JP2001288480A - Method and apparatus for plastic waste gasification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the reactor from corrosion and dioxins from generation by utilizing the characters of hot and supercritical water for the efficient disintegration of plastic waste into gas mainly comprising hydrogen and methane and by simultaneously causing dehalogenation in the reactor. SOLUTION: The halogen containing plastic waste is, together with an alkali metal compound, brought into contact with the high temperature water containing supercritical water for reaction for gasification. Pressure in a reactor 16 is kept at 15-40MPa, continuous temperature distribution of 200 deg.C-1,200 deg.C is formed from the reactor top down through the reactor bottom, thermal hydrolysis occurs in a hot water state 1st reaction region 16a for the generation of hydrogen halide, the hydrogen halide reacts with the alkali metal compound for the generation of its halide, the plastic waste reacts with subsupercritical water or supercritical water in a 2nd reaction region 16b for the generation of gas mainly comprising hydrogen and methane and a residue, and the residue is partially oxidized in a 3rd reaction region 16c for the generation of carbon monoxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for decomposing waste plastic into useful gas and reusing the gas.

[0002]

2. Description of the Related Art In recent years, an enormous amount of plastic has been discharged as domestic waste and industrial waste, and disposal or reuse thereof has become an important issue. Therefore, various methods have been proposed for gasifying and recycling waste plastic. As one of the methods, a method of thermally decomposing at a high temperature of 800 ° C. or more is known, but there is a problem that many harmful gases such as a chlorine gas and a carbon dioxide gas are generated.
In particular, the generated chlorine is a main cause of corrosion of the material of the reactor, and has a serious effect on the environment such as generation of dioxin. In order to solve the above-mentioned problems in the gasification method, a method of decomposing plastic into a gaseous substance by a simple method has been disclosed (JP-A-6-299169). In this decomposition method, high-temperature hot water including supercritical water is used for gasification of plastics, and gasification is performed by contacting and reacting with high-temperature hot water under a reaction catalyst.

[0003] However, Japanese Patent Application Laid-Open No. 6-299169
In the method disclosed in the above publication, the ratio of useful gas such as hydrogen gas in the gas generated by decomposition of plastic is low, and the conversion to gas is not practically sufficient. In order to solve this problem, the present applicant, when gasifying plastic by reacting it with water at a temperature of 200 ° C. or higher, uses a compound that releases halogen (eg, chlorine) in waste plastic during the reaction as a reaction catalyst. A gasification method characterized by using as a method has been proposed (JP-A-11-181449). In the gasification method described in this publication, a compound that releases a halogen at the time of reaction is used as a reaction catalyst to perform gasification, so that it can be efficiently decomposed into hydrogen gas.

[0004]

However, Japanese Patent Application Laid-Open No.
In the gasification method disclosed in Japanese Patent No. 181449, although halogen has a catalytic effect of accelerating gasification, there is a risk that hydrogen halide is generated and corrodes the inside of the reactor.
In this method, a tank for neutralizing hydrogen halide was provided outside the reactor, but this did not provide effective suppression. Further, JP-A-6-299169 and JP-A-11-11
Both methods described in JP-A-181449 are 500 ° C.
Due to the low temperature gasification performed below, it is difficult to further convert the char remaining as a residue after gasification to gas,
There was also a problem that the gasification rate in the whole did not increase.

[0005] An object of the present invention is to efficiently decompose a gas containing hydrogen and methane as main components by utilizing the characteristics of hot water and supercritical water, and simultaneously dehalogenate the gas in the reactor to corrode the reactor. Another object of the present invention is to provide a method and an apparatus for gasifying waste plastic, which suppress generation of dioxins.

