Method for shortening start-up time of polypropylene production and synchronously establishing reaction of reactors
By setting up cross-line pipelines and a fresh propylene flushing system in the polypropylene production process, the prepolymer reactor, the first reactor, and the second reactor can be started up simultaneously, which solves the problems of long start-up time, raw material waste, and high energy consumption, and achieves a more efficient start-up process.
Patent Information
- Application Number
- CN202511253318.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-03
- Publication Date
- 2025-11-11
AI Technical Summary
Existing polypropylene production processes suffer from problems such as long start-up times, significant raw material waste, high energy consumption, and the inability to achieve simultaneous reactor establishment.
By setting up cross-line pipelines between the prepolymer reactor and the first and second reactors, and using a fresh propylene flushing system, the synchronous establishment of the reaction in the prepolymer reactor, the first reactor, and the second reactor is achieved, including valve control on the cross-line pipelines and real-time monitoring of reaction conditions.
It significantly shortens start-up time, reduces propylene emissions by 30%, lowers energy consumption by 40%, and improves start-up efficiency and plant stability.
Smart Images
Figure CN120919919A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of polypropylene production technology, and in particular to a method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor. Background Technology
[0002] Existing polypropylene is produced using a continuous process. The continuous process for producing polypropylene includes: low-temperature prepolymerization and liquid-phase bulk polymerization in a vertical reactor with agitators, and gas-phase polymerization in a horizontal reactor with agitators. The main steps are prepolymerization, vertical reactor liquid-phase bulk polymerization, and horizontal reactor gas-phase polymerization. The production process includes: low-temperature prepolymerization in a prepolymerization reactor, then the material enters a vertical stirred polymerization reactor (first reactor) for slurry polymerization, and then the material enters a horizontal gas-phase polymerization reactor (second reactor) for another polymerization reaction to obtain the polypropylene product.
[0003] This process has the following problems in large-scale industrial production: 1. Long start-up time: The entire start-up time is the setup time of the polymerization reaction, that is, the time required for the polymer monomer (propylene) to continuously and stably produce high molecular weight compounds under catalysis. The existing start-up process involves sequentially starting the prepolymer reactor, the first reactor, and the second reactor, with start-up times of 18 minutes, 35 minutes, and 70 minutes respectively, totaling 123 minutes, which seriously affects production efficiency.
[0004] 2. Serious waste of raw materials: During the sequential start-up process, a large amount of unreacted propylene is generated. This part of the propylene can only be discharged and cannot be used, resulting in serious waste of propylene raw materials. About 5 tons of propylene need to be discharged during each start-up process.
[0005] 3. High energy consumption: Sequential operation leads to long equipment idling time, low energy utilization rate, and high overall energy consumption.
[0006] 4. Inability to achieve synchronous reaction establishment: In order to ensure that the pressure and reaction conditions of each reaction stage meet the requirements, the existing start-up process requires materials to enter each reactor sequentially, which reduces the overall start-up efficiency.
[0007] The information disclosed in the background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention
[0008] This application addresses the aforementioned technical problems by providing a method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor. This method can effectively shorten the start-up time, improve start-up efficiency, reduce propylene emissions, and lower energy consumption.
