Method and system for recovering carbon dioxide in polyurethane industrial alcoholysis process

Abstract

The invention relates to the technical field of carbon dioxide recovery, in particular to a method and a system for recovering carbon dioxide in an alcoholysis process of polyurethane industry, and the method comprises the following steps: acquiring CO2 concentrations at a gas inlet at the bottom of a spray tower, each spray layer and a gas outlet at the top of the spray tower at each moment in each acquisition period; the absorption liquid consumption of each spraying layer in each collection period is measured; calculating a relative change coefficient and a residual deviation value of each acquisition period; determining an absorption deviation value, an overall control deviation, a relative utilization rate and a hierarchical control deviation; the relative control deviation of each spraying layer in each collection period is determined; and adjusting the spraying speed of each spraying layer in the next collection period by combining a PID (Proportion Integration Differentiation) controller, and recovering CO2 generated in the polyurethane alcoholysis process. According to the invention, the phenomena of CO2 absorption residue and absorption liquid resource waste can be effectively avoided, and the absorption efficiency of the spray tower on CO2 in tail gas is improved.

Description

Technical Field

[0001] The present application relates to the technical field of carbon dioxide recovery, and in particular to a method and system for recovering carbon dioxide during industrial alcoholysis of polyurethane. Background Art

[0002] Polyurethane is a polymer synthetic material with excellent physical and chemical properties, such as high strength, good elasticity and chemical corrosion resistance. It is widely used in furniture, construction, pipe heating and other fields. In the process of polyurethane recycling, the tail gas produced will contain a large amount of carbon dioxide. This carbon dioxide comes from two aspects. One is the carbon dioxide produced in the polyurethane synthesis process, which is wrapped in the foam pores in the polyurethane and difficult to escape. The other is the carbon dioxide produced by the decomposition of the urethane bond of the polyurethane structure. For environmental protection and the reuse of carbon dioxide, the carbon dioxide generated in the process needs to be recycled.

[0003] Traditional methods generally use a spray tower controlled by a fixed spray speed to absorb carbon dioxide in the exhaust gas. However, during the decomposition process of polyurethane, the chemical reaction produced is unstable, resulting in large fluctuations in the CO2 content in the exhaust gas. The absorption tower cannot adjust the spray speed of the absorption liquid in time, which leads to a mismatch between the absorption tower's carbon dioxide capture capacity and the CO2 content during the CO2 recovery process, resulting in too low CO2 absorption rate or waste of absorption liquid. Summary of the invention

[0004] In order to solve the above technical problems, a method and system for recovering carbon dioxide during the polyurethane industrial alcoholysis process are provided to solve the existing problems.

[0005] The solution to the technical problem of the present application is to provide a method and system for recovering carbon dioxide during the polyurethane industrial alcoholysis process, comprising the following steps: In a first aspect, an embodiment of the present application provides a method for recovering carbon dioxide during industrial alcoholysis of polyurethane, the method comprising the following steps: Obtain the CO2 concentration at each time during each collection cycle at the air inlet at the bottom of the spray tower, each spray layer, and the air outlet at the top of the spray tower, as well as the absorption liquid consumption of each spray layer in each collection cycle; The relative coefficient of variation of each acquisition cycle is calculated by analyzing the discreteness of the rate of change of CO2 concentration at the air inlet at different times in each acquisition cycle; the residual CO2 concentration at the air outlet in each acquisition cycle is analyzed to calculate the residual deviation of each acquisition cycle; According to the difference in CO2 concentration between each spray layer and its adjacent spray layer in each collection period, the absorption amount of each spray layer in each collection period is determined, and based on the discrete situation of the absorption amount of all spray layers in each collection period, the absorption deviation amount of each collection period is determined; the residual deviation amount and the absorption deviation amount are integrated to obtain the overall control deviation of each collection period; Based on the absorption amount of each spray layer in each collection period and the absorption liquid consumption, the relative utilization rate of each spray layer in each collection period is determined; the deviation of the relative utilization rate of each spray layer in each collection period is analyzed to determine the level control deviation of each spray layer in each collection period, and the relative control deviation of each spray layer in each collection period is obtained by combining the relative variation coefficient and the overall control deviation; Based on the relative control deviation, in combination with the PID controller, the spraying speed of each spraying layer in the next collection cycle is adjusted to recover the CO2 generated in the polyurethane alcoholysis process.

