Amine recovery monitoring method and system for polyurethane synthesis tail gas

Abstract

The invention relates to the technical field of gas separation, in particular to an amine recovery monitoring method and system for polyurethane synthesis tail gas. The method comprises the following steps: preliminarily separating to obtain a triethylamine solution; collecting parameter values of different parameters for distillation of the triethylamine solution; acquiring a parameter sequence in a preset time period; decomposing the parameter sequence to obtain a periodic sequence and a trend sequence; obtaining periodic saliency values of different parameters based on the periodic sequence, and obtaining a fluctuation consistency coefficient based on the trend sequence; a distillation interference coefficient is obtained after weighting; pure triethylamine is obtained based on the distillation interference coefficient control system; collecting attribute values of different attributes, constructing a change characteristic value sequence through differences between data values and predicted values of the attributes in the sliding window, and obtaining a dehydration steady-state index based on sequence similarity and vapor pressure differences; and recycling and monitoring of triethylamine are realized based on the dehydration steady-state index. According to the method, the dehydration efficiency of the triethylamine is improved, and the purity of the recovered triethylamine is further improved.

Description

Technical Field

[0001] This application relates to the technical field of gas separation, and specifically relates to a method and system for amine recovery monitoring for polyurethane synthesis tail gas. Background Art

[0002] Polyurethane is a polymer material formed by the polycondensation reaction of polyisocyanates and polyols, and has excellent mechanical properties, wear resistance, oil resistance, plasticity and other characteristics. In the production process of polyurethane, amines are often used as catalysts, and their main function is to accelerate the reaction between isocyanates and polyols or water, thereby promoting the foaming and gelation processes. For example, amine catalysts such as triethylamine can significantly increase the reaction rate and regulate the foam formation rate and product quality.

[0003] Amines are volatile, and some amines will be discharged with the tail gas during the production process. If directly discharged, it will cause environmental pollution. Recycling the amines in the tail gas can not only reduce pollution, but also reuse the recycled amines in the production process, reduce production costs, and improve the recovery resource utilization rate. The recovery of amines requires separation and purification steps. Among them, the accuracy of process control in distillation and membrane dehydration in the purification step is crucial. During the actual operation process, the raw material composition and the state of the recovery equipment may change, which in turn affects the purity of the recovered amines. Different temperature changes will result in low separation purity of amines; existing amine recovery methods are difficult to quickly adapt to these dynamic changes during the monitoring process due to not deeply considering the comprehensive influence among the above factors, resulting in low purity of the recovered amines. Summary of the Invention

[0004] In order to solve the technical problem of low separation purity of amines, this application provides a method and system for amine recovery monitoring for polyurethane synthesis tail gas, and the specific technical solutions adopted are as follows: In the first aspect, this application proposes a method for amine recovery monitoring for polyurethane synthesis tail gas, and the method includes the following steps: Preliminarily separate the polyurethane synthesis tail gas to obtain a triethylamine solution; Add the triethylamine solution to other solutions and then distill, and collect the parameter values of different parameters at each moment; the parameters include the top temperature of the kettle, the bottom temperature of the kettle, the condenser flow rate, and the triethylamine concentration; The specific steps of distillation are as follows: Set an adjustment time period, and obtain the parameter sequence of each parameter therein; Decompose the parameter sequence to obtain a period sequence and a trend sequence; obtain the period significant value of the parameter sequence based on the fluctuation of the peak difference in the period sequence; Obtain the fluctuation consistency coefficient between two parameters according to the correlation coefficient of the trend sequence between the two parameters; use the periodic significant values of the top temperature of the kettle and the other parameters as weights to weight the fluctuation consistency coefficient between the top temperature of the kettle and the other parameters to obtain the distillation interference coefficient for the adjusted time period; Optimize the control parameters based on the distillation interference coefficient, and process the next time period to obtain pure triethylamine; The specific steps of membrane dehydration are as follows: Add pure triethylamine to the preheater and evaporator; collect the attribute values of different attributes for a preset time, including the evaporator temperature and the vapor pressures on both sides of the membrane; Set a sliding window, obtain the change characteristic value based on the difference between the data value of each attribute within the sliding window and the obtained predicted value, and construct a change characteristic value sequence; obtain the dehydration steady-state index based on the similarity of the change characteristic value sequence and the difference in the vapor pressures on both sides of the membrane; Realize the recovery and monitoring of triethylamine based on the comparison between the dehydration steady-state index and the membrane dehydration abnormal threshold.

