JPH0576890B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for preventing ignition during volume reduction treatment of waste plastics, in particular, by limiting the oxygen concentration in the treatment atmosphere to 15% by volume or less. Concerning methods for preventing ignition and thermal decomposition of waste plastics.

(Conventional technology) As a method for reducing the volume of waste plastic,
For example, in a volume reduction kiln consisting of a cylindrical head and a funnel-shaped lower part, hot air is introduced into the kiln from multiple nozzles provided on the outer periphery, that is, the side wall of the funnel-shaped lower part, and the waste plastics charged into the kiln are removed. A method of reducing the volume by direct heating to soften and melt is known, but in this method, it is necessary to prevent the generation of harmful gas components and odor components due to thermal decomposition of waste plastics, or to reduce the volume by burning waste plastics. In order to process the waste plastic without causing any decomposition, the basic operating conditions are to soften and melt the waste plastic at a temperature lower than the thermal decomposition temperature of the plastic. The temperature is set lower than the starting temperature.

Usually, waste plastics are a mixture of various plastics with different thermal characteristics such as ignition temperature, ignition temperature, and decomposition temperature, so the temperature of the hot air is lower than the decomposition temperature of any of the various plastics included. The temperature is set, which is generally in the range of 150-200℃.

However, in reality, despite heating at such low temperatures, in some cases thermal decomposition occurs and odor components are generated, and this progresses further, resulting in ignition and combustion. may reach.

The generation of odor components or ignition and combustion not only impede stable treatment operations but also cause safety and environmental conservation problems, and therefore measures to prevent this are required.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for preventing such thermal decomposition or ignition combustion of waste plastics as much as possible.

(Means for Solving the Problems) As a result of various studies aimed at solving the problems, the present inventors have obtained the following knowledge.

First of all, despite the low temperature atmosphere below the thermal decomposition temperature as mentioned above, plastics sometimes undergo thermal decomposition or ignition combustion.
It is assumed that the main cause is the oxidation heat generated by the plastic. Normally, plastics are hardly oxidized at ambient temperature, or even if they are oxidized, the oxidation rate is extremely low. However, when heated, such as in a volume reduction kiln, oxidation is significantly accelerated, and the heat of oxidation is increased. It is thought that there is an outbreak.

When plastic oxidation occurs in this way, if the plastics are sufficiently dispersed and the oxidation heat is dissipated, the temperature of the plastic itself will hardly rise, but the plastic will remain in a cohesive state. In this case, the oxidation heat is not sufficiently dissipated and accumulates inside the aggregate, causing the temperature to gradually rise.

If a part of the plastic sticks or sticks inside the volume reduction kiln and stays in an agglomerated state for a long time, the above-mentioned temperature rise will occur inside the kiln, and the plastic will eventually break down. It is expected that the temperature will rise above the temperature at which thermal decomposition begins, and in some cases even reach the ignition temperature.

Therefore, since it is difficult to dissipate oxidation heat, the present inventors focused on creating conditions where oxidation does not occur even at high temperatures. The present invention was completed based on the knowledge that the oxidation of plastics can be prevented or slowed down, and the thermal decomposition and combustion of plastics can be effectively prevented.

In addition, in the conventional method, to obtain hot air at a predetermined temperature, a method is used in which fuel such as kerosene is burned in a burner to generate high-temperature gas, which is diluted with air and adjusted to a predetermined temperature. However, in order to obtain the normally required hot air temperature of 150 to 200°C, it must be diluted with a large amount of air, and the hot air after dilution has a high oxygen concentration of around 20%. This was inevitable, and the situation was such that plastic oxidation was likely to proceed.

Here, the gist of the present invention is to introduce waste plastic into a waste plastic volume reduction kiln consisting of, for example, a cylindrical head and a funnel-shaped lower part, and introduce hot air from a nozzle provided on the outer periphery of the kiln. This is a method for preventing ignition in waste plastic volume reduction processing, which is characterized in that when performing waste plastic volume reduction processing, the oxygen concentration in the internal atmosphere of the volume reduction oven is limited to 15% by volume or less.