[0009] This application provides a method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor, including the following steps: Step S1: Assemble the reaction equipment: The prepolymer reactor is connected to the pipelines of the first reactor and the second reactor respectively. The prepolymer reactor and the second reactor are connected through a cross-line pipeline. A plunger valve, a stopcock valve, and a feed regulating valve are installed at intervals on the cross-line pipeline. The fresh propylene flushing system is connected to the cross-line pipeline. Step S2: Check whether the temperature and pressure of the first reactor and the second reactor meet the requirements for establishing an open-loop circulation, and determine whether the reaction equipment system has established an open-loop circulation. If both are yes, proceed to step S3. Step S3: After the catalysts and propylene raw materials are introduced into the prepolymer reactor, the prepolymerization reaction is carried out. When the reaction in the prepolymer reactor is established and the reaction slurry is started to be delivered to the first reactor, the second control valve group on the cross-line pipeline is opened, and the first control valve group on the pipeline of the prepolymer reactor and the first reactor is connected, so that the slurry enters the first reactor and the second reactor at the same time. Step S4: Open the control valve on the pipeline connecting the fresh propylene flushing system and the cross-line pipeline, as well as the control valve on the cross-line pipeline, and flush the cross-line pipeline with fresh propylene; Step S5: Obtain the prepolymer reactor pressure value in real time. Set the prepolymer reactor pressure base value to 2.65 MPa. When the real-time pressure value of the prepolymer reactor increases by 0.01 MPa relative to the base value, the opening of the discharge regulating valve of the second valve group increases by 2%. When the pressure value of prepolymer reactor 1 decreases by 0.01 MPa relative to the base value, the opening of the discharge regulating valve of the second valve group decreases by 2%. Step S6: Monitor the temperature and pressure parameters of the first and second reactors in real time, and make the following judgments: Judgment 1) If, after the jacket hot water steam valve of the first reactor is completely closed, the reactor temperature of the first reactor is ≥65℃, the pressure is ≥2.6MPa, and the opening degree of the condenser water valve of the first reactor is ≥3%, then the reaction in the first reactor has been established: Judgment 2) After the steam valve of the start-up heater of the second reactor is closed, if the temperature of the second reactor 3 is ≥80℃, the pressure is ≥2.0MPa, and the opening degree of the condenser water valve of the second reactor is ≥3%, then the reaction in the second reactor has been established. If both judgment 1) and judgment 2) result in "established", close all valves on the cross-line pipeline.
[0010] Preferably, in step S3, the initial opening degree of the first valve group and the second valve group is 5% of the total opening degree.
[0011] Preferably, it further includes: step S7: after the fresh propylene flushing system performs reverse flushing and forward flushing on the cross-line pipeline, the cross-line pipeline is shut off.
[0012] Preferably, step S7 includes: Step S71: A propylene flushing ball valve is installed on the fresh propylene flushing system and the connecting pipeline of the cross-line pipeline. A plunger valve is installed on the prepolymer reactor discharge pipe and a plug valve is installed on the cross-line pipeline. The propylene flushing ball valve and plunger valve are kept open for backflushing. Step S72: Open the feed regulating valve and maintain fresh propylene to flush the cross-line pipeline in the forward direction for 5 to 15 minutes. The flushed propylene flows to the second reactor. Step S73: Close the plunger valve, the feed regulating valve, and the plug valve in sequence, and then close the cross-line pipeline.
[0013] Preferably, in step S71: after continuously backflushing the cross-line pipeline for 5 to 15 minutes, the plunger valve is closed, and the backflushed propylene flows to the prepolymer reactor.
[0014] Preferably, the reaction equipment includes: multiple catalyst delivery pipes; one end of a catalyst delivery pipe is connected to the feed inlet of the prepolymer reactor, and the other end is connected to the catalyst A storage tank; One end of the other catalyst delivery pipe is connected to the feed inlet of the prepolymer reactor, and the other end is connected to the catalyst B storage tank; One end of the catalyst delivery pipe is connected to the feed inlet of the prepolymer reactor, and the other end is connected to the catalyst C storage tank.
[0015] Preferably, the reaction equipment includes: a propylene feed pipe; one end of the propylene feed pipe is connected to a propylene storage tank, and the other end is connected to the feed port of the prepolymer reactor.
[0016] Preferably, the cross-line conduit is a DN50 pipe.
[0017] Preferably, in step S4, the plunger valve, the plug valve, the feed regulating valve, and the propylene flushing ball valve are opened.
[0018] Preferably, both the prepolymerization vessel and the first reactor are vertical reaction vessels and are equipped with stirring components; The second reactor is a horizontal reaction vessel equipped with a stirring assembly.
[0019] The beneficial effects that this application can produce include: 1) The method provided in this application for shortening the start-up time of polypropylene production and establishing reactions simultaneously in each reactor can significantly shorten the start-up time, reduce raw material waste and energy consumption, improve the start-up efficiency and stability of the unit, reduce the start-up time to 67 minutes, and reduce propylene emissions by 30%. Attached Figure Description
[0020] Figure 1 A schematic diagram of the apparatus used in the method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor, as provided in at least one embodiment of this application. Figure 2A flowchart of a method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor, provided in at least one embodiment of this application; Legend: Prepolymer reactor 1, First reactor 2, Second reactor 3, Cross-line pipeline 131, Fresh propylene flushing system 4, Catalyst delivery pipe 3, Propylene feed pipe 31 Flushing propylene ball valve 11, plunger valve 12, plug valve 13, discharge regulating valve 14. Detailed Implementation
[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but this does not limit the present invention in any way. Any modifications or improvements made based on the teachings of the present invention shall fall within the protection scope of the present invention.
