JP5082557B2 - Manufacturing method of baked product using waste plastic - Google Patents

Description

  In the present invention, waste plastic that has not been conventionally used as a fuel is burned by being blown into a baking 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, quick lime 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.

On the other hand, it is known that waste plastic used as blown fuel or the like is preferably used after being granulated. As a particularly preferable method for granulating waste plastic, a method of granulating film plastic and solid plastic using a compression molding apparatus is known (for example, see Patent Document 3). Since granulated plastic molding with sufficient strength cannot be obtained when granulated film-like plastic, at least part of solid plastic is semi-molten or melted as a “core” effective to maintain the strength of the grain By carrying out the granulation so as to remain without making it into a solid, the strength of the granular plastic molding is dramatically increased, and the collapse at the time of pneumatic transportation or blowing can be effectively prevented.
JP 47-39124 A Japanese Patent Laid-Open No. 8-280533 JP 2001-341131 A

  When the waste plastic is blown into a lime firing furnace or the like, it is necessary to grind the waste plastic to a particle size that can be transported by airflow. Although the shape of the plastic after pulverization depends on the properties of the original plastic, the particle size range is wide, and the shape is variously various such as a film or a solid. Therefore, in order to adjust the shape, for example, a method of granulating into a granulated product by a compression molding granulation method using a ring die granulator or the like can be used. However, since the granulation method is a method in which only the surface is melted and granulated, the granulated material collapses and is pulverized by impact or the like during air flow transportation, and is easily clogged in the pipe. Further, when blown into the firing furnace, the pulverized plastic is transported to the kiln inlet side along the gas flow in the kiln and is blocked in the packed bed of the limestone preheating portion. Furthermore, the combustion position of the waste plastic shifts from the kiln inlet to the limestone packed bed, which causes troubles such as red heat at the kiln inlet.

  Further, 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, chlorine-containing synthetic resin is used for waste plastic. There is a problem of being included.

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.

  Therefore, the object of the present invention is to improve the transportation stability of the waste plastic and the combustion stability in the kiln 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. An object of the present invention is to provide a method for producing a baked product using waste plastic, which can be improved. Another object of the present invention is to provide a method for producing a baked product using waste plastic, which can reduce the chlorine concentration of the baked product even when the waste plastic contains a chlorine-containing synthetic resin. It is to provide.

The features of the present invention for solving such problems are as follows.
(1) When a raw material in a firing furnace is heated by combustion of fuel to produce a fired product, a solid fuel having an aspect ratio of 4 or more is granulated with waste plastic, and the resulting granulated product is used as the fuel. The manufacturing method of the baked product characterized by using as above.
(2) The method for producing a fired product according to (1), wherein a solid fuel that generates moisture by combustion and does not contain chlorine is used.

  According to the present invention, when using waste plastic as a fuel for a firing furnace, an extremely hard granulated product can be produced by mixing and extruding a solid fuel having a high aspect ratio to the waste plastic. The transportability and the combustion position in the firing furnace can be stably controlled. In addition, by using a solid fuel that does not contain chlorine and generates moisture by combustion, the chlorine concentration in the granulated product can be reduced, that is, the ratio of moisture to chlorine generated by combustion can be increased. The chlorine concentration of the fired product can be controlled to a very low level. For this reason, a baked product can be manufactured cheaply without limiting the use of the baked product.

  This facilitates the use of waste plastic as a fuel in a firing furnace, and promotes the recycling of waste plastic.

  In this invention, when manufacturing a baked product using the granulated material of a waste plastic as a fuel, the solid fuel whose aspect ratio is 4 or more is granulated with a waste plastic. By mixing a solid material having a large aspect ratio that does not melt in the granulation process, the plastic particles in the granulated product can be cross-linked to prevent the particles from being finely divided. FIG. 1 shows an image diagram of such a plastic granulated product. FIG. 1A is an example of a cross section of a conventional waste plastic granulated product, and particles of solid plastic 22 exist between layers of film-like plastic 21. FIG. 1B is a waste plastic granular material used in the present invention, and a solid fuel 23 having a high aspect ratio is bridged between film-like plastics 21. As a result, the strength of the granulated material is increased, and when the granulated material is subjected to an impact, the granulated material is not easily disintegrated, and can be prevented from being finely granulated. The present invention has been completed.

  The larger the aspect ratio of the solid fuel, the greater the effect of crosslinking between the plastic particles in the granulated product, which is preferable. If the aspect ratio is less than 4, the effect of increasing the strength of the granulated product is small.

  The solid fuel is preferably made of a material that can be used as a fuel in a firing furnace and does not change its shape due to melting or the like during the granulation process. More specifically, it is preferable to use a crushed biomass such as waste wood. Biomass is structurally fibrous, and when crushed and crushed, it becomes a crushed product with a high aspect ratio. The aspect ratio of the solid fuel is defined as the ratio of the major axis to the minor axis of the solid fuel (major axis / minor axis). The major axis is the longest diameter of the solid fuel, and the minor axis is defined as the equivalent circle diameter of the projected area perpendicular to the major axis. The aspect ratio of the solid fuel granulated with the waste plastic can be obtained by arbitrarily extracting 100 particles from the crushed solid fuel, measuring the aspect ratio, and averaging.

