JPH11314945A - Production of quicklime and calcined dolomite in rotary kiln utilizing waste plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain such a process for production which makes the characteristics of products constant by using waste plastics having fluctuating combustion characteristics as fuel in the process for producing quicklime and calcined dolomite in a rotary kiln. SOLUTION: In the process for producing the quicklime and calcined dolomite by blowing main fuel and the waste plastics below a prescribed particle size as part of the fuel into the rotary kiln, the exhaust gas temp. in the exhaust gas of the outlet of the rotary kiln is detected and the blowing rate of the waste plastic particles is so controlled that the detected temp. coincides with the pre-set temp. of the exhaust gases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing quicklime and calcined dolomite in a rotary kiln using waste plastics as fuel together with heavy oil as a main fuel,
More particularly, the present invention relates to a method for producing quicklime and calcined dolomite of a good quality by controlling the blowing speed of waste plastic into a rotary kiln.

[0002]

2. Description of the Related Art Waste plastic is a heat source having a high calorific value, but is discarded without being used as a fuel because the flammability of waste plastic is inferior to other fuels such as heavy oil and pulverized coal. . However, the recycling of waste plastics has been gradually attempted from the viewpoint of environmental problems or effective utilization of resources.

Paying attention to the fact that waste plastic is a resource having a high calorific value, various methods using waste plastic have been proposed. For example, JP-A-46-15037
Japanese Patent Application Publication (hereinafter referred to as "prior art 1") discloses a method for producing cement clinker using waste plastic.

Further, Japanese Patent Laid-Open Publication No.
"Prior art 2") discloses a method in which a fiber reinforced plastic is added to a rotary kiln for treatment. Further, Japanese Patent Publication No. 59-11545 (hereinafter referred to as "prior art 3") discloses a method for producing Portland cement using municipal waste.

Conventionally, it is well known that quicklime and calcined dolomite are produced by calcining limestone / dolomite, shells and the like as raw materials.
Rotary kilns are also known to be advantageous devices for burning various fuels because of the relatively large space through which the combustion gases pass through the charge.

FIG. 6 shows an outline of a conventional rotary kiln for producing quicklime and calcined dolomite. Less than,
An outline of a method for producing quicklime and calcined dolomite in a conventional rotary kiln will be described with reference to FIG. Raw stones such as quicklime and calcined dolomite are supplied from the raw stone silo 1 containing them to the great preheater 2, where they are preheated by exhaust gas discharged from the rotary kiln and then charged into the rotary kiln 6.

A rotary kiln is a cylindrical heating furnace constructed by lining a circular steel shell with a refractory material, and rotates around an axis at a constant speed during operation.
In FIG. 6, the limestone / dolomite charged from the left inlet passes through the rotating furnace and moves toward the right outlet. In the rotary kiln, as shown in FIG.
It is inclined upward with an inclination of 0 to 4/100. The charged limestone and dolomite rotate in the furnace while being fired, change into quick lime and burnt dolomite, and move toward the exit.

At the outlet of the rotary kiln, in addition to a heavy oil injection nozzle (not shown) used as a main fuel, a pulverized coal supply device 8 for supplying pulverized coal, for example, is also provided. The furnace is burned by the blown air, and the inside of the furnace is maintained at a high temperature of 1000 ° C. or higher. Limestone and dolomite are calcined by the heat generated by the combustion of the heavy oil and pulverized coal, and change into quicklime and calcined dolomite.

The air for burning the fuel passes through a great cooler 7 for cooling the discharged quicklime and calcined dolomite, thereby performing heat exchange with the quicklime and calcined dolomite. As a result, on the one hand, air cools hot quicklime and calcined dolomite, on the other hand, the air receives heat and becomes hot, and is blown into the rotary kiln from the outlet side, burning heavy oil and pulverized coal as the main fuel. Supply of hot air.

[0010] The temperature inside the rotary kiln is about 600 ° C at the outlet side of the furnace. In particular, the portion of the flame generated when the fuel is burned partially reaches 1500 ° C or more, which is accompanied by the decomposition reaction of limestone and dolomite. As a result, the temperature decreases to about 1000 ° C. at the limestone / dolomite charging inlet side, that is, at the exhaust gas outlet side. This high-temperature exhaust gas of about 1000 ° C. preheats the limestone and dolomite added to the great preheater 2 described above,
Here, after part of the heat is released, the heat passes through the waste heat boiler 3 and is discharged outside through the dry dust collector 4 and the wet dust collector 5.

