JP3523999B2 - Production method of quicklime and calcined dolomite in rotary kiln using waste plastic - Google Patents

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 by using waste plastic as a fuel together with heavy oil which is a main fuel.
In particular, the present invention relates to a method for producing a constant quality good quicklime / calcined dolomite 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 since the burnability of waste plastic is inferior to other fuels such as heavy oil and pulverized coal, it was discarded without being used as a fuel. . However, from the viewpoint of environmental problems or effective use of resources, waste plastics are gradually being reused.

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

Further, Japanese Patent Laid-Open No. 6-8247 (hereinafter, referred to as
"Prior Art 2" discloses a method of treating by adding a fiber reinforced plastic into a rotary kiln. Furthermore, Japanese Patent Publication No. 59-11545 (hereinafter referred to as "Prior Art 3") discloses a method for producing Portland cement using municipal waste.

[0005] It is well known that, in the past, quicklime / burned dolomite is produced by firing limestone / dolomite as a raw material, shells and the like.
Rotary kilns are also known to be convenient devices for burning a variety of fuels because of the relatively large space through which combustion gases pass for the charge.

FIG. 6 shows an outline of a conventional rotary kiln for producing quicklime / calcined dolomite. Less than,
An outline of a method for producing quicklime / calcined dolomite in a conventional rotary kiln will be described with reference to FIG. Rough 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 the exhaust gas discharged from the rotary kiln, and then charged into the rotary kiln 6.

The rotary kiln is a cylindrical heating furnace constructed by lining a circular iron skin with a refractory, and rotates at a constant speed around the shaft during operation.
In FIG. 6, the limestone / dolomite charged from the charging port on the left side passes through the rotating furnace and moves toward the outlet on the right side. In the rotary kiln, as shown in FIG. 6, the raw material charging port is 3/10 with respect to the outlet direction.
It inclines upward with an inclination of 0 to 4/100. The limestone and dolomite that have been charged rotate in the furnace while being baked, and change to quick lime and calcined 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 inside of the furnace is blown and burned by the blown air to maintain the inside of the furnace at a high temperature of 1000 ° C or higher. Due to the heat generated by the combustion of the heavy oil and pulverized coal, the limestone and dolomite are calcined and converted into quick lime and calcined dolomite.

The air for burning the fuel passes through a great cooler 7 for cooling the discharged quicklime / burned dolomite, thereby exchanging heat with the quicklime / burned dolomite. As a result, on the one hand, the air cools the hot lime and calcined dolomite, and on the other hand, the air receives heat and becomes hot, and is blown into the rotary kiln from the outlet side to burn heavy oil and pulverized coal as the main fuel. It becomes a source of high temperature air.

The temperature in the rotary kiln is about 600 ° C. at the outlet side of the furnace, and the flame part generated when the fuel burns is partially 1500 ° C. or higher, which is accompanied by the decomposition reaction of limestone and dolomite. Temperature decreases, and the temperature decreases to about 1000 ° C. on the inlet side of limestone / dolomite, that is, the exhaust gas outlet side. This high-temperature exhaust gas of about 1000 ° C. preheats the limestone and dolomite added to the above-mentioned great preheater 2,
Here, after discharging a part of the heat, it passes through the waste heat boiler 3, and then is discharged to the 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, in a rotary kiln, heavy oil is mainly used as a fuel, and pulverized coal is used as a part. However, these fuels are all high in cost, and it is required to produce quicklime / calcined dolomite at a lower cost.

These heavy oils contain 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
Since it has a heat capacity of about / kg, it may be a valuable heat source along with pulverized coal.

However, waste plastics are usually obtained in various shapes and, as described above, are not easily burned, so that they are currently discarded without being used as fuels. Waste plastics such as polyethylene, polypropylene, polystyrene and polyvinyl chloride are currently being produced in large quantities. Therefore, while reusing these waste plastics as heat sources to treat waste,
Using this cheap plastic as fuel, quicklime and
It is required to manufacture baked dolomite at low cost.
It should be noted that quick lime 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 / calcined dolomite using waste plastic in the above-mentioned rotary kiln is disclosed in JP-A-8-283051 (hereinafter referred to as "Prior Art 4").

In the prior art 4, a method for producing quicklime and calcined dolomite using waste plastic is (a)
During the production of quicklime and calcined dolomite in a rotary kiln, a step of making waste plastic particles into a fine bundle flow as a part of the fuel, (b) a fine bundle flow of waste plastic particles and the main fuel are blown into the rotary kiln to form a fine bundle flow. Of the main fuel is blown across the flame of the main fuel, and the unburned waste plastic particles are blown into the rotary kiln such that the dropping point is within the flame length of the main fuel.

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

[0017]

However, the prior arts 1 to 3 merely disclose the use of waste plastic, and the waste plastic is used as a fuel to produce the desired quicklime / calcined dolomite in the rotary kiln. There is no disclosure of how to do this.

