JPH07324716A - Method and apparatus for processing municipal dust - Google Patents

Abstract

PURPOSE:To enable a heat exchanger to be prevented from being decayed with hydrogen chloride with atomization of water into thermal cracking gas and in this case to perform an effective utilization of thermal energy held in the thermal cracked gas during the thermal cracking operation in the case that heat energy of the combustion discharged gas generated upon combustion of thermal decomposed product of municipal dust is recovered through its heat exchanging operation. CONSTITUTION:Municipal dust is thermally decomposed at about 450 deg.C at a first decomposing furnace 1. Thermal decomposed gas generated at the furnace is heated up to about 750 deg.C at a second decomposing furnace 2 and tar generated under a cooling of the thermal decomposed gas to a normal temperature at a wet type cleaning tower 4 is decomposed in advance. Thus, even if the thermal decomposed product is desalted under atomization of water at the wet type cleaning tower 4, there is no occasion that tar substance is discharged to cause a water discharging to be difficult. Heat contained in the thermal decomposing gas discharged out of the second decomposing furnace 2 is recovered by a heat exchanger 3 before its desalting operation and tis is applied as a heating source for the combustion air for a gas combustion furnace 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for treating municipal solid waste that thermally decomposes municipal solid waste generated from homes and offices and uses thermal energy generated by burning the thermal decomposition products.

[0002]

2. Description of the Related Art A waste treatment technology of this type is disclosed in Japanese Patent Laid-Open No.
It is disclosed in Japanese Patent Publication No. 49816. In the technique disclosed in the publication, a waste containing a combustible material is heated and pyrolyzed, and a pyrolysis product containing a pyrolysis gas generated thereby is combusted, and exhaust gas of this combustion is discharged to a waste heat boiler. To generate steam, which is then used to generate electricity and recover heat energy.

Further, when the pyrolysis product is burned, the combustion residue such as ash contained in the product produced by the pyrolysis is burned at a high temperature (for example, 1200 ° C. or higher) to form molten slag, thereby constructing the combustion residue. It can also be converted into slag that can be reused for things and road aggregates.

As described above, according to the technique disclosed in Japanese Patent Application Laid-Open No. 1-49816, the thermal decomposition product produced by thermally decomposing waste is burned and its thermal energy is converted into electric power for effective use. Besides, combustion residues such as ash can be slagged for recycling.

[0005]

However, according to the above-mentioned prior art, since the municipal solid waste to be treated contains wastes containing chlorine such as vinyl chloride garbage and raw garbage, the pyrolysis gas is It contains chlorine, and produces hydrogen chloride after combustion of pyrolysis products such as pyrolysis gas and char.This hydrogen chloride causes the transmission of high-temperature parts of heat exchangers such as waste heat boilers and high-temperature air heaters. There is a problem that the hot surface is corroded. It is known that the corrosion of the boiler heat transfer surface or the like due to the chlorine content occurs when the temperature of the combustion exhaust gas is approximately 330 ° C. and particularly rapidly at 500 ° C. to 700 ° C.

Therefore, in order to prevent corrosion of the high temperature air heater or the like due to hydrogen chloride, it is desirable to remove the chlorine content in the combustion exhaust gas before introducing it to the high temperature air heater or the like. Unlike the above-mentioned conventional technique, the removal of chlorine content separates combustion of pyrolysis gas and char, and sprays water or an alkaline aqueous solution such as an aqueous solution of sodium hydroxide on the pyrolysis gas in a wet washing tower. You can do that.

However, in the above-mentioned prior art, the thermal decomposition of municipal waste is generally carried out at about 450.degree.
When water or an alkaline aqueous solution is sprayed on the pyrolysis gas produced by pyrolysis at such a temperature, tar is generated, which causes difficulty in handling such as difficulty in wastewater treatment. Although it is possible to raise the thermal decomposition temperature above about 450 ° C, the thermal decomposition process in the above-mentioned conventional technology also has the purpose of separating and recovering municipal solid waste, and the aluminum content contained in the municipal solid waste ( , Which is taken out as a pyrolysis residue after the pyrolysis step.) Has a low melting point of 660 ° C., so that the pyrolysis temperature cannot actually be raised above about 450 ° C.

