JP2004216243A - Method and apparatus for melting treatment of waste using shell for basicity regulation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for melting treatment of waste by using a shell as a lime source for basicity regulation of molten slag, and an apparatus therefor. <P>SOLUTION: When the waste or ashes obtained by incineration of the waste or sludge is subjected to melting treatment independently or after blending, the shell is dried and deodorized by hot air, crushed to 0.3 to 20 mm grain size and then supplied as the lime source for basicity regulation of the molten slag. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for directly melting waste such as municipal solid waste, industrial waste, and sludge, a method for melting waste after incinerating the waste once to form ashes, and an apparatus for adjusting the basicity of molten slag. TECHNICAL FIELD The present invention relates to a method and apparatus for melting and processing waste materials using shells as a source of lime.
[0002]
[Prior art]
At present, most waste is treated by incineration, but there are problems such as the necessity of a treatment plant for incineration ash in incineration. In particular, in the metropolitan area, it is difficult to secure an incineration ash treatment plant, and the waste can be directly melted, or the waste incineration ash can be melted to reduce its volume and recycled. The need for processing is increasing. In addition, in order to recycle slag from molten waste, it must have physical properties (strength, particle size distribution) comparable to natural sand and crushed stone, and have chemical properties. It is.
[0003]
On the other hand, the component of the molten slag in the waste is rich in SiO ₂ silicate, has a high viscosity in the molten state, and is difficult to discharge from the melting furnace. If the temperature is increased to avoid this, erosion of the refractory is caused. Not preferred. Therefore, it is generally known to supply a lime source such as limestone, slaked lime, and quick lime to adjust the basicity CaO / SiO ₂ of the molten slag. By adjusting the basicity of the molten slag, the fluidity of the molten slag is improved, the slag is easily discharged, and a dense and strong slag can be obtained. Japanese Patent Application Laid-Open No. 2002-130630 (Patent Document 1) proposes a method of supplying shells as a lime source for adjusting the basicity of molten slag.
[0004]
[References]
(1) Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-130630)
[0005]
[Problems to be solved by the invention]
The method of using shells instead of limestone as a lime source for adjusting the basicity of the molten slag is two birds per stone because the shells also serve as waste. The prior art described above discloses a method of using shells as a lime source for adjusting the basicity of molten slag, but in that case, it is described that shells are supplied without processing, and before supply. Is not disclosed.
[0006]
However, when the shell is supplied to the melting furnace without being processed, a stink which remains and adheres to the shell and rots is generated. In addition, shells having a large shape such as oyster shells and complicated shapes are difficult to handle due to clogging at the hopper. Further, if the particle size of the shell is too large, the shell does not melt in the melting furnace, but is discharged as free CaO together with the molten slag, and the alkalinity of the slag increases, which is a problem when used as a civil engineering material. On the other hand, if the particle size of the shell is too small, it will be scattered outside the furnace by the gas passing through the furnace in the melting furnace, and will not function as a basicity adjusting material.
[0007]
As described above, the prior art does not describe a method for solving these problems when the shell is effectively used as a basicity adjusting material. The present invention provides an economical method for obtaining a lime source suitable for a reaction in a melting furnace and easy to handle when shells discarded as waste are effectively used as a lime source for adjusting basicity. It is an object of the present invention to provide a conventional shell processing method and apparatus.
[0008]
[Means for Solving the Problems]
The gist of the invention is that
(1) In a method of melting and processing waste, incinerated ash, or sludge alone or as a mixture, when supplying shells as a lime source for adjusting the basicity of molten slag, the shells are dried with hot air. A method for melting waste using shells as a basicity adjustment, wherein the shells are deodorized and then crushed to a particle size of 0.3 to 20 mm.
(2) A part of the exhaust gas after drying the shell is circulated and supplied for adjusting the temperature of the hot air for drying, and the remaining exhaust gas is heated and deodorized and discharged to the outside of the system. (1) A method for melting waste according to (1) using shells as the basicity adjustment.
[0009]
(3) The method for melting waste according to the above (1) or (2), wherein the shell is used for adjusting the basicity, wherein the temperature of hot air for drying and deodorizing the shell is 700 to 850 ° C. .
(4) Melting waste using shells as the basicity adjustment according to (1) to (3), wherein the temperature of the exhaust gas after shell drying is raised and deodorized to 700 to 850 ° C. Processing method.