Further, although the prior art 4 solves the problem of how and how to insert the waste plastic into the rotary kiln as described above,
There are the following problems. That is, in the prior art 4, the heat generation amount of the waste plastic is set in advance, and the blowing speed of the waste plastic into the rotary kiln is determined from the heat generation amount thus set and the required total heat generation amount of the waste plastic. Then, the waste plastic is blown into the rotary kiln at the blowing speed (constant) thus determined.

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

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

Water content of waste plastic is 0.5 to 10%
If it fluctuates in the range of,
It varies from about 00 to 8400 kcal / kg. Further, since the waste plastic has various components and the ratio thereof is not constant, the calorific value varies even if the water content is constant.

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

Therefore, when the blowing speed of the waste plastic is made constant by the method of the prior art 4, the total heat generation amount of the waste plastic into the rotary kiln fluctuates.
It is difficult to obtain a product with a certain quality and degree of baking. Furthermore, since a case where excessive waste plastic is blown in more than necessary occurs, 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 is not possible to follow the abrupt change in the heat generation amount of the waste plastic, and thus the waste plastic at such a long time interval. The control of the blowing rate of P has virtually no effect. Therefore, it is an object of the present invention to provide a method for producing quicklime / calcined dolomite having a constant quality and a certain degree of firing in a rotary kiln while coping with a rapid change in the heat value of waste plastic.

[0025]

Means for Solving the Problems The inventors have conducted extensive studies to overcome the above-mentioned problems of the prior art. As a result, the heat value of the waste plastic varies depending on the water content and type, and when the total heat value of the waste plastic blown into the rotary kiln changes, 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 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 manufacture quicklime and calcined dolomite while responding to a sudden change in the calorific value of the waste plastic. The present invention has led to the invention described below.

The first embodiment of the method for producing quicklime / calcined dolomite in a rotary kiln using waste plastic according to the present invention is to blow a main fuel and waste plastic particles having a predetermined particle diameter or less as a part of the fuel into the rotary kiln. In the method of producing quicklime / calcined dolomite, the exhaust gas temperature at the exhaust gas outlet of the rotary kiln is detected, so that the predetermined temperature of the exhaust gas at the preset exhaust gas outlet of the rotary kiln 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 decreased so that the detected exhaust gas temperature is 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 / calcined dolomite in a rotary kiln using waste plastic of the present invention, the waste plastic as a fuel is blown into the furnace as a fine bundle flow of particles having a diameter of 20 mm or less. It is a thing.

[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 a method for producing quicklime / calcined dolomite in a rotary kiln using waste plastic of the present invention. In FIG. 4, the solid charge flow is shown by a solid line, and the waste plastic flow is shown by a dashed line. Further, the gas flow is shown by a broken line. Rough stones such as quicklime and calcined dolomite, which are solid charges, are supplied from the raw stone silo 1 containing them to the great preheater 2, where they are preheated by the exhaust gas from the rotary kiln, and then charged into the rotary kiln 6. To be done.

Limestone and dolomite are charged from the left inlet of the rotary kiln, and heavy oil (not shown) or heavy oil and pulverized coal and waste plastic particles 13 are blown as main fuels from the right outlet of the rotary kiln. The charged limestone / dolomite rotates in the furnace while being burned by the combustion of the injected fuel, and changes into quick lime / calcined dolomite and moves toward the exit.

At the outlet of the rotary kiln, a pulverized coal supply device 8 for supplying pulverized coal as a fuel and a waste plastic blowing device 9 are provided. Below the waste plastic blowing device 9, a waste plastic quantitative supply device 10, For example, a table feeder is provided, and the waste plastic constant amount supply 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 detection device 12 is provided at the exhaust gas outlet of the rotary kiln, and the detected exhaust gas temperature 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 blowing nozzle located near the outlet. This waste plastic is burned by heavy oil as the main fuel blown into the furnace or hot air supplied from the outlet together with the heavy oil and pulverized coal, and the inside of the furnace is maintained at a high temperature of 1000 ° C or higher. The heat generated by the combustion of the heavy oil, the waste plastic, and the pulverized coal causes the limestone and dolomite to be burned and converted into quick lime and burnt dolomite.

Air for burning heavy oil, waste plastics and pulverized coal passes through a great cooler 7 for cooling the discharged quicklime / burned dolomite to perform heat exchange, while hot hot lime / burned hotlime is burned. The air that has cooled the dolomite and, on the other hand, has become hot is blown into the rotary kiln from the outlet side as described above, and serves as a supply source of hot air for burning heavy oil, waste plastic and pulverized coal.

In order to sufficiently burn the waste plastic which is difficult to burn, the waste plastic is added at least in the range where the oxygen concentration exists to some extent. That is, the 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 the heavy oil which is the main fuel. The blowing of heavy oil rotates the flame, for example, clockwise. On the other hand, since the furnace body of the rotary kiln is rotating in the clockwise direction, the solid charge is biased toward the position of the third quadrant of the cross section of the furnace body (as seen from the furnace body outlet side). .

