JP2001033013A - Method for heat treating material to be treated - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generating of dioxins by eliminating a low temperature area causing an incomplete combustion and to prevent the exhaustion of an unburned decomposed gas, by continuing the combustion of the gas in an exhaust gas burning furnace for a given time even after the exhaustion of a material to be treated in a heat treating furnace is completed. SOLUTION: A heat treating apparatus first starts heating of a second heating treating furnace (volume reducing furnace) 20 and a first heat treating furnace (dechlorinating furnace) 10 at a stage of charging no material to be treated. That is, a fuel such as an LNG or the like is burned in a gas burning furnace 35 and an exhaust gas burning furnace 41 to heat the respective furnaces. A hot gas generated in the furnace 35 is supplied to a heating cylinder 22 of the furnace 20 to heat a cylinder 21, and sent into a heating cylinder 12 of the furnace 10 from a communicating tube 37 to heat a cylinder 11. A heating temperature of the furnace 20 at this time is that for carbonizing a material to be treated, and a heating temperature of the furnace 10 is heated to a temperature for decomposing to precipitate harmful substance from the material. A heating temperature of the furnace 41 is heated to 800 deg.C or higher. Thus, exhausting of unburned decomposed gas is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat-treating an object to be treated such as waste, and more particularly, to the generation of dioxins generated at a low heat-treatment temperature when the operation of a heat treatment furnace is started and when it is stopped. Heat treatment method, and a harmful substance (hydrogen chloride, etc.) decomposed and precipitated from a treatment object by subjecting a treatment object containing an organic substance such as a halogen substance (chlorine, etc.) to a dry distillation treatment and a treatment agent. The present invention relates to a heat treatment method in which a harmless chloride is produced by an intimate reaction to obtain a harmless exhaust gas and a harmless residue.

[0002]

2. Description of the Related Art Various wastes such as industrial wastes and general wastes contain a large amount of organic substances (halogen substances).
It is widely known that when this is heated as an object to be treated, various harmful substances (for example, hydrogen chloride and dioxins) are precipitated and contained in exhaust gas. Therefore,
Since this exhaust gas cannot be directly discharged into the atmosphere, purification processing of the exhaust gas (suppression of discharge) is generally performed before the exhaust gas is discharged into the air.

As a general exhaust gas purifying device, there is a bag filter device disclosed in Japanese Patent Application Laid-Open No. 8-108026. This apparatus uses slaked lime as a purifying agent for exhaust gas to remove hydrogen chloride and dioxins in the exhaust gas.

[0004] Further, hydrogen chloride generated in large quantities by heat treatment is generally neutralized with caustic soda or the like and recovered with hydrochloric acid.

[0005] However, chlorine-based gas components also adhere to and are adsorbed to substances other than exhaust gas, such as slaked lime powder used in bag filters, fly ash in exhaust gas, and incineration residues (incinerated ash, etc.) for exhaust gas treatment. It is known that they produce highly toxic dioxins.

On the other hand, the applicant of the present application has proposed that an organic chlorine compound (hydrogen chloride), which is a halogen substance, performs "suppression of generation" instead of the conventional "suppression of emission", thereby producing harmful substances such as hydrogen chloride. It has been proposed to suppress the generation of waste gas, make the exhaust gas harmless, make the residue harmless, and reduce the damage of the treatment equipment due to chlorine.

That is, a treatment agent of an alkali substance is added to and mixed with the object to be treated and heated at a predetermined temperature to decompose and precipitate hydrogen chloride, and at the same time, contact and react with the added and mixed treatment agent to be harmless. Technology to displace and generate chloride
Already disclosed in JP-A-9-155326 and JP-A-10-437
13, JP-A-10-235186, JP-A-10-235
No. 35187, etc., and a treatment agent in which the treatment effect is increased by making the treatment agent porous and increasing the area of the contact reaction has been proposed (JP-A-10-193844).

[0008] Using these treatment agents, the material to be treated is heat-treated to obtain a carbide residue, and the carbide is used as a soil improving material, a water purification agent, a snow melting agent, and a heat insulator due to its porous nature. It can also be used as a recycled product in a wide range of fields, such as being used as fuel.

