JP2003147120A - Apparatus and method for thermal decomposition of plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance heat recovery efficiency in an apparatus for thermal decomposition of plastics and for distillation, and to carry on a stable distillation operation. SOLUTION: Combustion gas from a combustion gas-generating means 18 is fed into a heating part 7 of a thermal decomposition means 5. A by-pass line 22 is arranged in parallel with an exhaust gas-feeding line 21 from a heating part 7 of the thermal decomposition means 5 to a heating part 12 of a distillation means 9, and the exhaust gas-feeding line 21 and the by-pass line 22 are equipped with a flow rate regulation means 23 and 24, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal decomposition apparatus and a thermal decomposition method for thermally decomposing a plastic and distilling a product thereof, and more specifically, supplying exhaust gas from the heating section of the thermal decomposition means to the heating section of the distillation means. The present invention relates to a thermal decomposition device and a thermal decomposition method.

[0002]

2. Description of the Related Art Large amounts of plastics are discharged from factory facilities and households. It is desirable to put it in a reusable form, because the waste plastic will be polluted to the environment if it is discharged outside. Therefore, conventionally, a method of thermally decomposing waste plastic by thermal decomposition means and recovering it as fuel oil has been widely adopted.

As the thermal decomposition means, there are a tank type thermal decomposition tank system and a tubular reaction tube system, but the latter reaction tube system is preferable when performing continuous operation. The thermal decomposition means is provided with a heating section using an electric heater heating method or a high temperature gas heating method, but many high temperature gas heating methods using combustion gas generated by the combustion gas generating means are adopted. Since the thermal decomposition temperature is a high temperature in the range of 500 ° C. to 800 ° C. for polystyrene, for example, when the high temperature gas heating method is adopted,
The temperature of the combustion gas is set slightly higher than that.

However, since the added value is not so large only by converting waste plastic into fuel oil, recently, the product by thermal decomposition, that is, the product containing a monomer component derived from waste plastic is further used for distillation means such as a distillation column. A method of recovering a high-purity monomer by distilling with the method is being adopted.

As a thermal decomposition apparatus in which the thermal decomposition means and the distillation means are combined, there is one disclosed in Japanese Patent Laid-Open No. 2001-123007. The thermal decomposition apparatus disclosed in the publication discloses a supply means for continuously melting a styrene copolymer as waste plastic and supplying it to the thermal decomposition means, and a thermal decomposition of the supplied molten plastic in the absence of oxygen. It is provided with a thermal decomposition means, a heating part for heating the thermal decomposition means, a distillation means for distilling a product of thermal decomposition, and a heating part such as a reboiler for heating the distillation means. Then, the exhaust gas discharged from the heating part of the thermal decomposition means is supplied to the heating part of the distillation means as a heat source for heat recovery.

[0006]

However, the above publication makes no mention of the thermal energy balance between the thermal decomposition means and the distillation means, or the adjustment of the flow rate of the exhaust gas discharged from the heating section. According to the research conducted by the present inventors, the thermal decomposition apparatus is efficiently operated by the organically linked operation of the thermal decomposition means and the distillation means, but the heat quantity of the exhaust gas from the thermal decomposition means and the optimum amount required for the distillation means Calories do not always match,
It has been found that comprehensive and stable operation management or operation control is often difficult in systems with exhaust gas lines connected in series. Then, this invention makes it a subject to solve such a problem, and it aims at providing the novel thermal decomposition apparatus and thermal decomposition method for that.

[0007]

To solve the above problems, a plastic thermal decomposition apparatus according to the present invention comprises a thermal decomposition means for thermally decomposing a plastic, a distillation means for distilling a product of the thermal decomposition, and a thermal decomposition means. Pyrolysis comprising combustion gas generating means for supplying combustion gas as a heat source to the heating part of the decomposition means, and exhaust gas discharged from the heating part of the thermal decomposition means is supplied to the heating part of the distillation means through an exhaust gas supply path. It is a device. This apparatus is characterized in that a bypass passage is provided in parallel with the exhaust gas supply passage from the heating portion of the thermal decomposition means to the heating portion of the distillation means, and flow rate adjusting means is provided in each of the exhaust gas supply passage and the bypass passage. (Claim 1).

