JP2004352948A - Method for producing polymer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polymer, activating necessary warning alarms on changing a production grade of the polymer, while suppressing the activation of unnecessary warning alarms. <P>SOLUTION: This method for producing the polymer is provided by changing set values of controlling factors in changing the production grade of the polymer, measuring dependent factors intermittently or continuously, calculating predicted values of the dependent factors after a prescribed time by using moving averages from the measured values of the dependent factors and setting values (a PH value and a PL value) for warning alarms. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a polymer, and more particularly to a method for producing a polyethylene in which a polymer such as polyethylene or polypropylene is continuously polymerized while switching production brands.
[0002]
[Prior art]
In a polymerization plant for producing polymers commercially, there are many variables to be controlled, such as feed amounts of feedstocks and feed catalysts, polymerization temperature, polymerization pressure, and liquid levels in various reactors and storage tanks. These variables influence the index of the polymer to be produced (eg, molecular weight, molecular weight distribution, density, composition distribution, etc. of the polymer). It is also directly related to stable operation and safe operation of the plant. The variables to be controlled include a control factor whose target value is directly given as a set value during the polymerization reaction, and a dependent factor whose process value changes depending on the set value of the control factor.
[0003]
The values of the control factor and the dependent factor are measured by various detectors for that purpose, and are centrally displayed on, for example, a display device in the instrument room. These values can be remotely controlled in a distributed control system (DCS). In order to stabilize the quality of the product polymer, if these measured values deviate from the target values by more than the specified deviation value, a signal to that effect is generated and the operator is cautioned to fine-tune the control factors. Prompt. This designated deviation is abbreviated as DV.
[0004]
In addition, for stable operation, when a process value (PV value), which is an actually measured value in the operation, is out of a specified range, a warning alarm is activated to alert the operator. Generally, both the upper limit and the lower limit are set as the specified range. The former is called a set upper limit (PH value) for the process value, and the latter is called a set lower limit (PL value) for the process value.
[0005]
Further, for safety, when the detected value is out of the specified safety range, an emergency stop device called an interlock is activated together with a warning alarm to that effect to stop the reaction before the operation of the plant becomes uncontrollable. The set value for safety in such an emergency is called an interlock value. During polymerization of the polymer, the DV value, PH value, PL value, and interlock value are set appropriately to ensure stable operation for obtaining stable product quality, and to prevent failure of equipment and operators. You are driving safely.
[0006]
The interlock value is a fixed value, and usually, the set value is not changed in the process of manufacturing brand switching (product switching). The DV value, the PH value, and the PL value have different set values depending on the manufacturing brand, but are constant for each manufacturing brand. In the operation of conventional polymer manufacturing equipment, these values are written in software from the beginning, and are embedded and fixed in a computer for operation management, making it difficult for the operator to manually reset these values. Met. For this reason, until the operation of the apparatus is settled to a steady state, the measured values of the fluctuation factors are out of these specified ranges, and a warning alarm is frequently activated. Further, in order to prevent this, at the time of switching the manufacturing brand, it has been practiced to widen the range of the set value of the warning alarm.
[0007]
JP-A-08-127602 and JP-A-11-166003 describe a method capable of stably and efficiently performing a switching operation of a set value of a control factor when a brand of a polymer is switched. Here, Japanese Patent Application Laid-Open No. 08-127602 discloses a method for polymerizing a polymer in which the set value of a control factor is changed based on a model pattern at the time of manufacturing brand change, and the set value is followed by fuzzy control. Japanese Patent Application Laid-Open No. H11-166003 describes a method of using a simulator to simulately switch production brands and predict the behavior in the system in advance. However, these publications do not disclose or suggest how to set the DV value, the PH value, and the PL value at the time of switching the manufacturing brand.
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 08-127602 [Patent Document 2]
JP-A-11-166003
[Problems to be solved by the invention]
In view of the above, the present invention aims to improve the quality of a product polymer in the production of polymers such as polyethylene and polypropylene, enhance the reliability of warning alarms in order to obtain stable and safe operation, and deal with warning alarms. An object of the present invention is to provide a polymer production method capable of efficiently and stably producing a polymer.