[0006]

The invention according to claim 1 is
In a gasification method of waste plastics in which waste plastics are contacted and reacted with high-temperature hot water containing supercritical water together with an alkali metal compound in a reactor 16 to gasify the waste plastics, the waste plastics are formed by crushed waste plastic powder containing halogen. The pressure inside the reactor 16 is maintained at 15 to 40 MPa, and a continuous temperature distribution of 200 ° C. or more and 1200 ° C. or less is formed from the top of the reactor to the bottom of the reactor. The first reaction region 16a in a state, the bottom of the reactor and the vicinity thereof are a third reaction region 16c in a subcritical or supercritical state of water, and the space between the first and third reaction regions 16a and 16c inside the reactor is further defined. When the second reaction region 16b is in a subcritical or supercritical state of water, waste plastic in the slurry supplied to the first reaction region 16a is removed by the first reaction region 16a. Hydrolyzing to generate hydrogen halide, and reacting this hydrogen halide with an alkali metal compound in the slurry to generate a halide, and removing the waste plastic in the slurry supplied to the first reaction region 16a; The second reaction region 16b reacts with subcritical water or supercritical water to generate a gas mainly composed of hydrogen and methane and a residue of a primary decomposition product, and supplies the residue to the third reaction region 16c to remove the residue with an oxidizing agent. A gas containing carbon monoxide as a main component to produce a gas containing carbon monoxide as a main component. In the invention according to claim 1, the first to third reaction regions 16a, 16b, and 16c having different temperature ranges are formed in the reactor 16 by temperature control. In the first reaction region 16a at the top, waste plastic is thermally and hydrolyzed to generate hydrogen halide, and the hydrogen halide is reacted with an alkali metal compound to generate a halide. In the region 16b, the waste plastic is reacted with subcritical water or supercritical water to generate a gas mainly composed of hydrogen and methane and a residue of a primary decomposition product, and the residue is supplied to the bottom third reaction region 16c to be oxidized. The residue can be partially oxidized by the agent to generate a gas containing carbon monoxide as a main component. Accordingly, a region for neutralizing hydrogen halide generated by heat, hydrolysis and gasification is formed in the reactor 16 by the above method, and neutralization is performed simultaneously with gasification, so that corrosion of the reactor can be suppressed.

[0007] The invention according to claim 2 is the invention according to claim 1, wherein the reaction product excluding the ash produced in the reactor 16 is subjected to a gas containing hydrogen, methane and moisture in the solid-gas separator 36, This is a gasification method for waste plastics in which the gas is cooled, and the gas is cooled and the gas-liquid separator 42 separates the gas into a gas containing hydrogen and methane and water. In the invention according to claim 2, the reaction product excluding ash is separated into a solid-gas separator 36,
The gas-liquid separator 42 separates the mixture into a gas containing halide, hydrogen and methane, and water. Since the solid halide produced in the reactor 16 is dissolved, the solid-gas separator 3
6 facilitates separation.

As shown in FIG. 2, the invention according to claim 3 includes a pressure-resistant and heat-resistant vertical tubular reactor 16 in which both ends are sealed and a heater is provided around the reactor. The bottom portion of the reactor 16 is formed in the large diameter portion, the middle portion between the top and the bottom of the reactor 16 is formed in the cone portion in the small diameter portion, and the first reaction region 16a in the hot water state is formed in the large diameter portion. ,
The second reaction region 16 in a subcritical or supercritical state of water in the cone portion
b can be formed, and the inside of the small diameter portion can be formed to form the third reaction region 16c in a subcritical or supercritical state of water,
At the top of the reactor 16, there are provided a supply port 17 for a slurry obtained by mixing waste plastic, water and an alkali metal compound, and an outlet 28 for a reaction product excluding ash, and a bottom at or near the bottom of the reactor 16. The waste plastic gasifier is characterized in that a supply port 29 for water and an oxidant and a discharge port 31 for ash are provided in the respective sections. According to the third aspect of the present invention, the waste plastic is decomposed by the apparatus having the above-described structure, so that the waste plastic is efficiently decomposed into hydrogen, methane gas, and the like because the hydrogen halide acts as a catalyst. In the first reaction region 16a in the state, the alkali metal is dissolved,
Due to the neutralization reaction with the hydrogen halide, corrosion in the reactor can be suppressed.

