JPH10101841A - Thermal treatment of waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for thermally treating wastes containing chlorine, capable of separating generated hydrogen chloride in high efficiency by subjecting the wastes to a preliminary dechlorination treatment. SOLUTION: This method for thermally treating chlorine-containing wastes comprises heating, preferably thermally decomposing, the wastes at 200-600 deg.C to remove the chlorine. Therein, a gas containing steam in a molar amount of >=0.5 time, preferably >=2 times, that of the contained chlorine is charged to highly efficiently separate the chlorine compounds in the wastes. The employment of an oxygen-short gas, preferably a substantially oxygen-free, oxygen- removed gas, as the steam-containing gas enables to suppress the combustion of combustible materials in the wastes and prevent the production of dioxin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste heat treatment method for decomposing and removing harmful chlorine from waste with high efficiency.

[0002]

If chlorine-containing vinyl chloride resin or the like is mixed in the waste, thermal decomposition and combustion generate a large amount of hydrogen chloride, which not only causes great pollution, However, there is a problem of causing corrosion of the incinerator. In addition, when a product obtained by thermally decomposing or gasifying waste (a gas such as an oil or a hydrocarbon) is effectively used, it may cause a bad effect due to poisoning of the catalyst. Therefore, it is important to remove hydrogen chloride by pretreatment of waste. As a pretreatment method of chlorine-containing waste, there is a method of performing thermal decomposition in a decomposition tank by indirect heating using a heating medium, a heater, or the like. In this method, it is difficult to uniformly heat the solid inside the decomposition tank, and especially in the case of thermoplastic plastics, the softened / melted parts are fused together by local heating to form a lump, and the undecomposed hydrogen chloride is a molten plastic. There was a problem that the removal of hydrogen chloride was incomplete even when the pressure was reduced. Further, a dechlorination method in which a Ca compound is added to waste, followed by thermal decomposition, gasification, or combustion is performed. In this method, chlorine and a Ca compound are separated from the gas layer as solids in the form of CaCl ₂ by the following reaction.

CaO + 2HCl → CaCl ₂ + H ₂ O (1)

Focusing on such a reaction, a waste is mixed with an alkali metal compound (compound such as Ca, K, Mg, etc.),
The alkali metal compound is dechlorinated in a pyrolysis furnace, a combustion furnace, or a gasification furnace, or in a pyrolysis gas, a combustion gas, or a gasification product gas in front of a dust collector in a post-process of the furnace. In general, a method of spraying fine particles or a slurry is used.

[0005] More recently, in the case of plastic waste containing metals such as car shredder dust, residues after pyrolysis, gasification, or combustion containing CaCl ₂ or unburned metals produced by the above process are removed. Attempts have been made to recover the metal by treating it again in the blast furnace.
In this case, it is assumed that CaCl ₂ reverses the above reaction (1) at a high temperature of about 800 ° C. or more, decomposes again into HCl, and corrodes the furnace wall of the blast furnace. Further, in plastics, trace metals (Cd, Mg, Pb, Zn, C) which are easily combined with chlorine as plasticizers, stabilizers, or paints are contained.
u, Ca, etc.). When these generate chlorides and reuse metals, they re-decompose in the blast furnace,
HCl, which causes corrosion in blast furnaces and the like.

[0006] To summarize the problems of the conventional method,
It looks like this: 1) High temperature furnace dechlorination is inefficient. 2) Even if dechlorination is performed in the furnace, it is re-decomposed in a high-temperature gasification furnace or a combustion furnace at a temperature of 600 ° C. or higher in a later process. 3) When the dechlorination in the furnace is incomplete, the residual chlorine and the unburned hydrocarbons easily react to form harmful dioxins, and once formed, dioxins are difficult to decompose and are accompanied by gas as they are in the atmosphere. Released to the public causing pollution problems. 4) When dechlorination in the furnace is insufficient and hydrogen chloride gas is generated in the gasification furnace or the combustion furnace, it causes corrosion of the apparatus. Accordingly, the present invention provides a method for separating generated hydrogen chloride with high efficiency by pretreatment dechlorination in treating waste containing chlorine.

