Depolymerization system

Abstract

A depolymerization system (1) is provided with: a positive displacement pump (GP) for supplying a molten resin from a tank (TK1) for storing the molten resin to a depolymerization device (DR); and a pump control device (10) for controlling the pump (GP). A pump control device is provided with: a viscosity information acquisition unit (113) that acquires information on the viscosity of a molten resin in a tank (TK1); a density information acquisition unit (114) that acquires information on the density of the molten resin in the tank; a pressure difference information acquisition unit (115) that acquires information on the pressure difference between the pressure in the tank and the pressure in the depolymerization device; a command value calculation unit (116) that calculates a control command value corresponding to the target flow rate of the molten resin; a volumetric efficiency calculation unit (117) that calculates the volumetric efficiency of the pump on the basis of the acquired viscosity information, density information, and pressure difference information; a correction unit (118) that corrects the control command value on the basis of the volumetric efficiency of the pump; and an output unit (119) that outputs the corrected control command value to the pump.

Description

Technical Field

[0001] The invention relates to a depolymerization system for depolymerizing waste plastics to recover raw materials. Background Art

[0002] In recent years, initiatives to significantly reduce waste generation have been actively carried out by preventing and reducing waste generation, recycling and reusing waste. It is known that there is a technology for chemically recycling waste plastics into raw materials to achieve this goal. As such a technology, there is a device for adding alkali to crushed PET-containing resin for thermal decomposition treatment to recover benzene (for example, see Patent Document 1). In the device described in Patent Document 1, the resin containing PET and the alkali are continuously fed into the thermal decomposition device using a screw conveying feeding device.

[0003] However, when depolymerizing the molten resin to recover the raw material, it is conceivable to use the above-mentioned screw conveying type feeding device to feed the molten resin into the high-pressure depolymerization device while applying pressure. However, since the screw conveying type feeding device is expensive, it leads to increased costs.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2008-133398 (JP 2008-133398 A). Summary of the invention

[0007] A depolymerization system according to one embodiment of the present invention comprises: a resin tank storing molten resin; a water tank storing water; and a depolymerization device for causing the molten resin supplied from the resin tank and the water supplied from the water tank to undergo a depolymerization reaction. The depolymerization system further comprises a positive displacement pump for supplying the molten resin from the resin tank to the depolymerization device and a pump control device for controlling the pump. The pump control device is characterized in that it includes: a viscosity information acquisition unit, which acquires information on the viscosity of the molten resin in the resin tank; a density information acquisition unit, which acquires information on the density of the molten resin in the resin tank; a pressure difference information acquisition unit, which acquires information on the pressure difference between the pressure in the resin tank and the pressure in the depolymerization device; an instruction value calculation unit, which calculates a control instruction value corresponding to a target flow rate of the molten resin; a volumetric efficiency calculation unit, which calculates the volumetric efficiency of the pump based on the viscosity information acquired by the viscosity information acquisition unit, the density information acquired by the density information acquisition unit, and the pressure difference information acquired by the pressure difference information acquisition unit; a correction unit, which corrects the control instruction value calculated by the instruction value calculation unit based on the volumetric efficiency of the pump calculated by the volumetric efficiency calculation unit; and an output unit, which outputs the control instruction value corrected by the correction unit to the pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The objects, features and advantages of the present invention will be further clarified through the following description of the embodiments in conjunction with the accompanying drawings.

[0009] Figure 1 This is a diagram showing an example of the configuration of a deaggregation system according to an embodiment of the present invention.

[0010] Figure 2 It shows the control Figure 1 Diagram of the main part structure of the pump control device of each pump of the depolymerization system.

[0011] Figure 3 Is used to illustrate the Figure 2 FIG. 1 is a diagram of a process performed by the controller 100 .

[0012] Figure 4A It is used to describe the storage Figure 2 A diagram of information in the storage unit 120.

[0013] Figure 4B It is used to describe the storage Figure 2 FIG. 1 is a diagram of information in the storage unit 120.

[0014] Figure 5 It is a diagram for explaining the volumetric efficiency information of the gear pump.

[0015] Figure 6 Is used to illustrate the Figure 2 FIG. 1 is a diagram of another process performed by the controller 100 .