In the thermal decomposition apparatus, it is possible to provide a temperature control section for controlling the flow rate adjusting means of the exhaust gas supply path so that the temperature of the heating section of the distillation means becomes a preset value.

Further, in any one of the above thermal decomposition devices, a pressure control section for controlling the flow rate adjusting means of the bypass passage may be provided so that the pressure of the exhaust gas supply passage becomes a preset value. ).

Further, in the method for thermally decomposing plastics according to the present invention for solving the above-mentioned problems, the thermally decomposing means having a heating portion for heating the plastics with combustion gas thermally decomposes the plastics, and the product thereof is distilled means. In the thermal decomposition method, the exhaust gas of the combustion gas that is distilled from the heating unit of the thermal decomposition unit is supplied to the heating unit of the distillation unit through the exhaust gas supply passage. And this method, by providing a bypass passage in the exhaust gas supply path, the flow rate of the exhaust gas supplied from the exhaust gas supply path to the heating section is adjusted so that the temperature of the heating section of the distillation means becomes a preset value, The exhaust gas is branched into a bypass passage (claim 4).

In the above thermal decomposition method, the flow rate of the exhaust gas branched to the bypass passage can be adjusted so that the exhaust gas pressure in the exhaust gas supply passage becomes a preset value.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process flow diagram of a thermal decomposition apparatus according to the present invention. In the figure, 1 is a supply means, 2 is a hopper,
3 is a melting part, 4 is an extrusion part, 5 is a thermal decomposition means, 6 is a reaction tube, 7 is a heating part, 8 is a condenser, 9 is a distillation means, 10 is a first distillation column, 11 is a second distillation. Tower, 12 is heating part, 1
3, 14 are condensers, 15 is a decompression means, 16 is a monomer recovery tank, 17 is a heavy component recovery tank, 18 is a combustion gas generation means, 19 is a burner, 20 is a combustion gas supply passage, 21
Is an exhaust gas supply path, 22 is a bypass path, 23 and 24 are flow rate adjusting means, 25 is a temperature control unit, 26 is a temperature detector, and 27 is a temperature detector.
Is a temperature controller, 28 is a pressure controller, 29 is a pressure detector,
30 is a pressure controller, 31 is an exhaust fan, 32 to 34 are pumps, and a to k are pipes.

The supplying means 1 may be an extruder generally used for injection molding of plastic, or an extruder having a similar structure. The supply means 1 shown in the figure is such an extruder, and includes a hopper 2 for temporarily storing waste plastic, a melting section 3 for heating and mixing the plastic supplied from the hopper 2, and melting the melted plastic. An extrusion unit 4 that pushes out with a screw is provided. A plastic suitable for thermal decomposition, such as waste plastic, is finely crushed to a size of about 10 mm or less by a crusher and appropriately supplied to the hopper 2 by an air carrier or the like.

The thermal decomposition means 5 is a tubular reaction tube system,
The reaction tube 6 is arranged in the main body made of refractory insulation material,
The surrounding area is a space forming the heating unit 7. The thermal decomposition apparatus of the present invention may employ a tank-type thermal decomposition tank system. One end of the heating portion 7 is connected to the combustion gas generating means 18 via a combustion gas supply passage 20 formed of a duct or the like, and the other end is connected to an exhaust gas supply passage 21 formed of a duct or the like.
And an outlet side of the exhaust gas supply passage 21 connected to an exhaust fan 31. The combustion gas generating means 18 preferably includes a combustion chamber made of a refractory material, a burner 19 for burning heavy oil, and the like.

One end of the reaction tube 6 is connected to the supply means 1 via a pipe a, and the other end is connected to the condenser 8 via a pipe b. In addition, in order to suppress the generation of by-products due to thermal decomposition as much as possible and to obtain a target monomer component in a high yield, a reduced pressure (for example, a pressure of 20 Toor-1
Pyrolysis is desirable in the range of about 00Toor). The condenser 8 condenses and liquefies the decomposition gas, which is the product of the thermal decomposition means 5, by cooling with cooling water, and the obtained condensate is the first distillation column 10 constituting the distillation means 9. Is supplied to the middle stage.

