JP2007253431A - Method of utilizing waste plastic in rotary kiln - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of utilizing waste plastic in the rotary kiln which enables easy control of the blowing rate and combustion, allows improvement of combustibility of plastics of waste plastic and does not cause contamination of the product with foreign matter, in using waste plastic as a fuel for a rotary kiln. <P>SOLUTION: The method for utilizing waste plastic in a rotary kiln has a crushing process of crushing waste plastic to obtain a crushed product, a foreign matter removal process of removing foreign matter from the crushed product, a granulation process of extruding the crushed product after the removal of the foreign matter into a cylindrical product and granulating the cylindrical product to obtain a granulated product and a blowing process of blowing the granulated product into the rotary kiln. The granulated product of the waste plastic to be blown into the rotary kiln has an average index δ of a strength of ≥49 and preferably has a harmonic mean diameter of the granulated product immediately before being blown into the rotary kiln of ≥2 mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of burning waste plastic by blowing it into a rotary kiln furnace for producing quicklime, calcined dolomite, Portland cement and the like and using it as a fuel.

  Waste plastic, which is a used plastic, can be used as a heat source having a high calorific value, but has conventionally been subjected to landfill treatment and incineration treatment. However, since waste plastics are bulky, problems have arisen in which landfill disposal sites are quickly approaching, or environmental problems have arisen due to generation of harmful components when waste plastics are incinerated. Therefore, there is an increasing demand for recycling of waste plastics. For example, in the steel industry, waste plastics are recycled in large quantities by using waste plastics as carbon materials in blast furnaces and coke ovens.

  As a technique paying attention to the fact that waste plastic can be used as a heat source having a high calorific value, a method for producing a cement clinker using waste plastic is known (for example, see Patent Document 1). In the technique described in Patent Document 1, cement clinker can be manufactured at low cost by adding waste plastic to a raw material in a rotary kiln for manufacturing cement clinker, but a specific method for adding waste plastic is unknown.

  Conventionally, it is well known that quick lime, calcined dolomite, Portland cement and the like are manufactured using a rotary kiln. The rotary kiln is convenient for burning various fuels because the space through which the combustion gas passes is relatively large relative to the charge.

  In a rotary kiln, quicklime and calcined dolomite are produced by supplying limestone and dolomite rough from a silo to a great preheater for preheating the rough, preheating with exhaust gas from the rotary kiln, and then charging the rotary kiln. A rotary kiln is a cylindrical heating furnace in which a refractory is lined with a circular iron skin, and rotates around a cylindrical axis at a constant speed. The charged limestone and the like pass through the rotated furnace and move toward the exit. The raw material charging inlet is inclined 3/100 to 4/100 upward with respect to the outlet direction, and the charged limestone or the like moves in the furnace while rotating in the furnace while being fired.

  At the outlet, a device for supplying fuel is provided. The fuel is blown into the furnace through a nozzle and burned with air to keep the furnace at a high temperature of 1000 ° C. or higher. The limestone and raw dolomite ore are baked by the heat of combustion and converted into quick lime or baked dolomite.

  Air for fuel combustion exchanges heat with quicklime and calcined dolomite, and is blown into the rotary kiln as high-temperature air to burn the fuel. The temperature inside the rotary kiln is around 600 ° C on the outlet side, and the part where the flame where the fuel burns is partially 1500 ° C or higher. The temperature decreases with the decomposition reaction of limestone and dolomite, and on the gas outlet side Decreases to about 1000 ° C. This high temperature exhaust gas of about 1000 ° C. is used for preheating limestone and dolomite.

  The above is the outline of the rotary kiln facility for producing quicklime or calcined dolomite. Conventionally, rotary kilns mainly use pulverized coal as fuel, and partly use heavy oil. However, these fuels are all expensive. By using waste plastic having a high calorific value as fuel, quick lime or baked dolomite can be produced at a lower cost, which is expected to lead to fuel reduction and environmental problems.