[0009]

When heat-treating an object to be treated, it is known that a large amount of dioxins is generated at the start and stop of the operation when the heat treatment temperature of the object passes through a low temperature range. I have. This is due to the presence of an incomplete combustion region. In order not to form this incomplete combustion region, processing must be performed under operating conditions (for example, 24-hour continuous operation) in which operation start and stop are minimized. Is recommended.

However, in actuality, in order to operate continuously for 24 hours, it is necessary to accumulate a large amount of objects to be processed, and if the predetermined amount of objects to be processed cannot be secured continuously or intermittently occurs. Cannot be realized.

Moreover, even after the heat treatment furnace is stopped,
Decomposed gas remains in the furnace, and when the decomposed gas combustion furnace is shut down at the same time as the heat treatment furnace, unburned decomposed gas is discharged, causing an odor outside the facility.
There is also a danger of emitting harmful substances.

The present invention has been made in view of such problems, and an object of the present invention is to eliminate dioxins by eliminating a low temperature range where incomplete combustion occurs when a heat treatment furnace is started and stopped. An object of the present invention is to provide a heat treatment method which prevents generation of unburned cracked gas while preventing generation and operation of the heat treatment furnace at predetermined time intervals.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made it possible to operate a heat treatment furnace continuously for 24 hours, to ensure that even a small amount of an object to be treated, and to generate dioxins. As a method of safely treating, it is found that the material to be treated is carbonized, and for a certain time after the heat treatment furnace is stopped, the burning of the generated decomposition gas is continued to remove the bad smell and other adverse factors, and Has found that an object to be treated is rendered harmless by adding and mixing a treating agent of an alkaline substance that generates a harmless chloride by contacting with generated hydrogen chloride. The concrete means is to put the object to be treated into a heat treatment furnace and perform thermal decomposition treatment,
A method for heating an object to be processed in which generated decomposition gas is burned in an exhaust gas combustion furnace, wherein the combustion of the decomposition gas in the exhaust gas combustion furnace completes discharge of the object to be processed in the heat treatment furnace. It is characterized in that it is continued for a predetermined time thereafter.

In the heat treatment in the heat treatment furnace, it is desirable that the dechlorination treatment and the volume reduction treatment are performed in at least two different heat treatment furnaces.

The temperature inside the heat treatment furnace for dechlorination and volume reduction is 200 ° C. or more and 300 ° C., respectively.
C. or higher, and the furnace temperature of the exhaust gas combustion furnace is preferably 750 C. or higher.

[0016] In the dechlorination treatment in the heat treatment furnace, a treatment agent of an alkali substance is added to an object to be treated, mixed and heated, and a harmful substance of the generated decomposition gas is brought into contact with the treatment agent to cause a harmful reaction. By replacing substances with harmless reactants, harmless exhaust gas and residues can be achieved.

The treating agent used in the dechlorination treatment is a powder of an alkaline substance, and is desirably added in an amount of 5 to 30% by weight based on the treated material.

The treating agent for an alkaline substance is an alkali metal or an alkali metal compound which reacts with a harmful component decomposed and precipitated from an object to be treated by heating to form a harmless chloride;
At least one selected from alkaline earth metals and substances contained in alkaline earth metal compounds, or a mixture of two or more of them, including alkali metals such as Na and K, alkaline earth metals such as Ca, Alkaline earth metal compounds such as Sr, Ba and Ra are lime, slaked lime, calcium carbonate, dolomite and the like.

The alkali metal compound may be a hydroxide,
Sodium and potassium-based substances of carbonate, (a) sodium bicarbonate, another name, acidic sodium carbonate, sodium bicarbonate, sodium bicarbonate (common name, baking soda) (b) Sodium carbonate, another name, sodium carbonate, soda, soda ash , Washing soda, crystalline soda (c) sodium sesquicarbonate, also known as sodium monohydrogen dicarbonate, sodium tricarbonate, sodium sesquicarbonate (d) natural soda, also known as trona (e) potassium carbonate (f) potassium hydrogen carbonate (G) Sodium potassium carbonate (h) Sodium hydroxide (i) Potassium hydroxide A simple substance or a mixture of two or more kinds selected from potassium hydroxide is included.

Although caustic soda is effective for the detoxification effect of hydrogen chloride, it requires special handling.
It is preferable to select a substance that is easy to handle and harmless per se.

