阅读说明：本技术 聚合物改性装置的控制方法 (Method for controlling polymer modification apparatus ) 是由 孙冰 金艳 朱红伟 姜杰 文松 赵磊 于 2019-03-22 设计创作，主要内容包括：本发明涉及聚合物改性工艺的安全控制技术领域,公开了一种聚合物改性装置的控制方法。一种聚合物改性装置的控制方法,其特征在于,所述聚合物改性装置包括挤出单元、驱动单元、加热单元、脱挥单元、控制单元以及警报结构,挤出单元包括机筒以及设置于机筒内部的螺杆,控制方法包括：向机筒内部分别加入原料和塑化剂的步骤；加热单元对机筒内部加热的步骤；驱动单元驱动螺杆转动的步骤；脱挥单元向机筒内部引风进行脱挥的步骤,其中,当脱挥单元的脱挥风量小于预设风量时,控制单元控制警报结构发出警报。在本发明的聚合物改性装置的控制方法中,能够有效预防事故,使得整个聚合物改性工艺过程安全有效。(The invention relates to the technical field of safety control of a polymer modification process, and discloses a control method of a polymer modification device. A control method of a polymer modification device is characterized in that the polymer modification device comprises an extrusion unit, a driving unit, a heating unit, a devolatilization unit, a control unit and an alarm structure, the extrusion unit comprises a machine barrel and a screw arranged in the machine barrel, and the control method comprises the following steps: a step of adding a raw material and a plasticizer to the inside of the cylinder; a step of heating the inside of the cylinder by a heating unit; a step of driving the screw rod to rotate by the driving unit; and the devolatilization unit induces air into the machine barrel to perform devolatilization, wherein when the devolatilization air volume of the devolatilization unit is smaller than the preset air volume, the control unit controls the alarm structure to give an alarm. According to the control method of the polymer modification device, accidents can be effectively prevented, and the whole polymer modification process is safe and effective.)

1. A control method of a polymer modification apparatus, the polymer modification apparatus comprising an extrusion unit, a driving unit, a heating unit, a devolatilization unit, a control unit, and an alarm structure, the extrusion unit comprising a barrel and a screw disposed inside the barrel, the control method comprising:

a step of separately adding a raw material and a plasticizer to the inside of the cylinder;

a step of heating the inside of the cylinder by the heating unit;

the driving unit drives the screw to rotate;

a step of inducing air into the machine barrel by the devolatilization unit for devolatilization,

when the devolatilization air volume of the devolatilization unit is smaller than the preset air volume, the control unit controls the alarm structure to give an alarm.

2. The method of claim 1, wherein the predetermined air volume (X) is set to be equal to or less than a predetermined value_min) Obtained by the following calculation of formula (1):

wherein m is_kThe formation rate (g/h), M, of the kth combustible component_kIs the molecular mass of the kth combustible component, N_kIs the explosive limit of the kth combustible component.

3. The method for controlling a polymer modification apparatus according to claim 1, wherein when the devolatilization air volume of the devolatilization unit is smaller than the predetermined air volume (X)_min) 0.75 times higher, the polymer modification apparatus was stopped.

4. The method for controlling a polymer modification apparatus according to claim 1, wherein in the step of devolatilizing by introducing air into the inside of the cylinder by the devolatilization unit, a combustible gas concentration at the devolatilization unit is detected, and when the combustible gas concentration value is higher than a combustible gas lower explosive limit concentration value (N)_mix) When the alarm rate exceeds 10 percent, the control unit controls the alarm structure to give an alarm,

wherein the combustible gas lower explosive limit concentration value (N)_mix) Obtained by the following calculation of formula (2):

wherein m is_kThe formation rate (g/h), M, of the kth combustible component_kIs the molecular mass of the kth combustible component, N_kIs the explosive limit of the kth combustible component.

5. The method of claim 4, wherein the method is performed when the combustible gas concentration value is lower than the combustible gas explosion lower limit concentration value (N)_mix) Above 50%, the polymer modification unit is shut down.

6. The method for controlling a polymer modification apparatus according to claim 1, wherein in the step of heating the inside of the cylinder by the heating unit, a temperature inside the cylinder is detected, and when the detected temperature is more than 20 ℃ than a preset temperature, the control unit controls the alarm structure to give an alarm.