[0016] Figure 7 It is a diagram for explaining water pump volumetric efficiency information. DETAILED DESCRIPTION

[0017] Below, refer to Figure 1 to Figure 7 An embodiment of the present invention is described. The depolymerization system 1 of the embodiment of the present invention depolymerizes waste plastics used as components of vehicles (interior, bumper, etc.) to recover raw materials. The waste plastics are polyamide 6 (hereinafter referred to as PA6GF) mixed with glass fiber (hereinafter referred to as GF). The depolymerization system 1 depolymerizes polyamide 6 (hereinafter referred to as PA6) contained in the waste plastics to recover caprolactam (hereinafter referred to as CL). It should be noted that the waste plastics can also be substances other than PA6GF. That is, polymers other than polyamide 6 can also be depolymerized to recover monomers other than caprolactam.

[0018] Figure 1 : is a diagram showing an example of the structure of a depolymerization system according to an embodiment of the present invention. Figure 1As shown, the depolymerization system 1 includes a resin tank TK1 storing a molten resin SL, a water tank TK2 storing water WT, and a continuous depolymerization device (hereinafter referred to as a depolymerization device) DR for performing a depolymerization reaction between the molten resin supplied from the resin tank TK1 and the water supplied from the water tank TK2. Specifically, the molten resin SL is PA6 (hereinafter referred to as molten PA6) melted by ethylene glycol (hereinafter referred to as EG).

[0019] In addition, the depolymerization system 1 includes a pump GP for pressure-feeding the molten resin SL in the resin tank TK1 to the depolymerization device DR, and a pump WP for pressure-feeding the water WT in the water tank TK2 to the depolymerization device DR. The pumps GP and WP are positive displacement pumps, the pump GP is a gear pump, and the pump WP is a plunger pump. In addition, the depolymerization system 1 includes: a gear pump control unit PC1 for controlling the pump GP, a water pump control unit PC2 for controlling the pump WP, a flow rate setting unit 111, and a pressure control unit 112. The pressure control unit 112 controls the back pressure valve VL provided on the output side (downstream side) of the depolymerization device DR to maintain the pressure in the depolymerization device DR at a specified pressure value (hereinafter referred to as the pressure setting value).

[0020] However, when molten PA6 and water are supplied to the depolymerization device DR, the internal volume of the depolymerization device DR is fixed, so the residence time is determined by the supply amount, internal temperature and pressure. On the other hand, the gear pump that supplies molten PA6 may cause the volumetric efficiency to fluctuate due to external disturbances. When the volumetric efficiency of the gear pump fluctuates, the residence time of the molten PA6 in the depolymerization device DR becomes unstable. As a result, the yield of the generated monomer (CL) changes, and the monomer concentration (the ratio of CL containing the depolymerization liquid to water) of the treated liquid after the depolymerization reaction of molten PA6 and water (hereinafter referred to as the depolymerization liquid) changes. The depolymerization liquid is concentrated in the subsequent concentration step, and the CL is recovered as a concentrated liquid (hereinafter referred to as concentrated CL liquid) after the water contained in the depolymerization liquid is separated. However, as described above, when the monomer concentration of the depolymerization liquid changes, the concentration of the concentrated CL liquid becomes unstable and the quality becomes unstable. In order to cope with such a problem, the depolymerization system is constructed as follows in the present embodiment.

[0021] Figure 2 1 is a diagram showing the main part of the pump control device for controlling the pumps GP and WP of the depolymerization system 1. Figure 2As shown, the pump control device 10 includes a controller 100, rotation speed detection sensors RS1, RS2, pressure sensors PM1, PM2, temperature sensors TM1, TM2, and flow sensors FM1, FM2. The controller 100 includes a computer having a computing unit 110 such as a CPU, a storage unit 120 such as a ROM (read only memory), a RAM (random access memory), and other peripheral circuits. The rotation speed detection sensors RS1, RS2, the pressure sensors PM1, PM2, the temperature sensors TM1, TM2, and the flow sensors FM1, FM2 are connected to the controller 100, respectively.