It is desirable to use LNG or LPG as fuel for the gas combustion furnace and the exhaust gas combustion furnace for heating the heat treatment furnace.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a conceptual view of a heat treatment apparatus for an object to which a heat treatment method according to the present invention is applied. The heat treatment apparatus uses two heat treatment furnaces having the same configuration and performs a first heat treatment. This is a case where the furnace 10 is provided with a function of dechlorination by subjecting the material to be treated to dry distillation, and the second heat treatment furnace 20 is provided with a function of volume reduction by carbonization or incineration.

The first heat treatment furnace 10 has a rotatable cylindrical body 11 having a blade 11a (see FIG. 2) for moving an object to be processed while being stirred, and a gas duct on the outer periphery of the cylindrical body 11. A heating cylinder 12 that is formed and heats the cylindrical body 11 by introducing a hot gas; a supply port 13 provided at one end of the cylindrical body 11 to supply an object to be processed into the cylindrical body 11;
A discharge port 14 is provided at the other end of the cylindrical body 11, and the cylindrical body 11 is rotationally driven by a rotation driving unit 15. The rotation driving means 15 is a driving motor 15
a, a driving gear 15b, and a driven gear 15c provided on the cylindrical body 11.

16 is a supply duct surrounding the supply port 13 side, 17 is a discharge duct surrounding the discharge port 14 side, 18
Is a dynamic seal (mechanical seal) for sealing ducts 16 and 17 (not shown) in contact with the outer periphery of the cylindrical body 10 and a contact portion with the heating cylinder 12.

Reference numeral 19 denotes a support roller for rotatably supporting the cylindrical body 11 at both ends.

The basic structure of the second heat treatment furnace 20 is the same as that of the first heat treatment furnace 10 described above. Therefore, in the same or equivalent part, one digit of 20 is set to the same number (for example, 21 is a cylindrical body, 22 is a heating cylinder, and 29 is a supporting roller).
Description is omitted.

Numeral 30 denotes a hopper, which adds and mixes an object to be treated and a desalting material (hereinafter, referred to as a treating agent) composed of an alkali substance, and supplies the mixture through the supply port 13 of the cylinder 11 into the cylinder 11. I do. The material to be treated may be any of solid matter such as general waste and industrial waste, ash, and sludge.

The hopper 30 has a crushing function and a function of mixing the processing agent, and may mix the processing agent while crushing the solid material. May be mixed and charged.

The cylindrical body 11 of the first heat treatment furnace 10 and the cylindrical body 21 of the second heat treatment furnace 20 are disposed vertically, and the discharge duct 17 and the supply duct 26 of the cylinder 11 are arranged vertically.
Is communicated via a rotary valve 32, and
Discharge side duct 27 of cylindrical body 21 of second heat treatment furnace 20
Discharges the carbide or treated ash after the heat treatment to the melting tank via the rotary valve 33.

Reference numeral 35 denotes a gas combustion furnace, which burns LNG or LPG fuel to generate hot gas. This hot gas is supplied into a heating cylinder 22 provided on the outer periphery of the cylindrical body 21 and is supplied to the cylindrical body 2.
1 is heated and then sent into the heating cylinder 12 of the cylindrical body 11 through the connecting pipe 37. After the cylindrical body 11 is heated, it is used for heating the drying means 39 from the discharge pipe 38. It is sent to the unit 40.

Reference numeral 41 denotes an exhaust gas combustion furnace, which introduces exhaust gas generated during heat treatment in the first heat treatment furnace 10 and the second heat treatment furnace 20 through exhaust gas pipes e ₁ and e ₂ , and performs combustion treatment. I do.

After the gas is burned in the flue gas combustion furnace 41 to remove combustible components such as tar components, the flue gas cooling unit 40 cools the bag filter 42 to a suitable temperature for use and sends the bag filter 42 to the bag filter 42 where it is purified. And discharged from the chimney 43. It is preferable to use a heat exchanger for cooling while utilizing waste heat.

Reference numeral 44 denotes a dehydrating means, which is obtained by dissolving a treating agent or the like after reacting with the object to be treated reduced in the dissolving tank 34 in water, and separating the solid substance and the liquid by the dehydrating means 44. And
After the solid matter is dried by the drying means 39, a carbide or the like is taken out. On the other hand, the liquid is treated by a wastewater treatment means 45, which collects the treated treatment agent, injects a neutralizing agent or the like, processes the liquid, and then drains the liquid.