7. The method of claim 6, wherein the control unit controls the devolatilization unit to increase the devolatilization air volume and controls the heating unit to be turned off when the alarm time exceeds 5 minutes or the detected temperature is greater than 50 ℃ than a preset temperature.

8. The method of claim 6 or 7, wherein the preset temperature is 150 ℃ to 230 ℃.

9. The method of controlling a polymer modification apparatus as claimed in claim 1, further comprising a step of eliminating static electricity in the feedstock before feeding the feedstock to the interior of the barrel.

10. The method of claim 9, wherein the electrostatic energy is controlled to be 300mJ or less.

Technical Field

The invention relates to the technical field of safety control of a polymer modification process, in particular to a control method of a polymer modification device for controlling parameters such as temperature, flow, wind speed and the like in the physical modification process of a polymer.

Background

As the polymer modification apparatus, a screw extruder is generally used, and among them, a twin-screw extruder is most generally used. The twin-screw extruder generally comprises a transmission device, a feeding device, a charging barrel and a screw, is matched with a granulation system and the like for use, and is widely used for processing and forming extruded products. In the beginning of the last 90 th century, screw extrusion is rapidly developed, modification and forming processes are integrated, and the screw extrusion is widely applied to modification reactions of grafting, crosslinking, blocking and the like of polymers.

Wherein, the double screw extrusion technology can be used for modifying the thermoplastic processing performance of the polyvinyl alcohol, and the thermoplastic modification is carried out by blending and extruding glycerol, glycol, water, polymer with a complementary structure with the polyvinyl alcohol and other plasticizers with the polyvinyl alcohol. In the processing process, the dust explosion risk of the polyvinyl alcohol raw material often exists, the combustible gas explosion risk caused by volatilization or decomposition of the plasticizer and low-boiling-point components in the raw material in the heating extrusion process exists, and the reaction thermal runaway risk in the heating process exists. At present, no research is available for analyzing risks existing in the machining process, and no systematic and targeted safety control technology exists.

Aiming at the polyvinyl alcohol twin-screw extrusion modification technology, the invention provides a safety control scheme of systems such as temperature control, ignition energy control, ignition temperature control and the like, and can ensure the safe, stable and long-period operation of the technological process.

Disclosure of Invention

The invention aims to provide a safety control scheme capable of providing systems such as temperature control, ignition energy control, ignition temperature control and the like, and capable of ensuring safe, stable and long-period operation of a polymer modification process.

In order to achieve the above object, an aspect of the present invention provides a method for controlling a polymer modification apparatus, wherein the polymer modification apparatus includes an extrusion unit, a driving unit, a heating unit, a devolatilization unit, a control unit, and an alarm structure, the extrusion unit includes a cylinder and a screw disposed inside the cylinder, the method includes: a step of separately adding a raw material and a plasticizer to the inside of the cylinder; a step of heating the inside of the cylinder by the heating unit; the driving unit drives the screw to rotate; and the devolatilization unit is used for inducing air into the machine barrel to perform devolatilization, wherein when the devolatilization air volume of the devolatilization unit is smaller than the preset air volume, the control unit controls the alarm structure to give an alarm.

Preferably, the preset air volume X_minObtained by the following calculation of formula (1):

wherein m is_kThe formation rate (g/h), M, of the kth combustible component_kIs the molecular mass of the kth combustible component, N_kAs detonation of the kth combustible componentAnd (4) limiting.

Preferably, when the devolatilization air volume of the devolatilization unit is smaller than the preset air volume X_min0.75 times higher, the polymer modification apparatus was stopped.

Preferably, in the step of devolatilizing by inducing air into the barrel by the devolatilization unit, the concentration of the combustible gas at the devolatilization unit is detected, and when the concentration of the combustible gas is higher than the concentration of the combustible gas at the lower explosive limit N, the concentration of the combustible gas is lower than the concentration of the combustible gas at the lower explosive limit N_mixWhen the concentration exceeds 10%, the control unit controls the alarm structure to give an alarm, wherein the explosive lower limit concentration value N of the combustible gas_mixObtained by the following calculation of formula (2):

wherein m is_kThe formation rate (g/h), M, of the kth combustible component_kIs the molecular mass of the kth combustible component, N_kIs the explosive limit of the kth combustible component.