(5) A rotary kiln for drying and deodorizing shells having a hot air supply device, a crusher for crushing shells after drying and deodorization, and a circulation path for circulating a part of the dried exhaust gas to the hot air supply device of the rotary kiln. A waste melting apparatus using shells for adjusting the basicity, comprising a device for raising the temperature and deodorizing the remaining exhaust gas.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
An important point of the basicity adjustment method using a lime source is that the properties of the molten slag are suitable for civil engineering materials. In particular, it is important that free CaO is not generated from the molten slag. Next, the free CaO will be described. The waste slag has the same molecular structure as glass, is composed of a network structure of SiO ₂ , and has a state in which CaO molecules are incorporated in the network. Free CaO is present in the slag as CaO alone without being incorporated into the mesh. The slag containing free CaO dissolves CaO when it comes into contact with water, and increases alkalinity. Therefore, when slag is used effectively as a civil engineering material, its use is unpreferably restricted.
[0011]
On the other hand, CaCO ₃ , which is the main component of the shell, is thermally decomposed into CaO in the melting furnace, but the melting point of CaO is very high at 2570 ° C., and is usually about 1500 ° C. in the melting furnace. Does not dissolve in a simple substance. CaO reacts with and mixes with SiO ₂ , which is a main component of slag, so that its melting point is lowered to about 1400 ° C. to be melted. That is, CaO reacts sequentially from the surface and dissolves so that the candy melts and becomes smaller. Therefore, when the particle size of the lime source is too large, melting is not completed in the melting furnace, and free CaO remains in the slag.
[0012]
FIG. 1 is a graph showing the relationship between the particle size of the lime source and free CaO. The data on the shell of the present invention was obtained in a test run. It was found that there was a difference compared to the case of limestone. As shown in FIG. 1, the free CaO can be reduced to 0.2% or less by setting the particle size of the shell to 20 mm or less. On the other hand, in the case of limestone, the diameter is 10 mm or less, and free CaO is less likely to be generated even with a shell having a larger particle size. This is presumably because the shell is rich in reactivity even with the same component of CaCO ₃ . In addition, when it is necessary to further suppress free CaO depending on the use of the slag, it is preferable that the particle size of the shell be 3 mm or less.
[0013]
The smaller the particle size of the shell, the better the reactivity in the melting furnace and the less free CaO. On the other hand, the shell is more likely to be scattered by the gas passing through the furnace in the melting furnace. In the present invention, as a result of a test in a shaft furnace type melting furnace of the embodiment shown in FIG. 1, scattering was practically not a problem if it was 0.3 mm or more. The scattering phenomenon is caused not only by the relationship between the particle size of the charged shell and the gas flow velocity in the melting furnace, but also by the shell falling down while being heated in the melting furnace, cracking and powdering during the thermal decomposition process. to be influenced. In consideration of these influences, it was found that if it is 0.3 mm or more, it does not scatter and dissolves in the molten slag to exhibit the function as a basicity adjusting material. Therefore, the particle size of the shell is set to 0.3 to 20 mm.
[0014]
When crushing shells, crush them after drying. Drying is performed while blowing with hot air of 700 to 850 ° C. and stirring with a rotary kiln or the like. When dried at a high temperature exceeding 850 ° C., CaCO _3, which is a main component of the shell, is decomposed to CaO, which causes hygroscopicity, and thus requires care in handling, which is not preferable. On the other hand, when the temperature is lower than 700 ° C., the deodorization is not sufficiently performed, which is not preferable. When crushing shells, it is more economical to crush the shell as coarsely as possible, as long as the problem of free CaO does not occur. Further, since fine powder having a size of less than 0.3 mm is scattered in the melting furnace and does not contribute to the adjustment of the basicity, it is necessary to crush the fine powder by a method that generates less fine powder. In the present invention, a hammer crusher type crusher was used for crushing the shell in consideration of these particle size conditions. The molten slag produced by the method of the present invention has physical and chemical properties equivalent to those of natural sand and can be used as civil engineering materials.
[0015]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples.
FIG. 2 is a process chart showing a case where waste is directly melted using coke. As shown in FIG. 2, coke and dried and crushed shells are charged into the melting furnace 1 as waste and auxiliary materials from a charging device 2 at the upper part of the melting furnace 1. Municipal waste was disposed of as waste. Air and oxygen are supplied from a tuyere 3 provided around the lower part of the melting furnace 1. The waste, coke, and the like charged into the melting furnace 1 form a packed bed in the furnace, and a part of the coke and waste is burned by air and oxygen blown from the tuyere 3 at the lower part of the furnace. The combustion gas rises in the melting furnace from the bottom of the furnace, and the waste is preheated, dried and thermally decomposed by the sensible heat of the combustion gas. Steam, pyrolysis gas and fine dust generated in the process of drying and pyrolysis of the waste are discharged from the pyrolysis gas discharge pipe 5.