[0022] The rotation speed detection sensor RS1 detects the rotation speed of the pump GP. It should be noted that the rotation speed of the pump GP is more specifically the rotation speed of the motor MT1 used to drive the pump GP. The rotation speed detection sensor RS2 detects the rotation speed of the pump WP. It should be noted that the rotation speed of the pump WP is more specifically the rotation speed of the motor MT2 used to drive the pump WP. The pressure sensors PM1 and PM2 detect the pressure in the depolymerization device DR. The temperature sensor TM1 detects the temperature of the molten resin SL stored in the resin tank TK1. The temperature sensor TM2 detects the temperature of the water WT stored in the water tank TK2. The flow sensor FM1 detects the flow rate of the molten resin SL supplied from the pump GP to the depolymerization device DR. The flow sensor FM2 detects the flow rate of the water WT supplied from the pump WP to the depolymerization device DR.

[0023] The controller 100 has Figure 1 The flow rate setting unit 111 and the pressure control unit 112 are functional structures of the operation unit 110. In addition, the controller 100 has a viscosity information acquisition unit 113, a density information acquisition unit 114, a pressure difference information acquisition unit 115, a command value calculation unit 116, a volume efficiency calculation unit 117, a correction unit 118, and an output unit 119 as functional structures of the operation unit 110. The above-mentioned components 113 to 119 are Figure 1 The gear pump control unit PC1 functions as described above. Figure 1 The water pump control unit PC2 functions.

[0024] The viscosity information acquisition unit 113 acquires information on the viscosity of the molten resin SL in the resin tank TK1. Specifically, the viscosity information acquisition unit 113 converts the viscosity based on the temperature of the molten resin SL in the resin tank TK1 detected by the temperature sensor TM1, and acquires information on the viscosity of the molten resin SL. In addition, the viscosity information acquisition unit 113 acquires information on the viscosity of the molten resin SL in the water tank TK2. Specifically, the viscosity information acquisition unit 113 converts the viscosity based on the temperature of the water WT in the water tank TK2 detected by the temperature sensor TM2, and acquires information on the viscosity of the water WT.

[0025] The density information acquisition unit 114 acquires information on the density of the molten resin SL in the resin tank TK1. Specifically, the density information acquisition unit 114 converts the density based on the temperature of the molten resin SL in the resin tank TK1 detected by the temperature sensor TM1, and acquires information on the density of the molten resin SL. In addition, the density information acquisition unit 114 acquires information on the density of the water WT in the water tank TK2. Specifically, the density information acquisition unit 114 converts the density based on the temperature of the water WT in the water tank TK2 detected by the temperature sensor TM2, and acquires information on the density of the water WT.

[0026] The pressure difference information acquisition unit 115 acquires information on the pressure difference ΔP1 between the pressure in the resin tank TK1 and the pressure in the depolymerization device DR. In addition, the pressure difference information acquisition unit 115 acquires information on the pressure difference ΔP2 between the pressure in the water tank TK2 and the pressure in the depolymerization device DR. It should be noted that since the pressure in the resin tank TK1 is equal to the atmospheric pressure and the pressure (gauge pressure) in the depolymerization device DR is high pressure, when the resin tank TK1 is not pressurized, the pressure difference information acquisition unit 115 acquires the detection value of the pressure sensor PM1 as information indicating the above-mentioned pressure difference ΔP1. Similarly, since the pressure in the water tank TK2 is also equal to the atmospheric pressure, when the water tank TK2 is not pressurized, the pressure difference information acquisition unit 115 acquires the detection value of the pressure sensor PM2 as information indicating the above-mentioned pressure difference ΔP2.

[0027] The command value calculation unit 116 calculates the control command value of the pump GP corresponding to the target flow rate of the pump GP. Specifically, the command value calculation unit 116 calculates the rotation speed of the pump GP for discharging the target flow rate as the control command value. In addition, the command value calculation unit 116 calculates the control command value of the pump WP corresponding to the target flow rate of the pump WP. Specifically, the command value calculation unit 116 calculates the rotation speed of the pump WP for discharging the target flow rate as the control command value.

[0028] The volumetric efficiency calculation unit 117 calculates the volumetric efficiency of the pump GP based on the information on the viscosity of the molten resin SL obtained by the viscosity information acquisition unit 113, the information on the density of the molten resin SL obtained by the density information acquisition unit 114, and the information on the pressure difference ΔP1 obtained by the pressure difference information acquisition unit 115. In addition, the volumetric efficiency calculation unit 117 calculates the volumetric efficiency of the pump WP based on the information on the viscosity of the water WT obtained by the viscosity information acquisition unit 113, the information on the density of the water WT obtained by the density information acquisition unit 114, and the information on the pressure difference ΔP2 obtained by the pressure difference information acquisition unit 115.

