Ethylene vinyl acetate copolymer pipe reactor in-line wall cleaning process

Abstract

The application discloses an ethylene vinyl acetate copolymer tubular reactor online wall sticking cleaning method, relates to the technical field of tubular reactors, and can solve the problems of complicated and unsafe wall sticking offline cleaning process and can reduce the probability of incomplete wall sticking cleaning effect of online cleaning depending on the experience of operators. The method comprises the following steps: heating a heat-conducting medium in a reactor, and collecting heat transfer parameters of the reactor after wall sticking; a heat transfer model is established to obtain a functional relationship between the heat transfer rate of the heat-conducting medium and the temperature difference of the heat-conducting medium, output the temperature difference of the heat-conducting medium corresponding to the optimal heat transfer rate of the reactor before wall sticking, and input the collected temperature difference of the heat-conducting medium after wall sticking and output a reference flow; the flow of the heat-conducting medium in the reactor is adjusted based on the reference flow, and when the flow of the heat-conducting medium in the current reactor meets the wall sticking treatment end condition, the temperature of the heat-conducting medium in the reactor is reduced to a preset production condition.

Description

Technical Field

[0001] This application relates to the field of tubular reactor technology, and in particular to an online method for cleaning the wall adhesion of an ethylene-vinyl acetate copolymer tubular reactor. Background Technology

[0002] During the polymerization reaction, polymers with relatively high molecular weights are produced. Due to their high molecular weight and poor flowability, these polymers tend to adhere to the inner wall of the reaction tubes in a tubular reactor. When the adhesion is severe, it reduces the production rate of the ethylene-vinyl acetate copolymer tubular reactor and causes a sharp decrease in the heat exchange rate of the reaction tubes, which in turn makes the reaction temperature rise sharply and increases the probability of thermal decomposition of the reactants.

[0003] Existing technologies for cleaning the walls of tubular reactors containing ethylene-vinyl acetate copolymers include offline and online cleaning. Offline cleaning involves cleaning components such as flanges and high-pressure pipes connected to the reactor, and then subjecting the reaction tubes to high-temperature boiling in a specially designed oil bath followed by separate cleaning. Online cleaning, on the other hand, involves operators adjusting the hot water flow rate based on their experience to remove the adhering material.

[0004] Existing offline methods for cleaning sticky walls are not only cumbersome but also prone to accidents, while online methods rely on the operator's experience, which can easily lead to incomplete cleaning. Summary of the Invention

[0005] This application provides an online wall-adhesion cleaning method for a tubular reactor containing ethylene-vinyl acetate copolymer. This method can, to some extent, solve the problems of the cumbersome and unsafe offline wall-adhesion cleaning process and reduce the probability of incomplete cleaning when operators rely on their own experience for online wall-adhesion cleaning.

[0006] This application provides an online wall-adhesion cleaning method for an ethylene-vinyl acetate copolymer tubular reactor, the method comprising:

[0007] The heat transfer medium inside the reactor is heated, and the heat transfer parameters of the reactor are collected, wherein the heat transfer parameters include the temperature difference of the heat transfer medium after it adheres to the wall.

[0008] Establish a heat transfer model, obtain the functional relationship between the heat transfer rate of the heat transfer medium and the temperature difference of the heat transfer medium, output the temperature difference of the heat transfer medium corresponding to the optimal heat transfer rate of the reactor before wall adhesion, substitute the collected temperature difference of the heat transfer medium after wall adhesion and output the reference flow rate.

[0009] The flow rate of the heat transfer medium in the reactor is adjusted based on the reference flow rate. When the flow rate of the heat transfer medium in the reactor meets the conditions for the end of the wall adhesion treatment, the temperature of the heat transfer medium in the reactor is reduced to the preset production conditions.

[0010] In one possible implementation, establishing the heat transfer model includes:

[0011] A countercurrent heat transfer model with cylindrical partition walls was established for the heat exchange process of a tubular reactor.

[0012] In one possible implementation, the temperature difference of the heat transfer medium corresponding to the optimal reactor heat exchange rate before wall adhesion includes:

[0013] The temperature difference of the heat transfer medium in the reactor before it adheres to the wall and the heat exchange rate of the reactor are collected.

[0014] Establish the functional relationship between the heat exchange rate of the reactor and the temperature difference of the heat transfer medium;

[0015] Find the temperature difference of the heat transfer medium corresponding to the highest heat exchange rate in the reactor, and output the obtained temperature difference of the heat transfer medium.