[0006] Preferably, the calculating of the relative coefficient of variation of each acquisition cycle includes: The CO2 concentration at the air inlet at all times in each acquisition cycle is curve fitted, and the derivative of each time on the fitting curve is calculated and recorded as the inflow rate at each time in each acquisition cycle; The normalized result of the discrete degree of the inflow rate at the air inlet at all times in each collection period is taken as the relative variation coefficient of each collection period.

[0007] Preferably, the calculating of the residual deviation of each acquisition cycle includes: Calculate the mean value of CO2 concentration at the gas outlet at all times in each collection period and record it as CO2 residual concentration; No. Residual deviation of acquisition cycles The calculation formula is: ,in, For the outlet The residual CO2 concentration of each acquisition cycle, is the preset emission threshold, is the maximum value function.

[0008] Preferably, determining the absorption amount of each spray layer in each collection cycle includes: Calculate the mean value of CO2 concentration at all times in each spray layer during each acquisition cycle and record it as the average concentration; The CO2 residual concentration at the gas outlet and the average concentration of all spray layers in the same collection period are arranged from top to bottom according to the position of the spray tower, forming a CO2 concentration sequence for each collection period; The difference between each element in the CO2 concentration sequence and its previous element is calculated as the absorption amount of each spray layer in each acquisition cycle.

[0009] Preferably, the absorption deviation is the inverse of the standard deviation of the absorption of all spray layers in each collection cycle.

[0010] Preferably, the overall control deviation is the sum of the residual deviation and the absorption deviation.

[0011] Preferably, the relative utilization rate is the ratio between the absorption amount of each spray layer and the absorption liquid consumption in each collection cycle.

[0012] Preferably, the step of determining the level control deviation of each spray layer in each acquisition cycle includes: The difference between the relative utilization rate of each spray layer in each collection period and the average of the relative utilization rates of all spray layers is taken as the utilization rate deviation of each spray layer in each collection period; The product of the utilization rate deviation in each collection cycle and the sum of the absorption liquid consumption of all spray layers is used as the level control deviation of each spray layer in each collection cycle.

[0013] Preferably, the relative control deviation of the nth spray layer in the mth acquisition cycle is The calculation formula is: ,in, is the overall control deviation of the mth acquisition cycle, is the relative coefficient of variation of the mth acquisition cycle, It is the level control deviation of the nth spray layer in the mth collection cycle.

[0014] In a second aspect, an embodiment of the present application also provides a system for recovering carbon dioxide during the industrial alcoholysis of polyurethane, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of any one of the above-mentioned methods for recovering carbon dioxide during the industrial alcoholysis of polyurethane are implemented.

[0015] This application has at least the following beneficial effects: The present application calculates the relative coefficient of variation of each collection cycle by the fluctuation of the inflow of carbon dioxide at the air inlet. The beneficial effect is that the fluctuation of the carbon dioxide content is taken into account so that the speed of the absorption liquid sprayed by the subsequent spray tower can respond in time to adapt to the drastic changes in the exhaust gas composition. By adjusting the adjustment mode of the spray speed in the spray tower, when the inflow of carbon dioxide changes drastically, the overall spray speed of the spray tower is quickly adjusted. When the inflow of carbon dioxide changes less, the spray speed of each spray layer is adjusted by layering to avoid residual CO2 absorption or waste of absorption liquid, thereby improving the overall utilization efficiency of the absorption liquid. ; Calculate the residual deviation of each collection cycle, which has the beneficial effect of considering the residual CO2 at the outlet to reflect the CO2 absorption effect of the spray tower, thereby avoiding the absorption residual phenomenon of CO2; Calculate the absorption of each spray layer in each collection cycle to obtain the absorption deviation of each collection cycle, which has the beneficial effect of considering the absorption capacity of each spray layer to absorb CO2 to evaluate the absorption differences of different spray layers, thereby reflecting the possibility of waste of absorption liquid and not being effectively utilized; Determine the overall control deviation of each collection cycle, which has the beneficial effect of considering the deviation of the spray speed of the overall spray tower; Secondly, calculate the absorption deviation of each collection cycle The relative utilization rate of each spray layer has the beneficial effect of taking into account the difference between the amount of absorption liquid consumed by each spray layer and the amount of CO2 absorbed, so as to reflect the degree of effective utilization of the absorption liquid and avoid residual CO2 absorption or waste of resources; the hierarchical control deviation of each spray layer in each collection cycle is calculated, which has the beneficial effect of achieving a balance in the relative utilization rate of the absorption liquid of each spray layer through layered monitoring of the utilization rate of the absorption liquid, improving the utilization efficiency of the absorption liquid of the entire spray tower and reducing resource waste; finally, the relative control deviation of each spray layer in each collection cycle is obtained, and the PID controller is used to control the relative utilization rate of each spray layer in the next collection cycle. The spray speed can be adjusted to recover the CO2 produced in the polyurethane alcoholysis process. The beneficial effect is that the spray speed of each spray layer can be adjusted in real time. When the CO2 concentration flowing into the spray tower fluctuates violently, the overall spray speed can be adjusted quickly to avoid CO2 absorption residue or waste of resources. At the same time, when the CO2 content fluctuates slightly, the spray speed of different spray layers can be controlled in layers to improve the utilization efficiency of the absorption liquid. Compared with the traditional spray tower controlled by fixed spray speed, it can effectively avoid CO2 absorption residue and waste of absorption liquid resources, and improve the absorption efficiency of the spray tower for CO2 in the exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following is a further detailed description of a method for recovering carbon dioxide during industrial alcoholysis of polyurethane in the present application in conjunction with the accompanying drawings.

