A method and system for recovering carbon dioxide during the alcoholysis process of polyurethane industry

Abstract

This application relates to the technical field of carbon dioxide recovery, and specifically relates to a method and system for recovering carbon dioxide during the alcoholysis process of polyurethane industry. The method includes: obtaining the CO2 concentration at each moment in each collection period 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 consumption of the absorption liquid in each spray layer in each collection period; calculating the relative change coefficient and residual deviation amount of each collection period; determining the absorption deviation amount, overall control deviation, relative utilization rate, and hierarchical control deviation; determining the relative control deviation of each spray layer in each collection period; and combining with a PID controller to adjust the spray speed of each spray layer in the next collection period to recover the CO2 generated during the polyurethane alcoholysis process. This application can effectively avoid the phenomenon of residual CO2 absorption and waste of resources of the absorption liquid, and improve the absorption efficiency of the spray tower for CO2 in the tail gas.

Description

Technical Field

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

[0002] Polyurethane is a kind of polymer synthetic material with excellent physical and chemical properties, such as high strength, good elasticity and chemical corrosion resistance, etc., and is widely used in fields such as furniture, construction, and pipeline heating. During the polyurethane recovery process, a large amount of carbon dioxide will be contained in the tail gas. This carbon dioxide comes from two aspects. One is that the carbon dioxide generated during the polyurethane synthesis process is wrapped by the foam pores in the polyurethane and is difficult to escape. The other is the carbon dioxide generated by the decomposition of the urethane bond in the polyurethane structure. For environmental protection and the reuse of carbon dioxide, it is necessary to recover the carbon dioxide generated during the process.

[0003] In traditional methods, a spray tower with a fixed spray speed control is generally used to absorb carbon dioxide in the tail gas. However, during the polyurethane decomposition process, the chemical reaction generated is unstable, resulting in large fluctuations in the content of CO2 in the generated tail gas. The absorption tower cannot adjust the spray speed of the absorbent in time, and then during the carbon dioxide recovery process, the carbon dioxide capture ability of the absorption tower does not match the CO2 content, resulting in too low CO2 absorption rate or waste of absorbent. Summary of the Invention

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

[0005] The solution of the present application to solve the technical problems is to provide a method and system for recovering carbon dioxide during the alcoholysis process of polyurethane industry, including the following steps:

[0006] In the first aspect, an embodiment of the present application provides a method for recovering carbon dioxide during the alcoholysis process of polyurethane industry, and the method includes the following steps:

[0007] Obtain the CO2 concentration at each moment in each collection period 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, and the absorbent consumption of each spray layer in each collection period;

[0008] Calculate the relative change coefficient of each collection period through the discrete situation of the change rate of the CO2 concentration at different moments at the air inlet in each collection period; analyze the residual situation of the CO2 concentration at the air outlet in each collection period, and calculate the residual deviation amount of each collection period;

[0009] According to the difference in CO2 concentration between each spray layer and its adjacent spray layer within each collection period, determine the absorption amount of each spray layer within each collection period. Based on the dispersion of the absorption amounts of all spray layers within each collection period, determine the absorption deviation amount for each collection period; fuse the residual deviation amount and the absorption deviation amount to obtain the overall control deviation for each collection period.

[0010] Based on the absorption amount of each spray layer and the consumption amount of the absorption liquid within each collection period, determine the relative utilization rate of each spray layer within each collection period; analyze the deviation of the relative utilization rate of each spray layer within each collection period to determine the hierarchical control deviation of each spray layer within each collection period. Combine the relative change coefficient and the overall control deviation to obtain the relative control deviation of each spray layer within each collection period.

[0011] Based on the relative control deviation, in combination with a PID controller, adjust the spray speed of each spray layer in the next collection period to recover the CO2 generated during the polyurethane alcoholysis process.

[0012] Preferably, calculating the relative change coefficient for each collection period includes:

[0013] Perform curve fitting on the CO2 concentration at all times within each collection period at the air inlet, calculate the derivative at each time on the fitted curve, and denote it as the inflow rate at each time within each collection period.