Thus, according to the present invention, the oxygen concentration in the internal atmosphere of the volume reduction kiln is limited to 15% by volume or less, but this condition is limited to the temperature at which the waste plastics are heated after being blown into the volume reduction kiln. Recirculating the sagging hot air as a diluent gas to the hot air generator preferably eliminates air dilution and reduces the oxygen concentration of the hot air blown through the nozzle into the kiln.
This is achieved by reducing the amount of plastic to 15% by volume or less, thereby preventing or slowing down the oxidation of waste plastics, and even if plastic agglomeration occurs in the kiln, it will not start thermal decomposition. It is possible to avoid ignition and combustion.

The lower the oxygen concentration is, the better it is for preventing oxidation, but it is economically expensive to lower it too much, so it is generally preferred to be about 15 to 5% by volume.

Accordingly, according to another aspect of the invention,
For example, waste plastics are put into a waste plastics volume reduction kiln consisting of a cylindrical head and a funnel-shaped lower part, and hot air is introduced from a nozzle installed on the outer periphery of the kiln to reduce the volume of the waste plastics. The hot air used to heat the plastic is recovered from the upper part of the volume reduction kiln, passed through a hot air generator and reused, and the oxygen concentration of the hot air supplied to the volume reduction kiln is
This is a method for preventing ignition in waste plastic volume reduction processing, which is characterized by limiting the amount to 15% by volume or less.

According to yet another aspect, the present invention provides a method for reducing the volume of waste plastic by charging the waste plastic into a waste plastic volume reduction kiln and introducing hot air from a nozzle provided on the outer periphery of the kiln.
The hot air used to heat the waste plastic is recovered from the volume reduction kiln, and exhaust gas recovered from another appropriate combustion furnace is mixed with the recovered hot air and supplied to the volume reduction kiln, and its oxygen concentration is reduced to 15 volumes. This is a method for preventing ignition in waste plastic volume reduction processing, which is characterized by limiting the amount of ignition to below %.

(Operation) The present invention will be further described in detail with reference to the accompanying drawings.

The configuration of the apparatus according to the present invention is shown in FIG.

In the illustrated example, a furnace body 6 consisting of a cylindrical head 2 and a funnel-shaped lower part 4 is entirely surrounded by an envelope 8, and there is only one type of space 9 surrounded by the furnace body 6 and the envelope 8. It consists of a wind box and a heat insulator, through which hot air is sent into the kiln.

In the conventional device, the volume reduction processing device, that is, the volume reduction kiln 10
Conventionally, the hot air 12, which is the exhaust gas introduced into the waste plastic and used to heat the waste plastic, is released directly to the outside air, but in the present invention, the exhaust gas 12 is
2 is recirculated to the hot air generator 16 through the circulation fan 14. This hot air generator 16 is composed of a burner 18 . Thereby, there is no need to introduce fresh air other than the combustion air in the burner 18, and the oxygen concentration of the hot air can be lowered. Normally, the air ratio of the burner 18 is suppressed to 2 or less, and the pressure near the input port 20 of the volume reduction kiln 10 is raised slightly.
By preventing air from being sucked in, the oxygen concentration in the circulating gas can be suppressed to about 10% or less.

The hot air 22 prepared in this way is supplied to the input port 2.
0, and is blown into the furnace from a plurality of nozzles 26 provided on the outer circumference 24 of the volume reduction furnace 10.

FIG. 2 shows another suitable combustion furnace 26 (e.g. boiler,
FIG. 2 is a schematic explanatory diagram showing an example of using hot air, which is exhaust gas collected from a garbage incinerator, etc. If such exhaust gas is available in large quantities, there is no need to use a hot air generator consisting of a burner as shown in FIG.
It is sufficient to simply mix the above exhaust gas and the hot air recovered from the volume reduction kiln. Generally, the oxygen concentration of the combustion furnace exhaust gas is 2 to 3% by volume, and therefore some air may be added to this for cooling purposes. In the drawings, the same members are designated by the same reference numerals as in FIG.