[0005] In the above solution, the present application proposes an amine recovery monitoring method and system for polyurethane synthesis tail gas. The method includes three steps: triethylamine separation, acid-base conversion and distillation, and membrane dehydration. Among them, for the distillation step, it is regulated and monitored due to the influence of unstable feed rate, heating power, cooling system, and the factors of the evaporator and membrane pollution in the membrane dehydration step. By analyzing the correlation characteristics between the top temperature in the distillation kettle and the bottom temperature, condenser flow rate, and triethylamine concentration at the top of the rectifying column respectively, and the periodic fluctuation characteristics of the above data, the distillation interference coefficient of the distillation state is calculated. Based on this value, the reflux flow of the rectifying column is optimized and adjusted. Its advantage is that it can reduce the influence of raw material composition changes and unstable cooling system, and obtain relatively pure triethylamine; in the membrane dehydration step, by analyzing the synchronous characteristics of the evaporator temperature and the vapor pressures on both sides of the membrane and the fluctuation degree of the differential pressure, the dehydration steady-state index is calculated, and then the triethylamine dehydration step is monitored and evaluated. Its advantage is that it helps to improve the efficiency of triethylamine dehydration and further improve the purity of the recovered triethylamine.

[0006] In one embodiment, the method for preliminarily separating polyurethane synthesis tail gas to obtain a triethylamine solution is as follows: Convert triethylamine from gas state to liquid state by condensation method to separate the amine in the tail gas; place two condensers, and make the tail gas pass through the two condensers in sequence. The temperature of the first condenser needs to be greater than 89.5 °C and less than 200 °C, and the temperature of the second condenser needs to be less than 89.5 °C. The liquid after passing through the two condensers is the triethylamine solution after primary separation.

[0007] In one embodiment, the method for obtaining the period significance value of the parameter sequence based on the fluctuation of the peak difference in the period sequence is as follows: Process the obtained period sequence using polynomial fitting technology, and then extract the peaks from the fitting curve through derivative analysis; arrange the time values corresponding to all peak points in ascending order as the peak time sequence, and calculate the standard deviation of the first-order difference sequence of the obtained peak time sequence; take the reciprocal of the standard deviation as the period significance value of the parameter sequence.

[0008] In one embodiment, the method for obtaining the fluctuation consistency coefficient between two parameters based on the correlation coefficient of the trend sequence between the two parameters is as follows: Calculate the Spearman correlation coefficient of the trend sequence between the two parameters, and take the sum of the Spearman correlation coefficient and 1 as the fluctuation consistency coefficient.

[0009] In one embodiment, the method for obtaining the distillation interference coefficient of the adjustment time period by weighting the fluctuation consistency coefficient between the top temperature of the kettle and the remaining parameters with the period significance value of the top temperature and the remaining parameters is as follows: Let the sum of the period significance value of the top temperature of the kettle and any one of the remaining parameters divided by the sum of the period significance values of all parameters be used as the influence weight of any one parameter; The distillation interference coefficient is positively correlated with the influence weight and negatively correlated with the fluctuation consistency coefficient.

[0010] In one embodiment, the method for optimizing the control parameters based on the distillation interference coefficient is as follows: The optimization formula for the proportional term parameter is: ; where is the optimized proportional term parameter, is the preset adjustment parameter, represents the logarithmic function with base 10, represents the distillation interference coefficient.

[0011] In one embodiment, the method for obtaining the change characteristic value based on the difference between the data value of each attribute within the sliding window and the obtained predicted value, and constructing the change characteristic value sequence is as follows: Input the data value of this attribute within the sliding window, and output the predicted value through the single exponential smoothing algorithm; Calculate the cumulative sum of the differences between the predicted value and each data value in the sliding window, and take the cumulative sum as the change characteristic value of this attribute; Calculate a change characteristic value each time the sliding window slides, and obtain the change characteristic value sequence of this attribute by sorting the change characteristic values of all sliding windows corresponding to each attribute according to time.

[0012] In one embodiment, the method for obtaining the dehydration steady-state index based on the similarity of the sequence of change characteristic values and the difference in vapor pressure on both sides of the membrane is as follows: Calculate the SBD distance corresponding to all pairs of change characteristic sequences; take the reciprocal of the mean of all the SBD distances as the synchronization coefficient of temperature and vapor pressure; Calculate the difference between the vapor pressure data on both sides of the membrane at all the same moments, and take the ratio of the synchronization coefficient to the standard deviation of all the differences as the dehydration steady-state index.

[0013] In one embodiment, the method for realizing the recovery and monitoring of triethylamine based on the comparison between the dehydration steady-state index and the membrane dehydration abnormal threshold is as follows: After normalizing the dehydration steady-state index, if the normalized value is less than the preset membrane dehydration abnormal threshold, the efficiency is low and the vapor pressure needs to be adjusted; if S is greater than or equal to 0.6, the efficiency of the membrane dehydration process is good.

[0014] In a second aspect, an amine recovery monitoring system for polyurethane synthesis tail gas provided by an embodiment of the present application includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the above-mentioned amine recovery monitoring method for polyurethane synthesis tail gas are realized.

