JP2008195543A - Method of manufacturing fired product using waste plastic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a fired product using waste plastic, in which the concentration of chlorine in the fired product is controlled to be low even when the waste plastic contains a chlorine-containing synthetic resin in the manufacture of the fired product of quick lime, fired dolomite or the like using the waste plastic as fuel for a firing furnace such as a rotary kiln. <P>SOLUTION: In the method of manufacturing the fired product using the waste plastic, the waste plastic C containing the chlorine-containing resin as a part of the fuel A is used in the manufacture of heating and firing a raw material in the firing furnace by the combustion of the fuel A, and a surface layer part of the fired product after fired is removed to remove at least a part of a chlorine compound in the fired product. It is preferable to separate the surface layer from the fired product and to remove the separated surface layer part by sieving by striping and removing the surface layer part of the fired product after fired and rolling the fired product after fired in a rotary drum. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, waste plastic that has not been conventionally used as a fuel is burned by being blown into a kiln such as a rotary kiln for producing a calcined product such as quicklime, calcined dolomite, and Portland cement, and used as a fuel. The present invention relates to a method for manufacturing a fired product using waste plastic.

  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, the waste plastic has a low bulk density, and therefore, there are problems that the landfill disposal site is quickly approaching, and environmental problems such as generation of harmful components when the waste plastic is 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). According to 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 the 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 this combustion heat and changed to quick lime or baked dolomite.

  The 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 calcined dolomite can be manufactured at a lower cost, and it is expected to lead to fuel reduction and resolution of 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.
JP 47-39124 A Japanese Patent Laid-Open No. 8-280533

  In Patent Document 2, in order to completely burn waste plastic particles in a rotary kiln, a blowing method and a particle size are defined. In many cases, waste plastic contains a chlorine-containing synthetic resin. There is a problem that.

The chlorine-containing synthetic resin contained in the waste plastic generates hydrogen chloride by a dehydrochlorination reaction in an atmosphere of 250 ° C. or higher in the rotary kiln. The generated hydrogen chloride reacts with limestone, quicklime, dolomite, and calcined dolomite to form calcium chloride (CaCl ₂ ) and magnesium chloride (MgCl ₂ ), which are mixed into the product. The use of these quicklime and calcined dolomite mixed with halides is limited by the chlorine-containing concentration. Quicklime is used as a raw material for steelmaking and steelmaking in steelworks, and the incorporation of chlorine may cause equipment corrosion in the process of use. Therefore, depending on the application, it is necessary to remove the chlorine-containing synthetic resin from the waste plastic in advance.

  Also, when manufacturing other baked products, since chloride has a high vapor pressure, there is a problem that the yield of the product is reduced due to volatilization and dust is increased.

  Accordingly, an object of the present invention is a case where a waste plastic contains a chlorine-containing synthetic resin when producing a calcined product such as quick lime or calcined dolomite using the waste plastic as a fuel for a calcining furnace such as a rotary kiln. However, an object of the present invention is to provide a method for manufacturing a baked product using waste plastic, which can control the chlorine concentration of the baked product to a low level.

The features of the present invention for solving such problems are as follows.
(1) A method of using a waste plastic containing a chlorine-containing resin as a part of the fuel when a raw material in a firing furnace is heated by combustion of fuel to produce a fired product, A method for producing a fired product using waste plastic, wherein at least a part of the chlorine compound in the fired product is removed by removing a surface layer portion.
(2) The method for producing a fired product using the waste plastic according to (1), wherein a surface layer portion of the fired product after firing is peeled off and removed.
(3) The fired product after firing is rolled in a rotary drum to separate the surface layer portion of the fired product from the fired product, and the separated surface layer portion is removed by sieving ( A method for producing a baked product using the waste plastic according to 1) or (2).

  According to the present invention, when waste plastic is used as a fuel for a firing furnace, even if the waste plastic contains a chlorine-containing synthetic resin, the chlorine concentration of the calcined product such as quicklime or calcined dolomite is extremely low. Can be controlled. For this reason, a baked product can be manufactured cheaply without limiting the use of the baked product.