[0029] The correction unit 118 corrects the control command value of the pump GP calculated by the command value calculation unit 116 based on the volumetric efficiency of the pump GP calculated by the volumetric efficiency calculation unit 117. In addition, the correction unit 118 corrects the control command value of the pump WP calculated by the command value calculation unit 116 based on the volumetric efficiency of the pump WP calculated by the volumetric efficiency calculation unit 117.

[0030] The output unit 119 outputs the control command value of the pump GP corrected by the correction unit 118 to the pump GP. More specifically, the output unit 119 converts the corrected control command value into a rotation speed command value of the motor MT1, and outputs the rotation speed command value to the motor MT1. In addition, the output unit 119 outputs the control command value of the pump WP corrected by the correction unit 118 to the pump WP. More specifically, the output unit 119 converts the corrected control command value into a rotation speed command value of the motor MT2, and outputs the rotation speed command value to the motor MT2.

[0031] The storage unit 120 includes a resin property database (hereinafter referred to as a database) 121 , a gear pump volumetric efficiency DB 122 , a water property DB 123 , and a water pump volumetric efficiency DB 124 .

[0032] The resin characteristic DB 121 stores resin characteristic information described later. The gear pump volumetric efficiency DB 122 stores gear pump volumetric efficiency information described later. The water characteristic DB 123 stores water characteristic information described later. The water pump volumetric efficiency DB 124 stores water pump volumetric efficiency information described later.

[0033] Figure 3 It is a diagram for explaining the processing executed by the controller 100 of the pump control device 10 . Figure 3 An example of calculation processing of the control command value of the pump GP is shown in FIG. Figure 3 As shown, first, in steps S11 and S12 , based on the resin property information stored in the resin property DB 121 , the density ρ(Tx) and the viscosity μ(Tx) of the molten resin SL are calculated from the detection value Tx of the temperature sensor TM1 . Figure 4A and 4B 1 is a diagram for explaining resin property information stored in the resin property DB 121. The resin property information includes density information and viscosity information. Figure 4A The density ρ(T1) to ρ(T2) corresponding to the temperature T1 to T2 (T1 < Tx < T2) is shown as density information. Figure 4B , viscosities μ(T1) to μ(T2) corresponding to temperatures T1 to T2 are shown as viscosity information.

[0034] like Figure 4A and Figure 4BAs shown, the density information and the viscosity information are information showing the correlation between the temperature, density and viscosity of the molten resin SL. The resin property information is obtained in advance through experiments, etc., and stored in the resin property DB 121. The density ρ(Tx) corresponding to the detection value Tx of the temperature sensor TM1 is calculated by the following formula (i).

[0035] ρ(Tx)=(ρ(T2)-ρ(T1)) / (T2-T1)*(Tx-T1)+ρ(T1) (i)

[0036] Similarly, the viscosity μ(Tx) corresponding to the detection value Tx of the temperature sensor TM1 is calculated by the following formula (ii).

[0037] μ(Tx)=(μ(T2)-μ(T1)) / (T2-T1)*(Tx-T1)+μ(T1) (ii)

[0038] Next, in step S13, the pressure difference ΔP1 between the pressure in the resin tank TK1 and the pressure in the depolymerization device DR is calculated. As described above, since the pressure in the resin tank TK1 is substantially atmospheric pressure, the detection value Px of the pressure sensor PM1 is directly calculated as the pressure difference ΔP1.

[0039] Finally, in step S14 , the actual rotation speed of the pump GP is predicted. Figure 5 1 is a diagram showing a performance curve of the pump GP indicated by the gear pump volumetric efficiency information stored in the gear pump volumetric efficiency DB 122 . Figure 5 The performance curve shows the relationship between the discharge flow rate (discharge flow rate per unit time) of the pump GP and the volumetric efficiency. Figure 5 The volumetric efficiency η(Q1) to η(Q2) corresponding to the discharge flow rates Q1 to Q2 is shown in FIG. It should be noted that the discharge flow rate Q(n) per unit time of the pump GP when the rotation speed of the pump GP, more specifically the rotation speed of the motor MT1 is n [rmp] and the viscosity of the molten resin SL is μ, is calculated by the following formula (iii).