Next, a series of heat treatment methods for the object to be treated are as follows.
A description will be given with reference to a relationship diagram between the heating time and the temperature in FIG.

First, the time t in the stage where the object is not charged
_{In 1} , the second heat treatment furnace 20 (hereinafter, referred to as volume reduction furnace),
The heating operation of the first heat treatment furnace 10 (hereinafter, referred to as a dechlorination furnace) is started. That is, fuel such as LNG is burned in the gas combustion furnace 35 and the exhaust gas combustion furnace 41, and each furnace is heated.

The hot gas generated in the gas combustion furnace 35 is supplied to the heating cylinder 22 of the volume reduction furnace 20, and after heating the cylindrical body 21, is sent from the communication pipe 37 into the heating cylinder 12 of the dechlorination furnace 10. Then, the cylindrical body 11 is heated.

The heating temperature of the volume reduction furnace 20 at this time is set to a temperature (300 ° C. to 600 ° C.) at which the material to be treated is carbonized.
The heating temperature of the dechlorination furnace 10 is set to a temperature (200 ° C. to 400 ° C.) at which the harmful substance is decomposed and precipitated from the object. The heating temperature of the exhaust gas combustion furnace 41 is set to 800 ° C. or higher.

Then, as shown in FIG. 3, at time t ₂ when the temperature of the exhaust gas combustion furnace 41 has reached about 750 ° C., the material to be treated and the treatment agent are mixed from the popper 30 or while being mixed. It is supplied into the dechlorination furnace 10.

In the heat treatment in the dechlorination furnace 10, in this example, drying and dechlorination are performed. The temperature and time at which harmful components are precipitated from the object to be treated are investigated in advance, and the heat treatment is performed. Understand the nature of the object and process at a temperature and time that can adequately cover the findings.

The time and temperature are related to the state of the heat treatment furnace (conditions depending on the furnace such as the size and heating means), the amount of treatment, the treatment time, the treatment temperature, and the like. Must be performed sufficiently, and data must be collected and stored.

The heat treatment in the dechlorination furnace 10 is as follows.
Instead of "combustion and incineration", it is a process of dry distillation and "steaming and pyrolysis", in which chlorine-based gas and the like are decomposed and precipitated from the object to be treated and reacted with the treating agent to produce harmless salts.

As the treating agent to be mixed or added with the article to be treated, use is made of an alkali substance which forms a harmless chloride by reacting at least with HCl (hydrogen chloride). For example, JP-A-9-155326, JP-A-10-43731, and JP-A-10-235186, which the applicant of the present application previously filed,
As shown in JP-A-10-235187, alkaline earth metals, alkaline earth metal compounds, alkali metals, and alkali metal compounds, specifically, calcium, lime, slaked lime, calcium carbonate, dolomite, silicate (calcium silicate) Sodium bicarbonate, sodium carbonate, sodium sesquicarbonate, natural soda, sodium hydroxide,
One kind is selected from potassium hydroxide, potassium hydrogen carbonate, and potassium carbonate, or several kinds are mixed and used. As an amount to be used, 5 to 30% by weight of the material to be treated is mixed or added.

For example, sodium bicarbonate (Na
When HCO ₃ ) is used, a decomposition gas of the HCl component is generated in the dechlorination furnace which is the first heat treatment furnace.
Reacts immediately with sodium bicarbonate (NaHCO ₃ )
+ (HCl) → (NaCl) + (H ₂ O) + (CO ₂ ), producing harmless sodium chloride (NaCl) and eliminating harmful HCl from the decomposition gas. Thereby, the detoxification of the HCl component in the decomposition gas and the detoxification of the residue are simultaneously performed.

The object after the harmful components are precipitated is sent to the supply port 23 of the cylindrical body 21 of the volume reduction furnace 20 through the duct 17, the rotary valve 32, and the duct 26, where the object is carbonized. At a temperature (300 ° C. to 600 ° C.) for carbonization, or at 800 ° C. or more for incineration to reduce the volume.