The invention according to claim 4 is the invention according to claim 3, wherein the side wall and the bottom wall of the reactor 16 have a double structure consisting of an outer wall 16d and an inner wall 16e having a predetermined interval, respectively. An inlet 24 for water and oxidant was provided at the top of the outer wall 16d corresponding to the diameter, and a supply port 29 for water and oxidant was provided at the bottom or near the bottom of the inner wall 16e corresponding to the small diameter. It is a gasifier for waste plastic. In the invention according to claim 4, the oxidizing agent contains the reactor inner wall 16.
Since the temperature is raised by receiving heat from the outer surface of e, the thermal efficiency is good.
Also, the presence of the inner wall 16e lowers the inner surface temperature of the outer wall 16d, thereby improving the pressure resistance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The waste plastic of the present invention is a plastic containing halogen, specifically, resins such as polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, and polytetrafluoroethylene (product name). :Teflon)
Such as a fluorine-based resin. Alkali metal compounds are alkali metal oxides such as potassium and sodium,
Hydroxide, carbonate and the like. The alkali metal compound may be a mixture thereof. Examples of the oxidizing agent include oxygen, air, and hydrogen peroxide.

Next, an embodiment of the present invention will be described. As shown in FIG. 1, the waste plastic gasifier 10 of the present invention has a mixer 11 for mixing water, waste plastic and an alkali metal compound to prepare a slurry.
The mixer 11 includes a pipe 12, a pump 13 and a pipe 14.
Is connected so as to supply the slurry from a supply port 17 provided at the top of the reactor 16 via the. A heater 18 is provided in the conduit 14. A heater 1 is provided on the outer periphery of the mixer 11.
1a, and a stirrer 11b is provided therein.
The waste plastic is pulverized in advance by a pulverizer (not shown) to a particle size of several mm or less, preferably 100 μm or less according to the capacity of the pump 13 and supplied to the mixer 11.
20-6 waste plastic powder per 100% by weight of water
0% by weight, 1 to 10% by weight of alkali metal compound powder,
It is preferable to add and mix each to prepare a slurry. The water storage tank 19 is connected to an inlet 24 via a pipe 21, a pump 22, and a pipe 23, and a heater 26 is connected to the pipe 23.
Is provided. In addition, a pump 27 for supplying an oxidizing agent is connected to the pipe 23.

As shown in FIG. 2, the reactor 16 is made of heat-resistant and pressure-resistant, and is formed in a vertical tubular shape with both ends sealed. A heater (not shown) for keeping heat or heating is provided on the outer peripheral portion of the reactor 16. The reactor 16 has a large diameter portion at the top, a small diameter portion at the bottom, and a cone at the middle between the top and bottom. The large diameter portion has a first reaction region 16a, and the cone portion has a second diameter.
The reaction region 16b and the inside of the small diameter portion are configured such that the third reaction region 16c can be formed. At the top of the reactor 16 is provided an outlet 28 for the reaction products excluding ash. Reactor 1
6 is provided with a water and oxidant supply port 29 and an ash discharge port 31 at the bottom. The side wall and the bottom wall of the reactor 16 have an outer wall 16d and an inner wall 1 having a predetermined interval, respectively.
Outer wall 1 corresponding to the large diameter portion, having a double structure of 6e
6d, an inlet 24 for water and oxidant is provided at an upper portion, and a supply port 2 for water and oxidant is provided at a bottom of the inner wall 16e corresponding to the small diameter portion.
9 are provided.

Returning to FIG. 1, the discharge port 28 is connected to the supply port 3 of the solid-gas separator 36 through a pipe 32, a pressure reducing valve 33, and a pipe 34.
7 is connected. The solid-gas separator 36 is provided with a gas outlet 38 for taking out gas at the top and a solid fraction outlet 39 for taking out solid content at the bottom. The gas outlet 38 is connected to a supply port 43 of a gas-liquid separator 42 via a pipe 41. A cooler 44 is provided in the conduit 41. The gas-liquid separator 42 is provided with a gas outlet 46 for discharging gas at the top and a water outlet 47 at the bottom. Water outlet 47
Are connected to the mixer 11 and the water storage tank 19 via a pipe 48, respectively.