[0014] Take the normalized result of the dispersion degree of the inflow rates at all times within each collection period at the air inlet as the relative change coefficient for each collection period.

[0015] Preferably, calculating the residual deviation amount for each collection period includes:

[0016] Calculate the mean value of the CO2 concentration at all times within each collection period at the air outlet, and denote it as the CO2 residual concentration.

[0017] The residual deviation amount of the nth collection period is calculated by the formula: where is the CO2 residual concentration at the air outlet in the nth collection period, is the preset emission threshold, and

[0018] is the maximum value function.

[0019] Preferably, determining the absorption amount of each spray layer within each collection period includes: Calculate the mean value of the CO2 concentration at all times within each collection period for each spray layer, and denote it as the average concentration.

[0020] Arrange the CO2 residual concentration at the air outlet and the average concentration of all spray layers in the same collection period in order from the top to the bottom according to the position of the spray tower where they are located, to form a CO2 concentration sequence for each collection period;

[0021] 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 collection period.

[0022] Preferably, the absorption deviation amount is the opposite of the standard deviation of the absorption amounts of all spray layers in each collection period.

[0023] Preferably, the overall control deviation is the sum of the residual deviation amount and the absorption deviation amount.

[0024] Preferably, the relative utilization rate is the ratio of the absorption amount of each spray layer in each collection period to the consumption amount of the absorption liquid.

[0025] Preferably, determining the hierarchical control deviation of each spray layer in each collection period includes:

[0026] Take the difference between the relative utilization rate of each spray layer in each collection period and the average value of the relative utilization rates of all spray layers as the utilization rate deviation of each spray layer in each collection period;

[0027] Take the product of the utilization rate deviation in each collection period and the sum value of the consumption amounts of the absorption liquid of all spray layers as the hierarchical control deviation of each spray layer in each collection period.

[0028] Preferably, the relative control deviation of the nth spray layer in the mth collection period The calculation formula is: , where is the overall control deviation of the mth collection period, is the relative change coefficient of the mth collection period, is the hierarchical control deviation of the nth spray layer in the mth collection period.

[0029] In a second aspect, the embodiments of the present application further provide a system for recovering carbon dioxide during the alcoholysis of polyurethane industry, 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, it implements the steps of the method for recovering carbon dioxide during the alcoholysis of polyurethane industry according to any one of the above.

[0030] The present application has at least the following beneficial effects:

[0031] This application calculates the relative change coefficient for each collection cycle based on the fluctuation of the inflow rate of carbon dioxide at the air inlet. The beneficial effect is that it takes into account the fluctuating change of the carbon dioxide content, so that the spraying speed of the absorption liquid in the subsequent spray tower can respond in a timely manner to adapt to the drastic change of the tail gas composition. By adjusting the adjustment mode of the spraying speed in the spray tower, when the inflowing carbon dioxide changes drastically, the overall spraying speed of the spray tower can be quickly adjusted. When the inflowing carbon dioxide changes slightly, the spraying speed of each spraying layer is adjusted layer by layer to avoid residue in CO2 absorption or waste of the absorption liquid, and improve the overall utilization efficiency of the absorption liquid; calculate the residual deviation amount for each collection cycle, and the beneficial effect is that it takes into account the residual situation of CO2 at the air outlet to reflect the CO2 absorption effect of the spray tower, thus avoiding the phenomenon of residual CO2 absorption; calculate the absorption amount of each spraying layer in each collection cycle to obtain the absorption deviation amount for each collection cycle. The beneficial effect is that it takes into account the absorption capacity of each spraying layer to absorb CO2 to evaluate the absorption difference of different spraying layers, so as to reflect the possibility that the absorption liquid is wasted and not effectively utilized; determine the overall control deviation for each collection cycle, and the beneficial effect is that it takes into account the deviation of the spraying speed of the overall spray tower; secondly, calculate the relative utilization rate of each spraying layer in each collection cycle. The beneficial effect is that it takes into account the difference between the absorption liquid consumed by each spraying layer and the amount of CO2 absorbed to reflect the degree of effective utilization of the absorption liquid, and avoid residual CO2 absorption or resource waste; calculate the hierarchical control deviation of each spraying layer in each collection cycle. The beneficial effect is that by monitoring the utilization rate of the absorption liquid layer by layer, the relative utilization rate of the absorption liquid of each spraying layer can be balanced, improving the utilization efficiency of the absorption liquid in the entire spray tower and reducing resource waste; finally, obtain the relative control deviation of each spraying layer in each collection cycle, and through the PID controller, adjust the spraying speed of each spraying layer in the next collection cycle to recover the CO2 generated in the polyurethane alcoholysis process. The beneficial effect is that it can adjust the spraying speed of each spraying layer in real time. When the change of the CO2 concentration flowing into the spray tower fluctuates drastically, it can quickly adjust the overall spraying speed to avoid the situation of residual CO2 absorption or resource waste; at the same time, when the change of the CO2 content fluctuates slightly, by controlling the spraying speed of different spraying layers layer by layer, the utilization efficiency of the absorption liquid is improved. Compared with the traditional spray tower with fixed spraying speed control, it can effectively avoid the phenomenon of residual CO2 absorption and waste of the absorption liquid resources, and improve the absorption efficiency of the spray tower for CO2 in the tail gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The following further elaborates in detail a method for recovering carbon dioxide during the alcoholysis process of polyurethane in industry according to this application with reference to the accompanying drawings.

