JP2008127533A - Method of stopping pyrolysis system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of preventing a solution piping for supplying a plastic solution to a pyrolysis vessel from being blocked due to the retention of impurities. <P>SOLUTION: A method of stopping a pyrolysis system in which a plastic solution is supplied through a solution piping 20 to a pyrolysis vessel 2 to be subjected to the pyrolysis and the resultant pyrolysis gas is cooled to produce a produced oil comprises stopping the supply of the plastic solution to the pyrolysis vessel 2 and thereafter supplying the produced oil as a cleaning liquid to the solution piping 20 to discharge the plastic solution remaining in the inside of the solution piping 20 to the side of the pyrolysis vessel 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for stopping a pyrolysis system in which a plastic solution is pyrolyzed in a pyrolysis tank to produce a product oil. More specifically, the solution pipe for supplying the plastic solution to the pyrolysis tank has a small solid impurity remaining. The present invention relates to a method for stopping a thermal decomposition system that is prevented from being blocked.

  Various plastic wastes (waste plastics) are discharged from factories and households. If waste plastic is incinerated as it is, it will adversely affect the environment and cause resource losses. Therefore, a technology has been developed in which waste plastic is pyrolyzed with a pyrolyzer and resources are recovered as cracked oil. Plastics suitable for thermal decomposition are polystyrene, styrene resins such as styrene-acrylic copolymer (AS resin), styrene-acrylic-butadiene copolymer (ABS resin) (hereinafter simply referred to as polystyrene), polyethylene, and polypropylene. There are olefinic resins and the like.

  A large amount of waste plastic is discharged as polystyrene. Among them, expanded polystyrene is frequently used as a buffer material and a heat insulating material, and is therefore discharged in large quantities as waste plastic. Since the bulk density of expanded polystyrene is extremely low, a method of reducing the volume by dissolving in a solvent such as styrene monomer, benzene, or toluene and converting it to a polystyrene solution is generally adopted. The The following description describes a thermal decomposition technique using a polystyrene solution as a plastic solution, but the present invention is similarly applied to other plastic solutions.

  As a thermal decomposition system of a polystyrene solution, for example, one described in Patent Document 1 is known. The thermal decomposition system described in Patent Document 1 includes a thermal decomposition tank, and a heat exchange unit that heats the polystyrene solution is provided inside the thermal decomposition tank. The heat exchanging unit has a plurality of tubes arranged in parallel, and heats and decomposes the polystyrene solution continuously supplied to the pyrolysis tank with a heating medium (for example, high-temperature gas) flowing through each tube. It is like that.

  The polystyrene solution is supplied to the pyrolysis tank through a solution pipe. The cracked gas obtained by pyrolysis in the pyrolysis tank is supplied to the condenser from the top of the pyrolysis tank, where it is cooled and condensed, and stored in the product oil tank. The product oil is used as fuel oil as it is, or is distilled by a distillation apparatus and purified to a styrene monomer and used as a chemical raw material.

JP 2005-89485 A

  For example, a polystyrene solution obtained by dissolving waste foamed polystyrene with a solvent such as styrene often contains fine solid impurities such as fine dust, sludge or other impurities derived from waste foamed polystyrene. Exists in the polystyrene solution as a high-viscosity product, and most of it is accompanied by the polystyrene solution and flows into the thermal decomposition tank, but a part of the solution is settled or adhered to the solution pipe. In particular, when there is a horizontal portion in the solution pipe, the amount of residence in the portion is greatly increased, and in some cases, the solution pipe may be partially or completely blocked.

  On the other hand, although the thermal decomposition system can be operated continuously or batchwise, the system is stopped periodically or at any time in any operation method. When the pyrolysis system is stopped, the polystyrene solution stays in the solution pipe, but if the polystyrene solution stays for a long time, the dissolved polystyrene may reprecipitate and newly generate fine solid impurities such as sludge. is there.

  Such impurities also promote the occurrence of clogging of the solution piping. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the problem of blockage of solution piping in such a conventional pyrolysis system, and an object of the present invention is to provide a new method for stopping the pyrolysis system.