Next, the reaction by such an apparatus will be described. First, the pressure inside the reactor 16 is 15 to 40 MPa.
And from the first reaction zone 16a at the top of the reactor 16 to the third reaction zone 16c at the bottom via the second reaction zone 16b at the middle, and in the order of 200 ° C. or more and 1200 ° C.
A continuous temperature distribution below ℃ is formed. (a) Heat / Hydrolysis Reaction Step First, a slurry in which waste plastic, an alkali metal compound and water are mixed is introduced into a reactor 16 through a supply port 17. The slurry introduced into the reactor 16 enters the first reaction zone 16a at and near the top of the reactor. The waste plastics in the slurry are mixed in the first reaction zone 16a with the formulas (1) to (1).
The thermal decomposition reaction of the waste plastic is promoted as shown in (3), and at the same time, the hydrolysis reaction of the waste plastic is promoted as shown in formula (4), and as a result, hydrogen halide is generated. The generated hydrogen halide promotes the thermal decomposition of waste plastic (eg, vinyl chloride containing a large amount of Cl) under the atmosphere.

[0015] _{C n H m → C n '} H m' + C n "H m" ...... (1) C n H m → C n H m-2 + H 2 ...... (2) C n H m- It represents a halogen element _{1 X → C n H m-} 2 + HX ...... (3) C n H m-1 X + H 2 O → C n H m-1 OH + HX ...... (4) wherein X . (b) First gasification step The waste plastic in the slurry thermally and hydrolyzed in the first reaction zone 16a enters the second reaction zone 16b following the first reaction zone 16a, and the waste plastic in the slurry is as described above. A pyrolysis reaction or a reaction with subcritical water or supercritical water to cause a typical gasification reaction represented by the following formulas (5) and (6) to generate a gas containing hydrogen and methane as main components and a residue of a primary decomposition product. Generate.

C + 2H ₂ O → CO ₂ + 2H ₂ (5) C + 2H ₂ → CH ₄ (6) Here, a part of the alkali metal compound contained in the slurry acts as a gasification catalyst. I do. Other alkali metal compounds migrate to the first reaction region 16a at the top of the reactor and in the vicinity thereof, dissolve in hot water, and exist in the form of ions. (c) Second Gasification Step The oxidant and water are supplied into the reactor 16 from the water and oxidant supply port 29 provided at the bottom of the reactor 16 between the outer wall 16d and the inner wall 16e of the reactor 16. You. Thus, water flows from the bottom to the top of the reactor 16. The residue transferred from the second reaction region 16b to the bottom of the reactor and the third reaction region 16c in the vicinity thereof from the second reaction region 16b due to gravity settling is partially oxidized by reacting with oxygen as an oxidizing agent by the following formula.

C + 1 / 2O ₂ → CO (7) Since the equation (7) is an exothermic reaction, it is possible to provide necessary heat in the reactor 16. The carbon monoxide generated by the partial oxidation reaction migrates to the second reaction region 16b, and the equation (8)
Is used for the water gas shift reaction shown in FIG.

CO + H ₂ O → H ₂ + CO ₂ (8) The residue generated by the reaction is extracted as ash from the ash outlet 31 provided at the bottom of the reactor 16 and collected. (d) Neutralization-dehalogenation reaction step The first reaction region 16a has a high ionic product of water in a hot water state and has a high concentration of alkali metal dissolved therein. Equation (3) described above
And hydrogen halide generated by the reaction represented by the formula (4) is quickly neutralized as shown in the formula (9) by an alkali metal dissolved at a high concentration in hot water to produce a halide.

HX + MOH → MX + H ₂ O (9) Here, M represents an alkali metal element. Since the reaction shown in this equation (9) is a neutralization reaction and the equilibrium constant is very large,
Complete dehalogenation of the waste plastic becomes possible, and corrosion of the reactor and generation of dioxin are suppressed. Since the first reaction region 16a is in a hot water state, the generated halide is dissolved in the hot water. In the first reaction region 16a, the heat / hydrolysis reaction and the neutralization dehalogenation reaction are not separately performed, but are performed in combination with each other.