[0015] The beneficial effects of the present application are as follows: The present application proposes an amine recovery monitoring method and system for polyurethane synthesis tail gas. The method includes three steps: triethylamine separation, acid-base conversion and distillation, and membrane dehydration. Among them, for the distillation step, it is regulated and monitored due to the influence of unstable feed rate, heating power, cooling system, and the factors of evaporator and membrane fouling in the membrane dehydration step. By analyzing the relevant characteristics between the top temperature and the bottom temperature, condenser flow rate, and triethylamine concentration at the top of the rectifying column in the distillation kettle, as well as the periodic fluctuation characteristics of the above data, the distillation interference coefficient of the distillation state is calculated. Based on this value, the reflux flow of the rectifying column is optimized and adjusted. Its advantage is that it can reduce the influence of raw material composition changes and unstable cooling system, and obtain relatively pure triethylamine; in the membrane dehydration step, by analyzing the synchronization characteristics of the evaporator temperature and the vapor pressure on both sides of the membrane and the fluctuation degree of the partial pressure difference, the dehydration steady-state index is calculated, and then the triethylamine dehydration step is monitored and evaluated. Its advantage is that it helps to improve the efficiency of triethylamine dehydration and further improve the purity of the recovered triethylamine. Description of the Drawings

[0016] To more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 Flowchart of an amine recovery monitoring method for polyurethane synthesis tail gas provided by an embodiment of the present application; Figure 2 Flowchart of the method for the distillation step; Figure 3 Flowchart of the membrane dehydration step. Detailed implementation manners

[0018] To further elaborate on the technical means and effects adopted by the present application to achieve the intended invention purpose, the following, in combination with the accompanying drawings and preferred embodiments, details the specific implementation manners, structures, features, and effects of an amine recovery monitoring method and system for polyurethane synthesis tail gas proposed according to the present application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0020] An embodiment of an amine recovery monitoring method and system for polyurethane synthesis tail gas: The following specifically describes the specific solution of an amine recovery monitoring method for polyurethane synthesis tail gas provided by the present application in combination with the accompanying drawings.

[0021] Please refer to Figure 1 , which shows a flowchart of an amine recovery monitoring method for polyurethane synthesis tail gas provided by an embodiment of the present application. The method includes the following steps: Step S1, preliminarily separating the polyurethane synthesis tail gas to obtain a triethylamine solution.

[0022] The synthesis reaction process of polyurethane is the main source of polyurethane tail gas in rubber and plastic factories. When raw materials such as isocyanate and polyol undergo a polymerization reaction, due to incomplete reaction or under operating conditions such as high temperature and stirring, some raw materials and intermediate products will volatilize into the air to form tail gas. These tail gases contain various organic compounds, among which volatile organic compounds are the main components, including but not limited to isocyanate substances such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). In addition, the polyurethane synthesis tail gas may also contain amine catalysts. The types of these catalysts include but are not limited to bis(2-dimethylaminoethyl) ether, dimethylcyclohexylamine, and triethylamine. In the polyurethane production of this application, triethylamine is used as a catalyst, so triethylamine is separated and recovered from the synthesis tail gas.

[0023] Substances such as toluene diisocyanate and diphenylmethane diisocyanate in the tail gas have the characteristic of high boiling point, usually at or above, while the boiling point of triethylamine is about . Therefore, by utilizing the low boiling point characteristic of triethylamine, triethylamine is converted from a gaseous state to a liquid state through the condensation method to separate the amine from the tail gas. In this application, the mixed tail gas generated in polyurethane production is passed through two condensers in sequence. The temperature of the first condenser is controlled at or above, and is set to in this embodiment. At this time, substances such as toluene diisocyanate, diphenylmethane, and diphenylmethane diisocyanate will be preferentially converted into a liquid state, while triethylamine remains in a gaseous state. Then it flows through the second condenser, and the temperature of the second condenser is controlled at or below to convert triethylamine into a liquid state, thereby achieving the separation of triethylamine.

[0024] So far, the triethylamine solution after the initial separation is obtained.

[0025] Step S2, add the triethylamine solution to other solutions and then distill, and collect the parameter values of different parameters at each moment.

[0026] The separated triethylamine solution obtained through the above steps may contain other organic compound impurities, such as alcohols and acids. To extract and recover triethylamine, this application removes the impurities in the triethylamine solution through an acid-base conversion method.

[0027] First, add hydrochloric acid solution to the triethylamine solution to convert the amine into an ammonium salt and dissolve it in the aqueous phase. After oil-water separation, the aqueous phase is collected. Then, add sodium hydroxide solution to the obtained aqueous phase to convert the ammonium salt back into an amine. After the acid-base conversion, although most of the impurities have been removed, there may still be a small amount of water and other volatile impurities in the solution. This application uses the distillation method for further separation and purification. By heating to evaporate triethylamine and then collecting it through condensation, these impurities can be further removed and the purity of triethylamine can be improved.

[0028] Further, the triethylamine solution after acid-base treatment is then added to a distillation kettle, heated and vaporized in the distillation kettle. The distillation kettle is connected to a rectifying column. After stable operation with total reflux, the water-containing triethylamine vapor is taken out from the top of the rectifying column, and after being condensed by a distillation condenser, part of it is refluxed to the top of the rectifying column and part of it is taken out to a distillation receiving tank. During each distillation process, due to the fluctuations in the impurity content of the raw materials and the dynamic change characteristics of the operating parameters of these key equipment such as the distillation kettle, condenser, and rectifying column, the above factors will all have a significant impact on the extraction purity of triethylamine, and the reflux ratio can better control the product quality. To improve the product purity, it is necessary to monitor the operating parameters of the distillation system in real time, and then accurately regulate the reflux amount during the distillation process to achieve the efficient separation and purification of triethylamine.

