JP2002273459A - Hydrothermal oxidation reaction method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrothermal oxidation reaction method and apparatus capable of efficiently performing a hydrothermal oxidation reaction by minimizing corrosion of a hydrothermal oxidation reactor system including a preheater and a reactor. Get. SOLUTION: A liquid to be treated is supplied from a liquid to be treated tank 3 and is preheated by a preheater 4, and is supplied together with air, a combustion aid and water.
When the hydrothermal reaction is carried out by supplying the solution to the reactor 1, the neutralizing agent supplied from the neutralizing agent tank 8 is mixed with the liquid to be treated after preheating, and the mixed solution is supplied to the reactor 1, and the acid generated in the reactor is mixed. Or neutralize alkaline components to prevent corrosion.

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 supplying a preheated object to a reactor and performing a hydrothermal oxidation reaction in a supercritical or subcritical state of water, and in particular, to reduce corrosion of the apparatus. The present invention relates to a method and an apparatus for a hydrothermal oxidation reaction that can perform the reaction.

[0002]

2. Description of the Related Art Hydrothermal oxidation, represented by supercritical or subcritical hydrothermal oxidation, has attracted attention as a technique capable of completely decomposing waste liquid in a short time. Applications include treatment of harmful organic chlorine compounds such as dioxin and PCB,
Application to various factory wastewater, sewage sludge treatment, etc. is being actively studied. When performing these treatments, it is important to optimize the reaction temperature in order to obtain the desired decomposition performance. Therefore, in order to maintain the reaction temperature of the reactor,
A method of supplying a high-temperature and high-pressure fluid (supercritical water or the like) together with the liquid to be treated into the reactor, a method of externally heating the reactor, a method of preheating the liquid to be treated and then supplying the liquid to the reactor are performed. . Of these methods, the method of preheating is economical because there is no need to supply a liquid other than the liquid to be treated and the oxidizing agent, and the thermal energy of the processing fluid can be recovered through a heat exchanger or the like. It is advantageous.

On the other hand, in the hydrothermal oxidation reaction, halogen, phosphorus, sulfur components and the like in the liquid to be treated are converted into the corresponding acids, and the alkali metal salts of organic substances and the like become the corresponding alkali metal carbonates. The environment inside the reactor becomes acidic or alkaline. It is known that such a deviation in pH under high temperature and high pressure causes severe corrosion in the hydrothermal oxidation reactor, which is a serious problem in practical use.
Conventionally, in order to reduce this corrosion, a method of adding a neutralizing agent in an amount required to neutralize the acid or alkali generated in the liquid to be treated to the liquid to be treated and performing a hydrothermal oxidation reaction has been adopted. I have been. By this method, acid and alkali are neutralized in the reactor to the corresponding salt, so that the corrosion of the reactor can be considerably reduced.

However, conventionally, since the liquid to be treated is mixed with the neutralizing agent and supplied so that the pH at the time when the hydrothermal oxidation reaction is completed in the reactor is near neutral, the neutralizing agent is mixed. In some cases, the liquid to be treated may become acidic or alkaline. When such a liquid to be treated is preheated through a preheater, corrosion may occur in the preheater. Further, when the liquid to be treated is preheated in an acidic or alkaline state, the concentration of salts increases due to hydrolysis, and the corrosion of the preheater is further accelerated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydrothermal oxidation reaction system including a preheater and a reactor, which is capable of efficiently performing a hydrothermal oxidation reaction while minimizing corrosion. It is to obtain a thermal oxidation reaction method and apparatus.

[0006]

The present invention is the following hydrothermal oxidation reaction method and apparatus. (1) a preheating step of preheating the article to be treated, a supply step of mixing the article to be treated after preheating with a neutralizing agent and supplying the mixture to the reactor;
Performing a hydrothermal oxidation reaction in a supercritical or subcritical state of water in the presence of an oxidizing agent, in the presence of an oxidizing agent. (2) The method according to the above (1), further comprising a pH adjusting step of adjusting the object to be treated to a pH suitable for preheating. (3) A reactor for performing a hydrothermal oxidation reaction in a supercritical or subcritical state of water, a preheater for preheating an object to be processed, and a preheated object mixed with a neutralizing agent and supplied to the reactor And a hydrothermal reactor. (4) The apparatus according to the above (3), further including a pH adjusting device that adjusts the object to be treated to a pH suitable for preheating.