The above is the outline of the rotary kiln facility for producing quicklime and calcined dolomite. Conventionally, a rotary kiln mainly uses heavy oil as fuel, and uses pulverized coal as a part. However, all of these fuels are expensive, and it is required to produce quicklime and calcined dolomite at lower cost.

[0012] These heavy oils are about 10,000 kcal / k
g, pulverized coal has a calorific value of about 6000 kcal / kg. On the other hand, waste plastic is about 10,000 kcal
/ Kg of heat, which can be a valuable heat source together with pulverized coal.

However, waste plastics are usually obtained in various shapes and, as described above, are not easily combusted, and thus, at present, they have been dumped without being used as fuel. As the waste plastic, a large amount of waste such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride is generated at present. Therefore, while reusing these waste plastics as heat sources to treat waste,
Using this inexpensive plastic as fuel, quicklime
There is a demand for inexpensive production of calcined dolomite.
Note that quicklime and calcined dolomite are one of the important chemical raw materials widely used in the steel industry or the chemical industry.

A method for producing quicklime and calcined dolomite using waste plastic in the above-mentioned rotary kiln is disclosed in Japanese Patent Application Laid-Open No. Hei 8-283051 (hereinafter referred to as "prior art 4").

The method for producing quicklime and calcined dolomite using waste plastic in prior art 4 is as follows: (a)
A step of turning waste plastic particles into a fine flow as a part of fuel during the production of quick lime and calcined dolomite in a rotary kiln; (b) blowing the fine flow of waste plastic particles and the main fuel into the rotary kiln; At least partially crosses the flame of the main fuel and blows the unburned waste plastic particles so that the falling point in the rotary kiln is within a distance of the flame length of the main fuel.

That is, prior art 4 solves a method of charging waste plastic into a rotary kiln and a method of charging waste plastic at a desired position in a rotary kiln in order to more completely burn waste plastic that is not easy to burn. ing.

[0017]

However, the prior arts 1 to 3 merely disclose the use of waste plastics, and use the waste plastics as fuel to produce desirable quicklime and calcined dolomite in a rotary kiln. No method is disclosed.

Further, as described above, prior art 4 solves the problem of how to place waste plastic in a rotary kiln and at what position.
There are the following problems. That is, in the prior art 4, the calorific value of the waste plastic is set in advance, and the blowing speed of the waste plastic into the rotary kiln is determined from the calorific value thus set and the necessary total calorific value of the waste plastic. The waste plastic is blown into the rotary kiln at the blowing speed (constant) thus determined.

FIG. 3 shows a conventional flow for controlling the blowing speed of waste plastic. When operating a rotary kiln,
As described above, the blowing speed of the waste plastic is constant, but when the quality of the product and the degree of firing change, the blowing speed of the waste plastic is changed. In this case, the frequency of change is at least every 24 hours, based on the residence time of the limestone in the rotary kiln and the time until the product is inspected and determined.

The waste plastic used in the rotary kiln is obtained by crushing so-called waste plastic and forming it into particles having a particle size of about 10 mm.
During the molding process, the waste plastic generates heat, so that water is sprayed on the waste plastic as a coolant. The amount of water spray varies depending on the type, particle size, etc. of the plastic.
Therefore, the moisture content of the molded waste plastic is also 0.5%.
It varies in the range of 10% to 10%.

The water content of the waste plastic is 0.5 to 10%
Fluctuates within the range, the calorific value of the waste plastic becomes 94
It fluctuates by about 00 to 8400 kcal / kg. Further, since waste plastics have various components and their ratios are not constant, the calorific value varies even if the water content is constant.

The typical types of plastics and their calorific values are as follows. Polyethylene: 10300 kcal / kg Polypropylene: 10180 kcal / kg Polystyrene: 9650 kcal / kg Vinyl chloride: 5060 kcal / kg

Therefore, if the blowing speed of the waste plastic is made constant by the method of the prior art 4, the total calorific value of the waste plastic to the rotary kiln fluctuates.
It is difficult to obtain a product of a certain quality and firing degree. Furthermore, since excessive waste plastic is sometimes blown more than necessary, it cannot be said that the blowing method is good in terms of thermal efficiency.