  The present invention that solves the above problems is a method for stopping a pyrolysis system in which a plastic solution is supplied to a pyrolysis tank through a solution pipe and pyrolyzed, and the resulting cracked gas is cooled to produce product oil. After the supply of the plastic solution to the pyrolysis tank is stopped, the generated oil is supplied as a cleaning liquid to the solution pipe, and the plastic solution remaining inside the solution pipe is discharged to the pyrolysis tank side. (Claim 1).

  In the method for stopping the pyrolysis system, the inside of the supply pipe after the plastic solution remaining in the solution pipe flows out to the pyrolysis tank side can be filled with the product oil.

  In any one of the above pyrolysis system stopping methods, when the solution pipe includes a horizontal portion, the generated oil can be supplied to the solution pipe so that the generated oil flows at least through the horizontal portion. (Claim 3).

  In any one of the above thermal decomposition system stopping methods, the plastic solution obtained by dissolving waste foamed plastic with a solvent can be used.

  The method for stopping a thermal decomposition system according to the present invention, as described in claim 1, after stopping the supply of the plastic solution to the thermal decomposition tank, supplies the generated oil as a cleaning liquid to the solution pipe, The plastic solution remaining inside is discharged to the pyrolysis tank side. According to the present stop method, impurities such as sludge staying in the solution pipe are discharged to the pyrolysis tank side each time using the stop period of the pyrolysis system. There is no fear of blockage.

  If the polystyrene solution stays for a long time, the dissolved polystyrene reprecipitates and newly generates fine solid impurities such as sludge. According to this stopping method, most of the polystyrene solution is discharged to the pyrolysis tank side. Therefore, substantially no reprecipitation occurs. In this way, the stopping method can prevent the solution pipe from being blocked, and as a result, the service life or durability of the solution pipe can be improved.

  Further, since the produced oil as the cleaning liquid to be used can be generated in the thermal decomposition tank, it is not necessary to supply a new cleaning liquid from outside the system. Furthermore, the produced oil that has flowed into the pyrolysis tank together with the impurities can be evaporated and collected in a produced oil tank or the like when the operation of the pyrolysis system is resumed.

  In the method for stopping the pyrolysis system, as described in claim 2, after the plastic solution remaining in the solution pipe flows out to the pyrolysis tank side, the supply pipe may be filled with the product oil. it can. In this way, it is possible to prevent air from entering the solution pipe while the thermal decomposition system is stopped.

  In any one of the above thermal decomposition system stop methods, as described in claim 3, when the solution pipe includes a horizontal portion, the solution oil is disposed in the solution pipe so that the generated oil flows at least through the horizontal portion. The product oil can be supplied. If it does in this way, the obstruction | occlusion accident of the said horizontal part which is easy to raise | generate a stay can be prevented reliably.

  In any one of the above thermal decomposition system stopping methods, as described in claim 4, the plastic solution obtained by dissolving waste foamed plastic with a solvent can be used. In this way, the plastic re-deposited while the pyrolysis system is stopped can be redissolved with the product oil.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a process flow diagram in which a polystyrene solution is pyrolyzed by a pyrolysis system according to the present invention to produce a styrene solution as cracked oil. However, this embodiment can be similarly applied to the thermal decomposition of other thermally decomposable plastic solutions.

  A pyrolysis system 1 shown in FIG. 1 includes a pyrolysis tank 2, a heat exchange unit 3 disposed below the inside of the pyrolysis tank 2, heating gas generating means 4 for supplying heating gas to the heat exchange unit 3, and a pyrolysis tank. 2, a cracked gas discharge part 5 provided at the top of the thermal decomposition tank 2, a residue discharge part 6 provided at the bottom of the thermal decomposition tank 2, an auxiliary tank 8 that communicates with the side surface of the thermal decomposition tank 2 through a flow path 7, and an auxiliary tank 8. Is provided with a polystyrene solution supply unit 9, a condenser 10 and a product oil tank 11.