[0007]

In order to solve the above-mentioned problems, the present invention provides a pyrolysis furnace, a combustion furnace, or a gasification furnace by supplying steam to promote a dechlorination reaction and achieve high efficiency. It proposes a method for dechlorination. That is, the invention according to claim 1 focuses on the dechlorination treatment step, and heats chlorine-containing waste to 200 to 600 ° C., preferably in a method of dechlorinating by thermal decomposition. By supplying a gas containing water vapor in a molar amount of 0.5 times or more, preferably twice or more the molar amount, the chlorine compound in the waste is separated with high efficiency.

[0008] The invention of claim 2 focuses on waste including a dechlorination treatment step, and removes a gas containing water vapor having a molar amount of 0.5 times or more, preferably twice or more the molar amount of chlorine contained. While supplying, waste containing chlorine is 200 to 6
The dechlorination step of heating to 00 ° C. and thermally decomposing, and the waste subjected to the dechlorination treatment are further subjected to 350 to 1,000 ° C.
And pyrolysis, gasification, or combustion. At this time, by using an oxygen-deficient gas, preferably a deoxygenated gas substantially free of oxygen, as a gas containing water vapor, it is possible to suppress the combustion of combustibles in waste and prevent dioxin generation. it can.

[0009] The applicant of the present invention has disclosed Japanese Patent Application No. 7-194226.
(1) proposes a waste plastic heat treatment method that does not cause a trouble even if a thermosetting resin or solid foreign matter is mixed. This application was developed as a comprehensive system for recovering oil by pyrolysis of waste plastics, and it is characterized by mixing waste plastics with hot sand and heating to a temperature of 250-350 ° C. By
A first step (dechlorination step) of producing a treated product comprising a mixture of waste plastic and sand from which chlorine has been substantially removed, and adding high-temperature sand and / or additives to the treated product in the first step And a temperature of about 350 to 500 ° C., preferably about 400
By heating to ~ 480 ° C, gaseous high boiling oils,
A second step (pyrolysis step) of producing a pyrolysis product comprising a low-boiling oil and a low-molecular gas and a solid pyrolysis residue / sand mixture, and converting the pyrolysis product of the second step to a liquid high-boiling oil And low-boiling oil and low-molecular-weight gas are separated into high-boiling oil
A first gas-liquid separation step of refluxing the process, a second gas-liquid separation step of separating into a liquid low-boiling oil and a gaseous low molecular gas,
The solid pyrolysis residue / sand mixture of the process and the low-molecular gas of the second gas-liquid separation process are burned at about 500 to 1000 ° C. in a fluidized bed using sand as a medium to flow by air to produce hot sand. The oil recovery method comprises a third step (residue incineration step) in which part of the oil is recycled to the first or second step. The present invention is also applicable to the dechlorination step of the prior application. is there.

[0010] Examples of the waste containing chlorine include the following. A) Car shredder dust This is waste obtained by removing large metals such as engines, tires and wheels from automobiles and then pulverizing it. In addition to metals, plastics containing chlorine (electrical wiring etc.) are contained in about 30 Wt%. B) General waste mainly composed of plastics Waste containing a large amount of plastic separated from municipal waste. It is mainly composed of thermoplastic resin (polyethylene, polypropylene, polystyrene, etc.) and partially contains polyvinyl chloride,
It contains PETs, thermosetting resins, etc., and generally contains several percent of chlorine compounds. C) Plastic industrial waste Waste that contains a large amount of plastic, such as residual plastic from plastic die-cast products.

FIG. 1 shows the rate of weight loss in the pyrolysis of various plastics. Mitsubishi Heavy Industries Technical Report, 10 (5) P7
87 (1973)｝. As is apparent from this figure, thermoplastics generally soften and melt at about 120 to 230 ° C. and thermally decompose at higher temperatures. The thermosetting resin is thermally decomposed by heating without being softened or melted. As a plastic containing chlorine, polyvinyl chloride (PV)
C), polyvinylidene chloride. In these chlorine-containing plastics, most of the chlorine is desorbed as hydrogen chloride in the region of about 170 ° C. to 350 ° C., and when the temperature becomes high, thermal decomposition of other components proceeds. The model of chlorine desorption is shown below.