Further, if the generated pyrolysis gas is immediately sprayed with water or an aqueous alkaline solution such as an aqueous solution of sodium hydroxide, the thermal energy retained in the pyrolysis gas during the pyrolysis process is effectively utilized. There is also the problem that you cannot do it.

According to the present invention, in recovering the thermal energy of the combustion exhaust gas generated by burning the thermal decomposition products of municipal waste by heat exchange, the corrosion of hydrogen chloride in a heat exchanger or the like is prevented by using water for the thermal decomposition gas. Another object of the present invention is to provide a waste treatment method and apparatus that can be performed by spraying an alkaline aqueous solution.

Further, even if the corrosion of hydrogen chloride in a heat exchanger or the like is prevented by spraying water or an aqueous alkali solution onto the pyrolysis gas, the thermal energy retained in the pyrolysis gas during the pyrolysis process is effective. It is also an object to provide a waste treatment method and apparatus that can be utilized for

[0011]

A first aspect of the present invention for solving the above-mentioned problems is a process of heating and decomposing municipal waste and a process of burning the pyrolysis products produced in this pyrolysis process. In a method for treating municipal solid waste including, the pyrolysis gas in the pyrolysis product is heated at a predetermined temperature higher than the pyrolysis temperature, and the tar generated when the pyrolysis gas is cooled to room temperature is decomposed in advance. And a step of spraying water or an alkaline aqueous solution on the pyrolysis gas after the decomposition to remove chlorine from the pyrolysis gas before the combustion step. This is how to dispose of garbage.

A second invention is a method for treating municipal solid waste according to the first invention, wherein the predetermined temperature is any temperature of 650 ° C. or higher.

A third invention is the method for treating municipal solid waste according to the first invention, wherein the predetermined temperature is any temperature of 700 ° C. or higher and 800 ° C. or lower.

Any of the first to third inventions characterized by including a step of recovering the heat retained in the pyrolysis gas after the tar decomposition by heat exchange before the chlorine content removing step. A fourth invention is a method of treating such municipal waste.

A fifth invention is a method for treating municipal solid waste according to the fourth invention, characterized by including a step of heating combustion air in the combustion step by using at least a part of the recovered heat as a heat source.

[0016] In a municipal solid waste treatment apparatus comprising a pyrolyzer for heating and thermally decomposing municipal waste, and a combustor for burning the thermal decomposition products produced by the pyrolyzer, said thermal decomposition product A pyrolyzed gas in a substance is heated at a predetermined temperature higher than the pyrolysis temperature, and a tar decomposer for previously decomposing tar generated when the pyrolysis gas is cooled to room temperature,
A sixth aspect of the present invention is an apparatus for treating municipal solid waste, comprising: a wet cleaning tower that sprays water or an alkaline aqueous solution onto the thermally decomposed gas after the decomposition to remove chlorine from the thermally decomposed gas. And

The tar decomposer is operated at the predetermined temperature of 65.
A seventh aspect of the present invention is an apparatus for treating municipal solid waste according to the sixth aspect, which is characterized in that the temperature is 0 ° C. or higher.

The tar decomposer is operated at the predetermined temperature of 70.
An eighth aspect of the present invention is an apparatus for treating municipal solid waste according to the sixth aspect of the present invention, which is characterized in that the temperature is set to any value between 0 ° C and 800 ° C.

Before the chlorine content is removed by the wet cleaning tower, a heat recovery device for recovering the heat retained in the pyrolysis gas after the tar is decomposed by heat exchange is provided. A ninth aspect of the present invention is an apparatus for treating municipal solid waste according to any one of the sixth to eighth aspects.

According to a tenth aspect of the present invention, there is provided an apparatus for treating municipal solid waste according to the ninth aspect, which is provided with a heater for heating combustion air used in the combustor by using at least a part of the recovered heat as a heat source. And

[0021]

According to the present invention, since the pyrolysis gas after pyrolyzing municipal waste to separate the pyrolysis residue is heated, there is no problem even if it is heated at a temperature higher than the pyrolysis temperature (generally about 450 ° C). There is no.