[0029] Among them, the temperature state in the distillation kettle and the load of the condenser are important factors affecting the extraction purity. Therefore, in this application, temperature sensors are installed at the top and bottom of the distillation kettle to collect the top temperature data and bottom temperature data of the kettle. The load of the condenser is monitored by the flow rate of the condensate, and a flow sensor is installed inside the condenser to collect the flow rate data of the condensate. In addition, the purity of the triethylamine vapor at the top of the rectifying column can more intuitively reflect the current separation and extraction effect. Therefore, a fixed triethylamine gas detector is installed at the top of the rectifying column to collect the triethylamine concentration data. The time interval for collecting data by each of the above sensors is set to 1 second. Thus, the top temperature data, bottom temperature data, condenser flow rate data, and top triethylamine concentration data at each moment are obtained, and the top temperature, bottom temperature, condenser flow rate, and triethylamine concentration at each moment are recorded as parameters.

[0030] Thus, the top temperature, bottom temperature, condenser flow rate, and triethylamine concentration at each moment are obtained.

[0031] Step S3, obtain a parameter sequence in a preset time period; decompose the parameter sequence to obtain a periodic sequence and a trend sequence; obtain the periodic significant values of different parameters based on the periodic sequence, and obtain the fluctuation consistency coefficient based on the trend sequence; obtain a distillation interference coefficient after weighting; control the system based on the distillation interference coefficient to obtain pure triethylamine.

[0032] The top temperature and bottom temperature of the kettle are obtained through the above steps. The top temperature and bottom temperature states of the kettle are easily affected by the feed rate, heating power, and cooling system. The two respectively reflect the gas-phase temperature state at the top of the kettle and the liquid-phase temperature state at the bottom of the kettle during the distillation process.

[0033] Excessive temperatures at the top and bottom of the kettle may cause other high-boiling impurities to enter the distillate, and trigger the decomposition of heat-sensitive substances, further contaminating the product. While too low a temperature will make it difficult for triethylamine to fully evaporate and remain in the distillation kettle, resulting in incomplete separation and reduced separation efficiency. In addition, a synergistic balance needs to be achieved between the top and bottom kettle temperatures, and there is a high positive correlation in their change process to reduce cross-contamination between different components. The condenser flow rate reflects the load status of the condenser. Too low a condensate flow rate will cause poor separation between triethylamine and impurities. Moreover, the change in the condenser flow rate will affect the temperature distribution in the distillation kettle. If the condensation flow rate is too large, it may cause the temperature at the top of the kettle to be too low, affecting the vaporization and separation effect of triethylamine. On the contrary, too small a condensate flow rate will cause the temperature at the top of the tower to rise, increasing the risk of azeotropy of impurities and reducing the purity of triethylamine. The concentration of triethylamine at the top of the rectification tower more directly reflects the extraction efficiency of triethylamine, and has a certain correlation with the temperature at the top of the distillation kettle. Too low a temperature at the top of the kettle may cause insufficient volatilization of light components, all of which will lead to a decrease in the triethylamine concentration.

[0034] From the above analysis, it can be seen that under good distillation conditions, there is a positive correlation between the top kettle temperature data, the bottom kettle temperature data, the condenser flow rate data, and the triethylamine concentration data. And the fluctuation stability of each data item will affect the final separation purity.

[0035] S3.1, set an adjustment time period and obtain the parameter sequence of each parameter therein.

[0036] Since the separation purity of triethylamine is affected by various factors, if the control parameters remain unchanged, the separation purity will be greatly affected; set a time period with a preset time length. For each time period, record the previous adjacent time period as the adjustment time period, analyze the adjustment time period, and adjust the proportional parameter in the control algorithm of the adjustment time period, thereby improving the purity of triethylamine. In this embodiment, the length of each time period is 8 minutes. That is, the current time period is adjusted by analyzing the previous time period.

[0037] First, when the feed rate and heating power are unstable, it is easy to cause periodic fluctuations in the temperature in the distillation kettle. If the existing periodic fluctuations are more significant, it means that the temperature oscillations at the top and bottom of the kettle are more obvious, and it is more likely to affect the separation and extraction effect.

[0038] Furthermore, all the top kettle temperatures, bottom kettle temperatures, condenser flow rates, and the triethylamine concentration at the top of the tower within the adjustment time period are respectively constituted into four sequences, denoted as the top kettle temperature sequence, the bottom kettle temperature sequence, the condenser flow rate sequence, and the triethylamine concentration sequence at the top of the tower; the above four sequences are uniformly denoted as the parameter sequence.

[0039] S3.2. Decompose the parameter sequence to obtain the periodic sequence and the trend sequence; obtain the periodic significance value of the parameter sequence based on the fluctuation of the peak difference in the periodic sequence.