[0016]
On the other hand, the ash and non-combustibles of the waste, the coke and the shells are heated to a high temperature and descend to the furnace bottom. The coke burns with the air and oxygen blown from the tuyere 3, and the ash and non-combustibles are 1300 It is heated from 1500C to 1500C to be in a molten state. Slag in a molten state is discharged from the slag discharge port 4. The slag in the molten state is introduced into the granulation equipment and becomes fine sand-like particles. The gas discharged from the pyrolysis gas discharge pipe 5 is completely burned in the combustion furnace 6, heat is recovered in the boiler 7, cooled in the gas cooling tower 8, collected in the dust collector 9, and passed through the induction ventilator 10. Released from the chimney 11 to the atmosphere.
[0017]
FIG. 3 is a process diagram showing an apparatus for drying and crushing a shell according to the present invention. As shown in this figure, the shell is charged into a rotary kiln 12 and is contacted with a hot gas of 700 ° C. to 850 ° C. blown from a burner 15 for the rotary kiln to be dried and deodorized. The dried shell is charged into a crusher 13 and crushed to 20 mm or less. The crusher is a hammer crusher, and the crushing particle size is adjusted by changing the rotation speed of the hammer. The gas discharged from the rotary kiln 12 is circulated again to the rotary kiln by the circulation blower 17 and used for adjusting the temperature of the hot air. The remaining exhaust gas is led to the deodorizing furnace 14 where the temperature is raised to 700 to 850 ° C. by the deodorizing burner 16. Release to the atmosphere after deodorization. The method of circulating the exhaust gas for adjusting the temperature of the hot air is economical because the amount of the exhaust gas released to the atmosphere is small and the amount of heating heat for raising the temperature of the deodorizing furnace can be reduced as compared with the method of dilution with air . The shells used in the present invention are oysters and Aoyagi shells.
[0018]
【The invention's effect】
As described above, according to the present invention, shells that are waste can be effectively used as a basicity adjusting material for a melting furnace, and furthermore, by crushing shells to 0.3 to 20 mm, shells in a melting furnace can be obtained. And free CaO in the molten slag can be kept low, so that the slag can be effectively used as a civil engineering material. In addition, the shell is dried and crushed in a facility composed of a rotary kiln, a crusher, and a deodorizing furnace, so that the shell can be crushed into a predetermined particle size distribution and deodorized. By setting the temperature to 850 ° C., the shell can be dried and deodorized, and at the same time, the shell is not thermally decomposed into CaO, so that the shell can be easily handled after crushing. Further, by setting the temperature of the exhaust gas after drying the shell to 700 to 850 ° C., an extremely excellent effect such as the deodorization of the exhaust gas can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the particle size of a lime source and free CaO.
FIG. 2 is a process diagram showing a case where waste is directly melted using coke.
FIG. 3 is a process diagram showing an apparatus for drying and crushing shells according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Melting furnace 2 Charging device 3 Tuyere 4 Slag discharge port 5 Pyrolysis gas discharge pipe 6 Combustion furnace 7 Boiler 8 Gas cooling tower 9 Dust collector 10 Induction draft fan 11 Chimney 12 Rotary kiln 13 Crusher 14 Deodorizing furnace 15 Burner for rotary kiln 16 Burner 17 for deodorizing furnace Circulating blower

Claims (5)

Waste, ash obtained by incineration of waste, or a method of melting by mixing sludge alone or in combination, when supplying shells as a lime source for adjusting the basicity of molten slag, the shells were dried with hot air and deodorized. Thereafter, the shell is subjected to crushing to adjust the particle size of the shell to 0.3 to 20 mm. A part of the exhaust gas after drying the shell is circulated and supplied for adjusting the temperature of the hot air for drying, and the remaining exhaust gas is heated and deodorized and discharged out of the system. Waste melting method using shells as a basicity adjustment. The method for melting waste according to claim 1 or 2, wherein the temperature of hot air for drying and deodorizing the shell is 700 to 850 ° C. The method according to any one of claims 1 to 3, wherein the temperature of the exhaust gas after shell drying is raised and deodorized to 700 to 850 ° C. A rotary kiln for drying and deodorizing shells having a hot air supply device, a crusher for crushing shells after drying and deodorization, a circulation path for circulating a part of the dried exhaust gas to the hot air supply device of the rotary kiln, and a residual exhaust gas A waste melting apparatus using shells as a basicity adjustment, comprising a device for raising the temperature and deodorizing.

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