The pressure inside the reactor 16 is 15 to 40 MPa. Preferably it is 15 to 25 MPa. 15MPa
If it is less than 1, the thermal / hydrolysis and neutralization reactions are not efficiently performed because the solubility of alkali and the ionic product of water are low. 40
If it exceeds MPa, the reactor will be overloaded. The temperature of the reactor 16 is set such that the temperature at the top of the reactor is 200 ° C. or more and the temperature at the bottom of the reactor is 1200 ° C. or less. 2
If the temperature is lower than 00 ° C., a problem that heat and hydrolysis hardly occur is caused. If the temperature is higher than 1200 ° C., the load on the reactor becomes too high.

The reaction product excluding the ash is withdrawn from the outlet 28 at the top of the reactor 16, reduced in pressure to 0.1 MPa, and sent to the solid-gas separator 36. In the solid-gas separator 36, a halide precipitates and is separated from the product gas as a solid. The generated gas is cooled through the cooler 44 and has a temperature of 1
It is sent to the gas-liquid separator 42 at a temperature of 00 ° C. or less. Where hydrogen,
The gas is separated into water and gas containing methane as a main component, and the water is discharged from the bottom of the gas-liquid separator 42, sent to the mixer 11 and the water storage tank 19, and reused. The gas containing hydrogen and methane as main components is discharged from the upper part of the gas-liquid separator 42 and is recovered as a product. In this embodiment, an example is shown in which the oxidizing agent is supplied into the reactor together with water, but it may be configured to supply only the oxidizing agent.

[0022]

Next, examples of the present invention will be described together with comparative examples. <Example> First, a waste plastic simulated material containing discarded vinyl chloride was prepared. NaOH was added and mixed so that the molar ratio with chlorine contained in the waste plastic imitation was 1.2, and water was further added so that the slurry concentration became 30 to 80% by weight to prepare a slurry. Next, using a device having the same structure as in FIGS.
It was fed into the reactor at a rate of kg / h. 2 inside the reactor
The pressure was maintained at 5 MPa, and from the first reaction zone at the top of the reactor to the third reaction zone at the bottom through the second reaction zone in the middle,
A continuous temperature distribution from 00 ° C to 1200 ° C was formed. Specifically, the first reaction region is 200 to 340 ° C., the second reaction region is 340 to 800 ° C., and the third reaction region is 800
The reaction was performed while maintaining the temperature at ~ 1200 ° C. Unreacted material was recovered as a residue. The reaction product excluding the residue obtained from the outlet of the reactor is separated into a halide by a solid-gas separator, water is separated by a gas-liquid separator, and the extracted product gas is condensed by a gas condenser not shown, After measuring the gas amount with a flow meter, the generated gas was temporarily stored in a container. The gas stored in this container was sampled to analyze the components.

<Comparative Example> The same waste plastic simulated material as in the example was prepared.
The reaction was carried out under the same reaction conditions using an apparatus having the same structure as in the example except that was not added, and the gas components of the generated gas were analyzed. <Comparative evaluation> From the carbon content (C ₁ ) of the supplied waste plastic simulated material and the carbon content (C ₂ ) in the gas generated by the gasifier, the carbon conversion rate (C ₂ / C ₁ × 100%) was determined. I asked. Further, the pH value of the water extracted from the gas-liquid separator was measured. Table 1 shows the results of Examples and Comparative Examples.

[0024]

[Table 1]

The pH of the water extracted from the gas-liquid separator is higher in the example than in the comparative example in which NaOH was not added,
It can be seen that the acid concentration has decreased. In addition, the addition of the catalyst results in a high carbon conversion rate and efficient gas generation. After disassembling the reactor after the reaction and examining the surface etc.,
The degree of corrosion was lower with the addition of the catalyst than without.

[0026]

As described above, according to the present invention, the first to third reaction zones are formed inside the reactor by controlling the temperature, and the waste plastic is heated and hydrolyzed in the first reaction zone to form a halogen. Hydrogen halide, and reacting the hydrogen halide with an alkali metal compound in the slurry to generate a halide; and, in the second reaction zone, reacting the waste plastic with subcritical water or supercritical water to produce hydrogen and methane. By generating a gas containing as a main component and a residue of a primary decomposition product, supplying the residue to the third reaction region, and partially oxidizing the residue with an oxidizing agent to generate a gas mainly containing carbon monoxide, Utilizing the characteristics of hot water and supercritical water, waste plastics can be more efficiently converted to gas containing hydrogen and methane as main components, and simultaneously dehalogenated in the reactor, resulting in corrosion of the reactor and dioxin. It is possible to suppress the generation of class.
As a result, the life of the device can be extended.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a waste plastic gasifier according to an embodiment of the present invention.

