JP4003160B2 - Pyrolysis apparatus and pyrolysis method for plastic - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal decomposition apparatus and a thermal decomposition method for thermally decomposing plastic and distilling a product thereof, and more specifically, a thermal decomposition apparatus configured to supply exhaust gas from a heating section of a thermal decomposition means to a heating section of a distillation means. And a thermal decomposition method.
[0002]
[Prior art]
Large quantities of plastics are discharged from factory facilities and households. If waste plastic is discharged to the outside as it is, the environment will be polluted, so it is desirable to make it reusable. Therefore, conventionally, a method of thermally decomposing waste plastic by a thermal decomposition means and recovering it as fuel oil has been widely adopted.
[0003]
As the thermal decomposition means, there are a tank-type pyrolysis tank method and a tube-shaped reaction tube method, but the latter reaction tube method is desirable when continuous operation is performed. The pyrolysis means is provided with a heating section using an electric heater heating method or a high temperature gas heating method, and many high temperature gas heating methods using combustion gas generated by the combustion gas generation means are employed. The thermal decomposition temperature is, for example, a high temperature in the range of 500 ° C. to 800 ° C. for polystyrene. Therefore, when the high temperature gas heating method is adopted, the temperature of the combustion gas is set slightly higher than that.
[0004]
However, since the added value is not so great just by converting the waste plastic into fuel oil, recently, the product by pyrolysis, that is, the product containing monomer components derived from the waste plastic is further distilled by distillation means such as a distillation tower. Also, a method for recovering a high-purity monomer is being adopted.
[0005]
As a thermal decomposition apparatus combining a thermal decomposition means and a distillation means, there is one disclosed in JP 2001-123007 A. The thermal decomposition apparatus disclosed in the publication discloses a supply unit that continuously melts a styrene copolymer as waste plastic and supplies it to the thermal decomposition unit, and thermally decomposes the supplied molten plastic in the absence of oxygen. A thermal decomposition unit, a heating unit for heating the thermal decomposition unit, a distillation unit for distilling the product of thermal decomposition, and a heating unit such as a reboiler for heating the distillation unit are provided. The exhaust gas discharged from the heating section of the thermal decomposition means is supplied to the heating section of the distillation means as a heat source for heat recovery.
[0006]
[Problems to be solved by the invention]
However, the above publication does not mention anything about the thermal energy balance between the thermal decomposition means and the distillation means or the flow rate adjustment of the exhaust gas discharged from the heating section. According to the study by the present inventors, the pyrolysis apparatus is efficiently operated by an organic cooperative operation of the pyrolysis means and the distillation means, but the optimum amount of heat of the exhaust gas from the pyrolysis means and the distillation means is required. It has been found that the total amount of heat does not always match, and comprehensive and stable operation management or operation control is often difficult in a system having exhaust gas passages connected in series.
Therefore, the present invention has an object to solve such a problem, and an object thereof is to provide a new thermal decomposition apparatus and a thermal decomposition method therefor.
[0007]
[Means for Solving the Problems]
The plastic pyrolysis apparatus according to the present invention for solving the above-mentioned problems includes a thermal decomposition means 5 for thermally decomposing plastic, a distillation means 9 for distilling a product resulting from the thermal decomposition, and a heating section 7 of the thermal decomposition means 5. Is provided with combustion gas generation means 18 for supplying combustion gas as a heat source , exhaust gas from the heating section 7 of the thermal decomposition means 5 is discharged to the exhaust gas supply path 21, and the distillation means 9 is heated in the exhaust gas supply path 21. part 12 is arranged in the pyrolyzer which is adapted to supply exhaust gas, a bypass passage 22 of the exhaust gas provided in parallel to the heating portion 12 of the distillation unit 9, and the exhaust gas supply path to the heating portion 12 of the distillation unit each provided flow rate adjusting means 23, 24 to the bypass passage 22, the exhaust gas supply passage of the flow rate adjusting means 23 to the heating unit 12 to a value that the temperature of the heating portion 12 of the distillation unit 9 is predetermined A temperature controller 25 to be controlled is connected, and the pressure of the exhaust gas supply path 21 to which the exhaust gas discharged from the heating section 7 is supplied to the flow rate adjusting means 24 provided in the bypass path 22 is a preset value. A pressure control unit 28 is connected to control so as to become (Claim 1).