[0040] To analyze the periodic fluctuation characteristics, for any one of the parameter sequences, use the STL (Seasonal and Trend decomposition using Loess) sequence decomposition algorithm to decompose the parameter sequence, and output the periodic sequence, trend sequence and residual sequence of the parameter sequence.

[0041] Among them, the obtained periodic sequence can better reflect the periodic characteristics of the data itself. When the periodic characteristics are more significant, the distances between the fluctuation peaks in the obtained periodic sequence are more regular. Therefore, use the polynomial fitting technique to process the obtained periodic sequence, and then extract the peaks from the fitting curve through derivative analysis. The purpose of the fitting process is to avoid identifying local jitters in the sequence as peaks. Arrange the time values corresponding to all peak points in ascending order as the peak time sequence, and calculate the standard deviation of the first-order difference sequence of the obtained peak time sequence. The smaller the standard deviation, the more regular the distribution of the distances between the peaks, and the more significant the periodic fluctuation of this parameter sequence. Take the reciprocal of the standard deviation as the periodic significance value of this parameter sequence.

[0042] Among them, the greater the influence degree of the top kettle temperature fluctuation on the separation and purification effect, the greater its corresponding periodic significance value; and the temperature of the distillation kettle will affect the flow rate of the condensate and the concentration of triethylamine at the top of the rectification column, making the condenser flow rate data and triethylamine concentration data also have certain periodic fluctuation characteristics, which in turn affect the separation purity.

[0043] Step S3.3. Obtain the fluctuation consistency coefficient between two parameters according to the correlation coefficient of the trend sequences between the two parameters; use the periodic significance values of the top kettle temperature and the other parameters as weights to weight the fluctuation consistency coefficient between the top kettle temperature and the other parameters to obtain the distillation interference coefficient of the adjusted time period.

[0044] After obtaining the periodic significance of each parameter sequence through the above steps, further analyze the correlation characteristics between different parameters. Since the above steps obtain the trend sequences of different parameter sequences through the STL algorithm, and the data in the trend sequence reflects the overall change direction in a relatively long time, and there is a certain time delay in the correlation influence between parameter sequences, so the distillation state of the current period can be better evaluated by comparing the correlation characteristics between trend sequences.

[0045] The better the separation and purification effect during distillation, the more obvious the positive correlation between the top kettle temperature and other data. Conversely, the more obvious the corresponding negative correlation feature. Therefore, the correlation coefficient of the trend sequences corresponding to the top kettle temperature sequence and the other parameter sequences is calculated. In this embodiment, taking the top kettle temperature and the condensation flow rate data as examples, the Spearman correlation coefficient of the corresponding trend sequences of the two is calculated, and its value range is [-1, 1]. The sum of the Spearman correlation coefficient and 1 is used as the fluctuation consistency coefficient. The smaller the fluctuation consistency coefficient, the worse the coordination degree between the top kettle temperature and the condenser state during this period, and the more unfavorable it is for separation and purification. The same as the above steps, the fluctuation consistency coefficients of calculating the top kettle temperature with the bottom kettle temperature and the triethylamine concentration can be obtained respectively.

[0046] Since the periodic significant value reflects the stable characteristics of the operation of each device, and the stability degrees of different device parameters are inconsistent, which in turn have different degrees of influence on the separation and purification effect of the distillation process; and in this application, the bottom kettle temperature, the condenser flow rate, and the triethylamine concentration are all affected by the top kettle temperature. Therefore, based on the periodic significant values of the bottom kettle temperature, the condenser flow rate, and the triethylamine concentration respectively, the influence weight of each parameter except the top kettle temperature is obtained.

[0047] Preferably, in this embodiment, the expressions for the influence weights of the bottom kettle temperature, the condenser flow rate, and the triethylamine concentration are: , , , represents the periodic significant value of the top kettle temperature, represents the periodic significant value of the bottom kettle temperature, represents the periodic significant value of the condenser flow rate, represents the periodic significant value of the triethylamine concentration, represents the sum value of the periodic significant values of all parameters, represents the influence weight of the bottom kettle temperature, represents the influence weight of the condenser flow rate, represents the influence weight of the triethylamine concentration.

[0048] According to the influence weight of each parameter except the top kettle temperature and the fluctuation consistency coefficient between the top kettle temperature and the other parameters, the distillation interference coefficient is obtained.

[0049] The distillation interference coefficient has a positive correlation with the influence weight and a negative correlation with the fluctuation consistency coefficient.

[0050] It should be noted that positive correlation means that when one variable increases, the other variable also increases, and the change directions of the two variables are the same. When one variable changes from large to small or from small to large, the other variable also changes from large to small or from small to large; the specific relationship is determined by the actual application, and this application does not make special restrictions.

[0051] It should be noted that negative correlation means that when one variable increases, the other variable decreases accordingly. The change directions of the two variables are opposite. When one variable changes from large to small or from small to large, the other variable also changes from small to large or from large to small. The specific relationship is determined by actual applications and is not specifically restricted in this application.

