JPH10225668A - Thermal decomposition method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently fix a chlorine component discharged into thermal decomposition gas with thermal decomposition of a waste product with a simple means. SOLUTION: In a waste product treatment equipment having a thermal decomposition device for thermally decomposing the waste product, at least one kind among Ca(OH)2 , CaO and NaOH is preliminarily added to the waste product and is charged into the thermal decomposition device and is retained for more than 10mins. in a range of 250-300 deg.C, and then is heated at 400-800 deg.C in the same thermal decomposition device to obtain a thermal decomposition product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyrolysis method with high chlorine fixing efficiency in a waste treatment facility.

[0002]

2. Description of the Related Art In waste thermal decomposition equipment, HCl gas is generated during thermal decomposition, causing corrosion of equipment and generation of dioxin. For this reason, various methods have been studied so far for removing HCl gas from the pyrolysis gas.

As a method for removing HCl gas generated during thermal decomposition, a two-stage thermal decomposition method disclosed in Japanese Patent Application Laid-Open No. Sho 49-111470 is known. According to this, waste is treated using two pyrolyzers having different pyrolysis temperatures. The HCl gas generated in the preceding pyrolysis apparatus in which the pyrolysis temperature is set to 200 to 350 ° C. is once led out of the pyrolysis apparatus, dehydrochlorinated by a wet cleaning device, and then returned to the pyrolysis apparatus. Will be returned. According to the document, most of the HCl gas generated from vinyl chloride in the waste can be removed. The waste thus dehydrochlorinated has a thermal decomposition temperature of about 800
It is led to the subsequent pyrolysis device set at ° C. to complete the pyrolysis.

[0004] Therefore, in the known waste pyrolysis method, it is necessary not only to provide a pyrolysis apparatus dedicated to dehydrochlorination separately from the pyrolysis apparatus, but also to add a wet cleaning apparatus in consideration of high-concentration hydrochloric acid corrosion. The problem was that the equipment had to be complex and large-scale.

[0005] On the other hand, by mixing an alkaline solid such as Ca (OH) ₂ into the waste in advance, a reaction between the HCl gas generated during the subsequent pyrolysis and the alkaline solid causes a solid such as CaCl _{2 to be formed.} A method for fixing chlorine content has been devised and widely known. According to this method, it was considered that HCl gas generated during pyrolysis can be fixed only by adding a simple device for mixing waste and alkaline solid to a conventional pyrolysis device. However, when such a method is applied to an actual waste pyrolysis treatment, it is very difficult to secure a reaction rate between HCl gas and an alkaline solid, and it has not been an effective chlorine fixing method.

As a method for fixing chlorine content by mixing an alkaline solid in waste, a thermal decomposition method disclosed in JP-A-56-88491 is known. According to this, as a pretreatment, the waste is mixed with a granular inorganic substance containing an alkaline solid, and is heated and stirred and mixed at 120 to 250 ° C. to be converted into a granular mixed solid. The subsequent pyrolysis process is divided into two stages, the first stage at 250-400 ° C,
In the second stage, the solidified mixture is thermally decomposed at 400 to 800 ° C. In the first stage, it is stated that dechlorination of vinyl chloride is promoted to react with an alkaline solid, thereby fixing chlorine as chloride. Further, it is stated that 300 to 400 ° C. is the most suitable as the first-stage thermal decomposition temperature as a temperature range in which the dechlorination of vinyl chloride sufficiently proceeds and the generation of hydrocarbons from other wastes is suppressed.

[0007] In the official gazette of the known alkali solid addition pyrolysis method, there is no description of a specific apparatus configuration when applied to an actual waste treatment facility, but a large-scale pretreatment apparatus is required. It is clear that the advantage of the method of fixing chlorine with the addition of an alkali solid that the chlorine content can be removed with simple equipment is lost.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pyrolysis method for efficiently fixing chlorine released into waste pyrolysis gas without making the equipment complicated and large. And

[0009]

Means for Solving the Problems In order to solve this problem, the present inventors have focused on a chlorine fixation method by adding an alkaline solid which does not require special additional equipment, and studied a method for improving chlorine fixation efficiency. . As a result, it has been found that the reason why a sufficient reaction rate has not been obtained until now lies in the method of heating the waste during the pyrolysis.

FIG. 2 is a thermal decomposition curve of vinyl chloride, which is a main source of HCl gas contained in waste. As shown in the figure, vinyl chloride exhibits two-stage pyrolysis characteristics with increasing temperature, and it is known that the first-stage weight loss observed at 230 to 320 ° C. is derived from dehydrochlorination. Therefore, it has been considered that if an alkaline solid is mixed with the waste, HCl gas generated as the temperature rises in the pyrolysis apparatus immediately reacts with the alkaline solid, and the chlorine content is fixed. However, as already mentioned,
Even if the waste is treated by adding an alkaline solid,
The actual situation was that a chlorine fixation rate that was commensurate with the added amount was not obtained.