[0040] Q(n)=ΔP1 / (μ×n) (iii)

[0041] When the target flow rate of the molten resin SL is q1 [kg / h], the volume flow rate is converted using the information on the density and viscosity of the molten resin SL to calculate the theoretical rotation speed n1 of the pump GP corresponding to the target flow rate q1. Figure 5 As shown in FIG. 1 , since the volumetric efficiency decreases as the discharge flow rate of the pump GP increases, the desired discharge flow rate cannot be obtained even if the pump GP is rotated at the theoretical rotation speed n1. Figure 5The above-mentioned rotational speed n1 is corrected based on the characteristics of the pump GP, and the actual rotational speed of the pump GP is predicted. Specifically, the correction unit 118 uses the following formula (iv) to correct the rotational speed n1 based on the data at the rotational speed n1 and the rotational speed n+α. The actual rotational speed of the pump GP obtained by correcting the rotational speed n1 is hereinafter referred to as the predicted rotational speed Nx. α is, for example, 10. In formula (iv), RQ(n1) and RQ(n1+α) are respectively predicted values ​​of the actual discharge flow rate when the rotational speeds are n1 and n1+α, which are calculated by multiplying Q(n1) and Q(n1+α) by the corresponding volumetric efficiency.

[0042] It is calculated by multiplying Q(n1) and Q(n1+α) by the corresponding volumetric efficiency.

[0043] Nx=((n1+α)-n1) / (RQ(n1)-RQ(n1+α))*(q1-RQ(n1))+n1 (iv)

[0044] Figure 6 1 is a diagram for explaining another process executed by the controller 100 of the pump control device 10 . Figure 6 An example of the rotation control of the pump GP is shown in FIG. Figure 3 The processing is based on the predicted rotation speed Nx calculated based on the target flow rate, and the pump GP is instructed to rotate. Specifically, a control command value corresponding to the predicted rotation speed Nx is output to the pump GP. In step S22, the discharge flow rate Q of the pump GP is measured. Specifically, the discharge flow rate Q of the pump GP detected by the flow sensor FM1 is obtained. In step S23, feedback control (PID control) is performed in a manner that reduces the error between the target flow rate q1 and the discharge flow rate Q, and the control command value is updated. Then, based on the updated control command value, the processing of steps S21 to S23 is repeated. Thereafter, the processing of steps S21 to S23 is repeated in the same manner. In this way, the molten resin SL can be accurately supplied to the depolymerization device DR according to the target flow rate.

[0045] Figure 3The processing can also be applied to the calculation of the control command value of the pump WP. Specifically, first, based on the water characteristic information stored in the water characteristic DB123, the density ρ(Ty) and viscosity μ(Ty) of the molten resin SL are calculated according to the detection value Ty of the temperature sensor TM2. Similar to the resin characteristic information, the water characteristic information includes information (density information and viscosity information) showing the correlation between the temperature, density and viscosity of the water WT. The water characteristic information is obtained in advance through experiments, etc. and stored in the water characteristic DB123. Next, the density ρ(Ty) and viscosity μ(Ty) corresponding to the detection value Ty of the temperature sensor TM2 are calculated using the above formulas (i) and (ii). Next, the pressure difference ΔP2 between the pressure in the water tank TK2 and the pressure in the depolymerization device DR is calculated. Because the pressure in the water tank TK2 is also approximately atmospheric pressure, the detection value Px of the pressure sensor PM2 is calculated directly as the pressure difference ΔP2.

[0046] Finally, the correction unit 118 predicts the actual rotation speed of the pump WP. Specifically, first, when the target flow rate of water WT is q2 [kg / h], the volume flow rate is converted using the information of the density ρ and viscosity μ of water WT, and the theoretical rotation speed n2 of the pump WP corresponding to the target flow rate q2 is calculated. It should be noted that the plunger pump converts the rotational motion of the motor MT1 into reciprocating motion through the cam and crank mechanism, so the discharge flow rate of the pump W changes according to the rotation speed of the motor MT1. Specifically, when the speed becomes higher, the discharge volume per unit time increases. In addition, the lower the speed of the pump W rotates, the greater the internal leakage will be, and the lower the volumetric efficiency will be. Therefore, the above-mentioned rotation speed n2 is calculated by also taking into account the changing characteristics of the discharge flow rate relative to the rotation speed of the motor MT1. In addition, the above-mentioned rotation speed n2 is calculated by also taking into account the changing characteristics of the volumetric efficiency relative to the rotation speed of the motor MT1.