  The pyrolysis tank 2 is constituted by a closed tank surrounded by a heat insulating layer, and its supply unit 9 is connected to a polystyrene solution tank (not shown) via a solution pipe 20, and the solution pipe 20 is opened and closed with a pump 21. A valve 22 is provided. A discharge pipe 23 is connected to the residue discharge section 6 of the pyrolysis tank 2, and an open / close valve 24 is provided in the discharge pipe 23. Furthermore, the cracked gas discharge part 5 of the thermal decomposition tank 2 is connected to a condenser 10 via a cracked gas pipe 13, and a pipe 12 for circulating a cooling medium such as cooling water is provided in the condenser 10.

  The condenser 10 is connected with a pipe 14 for discharging the generated oil and a pipe 15 for discharging the non-condensed gas, and the tip of the pipe 14 communicates with the generated oil tank 11. Pipes 16, 17 are connected to the product oil tank 11, and product oil is supplied from the pipe 16 to a distillation apparatus or the like. The pipe 17 is provided with a pump 18 and a regulating valve 19, and the tip thereof is connected to the solution pipe 20. Is done. And the connection part (communication part) of the piping 17 with respect to the solution piping 20 turns into the supply point (A) of produced oil.

  The heating gas generating means 4 burns fuel such as styrene gas to generate high-temperature (for example, about 550 ° C.) combustion gas, and supplies it as a heating gas to the heat exchanging section 3 disposed in the thermal decomposition tank 2. It is. A supply pipe 25 is provided for supplying the heated gas flowing out from the heated gas generating means 4 to the heat exchanging section 3, and a discharge pipe 26 is provided for discharging the exhaust gas flowing out from the heat exchanging section 3. The heat exchanging unit 3 has a plurality of elongated tubes arranged in parallel, and the heated gas from the heated gas generating means 4 is divided into each tube, and the divided heated gas and the styrene solution contacting the surface of each tube and heat After exchanging, it is discharged through the discharge pipe 26.

  Next, a method for continuously pyrolyzing polystyrene by the pyrolysis system 1 of FIG. 1 will be described. Expanded polystyrene such as waste expanded polystyrene, which is a raw material for thermal decomposition, is finely pulverized by a pulverizer (not shown) to form expanded polystyrene pieces, which are supplied to a dissolution tank (not shown) that functions as a polystyrene solution tank. . For example, a styrene solution is supplied to the dissolution tank as a solvent for polystyrene, and the expanded polystyrene pieces are mixed with the solvent and stirred for a predetermined time with a stirring device to be dissolved into a polystyrene solution. The obtained polystyrene solution is continuously supplied from the solution pipe 20 to the supply unit 9 of the auxiliary tank 8 by the pump 21.

  The polystyrene solution supplied to the auxiliary tank 8 flows into the thermal decomposition tank 2 through the flow path 7 from there. Thus, the polystyrene solution of the pyrolysis raw material is finally continuously supplied to the pyrolysis tank 2 via the auxiliary tank 8. The polystyrene solution in the inside of the thermal decomposition tank 2 during normal operation is heated to its thermal decomposition temperature (for example, about 350 ° C. to 400 ° C.) in the heat exchanging unit 3 and thermally decomposed, and a decomposition gas mainly containing styrene. Is generated. The generated cracked gas flows out from the cracked gas discharge unit 5 to the pipe 13 and is condensed by being cooled by the condenser 10, and the condensed liquid (product oil) is recovered to the generated oil tank through the pipe 14. On the other hand, low-boiling components that are not condensed are discharged as uncondensed gas from the pipe 15 and used for fuel or the like.

  Since fine solid impurities that flow into the pyrolysis tank 2 or residues such as carbides generated by pyrolysis gradually accumulate at the bottom of the pyrolysis tank 2, the on-off valve 23 is appropriately opened to open an external recovery tank. Etc.