Next, the present invention will be described in detail with reference to specific examples thereof, but these are merely illustrative of the present invention, and the present invention is not limited thereto.

Example: The present invention reduces the oxygen concentration of hot air through exhaust gas recirculation, suppresses heat generation and temperature rise due to oxidation of plastics, and reduces thermal decomposition of plastics.
This is intended to prevent ignition and combustion, and its effectiveness was confirmed through a preliminary heating test and a large-scale field test using a large testing machine.

(Preliminary test) In the sample test, two samples were prepared by compression molding approximately 50 g of waste plastic from municipal waste, and one was placed in an air atmosphere and the other was placed in a heater at 180°C with the air shut off. This was done by comparing the temperature change at the center of the sample at that time. As a result, the temperature of the sample heated in an air atmosphere rapidly rose to exceed 300°C after about 20 minutes, but the temperature of the sample heated in an air-blocked state rose slowly, reaching about 300°C. in minutes
It reached 180℃ and then held for another hour, but
The temperature never exceeded 180°C.

These results confirmed that oxygen concentration has a large effect on plastic oxidation, and that cutting off oxygen can almost completely suppress oxidation heat generation.

(Practical test) Next, using a large volume reduction kiln test machine with a kiln internal volume of 2 m ³ as shown in Figure 1, exhaust gas (100°C) from the kiln was recirculated to increase the oxygen concentration of the hot air to 20%, 15% ( The effect of lowering the oxygen concentration on preventing plastic oxidation heat generation was investigated.

The test method was to keep the temperature of the blown hot air constant at 180℃, put 50 kg of waste plastic from municipal waste as a test material into a volume reduction kiln, and after sufficiently shrinking and melting, leave it for a long time to check the odor at that time. The generation and ignition combustion conditions were observed.

If the hot air collected from the top of the kiln is not recirculated and the oxygen concentration of the hot air is adjusted to 20%, approximately
After 15 minutes, the smoke became noticeable and then the fire started immediately.

The hot air exhaust gas collected from the top of the kiln is recirculated,
If the oxygen concentration is limited to 15% by volume, 30
Even after being left for a minute, no ignition was observed and the temperature did not rise to the decomposition temperature, so there was no overheating and no increase in odor was observed.

(Effects of the Invention) As detailed above, according to the present invention, there is no overheating part of waste plastic, and the conventional problems of ignition and odor generation during volume reduction processing are effectively prevented. Even small-scale facilities installed in densely populated areas can continue to operate with peace of mind without becoming a source of pollution.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for carrying out the method according to the invention; and FIG. 2 is a schematic diagram also showing a modification. 10: Volume reduction kiln, 12: Exhaust gas, 14: Circulation fan, 16: Hot air generator, 18: Burner, 20: Nozzle.

Claims (1)

[Scope of Claims] 1. When waste plastic is charged into a waste plastic volume reduction kiln and hot air is introduced from a nozzle provided on the outer periphery of the volume reduction kiln to reduce the volume of the waste plastic, A method for preventing ignition during volume reduction treatment of waste plastics, which is characterized by limiting the oxygen concentration in the internal atmosphere of a kiln to 15% by volume or less. 2. The hot air used to heat the waste plastic is recovered from the volume reduction kiln, passed through a hot air generator, and reused, and the oxygen concentration of the hot air from the hot air generator is limited to 15% by volume or less. A method for preventing ignition during volume reduction treatment of waste plastics according to claim 1. 3. When the hot air used to heat the waste plastic is recovered from the volume reduction kiln, exhaust gas from another appropriate combustion furnace is recovered and mixed with the above-mentioned recovered hot air for reuse, and its oxygen concentration is 15% by volume
A method for preventing ignition in waste plastic volume reduction treatment according to claim 1, which is limited to the following.