[0016] In one possible implementation, the functional relationship between the heat exchange rate of the reactor and the temperature difference of the heat transfer medium is expressed as:

[0017] Q1=KSΔT m

[0018] Where Q1 is the heat transfer rate of the reactor, in W; and K is the heat transfer coefficient of the reactor, in W / m³. 2 *K; S is the heat transfer area of ​​the reactor, in m². 2 ;ΔT m This represents the temperature difference of the heat-conducting medium, expressed in Kelvin (K).

[0019] In one possible implementation, the expression for the heat transfer coefficient of the reactor is:

[0020]

[0021] Where K is the heat transfer coefficient of the reactor; R i R is the internal thermal resistance of the reactor tubes. r R is the thermal resistance of the reactor tube wall. o This represents the external thermal resistance of the reactor tubes.

[0022] In one possible implementation, the reference flow rate is inversely proportional to the temperature difference of the heat transfer medium after it adheres to the wall.

[0023] In one possible implementation, the step of substituting the collected temperature difference of the heat-conducting medium after wall adhesion and outputting a reference flow rate is expressed as:

[0024]

[0025] Where Δt1 is the temperature difference of the heat transfer medium corresponding to the highest heat exchange rate of the reactor before wall adhesion, in K; Δt2 is the temperature difference of the heat transfer medium after wall adhesion, in K; M1 is the design flow rate of the reactor, in kg / s; and M2 is the reference flow rate, in kg / s.

[0026] In one possible implementation, adjusting the flow rate of the heat transfer medium in the reactor based on a reference flow rate includes:

[0027] When the difference between the currently calculated reference flow rate and the current flow rate of the heat transfer medium in the reactor exceeds a preset threshold, the flow rate of the current heat transfer medium in the reactor is adjusted.

[0028] In one possible implementation, the wall adhesion process termination condition includes:

[0029] The absolute value of the difference between the calculated reference flow rate and the reactor's design flow rate is less than the preset error value.

[0030] In one possible implementation, the wall adhesion process termination condition is expressed as:

[0031] M2≈M1

[0032] Where M1 is the design flow rate of the reactor, in kg / s; and M2 is the reference flow rate, in kg / s.

[0033] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0034] This application embodiment establishes a heat transfer model based on historical data of the tubular reactor, obtains a reference flow rate of the heat transfer medium that matches the current heat transfer rate, and adjusts the flow rate of the heat transfer medium in the reactor according to the obtained reference flow rate. This enables precise control of the reactor wall removal process, facilitating thorough cleaning of the reactor wall and reducing the probability of cumbersome and unsafe offline manual cleaning of reactor wall. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 A flowchart of an online wall-adhesion cleaning method for a tubular reactor provided in an embodiment of this application;

[0037] Figure 2 This is a flowchart illustrating the process of obtaining the temperature difference in the heat transfer medium loop of a tubular reactor using an online wall-adhesion cleaning method provided in this application embodiment. Detailed Implementation

[0038] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] In the description of the embodiments of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0040] Reference Figure 1 and Figure 2 , Figure 1 A flowchart of an online wall-adhesion cleaning method for a tubular reactor provided in an embodiment of this application; Figure 2 This is a flowchart illustrating the process of obtaining the temperature difference in the heat transfer medium loop of a tubular reactor using an online wall-adhesion cleaning method provided in this application embodiment.

[0041] This application provides an online wall cleaning method for a tubular reactor containing ethylene-vinyl acetate copolymer, the method comprising steps 101, 102 and 103.

[0042] Step 101: Heat the heat transfer medium in the reactor to the highest temperature allowed by the reactor's design conditions, and collect the heat transfer parameters of the reactor after it adheres to the wall. The heat transfer parameters include the temperature difference of the heat transfer medium after it adheres to the wall, the heat transfer rate before it adheres to the wall, and the temperature difference of the heat transfer medium before it adheres to the wall.

[0043] Step 102: Establish a heat transfer model, obtain the functional relationship between the heat transfer rate of the reactor and the temperature difference of the heat transfer medium, output the temperature difference of the heat transfer medium loop corresponding to the optimal heat transfer rate of the reactor before adhesion to the wall, substitute the collected heat transfer parameters, and output the reference flow rate.

[0044] Step 103: Adjust the flow rate of the heat transfer medium in the reactor based on the reference flow rate. When the conditions for ending the wall adhesion treatment are met, reduce the temperature of the heat transfer medium in the reactor to the preset production conditions.