  The mixing ratio of the solid fuel to the waste plastic may be 10 mass% or more. If it is 30 mass% or more, it is more preferable because stable air transportability and combustion stability can be secured.

  Further, as the solid fuel, it is preferable to use a substance that generates moisture by combustion and does not contain chlorine. By using a solid fuel that does not contain chlorine, the chlorine concentration in the granulated product can be reduced, and the moisture generated during the combustion process can also be used in the dehydrochlorination reaction (generation of calcium oxide) of calcium chloride generated in quicklime. This contributes to the production of quick lime and calcined dolomite with extremely low chlorine concentration. A crushed product of biomass such as waste wood is also suitable as the solid fuel of the present invention in this respect.

  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.

  Next, the manufacturing method of the baked product in the baking furnace (rotary kiln) using the concrete waste plastic is demonstrated using FIG. Waste plastic A and solid fuel B are crushed by crushing means 1 and crushing means 2 to a particle size that can be charged into granulator 4 and mixed by mixer 3. The mixed waste plastic A and solid fuel B are supplied to the granulator 4 and granulated to a particle size that can be air-transported to a firing furnace to obtain a granulated product C. The granulated product C is supplied into the firing furnace 7 by the air E together with the main fuel D supplied by the blowing means 6 in the blowing means 5 (air flow transport device), and used as a burning fuel for the limestone F. As a result, quick limestone G is produced.

  Next, the granulation method of waste plastic and solid fuel will be described in detail.

  The waste plastic to be blown is granulated to a blowable particle size 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, a mixture of waste plastic and solid fuel is granulated by compressing and extruding 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 together with the solid fuel with the rolling roller by the rolling roller. By cutting or scraping off the plastic molded product extruded through the ring die outer surface side from the outer surface of the ring die, a granular molded product serving as a furnace blowing material is obtained. Mainly, at least a part of the waste plastic is semi-molten or melted by frictional heat in the die hole, and then solidified to obtain a plastic / solid fuel mixture molded product (granulated product).

  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 compression molding apparatus as described above, the ring die 11 is driven to rotate in the direction of the arrow in the figure, and the rolling rollers 12a and 12b are rotated accordingly. The mixture of the waste plastic A and the solid fuel B is charged into the ring die 11, and the waste plastic A and the solid fuel B thus charged are mixed in the ring die 11, and are made into contact with the inner peripheral surface of the ring die 11 by the rolling rollers 12a and 12b. It is pressed into the die hole 10 of the ring die 11 while being compressed and crushed. 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 and the solid fuel granulated product 15 are obtained by being cut into pieces. Reference numeral 16 denotes a discharge port.

  The solid fuel used for granulation is usually crushed, and the crushed diameter can be equal to or slightly larger than the die hole of the ring die. The crushed solid fuel is mixed with waste plastic and granulated to improve the strength of the granulated product. The major axis of the crushed solid fuel used for granulation is preferably equal to or greater than the die diameter, and the aspect ratio is 4 or more. However, operation of the granulator is difficult when the minor axis is 1/3 or more of the die diameter.

  The hardness of the granulated product obtained from the above varies depending on the operating conditions of the granulator. In order to obtain a harder material, it is sufficient to increase the filling amount of the granulator and reduce the processing speed, but the productivity is lowered. Further, when the processing speed is further reduced, there may be a situation in which the waste plastic melts in the granulator and the granulator must be stopped. On the other hand, a plastic and solid fuel granulated product can be produced that is extremely hard (average strength index) as compared with granulation of only plastic under the same processing conditions. When blowing into a rotary kiln as a fuel, the air flow transportation method is usually taken, but the plastic granulated by the above method is stably inflated and may have a compressive strength of a certain level or more in order to be supplied into the rotary kiln. preferable.

The compressive strength of the granulated product is preferably evaluated using the average strength index δ. 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, and the mass fraction, and for all di defined by the following equation (w) This is the sum of products of δi and ωi.
δ = Σδiωi (w)
However, δi: ratio (N / mm) of load (N) and displacement (mm) when a load perpendicular to the side surface of the 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 intensity | strength of a granulated material is measured using an apparatus as shown in FIG. FIG. 4 is a schematic diagram showing a compression test method, and FIG. 4A shows a compression test apparatus. A load of W (N) is applied to the side surface in the length direction of the columnar granulated material 15 using the compression test apparatus 20 at a compression speed of 2 mm / min, and a load W (N) as shown in FIG. And the compression characteristic which is the relationship between the compression distance L (mm). When the strength δ of the granulated product is obtained as δ≡ΔW / ΔL from the compression characteristics, a graph as shown in FIG. 4C is obtained for the granulated product having each di (particle size). Moreover, FIG.4 (c) shows the relationship between the particle size and intensity | strength of a granulated material, and it turns out that it has high intensity | strength, so that a particle size is large. The average strength index δ is the sum of the products of the strength and mass fraction of the granulated product having each particle size (average diameter of cylindrical circular portion) di, and is defined by the above formula (w).