By heating the pyrolysis gas at a temperature higher than the pyrolysis temperature, tar generated when the pyrolysis gas is cooled to room temperature is reduced in molecular weight and decomposed in advance. Since municipal solid waste has a large amount of water, the pyrolysis gas contains a large amount of water vapor (generally about 56% of the pyrolysis gas). The amount of water vapor also contributes to heating the pyrolysis gas to a temperature higher than the pyrolysis temperature, so that the heated pyrolysis gas has an atmosphere in which a water-gas reaction as shown in the following formula (1) occurs. Becomes

[0023]

[Equation 1]

It is also considered that this is because the tar can be decomposed before it is cooled to room temperature. Therefore, even if water or an alkaline aqueous solution such as an aqueous solution of sodium hydroxide is sprayed on the pyrolysis gas for desalting, tar is generated due to the pyrolysis gas being cooled to room temperature, which makes wastewater treatment difficult. Problem does not occur, desalination can be carried out without problems, and heat exchangers such as high temperature air heaters are not corroded.

By raising the decomposition temperature of tar to about 750 ° C., tar can be decomposed almost completely and gasified. Therefore, as in the second and seventh inventions, it is desirable that the decomposition temperature of tar is 650 ° C. or higher. In particular, as in the third and eighth inventions, if the temperature is 700 ° C. or higher and 800 ° C. or lower, Tar is desirable because it can be decomposed almost completely and wasteful heat energy is not required.

When the pyrolysis gas is desalted by spraying water or an aqueous alkali solution such as an aqueous solution of sodium hydroxide, heat energy is wastefully lost, and the pyrolysis gas is at a high temperature. The amount of sprayed sodium oxide aqueous solution also becomes large. Therefore, if the heat of the pyrolysis gas is recovered before desalting by spraying water or an aqueous alkaline solution such as an aqueous solution of sodium hydroxide as in the fourth and ninth inventions, the heat is not wasted. It can be used for municipal waste treatment equipment, etc., and can effectively utilize thermal energy. As the usage destination, the fifth,
As in the tenth aspect of the invention, it is desirable to use it for heating the combustion air that combusts the thermal decomposition products.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of a municipal solid waste processing apparatus according to a first embodiment of the present invention. Reference numeral 1 is a first decomposition furnace as a thermal decomposer in the present invention, which heats municipal solid waste to perform thermal decomposition. In this embodiment, for example, a general pyrolysis drum is used. A large number of heating tubes (not shown) are provided in the thermal decomposition drum, and hot air is introduced into the heating tubes to perform thermal decomposition. Its pyrolysis temperature is generally 450
It is about ℃. The thermal decomposition gas generated by this thermal decomposition is sent to the second decomposition furnace 2 as a tar decomposer in the present invention, and the thermal decomposition residue remaining after thermal decomposition is separated into rubble, aluminum, iron and the like and char.

In the second cracking furnace 2, the pyrolysis gas is heated at a temperature higher than the pyrolysis temperature in the first cracking furnace 1,
Tar generated when the pyrolysis gas is cooled to room temperature is previously decomposed and gasified. The heating source is high-temperature air, and heating is performed by heat exchange between the high-temperature air and the pyrolysis gas. The pyrolyzed gas after decomposing tar is introduced into a heat exchanger 3 as a heat recovery unit in the present invention, cooled by exchanging heat with room temperature air, and then introduced into a scrubber type wet cleaning tower 4. . In the wet cleaning tower 4, water or an alkaline aqueous solution such as an aqueous sodium hydroxide solution is sprayed on the pyrolysis gas to remove the chlorine content contained in the pyrolysis gas.

The gas combustion furnace 5 and the high temperature melting furnace 6 are combustors in the present invention. In this embodiment,
The combustor is divided into a gas combustion furnace 5 and a high-temperature melting furnace 6, and in the former case, the pyrolysis gas after desalting is burned, and in the latter case, char separated from the pyrolysis residue is burned. The air heated by the heat exchange in the heat exchanger 3 is introduced into the gas combustion furnace 5 as combustion air. The pyrolysis gas after desalting is also introduced into the gas combustion furnace 5 to burn the pyrolysis gas, and the combustion exhaust gas is introduced into the high temperature melting furnace 6. In the gas combustion furnace 5,
Heat exchange between flue gas and air takes place, and this air is
It is circulated between the cracking furnace 1 and the second cracking furnace 2 and the gas combustion furnace 5 and serves as a heat source for the first cracking furnace 1 and the second cracking furnace 2.