[0010]
[Means for Solving the Problems]
By changing the DV value, PH value and / or PL value with time, which has been conventionally fixed for each production brand, the present inventors can efficiently produce high-quality polymers while reducing the burden on the operator. Having arrived at the fact that they can be manufactured, they have completed the present invention.
[0011]
That is, in the method for producing a polymer according to the present invention, in the method for producing a polymer in which a polymer is continuously polymerized, a step of changing a set value of at least one control factor, and the step of changing the set value of the control factor vary. Continuously or intermittently measuring the value of at least one dependent factor, and an allowable range including an allowable upper limit value and an allowable lower limit value of the dependent factor based on a temporal variation of the measured value of the dependent factor. Are sequentially set, and a step of generating a predetermined signal when the measured value of the dependent factor is out of the set allowable range.
[0012]
In the method for producing a polymer of the present invention, in a transient state when the set value of the control factor is changed, the allowable upper limit value and the allowable lower limit value of the dependent factor generally have a time-dependent value up to that of the dependent factor. Since it depends on the variation, an allowable range including at least one of the allowable upper limit value and the allowable lower limit value is determined based on the variation. This enables stable and safe operation of the polymerization apparatus.
[0013]
In a preferred aspect of the present invention, the allowable range includes a first allowable range for generating a signal prompting the operator to change the set value of the control factor, and a second allowable range for generating a warning alarm for warning the operator. Including tolerance. Here, the first allowable range is, for example, a DV value, and the second allowable range includes, for example, one or both of a PH value and a PL value that give a normal warning alarm to an operator.
[0014]
The method for producing a polymer according to the present invention preferably includes a step of changing the set value of the control factor when changing the brand of producing the polymer or when starting operation of the apparatus. Since the value of the variable factor fluctuates greatly due to the change of these manufacturing brands and the transient state after the start of operation, by setting such an allowable range, unnecessary warning alarms can be generated without generating unnecessary warning alarms. Since an alarm can be generated, the reliability of the warning alarm can be improved.
[0015]
The method for producing a polymer of the present invention is preferably applied to a polyethylene high-pressure production process, and the dependent factor is measured intermittently at a rate of once every 1 second to 10 minutes. In the high-pressure polyethylene production process, the change of the dependent factor is detected by detecting the variation of the dependent factor at a rate of preferably once every 1 second to 10 minutes, more preferably at a rate of once every 1 second to 1 minute. Particularly necessary warning alarms can be generated effectively.
[0016]
The method for producing a polymer of the present invention is particularly effectively used when the high-pressure polyethylene production process is a tubular process. In a tubular process, the variable to be managed, including the control factor and the dependent factor, may be as large as hundreds, for example, and it is necessary to monitor the variation of the dependent factor due to the change of the control factor. The nature is particularly high.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
In a preferred example of the method for producing a polymer according to the present invention, in a polymer production plant on a commercial scale, a process value (PV value), which is a specified range for stably operating the plant, is changed over time to convert the polymer. To manufacture. In particular, it can be used in a process in which various fluctuation factors (detection values) such as a raw material supply amount, a polymerization temperature, and a polymerization pressure, which are intensively monitored by DCS, change with time. For example, at the time of starting the polymerization operation, at the time of shutdown, or at the time of switching the brand of the polymer.
[0018]
The term "polymer production brand" in the method for producing a polymer of the present invention means a polymer of the same type or a different type having some or all of its physical properties different from each other, and specifically, a molecular weight, a molecular weight distribution, and a composition. , A product polymer that differs in at least one of the composition distributions. In order to switch the production brand of the polymer, it is necessary to switch process conditions in order to produce a polymer having different physical properties. In this switching, the operation of the reactor is stopped by changing the polymerization conditions such as the amount of the raw materials, the ratio of the raw materials when a plurality of the raw materials are used, the polymerization temperature, the polymerization pressure, or the supply amounts of various auxiliaries. To produce different brands of polymer without having to do so. It should be noted that the level monitoring of the reaction tank and the storage tank can be monitored by utilizing the method of the present invention at the time of starting the polymerization, at the time of shutting down, or in the steady operating state as well as the above.
[0019]
FIG. 1 shows a configuration of a control system used in a method for producing a polymer according to an embodiment of the present invention. The control system includes a high-order process computer 10 having advanced control such as manufacturing brand switching and an operation support function such as data collection and analysis, and a low-order distributed control system (DCS) unit 20 for distributed control of a polymer polymerization apparatus. And a gateway 30 for connecting the process computer 10 and the DCS unit 20 to control the polymer polymerization apparatus 40.