Further, as described above, even if the blowing amount of the waste plastic is changed every 24 hours, it cannot follow the rapid change in the calorific value of the waste plastic. The control of the blowing speed of the air does not actually have any effect. Accordingly, an object of the present invention is to provide a method for producing quicklime and calcined dolomite having a constant quality and a degree of calcining in a rotary kiln while responding to a rapid change in the calorific value of waste plastic.

[0025]

Means for Solving the Problems The inventors have made intensive studies to overcome the above-mentioned problems of the prior art. As a result, when the calorific value of the waste plastic fluctuates depending on its water content and type, and when the total calorific value of the waste plastic blown into the rotary kiln fluctuates, the exhaust gas temperature at the exhaust gas outlet of the rotary kiln changes.

That is, when the total calorific value of the waste plastic becomes larger than the set amount, the exhaust gas temperature at the exhaust gas outlet of the rotary kiln rises, and when the total calorific value becomes smaller than the set amount, the exhaust gas temperature at the exhaust gas outlet of the rotary kiln becomes larger. Therefore, by controlling the supply rate of waste plastic based on the exhaust gas temperature at the exhaust gas outlet of the rotary kiln, it is possible to produce quicklime and calcined dolomite while responding to rapid changes in the calorific value of waste plastic. I found out and made the following invention.

In the first aspect of the method for producing quicklime and calcined dolomite in a rotary kiln using waste plastic according to the present invention, waste plastic particles having a predetermined particle size or less as a main fuel and a part of fuel are blown into the rotary kiln. In a method for producing quicklime and calcined dolomite, the exhaust gas temperature at the exhaust gas outlet of the rotary kiln is detected, and the detected exhaust gas temperature at the exhaust gas outlet of the rotary kiln set in advance matches the detected exhaust gas temperature, The blowing speed of the waste plastic particles is controlled.

Further, in a second aspect of the present invention, when the detected exhaust gas temperature is higher than the predetermined temperature, the blowing speed of the waste plastic particles is reduced, and the detected exhaust gas temperature becomes lower than the predetermined temperature. When it is also low, the blowing speed of the waste plastic particles is increased.

Further, in the method for producing quicklime and calcined dolomite in a rotary kiln using waste plastic according to the present invention, waste plastic as fuel is blown into the furnace as a fine bundle of particles having a diameter of 20 mm or less. Things.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described with reference to the drawings. FIG. 4 is a diagram illustrating one embodiment of the method for producing quicklime and calcined dolomite in a rotary kiln using waste plastic according to the present invention. In FIG. 4, the flow of the solid charge is indicated by a solid line, and the flow of the waste plastic is indicated by a chain line. Further, the gas flow is indicated by broken lines. The ore such as quicklime and calcined dolomite, which are solid charges, is supplied from the ore silo 1 containing them to the great preheater 2 where it is preheated by the exhaust gas from the rotary kiln and then charged into the rotary kiln 6 Is done.

Limestone / dolomite is charged from the left inlet of the rotary kiln, and heavy oil (not shown) or heavy oil, pulverized coal, and waste plastic particles 13 are blown as main fuel from the right outlet of the rotary kiln. The charged limestone and dolomite are turned into quicklime and burnt dolomite while rotating in the furnace while being burned by the combustion of the injected fuel, and move toward the outlet.

At the outlet of the rotary kiln, a pulverized coal supply device 8 for supplying pulverized coal as fuel and a waste plastic blowing device 9 are provided. For example, a table feeder is provided, and the waste plastic metering device 10 is further provided with a waste plastic supply control device 11, for example, an electric proportional control device. Further, an exhaust gas temperature detecting device 12 is provided at the exhaust gas outlet of the rotary kiln, and the detected temperature of the exhaust gas is sent to the waste plastic supply control device 11.

Waste plastic particles having a diameter of 20 mm or less, preferably 15 mm or less, are blown into the furnace at a constant initial velocity as a fine bundle flow from a waste plastic injection nozzle located near the outlet. This waste plastic is burned by heavy oil as the main fuel blown into the furnace, or high-temperature air supplied from the outlet together with heavy oil and pulverized coal, thereby keeping the inside of the furnace at a high temperature of 1000 ° C. or higher. Limestone and dolomite are calcined by the heat generated by the combustion of the heavy oil, waste plastic and pulverized coal, and change into quicklime and calcined dolomite.