  Thereby, even if it is a waste plastic containing chlorine, the utilization as a fuel of a baking furnace is not restrict | limited, The recycling utilization of waste plastic is accelerated | stimulated.

  The firing furnace used in the present invention is a furnace for firing a raw material by heating the raw material and fuel in a container, and specifically includes a rotary kiln, a Merz furnace, and the like. Hereinafter, the present invention will be described using a rotary kiln. Moreover, the waste plastic used as a part of the fuel for the firing furnace is a used plastic, and usually consists of a foreign material or a mixed state of a plurality of types of plastics. General waste plastic, which is a waste from general households, is often contaminated with foreign substances, and usually requires pretreatment when used for recycling, but industrial waste plastics are generally less contaminated with foreign substances and have many types of plastics. It may not be a mixed state. Chlorine-containing synthetic resins are PVC (polyvinyl chloride), PVDC (polyvinylidene chloride) and the like, and waste plastics used in the present invention are waste plastics containing such chlorine-containing synthetic resins.

This invention is demonstrated using FIG. 1 as a case where limestone or a baked dolomite is manufactured as a baked product. FIG. 1 is an explanatory view showing the situation inside the rotary kiln, and the raw material 3 (limestone or dolomite rough) supplied to the rotary kiln 1 from the inlet 2 is combusted with the main fuel A injected from the inlet 5 on the rotary kiln outlet 4 side. Heated by the combustion gas generated by the reaction of the working air B, it becomes quick lime or calcined dolomite and moves to the outlet 4. The residence time of the raw material is generally about 60 minutes. In FIG. 1, the landing area E in the rotary kiln (inside the furnace) of the waste plastic C blown into the rotary kiln 1 as fuel from the waste plastic injection port 6 is seen from the outlet of the rotary kiln in order to improve combustibility. Although it is in the range of 1/2 to 2/3 of the length of the flame 7 of the main fuel, the production range E of hydrogen chloride is estimated to be the same as the landing range of the waste plastic. CaCl ₂ is generated from the position where hydrogen chloride is generated from the waste plastic, and the generated CaCl ₂ moves to the outlet 4 by the rolling of the rotary kiln 1. As shown in the upper graph of FIG. 1, the gas composition in the rotary kiln 1 is the same composition as the air containing a small amount of CO ₂ at the outlet side, and the O ₂ concentration decreases as the fuel burns as it proceeds to the inlet side. However, the CO ₂ and H ₂ O concentrations increase. CO ₂ is also generated by decomposition of limestone and the like. Further, as the fuel burns, O ₂ decreases at the rotary kiln inlet 2 and becomes exhaust gas composed of CO ₂ , H ₂ O, and N ₂ . Since the length of the main fuel flame 7 is usually from the kiln outlet to a position of ¼ to ３ of the kiln length, the generation position of HCl and the generation position of CaCl ₂ are from the kiln outlet. It is estimated that the position is 1/8 to 2/9 of the length. The temperature of the solid (raw material) and gas in the rotary kiln 1 is shown in the lower graph of FIG. Once generated, CaCl ₂ is thermodynamically stable in a CaO phase at high temperature and in an air atmosphere (CaCl ₂ decomposition priority region F), but the residence time from the kiln outlet 4 to the HCl generation position E is short, It is not sufficient for all the CaCl ₂ to be converted to CaO. Further, quick lime or calcined dolomite mixed with CaCl ₂ discharged from the rotary kiln outlet 4 is rapidly cooled because it receives heat exchange with the fuel combustion air D in the cooler 8 and is not easily converted into CaO.

The present inventors have conducted extensive study on how to easily remove the CaCl ₂ from quick lime or calcined dolomite CaCl ₂ is produced and mixed, CaCl ₂ is found to concentrate on the surface of burnt lime and burnt dolomite, quick lime and baking It was found that quick lime and calcined dolomite with extremely low chlorine concentration can be produced by removing only the surface layer of dolomite, and the present invention was completed.

  Next, the manufacturing method of the baked product in the baking furnace (rotary kiln) using the concrete waste plastic is demonstrated using FIG. The waste plastic is preferably used after being granulated, and the method for granulating the waste plastic will be described in detail below.

