JP4747981B2 - How to use waste plastic in firing furnaces - Google Patents

Description

  The present invention relates to a method in which waste plastic, which has not been used as a fuel so far, 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.

  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 raw dolomite from a silo to a great preheater for preheating the raw ore, 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.
Japanese Unexamined Patent Publication No. Sho 46-15037 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 using waste plastics in a firing furnace that can control the chlorine concentration of the fired product to a low level.

The features of the present invention for solving such problems are as follows.
(1) A method of using waste plastics containing a chlorine-containing resin as a part of the fuel when heating raw materials in a firing furnace by combustion of fuel to produce quick lime or fired dolomite , A method of using waste plastic in a firing furnace characterized by blowing water or water vapor into the furnace.
(2) The method for using waste plastic in a firing furnace as described in (1), wherein water or steam is blown together with fuel combustion air.
(3) The water or steam is blown so that the molar ratio of the amount of water or steam blown to the amount of chlorine blown from the waste plastic is 1 or more (1) or ( A method for using waste plastic in a firing furnace as described in 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.

  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 quick lime or a baked dolomite is manufactured as a baked product. FIG. 1 is an explanatory diagram showing the situation inside the rotary kiln. 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 air containing a little CO ₂ at the outlet side, and the O ₂ concentration decreases as the fuel burns as it advances toward 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 convert the CaCl ₂ generated in CaO, the rotary kiln, the CaCl ₂ generated by blowing water or water vapor is converted to CaO, the mixing of CaCl ₂ into quicklime The present invention has been completed by finding that it can be prevented. Water or water vapor is preferably blown together with fuel combustion air. The combustion air for blowing water or water vapor may be either directly blown into the rotary kiln (B) or blown into the rotary kiln (C) through the cooler 8 which is a heat exchanger for cooling quick lime or calcined dolomite. In addition, the chlorine content of the waste plastic is measured in advance, so that the molar ratio of the amount of water or steam blown to the amount of chlorine blown from the waste plastic is 1 or more and 20 or less. It is preferable to perform blowing.

  Next, a specific method of using waste plastic in a rotary kiln will be described with reference to FIG. The waste plastic is preferably used after being granulated, and the method for granulating the waste plastic will be described in detail below.

  According to the flow shown in FIG. 2, after crushing waste plastic in the crushing step 21, foreign matter removal using magnetic separation, wind separation, etc. and washing with water are performed in advance in the foreign matter removal step 22 to remove foreign matter other than plastic as much as possible. After that, it is supplied to the granulating step 23 and processed into a granulated product. The granulated product is blown into the rotary kiln 25 by a blowing step 24 for blowing the granulated product into the rotary kiln. In the granulating step 23, the crushed material from which foreign substances have been removed is extruded into a cylindrical shape and granulated. 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.

  For the granulation step, a known method used when granulating ordinary waste plastic 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 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. 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 suppressing the generation of CaCl ₂ when waste plastic is blown and used 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)
Therefore, if water or water vapor coexists in the system, the dechlorination reaction of CaCl ₂ proceeds, and mixing of CaCl ₂ into quick lime can be suppressed to a very low level. However, since the moisture concentration in the gas between the hydrogen chloride generation region in the rotary kiln and the kiln outlet is extremely low, in the present invention, the moisture concentration is increased by blowing water or water vapor into the rotary kiln. Water or steam is preferably blown together with the combustion air as the main fuel of the rotary kiln. Alternatively, it is preferable to install a water vapor or water spray lance at the rotary kiln outlet and blow water or water vapor into the rotary kiln. The blowing position of water or water vapor is preferably on the outlet side from the position where hydrogen chloride is generated, or on the inlet side from the waste plastic blowing lance or burner. The water or steam blown into the furnace converts CaCl ₂ into CaO, so that the produced quicklime or calcined dolomite has a reduced chlorine content. It is more effective to spray water or steam directly on quick lime or calcined dolomite that rolls in the rotary kiln.

  It is also possible to blow water or steam together with combustion air into a heat exchanger for cooling quick lime or calcined dolomite discharged from the rotary kiln. However, in this case, the gas temperature after blowing water or water vapor needs to be higher than the dew point of water.

  The amount of water or steam blown is preferably determined by measuring in advance the chlorine concentration in the waste plastic. Specifically, water or steam is blown so that “water / chlorine” or “steam / chlorine”, which is a molar ratio of the amount of water or steam blown to the amount of chlorine blown as waste plastic, becomes 1 or more. It is preferable. Particularly preferably, the molar ratio is 2 or more. Further, it is sufficient that the molar ratio of the amount of water or water vapor blown to the amount of chlorine blown is 50 or less. If too much water or water vapor is blown in, the temperature in the furnace is lowered, and the product quality may be deteriorated.

  Waste plastic was granulated using a granulator (ring die granulator) similar to that shown in FIG. 3 according to the flow of FIG. 2 to obtain a plastic molded product (granulated product).

  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), the blowing rate when plastic granulated material is not blown is 2.65 t / h, and the calorific value of plastic granulated material is 9130 kcal / kg. Replaced part of heavy oil. When the blowing rate of the plastic granulated product is changed at 0.38 t / h, 0.58 t / h, 0.88 t / h, and 1.15 t / h, the chlorine concentration in the manufactured quicklime is 105 ppm and 195 ppm, respectively. 335 ppm and 379 ppm.

  Next, the plastic granulated material was blown into the rotary kiln together with water vapor. A steam spray lance was installed at the bottom of the main fuel burner at the rotary kiln outlet, and was blown into the top of the quick lime in the rotary kiln. The amount of plastic granulated material blown was changed at 0.38 t / h, 0.58 t / h, 0.88 t / h, and 1.15 t / h, and the amount of water vapor blown was also changed. FIG. 4 shows the relationship between the plastic granulated product and the “water vapor / chlorine”, which is the molar ratio of the amount of water vapor and chlorine when water vapor is blown, and the chlorine concentration in the produced quicklime. The chlorine concentration in quicklime when no steam is blown is also indicated by a dotted line in FIG.

  According to FIG. 4, it turns out that the chlorine concentration in quicklime falls by water vapor | steam blowing. When the water vapor / chlorine (molar ratio) is 1 or more, the chlorine concentration in the quicklime clearly decreases. By blowing water vapor under the condition of water vapor / chlorine (molar ratio) 50, the chlorine concentration in the quick lime does not blow water vapor. It was reduced to 1/10. 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. 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 graph which shows the relationship between water vapor / chlorine amount (molar ratio) and the chlorine concentration in the manufactured quicklime.

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 21 Crushing process 22 Foreign matter removing process 23 Granulating process 24 Blowing process 25 Rotary kiln 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

Claims (3)

A method of using waste plastics containing a chlorine-containing resin as a part of the fuel when heating raw materials in a firing furnace by burning fuel to produce quick lime or calcined dolomite , A method of using waste plastic in a firing furnace characterized by blowing steam.   The method of using waste plastic in a firing furnace according to claim 1, wherein water or water vapor is blown together with fuel combustion air. The water or water vapor is blown so that a molar ratio between the amount of water or water vapor blown and the amount of chlorine blown from the waste plastic is 1 or more. Use of waste plastics in the firing furnace described.

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