In the rotary kiln, waste plastic is blown into the rotary kiln together with the main fuel and burned, and (a) a step of making the waste plastic particles into a fine bundle flow; and (b) a fine bundle flow of the waste plastic particles in the main fuel. There is known a method of burning waste plastic in a rotary kiln having a step of blowing and burning as fuel into the rotary kiln from the upper side of the blowing position (for example, see Patent Document 2). In Patent Document 2, it is preferable to blow the waste plastic particles blown into the rotary kiln as a fine bundle flow so that the landing range in the furnace is in the range of 1/10 to 2/3 of the flame length of the main fuel. It is said that.
Japanese Unexamined Patent Publication No. Sho 46-15037 Japanese Patent Laid-Open No. 8-280533

  In Patent Document 2, in order to completely burn the waste plastic particles in the rotary kiln, the blowing method and the particle size are stipulated, but simply by crushing the waste plastic, Therefore, it is very difficult to manage the blowing speed and the combustion management for controlling the landing position. When the waste plastic particles blown into the rotary kiln are mixed with waste plastic particles having a small particle size, they move to the exhaust gas outlet (raw material inlet) side along the flow of gas in the kiln, and as a result, are discharged into the exhaust gas system as soot. Further, since the waste plastic contains various foreign substances (metal, chlorine-containing synthetic resin, etc.), it is predicted that these foreign substances are mixed into the product (quick lime, baked dolomite).

  Accordingly, an object of the present invention is to provide a rotary kiln that can easily manage the blowing speed and combustion management of waste plastic and improve the combustibility of waste plastic particles when using waste plastic as fuel for the rotary kiln. It is to provide a method for using waste plastic in Japan. Moreover, the objective of this invention is providing the utilization method of the waste plastic in the rotary kiln which a foreign material does not mix in a product.

The features of the present invention for solving such problems are as follows.
(1) A method of using waste plastic in a rotary kiln, comprising a crushing step of crushing waste plastic to obtain a crushed product, a foreign matter removing step of removing foreign matter from the crushed product, and the crushed product from which foreign matter has been removed. A method for using waste plastic in a rotary kiln, comprising: a granulating step of extruding and granulating in a cylindrical shape to obtain a granulated product; and a blowing step of blowing the granulated product into the rotary kiln.
(2) The average strength index δ of the granulated product of waste plastic blown into the rotary kiln defined by the following formula (z) is 49 or more, and the harmonic mean diameter of the granulated product just before blowing is 2 mm or more. The method for using waste plastic in a rotary kiln according to (1), characterized in that
δ = Σδiωi (z)
(However, δi: Ratio (N / mm) of load (N) and displacement (mm) when a load perpendicular to the side surface of the cylindrical granule having a diameter di is applied, ωi: diameter (Mass fraction of granulated product of length di)

  According to the present invention, by using a granulated waste plastic that is processed into a granular shape and has a stable quality in a rotary kiln, blow management and combustion management are facilitated, and the furnace can be stably operated. Moreover, the quality of quicklime produced using a rotary kiln, a baked dolomite, etc. is stabilized by removing a foreign material when obtaining a granulated material from waste plastics.

  The present invention has been intensively studied to solve the above problems. Specifically, according to the flow shown in FIG. 1, the waste plastic is crushed in the crushing step 1 and then magnetically separated and winded in advance in the foreign matter removing step 2. After removing foreign matters other than plastic as much as possible by removing foreign matters using selection etc. and washing with water, etc., it is supplied to the granulating step 3 and processed into a granulated product. The granulated product is blown into the rotary kiln 5 by the blowing step 4 for blowing the granulated product into the rotary kiln. In the granulation step 3, the crushed material from which foreign substances have been removed is extruded into a cylindrical shape and granulated to obtain a granulated product. In accordance with the quality required for quick lime and calcined dolomite produced by a rotary kiln, if necessary, after removing chlorine-containing plastics such as vinyl chloride by the vinyl chloride separation process 6, granulation is performed in the granulation process 3. . The granulated product thus obtained is free from foreign substances other than plastic, has a constant property (narrow particle size range and stable quality), and is suitable as a fuel to be blown into a rotary kiln.

  In the granulation step, a granulation method such as the compression molding granulation method shown below, which is a known method used when granulating ordinary waste plastic, can be used. The compression molding granulation method is particularly suitable for granulation of a film-like waste plastic.

  In the compression molding granulation method, waste plastic is granulated by compressing and extruding waste plastic from a hole of a ring die having a plurality of die holes penetrating therethrough. For example, a compression molding apparatus including a ring die having a plurality of die holes penetrating the entire periphery thereof, and a rolling roller that is rotatably disposed in contact with the inner peripheral surface of the ring die inside the ring die The waste plastic thrown into the ring die is pressed into the die hole of the ring die while being compressed and crushed by the rolling roller with the inner peripheral surface of the ring die, and passes through the die hole. By cutting or scraping the plastic molded product extruded to the outer surface side of the ring die from the outer surface of the ring die, a granular plastic molded product as a furnace blowing material is obtained. A plastic molded product (granulated product) is obtained mainly by at least a part of the waste plastic being semi-molten or melted by frictional heat in the die hole and then solidified.