Preferably, when the concentration value of the combustible gas is higher than the explosive lower limit concentration value N of the combustible gas_mixAbove 50%, the polymer modification unit is shut down.

Preferably, in the step of heating the inside of the cylinder by the heating unit, the temperature inside the cylinder is detected, and the control unit controls the alarm structure to give an alarm when the detected temperature is greater than a preset temperature by 20 ℃.

Preferably, when the alarm time exceeds 5 minutes or the detected temperature is greater than 50 ℃ than a preset temperature, the control unit controls the devolatilization unit to increase the devolatilization air volume and controls the heating unit to be turned off.

Preferably, the preset temperature is 150 ℃ to 230 ℃.

Preferably, the control method further comprises the step of eliminating static electricity in the raw material before feeding the raw material to the inside of the cylinder.

Preferably, the electrostatic energy is controlled to be 300mJ or less.

In the control method of the polymer modification device, when the devolatilization air volume of the devolatilization unit is smaller than the preset air volume, the control unit controls the alarm structure to give an alarm so as to obtain the devolatilization air volume deficiency information in time, thereby effectively preventing accidents, avoiding unplanned parking and ensuring the safety and effectiveness of the whole polymer modification process. Other advantages of the present invention will be described in detail below.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic diagram of the structure of a polymer modification apparatus according to a preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of the structure of a devolatilization unit of a preferred embodiment of a polymer modification apparatus provided herein;

FIG. 3 is a schematic diagram of the hopper configuration of a preferred embodiment of a polymer modification apparatus provided in accordance with the present invention;

FIG. 4 is a schematic circuit diagram of a polymer modification apparatus according to a preferred embodiment of the present invention.

Description of the reference numerals

11 powder bin 12 loading hopper

13 plasticizer feed tank 14 barrel

15 screw rod 2 devolatilization pipe

21 atmospheric devolatilization tube 22 vacuum devolatilization tube

Temperature detector for 23 air volume instrument 31

32 temperature alarm 41 flow meter

42 flow alarm 5 static elimination structure

61 magnetic adsorption part 62 magnetic filter

7 induced draft fan 8 control unit

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in describing the present invention, in the case where it is judged that the description for the related well-known function or structure may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted.

The invention provides a method for controlling a polymer modification apparatus. In order to fully illustrate the advantages of the control method of the present invention, the present invention first illustrates an example of a polymer modification apparatus (as shown in FIGS. 1 to 3), and then illustrates the control method of the present invention. The control method of the present invention can be applied to polymer modification apparatuses other than the above-described examples.

The polymer modification device comprises an extrusion unit, a driving unit, a heating unit, a devolatilization unit, a control unit and an alarm structure.

The extrusion unit is the core structure of the polymer modification device and is used for extrusion molding of a target product (polymer). The extrusion unit comprises a powder bin 11, a hopper 12, a plasticizer feed tank 13, a barrel 14 and a screw 15. The hopper 12 is connected to the hopper 11, and the raw material is continuously supplied to the hopper 12. A hopper 12 and a plasticizer feed tank 13 are respectively connected to the cylinder 14 to feed the raw material to be modified (for example, polyvinyl alcohol powder) and the plasticizer to the inside of the cylinder 14, respectively. A screw 15 is provided inside the barrel 14 for agitating the reaction material (molten mixture of raw material and plasticizer) inside the barrel 14. In addition, along the material moving direction, the inside of the cylinder 14 may be roughly divided into a feeding section where the material and the plasticizer are separately fed, a melt blending section where the material and the plasticizer are mixed and melted with each other, and an extrusion section where the target product is extrusion-molded.

The heating unit is a structure for heating the cylinder 14, and may be a boiler structure provided below the cylinder 14 so as to heat the cylinder 14, but more preferably, the heating unit is an electric heating structure provided on an outer wall of the cylinder 14. The present invention is not particularly limited in terms of the specific structure of the heating unit, as long as it can provide heat to the interior of the barrel 14 to satisfy the temperature conditions of the polymer modification process.

The driving unit is preferably a motor as a structure for driving the screw 15 to rotate, but is not limited thereto.