  Next, a method for stopping the pyrolysis system shown in FIG. 1 will be described. When stopping the thermal decomposition system, first, the pump 21 is stopped to stop the supply of the polystyrene solution to the thermal decomposition tank 2 and the supply of the heating gas to the heat exchange unit 3. Next, when the pump 18 is operated and the adjustment valve 19 is opened, the generated oil stored in the generated oil tank 11 is supplied from the pipe 17 to the supply point (A) of the solution pipe 20. The product oil supplied to the solution pipe 20 is discharged to the pyrolysis tank 2 side. However, as the product oil flows through the solution pipe 20, the remaining fine solid impurities are accompanied by the product oil and pyrolyzed. It is discharged to the tank 2 side.

  In order to efficiently discharge the impurities remaining in the solution pipe 20, it is necessary to set the flow rate of the produced oil inside the solution pipe to a certain level, that is, to set the flow rate so that the remaining impurities can be discharged efficiently. is there. A preferable range of the flow rate can be determined in advance by experiments or the like, and the opening degree of the adjustment valve 19 is adjusted so that the set flow rate can be obtained.

  When the generated oil is supplied from the pipe 17 to the supply point (A) of the solution pipe 20 as described above, the generated oil flows through the inside of the solution pipe 20 on the downstream side from the supply point (A) and remains in the portion. Is discharged. Therefore, it is necessary to select the supply point (A) at a position upstream from the portion where the impurities stay. For example, when there is a horizontal portion in the solution pipe 20, the level of impurity retention in the horizontal portion is large, so a supply point (A) is provided in the solution pipe 20 upstream of the horizontal portion, and at least the horizontal portion is provided. It is desirable that the product oil be circulated in the part.

  In the example of FIG. 1, the vicinity of the outlet of the pump 21 provided in the solution pipe 20 is the supply point (A). However, if the pump 21 is arranged above a polystyrene solution tank (not shown), the supply point (A) is at this position. It is enough. If the polystyrene solution tank is located above the pyrolysis tank 2, an on-off valve can be provided instead of the pump 21.

  When the discharge of impurities by the produced oil is finished, the pump 18 is stopped and the regulating valve 19 is closed. At that time, when the solution pipe 20 is filled with the product oil as described above, the pump 18 may be stopped after the on-off valve 22 is closed.

  The method for stopping the thermal decomposition system of the present invention can be used for, for example, an apparatus for thermally decomposing a polystyrene solution obtained by dissolving foamed polystyrene in a solvent to produce a styrene solution as a product oil.

The process flow figure of the thermal decomposition system of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal decomposition system 2 Thermal decomposition tank 3 Heat exchange part 4 Heating gas generation means 5 Decomposition gas discharge part 6 Residue discharge part 7 Flow path 8 Auxiliary tank 9 Supply part 10 Condenser

11 Product oil tanks 12 to 17 Pipe 18 Pump 19 Adjustment valve 20 Solution pipe 21 Pump 22 On-off valve 23 Drain pipe 24 On-off valve 25 Pipe 26 Drain pipe

Claims (4)

  In the method of stopping the pyrolysis system in which the plastic solution is supplied to the pyrolysis tank 2 through the solution pipe 20 and pyrolyzed, and the resulting cracked gas is cooled to produce the produced oil, After the supply of the plastic solution is stopped, the generated oil is supplied to the solution pipe 20 as a cleaning liquid, and the plastic solution remaining in the solution pipe 20 is discharged to the pyrolysis tank 2 side. How to stop.   The method for stopping a thermal decomposition system according to claim 1, wherein the inside of the supply pipe 20 after the plastic solution remaining in the solution pipe 20 is discharged to the pyrolysis tank 2 side is filled with the generated oil.   In any one of Claim 1 or Claim 2, when the said solution piping 20 contains a horizontal part, the said production | generation oil is supplied to the said solution piping 20 so that the said production oil may distribute | circulate at least this horizontal part. A method for stopping a thermal decomposition system.   4. The method for stopping a thermal decomposition system according to claim 1, wherein the plastic solution is obtained by dissolving waste foamed plastic with a solvent.

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