The object to be treated in the present invention is not limited as long as it is capable of performing a hydrothermal oxidation reaction in a supercritical or subcritical state of water, and a waste liquid containing harmful organic substances such as dioxin and PCB. And organic waste liquids such as various factory waste liquids, night soil, sewage treatment sludge, etc., but may contain inorganic substances. Such objects to be treated are often near neutral, but may be acidic or alkaline. The liquid to be treated is suitable for the treatment, but may contain a solid as long as it can be supplied to the reactor.

The organic matter contained in the object to be treated is decomposed into carbon dioxide and water by a hydrothermal oxidation reaction. However, halogen, phosphorus, sulfur and the like become acidic components such as chloride, phosphoric acid and sulfuric acid, and alkali metals and alkaline earth metals become alkaline components such as hydroxides. Some of these react in the course of the hydrothermal oxidation reaction to form salts, but excess components remain as they are, and the environment in the reactor becomes acidic or alkaline. Severe corrosion occurs when hot or high pressure acidic or alkaline substances come into contact with the vessel wall. Further, when the temperature falls below the critical temperature, water is generated, so that the acidic or alkaline substance dissolves therein and dissociates, causing severe corrosion in the reactor and a system downstream of the reactor.

In the present invention, in order to prevent this, the reactant is mixed with a neutralizing agent in a reactor so that the reactant becomes neutral and the corrosion is reduced when the hydrothermal oxidation reaction is completed. The hydrothermal oxidation reaction is carried out to supply the neutralizing agent, and the neutralizing agent is mixed with the preheated object and supplied to the reactor. Even when acidic or alkaline components become excessive when the hydrothermal oxidation reaction is completed, these components may not exhibit acidity or alkalinity by binding to organic substances in the material to be treated before the hydrothermal oxidation reaction. Many. When a neutralizing agent is mixed with such a material to be treated, the material becomes acidic or alkaline. Therefore, if the mixture is preheated, corrosion occurs in the preheater. Heating in an acidic or alkaline state increases the ion concentration due to hydrolysis and promotes corrosion. However, by mixing a neutralizing agent after preheating, such corrosion is prevented.

In the present invention, when the object to be treated has a pH suitable for preheating, for example, when the pH is 3 to 10, the preheating is performed by directly supplying the preheater to the preheater without mixing the neutralizing agent. Corrosion of the vessel can be reduced. When the pH of the object to be treated is out of the pH range suitable for the preheating, the preheating can be performed by mixing with a neutralizing agent to adjust the pH to the above range. This prevents corrosion of the preheater in the preheating step. The object to be treated is decomposed by
If H fluctuates, at the end of preheating the appropriate pH
The neutralizing agent can be mixed so that

The object to be treated after preheating in this way is:
At the time of completion of the hydrothermal oxidation reaction, the neutralizing agent is mixed so as to have a pH range where corrosion is low, for example, pH 3 to 10, and the mixture is supplied from the supply device to the reactor, and the hydrothermal oxidation is performed in the presence of the oxidizing agent. Perform the reaction. This eliminates excess or deficiency of acidic or alkaline components in the resulting reactants, and reduces corrosion in the reactor and subsequent lines.

In the present invention, as the neutralizing agent to be used by mixing with the preheated material to be treated, a neutralizing agent which reacts with an acid or an alkali generated in a reactor to form a nearly neutral salt can be used. .
Acids include inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; and alkalis include inorganic acids such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and calcium oxide. Alkali, and organic acid salts such as sodium salt, potassium salt, calcium salt, and magnesium salt of an organic acid are included. Neutralizing agent to be used by mixing with the object to be treated before preheating neutralizes the acid or alkali contained in the object to be treated, or reacts with the acid or alkali generated by preheating to produce a salt close to neutral Neutralizing agents can be used.
As such a neutralizing agent, an organic acid can be used in addition to the neutralizing agent exemplified above.