[0033] Figure 1The flowchart of the steps of a method for recovering carbon dioxide during the alcoholysis of polyurethane in an industrial process provided by an embodiment of the present application;

[0034] Figure 2 The schematic installation diagram of a carbon dioxide detector in a spray tower provided by an embodiment of the present application;

[0035] Figure 3 The flowchart of the steps of a method for obtaining the absorption deviation amount in each collection period provided by an embodiment of the present application;

[0036] Figure 4 The flowchart of the steps of a method for obtaining the relative control deviation provided by an embodiment of the present application. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the following further elaborates in detail a method and system for recovering carbon dioxide during the alcoholysis of polyurethane in an industrial process proposed in the present application in combination with the accompanying drawings and implementation examples. It should be understood that the specific implementation examples described herein are only used to explain the present application and are not used to limit the present application.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs.

[0039] Please refer to Figure 1 , which shows the flowchart of the steps of a method for recovering carbon dioxide during the alcoholysis of polyurethane in an industrial process provided by an embodiment of the present application. The method includes the following steps:

[0040] Step 1, after the tail gas is transported to the spray tower equipment, the CO2 concentrations at each moment in each collection period 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 are obtained through a carbon dioxide detector, as well as the consumption of the absorption liquid in each spray layer in each collection period.

[0041] Polyurethane is a polymer compound composed of repeating urethane units. Due to its unique physical and chemical properties, it is widely used in the manufacture of various products. When recycling polyurethane waste, a large amount of carbon dioxide gas is generated during the decomposition by alcoholysis. This part of the gas mainly comes from two aspects. One is the decomposition of the urethane bond during the alcoholysis of polyurethane to generate carbon dioxide, and the other is that the carbon dioxide generated during the synthesis of polyurethane is wrapped by polyurethane and is difficult to escape, but a part of the carbon dioxide escapes due to the destruction of the structure of polyurethane during the alcoholysis process.

[0042] Among them, the process of decomposing polyurethane by alcoholysis is as follows: Polyurethane waste is used as raw material and added to an alcoholysis reactor. Ethylene glycol is used as an alcoholysis agent to carry out alcoholysis on polyurethane. During the alcoholysis process, due to the breaking of urethane bonds, a large amount of carbon dioxide gas will be generated in the polyurethane alcoholysis reaction. Therefore, it is necessary to recycle the generated carbon dioxide to achieve the purpose of environmental protection and resource reuse.

[0043] At the same time, in the alcoholysis reaction, volatile organic amines will also be generated, and some of the volatile organic amines 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 reuse.