[0017] Figure 1A flow chart of the steps of a method for recovering carbon dioxide during industrial alcoholysis of polyurethane provided in an embodiment of the present application; Figure 2 A schematic diagram of the installation of a carbon dioxide detector in a spray tower provided in an embodiment of the present application; Figure 3 A flowchart of the steps of the method for obtaining the absorption deviation amount of each acquisition cycle provided in an embodiment of the present application; Figure 4 A flowchart of the steps of a method for obtaining a relative control deviation provided in an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application more clearly understood, the following is a further detailed description of a method and system for recovering carbon dioxide in a polyurethane industrial alcoholysis process proposed in the present application in conjunction with the accompanying drawings and implementation examples. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application.

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

[0020] See also Figure 1 , which shows a flow chart of the steps of a method for recovering carbon dioxide during polyurethane industrial alcoholysis provided by an embodiment of the present application, the method comprising the following steps: Step 1: After the exhaust gas is transported to the spray tower equipment, the CO2 concentration at each moment in each collection cycle at the air inlet at the bottom of the spray tower, each spray layer, and the air outlet at the top of the spray tower is obtained through a carbon dioxide detector, as well as the absorption liquid consumption of each spray layer in each collection cycle.

[0021] Polyurethane is a polymer compound composed of repeated carbamate units. Due to its unique physical and chemical properties, it is widely used in the manufacture of various products. When polyurethane waste is recycled and decomposed by alcoholysis, a large amount of carbon dioxide gas will be produced. This part of the gas mainly comes from two aspects. One is the carbon dioxide produced by the breakage and decomposition of carbamate bonds during the alcoholysis of polyurethane. The other is that the carbon dioxide produced during the synthesis of polyurethane is wrapped by polyurethane and is difficult to escape. However, part of the carbon dioxide escapes due to the destruction of the structure of polyurethane during the alcoholysis process.

[0022] Among them, the process of decomposing polyurethane by alcoholysis is: adding polyurethane waste as raw material into the alcoholysis reactor, using ethylene glycol as an alcoholysis agent to alcoholyze the polyurethane. During the alcoholysis process, due to the breakage of the carbamate bond, a large amount of carbon dioxide gas will be generated in the polyurethane alcoholysis reaction. Therefore, the generated carbon dioxide needs to be recycled to achieve the purpose of environmental protection and resource recycling.

[0023] At the same time, volatile organic amines are also produced in the alcoholysis reaction, some of which are mixed with carbon dioxide. Therefore, when recovering carbon dioxide in the tail gas, triethylamine solution is used as an absorbent to absorb carbon dioxide in the tail gas. At the same time, the volatile organic amines in the tail gas can be used as a supplement to the absorbent to achieve the purpose of resource recycling.