[0047] Figure 7 This is a diagram showing a performance curve of the pump WP indicated by the water pump volumetric efficiency information stored in the water pump volumetric efficiency DB 124 . Figure 7 The performance curve shows the relationship between the flow rate (flow rate per unit time) and volumetric efficiency of the pump WP. Figure 7 The volumetric efficiency η(Q11) to η(Q12) corresponding to the discharge flow rates Q11 to Q12 is shown in FIG. The pump WP as a plunger pump has a higher volumetric efficiency than the pump GP. However, when the pressure difference ΔP2 increases, liquid leaks from the gap between the cylinder and the plunger, causing the following problems: Figure 7 The correction unit 118 takes into account the decrease in volumetric efficiency. Figure 7The above speed n2 is corrected based on the characteristics of the pump WP, and the actual speed of the pump WP is predicted. Hereinafter, the actual speed of the pump WP obtained by correcting the speed n2 is recorded as the predicted speed Ny. The calculation method of the predicted speed Ny is the same as the calculation method of the predicted speed Nx, so the description is omitted. The output unit 119 outputs a control command value corresponding to the predicted speed Ny calculated in this way to the pump WP. In the rotation control of the pump WP, by performing Figure 5 By repeatedly updating the control command value through the same feedback control (PID control), water WT corresponding to the target flow rate q2 [kg / h] can be accurately discharged from the pump WP.

[0048] According to this embodiment, the following effects can be achieved.

[0049] (1) The depolymerization system 1 includes: a resin tank TK1 that stores molten resin SL; a water tank TK2 that stores water WT; and a depolymerization device DR that causes the molten resin SL supplied from the resin tank TK1 and the water WT supplied from the water tank TK2 to undergo a depolymerization reaction. The depolymerization system 1 also includes: a pump GP that supplies the molten resin SL from the resin tank TK1 to the depolymerization device DR; and a pump control device 10 that controls the pump GP. The pump control device 10 includes: a viscosity information acquisition unit 113 that acquires information on the viscosity of the molten resin SL in the resin tank TK1; a density information acquisition unit 114 that acquires information on the density of the molten resin SL in the resin tank TK1; a pressure difference information acquisition unit 115 that acquires information on a first pressure difference (pressure difference ΔP1) between the pressure in the resin tank TK1 and the pressure in the depolymerization device DR; an instruction value calculation unit 116 that calculates a control instruction value (referred to as a first control instruction value) of the pump GP corresponding to a target flow rate (referred to as a first target flow rate) of the molten resin SL; and a pressure difference information acquisition unit 115 that acquires information on a first pressure difference (pressure difference ΔP1) between the pressure in the resin tank TK1 and the pressure in the depolymerization device DR. The volume efficiency calculation unit 117 calculates the volume efficiency of the pump GP based on the information on the viscosity of the molten resin SL obtained by the viscosity information acquisition unit 113, the information on the density of the molten resin SL obtained by the density information acquisition unit 114, and the information on the first pressure difference obtained by the pressure difference information acquisition unit 115; the correction unit 118 corrects the first control command value calculated by the command value calculation unit 116 based on the volume efficiency of the pump GP calculated by the volume efficiency calculation unit 117; and the output unit 119 outputs the first control command value corrected by the correction unit 118 to the pump GP. In addition, the depolymerization system 1 further includes a back pressure valve VL, which is provided on the output side of the depolymerization device DR and adjusts the pressure in the depolymerization device DR. Thus, the molten resin SL can be accurately supplied to the high-pressure depolymerization device DR using a gear pump that is cheaper than a twin-screw extruder. In addition, since the residence time of the molten resin SL in the depolymerization device DR can be made constant, the fluctuation of the yield of the generated monomer can also be suppressed.