[0044] The tail gas is collected above the alcoholysis reactor through a gas hood, and the collected tail gas is sent to a buffer tank. The buffer tank is connected to a blower, and 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 equipment such as a dry filter and a cooler to remove dust particles in the tail gas and reduce the temperature of the waste gas, preventing impurities and high temperature from damaging the subsequent carbon dioxide recovery equipment.

[0045] The tail gas generated during the alcoholysis process is transported to an absorption tower for carbon dioxide recovery. The absorption tower adopts a spray tower structure, and the absorbent is potassium carbonate.

[0046] There are multiple spray layers in the spray tower. Carbon dioxide detectors (MOT500-CO2-IR) are 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 respectively to measure the carbon dioxide content input into the spray tower and the carbon dioxide absorption situation of the spray tower. Secondly, flow meters are installed at each nozzle to collect the consumption of the absorbent in each spray layer.

[0047] The installation schematic diagram of the carbon dioxide detector in the spray tower provided in this embodiment is as Figure 2 shown, Figure 2 In the figure, A is the spray tower, B1 is the air inlet for the inflow of tail gas, B2 is the air outlet for the outflow of purified gas, B3 is the water outlet for the outflow of the absorbent, C is the carbon dioxide detector, D is the dehydration plate, E is the swirl plate, F is the nozzle, G is the circulation water pump, H is the pipeline, and I is the flow meter.

[0048] The acquisition frequency of the carbon dioxide detector is set to 1KHz. Therefore, each carbon dioxide detector will acquire 60,000 CO2 concentration data per minute, representing the change in carbon dioxide concentration in the past 1 minute.

[0049] Therefore, each minute is recorded as a collection period, and the CO2 concentrations at each moment within each collection period are obtained 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 consumption of the absorption liquid in each spray layer during each collection period.

[0050] In this embodiment, there are a total of 5 spray layers in the spray tower. As other implementation methods, the implementer can select the number of spray layers according to the actual situation. There is a separate PID (proportion integration differentiation) control unit on the nozzle in each spray layer to regulate the spraying speed of the nozzle.

[0051] Thus, the CO2 concentrations at each moment within each collection period are obtained 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 consumption of the absorption liquid in each spray layer during each collection period.

[0052] Step 2: Calculate the relative change coefficient of each collection period through the discrete situation of the change rate of the CO2 concentration at different moments at the air inlet within each collection period; analyze the residual situation of the CO2 concentration at the air outlet within each collection period and calculate the residual deviation amount of each collection period.

[0053] In the spray tower, the generation amount of carbon dioxide may fluctuate due to changes in the conditions of the polyurethane alcoholysis reaction. If the spray tower cannot respond to these changes in a timely manner, it will cause incomplete CO2 absorption, resulting in residual CO2 absorption, or the absorption liquid cannot be effectively utilized, leading to waste of resources.

[0054] When the CO2 content flowing in at the air inlet is relatively large, if the spraying speed cannot adapt to the change in the CO2 content in a timely manner, the CO2 concentration in the purified gas flowing out at the air outlet at the top of the spray tower will not meet the emission standard, resulting in residual CO2 absorption. Secondly, when the traditional spray tower controls the spraying speed, the same spraying speed is used for all spray layers. When the CO2 content flowing in at the air inlet at the bottom of the spray tower is relatively small, due to the different CO2 concentrations inside different spray layers in the spray tower, the same spraying speed may cause the absorption liquid in the upper layer of the spray tower to not fully react with sufficient CO2 in the atomized state, resulting in waste of the absorption liquid. By rapidly adjusting the overall spraying speed of the spray tower according to the drastic change in the CO2 content flowing in at the air inlet at the bottom of the spray tower to adapt to the drastic change in the tail gas composition, and when the CO2 content flowing in at the air inlet at the bottom of the spray tower changes relatively stably, the spraying speed of each spray layer of the spray tower is adjusted separately to improve the utilization rate of the absorption liquid.

[0055] 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:

[0056] 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;

[0057] 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.

[0058] 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;

[0059] 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.