[0022] Unless otherwise specified, all materials and instruments used in the following embodiments were obtained through commercial channels; and all detection methods used are existing methods unless otherwise specified.
[0023] Example: See Figures 1-2 The inlet of the prepolymer reactor 1 is connected to the catalyst delivery pipe 3 and the propylene feed pipe 31 of each catalyst. The prepolymer reactor 1 and the first reactor 2 are both vertical reaction vessels and are equipped with stirring components; the second reactor 3 is a horizontal reaction vessel and is equipped with stirring components.
[0024] Cross-line installation connecting prepolymer reactor 1 and second reactor 3: A DN50 pipe is used as a cross-line pipeline 131 to connect the plunger valve 12 at the bottom of prepolymer reactor 1 to the feed inlet of second reactor 3. A plunger valve 12, a stopcock valve 13, and a feed regulating valve 14 are installed at intervals on the cross-line pipeline 131.
[0025] The outlet of the fresh propylene flushing system 4 is connected to the cross-line pipeline 131. A flushing propylene ball valve 11 is installed on the connected pipeline. When the cross-line is started and put into operation, the cross-line pipeline is continuously flushed with flushing propylene.
[0026] Step S1: System status confirmation and preparation. Check whether the temperature and pressure of the first reactor 2 and the second reactor 3 meet the requirements. Confirm that the system has established an open-loop circulation. If it does, proceed to step S2. Establishing an open-loop circulation means that after opening all the valves of the reaction system to form an open-loop state, all propylene fed from the feed end can flow out from the outlet end. This indicates that an open-loop circulation has been established. After establishment, add catalyst B, catalyst C, catalyst A and propylene to the prepolymer reactor 1 in sequence. The feeding sequence can be controlled by opening the control valve on the catalyst delivery pipe 3 respectively.
[0027] Step S2: After introducing the catalysts and propylene raw materials into the prepolymerization reactor 1, a prepolymerization reaction is carried out. When the reaction in the prepolymerization reactor 1 is established and the reaction slurry begins to be delivered to the first reactor 2, the cross-line pipeline 131 from the prepolymerization reactor 1 to the second reactor 3 is opened, so that the slurry enters the first reactor 2 and the second reactor 3 simultaneously. Specifically, the valves (first valve group) on the pipeline connecting the prepolymerization reactor 1 and the first reactor 2, as well as the valves (second valve group) on the pipeline connecting the prepolymerization reactor 1 and the second reactor 3 are opened simultaneously. The first valve group is fully opened, and the initial opening degree of the second valve group is 5% of the total opening degree. Step S3: To prevent slurry from depositing and clogging in the cross-line pipeline 131 connecting the prepolymer reactor 1 to the second reactor 3, open the plunger valve 12, the stopcock valve 13, the feed regulating valve 14, and the flushing propylene ball valve 11 to continuously flush the cross-line pipeline connecting the prepolymer reactor 1 and the second reactor 3 with fresh propylene.