[0024] The tail gas is collected by a gas collecting hood above the alcoholysis reactor, and the collected tail gas is sent to a buffer tank, which is connected to a blower. The blower pressurizes the gas inside the buffer tank. When the pressure is sufficient, the connection valve between the blower and the pretreatment unit is opened to pretreat the tail gas. The pretreatment unit includes dry filters, coolers and other equipment to remove dust particles in the tail gas and reduce the exhaust gas temperature to prevent impurities and high temperature from damaging the subsequent carbon dioxide recovery equipment.

[0025] The tail gas generated during the alcoholysis process is transported to an absorption tower, where carbon dioxide is recovered. The absorption tower adopts a spray tower structure, and potassium carbonate is used as the absorption liquid.

[0026] There are multiple spray layers in the spray tower. A carbon dioxide detector (MOT500-CO2-IR) is installed in each spray layer to detect the concentration of carbon dioxide. At the same time, carbon dioxide detectors are installed at the gas inlet at the bottom of the spray tower and the gas outlet at the top of the spray tower to measure the carbon dioxide content input into the spray tower and the carbon dioxide absorption of the spray tower. Secondly, the consumption of absorption liquid in each spray layer is collected by installing a flow meter at each nozzle.

[0027] The installation diagram of the carbon dioxide detector in the spray tower provided in this embodiment is as follows Figure 2 As shown, Figure 2 In the figure, A is a spray tower, B1 is an air inlet for exhaust gas, B2 is an air outlet for purified gas, B3 is an outlet for absorption liquid, C is a carbon dioxide detector, D is a dehydration plate, E is a swirl plate, F is a nozzle, G is a circulating water pump, H is a pipeline, and I is a flow meter.

[0028] The collection frequency of the carbon dioxide detector is set to 1KHz. Therefore, each carbon dioxide detector will collect 60,000 CO2 concentration data in one minute, representing the change of carbon dioxide concentration in the past 1 minute.

[0029] Therefore, each minute is recorded as a collection cycle, and the CO2 concentration at each moment in each collection cycle at the air inlet at the bottom of the spray tower, each spray layer, and the air outlet at the top of the spray tower is obtained, as well as the absorption liquid consumption of each spray layer in each collection cycle.

[0030] In this embodiment, the spray tower has a total of 5 spray layers. As other implementation methods, the implementer can choose the number of spray layers according to actual conditions. There is a separate PID (proportion integration differentiation) control unit on the nozzle in each spray layer to regulate the spray speed of the nozzle.

[0031] At this point, the CO2 concentration at each moment in each collection cycle at the air inlet at the bottom of the spray tower, each spray layer, and the air outlet at the top of the spray tower, as well as the absorption liquid consumption of each spray layer in each collection cycle are obtained.

[0032] Step 2: Calculate the relative coefficient of variation of each collection period by analyzing the discreteness of the rate of change of the CO2 concentration at the air inlet at different times in each collection period; analyze the residual CO2 concentration at the air outlet in each collection period and calculate the residual deviation of each collection period.

[0033] In the spray tower, the amount of carbon dioxide generated may fluctuate due to changes in the conditions of the polyurethane alcoholysis reaction. If the spray tower cannot respond to these changes in time, it will cause incomplete CO2 absorption, resulting in residual CO2 absorption, or the absorption liquid cannot be effectively utilized, resulting in waste of resources.

[0034] When the CO2 content flowing into the air inlet is large, if the spraying speed cannot adapt to the change of CO2 content in time, the CO2 concentration in the purified gas flowing out of the air outlet at the top of the spray tower will not meet the emission standards, resulting in residual CO2 absorption; secondly, when the traditional spray tower controls the spraying speed, the same spraying speed is used for all spraying layers. When the CO2 content flowing into the air inlet at the bottom of the spray tower is small, due to the different CO2 concentrations inside different spraying layers in the spray tower, the same spraying speed may cause the absorption liquid in the upper layer of the spray tower to be unable to fully react with sufficient CO2 in the atomized state, resulting in waste of absorption liquid. According to the drastic change of the CO2 content flowing into the air inlet at the bottom of the spray tower, the overall spraying speed of the spray tower is quickly adjusted to adapt to the drastic change of the exhaust gas composition. When the CO2 content flowing into the air inlet at the bottom of the spray tower changes relatively stably, the spraying speed of each spraying layer of the spray tower is adjusted separately to improve the utilization rate of the absorption liquid.