[0012]

Embedded image

FIG. 2 shows the removal of H from PVC (polyvinyl chloride).
Shows Cl speed. Mitsubishi Heavy Industries Technical Report, 10 (5) P787
(1973)｝. As is clear from the figure, HCl is removed at 80% at 250 ° C. and almost 100% at 300 ° C. or more.
At 300 ° C., a long residence time of tens of minutes is required.
Although illustrated by way of example for PVC (polyvinyl chloride), it is understood that the plastic mixture starts to thermally decompose rapidly from around 250 ° C., and most of it decomposes by about 500 ° C.

In general, the above-mentioned waste contains metals (Ca, Fe, Cd, Pb, Mg, K, etc.) that react with chlorine, and reacts with HCl generated during thermal decomposition to produce chlorides. And remains in the solid after the dechlorination treatment. As a result, when these solids are gasified or burned, the chlorides re-decompose to produce HCl,
The molten chlorides are transported as mist into the gas and adhere to the heat transfer tubes of the boiler or the wall surfaces of the device, causing corrosion. Therefore, the present invention proposes to supply steam during thermal decomposition. That is, chloride generated during thermal decomposition is decomposed by the following reaction in the presence of steam to generate hydrogen chloride HCl.

CaCl ₂ + H ₂ O → 2HCl + CaO 2) FeCl ₂ + H ₂ O → 2HCl + FeO 3) CdCl ₂ + H ₂ O → 2HCl + CdO 4) PdCl ₂ + H ₂ O → 2HCl + PdO 5) MgCl ₂ + H _{2 O → 2HCl + MgO ...... 6} ) KCl + H 2 O → HCl + KOH ...... 7)

In this decomposition reaction, the higher the water vapor concentration, the higher the chlorine decomposition rate. However, O ₂
When HCl is contained, HCl is decomposed into Cl ₂ by the following reaction, and reacts with an organic substance to easily generate dioxin. 2HCl + (1/2) O ₂ → Cl ₂ + H ₂ O (organic substance) + Cl ₂ → Organic chlorine compound (including dioxin)

As described above, by containing water vapor in an oxygen-deficient gas, preferably a deoxidized gas substantially containing no oxygen, it becomes possible to dechlorinate waste plastic without producing dioxin.

Therefore, according to the method of the present invention, 35
In order to perform dechlorination in a pretreatment step before the step of pyrolysis, gasification, or combustion at 0 ° C to 1,000 ° C, chlorine is contained in the gas generated in the pyrolysis, gasification, or combustion step. Since it is hardly contained and chlorine does not remain in the residue, pollution-free and effective utilization of the generated gas and the residue is facilitated. The process of pyrolyzing, gasifying, or burning waste at 350 ° C to 1,000 ° C is only a process of pyrolyzing, gasifying, or burning dechlorinated waste plastic at 600 ° C to 1,000 ° C. Japanese Patent Application 7-194
As shown in No. 226, by adding an additive or the like to the dechlorinated waste plastic and heating it to a temperature of about 350 to 500 ° C., preferably about 400 to 480 ° C., a gaseous high-boiling oil or low-boiling oil And a pyrolysis step of producing a pyrolysis product composed of a low-molecular gas, and a residue incineration step of burning the pyrolysis residue of the pyrolysis step at about 500 to 1000 ° C.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[Comparative Example 1] (Conventional method) Car shredder dust was confused with an average particle size of 10 mm.
It was supplied to a fluidized bed incinerator and burned at 850 ° C. Table 1 below shows the elemental analysis values of the raw materials used in this comparative example.