Into the high-temperature melting furnace 6, in addition to char separated from the pyrolysis residue and combustion exhaust gas cooled by heat exchange with air in the gas combustion furnace 5, normal temperature air is introduced under a predetermined excess oxygen condition. Burns at high temperature. Temperature is over 1200 ℃,
Preferably, it is set to about 1300 ° C., which is about 100 to 150 ° C. higher than the melting temperature of ash. The molten ash produced by this combustion is
For example, from the bottom of the furnace to a cooling water tank (not shown) for rapid cooling,
Collect as slag. In addition, 8 is the waste in the first decomposition furnace 1
9 to 13 are fans (or blowers) for introducing and circulating air or the like. If the exhaust gas discharged from the gas combustion furnace 5 has a sufficient amount of heat, a steam superheater 7 may be provided as a heat source for generating superheated steam from saturated steam.

The combustion exhaust gas generated by the combustion in the high temperature melting furnace 6 is introduced into a waste heat boiler (not shown), and this waste heat boiler generates superheated steam having a higher temperature than the high temperature combustion exhaust gas, and this superheated steam is, for example, illustrated. Not introduced to the turbine and used for power generation.

Next, the operation of this embodiment will be described. According to the present embodiment, the pyrolysis gas produced by pyrolyzing the municipal solid waste in the first cracking furnace 1 is heated in the second cracking furnace 2, so there is no problem even if it is heated at a temperature higher than the pyrolysis temperature. There is no.

By this heating, the tar generated by cooling the pyrolysis gas to room temperature is previously reduced in molecular weight and decomposed. Therefore, even if water or an alkaline aqueous solution such as an aqueous sodium hydroxide solution is sprayed on the pyrolysis gas in the wet cleaning tower 4 for desalting thereafter, there is no problem that tar is generated and wastewater treatment becomes difficult. It can be desalted and will not corrode a heat exchanger such as an exhaust heat boiler (not shown).

By raising the decomposition temperature of tar to about 750 ° C., the tar is decomposed and the pyrolysis gas can be almost completely gasified. Therefore, the decomposition temperature of tar is 650.
It is desirable to set the temperature to about 0 ° C. or higher, and particularly to set the temperature to 700 ° C. or higher and 800 ° C. or lower, because the tar can be decomposed almost completely and unnecessary heat energy is not required.

When the pyrolysis gas is desalted by spraying water or an aqueous alkali solution such as an aqueous solution of sodium hydroxide, the thermal energy is wastefully lost, and since the pyrolysis gas is at a high temperature, the required spray amount is also required. There will be many. However, in the present embodiment, the heat of the pyrolysis gas is recovered by the heat exchanger 3 before desalting, so that the gas combustion furnace 5 does not wastefully release the heat, for example, as in the configuration of the present embodiment. It can be used as a preheating heat source for combustion air.

In the present embodiment, the combustor according to the present invention is divided into a gas combustion furnace 5 and a high temperature melting furnace 6, and the pyrolysis gas is the former, and the char separated from the pyrolysis residue is the latter, respectively. It is configured to burn. In the high temperature melting furnace 6, there is no problem because the temperature can be raised to such an extent that ash and the like can be melted into slag by using only char.
As described above, the high temperature melting furnace 6 can be downsized by burning only the char separated from the pyrolysis residue in the high temperature melting furnace 6.

Although the pyrolysis gas containing chlorine flows through the second decomposition furnace 2 and the heat exchanger 3, the pyrolysis gas flow section of these devices is in a reducing atmosphere with a low oxygen content.
Also, since it does not contain ash since it is before combustion,
Corrosion of these devices progresses slowly and there is not much need to worry about corrosion.

Next, a second embodiment of the present invention will be described. FIG. 2 is a system diagram of a municipal solid waste treatment apparatus according to a second embodiment of the present invention. Members having the same reference numerals as those in FIG. 1 are the same members as those in the first embodiment, and detailed description thereof will be omitted. The difference between the second embodiment and the first embodiment is that the combustion exhaust gas discharged from the gas combustion furnace 5 is not introduced into the high temperature melting furnace 6 and the saturated steam is heated by the steam superheater 7 as it is. The point is to get superheated steam. According to the configuration of this embodiment, the same operation as that of the first embodiment can be achieved.