[0010]
Further, in the method for thermally decomposing plastic according to the present invention for solving the above-mentioned problems, the plastic is pyrolyzed by the pyrolyzing means 5 having the heating section 7 for heating the plastic with combustion gas, and the product is distilled by means 9 And the exhaust gas of the combustion gas from the heating part 7 of the thermal decomposition means 5 is discharged to the exhaust gas supply path 21, and the heating part 12 of the distillation means 9 is arranged in the exhaust gas supply path 21 to supply the exhaust gas. In the pyrolysis method as described above,
An exhaust gas bypass path 22 is provided in parallel with the heating section 12 of the distillation means 9 so that the temperature of the heating section 12 of the distillation means 9 is set to a preset value from the exhaust gas supply path 21 to the heating section of the distillation means 9. The exhaust gas flow rate supplied to the exhaust gas supply channel 21 is adjusted, the exhaust gas flow rate of the bypass channel 22 is adjusted so that the pressure of the exhaust gas in the exhaust gas supply channel 21 becomes a preset value, and excess exhaust gas is branched to the bypass channel 22. (Claim 2 ).
[0012]
DETAILED DESCRIPTION OF THE INVENTION
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 section, 4 is an extrusion section, 5 is a thermal decomposition means, 6 is a reaction tube, 7 is a heating section, 8 is a condenser, 9 is a distillation means, 10 is 1st distillation column, 11 is 2nd distillation column, 12 is a heating part, 13 and 14 are condensers, 15 is a decompression means, 16 is a monomer recovery tank, 17 is a heavy component recovery tank, 18 is combustion gas generation Means, 19 is a burner, 20 is a combustion gas supply path, 21 is an exhaust gas supply path, 22 is a bypass path, 23 and 24 are flow rate adjusting means, 25 is a temperature controller, 26 is a temperature detector, 27 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.
[0013]
As the supply means 1, an extruder generally used for plastic injection molding or an extruder having a similar structure can be used. The supply means 1 shown in the figure is such an extruder, and a hopper 2 that temporarily stores waste plastic, a melting part 3 that heats and melts the plastic supplied from the hopper 2, and rotates the molten plastic. The extrusion part 4 extruded with a screw is provided. A plastic suitable for thermal decomposition such as waste plastic is finely pulverized to about 10 mm or less by a pulverizer, and is appropriately supplied to the hopper 2 by an air conveyor or the like.
[0014]
The thermal decomposition means 5 is a tubular reaction tube system, in which a reaction tube 6 is arranged in a main body made of a refractory heat insulating material, and its periphery is a space that constitutes the heating unit 7. In addition, the thermal decomposition apparatus of this invention can also employ | adopt a tank-shaped thermal decomposition tank system.
One end of the heating unit 7 is connected to the combustion gas generating means 18 via a combustion gas supply path 20 made of a duct or the like, and the other end is an exhaust gas supply path 21 made of a duct or the like, and the heating part of the distillation means 9. 12 and a bypass path 22 in parallel with the heating unit 12 , and their outlet sides are connected to an exhaust fan 31. The combustion gas generating means 18 preferably includes a combustion chamber made of a refractory material and a burner 19 for burning heavy oil.
[0015]
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 order to suppress generation of by-products due to thermal decomposition as much as possible and to obtain a target monomer component with high yield, it is desirable to perform thermal decomposition under reduced pressure (for example, a pressure range of about 20 Toor to 100 Toor).
The condenser 8 condenses and liquefies the decomposition gas, which is a product of the thermal decomposition means 5, by cooling with cooling water, and the obtained condensate is a first distillation column 10 constituting the distillation means 9. To the middle stage.
[0016]
The distillation means 9 includes a first distillation column 10 and a second distillation column 11. However, in some cases, when the target monomer purity does not have to be so high, the distillation means 9 may be composed of only the first distillation column 10. A heating unit 12 made of a reboiler is provided below the distillation columns 10 and 11. The tower-type distillation section has a tray type or a packed type filled with lashing, poling, and other high-performance ordered packings. However, when performing vacuum distillation (for example, 20 Toor to 100 Toor) that can be distilled at a low temperature. The latter filling type is desirable.
[0017]
A condenser 13 that cools and condenses the distillate component is connected to the top of the first distillation column 10, and a decompression means 15 configured by a vacuum pump or the like is connected to the condenser 13 via a pipe e. Is done. The condensate obtained in the condenser 13 is refluxed to the top of the tower by a reflux pipe d provided with a pump 32, and a slight amount of gas components (usually about 1% of the amount of plastic input) is not condensed. Then, it is discharged from the outlet side of the decompression means 15. Since this exhaust component contains malodorous substances, it is desirable to incinerate in an incinerator or to combust in the combustion gas generating means 18.