[0020]
The process computer 10 has a function of changing a set value of a warning alarm set for a dependent factor over time and sequentially inputting new set values. The process computer 10 accumulates the measured values of the variation factors sent from a number of detection elements 41 installed in the polymer polymerization apparatus to the DCS 20, and calculates the estimated value of the dependent factor after a certain period of time from the variation range. . Next, the PH value, the PL value, and the DV value corresponding to the predicted value are input to the DCS 20 as a set value of a warning alarm after a lapse of a predetermined time from the measurement time of the last received measurement value.
[0021]
Monitoring of plant operation and setting change of control factors are performed remotely in the instrument room. A DCS (distributed control system) 20 is installed in such an instrument room. The detection element 41 illustrated in FIG. 1 is, for example, various sensors such as a thermometer, a pressure gauge, or a flow meter, and one of them is illustrated in FIG. Based on the measurement values of these detection elements 41, a control signal is input to a control element 42 for controlling the process amount, and the operation of the polymerization apparatus is controlled so that the temperature, pressure or flow rate becomes a desired value. The control element is, for example, a flow control valve for controlling the feed amount of the raw material or the auxiliary agent. These electric signals are centrally displayed on the monitor in the instrument room, and the operator can efficiently change the conditions using the DCS.
[0022]
For the purpose of product quality control, if the measured value, for example, the temperature at which the polymerization apparatus is stable exceeds a first threshold value (for example, the temperature of the reactor is normal temperature ± 5 ° C.), a first warning alarm is issued. It is displayed and prompts the operator to take a predetermined action including fine adjustment of the set value. In addition, for stable operation, when the actual measured value exceeds the second threshold value (for example, when the temperature of the reactor is normal temperature ± 10 ° C.), the fact is displayed, and the measured value of the dependent factor is in the warning range. Notify the operator that there is. Furthermore, for safe driving, when the measured actual operation value exceeds a third threshold value (for example, when the temperature of the reactor is 300 ° C.), the fact is displayed and the runaway of the chemical reaction is prevented. Activate the emergency stop device to avoid it. Each of these threshold values is set as such a fixed value when the polymerization apparatus is in a stable state, and as a deviation from a predicted value when the polymerization apparatus is in a transient state. Further, these thresholds are determined for each specific manufacturing brand.
[0023]
At least two points, preferably three to ten points, are used as data collection points required by the upper process computer 10 to calculate the predicted value. In addition, the process computer 10 uses the data collection time calculated by multiplying the data collection period (1 second to 10 minutes) by the DCS by the data collection point as one unit, and calculates the calculated predicted value as the next value. Adopt the set value in the unit. Here, the “predicted value” refers to a value at the time when a time corresponding to the data collection cycle has elapsed from the time of the last data collection in the one unit. For example, in the case where measurement values are collected every 30 seconds, if the measurement data collection points from a certain point in time are A, B, C, and D, these four points belong to one unit. The predicted value calculated based on the fluctuation of the measured value in one unit is reflected on the set value of the warning alarm in the next one unit (that is, from 30 seconds after D to 120 seconds after D). If the time interval is shorter than the range of 1 second to 10 minutes, it is against economic rationality, and if the time interval is longer than this range, it is possible to sufficiently cope with manual setting by the operator.
As a means for inputting a predicted value, a control system that can communicate with a process computer that changes a control factor can be exemplified. For example, a process computer dedicated to control can be exemplified. In addition to a process computer dedicated to such control, a commercially available personal computer can be used to obtain commercially available software for numerical calculation (for example, “Excel” macro or visual basic) and commercially available software for communication with DCS. The purpose can be achieved also by combining software (for example, software “TriFellows” (trade name) manufactured by Yokogawa Electric Corporation).
