comprises: When the polyethylene unit is in operation, liquid ethylene from the ethylene tank area is passed through an ethylene vaporization unit to exchange heat with a propylene stream from a propylene refrigeration compressor in an olefin separation unit to obtain a gaseous ethylene feed for input to the polyethylene unit; unqualified ethylene from the ethylene tank area is heated and vaporized in an ethylene emergency vaporizer and then fed to an ethylene recycling unit of the olefin separation unit for recycling; and purge gas from the polyethylene unit is passed into a refining stripping tower of the olefin separation unit for use as stripping gas; When the polyethylene unit is shut down, the gaseous ethylene at the top of the ethylene tank area is fed into an ethylene vaporization unit to exchange heat with the propylene flow of the propylene refrigeration compressor, and then fed into the ethylene recycling unit for recycling and / or fed into the refining stripping tower for use as stripping gas; When the ethylene vaporization unit is shut down while the polyethylene device is in operation, the liquid ethylene in the ethylene tank area is fed into the ethylene emergency vaporizer for vaporization to obtain gaseous ethylene feed for input into the polyethylene device.

2. The method according to claim 1, characterized in that The ethylene vaporization unit includes a first heat exchanger, a second heat exchanger and a third heat exchanger, and the propylene flow of the propylene refrigeration compressor includes a first propylene flow, a second propylene flow and a third propylene flow of different temperatures; When the polyethylene unit is in operation, the liquid ethylene flows through the first heat exchanger, the second heat exchanger, and the third heat exchanger in sequence, and exchanges heat with the first propylene stream, the second propylene stream, and the third propylene stream in sequence; When the polyethylene unit is shut down, the gaseous ethylene at the top of the ethylene tank area flows through the first heat exchanger, the second heat exchanger and the third heat exchanger in sequence, and exchanges heat with the first propylene flow, the second propylene flow and the third propylene flow in sequence.

3. The method according to claim 1 or 2, characterized in that When the polyethylene unit is shut down, nitrogen replacement of the pipeline is first performed, and then the gaseous ethylene at the top of the ethylene tank area passes through the ethylene vaporization unit to exchange heat with the propylene flow of the propylene refrigeration compressor.

4. The method according to claim 1 or 2, characterized in that The ethylene recycling device includes a depropanizer and / or a compression device.

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