The distillation means 9 comprises a first distillation column 10 and a second distillation column 11. However, in some cases, if the desired monomer purity does not need to be so high, the distillation means 9 may be composed of only the first distillation column 10. A heating unit 12 including a reboiler is provided below the distillation columns 10 and 11. The column-type distillation unit may be a tray type or a filling type filled with lashing, poling, or other high-performance ordered packing, but when performing vacuum distillation (for example, 20Toor-100Toor) that can distill at a low temperature. The latter filling method is desirable.

A condenser 13 for cooling and condensing distillate components is connected to the top of the first distillation column 10, and the decompression means constituted by a vacuum pump or the like via the pipe e to the condenser 13. 15 are connected. The condensate obtained in the condenser 13 is recirculated to the top of the tower through a reflux pipe d provided with a pump 32, and a slight amount of gas components that do not condense (usually about 1% of the amount of plastic input) is in the pipe e. Then, it is discharged from the outlet side of the pressure reducing means 15. Since this discharged component contains a malodorous substance, it is desirable to incinerate it in an incinerator or combust it in the combustion gas generating means 18.

A pipe f for discharging the high boiling point component separated by distillation is connected to the lower part of the first distillation column 10 (the reboiler part constituting the heating part 12 in this example), and the pipe f is the second pipe. It is connected to the middle stage of the distillation column 11. The second distillation column 11 is also configured similarly to the first distillation column 10. That is, a condenser 14 for cooling and condensing distillate components is connected to the top of the second distillation column 11, and the obtained condensate is refluxed to the top of the column through a reflux pipe i provided with a pump 33. To be done.
Further, the pressure reducing means 15 is connected to the condenser 14 via a pipe e.
Are connected to discharge a small amount of uncondensed components from the outlet side of the pressure reducing means 15.

Further, a monomer recovery tank 16 is connected to the condenser 14 via a pipe h, and a high-purity monomer component which is a condensate obtained in the condenser 14 is recovered in the monomer recovery tank 16. On the other hand, a heavy component tank 17 is connected to the bottom of the second distillation column 11 via a pipe j, and the heavy component separated by distillation is stored in the heavy component tank 17.

First distillation column 10 and second distillation column 11
An exhaust gas supply path 21 is connected to each of the heating units 12, and a flow rate adjusting means 23 including a remotely operable adjustment valve or an adjustment damper is provided in the exhaust gas supply path 21. Each flow rate adjusting unit 23 is controlled by an independent temperature control unit 25. Each temperature control unit 25 includes a temperature detector 26 that detects the temperature of the heating unit 12, and a temperature controller 27 that drives and controls the flow rate adjusting unit 23 so that the detected temperature value becomes a preset value. . The temperature controller 27 preferably has a PID (proportional / integral / derivative) control mode.

A bypass line 22 is connected to the exhaust gas supply line 21, and a flow rate adjusting unit 24 is provided in the bypass line 22. The flow rate adjusting unit 24 is controlled by a pressure control unit 28. The pressure control unit 28 includes a pressure detector 29 that detects the pressure of the exhaust gas supply passage 21, and a pressure controller 30 that drives and controls the flow rate adjusting means 24 so that the detected pressure value becomes a preset value. . The pressure controller 30 is also a PI
It is desirable to use one that has a D control mode.

Next, a method of thermally decomposing a plastic using the above-mentioned thermal decomposition apparatus will be described. The following conditions apply when polystyrene is used as the plastic, but for other thermally decomposable plastics,
Needless to say, it can be carried out according to this.

First, the pressure reducing means 15 is operated to operate the reaction tube 6, the first distillation column 10 and the second distillation column 1 of the thermal decomposition means 5.
Each of the internal air of No. 1 and the inside of the pipes connecting them are replaced with an inert gas such as nitrogen so as to be in an oxygen-free state, and their internal pressure is, for example, 20 Toor-10.
A pressure control valve or the like provided in the pressure reducing means 15 is adjusted so as to be 0Toor. At the same time, the combustion gas generating means 18
Is operated to supply combustion gas to the heating section 7 of the thermal decomposition means 5 and the temperature of the reaction tube 6 is raised to, for example, 500 ° C to 800 ° C.