[0025]
The process for producing a polymer that can utilize the method of the present invention is not particularly limited. For example, the method of the present invention can be used in a high-pressure polymerization process, a slurry polymerization process, a bulk polymerization process, a solution polymerization process, or a gas phase polymerization process. Among them, it is particularly effective to apply to a high-pressure polymerization process. In the high-pressure polymerization process, the production conditions of the polymer are severe. For example, it is necessary to control the polymerization temperature under a high temperature condition of 100 to 300 ° C. and the polymerization pressure under a high pressure condition of 200 to 3000 kg / cm ² . It is preferable to apply to a radical polymerization process among high pressure polymerization processes. In this process, indices such as the molecular weight and density of the polymer depend on the polymerization temperature and the polymerization pressure.
[0026]
The DV value, PH value and / or PL value to be controlled include various temperatures and pressures in polymerization, various flow rates, and amounts of raw materials or auxiliaries to be supplied. All of these may change the setting value over time, or separately, for example, may only change the PH value over time. Of these, it is particularly preferable to change the set value of the polymerization temperature over time. For example, in the case of the tubular process among the high-pressure radical polymerization processes, the polymerization reactor forms a long tubular structure, and the number of installed temperature sensors may exceed one hundred. By changing the settings of the DV value, PH value, and PL value with time, the burden on the operator when monitoring the warning alarm can be greatly reduced.
[0027]
In addition, the method of the present invention is preferably used particularly when the production brand is switched in continuous polymerization. This is because brand switching often requires a significant change in polymerization conditions. Further, when the number of control factors is large and the number of warning alarms is large, the operation of the operator becomes complicated, which is more advantageous. In addition, if the warning alarm is activated only in an abnormal situation, it is possible for the operator to cope with the processing at an early stage, and it can be expected that the operator will shift to a new steady state in a short time. Preventing troubles results in a reduction in non-grade products, which is desirable from the viewpoint of improving product quality and efficient production.
[0028]
The polymer produced by the method of the present invention is not particularly limited, and examples thereof include polyolefins such as polyethylene and polypropylene. These polymers can be produced with a molecular weight of 0.01 to 500 (g / 10 min) in MFR and a density of 0.860 to 0.970 g / cm3.
[0029]
As a polymerization catalyst for producing a polyolefin, in the case of radical polymerization, a compound serving as a radical generation source such as peroxide can be exemplified. In the case of ionic polymerization, for example, a Ziegler-Natta catalyst, a metallocene catalyst or a so-called single-site catalyst can be exemplified. Known catalysts can be used without any limitation.
[0030]
In one embodiment of the present invention, as shown in FIG. 2, upon switching from the first manufactured brand to the second manufactured brand, the current value of the dependent factor is sequentially measured after changing the set value of the control factor. Based on the measured value, a predicted value at a time after a certain time has elapsed from the current time is calculated. Further, a value higher than the predicted value by a predetermined width is set to the PH value at the time, and a value lower than the predicted value by a predetermined width is set to the PL value at the time. In this case, when the measured value is larger than the predicted value by a certain value or more (or smaller than a certain value), the warning alarm A1 is activated. The measurement, prediction, and setting of the dependent factor continued until the measured value of the dependent factor became stable, and after the measured value was stabilized, the PH value and the PL value were determined for the manufactured brand, respectively. It is a predetermined value. The DV value can be set similarly.
[0031]
FIGS. 3A and 3B are graphs respectively illustrating the relationship between the PH value and the interlock value. FIG. 7A shows an example in which the PH value set from the predicted value temporarily exceeds the interlock value set as a constant value. In this case, there is a problem that the function of the PH alarm which originally warns before the interlock value is lost. In FIG. 5B, by providing an upper limit value of the PH value that can be set by the computer, the PH value always falls below the interlock value, and the PH alarm function is activated.
[0032]
FIG. 4 schematically shows a state where the next set PH value and set PL value are obtained from the measured values. When the manufacturing brand is switched, the set value of the dependent factor is made to follow the measured value. The time interval in the measurement of the dependent factor is configurable, for example set to 30 seconds. An average value Yn is obtained based on the measured values of n (for example, 4 to 6; four examples are shown in FIG. 4) of the dependent factors. The predicted value of the dependent factor at the next measurement time point is calculated based on the gradient of the average value Yn. From the calculated predicted value, the next set PH value and set PL value are set in consideration of an allowable deviation. Software is configured so that the measurement time interval, the number of data n, and the time for which the PH value and the PL value follow the predicted value can be arbitrarily set in accordance with the switching time of the process and the manufacturing brand.