FIG. 2 is a sectional configuration view of a reactor which is a main part of the apparatus of FIG.

[Explanation of symbols]

 Reference Signs List 16 reactor 16a first reaction area 16b second reaction area 16c third reaction area 17 slurry supply port 24 water and oxidant introduction port 28 reaction product discharge port 29 water and oxidant supply port 31 ash discharge port 36 solid-gas separation Vessel 42 gas-liquid separator

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kenji Nishimura 1002, 6-headed, Mukaiyama, Naka-cho, Naka-gun, Naka-gun, Ibaraki Prefecture F-term in Mitsubishi Materials Corporation Environment and Energy Laboratory 4F301 AA17 CA23 CA27 CA41 CA52 CA72 CA73 4G040 BA02 FA02 FB02 FC08 FE06

Claims (4)

[Claims] 1. Contacting waste plastic with high-temperature hot water containing supercritical water together with an alkali metal compound in a reactor (16);
In the gasification method of waste plastics to be gasified by reacting, the waste plastic is a crushed waste plastic powder containing halogen, the pressure in the reactor (16) is maintained at 15 to 40 MPa, and the reaction is performed. 200 ° C. from the top to the bottom of the reactor
Forming a continuous temperature distribution of not less than 1200 ° C. and the first reaction zone in a hot water state at the top of the reactor and in the vicinity thereof
(16a), the bottom of the reactor and the vicinity thereof is a third reaction region (16c) in a subcritical or supercritical state of water, and the first and third reaction regions (16a, 16c) inside the reactor are When the second reaction zone (16b) is in a subcritical or supercritical state of water, the waste plastic in the slurry supplied to the first reaction zone (16a) is heated in the first reaction zone (16a). Hydrolyzing to generate hydrogen halide, and reacting the hydrogen halide with the alkali metal compound in the slurry to generate a halide, and in the slurry supplied to the first reaction region (16a), The waste plastic is reacted with subcritical water or supercritical water in the second reaction zone (16b) to generate a gas mainly composed of hydrogen and methane and a residue of a primary decomposition product, and the third reaction zone (16c) And supplying the residue to the oxidizing agent to partially oxidize the residue, A gasification method for waste plastics, wherein a gas containing carbon as a main component is generated. 2. A reaction product excluding ash generated in the reactor (16) is separated into a gas containing hydrogen, methane and moisture and a solid halide by a solid-gas separator (36), and the gas is cooled. The method for gasifying waste plastic according to claim 1, wherein the gas is separated into water and gas containing hydrogen and methane by a gas-liquid separator (42). 3. A pressure-resistant and heat-resistant vertical tubular reactor (16) having both ends sealed and a heater provided on the periphery thereof, wherein the top of the reactor (16) has a large-diameter portion and the reactor ( The bottom part of (16) is formed in a small diameter part, and the middle part between the top part and the bottom part of the reactor (16) is formed in a cone part, and the large diameter part is capable of forming a first reaction area (16a) in a hot water state. A second reaction region in which the inside of the cone portion is in a subcritical or supercritical state of water.
(16b) is formed, and the inside of the small diameter portion is formed so as to be able to form a third reaction zone (16c) in a subcritical or supercritical state of water, and waste plastic and water are formed on top of the reactor (16). And a discharge port (28) for a reaction product excluding ash, and water is provided at the bottom or a side near the bottom of the reactor (16). And an oxidizing agent supply port (29) and the ash discharge port (31). 4. A side wall and a bottom wall of the reactor (16) have a double structure comprising an outer wall (16d) and an inner wall (16e) having a predetermined interval, and the outer wall (16d) corresponding to a large diameter portion. An inlet (24) for water and an oxidizing agent is provided at the upper part, and a supply port (29) for the water and the oxidizing agent is provided at the bottom or a side near the bottom of the inner wall (16e) corresponding to the small diameter portion. The waste plastic gasifier according to claim 3.