Further, the exhaust gas discharged from the heating section 7 to the exhaust gas supply passage 21 is supplied to each heating section 12 of the first distillation column 10 and the second distillation column 11 to raise them to a predetermined temperature. The temperature of each heating unit 12 is adjusted to a range of about 70 to 150 ° C. by the flow rate adjusting unit 23, which is driven and controlled by the temperature control unit 25.

When the exhaust fan 31 is operated with a constant suction force, the flow rate adjusting means 23 adjusts the flow rate of the exhaust gas in the exhaust gas supply passage 21. If the flow rate of the exhaust gas changes, the flow rate of the combustion gas supplied to the heating unit 7 of the thermal decomposition means 5 also changes accordingly, which is not preferable. That is, the thermal energy consumed by the thermal decomposition means 5 must be uniquely determined by the amount of heat required for the thermal decomposition of the plastic, and it is not preferable that it fluctuates due to other factors.

Therefore, in the thermal decomposition apparatus of the present invention, the flow rate adjusting means 24 of the bypass passage 22 is adjusted in inverse proportion to the flow rate adjusting means 23 so that the combustion gas flow rate can be maintained constant. Although it is possible to perform the inverse proportional control manually to some extent, it is desirable to perform it automatically. In the present embodiment, the combustion gas flow rate is maintained at a predetermined value by automatically controlling the pressure of the exhaust gas supply passage 21. That is, by automatically controlling the pressure of the exhaust gas supply passage 21 to a predetermined value, the pressure on the upstream side of that,
In particular, the internal pressure of the combustion gas generating means 18 can be stabilized.

When the furnace pressure of the combustion gas generating means 18 fluctuates, the combustion of the burner of the combustion gas generating means 18 becomes unstable, and especially when the flow rate adjusting means 23 of the exhaust gas supply passage 21 is fully closed. Also fluctuates accordingly, and the combustion instability becomes larger. The optimum combustion atmosphere of the burner 19 in the combustion gas generating means 18 adopted in the present embodiment is a negative pressure region where the furnace pressure is several tens of mm of water head.

In this embodiment, the pressure controller 28 adjusts the flow rate adjusting means 24 provided in the bypass passage 22 so that the pressure in the exhaust gas supply passage 21 becomes a preset value. For example, the exhaust gas flow rate adjusting means 23 of the exhaust gas supply passage 21
Is adjusted in the closing direction, the pressure in the exhaust gas supply passage 21 rises above a preset value. Then pressure detector 2
The pressure controller 30 that receives the pressure increase signal from the flow controller 9 returns the pressure to a preset value.
Adjust 4 to open. On the contrary, when the exhaust gas supply flow rate increases and the pressure of the exhaust gas supply path 21 decreases, the flow rate adjusting means 24 is adjusted in the closing direction so that the bypass flow rate of the bypass path 22 decreases accordingly.

Next, the plastic to be pyrolyzed is continuously supplied from the hopper 2 to the melting section 3, where it is heated to about 200 ° C. to be melted and discharged from the extruding section 4 into the pipe a. The molten plastic flowing into the pipe a is pyrolyzed by the thermal decomposition means 5.
Is continuously supplied to one end of the reaction tube 6 and is heated by the heating unit 7 while passing through the reaction tube 6 to be thermally decomposed.

The product produced by thermal decomposition and evaporated is
It is discharged from the pipe b, cooled in the condenser 8 and condensed. For example, polystyrene is 500 ° C. to 800 ° C., pressure is 50 Too
When pyrolyzed by r, about 70% of the evaporated product becomes a styrene monomer, and in addition, styrene dimer, styrene trimer, toluene, and other high boiling point components are produced as by-products.

The condensate has a first pressure adjusted to the above pressure range.
Is supplied to the middle stage of the distillation column 10 and is separated by vacuum distillation into a low boiling point component such as toluene and a high boiling point component containing styrene. The distillation temperature can be controlled by the temperature of the heating section 12 provided therebelow, and is usually 50 to 60.
Operate in the range of about ℃. The low boiling point component is about 3 to 5% of the plastic supplied to the thermal decomposition means 5, and most of it is condensed in the condenser 13 and refluxed to the top of the first distillation column 10 by the pump 32. The reflux ratio is usually 20-5.
It is about 0.