[0035] Based on the above analysis, the relative coefficient of variation of each collection period is calculated by the fluctuation of the change rate of CO2 concentration at the air inlet at the bottom of the spray tower at different times in each collection period, which is specifically: The CO2 concentration at the air inlet at all times in each acquisition cycle is curve fitted, and the derivative of each time on the fitting curve is calculated and recorded as the inflow rate at each time in each acquisition cycle; In this embodiment, the least square method is used for curve fitting, wherein the least square method is a well-known technology and will not be described in detail here.

[0036] The normalized result of the discrete degree of the inflow rate at the air inlet at all times in each collection period is used as the relative variation coefficient of each collection period; In this embodiment, the degree of discreteness is measured by calculating the standard deviation of the inflow rate at all times in each collection cycle at the air inlet. As other implementations, the implementer may adopt other methods of the prior art to measure the degree of discreteness, such as variance, etc. Secondly, the sigmoid function is used for normalization. As other implementations, the implementer may adopt other methods of the prior art, such as tanh function, etc. This embodiment does not impose any special restrictions on this.

[0037] It should be noted that, through the relative variation coefficient, the change rate of the CO2 flowing into the air inlet is monitored in real time. The larger the relative variation coefficient, the more drastic the change of the CO2 concentration at the air inlet during the corresponding collection period, and the smaller the relative variation coefficient, the more stable the change of the CO2 concentration at the air inlet during the corresponding collection period.

[0038] Furthermore, the residual deviation is determined by the deviation between the average concentration of CO2 in each collection period at the outlet and the normal concentration of CO2 in the atmosphere to evaluate the CO2 absorption effect of the spray tower, specifically: Calculate the mean value of CO2 concentration at the gas outlet at all times in each collection period and record it as CO2 residual concentration; The calculation formula for the residual deviation of each acquisition cycle is: in, For the The residual deviation of the acquisition cycle, For the outlet The residual CO2 concentration of each acquisition cycle, is the preset emission threshold, is the maximum value function.

[0039] It should be noted that the normal concentration of CO2 in the atmosphere is about 0.04%, that is, the volume of carbon dioxide accounts for 0.04% of the total volume of air, which is equivalent to a ppm concentration of 400 ppm. Therefore, the preset emission threshold is 400 ppm.

[0040] It should be noted that if Greater than , indicating that the overall spraying speed of the spray tower is too slow, resulting in incomplete CO2 absorption. The larger the residual deviation, the poorer the CO2 absorption effect of the spray tower. The spraying speed of the spray tower should be increased to avoid CO2 absorption residual phenomenon.

[0041] At this point, the residual deviation of the spray tower in each collection cycle is obtained.

[0042] Step 3, according to the difference in CO2 concentration between each spray layer and its adjacent spray layer in each collection cycle, determine the absorption amount of each spray layer in each collection cycle, and based on the discreteness of the absorption amount of all spray layers in each collection cycle, determine the absorption deviation of each collection cycle; merge the residual deviation and the absorption deviation to obtain the overall control deviation of each collection cycle.

[0043] At the same time, when the inflow concentration of CO2 decreases, if the spraying speed of each spray layer inside the spray tower remains unchanged, the concentration of the inflowing carbon dioxide may have been absorbed by the sprayed atomized absorption liquid at the bottom of the spray tower, and the carbon dioxide content in the upper spray layer is already very close to the preset emission threshold. , the CO2 concentration in the upper spray layer is low, and its absorption liquid hardly absorbs CO2, which will cause the absorption liquid in the upper spray layer to be wasted. Therefore, this phenomenon shows that the overall spray speed inside the spray tower is too fast at this time, and the spray speed should be reduced to avoid energy waste.

[0044] Therefore, the absorption deviation is calculated by the difference in CO2 concentration between different spray layers to reflect the uniformity of CO2 concentration absorbed by different spray layers. The step flow chart of the method for obtaining the absorption deviation of each collection cycle provided in the embodiment of the present application is as follows: Figure 3 As shown, specifically including: Calculate the mean value of CO2 concentration of each spray layer at all times in each collection period as the average concentration of each spray layer in each collection period; The CO2 residual concentration at the gas outlet and the average concentration of all spray layers in the same collection period are arranged from top to bottom according to the position of the spray tower, forming a CO2 concentration sequence for each collection period; It should be noted that, assuming that the spray layers are numbered from bottom to top, the structure of the entire spray tower is the bottom where the air inlet is located, the first spray layer, the second spray layer, the third spray layer, the fourth spray layer, the fifth spray layer, and the top where the air outlet is located. The average concentrations of the first spray layer, the second spray layer, the third spray layer, the fourth spray layer, and the fifth spray layer in the collection cycle are , the CO2 residual concentration at the outlet is , then the CO2 concentration series is .