  In accordance with the flow shown in FIG. 2, waste plastic C and fuel A are blown into the firing furnace 22 by the blowing means 20 and 21 and burned with the air B to generate high-temperature gas. Limestone H is supplied into the firing furnace 22 from a position facing the fuel A, and the limestone H is fired into quicklime I by a high-temperature gas. The obtained quicklime I is supplied to the surface layer removing means 23, and after the calcium chloride concentrated on the surface is removed, the separation step 24 separates the quicklime I having a high calcium chloride concentration and the quicklime K having a low calcium chloride concentration.

  The waste plastic to be blown may be crushed to a blowable particle size or may be granulated using a known method. The granulated product has a constant property (narrow particle size range and stable quality) and is suitable as a fuel to be injected into a firing furnace. The waste plastic is preferably processed into a granulated product after being crushed and subjected to foreign matter removal using magnetic separation, wind separation, etc. and washing with water in advance to remove foreign matter other than plastic as much as possible. For granulation, a known method used when granulating ordinary waste plastics may be used. For example, a granulation method such as the compression molding granulation method shown below 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 view 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. It 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.

  The granulated product of waste plastic produced by the above method is used as a part of fuel in a rotary kiln for producing quicklime or calcined dolomite. As a method of using as fuel, waste plastic may be blown into the rotary kiln using a lance or a dedicated burner by a normal air flow transportation system.

A method for removing calcium chloride (CaCl ₂ ) from the baked product when using waste plastic as part of the fuel in the rotary kiln as described above will be described. CaCl ₂ is produced by the following reaction formulas (c) and (d).
CaCO ₃ + 2HCl = CaCl ₂ + CO ₂ + H ₂ O (c)
CaO + 2HCl = CaCl ₂ + H ₂ O (d)
HCl reacts from the surface of CaCO ₃ and / or CaO to become CaCl ₂ . CaCl ₂ concentrated on the surface is extremely brittle and can be easily removed from the particle surface by friction between particles. FIG. 4 shows the quicklime recovered by aerating air containing hydrogen chloride (hydrogen chloride concentration 600 ppm) for 90 minutes at 24 ml (particle size: particle size 3 mm to 5 mm, 100 mass%) heated to 900 ° C. for 90 minutes. The sample after filling in a non-cylinder, rotating the cylinder 500 times and applying frictional force and impact force to quicklime is shown in a particle size range (0.5 mm or less, 0.5 to 1.0 mm, 1.0). It is a graph which shows the result of having measured the chlorine density | concentration of the quick lime of each particle size range, after classifying to -2.0 mm, 2.0-3.0 mm, and 3 mm exceeding). In addition, the chlorine concentration by the elemental analysis of the whole particle | grains before classification was 0.73 mass%. According to FIG. 4, it turns out that the chlorine density | concentration of fine quicklime is high. This indicates that the CaCl ₂ concentration of the finely divided particle surface layer is high, and the CaCl ₂ concentration becomes lower as it goes inside. Therefore, the chlorine concentration of the fired product can be lowered by removing the surface layer portion of the fired product.

As a means for removing the surface layer portion in order to remove CaCl ₂ from the fired product, it is not a method of breaking particles such as a compression crushing method such as a jaw crusher or an impact crushing method such as a hammer crusher, but only the surface is peeled off. The method of removing is preferable. Specifically, it is preferable to use a rotary drum such as a rotary kiln, an Elofold mill, a ball mill (rolling, vibration), or a vibration mill in which the raw material itself is a grinding medium. It is also possible to use a method in which no grinding medium is added even with a ball mill. The surface layer portion can also be removed by sieving the fired product using a vibration sieve while applying a frictional force.

The quick lime having a high CaCl ₂ concentration removed by the surface removing means is fine powder, and the separation can be performed by a sieve sorter, wind sorting, or the like. The sieve sorter includes a vibration type, a gyro type (horizontal circular motion), a cylindrical rotary type, and an air type, and a known method capable of removing fine powder can be appropriately used.