[0033]
When calculating the set values of the PH value and the PL value from the predicted values, select either the absolute value (fixed value) or the ratio to the measured value according to the dependent factor to be treated and / or its measured value. Is preferred. For example, when measuring the flow rate of a pump that adjusts the flow rate with a plunger stroke or the like as a dependent factor, the amplitude of the measured value varies depending on the flow rate (for example, in the case of a low flow rate of 10 L / Hr, the amplitude is ± 1 L). / Hr, whereas at 100 L / Hr, which is a high flow rate, there is a characteristic that the swing width expands to ± 10 L / Hr.) In such a case, the “ratio” is adopted regardless of the flow rate. The setting is such that the predicted value is ± 10%.
[0034]
The method for producing a polymer of the present invention was applied to switching of production brands in a tubular process, which is ethylene polymerization by a high-pressure radical method. In the tubular process, the reactor has an elongated tubular shape, is about 1500 m long, and has about 100 temperature sensors installed. Conventionally, when a manufacturing brand is switched, if the process involves a transitional state at the time of the switching, the transition width of the variable factor accompanying the brand change is sufficiently larger than the warning alarm set for the variable factor. It is usually large. Therefore, immediately after entering the transitional state, the setting range of the warning alarm was set to a value sufficiently larger than the transition width, and after the process transitioned to the steady state, the setting value for the new brand was changed. . Also. In another example, at an appropriate point in time when the process is in a transient state, the PH and PL values of all dependent factors are changed at once.
That is, when the process at the time of brand switching is in a transitional state, it is difficult to detect a process change by an alarm at an early stage.
[0035]
In the manufacturing process by the high-pressure radical method to which the method of the present invention was applied, the DV value, the PH alarm, and the PL alarm were calculated from the predicted values. As a result, good product quality was obtained, and stable and safe operation became possible, and the burden on the operator was greatly reduced. Similar effects can be expected for operating factors other than the reaction temperature (polymerization pressure, supply amounts of various auxiliaries, etc.).
[0036]
As described above, the present invention has been described based on the preferred embodiments. However, the method for producing the polymer of the present invention is not limited to only the configuration of the above-described embodiment, and may be variously changed from the configuration of the above-described embodiment. Modifications and changes of the above are also included in the scope of the present invention.
[0037]
【The invention's effect】
As described above, according to the method for producing a polymer according to the present invention, even in a transitional state of a process such as a production brand change, unnecessary warning alarms are prevented from being activated while unnecessary warning alarms are activated. This makes it possible to improve the product quality, stably and safely drive the device, and reduce the burden on the operator.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a control system for implementing a method for producing a polymer according to an embodiment of the present invention.
FIG. 2 is a graph showing a relationship between a predicted value of a dependent factor and a set value of a warning alarm.
FIG. 3 is a graph showing a relationship between a set value of a warning alarm and an interlock value.
FIG. 4 is a graph showing a state where a predicted value is obtained from a measured value of a control factor.
[Explanation of symbols]
10: Process computer 20: DCS unit 30: Gateway 40: Superposition unit 41: Detection element 42: Control element

Claims (5)

In a method for producing a polymer by continuously polymerizing a polymer,
Changing a setting of at least one control factor;
Continuously or intermittently measuring the value of at least one dependent factor that varies depending on the set value of the control factor;
Based on the temporal variation of the measured value of the dependent factor, sequentially setting an allowable range including at least one of an allowable upper limit and an allowable lower limit of the dependent factor,
Generating a predetermined signal when the measured value of the dependent factor deviates from the set allowable range. The allowable range includes a first allowable range for generating a signal urging the operator to change the set value of the control factor, and a second allowable range for generating a warning alarm notifying the operator of the occurrence of an abnormality. The method for producing a polymer according to claim 1, comprising: The method for producing a polymer according to claim 1 or 2, wherein a step of changing the set value of the control factor when changing the brand of production of the polymer is provided. The method for producing a polymer according to any one of claims 1 to 3, wherein the method for producing a polymer is applied to a polyethylene high-pressure production process, and the dependent factor is measured intermittently at a rate of once every 1 second to 10 minutes. . The polymer production method according to claim 5, wherein the polyethylene high-pressure production process is a tubular process.

Images