In the volume reducing furnace 20 for performing the volume reducing process, H
Since there is no decomposition gas containing harmful components such as Cl and dioxins, the carbonized or incinerated object does not absorb it.

The reduced volume of the object to be treated and the treatment agent after the reaction are discharged into the dissolution tank 34 via the duct 27 and the rotary valve 33. In the dissolving tank 34, the reduced volume of the object to be treated, the treated agent after the reaction, and the like are dissolved in water, which is separated into a solid and a liquid by a dehydrating means 44, and the solid is dried by a drying means. After being dried at 39, the liquid is taken out. On the other hand, the liquid is treated by injecting a neutralizing agent or the like by a water treatment means 45 and then drained.

The temperature of the volume reduction furnace 20 is controlled by the gas combustion furnace 35.
And the temperature of the dechlorination furnace 10 can be controlled by adjusting the amount of temperature-adjusted air 36 supplied to the connecting pipe 37.

On the other hand, the exhaust gas generated in the dechlorination furnace 10 and the volume reduction furnace 20 is introduced into the exhaust gas combustion furnace 41 from the gas discharge pipes e ₁ and e ₂ and burned. This exhaust gas combustion furnace 41
Combustion at 85% to prevent the production of dioxins
0 ° C., 800 ° C. to 90 °
0 ° C. is desirable. In FIG. 3, even when heated at 750 ° C., the temperature is raised to 800 ° C. or more by the combustion of the generated exhaust gas.

After combustible components such as tar components and remaining harmful substances are removed by burning in the exhaust gas combustion furnace 41,
The exhaust gas is cooled by the exhaust gas cooling unit 40 to a temperature suitable for use of the bag filter 42, and is discharged from the chimney 43 via the bag filter 42.

Although the harmful chlorine-based gas is not basically contained in the exhaust gas generated by the heat treatment in the heat treatment furnace as described above, the properties of the object to be treated vary widely. Yes,
In addition, the chlorine component may not be completely removed due to incomplete reaction or the like due to processing conditions or the like. However, the chlorine component is decomposed by burning and completely removed.

When the heating of the heat treatment furnace is stopped, as shown in FIG.
As shown in the figure, first, the charging of the object to be processed is stopped at a time t ₃ , and after the time is stopped, the volume reducing furnace 20 and the dechlorination furnace are set at a time t _{4 when the} time for discharging all the heat-processed objects is measured. The heating of 10 is stopped. And the exhaust gas combustion furnace 41 is
After heating stop volume reduction furnace 20 and dechlorination reactor 10 also continues to burn, at time t ₅ after a predetermined time (30-60 minutes), and stops the operation of the gas combustion furnace 41 (combustion).

It is preferable that the rotation of the dechlorination furnace 10 and the volume reduction furnace 20 be stopped when the temperature in the furnace becomes 200 ° C. or less.

When the operation of the exhaust gas combustion furnace 41 is finally stopped as described above, the following effects are obtained.

That is, in the dechlorination furnace 10 and the volume reduction furnace 20,
Decomposed gas remains and is discharged by induction with a blower.If this gas is discharged without burning, it will emit exhaust gas with a bad smell, and furthermore, exhaust gas containing harmful substances will be emitted. There is a risk of emission. Therefore, the fear is eliminated by continuing the combustion even after the dechlorination furnace and the volume reduction furnace are stopped.

As described above, since incomplete combustion in a low-temperature region, which is a cause of generation of dioxin in the heating treatment of the object to be treated and the combustion treatment of exhaust gas, is eliminated, the generation of dioxins can be prevented even if the operation is repeated every day. There is no fear.

Therefore, the daily waste disposal operation is started, for example, at 8:00 am,
After 60 minutes, an operation cycle in which the operation is stopped at 3:00 pm and the operation is ended at 5:00 pm is set, and various equipments of the heat treatment facility are configured to meet this cycle. Processing facility can be realized.

[0058]

As described above, the present invention operates the cracked gas combustion furnace even after the heating of the heat treatment furnace is stopped and continues burning the generated cracked gas, so that unburned cracked gas is discharged. No odor and other adverse factors can be removed.