[0018]
A pipe f for discharging a high-boiling component separated by distillation is connected to the lower part of the first distillation column 10 (in this example, the reboiler part constituting the heating unit 12), and the pipe f is connected to the second distillation column 11. Connected to the middle stage.
The second distillation column 11 is configured in the same manner as the first distillation column 10. That is, a condenser 14 for cooling and condensing the distillate component is connected to the top of the second distillation column 11, and the resulting condensate is refluxed to the top of the tower through a reflux pipe i provided with a pump 33. Is done. Further, the pressure reducing means 15 is connected to the condenser 14 via a pipe e, and a small amount of uncondensed components is discharged from the outlet side of the pressure reducing means 15.
[0019]
Furthermore, a monomer recovery tank 16 is connected to the condenser 14 via a pipe h, and a high-purity monomer component that 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 a heavy component separated by distillation is stored in the heavy component tank 17.
[0020]
An exhaust gas supply path 21 is connected to each heating unit 12 of the first distillation column 10 and the second distillation column 11, and a flow rate adjusting means including an adjustment valve or an adjustment damper that can be remotely operated to the exhaust gas supply path 21. 23 is provided.
Each flow rate adjusting means 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 means 23 so that the temperature detection value becomes a preset value. . The temperature controller 27 preferably has a PID (proportional / integral / derivative) control mode.
[0021]
A bypass path 22 is connected in parallel to the heating unit 12 of the exhaust gas supply path 21 , and a flow rate adjusting unit 24 is provided in the bypass path 22, and 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 in the exhaust gas supply passage 21 and a pressure controller 30 that drives and controls the flow rate adjusting unit 24 so that the detected pressure value becomes a preset value. . It is desirable to use the pressure controller 30 having the PID control mode.
[0022]
Next, a method for thermally decomposing plastic using the above pyrolyzer will be described. In addition, although the following conditions are the cases where polystyrene is used as a plastic, it goes without saying that other thermally decomposable plastics can be implemented in accordance with this.
[0023]
First, the decompression means 15 is operated, and the reaction tank 6 of the thermal decomposition means 5, the internal air of the first distillation column 10 and the second distillation column 11, and the pipes connecting them to the interior of the piping are connected to a While substituting with active gas to make it oxygen-free, the pressure adjusting valve provided in the decompression means 15 is adjusted so that the internal pressure thereof becomes, for example, 20 Toor to 100 Toor. At the same time, the combustion gas generating means 18 is operated to supply the combustion gas to the heating section 7 of the thermal decomposition means 5, and the temperature of the reaction vessel 6 is raised to, for example, 500 ° C to 800 ° C.
[0024]
Further, the exhaust gas discharged from the heating unit 7 to the exhaust gas supply path 21 is supplied to each heating unit 12 of the first distillation column 10 and the second distillation column 11, and the temperature is raised 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 that is driven and controlled by the temperature control unit 25.
[0025]
When the exhaust fan 31 is operated with a constant suction force, the exhaust gas flow rate in the exhaust gas supply path 21 is changed by the adjustment of the flow rate adjusting means 23. If the exhaust gas flow rate changes, the flow rate of the combustion gas supplied to the heating unit 7 of the thermal decomposition means 5 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 the thermal energy fluctuates due to other factors.
[0026]
Therefore, in the thermal decomposition apparatus of the present invention, the flow rate of the combustion gas can be kept constant by adjusting the flow rate adjusting means 24 of the bypass passage 22 in inverse proportion to the flow rate adjusting means 23. Although this inverse proportional control can be performed 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, in particular, the furnace pressure of the combustion gas generating means 18 can be stabilized.
[0027]
When the furnace pressure of the combustion gas generating means 18 fluctuates, the combustion of the burner of the combustion gas generating means 18 also becomes unstable. In particular, when the flow rate adjusting means 23 of the heating unit 12 is fully closed, the furnace pressure also changes accordingly. Fluctuates and combustion instability becomes greater. Note that the optimum combustion atmosphere of the burner 19 in the combustion gas generation means 18 employed in the present embodiment is a negative pressure region in which the pressure in the furnace is several tens of millimeters of water head.
[0028]
In the present embodiment, the flow rate adjusting means 24 provided in the bypass path 22 is adjusted by the pressure control unit 28 so that the pressure of the exhaust gas supply path 21 becomes a preset value. For example, when the exhaust gas flow rate adjusting means 23 of the heating unit 12 is adjusted in the closing direction, the pressure of the exhaust gas supply path 21 rises from a preset value. Then, the pressure controller 30 that has received the pressure increase signal from the pressure detector 29 adjusts the flow rate adjusting means 24 in the opening direction so as to return the pressure to a preset value. Conversely, when the exhaust gas supply flow rate increases and the pressure of the exhaust gas supply channel 21 decreases, the flow rate adjusting means 24 is adjusted in the closing direction so that the bypass flow rate of the bypass channel 22 decreases accordingly.