[0028] Step S4: Obtain the pressure value of prepolymer reactor 1 in real time, set the base pressure value of prepolymer reactor 1 to 2.65 MPa. When the real-time pressure value of prepolymer reactor 1 increases by 0.01 MPa relative to the base value, the opening of the discharge regulating valve (14) of the second valve group increases by 2%. When the real-time pressure value of prepolymer reactor 1 decreases by 0.01 MPa relative to the base value, the opening of the discharge regulating valve (14) of the second valve group decreases by 2%. Step S5: Monitor the temperature and pressure parameters of the first reactor 2 and the second reactor 3 in real time, and make the following judgments: 1) If the hot water steam valve of the jacket of the first reactor 2 is completely closed, and the reactor temperature in the first reactor 2 is ≥65℃, the pressure is ≥2.6MPa, and the opening degree of the condenser water valve of the first reactor 2 is ≥3%, then the reaction in the first reactor 2 is established: 2) If the steam valve of the start-up heater of the second reactor 3 is completely closed, and the temperature of the second reactor 3 is ≥80℃, the pressure is ≥2.0MPa, and the opening degree of the condenser water valve of the second reactor 3 is ≥3%, then the reaction in the second reactor 3 is established: If both judgment 1) and judgment 2) result in an established condition, then gradually close the cross-line regulating valve; if neither judgment result is an established condition, then keep the opening of each valve unchanged. Step S7: A flushing propylene ball valve 11 is installed on the connecting pipeline of the fresh propylene flushing system 4 and the cross-line pipeline 131. A plunger valve 12 is installed on the discharge pipe of the prepolymer reactor 1. The flushing propylene ball valve 11 and the plunger valve 12 are kept open to continuously flush the cross-line pipeline 131 in reverse. The flushed propylene flows to the prepolymer reactor 1. After flushing for 5 minutes, the plunger valve 12 is closed. Step S8: Open the feed regulating valve 14 on the cross-line pipeline 131 to maintain the fresh propylene to flush the cross-line pipeline 131 in the forward direction. The flushed propylene flows to the second reactor 3 and continues to flush for 15 minutes.
[0029] Step S9: Sequentially close the stopcock valve 13, feed regulating valve 14, and plunger valve 12 on the cross-line pipeline 131. The fresh propylene flushing system 4 performs flushing before the cross-line is started and after it is shut down, with each flushing lasting 5-15 minutes. This is to prevent polypropylene from flowing back into the pipeline from the reactors and causing blockages, and to maintain the pressure in each reactor. After the cross-line is shut down, the fresh propylene flushing is cut off, and then the cross-line system is isolated.
[0030] Using the above method, the reaction times for prepolymer reactor 1, first reactor 2, and second reactor 3 are 13 minutes, 32 minutes, and 67 minutes, respectively (timing starts from the injection of catalyst A into the reactor). The amount of propylene discharged as flushing is 3~3.5 tons. Energy consumption is 170.67~191.05 kgoe.
[0031] Comparative Example The difference from the previous embodiment is that no cross-line pipeline 131 was installed; the reaction was established sequentially in the prepolymer reactor 1, the first reactor 2, and the second reactor 3. The reaction establishment times in the prepolymer reactor 1, the first reactor 2, and the second reactor 3 were 18 minutes, 53 minutes, and 123 minutes, respectively (timing started from the injection of catalyst A into the reactor). The amount of propylene discharged for flushing was 4.5~5.5 tons. Energy consumption was 313.32~333.7 kgoe.
[0032] Comparative examples and comparative cases show that, using the method provided in this application, the reaction time in the second and first reactors is reduced to 70 minutes, and propylene emissions are reduced by 30% throughout the reaction process. Energy consumption is reduced by 40%, effectively improving start-up efficiency, reducing start-up time, and reducing material waste.