When the heating of the heat treatment furnace is stopped, the charging of the object to be treated is stopped, and after the discharge of the object to be heated is completed, the operation of the exhaust gas combustion furnace is stopped after a predetermined time. Therefore, there is no generation of dioxins due to incomplete combustion at the start and stop of operation, and it is harmless by adding and mixing an alkaline substance treating agent and reacting it with hydrogen chloride. Since it is replaced with chloride, harmless exhaust gas and residue can be obtained, and safe and stable heat treatment can be performed not only at the start and stop of the operation, but also in all treatment steps, which is an extremely environmentally favorable treatment effect. Demonstrate.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a heat treatment apparatus for an object to be treated for explaining a heat treatment method of the present invention.

FIG. 2 is a sectional view of a rotating cylinder.

FIG. 3 is a relationship diagram of heating time and heating temperature for explaining the heat treatment method of the present invention.

[Explanation of symbols]

 10, 20 ... heat treatment furnace 11, 21 ... cylindrical body 12, 22 ... heating cylinder 13, 23 ... supply port 14, 24 ... discharge port 15, 25 ... rotation drive means 16, 26 ... supply side duct 17, 27 ... discharge Side duct 18 ... Dynamic seal 19, 29 ... Support roller 30 ... Hopper 31, 32, 33 ... Rotary valve 34 ... Melting tank 35 ... Gas combustion furnace 36 ... Temperature adjusted air 37 ... Connecting pipe 38 ... Discharge pipe 39 ... Drying Means 40: Exhaust gas cooling unit 41: Exhaust gas combustion furnace 42: Bag filter 43: Chimney 44: Dewatering means 45: Wastewater treatment means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B09B 3/00 304H F-term (Reference) 3K061 AA07 AA24 AB02 AC01 BA05 BA08 BA10 CA01 CA07 FA10 FA21 3K065 AA07 AA23 AB02 AC01 BA05 BA08 BA10 CA16 3K078 AA05 AA08 AA10 BA06 BA08 BA26 CA02 CA21 4D004 AA46 AB07 BA03 CA24 CA41 CA42 CB09 CB34 CC12 DA03 DA06

Claims (8)

[Claims] 1. A method for heating an object to be treated, wherein the object to be treated is charged into a heat treatment furnace for thermal decomposition treatment, and the generated decomposition gas is burned in an exhaust gas combustion furnace. Combustion of the decomposition gas is continued for a predetermined time even after the discharge of the object in the heat treatment furnace is completed. 2. The heat treatment method for an object to be processed according to claim 1, wherein the heat treatment in the heat treatment furnace is such that the dechlorination treatment and the volume reduction treatment are performed in at least two different heat treatment furnaces. . 3. The furnace temperature of the heat treatment furnace for dechlorination treatment and volume reduction treatment is 200 ° C. or more and 300 ° C. or more, respectively, and the furnace temperature of the exhaust gas combustion furnace is 750 ° C. or more. The method for heat-treating an object to be processed according to claim 1 or 2. 4. The dechlorination treatment comprises adding a treatment agent for an alkaline substance to an object to be treated, heating the mixture, contacting the harmful substance of the generated decomposition gas with the treatment agent, and reacting the harmful substance harmlessly. 4. The heat treatment method for an object to be treated according to claim 2, wherein the exhaust gas / residue is rendered harmless by substituting the substance. 5. The processing object according to claim 2, wherein the processing agent is a powder of an alkaline substance and is added in an amount of 5 to 30% by weight based on the processing object. Heat treatment method. 6. A treatment agent for an alkaline substance, which reacts with a harmful component decomposed and precipitated from an object to be treated by heating to form a harmless chloride, an alkali metal compound, an alkaline earth metal, and an alkaline earth. The method for heat treating an object to be treated according to claim 4 or 5, wherein at least one kind is selected from substances contained in the metal compound, or a mixture of two or more kinds. 7. The alkali metal compound is selected from the group consisting of sodium hydrogencarbonate, sodium carbonate, sodium sesquicarbonate, natural soda, potassium carbonate, potassium hydrogencarbonate, sodium potassium carbonate, sodium hydroxide, and potassium hydroxide, or a plurality thereof. 7. The method for heat treating an object to be treated according to claim 6, wherein 8. An object to be treated according to claim 1, wherein LNG or LPG is used as a fuel for a gas combustion furnace and an exhaust gas combustion furnace for heating the heat treatment furnace. Heat treatment method.