[0060] 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.

[0061] 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:

[0062] 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;

[0063] The calculation formula for the residual deviation of each acquisition cycle is:

[0064]

[0065] 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.

[0066] It should be noted that the normal concentration of CO2 in the atmosphere is approximately 0.04%, that is, the volume of carbon dioxide accounts for 0.04% of the total volume of air. Converted to ppm concentration, it is 400 ppm. Therefore, the preset emission threshold is set at 400 ppm.

[0067] It should be noted that if is greater than , it indicates that the overall spraying speed of the spray tower is too slow at this time, resulting in incomplete CO2 absorption. The greater the resulting residual deviation, the worse the CO2 absorption effect of the spray tower at this time. The spraying speed of the spray tower should be increased to avoid the phenomenon of CO2 absorption residue.

[0068] Thus, the residual deviation of the spray tower in each collection cycle is obtained.

[0069] 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. Based on the dispersion of the absorption amounts of all spray layers in each collection cycle, determine the absorption deviation of each collection cycle; fuse the residual deviation and the absorption deviation to obtain the overall control deviation of each collection cycle.

[0070] 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 inflowing carbon dioxide concentration may have been absorbed by the atomized absorption liquid sprayed at the bottom layer of the spray tower. In the upper spray layer, the content of carbon dioxide is already very close to the preset emission threshold , then the CO2 concentration in the upper spray layer is low, and its absorption liquid hardly undergoes CO2 absorption, which will cause waste of the absorption liquid in the upper spray layer. Therefore, this phenomenon indicates that the overall spraying speed inside the spray tower is too fast at this time, and the spraying speed should be adjusted downward to avoid energy waste.

[0071] Therefore, by calculating the absorption deviation based on the difference in CO2 concentration between different spray layers to reflect the uniformity of CO2 concentration absorption by different spray layers, the step flowchart of the method for obtaining the absorption deviation of each collection cycle provided by the embodiment of the present application is as Figure 3 shown, specifically including:

[0072] Calculate the mean value of the CO2 concentration of each spray layer at all times in each collection cycle as the average concentration of each spray layer in each collection cycle;

[0073] Arrange the CO2 residual concentration at the outlet and the average concentrations of all spray layers in the same collection cycle from top to bottom according to the position in the spray tower to form the CO2 concentration sequence of each collection cycle.

[0074] It should be noted that assuming 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. If 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 th collection period are respectively , and the CO2 residual concentration at the air outlet is , then the CO2 concentration sequence is .

[0075] Calculate the difference between each element in the CO2 concentration sequence and its previous element, and use it as the absorption amount of each spray layer in each collection period;

[0076] Take the opposite of the standard deviation of the absorption amounts of all spray layers in each collection period as the absorption deviation amount of each collection period;

[0077] It should be noted that the absorption amount is the difference in CO2 concentration between each spray layer and the adjacent upper spray layer, which reflects the absorption effect of each spray layer on CO2. When the spray speed inside the spray tower is reasonable, the 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 and the overall spray speed inside the spray tower is too fast, and the CO2 has been atomized and absorbed by the absorption liquid in the lower spray layer, the absorption liquid in the upper spray layer will be wasted. Therefore, the smaller the absorption deviation amount, 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 adjusted downward; secondly, the purpose of taking the opposite of the standard deviation is to adjust the value of the standard deviation so that when the spray speed is adjusted downward by the PID controller later, the absorption deviation amount is negative.

[0078] Furthermore, based on the residual deviation amount and the absorption deviation amount, determine the overall control deviation, specifically:

[0079] Take the sum of the residual deviation amount and the absorption deviation amount as the overall control deviation of each collection period;

[0080] It should be noted that when the overall spray speed of the spray tower is too high, the overall control deviation is negative, and vice versa. The main reason is that when the overall spray speed of the spray tower is too high, the overall absorption amount of CO2 by the spray tower is high, so the CO2 content in the gas flowing out of the air outlet is low. Therefore, the residual deviation amount is 0 or a smaller value, and there is a large difference in the CO2 concentration absorption between different spray layers. Then, the absorption deviation amount is negative and has a large absolute value. Therefore, the obtained overall control deviation is negative. When the overall spraying speed of the spray tower is too low, the overall CO2 absorption amount of the spray tower is low, and the CO2 content in the gas flowing out of the outlet is high. Therefore, the residual deviation amount is large and positive, and the difference in the CO2 concentration absorption between different spray layers is small. Then, the absorption deviation amount is negative and has a small absolute value. Therefore, the obtained overall control deviation is positive.