[0033] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor, characterized in that, Includes the following steps: Step S1: Assemble the reaction equipment: The prepolymer reactor (1) is connected to the first reactor (2) and the second reactor (3) respectively. The prepolymer reactor (1) and the second reactor (3) are connected through a cross-line pipeline (131). A plunger valve (12), a stopcock valve (13), and a feed regulating valve (14) are installed at intervals on the cross-line pipeline (131). The fresh propylene flushing system (4) is connected to the cross-line pipeline (131). Step S2: Check whether the temperature and pressure of the first reactor (2) and the second reactor (3) meet the requirements for establishing an open-loop circulation, and determine whether the reaction equipment system has established an open-loop circulation. If both are yes, then proceed to step S3. Step S3: After the catalysts and propylene raw materials are introduced into the prepolymer reactor (1), the prepolymerization reaction is carried out. When the reaction in the prepolymer reactor (1) is established and the reaction slurry is started to be delivered to the first reactor (2), the second control valve group on the cross-line pipeline (131) is opened to connect the first control valve group on the pipeline of the prepolymer reactor (1) and the first reactor (2) so that the slurry enters the first reactor (2) and the second reactor (3) at the same time. Step S4: Open the control valve on the pipeline connecting the fresh propylene flushing system (4) and the cross-line pipeline (131), and the control valve on the cross-line pipeline (131) to flush the cross-line pipeline (131) with fresh propylene. Step S5: Obtain the pressure value of the prepolymer reactor (1) in real time. Set the base pressure value of the prepolymer reactor (1) to 2.65 MPa. When the real-time pressure value of the prepolymer reactor (1) increases by 0.01 MPa relative to the base value, the opening of the discharge regulating valve (14) of the second valve group increases by 2%. When the pressure value of the prepolymer reactor 1 decreases by 0.01 MPa relative to the base value, the opening of the discharge regulating valve (14) of the second valve group decreases by 2%. Step S6: Monitor the temperature and pressure parameters of the first reactor (2) and the second reactor (3) in real time, and make the following judgments: Judgment 1) After the jacket hot water steam valve of the first reactor (2) is closed, if the reactor temperature of the first reactor (2) is ≥65℃, the pressure is ≥2.6MPa, and the opening degree of the condenser water valve of the first reactor (2) is ≥3%, then the reaction of the first reactor (2) has been established: Judgment 2) After the start-up heater steam valve of the second reactor (3) is closed, if the temperature of the second reactor (3) is ≥80℃, the pressure is ≥2.0MPa, and the opening degree of the condenser water valve of the second reactor (3) is ≥3%, then the reaction in the second reactor (3) has been established: When the results of judgment 1) and judgment 2) are both established, close all valves on the cross-line pipeline (131).
2. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 1, characterized in that, In step S3, the initial opening degree of the first valve group and the second valve group is 5% of the total opening degree.
3. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 1, characterized in that, It also includes: Step S7: After the fresh propylene flushing system (4) performs reverse flushing and forward flushing on the cross-line pipeline (131), the cross-line pipeline (131) is shut off.
4. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 3, characterized in that, Step S7 includes: Step S71: A flushing propylene ball valve (11) is installed on the connecting pipeline of the fresh propylene flushing system (4) and the cross-line pipeline (131), a plunger valve (12) is installed on the discharge pipe of the prepolymer reactor (1), and a stopcock valve (14) is installed on the cross-line pipeline (131). The flushing propylene ball valve (11) and the plunger valve (12) are kept open for backwashing. Step S72: Open the feed regulating valve (14) and maintain the fresh propylene to flush the cross-line pipeline (131) in the forward direction for 5 to 15 minutes. The flushed propylene flows to the second reactor (3). Step S73: Close the plunger valve (12), the feed regulating valve (14), and the plug valve (13) in sequence, and then close the cross-line pipeline (131).
5. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 4, characterized in that, Step S71: After continuously backflushing the cross-line pipeline (131) for 5 to 15 minutes, close the plunger valve (12) and backflush the propylene to the prepolymer reactor (1).
6. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 1, characterized in that, The reaction equipment includes: multiple catalyst delivery pipes (3); one end of a catalyst delivery pipe (3) is connected to the feed port of the prepolymer reactor (1), and the other end is connected to the catalyst A storage tank; One end of another catalyst delivery pipe (3) is connected to the feed port of the prepolymer reactor (1), and the other end is connected to the catalyst B storage tank; One end of the catalyst delivery pipe (3) is connected to the feed port of the prepolymer reactor (1), and the other end is connected to the catalyst C storage tank.
7. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 1, characterized in that, The reaction equipment includes: a propylene feed pipe (31); one end of the propylene feed pipe (31) is connected to a propylene storage tank, and the other end is connected to the feed port of the prepolymer reactor (1).
8. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 1, characterized in that, The cross-line pipeline (131) is a DN50 pipe.
9. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 4, characterized in that, In step S4, open the plunger valve (12), the plug valve (13), the feed regulating valve (14), and the propylene flushing ball valve (11).
10. The method for shortening the start-up time of polypropylene production and simultaneously establishing reactions in each reactor according to claim 1, characterized in that, Both the prepolymer reactor (1) and the first reactor (2) are vertical reaction vessels and are equipped with stirring components; The second reactor (3) is a horizontal reaction vessel and is equipped with a stirring assembly.