[0052] Preferably, in this embodiment, the expression of the distillation interference coefficient is: , represents the influence weight of the bottom temperature of the kettle, represents the influence weight of the condenser flow rate, represents the influence weight of the triethylamine concentration, represents the fluctuation consistency coefficient of the top temperature and the bottom temperature of the kettle, represents the fluctuation consistency coefficient of the top temperature and the condenser flow rate, represents the fluctuation consistency coefficient of the top temperature and the triethylamine concentration, represents the distillation interference coefficient; is a very small constant, taking 0.01, aiming to prevent the denominator from being 0; Thus, the distillation interference coefficient of the adjustment time period is obtained. The larger the distillation interference coefficient, the greater the interference of the equipment operation and the feed during the distillation process.

[0053] So far, the distillation interference coefficient of the adjustment time period has been obtained.

[0054] Step S3.4, optimize the control parameters based on the distillation interference coefficient and process the next time period to obtain pure triethylamine.

[0055] Through the above steps, the distillation interference coefficient of the adjustment time period is obtained. To reduce the influence of the distillation interference coefficient, this application controls the reflux flow rate of the rectifying column through a regulating valve, thereby improving the separation purity. Among them, the opening degree of the regulating valve is controlled by the PID algorithm. And the reflux flow rate of the current time period is adjusted according to the distillation state of the previous time period. Specifically, if the The larger the value, the greater the degree of interference suffered by the distillation process. Then, the proportional term parameter in the PID algorithm is increased accordingly to improve the response rate of the system; otherwise, the corresponding proportional term can be reduced to avoid overshoot.

[0056] Set the initial value of the proportional term parameter in the PID to 1. The specific optimization formula for the proportional term parameter is: . Among them is the optimized proportional term parameter, is the adjustment parameter, and its value range is set to [1, 3] according to empirical values, represents the logarithmic function with base 10.

[0057] After adjusting the PID control parameters, the current reflux flow rate and the expected reflux flow rate are input into the PID control system. After being processed by the system, purer triethylamine is obtained. The specific implementation flow chart of the distillation step is as follows: Figure 2 shown.

[0058] At this point, the distillation system was precisely controlled, achieving efficient separation and purification of triethylamine.

[0059] Step S4, collecting attribute values of different attributes, constructing a change characteristic value sequence through the difference between the data value and the predicted value of the attribute in the sliding window, and obtaining a dehydration steady-state index based on sequence similarity and vapor pressure difference; and realizing the recovery and monitoring of triethylamine based on the dehydration steady-state index.

[0060] S4.1, adding pure triethylamine to the preheater and the evaporator; collecting the attribute values of different attributes at the preset time, including the evaporator temperature and the vapor pressure on both sides of the collection membrane.

[0061] Although distillation purification can remove most impurities and water, the obtained liquid triethylamine may still contain a small amount of water. Triethylamine is very sensitive to water, and trace water will affect its purity and subsequent performance, and cannot meet the requirements of industrial applications. Therefore, mold dehydration treatment is required. The effect of distillation purification directly affects the efficiency and cost of mold dehydration treatment. The lower the water content after distillation, the higher the efficiency of mold dehydration treatment, and the higher the accuracy of amine recovery monitoring.

[0062] The liquid triethylamine obtained in the previous step enters the preheater and evaporator through the raw material pump, and enters the membrane separation unit in the form of steam after reaching a certain temperature. The moisture and a small amount of organic matter in the raw material permeate from the upstream side of the membrane to the downstream side of the membrane through the membrane assembly. The finished product is obtained at the last stage of the upstream side of the membrane. The downstream side of the membrane adopts the method of vacuuming and condensing to form the steam partial pressure difference of the components on the upstream and downstream sides. The permeate vapor enters the condenser under the suction of the vacuum unit, and the condensed permeate is discharged by the pump and then processed.

[0063] During the membrane dehydration process, the dehydration performance may be reduced due to unstable evaporator heating power or membrane pollution and clogging factors. Changes in evaporator temperature and pressure difference between the upstream and downstream sides of the membrane are key factors affecting the quality of amine recovery. Real-time monitoring of the two parameters helps to ensure efficient dehydration of triethylamine and product quality. Evaporator temperature and membrane pressure difference need to be maintained within the standard range. Excessive evaporator temperature will cause the vapor pressure on the upstream side of the membrane to increase. When the permeation efficiency of the membrane is affected, the vapor pressure measured downstream of the membrane will become unstable. This will lead to unstable changes in the vapor partial pressure difference on both sides of the membrane, and the partial pressure difference is the key driving force for membrane dehydration. The vacuum degree on the downstream side needs to be precisely controlled to ensure sufficient and stable partial pressure difference, thereby improving dehydration efficiency.

[0064] Therefore, during the dehydration process of this application, the temperature of the evaporator and the steam pressures on both the upstream and downstream sides of the membrane are monitored. The temperature data of the evaporator is collected by a temperature sensor, and the steam pressure data on both sides of the membrane is collected by pressure sensors. The acquisition time interval for each item of data is 1 second. Thus, the temperature of the evaporator and the steam pressures on both sides of the collected membrane are obtained.