The devolatilization unit is used for removing low boiling point components in the reaction materials. In the polymer modification process, some low-boiling point components exist, and if the low-boiling point components are not removed in time and the concentration is too high, the low-boiling point components become blasting substances and cause explosion accidents. In order to devolatilize low boiling point components in the reaction material, the devolatilization unit includes a devolatilization pipe 2 disposed near the screw 15 and an induced draft fan 7 connected to the devolatilization pipe 2, and air inside the cylinder 14 is extracted through the devolatilization pipe 2 and the induced draft fan 7 to remove the low boiling point components in the reaction material. In the present invention, the low boiling components are, for example, water, methanol, methyl acetate, etc., but the processes are different.

The control unit 8 is electrically connected with the heating unit, the driving unit, the induced draft fan, the air flow meter, the combustible gas detector, the temperature detector, the flow meter and the alarm structure respectively. That is, all electrically controlled structures may be connected to the control unit 8 and controlled by the control unit 8.

The alarm structure may be one or plural, and for example, a separate temperature alarm 32 and a separate flow alarm 42 may be provided for the temperature parameter and the flow parameter, respectively. The alarm structure may provide the danger information by sound, light or other means, and when the alarm structure is plural, the same or different alarm modes may be used with respect to each other, and the present invention is not particularly limited thereto.

Aiming at various potential safety hazards existing in a polymer modification device, such as combustible gas explosion risks caused by volatilization or decomposition of plasticizers and low-boiling-point components in raw materials in a hot extrusion process, reaction thermal runaway risks in a heating process, yield reduction caused by too low content of plasticizers, explosion risks of raw material dust and the like, the invention provides the following control method.

The control method of the polymer modification apparatus of the present invention comprises the steps of:

1. respectively adding raw materials and a plasticizer into the cylinder;

2. a heating unit heats the interior of the barrel;

3. the driving unit drives the screw rod to rotate;

4. the devolatilization unit induces air to the inner part of the machine barrel for devolatilization.

In the devolatilization process of the devolatilization unit, the devolatilization air volume of the devolatilization unit (specifically, the devolatilization air volume provided by the induced draft fan 7) is very important, if the devolatilization air volume is too small, low-boiling-point components cannot be removed in time, the content of the low-boiling-point components is increased, and explosion accidents are likely to be caused in a high-temperature environment. Therefore, in the present invention, a wind meter 23 is provided in the devolatilization pipe 2 to detect the devolatilization wind amount of the devolatilization unit. On this basis, when the devolatilization air volume of the devolatilization unit is smaller than the preset air volume, the control unit 8 controls the alarm structure to give an alarm, and measures can be taken in time when the alarm is obtained so as to prevent safety accidents.

More specifically, the devolatilization air volume should be larger than the air volume corresponding to the lower explosion limit of the combustible gas, and the closer to the air volume corresponding to the lower explosion limit of the combustible gas, the higher the possibility of explosion of the combustible gas, and in order to ensure that the combustible gas does not explode, the minimum air volume of the devolatilization unit is preferably set to be twice the air volume corresponding to the lower explosion limit of the combustible gas (hereinafter, also referred to as a preset air volume X)_min) Above, the minimum air volume X_minCan be obtained by the following calculation of formula (1):

wherein m is_kThe formation rate (g/h), M, of the kth combustible component_kIs the molecular mass of the kth combustible component, N_kIs the explosive limit of the kth combustible component.

When the detection value of the air flow meter 23 is smaller than the preset air volume X_minIn the meantime, an alarm may be issued through an alarm structure (to be described in detail below), and when the detection value of the air flow meter 23 is less than 0.75 times of the preset air flow, the polymer modification apparatus may be stopped, thereby preventing a safety accident from occurring. Of course, the above control conditions are only preferred embodiments, and may beThe adjustment is performed according to the actual working condition, and the invention is not limited.

In the invention, the air gauge 23 arranged at the devolatilization pipe 2 can detect the actual devolatilization air volume, thereby being capable of acquiring the devolatilization air volume information in time, effectively preventing accidents based on the information, avoiding unplanned parking and ensuring the whole polymer modification process to be safe and effective.