[0039]

According to the present invention described above, in recovering the thermal energy of the combustion exhaust gas generated by burning the thermal decomposition products of municipal waste by heat exchange, the corrosion of hydrogen chloride in a heat exchanger or the like is prevented. It is possible to provide a method and an apparatus for treating municipal solid waste, which can be performed by spraying water or an alkaline aqueous solution onto the pyrolysis gas.

Even if corrosion of hydrogen chloride in a heat exchanger or the like is prevented by spraying water or an aqueous alkaline solution onto the pyrolysis gas, the heat retained in the pyrolysis gas during the pyrolysis It is also possible to provide a method and apparatus for treating municipal solid waste that does not hinder effective use of energy.

[Brief description of drawings]

FIG. 1 is a system diagram of an apparatus for treating municipal solid waste according to a first embodiment of the present invention.

FIG. 2 is a system diagram of a municipal solid waste treatment device according to a second embodiment of the present invention.

[Explanation of symbols]

 1 First Decomposition Furnace 2 Second Decomposition Furnace 3 Heat Exchanger 4 Wet Washing Tower 5 Gas Combustion Furnace 6 High Temperature Melting Furnace 7 Steam Superheater 8 Feeder 9, 10, 11, 12, 13 Fan (or Blower)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B09B 3/00 ZAB B09B 3/00 302 C

Claims (10)

[Claims] 1. A process for heating and decomposing municipal solid waste,
In a method of treating municipal solid waste, which comprises a step of burning a thermal decomposition product generated in this thermal decomposition step, heating the thermal decomposition gas in the thermal decomposition product at a predetermined temperature higher than the thermal decomposition temperature, A step of previously decomposing the tar generated when the pyrolysis gas is cooled to room temperature, and a step of spraying water or an alkaline aqueous solution onto the pyrolysis gas after the decomposition to remove chlorine from the pyrolysis gas A method for treating municipal solid waste, comprising: before the combustion step. 2. The method for treating municipal solid waste according to claim 1, wherein the predetermined temperature is any temperature of 650 ° C. or higher. 3. The method for treating municipal solid waste according to claim 1, wherein the predetermined temperature is any temperature of 700 ° C. or higher and 800 ° C. or lower. 4. The method according to claim 1, further comprising a step of recovering the heat retained by the pyrolysis gas after the tar decomposition by heat exchange before the chlorine content removing step.
The method for treating municipal solid waste according to any one of the items. 5. The method for treating municipal solid waste according to claim 4, further comprising the step of heating the combustion air in the combustion step by using at least a part of the recovered heat as a heat source. 6. An apparatus for treating municipal solid waste, comprising: a pyrolyzer that heats and thermally decomposes municipal waste; and a combustor that combusts a thermal decomposition product produced by the pyrolyzer. A thermal decomposition gas in the decomposition product is heated at a predetermined temperature higher than the thermal decomposition temperature, and a tar decomposer for preliminarily decomposing tar generated when the thermal decomposition gas is cooled to room temperature, and the heat after the decomposition. An apparatus for treating municipal solid waste, comprising: a wet cleaning tower that sprays water or an alkaline aqueous solution onto a decomposition gas to remove chlorine from the thermal decomposition gas. 7. The tar decomposer operates at the predetermined temperature of 6
7. The municipal solid waste treatment device according to claim 6, wherein the temperature is any temperature of 50 [deg.] C. or higher. 8. The tar decomposer is operated at the predetermined temperature of 7
7. The municipal solid waste treatment device according to claim 6, wherein the temperature is set to any temperature of 00 ° C. or higher and 800 ° C. or lower. 9. A heat recovery device for recovering the heat retained by the pyrolysis gas after the tar is decomposed by heat exchange before the chlorine content is removed by the wet cleaning tower. 9. The municipal solid waste treatment device according to claim 6, wherein: 10. The apparatus for treating municipal solid waste according to claim 9, further comprising a heater for heating combustion air used for the combustor by using at least a part of the recovered heat as a heat source.