When the neutralizing agent is mixed into the preheated object to be treated, the neutralizing agent is combined before the preheated object is supplied to the reactor, and supplied into the reactor together with the object to be treated. can do. The oxidizing agent used for the hydrothermal oxidation reaction may be added to the object before or after preheating.
In order to reduce the corrosion of the preheater, it is desirable to mix the preheated material into the object to be treated or to mix it in the reactor. As the oxidizing agent, air, oxygen, liquid oxygen, hydrogen peroxide, nitric acid, nitrous acid, nitrate, nitrite and the like can be used.

In order to add a neutralizing agent to a high-temperature and high-pressure treatment object, the neutralizing agent also needs to be sent through a high-pressure pump. At this time, a high-pressure pump dedicated to the neutralizing agent may be prepared, but it will increase the cost, so that the neutralizing agent is mixed with the low-pressure part of the water supply line used for diluting the treatment object and cleaning the inside of the system. It is preferable to provide a means and feed the solution together with water. The amount of the neutralizing agent to be added may be controlled by adding a neutralizing agent amount calculated in advance from the analysis value and the flow rate of the object to be treated. It is preferable to control the means for adding the neutralizing agent so as to keep the value at the optimum value. As the neutralizing agent supply means, a liquid supply pump can be used if it is liquid, and a powder supply means can be used if it is solid. When the material to be treated mixed with the neutralizing agent is supplied to the reactor, the oxidizing agent, the material to be treated and the neutralizing agent are thoroughly mixed in the reactor by using a nozzle or sprayer in the supply device into the reactor. It is desirable to use what is done. If the mixing is not sufficiently performed when the mixture is supplied to the reactor, not only the oxidation reaction does not sufficiently proceed, but also pH unevenness occurs in the reactor, which may cause corrosion.

In the reactor, the material to be treated is oxidatively decomposed by a hydrothermal oxidation reaction. As the oxidizing agent, air, oxygen, liquid oxygen, hydrogen peroxide, nitric acid, nitrous acid, nitrate, nitrite and the like can be used. Due to the decomposition of organic substances by the hydrothermal oxidation reaction, halogens, phosphorus, sulfur, etc. in the object to be treated become the corresponding acidic components, and the alkali metal or alkaline earth metal becomes the alkaline component and reacts with the neutralizing agent at the same time. To form a salt. If the reaction conditions are above the critical temperature, the generated salt precipitates in the reactor,
May accumulate in the reactor. Therefore, it is desirable to provide a means for moving the precipitated salts out of the reactor. For example, as disclosed in JP-A-11-156186, a method of scraping salt with a scraper and adding cooling water to discharge the scraped salt can be applied. Other methods for discharging the deposited salt in the reactor include Japanese Patent No. 2726293 and Japanese Patent Application Laid-Open No. 9-299966.
And the method described in JP-A-10-15566.

After the reaction, the fluid undergoes cooling, decompression, gas-liquid separation, etc., and is separated into treated water and treated gas before being discharged. In this process, if the pH is acidic or alkaline, the system after the reactor may corrode. Therefore, a means for adding a neutralizing agent to the fluid after the reaction may be provided. Also in this case, the amount of the neutralizing agent to be added may be adjusted so that the pH value of the processing solution becomes appropriate.

[0017]

According to the present invention, a hydrothermal oxidation reactor system including a preheater and a reactor can be corroded by mixing a neutralizing agent into a preheated object and supplying the neutralizer to the reactor. The hydrothermal oxidation reaction can be performed efficiently with as little as possible. Further, by preheating the work to be adjusted to a pH suitable for preheating, corrosion in the preheater can be further reduced.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 5 are flow charts showing a hydrothermal oxidation reaction method and apparatus of another embodiment.

In FIG. 1, reference numeral 1 denotes a reactor which is configured to perform a hydrothermal oxidation reaction in a supercritical or subcritical state of water. A supply device 2 is provided at an upper portion of the reactor 1, a line L 1 having a high-pressure pump P 1 and a preheater 4 is connected from the liquid tank 3 to be treated, a line L 2 is connected from an air compressor 5, and a fuel tank 6 is provided. A line L3 having the high-pressure pump P2 is connected, and a line L4 having the high-pressure pump P3 is connected from the water tank 7. A line L5 having a pump P4 is connected from the neutralizing agent tank 8 to the suction side of the high-pressure pump P3 of the line L4. Line L from the bottom of reactor 1
6 communicates with a shell 4a of the preheater 4, and a line L7 having a cooler 9 from the shell 4a of the preheater 4 is connected to a gas-liquid separator 10a.
Contact A pressure reducing valve V1 is provided above the gas-liquid separator 10.
And a line L9 having a pressure reducing valve V2 and a pH meter pHa is connected to a lower portion.