[0045] Calculate the difference between each element in the CO2 concentration sequence and its previous element as the absorption amount of each spray layer in each acquisition cycle; The inverse of the standard deviation of the absorption of all spray layers in each collection period is used as the absorption deviation of each collection period; It should be noted that the absorption amount is the difference between the CO2 concentration of each spray layer and the upper spray layer adjacent to it, which reflects the absorption effect of each spray layer on CO2. When the spray speed inside the spray tower is reasonable, the absorption amount of CO2 absorbed by the absorption liquid in each spray layer is uniform, indicating that the absorption liquid in the upper spray layer is not wasted. When the inflow concentration of CO2 decreases, when the overall spray speed inside the spray tower is too fast, CO2 has been absorbed by the atomization of the absorption liquid in the lower spray layer, and the absorption liquid in the upper spray layer will be wasted. Therefore, the smaller the absorption deviation, the greater the difference in the amount of CO2 absorbed by different spray layers. At this time, the overall spray speed inside the spray tower should be reduced; secondly, the purpose of taking the opposite of the standard deviation is to numerically adjust the standard deviation, so that when the spray speed is subsequently reduced through the PID controller, the absorption deviation is a negative number.

[0046] Further, based on the residual deviation and the absorption deviation, the overall control deviation is determined, specifically: The sum of the residual deviation and the absorption deviation is used as the overall control deviation of each acquisition cycle; It should be noted that when the overall spray speed of the spray tower is too high, the overall control deviation is a negative number, otherwise it is a positive number. The main reason is that when the overall spray speed of the spray tower is too high, the overall absorption of CO2 by the spray tower is high, and the CO2 content in the gas flowing out of the outlet is low. Therefore, the residual deviation is 0 or a smaller value, and the absorption difference of CO2 concentration between different spray layers is large, then the absorption deviation is negative and the absolute value is large, so the overall control deviation is negative; when the overall spray speed of the spray tower is too low, the overall absorption of CO2 by the spray tower is low, and the CO2 content in the gas flowing out of the outlet is high, so the residual deviation is is large and positive, and the absorption difference of CO2 concentration between different spray layers is small, then the absorption deviation is negative and the absolute value is small, therefore, the obtained overall control deviation is positive.

[0047] At this point, the overall control deviation of each acquisition cycle is obtained.

[0048] Step 4, based on the absorption amount of each spray layer in each collection cycle and the absorption liquid consumption, determine the relative utilization rate of each spray layer in each collection cycle; analyze the deviation of the relative utilization rate of each spray layer in each collection cycle, determine the level control deviation of each spray layer in each collection cycle, and combine the relative variation coefficient and the overall control deviation to obtain the relative control deviation of each spray layer in each collection cycle; based on the relative control deviation, in combination with the PID controller, adjust the spray speed of each spray layer in the next collection cycle to recover the CO2 generated in the polyurethane alcoholysis process.

[0049] In order to avoid the situation where the control strategy of the spray speed of different spray layers is inconsistent with the change of CO2 inflow when the CO2 inflow changes, for example, when the CO2 inflow increases, the spray speed of some spray layers decreases instead. The overall utilization rate of the absorption liquid can be improved by performing layered control on the spray speed of different spray layers of the spray tower.

[0050] Therefore, the absorption liquid consumption and CO2 absorption in each spray layer are used to analyze the utilization rate of the absorption liquid in each spray layer and calculate the level control deviation, which is as follows: The ratio between the absorption amount of each spray layer in each collection cycle and the absorption liquid consumption is used as the relative utilization rate of each spray layer in each collection cycle; The difference between the relative utilization rate of each spray layer in each collection period and the average of the relative utilization rates of all spray layers is taken as the utilization rate deviation of each spray layer in each collection period; It should be noted that if the utilization deviation is a negative number, it means that the relative utilization rate of the absorption liquid of the corresponding spray layer is low, and the spraying speed of the corresponding spray layer should be reduced; if the utilization deviation is a positive number, it means that the relative utilization rate of the absorption liquid of the corresponding spray layer is high, and the utilization rate of the absorption liquid of the corresponding spray layer may be close to saturation, and the spraying speed of the corresponding spray layer should be increased.