In the invention, besides the potential safety hazard is judged by the devolatilization air volume, the safety of the polymer modification device can be judged by directly detecting the concentration of combustible gas. That is, it is preferable that, in the step of devolatilizing by drawing air into the inside of the barrel by the devolatilization unit, the combustible gas concentration at the devolatilization unit is detected. Specifically, a combustible gas detector is arranged at the devolatilization pipe 2 to detect the concentration of the combustible gas at the devolatilization pipe 2. And judging whether the concentration of the combustible gas is in a safe value range or not according to the detection value of the combustible gas detector, and if the concentration of the combustible gas is in a dangerous value range, taking some precautionary measures.

Specifically, the combustible gas concentration should be less than the combustible gas explosion lower limit concentration value N_mixLower explosive limit concentration value N of combustible gas_mixObtained by the following calculation of formula (2):

wherein m is_kThe formation rate (g/h), M, of the kth combustible component_kIs the molecular mass of the kth combustible component, N_kIs the explosive limit of the kth combustible component.

When the concentration value of the combustible gas detected by the combustible gas detector is higher than the lower explosion limit concentration value N of the combustible gas_mixWhen the concentration exceeds 10%, an alarm can be given by an alarm structure (described in detail below), and when the detected combustible gas concentration value of the combustible gas detector is higher than the combustible gas explosion lower limit concentration value N_mixWhen the content exceeds 50%, the polymer modification apparatus can be stopped, thereby effectively preventing the occurrence of explosion accidents. Of course, the above control conditions are only preferred embodiments, and may be the same as those of the above embodimentsThe adjustment is performed according to the actual working condition, and the invention is not limited.

In the present invention, in order to improve the devolatilization efficiency, a plurality of devolatilization tubes 2 may be provided, and a plurality of devolatilization tubes 2 may be connected in parallel to the induced draft fan 7. A plurality of devolatilization tubes 2 are preferably disposed in the barrel 14 at the melt-blending stage, and the plurality of devolatilization tubes 2 are disposed at equidistant intervals. In addition, the devolatilization process can be carried out under normal pressure, but in the modification process of polyvinyl alcohol, the reaction substance is in the form of glue solution, and in the devolatilization process, along with the continuous removal of methanol, the glue solution has higher and higher viscosity, and when the volatile components are removed, the larger adsorption force from the glue solution needs to be overcome. In view of this, the plurality of devolatilization tubes may include an atmospheric devolatilization tube 21 and/or a vacuum devolatilization tube 22, and in the present invention, it is preferable that the atmospheric devolatilization tube 21 and the vacuum devolatilization tube 22 are sequentially disposed in a material moving direction (from right to left in fig. 2) as shown in fig. 2, thereby performing atmospheric devolatilization and vacuum devolatilization on the reaction substances and greatly improving devolatilization efficiency. The atmospheric devolatilization tube 21 is funnel-shaped, and the vacuum devolatilization tube 22 is a straight tube. To concentrate the vacuum devolatilization. The normal pressure devolatilization pipe 21 and the vacuum devolatilization pipe 22 are combined and arranged in the moving direction of the materials, so that the reaction materials can be devolatilized twice, and the second devolatilization is vacuum devolatilization, so that the content of low-boiling-point components can be greatly reduced, and the explosion hidden danger can be greatly reduced and eliminated.

In addition, the devolatilization process is not only related to the devolatilization air volume, but also the temperature is a major factor affecting the devolatilization process. Thus, preferably, in the step of heating the inside of the cylinder by the heating unit, the temperature inside the cylinder is detected. The specific implementation method comprises the following steps: as shown in fig. 1, a plurality of temperature detectors 31 may be disposed at intervals along the material moving direction inside the cylinder 14 for detecting the temperature inside the cylinder.

According to the temperature characteristic of the reaction process, the interior of the machine barrel can be divided into a temperature rising section, a constant temperature section and a heat preservation section along the material moving direction, and a temperature detector 31 is arranged on each temperature section so as to comprehensively detect the reaction temperature of the polymer modification device. When the reaction temperature is higher than the upper limit of the process temperature, not only the yield of the target product but also the devolatilization efficiency is lowered. In view of this, when the detection value of the temperature detector 31 is greater than 20 ℃ than the preset temperature (upper limit value of the process temperature), an alarm may be issued by an alarm structure (described in detail below), and when the alarm time exceeds 5 minutes or the detection value of the temperature detector 31 is greater than 50 ℃ than the preset temperature, the heating unit may be turned off, thereby stopping heating of the reaction material, and simultaneously increasing the devolatilization air volume of the induced draft fan, cutting off the heat source, and simultaneously reducing heat by the devolatilization air.