The hydrothermal oxidation reaction by the above apparatus is performed as follows. First, the liquid to be treated is pressurized by the high-pressure pump P1 from the liquid tank 3 to be treated through the line L1, preheated by the preheater 4 and sent to the supply device 2, and the air as the oxidant is compressed by the air compressor 5 and supplied from the line L2. When the water is sent to the apparatus 2 and the fuel is pressurized by the high pressure pump P2 from the fuel tank 6 through the line L3 by the high pressure pump P2 and sent to the supply device 2, and the water is pressurized and sent by the high pressure pump P3 through the line L4 from the water tank 7, the neutralizing agent is used. Pump P from tank 8 through line L5
Then, the neutralizer is injected into the supply device 2 through the supply device 4. In the supply device 2, the liquid to be treated, air, an auxiliary agent, water, a neutralizing agent, and the like are mixed and supplied to the reactor 1. In the reactor 1, in a supercritical or subcritical state, the oxidizable substance in the liquid to be treated is oxidatively decomposed by air as an oxidizing agent.

At the start of the operation of the apparatus, combustion is carried out by supplying only air and an auxiliary agent, and when the reactor 1 is in a supercritical or subcritical state, the liquid to be treated and water are supplied to produce hydrothermal energy. Perform an oxidation reaction. When the calorific value of the liquid to be treated is high, the reaction can be carried out by reducing the amount of the auxiliary agent or by adding water for dilution. The reaction fluid generated in the reactor 1 is a line L
6, the liquid to be treated is preheated by entering the preheater 4 and then cooled by entering the cooler 9 from the line L7 and entering the gas-liquid separator 10 for gas-liquid separation. The separated gas is reduced in pressure from the line L8 by the pressure reducing valve V1, and is discharged as a processing gas. The separated liquid is reduced in pressure by a pressure reducing valve V2 from a line L9, and is discharged as a processing liquid through a pH meter pHa. The pH meter pHa measures the pH of the processing solution, and adjusts the supply amount of the neutralizing agent by the pump P4 so that the detected value becomes neutral (pH 3 to 10).

The embodiment of FIG. 1 is applied when the liquid to be treated is neutral and non-corrosive, or becomes neutral when pre-heated and loses corrosiveness. It is preheated in the vessel 4, but at the preheating stage it is neutral and no corrosion occurs. Then, a neutralizing agent is mixed with the liquid to be treated after the preheating in the supply device 2 and supplied to the reactor 1 to neutralize the acidic or alkaline substance generated by the hydrothermal oxidation reaction, and the reactor 1 or the following is neutralized. Can prevent corrosion in the system. The injection amount of the neutralizing agent can be maintained at a low corrosion value by controlling the pump P4 so as to maintain the pH of the processing solution within a predetermined range by using a pH meter pHa.

The apparatus shown in FIG. 2 is substantially the same as that shown in FIG. 1, except that an external heater 11 is provided in the preheater 4 and a line L6 from the lower part of the reactor 1 has a line L7 having a cooler 9. Is connected to the gas-liquid separator 10. Other configurations are the same as those in FIG.

The method of hydrothermal oxidation reaction by the above apparatus is performed in substantially the same manner as in FIG. 1, but the liquid to be treated supplied from the liquid to be treated tank 3 through the line L1 by the high pressure pump P1 is supplied to the preheater 4 by an external heater. Heated by 11, mixed with air, a combustion aid, water, a neutralizing agent and the like in the supply device 2 and supplied to the reactor 1 to perform a hydrothermal oxidation reaction. The hydrothermal oxidation reaction fluid generated in the reactor 1 is taken out from the line L6, cooled by the cooler 9, and separated by the gas-liquid separator 10 into gas and liquid. The point of corrosion prevention by the supply of the neutralizing agent is the same as in the case of FIG.