  Waste plastic produced by the above method and a granulated product of solid fuel are used as a part of fuel in a rotary kiln for producing quick lime or calcined dolomite. As a method of using as fuel, waste plastic and waste wood granulated material may be blown into a rotary kiln using a lance or a dedicated burner by a normal air transportation method.

When using the waste plastics and solid fuel granules produced as described above as part of the rotary kiln fuel, water is generated by combustion, and the fired product when using solid fuel that does not contain chlorine The removal of calcium chloride (CaCl ₂ ) from can be explained by the following reaction formula. CaCl ₂ is produced by the following reaction formulas (x) and (y), and dehydrochlorinated by (z).
CaCO ₃ + 2HCl = CaCl ₂ + CO ₂ + H ₂ O (x)
CaO + 2HCl = CaCl ₂ + H ₂ O (y)
CaCl ₂ + H ₂ O (generated by combustion) = CaO + 2HCl (z)

  Using the same granulator (ring die granulator) as shown in FIG. 3, granulate waste plastic and waste wood to obtain plastic and waste wood molding (granulated material). Limestone was fired using a rotary kiln according to the flow.

  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 wood was pulverized to 10 mm or less (aspect ratio = 5.5), and Table 1 also shows the chemical composition.

  The mixture of waste plastic and waste wood (10 mm or less) was supplied to a granulator under the condition of 1.0 t / h and granulated. 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. FIG. 5 shows the average strength index of the granulated product when the waste wood mixing ratio is changed.

  These granulated materials (waste wood 0, 10, 20, 30, 50, 66 mass%) were blown into a lime-fired rotary kiln with a production volume of quick lime of 500 t / day from a blow lance installed on the main fuel burner at the outlet of the rotary kiln. . The carrier gas velocity at the outlet of the blowing lance was 20 m / s (= the blowing velocity of the granulated product), and the dropping position of the granulated product in the kiln was about 15 m from the kiln outlet. The granulated material was blown into the rotary kiln at 0.54 t / h, and the amount of heavy oil blown (heat generation amount: 9800 kcal / kg) was adjusted according to the heat generation amount. FIG. 6 shows the exhaust gas temperature at the kiln outlet (preheating furnace inlet) and the chlorine concentration in the product quicklime. The kiln exhaust gas temperature has a small fluctuation range at a waste wood ratio of 30 mass% or more, and stable granulation can be combusted. Moreover, the chlorine concentration in quicklime can be made into 100 ppm or less because waste wood mixing ratio shall be 30 mass% or more.

  By using the method of the present invention, the combustion of the granulated material in the kiln is stabilized, the chlorine content concentration of quicklime is reduced, and there is no restriction on the chlorine concentration contained in the waste plastic, and quicklime is used for various applications. It became possible to use.

  In the same manner as in Example 1, the waste wood was pulverized to 8 mm or less (aspect ratio = 4.1) to produce cylindrical particles of waste wood of 10 mass%, 33 mass%, and 50 mass%. The average strength index was 220, 230, and 370 N / mm, respectively, and a granulated product having higher strength than that obtained by granulating without mixing waste wood was obtained.

[Comparative example]
As in Example 1, waste wood was crushed to 6 mm or less (aspect ratio = 3.1), 3 mm or less (aspect ratio = 1.7), and cylinders of 10 mass% and 33 mass% of waste wood were used for each. Shaped granules were produced and the average strength index was measured. The relationship between the aspect ratio and the average intensity index is also shown in FIG. Granules having an aspect ratio of 3.1 and 1.7 were low in strength and were observed to be pulverized after air transportation.

Explanatory drawing which shows the image of (a) plastic granulated material, (b) plastic and solid fuel granulated material. 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 figure which shows the measuring method of a particle | grain average intensity | strength index. The graph which shows the change of the average intensity | strength index | exponent of a plastic and solid fuel granulated material. The graph which shows the kiln exit exhaust gas temperature at the time of plastics and solid fuel granule blowing, and the chlorine concentration in quicklime. The graph which shows the relationship between an aspect ratio and an average intensity index.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crushing means 2 Crushing means 3 Mixer 4 Granulator 5 Blowing means 6 Blowing means 7 Baking furnace 10 Die hole 11 Ring die 12a, 12b Rolling roller 13 Cutter 14 Input port 15 Plastic, solid fuel granulated material 16 Exhaust Outlet 20 Compression test apparatus 21 Film plastic 22 Solid plastic 23 High aspect ratio solid fuel A Waste plastic B Solid fuel C Granulated material D Main fuel E Air F Limestone G Quicklime

Claims (2)

When the raw material in the firing furnace is heated by burning the fuel to produce a fired product , the waste wood is granulated with a waste plastic together with a ring die granulator, and the resulting granulated product is used as the fuel. A method for producing a fired product to be used ,
The major axis of the waste wood to be granulated is not less than the die diameter of the ring die granulator, and the aspect ratio of the waste wood is not less than 4, and
A method for producing a baked product, wherein the waste plastic includes a film-like one .   The method for producing a baked product according to claim 1, wherein waste wood is produced by combustion and contains no chlorine.

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