  The removal amount of the surface layer portion of the fired product is preferably determined according to the chlorine concentration of the waste plastic used as the fuel. More preferably, the chlorine concentration of the fired product from which the surface layer portion has been removed is measured, and feedback control is performed in which the removal amount of the surface layer portion is determined according to the measured value.

  The surface layer portion removed from the baked product is a fine powder having a high chlorine concentration, so its use is limited. However, it can be used for various purposes by applying a dechlorination treatment.

  Waste plastic is granulated using a granulator (ring die granulator) similar to that shown in FIG. 3 to obtain a plastic molding (granulated product), and a rotary kiln is used according to the flow of FIG. Limestone was fired.

  The waste plastic used is waste from general households. In the state where multiple types of plastic and foreign materials are mixed, polyethylene 32 mass%, polypropylene 31 mass%, polystyrene 22 mass%, polyvinyl chloride 4 mass%, and others (paper, etc.) ) 11 mass% and contained 1.32 mass% of chlorine. Table 1 shows the chemical composition of waste plastic.

  The waste plastic was granulated by supplying it to a granulator under the condition of 1.0 t / h. 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 cylindrical granule was produced.

  This plastic granulated material was blown into a lime-fired rotary kiln with a quick lime production amount of 500 t / day from a blow lance installed on the main fuel burner at the outlet of the rotary kiln. The drop position of the plastic granulated material was controlled by adjusting the carrier gas speed. The main fuel of the rotary kiln is heavy oil (calorific value: 9800 kcal / kg), plastic granulated product (calorific value: 9130 kcal / kg) is blown to 0.54 t / h, and heavy oil blown amount is 1.98 t / h. . When the plastic granulated product was blown, the chlorine concentration in the calcined quicklime was 151 ppm, and about 40 mass% of the amount of chlorine charged into the rotary kiln was transferred to quicklime.

  Further, the obtained quicklime is rolled and discharged in the rotary kiln (inner diameter: 1.5 m, length: 5 m, inclination angle: 1.7 degrees, residence time: about 14 minutes) using the second rotary kiln as the surface layer removing means. Thereafter, a horizontal swirling sieve (sieving mesh: 3 mm) was used as a separation step, and sieved to remove powder of 3 mm or less. This second rotary kiln was rolling only and was not heated. The yield of quick lime of 3 mm or more was 98.42 mass%, and the chlorine concentration was lowered to 48 ppm. The chlorine concentration of 3 mm or less quicklime was 6600 ppm.

  By using the method of the present invention, the chlorine content concentration of quicklime is reduced, and quicklime can be used for various purposes without being restricted by the chlorine concentration contained in the waste plastic.

Explanatory drawing which shows the condition in a rotary kiln. The processing flow which shows one Embodiment of this invention. Schematic of an example of a granulator used in the compression molding granulation method (ring die granulator). The graph which shows the chlorine concentration of quicklime after classification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotary kiln 2 Inlet 3 Raw material 4 Outlet 5 Blowing port 6 Waste plastic blowing port 7 Flame of main fuel 10 Die hole 11 Ring die 12 (12a, 12b) Rolling roller 13 Cutter 14 Input port 15 Plastic granulated material 16 Discharge port 20 Blowing means 21 Blowing means 22 Firing furnace 23 Surface layer removing means 24 Separation process A Main fuel B Combustion air C Waste plastic D Combustion air E HCl generation area F CaCl ₂ decomposition priority area G CaCl ₂ generation priority area H Limestone I Quicklime J Quick lime with high calcium chloride concentration K Quick lime with low calcium chloride concentration

Claims (3)

  A method of using a waste plastic containing a chlorine-containing resin as a part of the fuel when a raw material in a firing furnace is heated by combustion of fuel to produce a fired product, and a surface layer portion of the fired product after firing is used. A method for producing a baked product using waste plastic, wherein at least a part of the chlorine compound in the baked product is removed by removing.   The method for producing a fired product using waste plastic according to claim 1, wherein the surface layer portion of the fired product after firing is peeled off and removed.   The roll of the fired product after firing in a rotating drum separates the surface layer portion of the fired product from the fired product, and the separated surface layer portion is removed by sieving. A method for producing a baked product using the waste plastic according to claim 2.

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