[0029]
Next, the plastic to be thermally decomposed is continuously supplied from the hopper 2 to the melting section 3 where it is heated to about 200 ° C. to melt and discharged from the extrusion section 4 to the pipe a. The molten plastic that has flowed into the pipe a is continuously supplied to one end of the reaction tube 6 in the thermal decomposition means 5, and is heated and thermally decomposed by the heating unit 7 while passing through the reaction tube 6.
[0030]
The product generated and evaporated by thermal decomposition is discharged from the pipe b, cooled by the condenser 8, and condensed. For example, when polystyrene is pyrolyzed at 500 ° C. to 800 ° C. under a pressure of 50 Torr, about 70% of the evaporated product becomes styrene monomer, and other products such as styrene dimer, styrene trimer, toluene, and other high-boiling components are by-products. Generate as
[0031]
The condensate is supplied to the middle stage of the first distillation column 10 adjusted to the above pressure range, and is separated into a low boiling point component such as toluene and a higher boiling point component containing styrene by vacuum distillation. The distillation temperature can be controlled by the temperature of the heating unit 12 provided in the lower part, and is usually operated in the range of about 50 to 60 ° C.
The low boiling point component is about 3 to 5% of the plastic supplied to the thermal decomposition means 5, most of which is condensed by the condenser 13 and refluxed to the top of the first distillation column 10 by the pump 32. The reflux ratio is usually about 20-50.
[0032]
The high-boiling 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 quite high, it is desirable to cool appropriately with a cooler (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, where it is further distilled under reduced pressure. The temperature of the 2nd distillation column 11 can also be adjusted with the temperature of the heating part 12 provided in the lower part, and is normally set to the range of about 60-70 degreeC.
[0033]
In the second distillation column 11, the styrene monomer, which is a low boiling point component distilled from the top of the column, is cooled and condensed by the condenser 14, and the condensate is recovered from the pipe h to the monomer recovery tank 16, and partly pumped. 33 reflux to the top of the column. The reflux ratio is usually about 2-3.
[0034]
The styrene dimer, styrene trimer, and other heavy components separated in the second distillation column 11 are about 20 to 30% of the supplied components, and they are connected to the pipe j from the lower portion of the second distillation column 11. After that, it is recovered in 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 burned there as fuel. By such an operation, styrene monomer having a purity of 99% is recovered about 70% of the polymer supply amount.
[0035]
When the temperature of the combustion gas supplied to the heating unit 7 of the thermal decomposition means 5 is about 800 ° C., the temperature of the exhaust gas discharged from the heating unit 7 is about 600 degrees, and the high temperature exhaust gas passes through the exhaust gas supply path 21. It is supplied to the heating unit 12 of the first distillation column 10 and the second distillation column 11, respectively.
[0036]
The temperature of each heating unit 12 is adjusted by the flow rate adjusting means 23 controlled by the temperature adjusting unit 25 as described above, and the pressure of the exhaust gas supply path 21 is further controlled by the pressure control unit 28. Adjustment is performed by the adjusting means 24. Then, by cooperative adjustment 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 constituted by the first distillation column 10 and the second distillation column 11 are changed. The mismatch of the 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 generation means 18 is also eliminated.
[0037]
【The invention's effect】
As described above, the thermal decomposition apparatus according to the present invention discharges exhaust gas from the heating section of the thermal decomposition means to the exhaust gas supply path, and supplies the exhaust gas by arranging the heating section of the distillation means in the exhaust gas supply path. As a result, the heat energy recovery rate is improved. Furthermore, since a bypass passage is provided in parallel with the heating section of the distillation means, and a flow rate adjusting means is provided for each of the exhaust gas supply path and the bypass path to the heating section, the heat energy consumed by the pyrolysis means and the distillation due to these adjustments. The inconsistency of the heat energy consumed by the means can be eliminated, and the heat balance of the entire system is stabilized.
Further, since the pressure control unit for controlling the flow rate adjusting means of the bypass path is provided so that the pressure of the exhaust gas supply path becomes a preset value, in addition to the effect of stabilizing the distillation operation, the burner in the combustion gas generating means The combustion instability can be eliminated.