Air for combustion of heavy oil, waste plastics and pulverized coal exchanges heat by passing through a great cooler 7 for cooling the discharged quicklime and calcined dolomite. The dolomite is cooled while the hot air is blown into the rotary kiln from the outlet side as described above, and serves as a hot air supply source for burning heavy oil, waste plastics and pulverized coal.

In order to sufficiently burn the hardly combustible waste plastic, the waste plastic is introduced at least in a range where the oxygen concentration exists to some extent. That is, waste plastic is made into a fine bundle flow by the blowing nozzle, and the fine bundle flow is dropped so as to cross the flame formed by heavy oil as the main fuel. The injection of heavy oil rotates the flame, for example, clockwise. On the other hand, since the furnace body of the rotary kiln is rotating clockwise, the solid charge is present in a state where it is biased in the position of the third quadrant of the cross section of the furnace body (as viewed from the furnace body outlet side). .

Therefore, by disposing a waste plastic blowing nozzle above the nozzle for blowing heavy oil,
The waste plastic falls to a position in the fourth quadrant (as viewed from the furnace body outlet side) of the cross section of the furnace body. As a result, the particles of the dropped waste plastic do not mix with the solid lime and calcined dolomite, which is a solid charge, and the quality of the calcined lime and calcined dolomite is maintained in a good state.

The temperature inside the rotary kiln is about 600 ° C. at the outlet side, and particularly, the portion of the flame generated when heavy oil is burned partially becomes 1500 ° C. or more, and the temperature accompanying the decomposition reaction of limestone and dolomite. At the inlet of limestone / dolomite, that is, at the outlet of gas, the temperature drops to about 1000 ° C. This 100
The high-temperature exhaust gas of about 0 ° C. preheats the limestone and dolomite added to the above-mentioned great preheater 2, releases a part of the heat, passes through the waste heat boiler 3, and is discharged outside. You.

FIG. 1 shows a control flow of the blowing speed of the waste plastic of the present invention. First, a predetermined exhaust gas temperature is set. When the detected exhaust gas temperature matches the set temperature, the operation is continued. When the detected exhaust gas temperature is higher than the predetermined temperature, the blowing speed of the waste plastic particles is reduced, and when the detected exhaust gas temperature is lower than the predetermined temperature, the blowing speed of the waste plastic particles is increased.

The blowing speed can be controlled by a conventional feedback method, for example, by a control method of inducing the current value to a predetermined set value by a PID operation. By controlling the blowing speed of the waste plastic by the control method described above, it is possible to cope with a rapid change in the calorific value of the waste plastic.

Further, the quality of a product is determined by its shape, color and size, especially the rate of removal of carbon dioxide from the ore. This determination is made, for example, every 24 hours, and the set value of the exhaust gas temperature can be changed. Thus, quicklime and calcined dolomite having a certain quality and a degree of calcining can be produced.

[0041]

EXAMPLE As shown in the table of FIG. 7, the total length is about 50 m, the inner diameter is 2.8 m, the inclination is 3.5 / 100, and the rotation speed is 1.0 rpm.
An experiment was conducted using a rotary kiln to inject waste plastic as fuel. In this apparatus, heavy oil and waste plastic, heavy oil and waste plastic, and pulverized coal were used as fuel. The operation results are shown in the table of FIG.

In this rotary kiln, 200 tons of quicklime and calcined dolomite were produced per day. In Case 1, waste plastic (polyethylene particles) was blown at about 140 kg / h at the start of operation, and in Case 2, at the start of operation, blown at about 370 kg / h, and the blowing rate of waste plastic by the method of the present invention described above. For at least 24 hours.
For comparison, a normal operation was performed according to the flow of the conventional waste plastic blowing speed shown in FIG. 3 as a normal operation. In normal operation, waste plastic is reduced to about 16
Blowing was performed at a constant blowing speed of 0 kg / h.

FIG. 2 shows the results of the blowing amount of waste plastic and the exhaust gas temperature at the exhaust gas outlet in case 2 according to the method of the present invention, in the case of normal operation by the conventional method, and in the exhaust gas outlet. In cases 1 and 2 of the present invention, the predetermined temperature was set to 1000 ° C.

As is clear from FIG. 2, according to the conventional method, since the amount of blowing waste plastic (blowing speed) is constant, the temperature of the exhaust gas at the exhaust gas outlet fluctuates greatly. Therefore, as shown in FIG. 5, it can be seen that it is difficult to obtain quicklime and calcined dolomite of constant quality and calcining degree.