  As a granulating apparatus used in the compression molding granulation method, for example, a ring die having a plurality of die holes penetrating the entire circumference and rotatably supported by the apparatus main body and rotated by a driving apparatus, and an apparatus main body It is known to have one or two or more rolling rollers that are rotatably supported and arranged in contact with the inner peripheral surface of the ring die inside the ring die. The rolling roller is pressed and granulated into the die hole of the ring die while being compressed and crushed between the inner peripheral surface of the ring die.

  A schematic diagram of an example of a granulating apparatus used in the compression molding granulation method is shown in FIG. This plastic compression molding apparatus includes a ring die 11 having a plurality of die holes 10 penetrating the entire periphery thereof, and a rolling element disposed rotatably inside the ring die 11 so as to contact the inner peripheral surface of the ring die. Rollers 12 a and 12 b and a cutter 13 disposed outside the ring die 11 are provided.

  The ring die 11 is composed of a ring body having an appropriate width, is rotatably supported by a device body (not shown), and is rotationally driven by a drive device (not shown). A plurality of die holes 10 are provided in the circumferential direction and the width direction of the ring die 11. These die holes 10 are provided so as to penetrate between the inner side (inner peripheral surface) and the outer side (outer peripheral surface) of the ring die 11 along the radial direction of the ring die 11. The hole diameter (diameter) of the die hole 10 is determined according to the size (diameter) of the granular plastic molding to be granulated, but is usually about 2 to 15 mm. The length of the die hole 10 (the thickness of the ring tie 5) is usually about 30 to 150 mm.

  The rolling rollers 12a and 12b are rotatably supported by the apparatus main body and are disposed in a state of facing the inner side of the ring die 11 by 180 °. These rolling rollers 12a and 12b are non-driving free roller bodies and are in contact with the inner peripheral surface of the ring die 11, and thus rotate with the rotation of the ring die 11 due to friction with the inner peripheral surface. The number of the rolling rollers 12 is arbitrary, and one or three or more may be provided.

  The cutter 13 is provided so that the cutting edge thereof is in contact with the outer peripheral surface of the ring die 11 or located in the vicinity of the outer peripheral surface, and a plastic molded product that is extruded in a rod shape from the die hole 10 to the outside of the ring die 11 is appropriately used. It is cut into a long length (or scraped off from the outer peripheral surface of the ring die).

  In the plastic compression molding apparatus as described above, the ring die 11 is driven to rotate in the direction of the arrow in the drawing, and the rolling rollers 12a and 12b are rotated accordingly. Waste plastic 2 is put inside, and the thrown plastic is mixed in the ring die 11 and is compressed and crushed between the inner peripheral surface of the ring die 11 by the rolling rollers 12a and 12b. Is pushed into the die hole 10. The waste plastic pushed into the die hole 10 passes through the die hole and is sequentially extruded in the form of a rod on the outer surface side of the ring die 11, and this plastic molding is appropriately lengthened by the cutter 13. The cylindrical plastic granulated material 15 is obtained by being cut into pieces. Reference numeral 16 denotes a discharge port.

Plastic granules manufactured using the above method are manufactured with different hardness (average strength index) by changing the manufacturing conditions (processing speed), the die hole diameter of the ring die, and the die length. be able to. When the fuel is blown into the rotary kiln, the air transport method is usually used. However, in order to stably feed the plastic granulated by the above method and supply the plastic into the rotary kiln, the compression strength and the particle size are more than a certain level. It is preferable that the average strength index δ of the granulated product of waste plastic blown into the rotary kiln is 49 or more, and the harmonic average diameter of the granulated product immediately before blowing is 2 mm or more. In addition, the harmonic average diameter of the granulated product immediately before blowing is 5 kg of the granulated product, and it is shrunk from the sample, and a sample of at least about 250 g is measured and the sieve mesh is (11.1 mm, 9.52 mm, The particle size distribution is measured with a sieve of 6.70 mm, 4.75 mm, 2.80 mm), and the mass fraction wp of the granulated material divided by each sieve is obtained and calculated by the following equation (x).
Harmonic average diameter [Dph] = 1 / (Σ (mass fraction [wp] / representative length [Lr])) (x)
The representative length in the above equation (x) is obtained by the following equation (y).
Representative length = ((upper sieve mesh [mm]) · (lower sieve mesh [mm])) ^1/2 ... (y)
However, the representative length of the granulated material that did not pass through all the sieve mesh is 13.44 mm, and the representative length of the granulated product that passed through all the sieve mesh is 1.00 mm.