The high boiling point components separated by the distillation operation are discharged from the lower part of the first distillation column 10. Since the temperature of the high boiling point component at the time of discharge is considerably high, it is desirable to appropriately cool it with a cooler or the like not shown. The high boiling point component is then fed to the middle stage of the second distillation column 11 adjusted to the above pressure range, and further distilled under reduced pressure there. The temperature of the second distillation column 11 can also be adjusted by the temperature of the heating section 12 provided below it, and is usually set in the range of about 60 to 70 ° C.

In the second distillation column 11, the styrene monomer, which is a low-boiling component distilled from the top of the column, is cooled and condensed in the condenser 14, and the condensate is recovered in the monomer recovery tank 16 through the pipe h. Part is refluxed by the pump 33 to the top of the column. The reflux ratio is usually about 2-3.

The styrene dimer, styrene trimer, and other heavy components separated in the second distillation column 11 are
It is about 20 to 30% of the supplied components, and they are recovered from the lower part of the second distillation column 11 through the pipe j to the heavy component recovery tank 17. The heavy component stored in the heavy component recovery tank is supplied to the burner 19 of the combustion gas generating means 18 by the pump 34, and is burned there as fuel.
By such an operation, styrene monomer having a purity of 99% is recovered by about 70% of the amount of the polymer supplied.

When the temperature of the combustion gas supplied to the heating part 7 of the thermal decomposition means 5 is about 800 ° C., the temperature of the exhaust gas discharged from the heating part 7 is about 600 ° C., and the high temperature exhaust gas is supplied to the exhaust gas supply path. It is supplied to the heating parts 12 of the first distillation column 10 and the second distillation column 11 via 21 respectively.

The temperature of each heating section 12 is adjusted by the flow rate adjusting means 23 controlled by the temperature adjusting section 25 as described above, and the pressure of the exhaust gas supply path 21 is controlled by the pressure control section 28. 22 flow rate adjusting means 24
Is adjusted by. Then, by the coordinated adjusting operation of the flow rate adjusting means 23 and the flow rate adjusting means 24, the thermal energy consumed by the thermal decomposition means 5 and the distillation means 9 composed of the first distillation column 10 and the second distillation column 11 are obtained. Dissimilarity of consumed heat energy is eliminated and the heat balance of the entire system is stabilized. Further, the combustion instability of the burner 19 in the combustion gas generating means 18 is eliminated.

[0037]

As described above, the thermal decomposition apparatus according to the present invention is constructed so that the exhaust gas discharged from the heating section of the thermal decomposition means is supplied to the heating section of the distillation means through the exhaust gas supply passage, so that the thermal energy Recovery rate is improved. Further, a bypass passage is provided in parallel with the exhaust gas supply passage from the heating portion of the thermal decomposition means to the heating portion of the distillation means, and flow rate adjusting means is provided in each of the exhaust gas supply passage and the bypass passage. It is possible to eliminate the discrepancy between the heat energy consumed by the and the heat energy consumed by the distillation means and stabilize the heat balance of the entire system.

In the above thermal decomposition apparatus, it is possible to provide a temperature control section for controlling the flow rate adjusting means of the exhaust gas supply path so that the temperature of the heating section of the distillation means becomes a preset value. By doing so, the temperature of the distillation means can be automatically adjusted to stabilize the distillation operation.

Further, in any one of the above thermal decomposition devices, it is possible to provide a pressure control section for controlling the flow rate adjusting means of the bypass passage so that the pressure of the exhaust gas supply passage becomes a preset value. By doing so, in addition to the effect of stabilizing the distillation operation, the combustion instability of the burner in the combustion gas generating means can be eliminated.

Further, in the plastic thermal decomposition method according to the present invention, since the exhaust gas of the combustion gas discharged from the heating part of the thermal decomposition means is supplied to the heating part of the distillation means through the exhaust gas supply path, Energy recovery rate is improved.
Furthermore, a bypass passage is provided in the exhaust gas supply passage, and the flow rate of the exhaust gas supplied from the exhaust gas supply passage to the heating portion is adjusted so that the temperature of the heating portion of the distillation means becomes a preset value, and the surplus exhaust gas is bypassed. Since the heat energy consumed by the thermal decomposition means and the heat energy consumed by the distillation means can be resolved, the heat balance of the entire system is stabilized.