On the other hand, according to the method of the present invention, the temperature of the exhaust gas at the exhaust gas outlet is detected and the blowing speed of the waste plastic is controlled based on the detected temperature, so that the blowing amount of the waste plastic matches the predetermined blowing speed. When the amount is small or large, it is greatly changed so as to compensate for it, and as a result, the exhaust gas temperature is controlled within a certain range.

Therefore, as shown in FIG. 5, it is possible to obtain quicklime and calcined dolomite having a constant quality and a degree of calcining, and an extremely efficient operation is performed. Specifically, the decomposition rate of the conventional method is 96 to 99%, but in the present invention, it is 97% or more, the dispersion is small, and the decomposition rate is high.

At this time, in consideration of the heat generated by the combustion of the waste plastic, the corresponding amount of the main fuel was reduced. When calculated from the calorific value, the amount of waste plastic injected (co-firing rate) is about 10% in case 1 and about 2% in case 2.
0%. The decomposition rate shown here is a percentage of the difference between the amount of carbon dioxide in the input limestone and dolomite and the amount of carbon dioxide remaining in the product quicklime and calcined dolomite.

From the results shown in FIG. 5, there was no significant change in the concentration of the combustion gas at the outlet, and a good product was obtained even in consideration of the decomposition rate. The composition of the exhaust gas at the charging port was analyzed and found to be the same as in normal operation.

[0049]

As described above, while controlling the blowing speed of the waste plastic particles by the method of the present invention, by blowing the waste plastic particles into an appropriate place in the rotary kiln, the calorific value of the waste plastic particles can be increased. While responding to the rapid fluctuation of
Moreover, quick lime with a certain quality and degree of firing
Burned dolomite could be produced.

Further, since waste plastic is inexpensive in terms of cost, it can greatly contribute to a reduction in production cost.
Therefore, while waste plastics, which have been mainly dumped, can be effectively used as a heat source, they can also contribute to the reduction of wastes, which proves that the invention is extremely environmentally effective.

[Brief description of the drawings]

FIG. 1 is a diagram showing a control flow of a blowing speed of waste plastic by a method of the present invention.

FIG. 2 is a diagram showing a change over time of a blowing amount of waste plastic and a temperature of exhaust gas at an exhaust gas outlet according to the method of the present invention.

FIG. 3 is a diagram showing a control flow of a blowing speed of waste plastic by a conventional method.

FIG. 4 is a diagram illustrating one embodiment of a method for producing quicklime and calcined dolomite in a rotary kiln using waste plastic according to the present invention.

FIG. 5 is a diagram showing operation test results.

FIG. 6 is a diagram illustrating a method for producing quicklime and calcined dolomite in a conventional rotary kiln.

FIG. 7 is a view showing specifications of a rotary kiln facility.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rough silo 2 Great preheater 3 Waste heat boiler 4 Dry dust collector 5 Wet dust collector 6 Rotary kiln 7 Great cooler 8 Pulverized coal supply device 9 Waste plastic injection device 10 Waste plastic quantitative supply device 11 Waste plastic supply control device 12 Exhaust gas temperature detection device 13 Waste plastic

 ────────────────────────────────────────────────── ─── Continued from the front page (72) Inventor Takuya Kadowaki 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (3)

[Claims] 1. A method for producing quicklime and calcined dolomite by blowing a main fuel and waste plastic having a predetermined particle size or less as a part of a fuel into a rotary kiln, wherein the exhaust gas temperature at an exhaust gas outlet of the rotary kiln is reduced. The production of quicklime and calcined dolomite in a rotary kiln using waste plastics, characterized in that the blowing rate of the waste plastic particles is controlled so that this temperature matches a preset temperature of the exhaust gas. Method. 2. When the detected exhaust gas temperature is higher than the predetermined temperature, the blowing speed of the waste plastic particles is reduced, and when the detected exhaust gas temperature is lower than the predetermined temperature, the waste plastic particles are reduced. The method for producing quicklime and calcined dolomite in a rotary kiln using waste plastic according to claim 1, wherein the blowing speed of the lime is increased. 3. The production of quicklime and calcined dolomite in a rotary kiln using waste plastic according to claim 1, wherein the waste plastic is blown into a furnace as a fine bundle of particles having a diameter of 20 mm or less. Method.