[0065] S4.2, set a sliding window, obtain a change characteristic value based on the difference between the data value of each attribute within the sliding window and the obtained predicted value, and construct a change characteristic value sequence; obtain a dehydration steady-state index based on the similarity of the change characteristic value sequence and the difference in the steam pressures on both sides of the membrane.

[0066] Since the increase in temperature will cause a rapid increase in the steam pressure on the upstream side, therefore, to analyze the changes and relationship characteristics of temperature and pressure in the short term, set a sliding window with a sliding step size of 1; in this embodiment, the value of the sliding window is 7; and since the changes in temperature and steam pressure are relatively rapid, to facilitate real-time optimization and adjustment, set the adjustment interval length of membrane dehydration to 1 minute, and the sliding window slides within this adjustment interval length.

[0067] The increase in the temperature of the evaporator will cause an increase in the steam pressure on the upstream side of the membrane. To maintain the stability of the differential pressure, it is necessary to correspondingly increase the steam pressure on the downstream side of the membrane. Therefore, further analyze the change difference characteristics between temperature and pressure.

[0068] Record the collected temperature of the evaporator and the steam pressures on both sides of the collected membrane as attributes. For each attribute, input the data value of this attribute within the sliding window, and output a predicted value through a single exponential smoothing algorithm; then calculate the cumulative sum of the differences between the predicted value and each data value in the sliding window, and use the cumulative sum as the change characteristic value of this attribute. The magnitude of the obtained change characteristic value reflects the change direction and degree of the data within the sliding window. Thus, during the sliding of the window, the corresponding change characteristic value at the corresponding moment can be calculated, and the change characteristic sequences of each attribute within the adjustment interval are arranged in ascending order of time.

[0069] Furthermore, during the membrane dehydration operation, the steam pressure on the downstream side of the membrane needs to change synchronously with the steam pressure on the upstream side of the membrane, and there is a strong correlation between the steam pressure on the upstream side of the membrane and the temperature of the evaporator. Therefore, to analyze the current dehydration state, first calculate the SBD (Shape Based Distance) distances corresponding to all pairwise combinations of all change characteristic sequences. Take the reciprocal of the mean of all the SBD distances as the synchronization coefficient of temperature and steam pressure. The larger the obtained synchronization coefficient, the more synchronous the change between the temperature of the evaporator and the steam pressure.

[0070] In addition, in combination with the fluctuation degree characteristics of the wind pressure difference on both sides of the membrane, the efficiency of the membrane dehydration process is further analyzed. The difference between the steam pressure data on both sides at all the same moments is calculated respectively, and the ratio of the synchronization coefficient to the standard deviation of all the said differences is used as the dehydration steady-state index. The larger the dehydration steady-state index, the better the dehydration state at the current regulation interval time. The corresponding dehydration steady-state index is calculated for each regulation interval.

[0071] S4.3, based on the comparison between the dehydration steady-state index and the membrane dehydration abnormal threshold, realizes the recovery and monitoring of triethylamine.

[0072] The dehydration steady-state index of each regulation interval is calculated according to the above steps. For quantitative evaluation, the softmax function is used to normalize the steady-state coefficient, and the obtained result is denoted as S. The membrane dehydration abnormal threshold is set to 0.6.

[0073] If S is less than 0.6, it is considered that the efficiency of the membrane dehydration process during amine recovery is low, and the steam pressure state on the downstream side of the membrane needs to be adjusted accordingly in the next regulation interval to ensure that the partial pressure difference on both sides of the membrane is within the target range. Specifically, if the steam pressure on the upstream side of the membrane increases, the suction power of the vacuum unit on the downstream side of the membrane is reduced to increase the steam pressure on the downstream side; conversely, the suction power of the vacuum unit on the downstream side of the membrane is increased to reduce the steam pressure on the downstream side, and the increased or decreased pressure value is the same as the change amount of the steam pressure on the upstream side of the membrane.

[0074] If S is greater than or equal to 0.6, it is considered that the efficiency of the membrane dehydration process is good. The implementation flow chart of the membrane dehydration step is as Figure 3 shown.

[0075] Through the above steps, the recovery and monitoring of triethylamine are further realized.

[0076] Based on the same inventive concept as the above method, an embodiment of the present invention further provides an amine recovery monitoring system for polyurethane synthesis tail gas, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned amine recovery monitoring methods for polyurethane synthesis tail gas are realized.

