JPH11216445A - Treatment of waste plastics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reutilize waste plastics containing heavy metals and chlorine. SOLUTION: Waste plastic are burned and decomposed with gaseous oxygen at 1300-1600 deg.C and the gas consisting essentially of CO and H2 is recovered and the heavy metals are volatilized as a metallic vapor, after cooled, solidified and recovered with a dust collector. Chlorine is recovered as hydrogen chloride and is effectively utilized. The inorganic matters in the waste plastics are separated from a gasification furnace bottom as a fused product to be effectively utilized a water-granulated slag.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic processing method for recovering fuel gas, heavy metals and hydrochloric acid from plastics containing chlorine and heavy metals.

[0002]

2. Description of the Related Art In recent years, recycling of waste plastics has been promoted due to a demand for resource recycling, but at present, waste plastics are still often discarded or incinerated. As a method of utilizing waste plastic, a method of collecting light oil by liquefaction has been developed in addition to recycling. The liquefaction of plastic is advantageous in that it can be used as petroleum products by recovering it with a liquid fuel, but from the point that residues are generated and disposal of the residues becomes a problem, and the hydrochloric acid generated degrades the liquefaction catalyst. In addition to the necessity of separating them in advance, the cost of recovered light oil, which has high equipment costs and operating costs, is higher than the price of commercially available light oil, and is currently not economically viable. In addition, as a method of using a large amount of waste plastic as fuel, by injecting pulverized coal simultaneously from the tuyere of a blast furnace and using it as a reducing agent for iron ore,
Although a method of reducing pulverized coal has been recently implemented, chlorine-containing plastics such as vinyl chloride decompose to generate hydrochloric acid gas, which corrodes a dust collector and a gas pipe at a later stage, and thus need to be removed in advance.

[0003] Vinyl chloride, which is a representative of plastics containing chlorine, is added with zinc as a stabilizer. Further, many of the plastics for covering electric wires use vinyl chloride and contain a large amount of lead. . When such waste plastics containing heavy metals are liquefied, heavy metals remain in the residues, and a method of treating the residues containing the heavy metals becomes an issue.
In addition, when the blast furnace is blown into the blast furnace, the molten metal is contaminated by the heavy metal, and at the same time, the heavy metal is mixed into the blast furnace dust, and the blast furnace dust treatment becomes a problem.

[0004] As a method for treating chlorine-containing plastics, Japanese Patent Application Laid-Open No. 6-316562 discloses a method for treating plastics containing 250 to 6 particles.
A method has been proposed in which pyrolysis is performed at 00 ° C. to remove generated hydrogen chloride, and the remaining carbon is used as a fuel.
Also, Japanese Patent Application Laid-Open No. Hei 7-233373 proposes a method in which a high-temperature gas obtained by burning a fuel is blown into waste plastics to melt and thermally decompose, and at the same time, hydrochloric acid gas generated from combustion exhaust gas is removed. And heating, and liquefaction residues are generated, and processing becomes an issue.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to use waste plastic containing chlorine and heavy metals, which becomes a problem in liquefaction of waste plastic and blast furnace blowing treatment, as a fuel or chemical raw material gas. At the same time as recovering and separating heavy metals and recovering chlorine components as hydrochloric acid, it can be used effectively, and at the same time, inorganic substances attached to or contained in waste plastic can be effectively used as resources free of heavy metals. Another object of the present invention is to provide a method for effectively utilizing waste plastic without producing waste.

[0006]

Means of the present invention for solving the above problems are as follows.

(1) A plastic containing chlorine and heavy metals is reacted with oxygen gas in a gasification furnace at 1300 to 1600 ° C. to decompose them into CO, H ₂ and HCl gases, and to evaporate heavy metals as metal vapor. The heavy metal is entrained with the gas to separate it from the slag contained in the plastic, and further cooled by a boiler or water spray cooling in a cooling furnace provided at the subsequent stage of the gasification furnace to convert the heavy metal into a metal or metal. This is a method for treating waste plastic, which comprises converting into chlorides or metal oxides, solidifying, collecting with a dust collector, and separating.

(2) The method for treating waste plastic according to (1), wherein a hydrochloric acid recovery device is provided downstream of the dust collector to recover hydrochloric acid in the gas.