[0081] Thus, the overall control deviation of each collection period is obtained.

[0082] Step 4: Based on the absorption amount and the absorbent consumption of each spray layer in each collection period, determine the relative utilization rate of each spray layer in each collection period; analyze the deviation of the relative utilization rate of each spray layer in each collection period, determine the hierarchical control deviation of each spray layer in each collection period, and combine the relative change coefficient and the overall control deviation to obtain the relative control deviation of each spray layer in each collection period; based on the relative control deviation, combine with a PID controller to adjust the spraying speed of each spray layer in the next collection period to recover the CO2 generated in the polyurethane alcoholysis process.

[0083] To avoid the control strategy of the spraying speed of different spray layers not matching the change in the CO2 inflow rate when the CO2 inflow rate changes. For example, when the CO2 inflow rate increases, the spraying speed of some spray layers decreases instead. By performing hierarchical control between the spraying speeds of different spray layers of the spray tower, the overall utilization rate of the absorbent is improved.

[0084] Therefore, by analyzing the utilization rate of the absorbent in each spray layer through the absorbent consumption and CO2 absorption amount in each spray layer, the hierarchical control deviation is calculated. Specifically:

[0085] Take the ratio between the absorption amount and the absorbent consumption of each spray layer in each collection period as the relative utilization rate of each spray layer in each collection period;

[0086] Take the difference between the relative utilization rate of each spray layer in each collection period and the average value of the relative utilization rates of all spray layers as the utilization rate deviation of each spray layer in each collection period;

[0087] It should be noted that if the utilization rate deviation is negative, it means that the relative utilization rate of the absorbent in the corresponding spray layer is low, and the spraying speed of the corresponding spray layer should be reduced; if the utilization rate deviation is positive, it means that the relative utilization rate of the absorbent in the corresponding spray layer is high, and the utilization rate of the absorbent in the corresponding spray layer may be close to saturation. At this time, the spraying speed of the corresponding spray layer should be increased.

[0088] 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;

[0089] 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.

[0090] 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:

[0091]

[0092] 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.

[0093] 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.

[0094] Input the relative control deviation into the PID (proportion integration differentiation) controller of each spray layer to adjust the spray speed of each spray layer in the next acquisition cycle, and recover the CO2 generated during the alcoholysis process of polyurethane.

[0095] It should be noted that the PID controller is a well-known technology and will not be elaborated here.

[0096] After the tail gas is absorbed by the spray tower, the purified tail gas is discharged from the air outlet. After the obtained absorption liquid flows out from the water outlet below the spray tower, it is sent to the regeneration tower for heating and desorption. In the regeneration tower, the absorption liquid is heated to cause the carbon dioxide in the absorption liquid to precipitate 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.

[0097] Compress the collected CO2 gas through a compressor, then condense it into liquid CO2 in a condenser, and send it to a storage tank for storage.

[0098] Based on the same inventive concept as the above method, the embodiment of the present application also provides a system for recovering carbon dioxide during the alcoholysis process of polyurethane industry, 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, it implements the steps of any one of the above methods for recovering carbon dioxide during the alcoholysis process of polyurethane industry.

[0099] It should be understood that although Figure 1 the steps in the flowchart are shown in sequence according to the indication of the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear description in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover, Figure 1 at least a part of the steps in

[0100] can include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same moment, but can be executed at different moments. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed alternately or in turn with at least a part of other steps or sub-steps or stages of other steps.

[0101] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several variations and improvements can still be made. Therefore, any simple modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application all 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.

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