[0077] It should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

[0078] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

Claims

1. A method for amine recovery monitoring for polyurethane synthesis tail gas, characterized in that, The method includes the following steps: Preliminarily separate the polyurethane synthesis tail gas to obtain a triethylamine solution; Add the triethylamine solution to other solutions and then perform distillation, and collect the parameter values of different parameters at each moment; the parameters include the top temperature of the kettle, the bottom temperature of the kettle, the condenser flow rate, and the triethylamine concentration; The specific steps of distillation are as follows: Set an adjustment time period and obtain the parameter sequence of each parameter therein; Decompose the parameter sequence to obtain a periodic sequence and a trend sequence; obtain the periodic significance value of the parameter sequence based on the fluctuation of the peak difference in the periodic sequence; Obtain the fluctuation consistency coefficient between two parameters according to the correlation coefficient of the trend sequences between the two parameters; use the periodic significance value of the top temperature of the kettle and the other parameters as weights to weight the fluctuation consistency coefficient between the top temperature of the kettle and the other parameters to obtain the distillation interference coefficient of the adjustment time period; Optimize the control parameters based on the distillation interference coefficient and process the next time period to obtain pure triethylamine; The specific steps of membrane dehydration are as follows: Add pure triethylamine to a preheater and an evaporator; collect the attribute values of different attributes at a preset time, including the evaporator temperature, and collect the vapor pressures on both sides of the membrane; Set a sliding window, obtain the change characteristic value based on the difference between the data value of each attribute within the sliding window and the obtained predicted value, and construct a change characteristic value sequence; obtain the dehydration steady-state index based on the similarity of the change characteristic value sequence and the difference in the vapor pressures on both sides of the membrane; Realize the recovery and monitoring of triethylamine based on the comparison between the dehydration steady-state index and the membrane dehydration abnormal threshold.

2. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that The method for preliminarily separating the polyurethane synthesis tail gas to obtain a triethylamine solution is as follows: Convert triethylamine from a gaseous state to a liquid state through a condensation method to separate the amine in the tail gas; place two condensers, and let the tail gas pass through the two condensers in sequence. The temperature of the first condenser needs to be greater than 89.5 °C and less than 200 °C, and the temperature of the second condenser needs to be less than 89.5 °C. The liquid after passing through the two condensers is the triethylamine solution after primary separation.

3. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that, The method for obtaining the periodic significance value of the parameter sequence based on the fluctuation of the peak difference in the periodic sequence is as follows: Process the obtained periodic sequence using polynomial fitting technology, and then extract the peaks from the fitting curve through derivative analysis; arrange the moment values corresponding to all peak points in ascending order as the peak moment sequence, and calculate the standard deviation of the first-order difference sequence of the obtained peak moment sequence; take the reciprocal of the standard deviation as the periodic significance value of the parameter sequence.

4. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that, The method for obtaining the fluctuation consistency coefficient between two parameters according to the correlation coefficient of the trend sequences between the two parameters is as follows: Calculate the Spearman correlation coefficient of the trend sequences between the two parameters, and take the sum of the Spearman correlation coefficient and 1 as the fluctuation consistency coefficient.

5. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that, The method for weighting the fluctuation consistency coefficient between the top temperature of the kettle and the other parameters with the periodic significance value of the top temperature of the kettle and the other parameters to obtain the distillation interference coefficient of the adjustment time period is as follows: Let the sum of the periodic significance value of the top temperature of the kettle and any other parameter be divided by the sum of the periodic significance values of all parameters as the influence weight of any parameter; The distillation interference coefficient is positively correlated with the influence weight and negatively correlated with the fluctuation consistency coefficient.

6. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that, The method for optimizing control parameters based on the distillation interference coefficient is as follows: The optimization formula for the proportional term parameter is as follows: ; where is the optimized proportional term parameter, is the preset adjustment parameter, represents the logarithmic function with base 10, represents the distillation interference coefficient.

7. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, wherein The method for obtaining the change characteristic value based on the difference between the data value of each attribute in the sliding window and the obtained predicted value and constructing the change characteristic value sequence is as follows: Input the data value of this attribute in the sliding window, and output the predicted value through the single exponential smoothing algorithm; Calculate the sum of the differences between the predicted value and each data value in the sliding window, and use the sum as the change characteristic value of this attribute; Calculate a change characteristic value each time the sliding window slides, and obtain the change characteristic value sequence of this attribute by sorting the change characteristic values of all sliding windows corresponding to each attribute in time order.

8. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that The method for obtaining the dehydration steady-state index based on the similarity of the change characteristic value sequence and the difference in vapor pressure on both sides of the membrane is as follows: Calculate the SBD distance corresponding to all pairwise combinations of all change characteristic sequences; take the reciprocal of the mean of all the SBD distances as the synchronization coefficient of temperature and vapor pressure; Calculate the difference between the vapor pressure data on both sides of the membrane at all the same moments, and take the ratio of the synchronization coefficient to the standard deviation of all the differences as the dehydration steady-state index.

9. The amine recovery monitoring method for polyurethane synthesis tail gas according to claim 1, characterized in that, The method for realizing the recovery and monitoring of triethylamine based on the comparison between the dehydration steady-state index and the membrane dehydration abnormal threshold is as follows: After normalizing the dehydration steady-state index, if the normalized value is less than the preset membrane dehydration abnormal threshold, the efficiency is low and the vapor pressure needs to be adjusted; if S is greater than or equal to 0.6, the efficiency of the membrane dehydration process is good.

10. An amine recovery monitoring system for polyurethane synthesis tail gas, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it realizes the steps of an amine recovery monitoring method for polyurethane synthesis tail gas according to any one of claims 1-9.

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