The present inventors paid attention to the temperature dependence of the reaction rate between HCl gas and alkaline solid, and investigated the reaction rate with HCl gas using Ca (OH) ₂ which is a typical alkaline solid. . As a result, it was found that the reaction rate sharply decreased with increasing temperature and approached 0% at 400 ° C. or higher. FIG. 3 shows the temperature dependence of the reaction rate.
From this figure, it can be seen that the temperature needs to be kept lower to ensure a sufficient reaction rate. Further, if the reduction in the reaction rate due to contamination of the surface of the alkaline solid when premixed with the waste is estimated to be 10%, it is necessary to lower the temperature to 350 ° C. or lower in order to promote an effective chlorine fixing reaction. You can see that. Therefore, in order to efficiently react the HCl gas contained in the vinyl chloride with Ca (OH) ₂ , it was found that it was necessary to stay in the temperature range of 230 to 350C.

FIG. 4 shows the relationship between the HCl removal rate and the heating temperature when vinyl chloride is heated in an electric furnace for 60 minutes. The HCl removal rate in the figure was obtained by analyzing the residual Cl amount of vinyl chloride after heating. FIG. 4 shows that the heating temperature should be 250 ° C. or higher in order to obtain a sufficient HCl removal rate in a short time. That is, from the viewpoint of the HCl removal rate, in order to complete the HCl removal in a shorter time, the retention temperature is preferably set to 250 ° C. or higher. Further, in order to suppress the addition amount of the alkaline solid and prevent the running cost from being unnecessarily increased, it is practical to set the reaction rate shown in FIG. 3 to at least 25% or more. The residence temperature is preferably set to 300 ° C. or lower. Therefore, a more preferable range of the residence temperature is 250 to 300.
° C.

In view of the above, the present inventors have found that in order to efficiently fix the chlorine content in the waste with an alkaline solid in the process of thermal decomposition of the waste, the waste must be 230 to 350 ppm.
It is necessary to stay in the temperature range of 2 ° C., more preferably 2
It was concluded that an appropriate time of residence at 50-300 ° C. should be reached.

Accordingly, the present inventors have developed a pyrolysis method capable of ensuring a sufficient residence time in the above-mentioned temperature range and continuously performing pyrolysis at 400 ° C. or higher in a single pyrolysis apparatus. It was investigated.

FIG. 1 is a diagram showing the relationship between the pyrolysis time and the waste temperature. The figure shows an example of a temperature rise curve of the waste in the conventional method and the pyrolysis method of the present invention. When a single pyrolysis apparatus is used, in the conventional pyrolysis method, the waste is heated to the final pyrolysis temperature immediately after being put into the pyrolysis apparatus.
Is 8 minutes or less at 250 to 300 ° C. for 3 minutes or less. On the other hand, the present inventors have introduced a temperature distribution in the pyrolysis apparatus or changed a temperature control program when heating the waste, and particularly, the residence time of the waste at 250 to 300 ° C. It has been found that the reaction between the generated HCl gas and the alkaline solid progresses by ensuring that the temperature is sufficiently high, and the chlorine fixing efficiency is remarkably improved.

In order to impart the thermal history shown in FIG. 1 to waste, a thermal decomposition apparatus such as a rotary kiln furnace is suitable. In a rotary kiln, by setting an appropriate temperature gradient in the retort in which wastes are heated and transported in advance, it is possible to continuously treat a large amount of wastes while providing an optimal heat history. Further, when the batch processing is performed on an appropriate waste, when the pyrolysis tank filled with the waste is heated, the waste temperature can be precisely controlled so that the heat history shown in FIG. 1 can be given. good.

According to the present invention, since the effect is immediately exhibited by giving the thermal history as shown in FIG. 1 to the waste to which the alkaline solid is added, a single thermal decomposition apparatus capable of providing the thermal history is provided. If so, the configuration, heating means, and the like are not limited at all.

Up to now, Ca (OH) has been increased with increasing temperature.
It was widely known that the reactivity of ₂ with HCl gas was reduced. However, up to the dehydration temperature of 580 ° C., Ca (O
Since H) ₂ was considered to have a constant reaction rate, it was expected that the reaction of fixing chlorine would proceed sufficiently at least at 400 ° C. or lower. Therefore, there is no example of precisely controlling the holding temperature within a very narrow temperature range with respect to the method of heating the waste to which the alkaline solid is added, and the fixing rate of the chlorine content has remained at a low level.

By applying the pyrolysis method of the present invention, the chlorine transferred from the waste to the pyrolysis gas can be efficiently fixed without making the equipment complicated and large. Thereby, the chlorine content in the gas generated by the thermal decomposition of the waste is significantly reduced, corrosion by HCl gas is avoided, and when this is used for combustion, the generation of dioxins can be suppressed.