[0020]

[Table 1]

As a result, as shown in Table 2 below, 5.3 wt% of a chlorine compound is contained in the combustion residue discharged from the furnace bottom of the combustion furnace, and chlorine reacts with the metal component by combustion. To produce chloride. As a result, it is difficult to reuse the metal component as chloride.

[0022]

[Table 2]

Example 1 (Method of the Present Invention) The same raw materials as in the comparative example were used (see Table 1). Raw material was put into dechlorination furnace being rotated, the water concentration of 40 vol.%, N ₂
While passing a humidified gas having a concentration of 60 vol.
For 20 minutes. As a result, the removal rate of hydrogen chloride in the raw material was 94%. Also, the weight of the raw material is
Only 9 wt% was reduced, and thermal decomposition of hydrocarbons in the raw material hardly occurred, and only dechlorination proceeded. The dechlorination furnace may be a horizontal rotary kiln, a screw conveyor, a vertical stirring tank having a double helical ribbon structure, a horizontal single-shaft or twin-shaft stirring tank, or the like.

Example 2 (Method of the Present Invention) Comparative Example 2 (Conventional Method) A waste mainly composed of plastics was used as a raw material and burned after dechlorination. 1) dechlorination conditions processing conditions: 320 ° C. The feed gas: Example 2 There humidification:.. Water content 40 vol%, N ₂ concentration 60 vol% Comparative Example 2 None humidification:. N ₂ concentration 100 vol% Table 3 The following shows the elemental analysis values of the raw materials used in this example and the comparative example.

[0025]

[Table 3]

FIG. 3 shows the operation results. As is clear from the operation results, the dechlorination rate in Comparative Example 2 was about 60%, while the operation time in Example 2 was about 30 minutes, and the dechlorination rate reached 100%. Therefore, as is clear from Examples 1 and 2, it can be understood that the humidification significantly improved the dechlorination rate.

FIG. 4 shows the effect of the steam addition ratio H ₂ O / Cl (molar ratio). By adding steam, specifically, as the addition ratio, when the steam addition ratio H ₂ O / Cl (molar ratio) is about 0.5 or more, the dechlorination rate is improved to about 80%,
At about 2.0 or more, it reaches 95% or more, and the effect is large.

[0028]

According to the present invention as described above, the following effects can be obtained. A) Highly efficient separation of chlorine compounds as HCl. B) Therefore, the separated HCl can be easily removed from the solid by wet treatment or the like. C) The waste (solid matter) after dechlorination can be gasified or burned in the next step without causing problems such as equipment corrosion and catalyst poisoning. D) No by-products of harmful substances such as dioxin are generated. From the above, the present invention is industrially useful.

[Brief description of the drawings]

FIG. 1 is a graph showing the rate of weight loss in the thermal decomposition of various plastics, and particularly illustrating the thermal decomposition characteristics of plastics.

FIG. 2 is a graph showing the HCl removal rate of PVC (polyvinyl chloride).

FIG. 3 is a graph illustrating the effect of the present invention, and shows the change over time in the dechlorination rate without humidification (Comparative Example) and with humidification (Example).

FIG. 4 is a graph showing a dechlorination rate depending on a steam addition ratio H ₂ O / Cl (molar ratio).

Claims (3)

[Claims] 1. A method for producing a waste containing chlorine, comprising:
In the method of dechlorination by heating to 0 ° C., by supplying a gas containing water vapor in a molar amount of 0.5 times or more, preferably twice or more the molar amount of chlorine contained, A waste heat treatment method comprising separating a compound with high efficiency. (2) at least 0.5 times the molar amount of chlorine contained,
Preferably, the chlorine-containing waste is supplied to a gas containing 200 times or more of the molar amount of water vapor while supplying a gas containing twice or more times the amount of water vapor.
A dechlorination step of thermally decomposing by heating to a temperature of ℃,
Pyrolyzing, gasifying, or burning at 1,000 ° C. 3. The method for heat treatment of waste according to claim 1, wherein an oxygen-deficient gas or a deoxidized gas substantially containing no oxygen is used as the gas containing water vapor.