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

The temperature in the rotary kiln is about 600 ° C. at the outlet side, and the flame part generated when heavy oil burns is partially 1500 ° C. or higher, which is accompanied by the decomposition reaction of limestone and dolomite. On the charging side of limestone / dolomite, that is, on the gas discharge side, the temperature drops to about 1000 ° C. This 100
Exhaust gas with a high temperature of about 0 ° C preheats the limestone and dolomite added to the above-mentioned great preheater 2, releases a part of the heat there, and then passes through the waste heat boiler 3 before being discharged to the outside. It

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. If the detected exhaust gas temperature matches the set temperature, continue operation. 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, a control method of inducing a 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 sudden change in the heat value of the waste plastic.

Further, the quality of the product is judged by the shape, color and size, particularly the removal rate of carbon dioxide gas in the rough. This determination can be performed, for example, every 24 hours to change the exhaust gas temperature set value. Thus, quicklime / calcined dolomite having a certain quality and degree of baking 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.
Experiments were conducted by using waste plastic as a fuel using a rotary kiln. In this device, heavy oil and waste plastic, heavy oil and waste plastic, and pulverized coal were used as fuel. The table in FIG. 5 shows the operation results.

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

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

As is apparent from FIG. 2, according to the conventional method, the exhaust gas temperature at the exhaust gas outlet fluctuates greatly because the injection amount (blowing speed) of the waste plastic is constant. Therefore, as shown in FIG. 5, it is understood that it is difficult to obtain quick lime / burnt dolomite having a certain quality and degree of firing.

On the other hand, according to the method of the present invention, the exhaust gas temperature at the exhaust gas outlet is detected, and the blowing speed of the waste plastic is controlled by the temperature, so that the blowing amount of the waste plastic matches the predetermined blowing speed. Is controlled so that the exhaust gas temperature is controlled so that the exhaust gas temperature fluctuates greatly when the amount is small or large, and the exhaust gas temperature is controlled within a certain range.

Therefore, as shown in FIG. 5, quick lime / calcined dolomite having a certain quality and a certain degree of calcination can be obtained, and 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, and there is little variation and the decomposition rate is high.

At this time, in consideration of the heat generation due to the combustion of the waste plastic, the main fuel corresponding to that amount was reduced. Calculating from the calorific value, the amount of waste plastic blown (mixing rate) is about 10% in case 1 and about 2 in case 2.
It is 0%. The decomposition rate shown here is the percentage of the difference between the amount of carbon dioxide gas in the limestone and the dolomite that was input and the amount of carbon dioxide gas that remained 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 in consideration of the decomposition rate. In addition, when the composition of the exhaust gas at the inlet was analyzed, it was 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, the amount of heat generated by the waste plastic can be controlled by blowing the waste plastic particles in an appropriate manner and at an appropriate point in the rotary kiln. While responding to the rapid fluctuations in
Moreover, quicklime with a certain quality and degree of firing
It was possible to produce baked dolomite.

Further, since the waste plastic is low in cost, it was possible to greatly contribute to the reduction of the production cost.
Therefore, while waste plastic that has been mainly discarded in the past can be effectively used as a heat source, it can also contribute to reduction of waste, and it has been proved that the invention is extremely effective in terms of the environment.

[Brief description of drawings]

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

FIG. 2 is a diagram showing changes over time in the amount of waste plastic blown in and the exhaust gas temperature at the 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 / calcined dolomite in a rotary kiln using the waste plastic of the present invention.

FIG. 5 is a diagram showing an operation test result.

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

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

[Explanation of symbols]

1 rough stone silo 2 Great preheater 3 Waste heat boiler 4 Dry type dust collector 5 Wet dust collector 6 rotary kiln 7 Great cooler 8 Pulverized coal feeder 9 Waste plastic blowing device 10 Waste plastic quantitative supply device 11 Waste plastic supply control device 12 Exhaust gas temperature detector 13 Waste plastic

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-8-283052 (JP, A) JP-A-8-283053 (JP, A) JP-A-8-283051 (JP, A) JP-A-53- 140297 (JP, A) JP-A-56-37414 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 2/00-32/02 F23G 5/20 F23G 7/12

Claims (2)

(57) [Claims] 1. A method for producing quicklime / calcined dolomite by injecting a main fuel and a waste plastic having a particle size not larger than a predetermined particle size as a part of the fuel into a rotary kiln, the exhaust gas temperature at an exhaust gas outlet of the rotary kiln. Is detected, and the detected exhaust gas temperature is higher than the predetermined temperature.
When it is also high, the blowing speed of the waste plastic particles
And the detected exhaust gas temperature is lower than the predetermined temperature.
When it is also low, the blowing speed of the waste plastic particles
Of the quicklime / burned dolomite in the rotary kiln using waste plastic, characterized in that the blowing speed of the waste plastic particles is controlled so that this temperature matches the temperature of the exhaust gas set in advance. Production method. 2. The method for producing quicklime / burned dolomite in a rotary kiln according to claim 1, wherein the waste plastic is blown into the furnace as a fine bundle flow of particles having a diameter of 20 mm or less.