  A rotary kiln usually used for calcination burns heavy oil or fuel gas as fuel, and calcines limestone with the combustion gas. The speed of the combustion gas in the rotary kiln is about 5m / s to 10m / s, although it depends on the amount of fuel and the inner diameter of the rotary kiln, and there is waste plastic granulated material having an end speed equivalent to the gas speed in the kiln. , Accompanying the combustion gas, discharged from the kiln, and transferred to an exhaust gas treatment device as unburned waste plastic and / or soot. Therefore, it is preferable to blow in a synthetic resin having a particle diameter equal to or larger than the particle end speed corresponding to 10 m / s as the waste plastic granulated material immediately after blowing. Such a particle diameter is about 2 mm in a waste plastic granulated product produced by extrusion granulation into a cylindrical shape. Therefore, the particle diameter (harmonic average diameter) of the granulated product is preferably 2 mm or more. As a result of studies by the present inventors, by producing the granulated product so that the average strength index is ensured to be 49 N / mm or more, the granulated product is hardly pulverized immediately after blowing, and particles of less than 2 mm. It was found that the ratio of can be extremely small. Therefore, by using waste plastic granulated material having an average strength index of 49 N / mm or more as a fuel for a rotary kiln, the particle size at the time of blowing is kept at 2 mm or more, and granulation with a particle size of 2 mm or more with high combustion efficiency. It is possible to blow in as a product, and it is possible to replace a conventionally used fuel.

Note that the average strength index δ is a load perpendicular to the side surface in the length direction of the particle in the case of a columnar particle for a particle having a distribution in the diameter length d (speed: 2 mm / min). Is the sum of the ratio (N / mm) of the load (N) and the displacement (mm) when a constant is applied, multiplied by the mass fraction, and for all di defined by the following equation (z) This is the sum of products of δi and ωi.
δ = Σδiωi (z)
However, δi: ratio (N / mm) of load (N) and displacement (mm) when a load perpendicular to the side surface of a cylindrical granulated product having a diameter of di (velocity constant at 2 mm / min) is applied. ), Ωi: mass fraction of the granulated product having a diameter di.

  The strength of the granulated product is measured using, for example, an apparatus as shown in FIG. FIG. 3 is a schematic diagram showing a compression test method. A compression test apparatus 20 is used to apply a load of W (N) at a compression speed of 2 mm / min to the side surface in the length direction of the columnar granulated product 15. The compression characteristic which is the relationship between the weight W (N) and the compression distance L (mm) as shown in FIG. 4 is measured. When the strength δ of the granulated product is obtained as δ≡ΔW / ΔL from the compression characteristics, a graph as shown in FIG. 5 is obtained for the granulated product having each di (particle diameter). FIG. 5 shows the relationship between the particle size and strength of the granulated product, and it can be seen that the larger the particle size, the higher the strength. The average strength index δ is the sum of products of strength and mass fraction of a granulated product having each particle size (average diameter of cylindrical circular portion) di, and is defined by the above formula (z).

  Waste plastic was granulated using a granulator (ring die granulator) similar to that shown in FIG. 2 in accordance with the flow of FIG. 1 to obtain a plastic molded product (granulated product).

  The waste plastic used is a waste from general households, in a state where a plurality of types of plastics and foreign substances are mixed, polyethylene 32 mass%, polypropylene 31 mass%, polystyrene 22 mass%, and others (paper, etc.) 15 mass%, A vinyl chloride separation step was unnecessary. Table 1 shows the chemical composition of waste plastic.

  Waste plastic was supplied to the granulator in the range of 0.5 t / h to 2.0 t / h, and the granulated product was produced by changing the treatment speed. The granulator has a ring die inner diameter of 840 mm, a width of 240 mm, a ring die thickness (die length) of 60 mm, a rolling roller diameter of 405 mm, 10,000 holes with a die diameter of 6 mm, a diameter of about 6 mm, and a length of about 10 to 20 mm. A columnar (cylindrical) granulated product was produced. The produced plastic granulated material was transported under the conditions of 900 kg / h at a pipe diameter of 40 mm, a pipe length of 40 m (two vent portions, R400), and a gas flow rate of 25 m / s, and the plastic granulated material after transportation was recovered. The average strength index δ of the granulated product immediately after molding and the mass ratio (2 mm or less powder rate) of particles of 2 mm or less of the plastic granulated product after airflow transportation were measured using a sieve. FIG. 6 shows the relationship between the average strength index and the waste plastic treatment speed, and FIG. 7 shows the relationship between the powder ratio of 2 mm or less and the average strength index.