The alkaline solid to be added is usually Ca
(OH) ₂ is used, but CaO can be selected if the waste contains sufficient moisture. CaO reacts with moisture when mixed with waste, immediately generates Ca (OH) ₂ and contributes to fixation of chlorine. When the amount of water in the waste is very small, NaOH can be selected. NaOH is Ca
Although it is more expensive than (OH) ₂ , it has high reactivity with HCl gas, and thus is effective in improving the fixing rate of chlorine.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments.

FIG. 5 is a schematic diagram of an externally heated rotary kiln furnace used to verify the effect of chlorine fixation by the pyrolysis method of the present invention. The waste crushed to about 15mm
It is loaded into a two-stage damper type input hopper 1 and is supplied to a screw feeder 2 in a state where intrusion of outside air is blocked. The waste is introduced into the retort 3 by a screw feeder at a substantially constant supply amount and is thermally decomposed. The pyrolyzed waste is separated into a pyrolysis residue and a pyrolysis gas by the separation device 4.
Further, the heating electric furnace 5 is a four-split type, and the temperature of the four electric furnaces can be controlled separately. By utilizing this, it is possible to introduce a desired temperature gradient in the direction of the rotation axis in the retort.

Using this apparatus, a simulated waste containing Ca (OH) ₂ and vinyl chloride is thermally decomposed at various residence times at 250 to 300 ° C., and the chlorine content due to Ca (OH) _{2 is} decomposed. The fixation rate to the residue was examined. The fixation rate was evaluated by analyzing the chlorine content in the recovered pyrolysis residue. The composition of the simulated waste is paper / 78 wt.%, Vinyl chloride / 10 w
t.%, and a Ca (OH) ₂ /12wt.%. The final pyrolysis temperature was 500 ° C, and the residence time at 500 ° C was 6 ° C.
0 minutes.

FIG. 6 shows the results of the examples and comparative examples.
It shows the relationship between the residence time at 0 ° C. and the percentage of chlorine fixed to the residue. The fixation rate increases with an increase in the residence time, but the increase in the fixation rate is small at a time longer than 10 minutes. This is considered to be due to approaching the upper limit of the fixed rate determined from the reaction rate shown in FIG. From this result, in order to obtain sufficient chlorine fixation rate,
It has been found that the residence time of the waste at the station should be at least 10 minutes. Further, even if a residence time exceeding 30 minutes is taken, the amount of improvement in the reaction rate is small, so that it was found that it is appropriate to set it to 10 to 30 minutes.

[0025]

By applying the pyrolysis method of the present invention to a waste treatment facility, it is possible to efficiently fix chlorine released into the pyrolysis gas without making the facility complicated and large. it can. This can prevent corrosion of equipment derived from HCl, and can avoid generation of dioxin when the pyrolysis gas is burned.

[Brief description of the drawings]

FIG. 1 is a graph showing the thermal decomposition characteristics of vinyl chloride.

FIG. 2 is a characteristic diagram of temperature dependence of a reaction rate between Ca (OH) ₂ and HCl gas.

FIG. 3 is a graph showing a temperature rise characteristic of waste by the pyrolysis method of the present invention and the conventional pyrolysis method.

FIG. 4 is a characteristic diagram showing the relationship between the heating temperature and the HCl removal rate when vinyl chloride is heated for 60 minutes.

FIG. 5 is an explanatory diagram of a rotary kiln furnace that has verified the effect of the thermal decomposition method of the present invention.

FIG. 6: 250 to 300 ° C. of Examples and Comparative Examples of the present invention
Diagram of residence time and chlorine fixation rate in a room.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Input hopper, 2 ... Screw feeder, 3 ... Retort, 4 ... Separation apparatus, 5 ... Electric furnace for heating.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshio Yamashita 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. A waste treatment facility having a pyrolyzer for thermally decomposing waste, using Ca (OH) ₂ , CaO and NaO.
In the thermal decomposition method of heating the waste to which at least one alkaline solid of H is added to fix the chlorine content in the waste, the waste to which the alkaline solid is added is heated at 230 to 350 ° C. in the thermal decomposition apparatus. , The chlorine content in the waste is released as HCl and, at the same time, fixed as chloride with an alkaline solid, and then heated to 400 to 800 ° C in the same pyrolysis apparatus to generate pyrolysis. A pyrolysis method characterized by obtaining a product. 2. The thermal decomposition method according to claim 1, wherein the temperature at which the chlorine content in the waste is fixed as chloride is 250 to 300 ° C., and the residence time in the temperature range is 10 minutes or more. 3. The thermal decomposition method according to claim 1, wherein the thermal decomposition device comprises a rotary pyrolysis drum device.