[0050] (2) The pump control device 10 further includes a flow sensor FM1 for detecting the discharge flow rate of the pump GP. The correction unit 118 calculates the error (referred to as the first error) between the detection value of the flow sensor FM1 as the first flow detection unit and the first target flow rate, and updates the first control command value of the pump GP based on the first error. The output unit 119 outputs the updated first control command value to the pump GP. In this way, the flow rate fluctuation of the pump GP can be suppressed, and the molten resin SL can be accurately supplied to the depolymerization device DR according to the target flow rate.

[0051] (3) The depolymerization system 1 further includes a pump WP for supplying water WT from the water tank TK2 to the depolymerization device DR. The pump control device 10 also controls the pump WP. In this case, the viscosity information acquisition unit 113 acquires information on the viscosity of the water WT in the water tank TK2, the density information acquisition unit 114 acquires information on the density of the water WT in the water tank TK2, the pressure difference information acquisition unit 115 acquires information on the second pressure difference (pressure difference ΔP2) between the pressure in the water tank TK2 and the pressure in the depolymerization device DR, and calculates a control instruction value (referred to as a second control instruction value) of the pump WP corresponding to a target flow rate (referred to as a second target flow rate) of the water WT, the volumetric efficiency calculation unit 117 calculates the volumetric efficiency of the pump WP based on the information on the viscosity of the water WT acquired by the viscosity information acquisition unit 113, the information on the density of the water WT acquired by the density information acquisition unit 114, and the information on the second pressure difference acquired by the pressure difference information acquisition unit 115, the correction unit 118 corrects the second control instruction value calculated by the instruction value calculation unit 116 based on the volumetric efficiency of the pump WP calculated by the volumetric efficiency calculation unit 117, and the output unit 119 outputs the second control instruction value corrected by the correction unit 118 to the pump WP. In addition, the depolymerization system 1 is further provided with a flow sensor FM2 as a second flow detection unit for detecting the discharge flow rate of the pump WP. The correction unit 118 calculates the error (referred to as the second error) between the detection value of the flow sensor FM2 and the second target flow rate, updates the second control command value based on the second error, and the output unit 119 outputs the updated second control command value to the pump WP. Thus, the flow rate fluctuation of the pump WP can be suppressed, and the water WT can be accurately supplied to the depolymerization device DR at the target flow rate.

[0052] The above-described embodiment can be modified in various forms. Modifications will be described below.

[0053] In the above embodiment, the depolymerization system 1 shows an example of depolymerizing PA6 contained in PA6GF to recover caprolactam, but the waste plastic may also be a substance other than PA6GF. That is, the depolymerization system may also depolymerize polymers other than PA6 to recover monomers other than caprolactam.

[0054] In addition, in the above-mentioned embodiment, the rotation speed detection sensor RS1 as the first rotation speed detection unit detects the rotation speed of the motor MT1 for driving the pump GP as the first pump as the rotation speed of the pump GP. In addition, the rotation speed detection sensor RS2 as the second rotation speed detection unit detects the rotation speed of the motor MT2 for driving the pump WP as the second pump as the rotation speed of the pump WP. However, the configuration of the first rotation speed detection unit and the second rotation speed detection unit is not limited to this. For example, the first rotation speed detection unit can also detect the rotation speed of the pump GP itself from the pump GP.

[0055] In addition, in the above embodiment, the case where the pump WP as the second pump is a plunger pump is taken as an example, but the second pump may also be a diaphragm pump. In the above embodiment, an example is also shown in which a back pressure valve VL is provided on the downstream side of the depolymerization device DR, but a flow control valve may be provided instead of the back pressure valve VL, and the pressure control unit 112 controls the flow control valve so that the pressure in the depolymerization device DR is maintained at a specified pressure value (pressure setting value).

[0056] The above description is merely an example, and the above embodiment and modified examples do not limit the present invention unless the features of the present invention are impaired. One or more of the above embodiment and modified examples can be arbitrarily combined, and the modified examples can be combined with each other.

[0057] According to the present invention, fluctuation in the yield of raw materials can be suppressed at low cost.

[0058] The present invention has been described above in conjunction with preferred embodiments, but it should be understood by those skilled in the art that various modifications and changes can be made without departing from the scope of the claims.