The apparatus shown in FIG. 3 differs from the apparatus shown in FIG. 1 in that a line L6 having a heat exchanger 12 for heat recovery is connected to a gas-liquid separator 10 via a line L7 having a cooler 9.
Lines L11 and L12 communicate between the shell 12a of the heat exchanger 12 and the shell 4a of the preheater 4. Other configurations are the same as those in FIG.

The hydrothermal oxidation reaction method using the above apparatus is shown in FIG.
The heat medium is circulated between the heat exchanger 12 and the shells 12a and 4a of the preheater 4 through the lines L11 and L12, and the liquid to be treated supplied from the liquid tank 3 is Is preheated by the heat medium in the preheater 4. Further, the reaction fluid taken out of the reactor 1 is recovered in heat by cooling with a heat medium in a heat exchanger 12, further cooled in a cooler 9 and supplied to a gas-liquid separator 10. Other operations are the same as those in FIG.

The apparatus shown in FIG. 4 is different from the apparatus shown in FIG. 1 in that a pH meter pHb is provided in the liquid tank 3 to be treated and a neutralizing agent tank 13 is provided.
A line L13 having a pump P5 communicates with the liquid tank 3 to be treated. The pump P5 is controlled so that the measured value of the pH meter pHb becomes a predetermined value. Other configurations are the same as those in FIG.

The hydrothermal oxidation reaction by the above-described apparatus is performed in substantially the same manner as in the case of FIG. 1, but the pH of the liquid to be treated in the liquid to be treated 3 is measured by a pH meter pHb.
A neutralizing agent is injected from 3 through a line L13 by a pump P5, and the liquid to be treated is adjusted to have a pH of 3 to 10 suitable for preheating. This embodiment is used when the liquid to be treated is corrosive instead of neutral, or when corrosive pH is at the preheating stage.
In this case, the pH is adjusted before preheating, and the corrosion of the preheater 1 can be further reduced. Corrosion prevention in the reactor 1 is performed by the neutralizing agent injected from the neutralizing agent tank 8 as in the case of FIG.

In the apparatus shown in FIG. 5, the reactor 1 has a ceramic heater 14 on the outer periphery, and the preheater 4 also has an external heater 11. Reference numeral 15 denotes an oxidant tank, and a line L14 having a high-pressure pump P6 and a preheater 16 is connected to the supply device 2. The preheater 16 has an external heater 17. Neutralizer tank 8
A line L5 having a high-pressure pump P3 communicates with the supply device 2. A line L6 having a cooler 9 and a pressure reducing valve V3 communicates with the gas-liquid separator 10 from the lower part of the reactor 1. The pressure reducing valve V in the line L8 is omitted, and a low pressure valve V4 is provided in the line L9 instead of the pressure reducing valve V2. Other configurations are the same as those in FIG.

In the hydrothermal oxidation method using the above apparatus, when the liquid to be treated is supplied from the liquid tank 3 to be treated by the high-pressure pump P1, the liquid is preheated by the external heater 11 in the preheater 4 and supplied. When the oxidizing agent such as hydrogen peroxide solution is supplied by the high-pressure pump P6, the oxidizing agent is preheated and supplied by the external heater 17 in the preheater 16, and a neutralizing agent such as an aqueous alkali solution is supplied from the neutralizing agent tank 8 by the high-pressure pump P3. Supply and supply device 2
These are mixed and supplied to the reactor 1. In the reactor 1, a hydrothermal oxidation reaction is performed using the ceramic heater 14 as an auxiliary heat source. The reaction fluid in the reactor 1 is cooled by the cooler 9 from the line L6, decompressed by the pressure reducing valve V3, and introduced into the gas-liquid separator 10 to perform gas-liquid separation. Other operations are the same as in the case of FIG.