[0038]
In the above thermal decomposition apparatus, a temperature control unit for controlling the flow rate adjusting unit of the exhaust gas supply path can be provided so that the temperature of the heating unit of the distillation unit becomes a preset value. In this way, the distillation operation can be stabilized by automatically adjusting the temperature of the distillation means.
[0040]
The plastic pyrolysis method according to the present invention exhausts the exhaust gas of combustion gas from the heating section of the pyrolysis means to the exhaust gas supply path, and the heating section of the distillation means is disposed in the exhaust gas supply path to discharge the exhaust gas. Since the energy is supplied, the heat energy recovery rate is improved. Further, a bypass path is provided in parallel with the heating unit of the distillation unit, and the flow rate of the exhaust gas supplied to the heating unit is adjusted so that the temperature of the heating unit of the distillation unit becomes a preset value, thereby bypassing excess exhaust gas. Since the branching is made to the path, the mismatch between the thermal energy consumed by the thermal decomposition means and the thermal energy consumed by the distillation means can be eliminated, and the thermal balance of the entire system is stabilized.
[0041]
Furthermore, since the flow rate of the exhaust gas branched to the bypass passage is adjusted so that the exhaust gas pressure in the exhaust gas supply passage becomes a preset value, in addition to the stabilization effect, the combustion instability of the burner in the combustion gas generation means is reduced. Can be resolved.
[Brief description of the drawings]
FIG. 1 is a process flow diagram of a thermal decomposition apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Supply means 2 Hopper 3 Melting part 4 Extrusion part 5 Thermal decomposition means 6 Reaction tube 7 Heating part 8 Condenser 9 Distilling means 10 First distillation tower 11 Second distillation tower 12 Heating parts 13, 14 Condenser 15 Decompression means 16 Monomer recovery tank 17 Heavy component recovery tank 18 Combustion gas generation means 19 Burner 20 Combustion gas supply path 21 Exhaust gas supply path 22 Bypass path 23 Flow rate adjustment means 24 Flow rate adjustment means 25 Temperature controller 26 Temperature detector 27 Temperature controller 28 Pressure controller 29 Pressure detector 30 Pressure controller 31 Exhaust fans 32 to 34 Pumps a to k Piping

Claims (2)

A thermal decomposition means 5 for thermally decomposing plastic, a distillation means 9 for distilling the product of the thermal decomposition, and a combustion gas generating means 18 for supplying a combustion gas as a heat source to the heating section 7 of the thermal decomposition means 5, In the thermal decomposition apparatus in which the exhaust gas from the heating section 7 of the thermal decomposition means 5 is discharged to the exhaust gas supply path 21 and the heating section 12 of the distillation means 9 is arranged in the exhaust gas supply path 21 to supply the exhaust gas .
Wherein the heating portion 12 of the distillation unit 9 the exhaust gas bypass passage 22 provided in parallel, respectively provided flow rate adjusting means 23, 24 to the exhaust gas supply passage and the bypass passage 22 to the heating portion 12 of the distillation unit, the heating unit 12 A temperature control unit 25 for controlling the temperature of the heating unit 12 of the distillation unit 9 to be a predetermined value is connected to the flow rate adjustment unit 23 of the exhaust gas supply path to the exhaust path, and is provided in the bypass path 22. The flow rate adjusting unit 24 is connected to a pressure control unit 28 for controlling the pressure of the exhaust gas supply path 21 to which the exhaust gas discharged from the heating unit 7 is supplied to a preset value. Plastic pyrolysis equipment. The plastic is pyrolyzed by the pyrolysis means 5 having the heating section 7 for heating the plastic with the combustion gas, the product is distilled by the distillation means 9, and the exhaust gas of the combustion gas from the heating section 7 of the pyrolysis means 5 is removed. In the pyrolysis method in which the exhaust gas is supplied to the exhaust gas supply passage 21 and the heating unit 12 of the distillation means 9 is arranged in the exhaust gas supply passage 21 to supply the exhaust gas .
An exhaust gas bypass path 22 is provided in parallel with the heating section 12 of the distillation means 9, and the heating section of the distillation means 9 from the exhaust gas supply path 21 so that the temperature of the heating section 12 of the distillation means 9 becomes a preset value. The exhaust gas flow rate supplied to the exhaust gas supply channel 21 is adjusted, the exhaust gas flow rate of the bypass channel 22 is adjusted so that the pressure of the exhaust gas in the exhaust gas supply channel 21 becomes a preset value, and excess exhaust gas is branched to the bypass channel 22. A method for thermally decomposing plastics.

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