Claims

1. A depolymerization system comprising a resin tank (TK1) for storing molten resin, a water tank (TK2) for storing water, and a depolymerization device (DR) for causing the molten resin supplied from the resin tank (TK1) and the water supplied from the water tank (TK2) to undergo a depolymerization reaction, wherein: Also available: a pump (GP) which is a positive displacement pump and supplies the molten resin from the resin tank (TK1) to the depolymerization device (DR); and a pump control device (10) for controlling said pump (GP), The pump control device (10) comprises: a viscosity information acquisition unit (113) for acquiring information on the viscosity of the molten resin in the resin tank (TK1); a density information acquisition unit (114) for acquiring information on the density of the molten resin in the resin tank (TK1); a pressure difference information acquisition unit (115) for acquiring information on a pressure difference between the pressure in the resin tank (TK1) and the pressure in the depolymerization device (DR); an instruction value calculation unit (116) for calculating a control instruction value corresponding to a target flow rate of the molten resin; a volumetric efficiency calculation unit (117) for calculating the volumetric efficiency of the pump (GP) based on the viscosity information acquired by the viscosity information acquisition unit (113), the density information acquired by the density information acquisition unit (114), and the pressure difference information acquired by the pressure difference information acquisition unit (115); a correction unit (118) for correcting the control command value calculated by the command value calculation unit (116) based on the volumetric efficiency of the pump (GP) calculated by the volumetric efficiency calculation unit (117); and An output unit (119) outputs the control command value corrected by the correction unit (118) to the pump (GP).

2. The depolymerization system according to claim 1, characterized in that: The pump control device (10) further comprises a flow rate detection unit (FM1) for detecting a discharge flow rate of the pump (GP). The correction unit (118) calculates an error between the detection value of the flow detection unit (FM1) and the target flow rate, and updates the control instruction value according to the error. The output unit (119) outputs the updated control command value to the pump (GP).

3. The depolymerization system according to claim 1, characterized in that: The pump (GP) is a first pump, the control instruction value is a first control instruction value, the pressure difference is a first pressure difference, and the target flow rate is a first target flow rate, The depolymerization system further comprises a second positive displacement pump (WP) for supplying the water from the water tank (TK2) to the depolymerization device (DR). The viscosity information acquisition unit (113) acquires information on the viscosity of the water in the water tank (TK2). The density information acquisition unit (114) acquires information on the density of the water in the water tank (TK2). The pressure difference information acquisition unit (115) acquires information on a second pressure difference, which is a pressure difference between the pressure in the water tank (TK2) and the pressure in the depolymerization device (DR). The command value calculation unit (116) calculates a second control command value corresponding to the second target flow rate of water. The volumetric efficiency calculation unit (117) calculates the volumetric efficiency of the second pump (WP) based on the information on the viscosity of the water obtained by the viscosity information acquisition unit (113), the information on the density of the water obtained by the density information acquisition unit (114), and the information on the second pressure difference obtained by the pressure difference information acquisition unit (115). The correction unit (118) corrects the second control command value calculated by the command value calculation unit (116) based on the volumetric efficiency of the second pump (WP) calculated by the volumetric efficiency calculation unit (117). The output unit (119) outputs the second control instruction value corrected by the correction unit (118) to the second pump (WP).

4. The depolymerization system according to claim 3, characterized in that: The flow detection unit (FM1) is a first flow detection unit, The depolymerization system further comprises a second flow rate detection unit (FM2) for detecting the discharge flow rate of the second pump (WP). The correction unit (118) calculates an error between a detection value of the second flow rate detection unit (FM2) and the second target flow rate, and updates the second control instruction value according to the error. The output unit (119) outputs the updated second control command value to the second pump (WP).

5. The depolymerization system according to claim 3, characterized in that: The first pump (GP) is a gear pump, the second pump (WP) is a plunger pump, The first control instruction value is the rotation speed of the motor driving the gear pump, and the second control instruction value is the rotation speed of the motor driving the plunger pump.

6. The depolymerization system according to any one of claims 1 to 4, characterized in that Also available: A back pressure valve (VL) is provided at the output side of the depolymerization device (DR) to adjust the pressure in the depolymerization device (DR).

7. The depolymerization system according to any one of claims 1 to 4, characterized in that Also available: A flow control valve is provided at the output side of the depolymerization device (DR) to adjust the pressure in the depolymerization device (DR).

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