[0031]

Embodiments of the present invention will be described below. Example 1 The effect of the present invention was verified with the processing system shown in FIG.
As a sample (treatment liquid), an aqueous solution of trichloroacetic acid (5 wt.
%). The sample was sent by the high-pressure pump P1, and was preheated to 330 ° C. by the heater 11 in the preheater 4 (the material of the preheating portion was SUS316). An aqueous NaOH solution as a neutralizing agent and a preheated aqueous hydrogen peroxide solution as an oxidizing agent were combined with the preheated sample by the supply device 2 and introduced into the reactor 1. The reaction temperature of the reactor 1 can be controlled by a ceramic heater 14 as an external heater. The inner surface of the reactor is lined with Ti. The hydrothermal oxidation reaction was performed in a reactor under supercritical water conditions (600 ° C., 23 MPa). The processing fluid was cooled and depressurized, followed by gas-liquid separation to obtain a processing gas and a processing liquid. At this time, the processing liquid was appropriately sampled, and the total organic carbon content (TOC), Na concentration, heavy metal concentration, and the like were analyzed. By adding a neutralizing agent to the waste liquid after preheating and performing a hydrothermal oxidation reaction, the treatment liquid has a pH of 4 to
8 and hardly any heavy metals were detected. After cutting the preheating tube of the preheater and observing the cross section,
Little corrosion was observed.

Comparative Example 1 In Example 1, when the neutralizing agent was added to the sample before preheating and was not added after preheating, the treating solution maintained pH 4 to 8, but the treating solution contained Cr and Ni. Slightly detected. After the test, the preheating tube was cut and the cross section was observed. As a result, a slight decrease in wall thickness due to corrosion was observed.

Example 2 Sulfuric acid was added to an aqueous solution of trichloroacetic acid (5 wt%), and p
A sample made into H2 was used. The solution was further neutralized with NaOH to pH 7 and the solution was preheated. Add a neutralizing agent to the preheated sample so that the pH of the processing solution is near neutral,
Hydrothermal oxidation treatment. As a result, the treatment liquid maintained pH 3 to 8, and hardly any heavy metals were detected. After the test, the preheating tube was cut and the cross section was observed. As a result, almost no corrosion was observed.

Comparative Example 2 Sulfuric acid was added to an aqueous solution of trichloroacetic acid (5 wt%),
A sample made into H2 was used. A neutralizing agent was added to the preheated sample so that the pH of the processing solution was around neutral, and the sample was treated.
Cr and Ni were slightly detected in the treatment liquid. After the test, the preheating tube was cut and the cross section was observed. As a result, a slight decrease in wall thickness due to corrosion was observed.

[Brief description of the drawings]

FIG. 1 is a flowchart of a hydrothermal oxidation reaction method and apparatus according to an embodiment.

FIG. 2 is a flowchart of a hydrothermal oxidation reaction method and apparatus according to another embodiment.

FIG. 3 is a flowchart of a method and apparatus for a hydrothermal oxidation reaction according to still another embodiment.

FIG. 4 is a flowchart of a hydrothermal oxidation reaction method and apparatus according to still another embodiment.

FIG. 5 is a flowchart of a hydrothermal oxidation reaction method and apparatus according to still another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor 2 Supply device 3 Liquid tank to be processed 4, 16 Preheater 5 Air compressor 6 Fuel tank 7 Water tank 8, 13 Neutralizer tank 9 Cooler 10 Gas-liquid separator 11, 17 External heater 12 Heat exchanger 14 Ceramic heater 15 Oxidizer tank

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 598124412 General Atomics Inc. San Diego, California, USA General Atomics Coat 3550 (72) Inventor Hiroshi Obuse 3-4-7 Nishishinjuku, Shinjuku-ku, Tokyo Kurita, Tokyo Industrial Co., Ltd. F term (reference) 4D050 AA13 AA15 AA16 AB06 AB11 AB23 AB31 BB01 BB08 BB09 BC01 BC02 BD06 CA13

Claims (4)

[Claims] 1. A preheating step of preheating an object to be treated, a supply step of mixing the object to be treated after preheating with a neutralizing agent and supplying the mixture to a reactor, Performing a hydrothermal oxidation reaction in a supercritical or subcritical state of water in the presence of water. 2. The method according to claim 1, further comprising the step of adjusting a pH of the object to be treated to a pH suitable for preheating. 3. A reactor for performing a hydrothermal oxidation reaction in a supercritical or subcritical state of water, a preheater for preheating an object to be processed, and a reactor for mixing the preheated object with a neutralizing agent. And a supply device for supplying to the reactor. 4. The apparatus according to claim 3, further comprising a pH adjusting device for adjusting the object to be treated to a pH suitable for preheating.