Furthermore, in the above-mentioned thermal decomposition method, the flow rate of the exhaust gas branched to the bypass passage can be adjusted so that the exhaust gas pressure in the exhaust gas supply passage becomes a preset value. By doing so, in addition to the above-described stabilizing effect, the combustion instability of the burner in the combustion gas generating means can be eliminated.

[Brief description of drawings]

FIG. 1 is a process flow diagram of a thermal decomposition apparatus according to the present invention.

[Explanation of symbols]

1 supply means 2 hoppers 3 fusion zone 4 Extruder 5 Pyrolysis means 6 reaction tubes 7 heating section 8 condenser 9 Distillation means 10 First distillation column 11 Second distillation column 12 heating part 13,14 condenser 15 Decompression means 16 Monomer recovery tank 17 Heavy component recovery tank 18 Combustion gas generation means 19 burners 20 Combustion gas supply path 21 Exhaust gas supply channel 22 Bypass 23 Flow rate adjusting means 24 Flow rate adjusting means 25 Temperature controller 26 Temperature detector 27 Temperature controller 28 Pressure control unit 29 Pressure detector 30 Pressure controller 31 Exhaust fan 32-34 pump ak piping

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshinori Koyama             5-37 Kamata, Ota-ku, Tokyo             Runt Construction Co., Ltd. F term (reference) 4D076 AA16 AA22 BB03 BB23 CB11                       CD22 DA07 DA28 EA12Y                       EA16Y FA02 FA12 HA03                       JA02 JA04                 4F301 AA15 CA09 CA27 CA36 CA42                       CA52 CA64 CA72 CA73 CA74                 4H006 AA04 AA05 AB46 AC91 AD11                       BC10 BC11

Claims (5)

[Claims] 1. A thermal decomposition means 5 for thermally decomposing a plastic.
A distillation means 9 for distilling a product of the thermal decomposition; and a combustion gas generating means 18 for supplying a combustion gas as a heat source to the heating part 7 of the thermal decomposition means 5. In the thermal decomposition apparatus in which the exhaust gas to be discharged is supplied to the heating section 12 of the distillation means 9 through the exhaust gas supply path 21, the exhaust gas supply path 21 from the heating section 7 of the thermal decomposition means 5 to the heating section 12 of the distillation means 9 is provided. Bypass 2 in parallel with
2 is provided, and the exhaust gas supply passage 21 and the bypass passage 22 are provided with flow rate adjusting means 23 and 24, respectively. 2. A temperature control section 25 for controlling the flow rate adjusting means 23 of the exhaust gas supply passage 21 is provided so that the temperature of the heating section 12 of the distillation means 9 becomes a preset value. 1. The thermal decomposition apparatus for plastic according to 1. 3. The pressure control unit 28 for controlling the flow rate adjusting means 24 of the bypass passage 22 is provided so that the pressure of the exhaust gas supply passage 21 becomes a preset value. 2. The thermal decomposition apparatus for plastic according to 2. 4. The plastic is thermally decomposed by a thermal decomposition means 5 having a heating part 7 for heating the plastic with combustion gas,
The pyrolysis method in which the product is distilled by the distillation means 9 and the exhaust gas of the combustion gas discharged from the heating part 7 of the thermal decomposition means 5 is supplied to the heating part 12 of the distillation means 9 through the exhaust gas supply path 21. At the exhaust gas supply path 21, the bypass path 2
2 is provided and the flow rate of the exhaust gas supplied from the exhaust gas supply passage 21 to the heating unit 12 of the distillation means 9 is adjusted so that the temperature of the heating part 12 of the distillation means 9 becomes a preset value, and excess exhaust gas is removed. A thermal decomposition method for plastics, characterized by branching to a bypass 22. 5. The method of thermal decomposition of plastic according to claim 4, wherein the flow rate of the exhaust gas branched to the bypass passage 22 is adjusted so that the exhaust gas pressure of the exhaust gas supply passage 21 becomes a preset value. .