(3) The waste according to (1), wherein a slag tap is provided at a lower portion of the gasification furnace to melt the inorganic substance in the plastic and the attached inorganic substance, and then cool and solidify to collect. This is a method for processing plastic.

In the present invention, waste plastic is reacted with oxygen gas at a high temperature of 1300 to 1600 ° C. in a gasification furnace to decompose the plastic into mainly CO, H ₂ , and HCl gases, and convert heavy metals into metal vapor. Accompany with gas. Next, the temperature is lowered in the cooling furnace and the gas composition becomes the oxidation condition of the heavy metal, the metal chloride or oxide is solidified, the heavy metal is collected by the dust collector, and then the hydrochloric acid gas is absorbed in the water. Hydrochloric acid is recovered, and unrecovered hydrochloric acid gas and chlorine gas are removed by a detoxification tower and then used as fuel gas or chemical raw material gas. Inorganic substances adhering to or contained in the waste plastic are melted in a gasification furnace, discharged from a slag tap, cooled and solidified in a water tank, and recovered to recover slag containing no heavy metal.

[0011]

DETAILED DESCRIPTION OF THE INVENTION It is known that chlorine-containing waste plastics do not generate harmful organic compounds containing chlorine when burned at high temperatures. Although high-temperature combustion is possible even with air combustion, the amount of exhaust gas increases to
In the high temperature combustion of 0 ° C. or more, almost complete combustion occurs, and the ratio of useful CO and H _{2 in} the product gas is small, most of which becomes CO ₂ and H ₂ O. Further, nitrogen gas is reduced to 50%. Only low-calorie gas containing the above can be obtained. In a reducing atmosphere under high temperature conditions, heavy metals become metal vapor and are present in the gas and can be separated from slag, but in an oxidizing atmosphere, they exist as oxides, and almost all metal oxides are present. Since it does not volatilize, it becomes impossible to separate it because it is contained in the slag. However, by burning with oxygen gas, it becomes possible to reduce the amount of combustion gas, and the sensible heat of combustion gas is greatly reduced, making it possible to obtain high-calorie gas mainly composed of CO and H ₂ gas. Attention was paid to the fact that heavy metals are also in a metallic state, and metals having a high vapor pressure, such as lead and zinc, are present in gas as metal vapor and are not included in slag. Further, since the concentration of hydrochloric acid gas in the generated gas increases and the amount of gas decreases, the capacities of the dust collecting facility, the hydrochloric acid collecting facility, and the detoxifying facility can be reduced. Furthermore, at a high temperature of 1300 ° C. or higher, the inorganic substances contained in the waste plastics are also melted, so that they can be easily separated from the gas. The inorganic substance has a high melting point depending on the component. In such a case, the melting point can be lowered by adjusting the component with an additive. The gasification temperature is preferably higher at a higher temperature from the viewpoint of melting inorganic substances and preventing generation of harmful organic compounds including chlorine, but is preferably 1600 ° C from the viewpoint of preventing the heat resistance of the gasification furnace and the increase in heat loss.
The following is assumed.

Next, the behavior of heavy metals will be described. The change in free energy of the reaction as a function of the temperature of lead is shown in FIG. The change in free energy indicates that the smaller the value (the larger-is below the graph in FIG. 2), the more the reaction proceeds. The equilibrium between lead and oxygen is C in the presence of CO and H _2.
As shown in FIG. 2, the temperature is higher than the reaction between O and H ₂ and oxygen, and therefore, metal oxide is present instead of lead oxide. In the reaction between lead and chlorine, it is shown that it exists as metal lead at 900 ° C. or higher and becomes lead chloride at 900 ° C. or lower. The same is true for zinc, but the equilibrium between zinc and oxygen is CO / (CO + CO
₂₎ = 0.05 or more zinc metal, in the gas composition _{CO / (CO + CO 2)} = 0.5 from becoming zinc oxide at a cooling temperature of 800 ° C. In _{CO / (CO + CO 2)} = 0.95 or less, the gas The difference from lead is that it becomes metallic zinc in a chemical furnace and zinc oxide in a cooling furnace. As a result, zinc and lead can be separated from slag as metal vapor in a high-temperature gasifier, and solidified as metal, metal chloride or metal oxide before the dust collector where the temperature has dropped, and collected by the dust collector. We focused on what we could do. The vapor pressure of the metal is 1400 ° C and zinc is 760 mmH
g or more and lead is 60 mmHg or more, these metals are present in the gas. On the other hand, in a cooling furnace, lead chloride having a high vapor pressure is only 1.3 × 10 ⁻¹¹ mmHg, which indicates that almost all can be recovered as a solid.