[0045] By establishing a heat transfer model based on historical data of the tubular reactor, a reference flow rate of the heat transfer medium matching the current heat transfer rate is obtained. The flow rate of the heat transfer medium in the reactor is adjusted according to the obtained reference flow rate, thereby achieving precise control of the reactor wall removal process. This facilitates thorough cleaning of the reactor wall and reduces the probability of cumbersome and unsafe offline manual cleaning of reactor walls.

[0046] In some embodiments, in order to improve the convenience of obtaining the factors affecting the heat transfer process during the wall adhesion process of the reactor, the online wall adhesion cleaning method for the tubular reactor of ethylene vinyl acetate copolymer provided in this application establishes a cylindrical wall countercurrent heat transfer model for the heat exchange process of the tubular reactor during the establishment of the heat transfer model.

[0047] Since traditional tubular heat exchangers can be approximated as cylindrical, establishing a cylindrical wall countercurrent heat transfer model for the heat exchange process of a tubular reactor can increase the probability of matching the reaction process with the actual heat exchange process of a tubular reactor, improve the accuracy of the obtained reference flow rate for adjusting the flow rate of the heat transfer medium in the reactor, and thus provide a reference for adjusting the flow rate of the heat transfer medium in the reactor.

[0048] In some embodiments, in order to analyze the influencing factors after wall adhesion in a tubular reactor, the online wall adhesion cleaning method for a tubular reactor provided in this application includes steps 201, 202 and 203 during the process of outputting the optimal heat transfer rate of the reactor before wall adhesion.

[0049] Step 201: Collect the temperature difference of the heat transfer medium in the reactor before it adheres to the wall and the heat exchange rate of the reactor.

[0050] Step 202: Establish the functional relationship between the heat exchange rate of the reactor and the temperature difference of the heat transfer medium.

[0051] Step 203: Find the temperature difference of the heat transfer medium corresponding to the highest heat exchange rate of the reactor, and output the obtained temperature difference of the heat transfer medium.

[0052] Based on the temperature difference of the heat transfer medium inside the reactor before adhesion to the wall and the heat exchange rate of the reactor, the optimal heat exchange rate of the reactor is iteratively found. A functional relationship is established between the heat exchange rate of the reactor and the temperature difference of the heat transfer medium, and the temperature difference of the heat transfer medium corresponding to the highest heat exchange rate of the reactor is output. This facilitates the output of the temperature difference of the heat transfer medium for reference in subsequent processing, and improves the convenience of providing accurate reference for subsequent processing.

[0053] In some embodiments, the functional relationship between the heat transfer rate of the reactor and the temperature difference of the heat transfer medium is expressed as follows:

[0054] Q1=KSΔT m

[0055] Where Q1 is the heat transfer rate of the reactor, in W; and K is the heat transfer coefficient of the reactor, in W / m³. 2 *K; S is the heat transfer area of ​​the reactor, in m². 2 ;ΔT m This represents the temperature difference of the heat-conducting medium, expressed in Kelvin (K).

[0056] According to the heat transfer calculation formula based on chemical engineering principles, in actual production processes, since the reaction pressure of the reactor is constant, the pressure of the hot water pump is constant, and the diameter, material, and internal and external media of the reactor's reaction tubes are all constant, it can be known that the heat transfer area S of the reactor remains unchanged.

[0057] Therefore, it can be concluded that when the reactor wall sticks, the main reason according to the formula is that the ethylene-vinyl acetate copolymer sticks to the reactor tube wall, which leads to an increase in the thermal resistance of the reactor, specifically manifested as a change in the heat transfer coefficient of the reactor.

[0058] In some embodiments, the expression for the heat transfer coefficient of the reactor is:

[0059]

[0060] Where K is the heat transfer coefficient of the reactor; R i R is the internal thermal resistance of the reactor tubes. r R is the thermal resistance of the reactor tube wall. o This represents the external thermal resistance of the reactor tubes.

[0061] Assume ΔT m The thermal resistance R inside the reactor tube remains unchanged. i Increasing the amount of initiator peroxide leads to a decrease in the reactor's heat transfer coefficient K, which in turn reduces the reactor's heat exchange rate Q1. In actual production, the reaction temperature peak is controlled at a certain value. When the reactor's heat exchange rate Q1 decreases, the temperature peak will inevitably become too high. It is necessary to reduce the amount of initiator peroxide to ensure a constant temperature peak, thereby reducing the reaction load.