In the polymer modification apparatus of the present invention, the predetermined temperature is preferably 150 ℃ to 230 ℃, more preferably 180 ℃ to 210 ℃, but the present invention is not limited thereto, and the reaction temperature is determined according to the plasticizer component and the material properties.

In addition to the reaction temperature of the materials, the amount of plasticizer added is also a factor related to the yield of the target product, and should be kept above a certain value. The purpose of adding the plasticizer is to lower the melting temperature of the material. If the plasticizer flow is too low, the material which should be liquid is changed into a material with higher hardness, and the equipment is damaged during operation, so that the equipment is stopped. In order to avoid this phenomenon, a flow meter 41 is provided on the plasticizer feed tank 13, and the flow meter 41 is used to detect the flow rate of the plasticizer, and when the detection value of the flow meter 41 is less than 10% of the interlock value, the power supply may be cut off and the polymer modification apparatus may be stopped while an alarm is issued by an alarm mechanism (to be described in detail below). The above-mentioned interlock value may be determined depending on the plasticizer component and the material properties.

In addition, static electricity may exist in the powder bin, and in order to prevent the occurrence of static spark, the control method further includes the step of eliminating the static electricity in the raw material before the raw material is fed into the cylinder. The specific implementation method comprises the following steps: and a static electricity eliminating structure 5 is arranged at the bin opening of the powder bin 11 or outside the powder bin. When the electrostatic eliminating structure 5 is disposed at the bin opening of the powder bin 11, the electrostatic eliminating structure 5 may be an electrostatic eliminating rod, but as a more preferable embodiment, the electrostatic eliminating structure 5 is an ion wind electrostatic eliminator disposed outside the powder bin 11, and the electrostatic eliminating effect of the ion wind electrostatic eliminator is very excellent. The static elimination structure can be quickly neutralized with charges accumulated on the surface of the powder, and static hazards of the storage bin part are eliminated and reduced. Among them, it should be noted that when the electrostatic energy for eliminating static electricity is too high, the powder may be ignited to cause loss and contamination of the raw material, and in order to prevent ignition of the powder, the electrostatic energy is preferably controlled to be 300mJ or less.

In addition, as shown in fig. 1, the hopper 12 is shaped like a funnel, and the material thereof is preferably stainless steel. In addition, the loading hopper 12 may include a loading portion and a discharging portion, in order to prevent the damage of the screw 13 caused by the metal impurities entering the cylinder 14 along with the raw materials, a magnetic adsorption member 61 is disposed on the inner wall of the loading portion, and the magnetic adsorption member 61 is preferably a neodymium iron boron magnet. Further preferably, a magnetic filter 62 can also be provided in the blanking portion, the magnetic filter 62 preferably being a magnetic frame. The two-stage metal removing structure is arranged from top to bottom, so that most metals in the raw materials can be removed.

As shown in fig. 4, as a control method of the polymer modification apparatus according to the preferred embodiment of the present invention, the control process of the control unit is as follows: when the detection value of the air flow meter is smaller than the preset air volume, the alarm structure gives an alarm, and when the detection value of the air flow meter is smaller than 0.75 time of the preset air volume, the polymer modification device is stopped; when the combustible gas concentration detected by the combustible gas detector is higher than the combustible gas explosion lower limit concentration value N_mixWhen the concentration value exceeds 10 percent, the alarm structure gives an alarm, and when the concentration value of the combustible gas detected by the combustible gas detector is higher than the concentration value N of the combustible gas explosion lower limit_mixStopping the polymer modification device when the concentration of the polymer is over 50 percent; when the detection value of the temperature detector is higher than the preset temperature by 20 ℃, the alarm structure gives an alarm, and when the alarm time exceeds 5 minutes or the detection value of the temperature detector is higher than the preset temperature by 50 ℃, the heating unit is closed, and the devolatilization air volume of the induced draft fan is increased.

The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.