FIG. 1 shows an embodiment of an apparatus for implementing the method of the present invention. It is substantially composed of a gasification furnace 1, gas coolers 2, 3, a dust collector 5, and a hydrochloric acid absorption tower 6, and is provided with a cyclone 4 and an abatement tower 7 attached thereto.

The gasification furnace 1 is provided with a burner 8 on the side wall of the furnace body, which burns and reacts with the waste plastic after being pulverized and conveyed by gas and oxygen.
Is provided, and a water tank 9 is further provided thereunder.
The structure of the gasifier 1 is the same as that of a gas-bed coal gasifier, and is composed of a refractory furnace wall having a thickness of 20 to 50 mm, and the space between the refractory and the iron shell is cooled by a water-cooled pipe or a boiler water pipe. Thus, even if the furnace temperature is 1600 ° C., the refractory can be protected at 1400 ° C. or less. The cooling is preferably performed with a boiler water pipe and kept at a temperature of 200 to 300 ° C. in order to prevent the cooling pipe from being corroded at low temperature by contact with hydrochloric acid gas in the gas. Although not shown in FIG. 1, a preheating burner is provided between the slag tap 8 and the water tank 9 to raise the temperature of the gasification furnace to the ignition temperature of the waste plastic or more. Start operation with a preheated burner at a temperature above the ignition temperature of waste plastic.
Then, the waste plastic and oxygen are supplied to the burner 8 and burned. In the initial stage of combustion, a large amount of oxygen is supplied to raise the temperature, and when the temperature approaches a predetermined temperature, the amount of oxygen is reduced to a target temperature.

A gas cooling furnace 2 is provided above the gasification furnace 1, and a water spray type gas cooler 3, a cyclone 4, a dust collector 5, a hydrochloric acid absorption tower 6, and a detoxification tower 7 are provided in the subsequent stage. Are linked by The gas cooling furnace 2 can employ water spray cooling or a boiler, but it is preferable to use both a water spray for converting a heavy metal into a gas composition to be a metal chloride or a metal oxide and a boiler for heat recovery. FIG. 1 shows an embodiment in which a water spray nozzle 11 and a boiler heat transfer tube 12 are arranged at a gas inlet portion below the gas cooler 2, and both water spray cooling and a boiler are used. The gas cooler 2 cools the gas to a temperature of 200 to 300 ° C. to collect steam. The gas cooler 3 cools the gas to a temperature of 150 to 200 ° C. by water spray cooling to solidify heavy metal. The substances or oxides are collected by the cyclone 4 and the dust collector 5 together with the slag scattered and unburned organic substances. The cyclone 4 can be omitted. However, since metal oxides and chlorides of heavy metals are fine powder solidified from the gas, it is difficult to collect the cyclone 4 and the slag scattered in the gas is used in the cyclone 4. It is preferable to collect the metal first and then collect the metal with the dust collector 5 from the viewpoint that the concentration of the collected metal increases and the metal is reused. The dust collector 5 is preferably a highly efficient system such as a bag filter. The hydrochloric acid absorption tower 6 and the abatement tower 7 are absorption towers filled with teralet or the like.

The waste plastic is injected into the gasification furnace 1 together with the oxygen gas from the burner 7 and mainly emits CO, H ₂ , H
It is decomposed into Cl, and heavy metals become metal vapor. The generated gas is cooled in a cooling furnace 2 above the gasification furnace using one or both of a water spray and a boiler, and then cooled to about 150 to 200 ° C. in a gas cooler 3, and is cooled in a cyclone 4 and a dust collector 5. Removes heavy metal chlorides or oxides, fly ash-like inorganics and unburned carbon. Next, the hydrochloric acid absorption tower 6
The hydrochloric acid gas is absorbed by the water, and most of the hydrochloric acid gas is recovered. The remaining hydrochloric acid gas and chlorine gas by-produced are removed in an abatement tower 7 with an aqueous alkali solution such as caustic soda to obtain a clean gas, which is used as a fuel gas or a chemical raw material gas.
The inorganic substances contained in the waste plastic are melted in the gasifier 1 and fall from the slag tap 10 to the water tank 9 to obtain granulated slag containing no heavy metal.