[0062] In some embodiments, the calculation formula obtained based on the heat transfer rate of the heat transfer medium is as follows:

[0063] Q2=C1M1Δt1

[0064] Q′1=C2M2Δt2

[0065] Wherein, Q2 represents the heat transfer rate of the heat transfer medium before wall adhesion, in W; C1 represents the specific heat capacity of the heat transfer medium before wall adhesion, in J / kg*K; M1 represents the flow rate of the heat transfer medium before wall adhesion, in kg / s; Δt1 represents the temperature difference of the heat transfer medium before wall adhesion, in K; Q′1 represents the heat transfer rate of the heat transfer medium after wall adhesion, in W; C2 represents the specific heat capacity of the heat transfer medium after wall adhesion, in J / kg*K; M2 represents the flow rate of the heat transfer medium after wall adhesion, in kg / s; Δt2 represents the temperature difference of the heat transfer medium after wall adhesion, in K.

[0066] Since the heat transfer medium remains constant before and after wall adhesion, the specific heat capacity C1 of the heat transfer medium before wall adhesion is equal to the specific heat capacity C2 of the heat transfer medium before wall adhesion, i.e., C1 = C2.

[0067] When the heat transfer rate of the heat transfer medium before and after wall adhesion is the same, i.e., Q2 = Q′1, the value of the reference flow rate M2 can be obtained as being inversely proportional to the value of the temperature difference Δt2 of the heat transfer medium after wall adhesion, as expressed below:

[0068]

[0069] Where Δt1 is the temperature difference of the heat transfer medium corresponding to the highest heat exchange rate of the reactor before wall adhesion, in K; Δt2 is the temperature difference of the heat transfer medium after wall adhesion, in K; M1 is the design flow rate of the reactor, in kg / s; and M2 is the reference flow rate, in kg / s.

[0070] By establishing a functional relationship between the reference flow rate and the temperature difference of the heat transfer medium after wall adhesion, the relationship between the reference flow rate of the tubular reactor and the temperature difference of the heat transfer medium after wall adhesion can be obtained intuitively. This makes it convenient to obtain a reference flow rate that matches the temperature difference of the heat transfer medium after wall adhesion according to the above formula, thereby improving the convenience for operators to adjust the flow rate of the heat transfer medium according to the reference flow rate.

[0071] In some embodiments, the reactor online wall-adhesion cleaning method provided in this application, in the process of adjusting the flow rate of the heat transfer medium in the reactor based on the reference flow rate, includes the following method: when the difference between the currently calculated reference flow rate and the current flow rate of the heat transfer medium in the reactor exceeds a preset threshold, the flow rate of the heat transfer medium in the reactor is adjusted.

[0072] The preset threshold is the difference between the average flow rate obtained from the heat transfer rate of the heat transfer medium before and after the reactor wall adheres. In this embodiment, the preset threshold is set to 5-10 t / h. When the difference between the current flow rate of the heat transfer medium in the reactor and the calculated reference flow rate is greater than the preset threshold, the flow rate of the heat transfer medium in the current reaction tube is adjusted in time, so as to facilitate the heat transfer medium in the current reaction tube to maintain a stable heat exchange efficiency during the process of cleaning the wall.

[0073] In some embodiments, the wall adhesion treatment termination condition of the reactor online wall adhesion cleaning method provided in this application is: the absolute value of the difference between the calculated reference flow rate and the reactor design flow rate is less than a preset error value, and the preset error value is obtained according to the reactor design conditions.

[0074] When the absolute value of the difference between the calculated reference flow rate and the reactor's design flow rate is less than the preset error value, it can be approximated as the temperature difference of the heat transfer medium after sticking to the wall being the same as the temperature difference of the heat transfer medium before sticking to the wall. That is, the sticking to the reactor wall has been cleared. When the difference between the reactor's reference flow rate and the design flow rate is less than the preset error, the reactor temperature should be reduced as soon as possible to restore the reactor to its normal operating state, thereby achieving the goal of maintaining the production efficiency of ethylene-vinyl acetate copolymer.

[0075] In some embodiments, the wall adhesion processing termination condition disclosed in this application is expressed as:

[0076] M2≈M1

[0077] Where M1 is the design flow rate of the reactor, in kg / s; and M2 is the reference flow rate, in kg / s.