  According to FIG. 6, it can be seen that the average strength index of the granulated product can be controlled by changing the processing rate of the waste plastic. Moreover, according to FIG. 7, when the average strength index is about 49 N / mm (5 kgf / mm) or more, it can be seen that the ratio of the powdery material of 2 mm or less can be 10 mass% or less.

  Among the plastic granules produced, the average strength index 24.5 N / mm (2.5 kgf / mm), 64.7 N / mm (6.6 kgf / mm), 97.0 N / mm (9.9 kgf / mm) Were used to blow into a lime-fired rotary kiln with a production volume of quick lime of 500 t / day, and the replacement rate with existing fuel (heavy oil) was calculated. The amount of heavy oil injected before plastic injection was 2.65 t / h and the calorific value was 9800 kcal / kg. The calorific value of plastic is 9800 kcal / kg. When the plastic granulated material was blown, the amount of plastic granulated material blown was 840 kg / h, and the shortage was compensated by blowing heavy oil.

  In any of the plastic granulated products having any average strength index, foreign materials such as metals were not mixed in the granulated product. Therefore, no foreign substances such as metals were detected in the manufactured lime. Further, the exhaust gas from the lime-fired rotary kiln was sampled and analyzed for gas, but no contamination such as hydrochloric acid was found in the exhaust gas.

  When a plastic granulated product having an average strength index of 24.5 N / mm was used, the amount of heavy oil blown was 2.3 t / h, and the replacement rate was 43 mass%. In the conventional technology, when the waste plastic is simply crushed and burned with a wide particle size configuration, the best combustibility is shown, and the replacement rate is 70%. Although it was slightly lower than the waste plastic crushed material, no soot or the like due to incomplete combustion was observed in the exhaust gas, and stable combustion was achieved.

  When a granulated product having an average strength index of 64.7 N / mm is used, a heavy oil blowing amount of 1.95 t / h is used, and when a granulated product having a particle strength index of 97.0 N / mm is used, 1.88 t / h. The amount of heavy oil blown in h, the replacement ratios were 86 mass% and 95 mass%, and the plastic granulated product with a high average strength index had very high combustibility.

Waste plastic processing flow for rotary kilns. Schematic of an example of a granulator used in the compression molding granulation method (ring die granulator). The schematic diagram which shows the compression test method (measurement method of an average intensity | strength index). The graph which shows the relationship between a compression characteristic and the intensity | strength of a granulated material (measurement method of an average intensity | strength index). The graph which shows the relationship between the particle size and intensity | strength of a granulated material (measurement method of an average intensity | strength index). The graph which shows the relationship between an average intensity index and waste plastic processing speed. The graph which shows the relationship between 2 mm or less powder rate and an average intensity index.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crushing process 2 Foreign material removal process 3 Granulation process 4 Blowing process 5 Rotary kiln 6 Vinyl chloride separation process 10 Die hole 11 Ring die 12 (12a, 12b) Rolling roller 13 Cutter 14 Input port 15 Plastic granulated material 16 Discharge port 20 Compression Test equipment

Claims (2)

  It is a method of using waste plastic in a rotary kiln, a crushing step of crushing waste plastic to obtain a crushed material, a foreign material removing step of removing foreign material from the crushed material, and the crushed material from which foreign material has been removed into a cylindrical shape A method of using waste plastic in a rotary kiln, comprising: a granulating step of obtaining a granulated product by extrusion granulation; and a blowing step of blowing the granulated product into the rotary kiln. The average strength index δ of the granulated product of waste plastic blown into the rotary kiln defined by the following formula (z) is 49 or more, and the harmonic mean diameter of the granulated product immediately before blowing is 2 mm or more, The method of using waste plastic in the rotary kiln according to claim 1.
δ = Σδiωi (z)
(However, δi: Ratio (N / mm) of load (N) and displacement (mm) when a load perpendicular to the side surface of the cylindrical granule having a diameter di is applied, ωi: diameter (Mass fraction of granulated product of length di)

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