[0017]

EXAMPLE Next, an example in which waste plastic containing vinyl chloride and heavy metal according to the present invention is treated at 5 T / H will be described. The waste plastic having the composition shown in Table 1 was pulverized to 5 mm or less, transported with nitrogen gas at 400 Nm ³ / H, and supplied to the burner.

[0018]

[Table 1] Oxygen gas 1700 Nm ³ / H and steam 1600 Nm ³ / H were blown in from a burner, and the gasification furnace temperature was 1430 ° C.
Was reacted. The steam was used to adjust the gasifier temperature. The gas was sprayed with 3.2 T / H of cooling water in a cooling furnace, and then cooled to 300 ° C. with a boiler to obtain 4 T / H of steam. Next, water was sprayed to 150 ° C. with a gas cooler, and after cooling, heavy metals and slag were collected with a cyclone and a bag filter, and 14.5 T / H of 18% hydrochloric acid was collected with a hydrochloric acid recovery tower. The recovered gas amount was 8930 Nm ³ / H in dry gas amount, and the gas composition is shown in Table 2.

[0019]

[Table 2] As gas calories, a gas having a calorie and composition close to that of the converter gas generated at an ironworks at 2015 kcal / Nm ³ is obtained, and can be effectively used as a fuel for a heating furnace, a boiler and the like. Hydrogen chloride gas in the gas was 1 ppm or less and chlorine gas was 5 ppm, and no organic chlorine compound was detected.
The organic chlorine compound has a gasification temperature of 1400 ° C. in this embodiment.
Therefore, it is highly probable that the organic matter was completely decomposed in the gasifier and was not generated in the boiler. Table 3 shows the solids recovered from the slag, cyclone and bag filter and the concentrations of zinc and lead.

[0020]

[Table 3] About 90% of inorganic substances other than heavy metals were recovered in the slag, and zinc and lead were below the detection limit. In the cyclone and bag filter, a mixture of slag components, zinc and lead was recovered. In the cyclone, a large amount of slag components having a large particle size was collected, but in the bag filter, the amount of recovered zinc and lead components was large. By recycling to the furnace,
It can be seen that it is possible to increase the amount of slag recovered and the amount of zinc and lead recovered by the bag filter. Most of the heavy metals collected by the bag filter are chlorides, and in this embodiment, there is an excess of hydrochloric acid. When the amount of hydrochloric acid is small, the heavy metals are collected as metal oxides. The bag filter collection contains more than 50% of metal and can be reused by recycling it to a metal smelting plant. The heavy metals in the recovered hydrochloric acid were 0.5 and 0.4 ppm for zinc and lead, respectively.
It was below.

[0021]

According to the present invention, a plastic containing a heavy metal and chlorine is reacted with oxygen gas at a high temperature,
It can be effectively recovered as fuel or chemical raw material gas, and heavy metals contained in waste plastic can be recovered as chlorides or oxides, and chlorine can be recovered as hydrochloric acid, and inorganic substances can also be used as slag. it can.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a waste plastic processing method and apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the behavior of lead of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gasifier 2 Gas cooler 3 Gas cooler 4 Cyclone 5 Dust collector 6 Hydrochloric acid absorption tower 7 Detoxification tower 8 Burner 9 Water tank 10 Slag tap 11 Water spray nozzle 12 Boiler

Claims (3)

[Claims] 1. A plastic containing chlorine and heavy metal is reacted with oxygen gas in a gasification furnace at 1300 to 1600 ° C. to decompose into CO, H ₂ and HCl gas,
The heavy metal is evaporated as metal vapor, the heavy metal accompanies the gas, separates it from the slag contained in the plastic, and is further cooled by a boiler or water spray cooling in a cooling furnace provided at the subsequent stage of the gasification furnace. And heavy metal to metal,
A method for treating waste plastics, comprising converting into a metal chloride or metal oxide, solidifying, collecting with a dust collector, and separating. 2. The method according to claim 1, wherein a hydrochloric acid recovery device is provided downstream of the dust collector to recover hydrochloric acid in the gas.
The method for treating waste plastic described in the above. 3. The waste plastic according to claim 1, wherein a slag tap is provided at a lower portion of the gasification furnace to melt and then solidify by cooling after melting the inorganic substance and the attached inorganic substance in the plastic. Processing method.