[0078] When the calculated reference flow rate is similar to the reactor's design flow rate, it indicates that the temperature difference of the heat transfer medium after wall adhesion is close to the same as that before wall adhesion, and the wall adhesion of the reactor has been cleared. Therefore, by using the similarity between the reference flow rate and the design flow rate as the condition for the end of wall adhesion clearing, the probability of a decrease in the production efficiency of ethylene-vinyl acetate copolymer can be reduced.

[0079] The online wall-adhesion cleaning method for ethylene-vinyl acetate copolymer tubular reactors provided in this application establishes a heat transfer model based on historical data of the tubular reactor, obtains a reference flow rate of the heat transfer medium that matches the current heat transfer rate based on the heat transfer model, and adjusts the flow rate of the heat transfer medium in the reactor according to the obtained reference flow rate. This achieves precise control of the reactor wall-adhesion removal process, thereby facilitating thorough cleaning of the reactor walls and reducing the probability of cumbersome and unsafe offline manual cleaning of reactor walls.

[0080] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0081] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for online wall cleaning of an ethylene-vinyl acetate copolymer tubular reactor, characterized in that, The method includes: The heat transfer medium inside the reactor is heated, and the heat transfer parameters of the reactor are collected, wherein the heat transfer parameters include the temperature difference of the heat transfer medium after it adheres to the wall. Establish a heat transfer model, obtain the functional relationship between the heat transfer rate of the heat transfer medium and the temperature difference of the heat transfer medium, output the temperature difference of the heat transfer medium corresponding to the optimal heat transfer rate of the reactor before wall adhesion, substitute the collected temperature difference of the heat transfer medium after wall adhesion and output the reference flow rate. The flow rate of the heat transfer medium in the reactor is adjusted based on the reference flow rate. When the flow rate of the heat transfer medium in the reactor meets the conditions for the end of the wall adhesion treatment, the temperature of the heat transfer medium in the reactor is reduced to the preset production conditions. The establishment of the heat transfer model includes: A countercurrent heat transfer model with cylindrical partition walls was established for the heat exchange process of a tubular reactor. The optimal reactor heat exchange rate before wall adhesion corresponds to the temperature difference of the heat transfer medium, including: The temperature difference of the heat transfer medium in the reactor before it adheres to the wall and the heat exchange rate of the reactor are collected. Establish the functional relationship between the heat exchange rate of the reactor and the temperature difference of the heat transfer medium; Find the temperature difference of the heat transfer medium corresponding to the highest heat exchange rate in the reactor, and output the obtained temperature difference of the heat transfer medium; The established functional relationship between the heat exchange rate of the reactor and the temperature difference of the heat transfer medium is expressed as: in, The heat exchange rate of the reactor is expressed in W. The heat transfer coefficient of the reactor is expressed in W / m². K; The heat transfer area of ​​the reactor, in units of ; This refers to the temperature difference of the heat-conducting medium, expressed in Kelvin (K). The temperature difference of the heat-conducting medium after wall adhesion, which is collected and then output as a reference flow rate, is expressed as follows: in, This represents the temperature difference of the heat transfer medium corresponding to the highest heat transfer rate of the reactor before it adheres to the wall, expressed in K. This represents the temperature difference of the heat transfer medium after it adheres to the wall, expressed in Kelvin (K). The design flow rate of the reactor is expressed in kg / s. For reference flow rate, the unit is kg / s; The conditions for ending the wall adhesion process include: The absolute value of the difference between the calculated reference flow rate and the reactor's design flow rate is less than a preset error value; the wall adhesion treatment termination condition is expressed as follows: .

2. The online wall-adhesion cleaning method for a tubular reactor containing ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The expression for the heat transfer coefficient of the reactor is: in, The heat transfer coefficient of the reactor; The internal thermal resistance of the reactor tubes; The thermal resistance of the reactor tube wall; This represents the external thermal resistance of the reactor tubes.

3. The online wall-adhesion cleaning method for a tubular reactor containing ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The reference flow rate is inversely proportional to the temperature difference of the heat transfer medium after it adheres to the wall.

4. The method for online wall cleaning of a tubular reactor containing ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The adjustment of the flow rate of the heat transfer medium in the reactor based on the reference flow rate includes: When the difference between the currently calculated reference flow rate and the current flow rate of the heat transfer medium in the reactor exceeds a preset threshold, the flow rate of the current heat transfer medium in the reactor is adjusted.

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