[0051] The product of the utilization rate deviation in each collection cycle and the sum of the absorption liquid consumption of all spray layers is used as the level control deviation of each spray layer in each collection cycle; It should be noted that the hierarchical control deviation reflects the deviation of the relative utilization rate of the absorption liquid of each spray layer of the spray tower relative to all spray layers, so that the relative utilization rate of the absorption liquid in different spray layers is balanced, ensuring that the utilization rate of each layer of absorption liquid is as close to the optimal value as possible, thereby reducing resource waste.

[0052] Further, based on the relative variation coefficient, the overall control deviation and the hierarchical control deviation, the relative control deviation of each spray layer is determined to control the spray speed of the corresponding spray layer, specifically: in, is the relative control deviation of the nth spray layer in the mth acquisition cycle, is the overall control deviation of the mth acquisition cycle, is the relative coefficient of variation of the mth acquisition cycle, It is the level control deviation of the nth spray layer in the mth collection cycle.

[0053] It should be noted that, through the overall control deviation, it is ensured that the PID controller can monitor the distribution of carbon dioxide concentration inside the spray tower in real time, and timely adjust the overall spray speed of the spray tower to avoid CO2 absorption residue or waste of absorption liquid; secondly, through the hierarchical control deviation, the spray speed of each spray layer of the spray tower is differentially adjusted to improve the utilization rate of the absorption liquid in the spray tower; the relative variation coefficient is used to monitor the change of the concentration of the incoming CO2 and regulate the control mode of the spray tower. When the concentration of the incoming CO2 changes drastically, the closer the relative variation coefficient is to 1, the lower the impact of the hierarchical control deviation on the PID controller is, and the overall spray speed of the spray tower is quickly adjusted through the overall control deviation to adapt to the drastic changes in the exhaust gas composition, so as to avoid the spray speed adjustment strategy of the spray layer being inconsistent with the change in the amount of incoming CO2; when the change in the concentration of the incoming CO2 is relatively stable, the impact of the hierarchical control deviation on the PID controller is increased, and the spray speed of different spray layers is adjusted to avoid waste of absorption liquid; the step flow chart of the relative control deviation acquisition method provided in the embodiment of the present application is as follows Figure 4 shown.

[0054] The relative control deviation is input into the PID (proportion integration differentiation) controller of each spray layer, the spray speed of each spray layer in the next collection cycle is adjusted, and the CO2 generated in the polyurethane alcoholysis process is recovered; It should be noted that the PID controller is a well-known technology and will not be described in detail here.

[0055] After the tail gas is absorbed by the spray tower, the purified tail gas is discharged from the gas outlet, and the resulting absorption liquid flows out from the water outlet at the bottom of the spray tower and is sent to the regeneration tower for heating and analysis. In the regeneration tower, the absorption liquid is heated to precipitate the carbon dioxide in the absorption liquid from the liquid phase, and the precipitated CO2 in the absorption liquid is collected; at the same time, the absorption liquid is regenerated and circulated to the spray tower to continue to be used as an absorbent.

[0056] The collected CO2 gas is compressed by a compressor, then condensed in a condenser to form liquid CO2, and sent to a storage tank for storage.

[0057] Based on the same inventive concept as the above method, an embodiment of the present application also provides a system for recovering carbon dioxide during industrial alcoholysis of polyurethane, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of any one of the above methods for recovering carbon dioxide during industrial alcoholysis of polyurethane are implemented.

[0058] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0059] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0060] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the present application. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application without departing from the content of the technical solution of the present application, shall fall within the protection scope of the technical solution of the present application.

Claims

1. A method for recovering carbon dioxide during polyurethane industrial alcoholysis, characterized in that: The method comprises the following steps: Obtain the CO2 concentration at each time during each collection cycle at the air inlet at the bottom of the spray tower, each spray layer, and the air outlet at the top of the spray tower, as well as the absorption liquid consumption of each spray layer in each collection cycle; The relative coefficient of variation of each acquisition cycle is calculated by analyzing the discreteness of the rate of change of CO2 concentration at the air inlet at different times in each acquisition cycle; the residual CO2 concentration at the air outlet in each acquisition cycle is analyzed to calculate the residual deviation of each acquisition cycle; According to the difference in CO2 concentration between each spray layer and its adjacent spray layer in each collection period, the absorption amount of each spray layer in each collection period is determined, and based on the discrete situation of the absorption amount of all spray layers in each collection period, the absorption deviation amount of each collection period is determined; the residual deviation amount and the absorption deviation amount are integrated to obtain the overall control deviation of each collection period; Based on the absorption amount of each spray layer in each collection period and the absorption liquid consumption, the relative utilization rate of each spray layer in each collection period is determined; the deviation of the relative utilization rate of each spray layer in each collection period is analyzed to determine the level control deviation of each spray layer in each collection period, and the relative control deviation of each spray layer in each collection period is obtained by combining the relative variation coefficient and the overall control deviation; Based on the relative control deviation, in combination with the PID controller, the spraying speed of each spraying layer in the next collection cycle is adjusted to recover the CO2 generated in the polyurethane alcoholysis process.

2. The method for recovering carbon dioxide in a polyurethane industrial alcoholysis process according to claim 1, characterized in that: The step of calculating the relative coefficient of variation of each acquisition cycle includes: The CO2 concentration at the air inlet at all times in each acquisition cycle is curve fitted, and the derivative of each time on the fitting curve is calculated and recorded as the inflow rate at each time in each acquisition cycle; The normalized result of the discrete degree of the inflow rate at the air inlet at all times in each collection period is taken as the relative variation coefficient of each collection period.

3. The method for recovering carbon dioxide in a polyurethane industrial alcoholysis process according to claim 1, characterized in that: The calculation of the residual deviation of each acquisition cycle includes: Calculate the mean value of CO2 concentration at the gas outlet at all times in each collection period and record it as CO2 residual concentration; No. Residual deviation of acquisition cycles The calculation formula is: ,in, For the outlet The residual CO2 concentration of each acquisition cycle, is the preset emission threshold, is the maximum value function.

4. The method for recovering carbon dioxide in a polyurethane industrial alcoholysis process as claimed in claim 3, characterized in that: Determining the absorption amount of each spray layer in each collection cycle includes: Calculate the mean value of CO2 concentration at all times in each spray layer during each acquisition cycle and record it as the average concentration; The CO2 residual concentration at the gas outlet and the average concentration of all spray layers in the same collection period are arranged from top to bottom according to the position of the spray tower, forming a CO2 concentration sequence for each collection period; The difference between each element in the CO2 concentration sequence and its previous element is calculated as the absorption amount of each spray layer in each acquisition cycle.

5. The method for recovering carbon dioxide in a polyurethane industrial alcoholysis process according to claim 1, characterized in that: The absorption deviation is the inverse of the standard deviation of the absorption of all spray layers in each collection cycle.

6. The method for recovering carbon dioxide in a polyurethane industrial alcoholysis process according to claim 1, characterized in that: The overall control deviation is the sum of the residual deviation and the absorption deviation.

7. The method for recovering carbon dioxide during industrial alcoholysis of polyurethane according to claim 1, characterized in that: The relative utilization rate is the ratio between the absorption amount of each spray layer and the absorption liquid consumption in each collection cycle.

8. The method for recovering carbon dioxide during industrial alcoholysis of polyurethane according to claim 1, characterized in that: Determining the level control deviation of each spray layer in each acquisition cycle includes: The difference between the relative utilization rate of each spray layer in each collection period and the average of the relative utilization rates of all spray layers is taken as the utilization rate deviation of each spray layer in each collection period; The product of the utilization rate deviation in each collection cycle and the sum of the absorption liquid consumption of all spray layers is used as the level control deviation of each spray layer in each collection cycle.

9. The method for recovering carbon dioxide in a polyurethane industrial alcoholysis process according to claim 1, characterized in that: Relative control deviation of the nth spray layer in the mth acquisition cycle The calculation formula is: ,in, is the overall control deviation of the mth acquisition cycle, is the relative coefficient of variation of the mth acquisition cycle, It is the level control deviation of the nth spray layer in the mth collection cycle.

10. A system for recovering carbon dioxide during polyurethane industrial alcoholysis, 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, the steps of the method for recovering carbon dioxide during industrial alcoholysis of polyurethane as described in any one of claims 1 to 9 are implemented.

Images