JP2003236569A - Method of hydrothermal oxidation reaction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of a hydrothermal oxidation reaction wherein a hydrothermal reactor can be operated safely and for a long term by reducing corrosion thereof and at low cost by reducing the used amount of a neutralizing agent. <P>SOLUTION: Waste liquid A and waste liquid B are introduced through a passage 11 and a passage 12, respectively, to a mixing vessel 1 and mixed with each other in such a manner that the value Z represented by equation (1) (wherein [Na], [K],... each denotes molar concentration of each atom contained in mixed waste liquid) satisfies -0.01≤Z≤+0.01. The mixed waste liquid 13 is sent to a supplying apparatus 2a of the hydrothermal reactor 2 and mixed with an oxidizing agent there and the mixed flow thereof is supplied to the hydrothermal reactor 2 in downward flow to perform the hydrothermal oxidation reaction. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrothermal oxidation reaction method for carrying out an oxidation reaction under supercritical or subcritical conditions of water, and more particularly to a hydrothermal oxidation reaction method suitable for decomposing wastes. is there.

[0002]

2. Description of the Related Art Hydrothermal oxidation reaction treatment, in which an oxidation reaction is carried out under supercritical or subcritical conditions of water, has been attracting attention as a technology capable of oxidatively decomposing organic matter in waste liquid to a high level in a short time. By performing the hydrothermal oxidation reaction, the organic components in the liquid to be treated are decomposed into carbon dioxide, and the nitrogen components are decomposed into nitrogen gas (ammonia and nitrate nitrogen are also generated depending on the conditions). Heteroatoms such as phosphorus and sulfur are also oxidized to phosphate ions and sulfate ions, respectively.

As a major issue for practical application of hydrothermal oxidation reaction,
Corrosion of the material of the processing equipment. Generally, corrosion by an acid contained in the liquid to be treated or an acid generated by a hydrothermal oxidation reaction is large, but corrosion by an alkali is also reported. In the conventional hydrothermal oxidation reaction method, the liquid to be treated is analyzed in advance to obtain an estimated acid production amount, and a sufficient amount of a neutralizing agent for neutralizing the estimated acid production amount is supplied before the reactor is supplied (see Table 3
500264) or a method of supplying the reaction fluid after the reaction (JP-A-10-314770, JP-A-11-156186). The amount of the neutralizing agent added is determined by decompressing and cooling the hydrothermally oxidized water after the reaction to determine the pH, and the pH is an appropriate value (usually pH
It was dealt with by adjusting so as to be 3 to 11).

On the other hand, in many cases, a plurality of waste liquids must be treated in the actual hydrothermal oxidation reaction. In such a case, the amount of neutralizing agent required for each waste liquid should be calculated, and the treatment should be performed while adding the necessary neutralizing agent for each waste liquid. It is necessary to take measures such as addition. Such measures have many inconveniences such as complicated operation management, increased cost due to the need for a plurality of neutralizer supply means, and increased cost due to the large amount of neutralizer. .

As a practical problem, even if the pH of the liquid to be treated is simply adjusted to be near neutral, chloride ions and sulfate ions will be generated due to the decomposition of the reactant due to the hydrothermal oxidation reaction. , Phosphate ions, etc. are generated, and organic amines, ammonia, organic acids, etc. that have affected the pH value are decomposed, so that the pH of the treated water often fluctuates greatly. Therefore, the hydrothermal reactor It is difficult to prevent corrosion.

[0006]

The object of the present invention is to reduce corrosion of the hydrothermal oxidation reactor to enable safe and long-term operation, and to reduce the amount of the neutralizing agent used. It is to propose a hydrothermal oxidation reaction method that can be operated at low cost.

[0007]

Means for Solving the Problems As a result of studying a method for solving the above-mentioned problems, the present inventor has conducted a waste liquid treatment under the condition that the balance of elements contained in the treated water after the hydrothermal oxidation reaction satisfies a specific condition. It was found that the thermal oxidation reaction can prevent corrosion and reduce the amount of the neutralizing agent used.

That is, the present invention is the following hydrothermal oxidation reaction method. (1) A hydrothermal oxidation reaction method for oxidizing a reactant contained in a liquid to be treated in a supercritical or subcritical state of water,
The value of Z represented by the following mathematical formula (1) showing the relationship of the content of each element contained in the liquid to be treated is −0.01 ≦ Z ≦ +
A hydrothermal oxidation reaction method in which a hydrothermal oxidation reaction is carried out in a state of satisfying 0.01.

[Equation 3] (In the formula (1), [Na], [K], [Mg], and [C]
a], [F], [Cl], [Br], [P] and [S] are molar concentrations (mol) of each atom contained in the liquid to be treated.
/ L). (2) A hydrothermal oxidation reaction method for oxidizing a substance to be reacted contained in a liquid to be treated in a supercritical or subcritical state of water,
The value of Z represented by the mathematical formula (1) showing the relationship of the content of each element contained in the liquid to be treated is −0.01 ≦ Z ≦ +
A hydrothermal oxidation reaction method in which two or more kinds of liquids to be treated are mixed so as to satisfy 0.01 and a hydrothermal oxidation reaction is performed.

The reactant to be treated in the present invention is a substance to be subjected to a hydrothermal oxidation reaction in a supercritical or subcritical state of water, and the liquid to be treated is a liquid substance containing such a reactant. Is. Specific examples of the reactants include organic substances in waste liquid discharged from factories, surplus sludge and the like. Specific examples of the liquid to be treated include waste liquid containing organic substances discharged from factories and the like, and excess sludge discharged from the aerobic treatment process of the waste liquid.

In order to keep the pH of the liquid to be treated after the hydrothermal treatment within an appropriate range and prevent corrosion of the apparatus, Na, K, Mg, Ca, F, Cl, Br, etc. contained in the liquid to be treated are contained. The relationship between the contents of P and S atoms is such that the value of Z is −0.01 ≦ Z ≦ +, with the value of Z represented by the mathematical formula (1) as an index.
0.01, preferably −0.001 ≦ Z ≦ + 0.001
The hydrothermal oxidation reaction is performed under the condition that Here, the content of Na atoms means not only Na ions dissolved in the liquid to be treated but also Na atoms contained in the reactant in the form of being released as Na ions in the treated water by hydrothermal oxidation reaction. Etc. is the total amount of Na atoms contained in the liquid to be treated in all forms. The same applies to the contents of other atoms such as K atoms.

The liquid to be treated having the value of Z within the above range can be directly used for the hydrothermal oxidation reaction. On the other hand, the liquid to be treated having a Z value outside the above range can be subjected to a hydrothermal oxidation reaction after being adjusted so that the Z value falls within the above range. For example, in order to adjust the value of Z to the above range, a method of mixing a liquid to be treated (waste liquid) whose pH becomes acidic after the hydrothermal oxidation reaction with a liquid to be treated (waste liquid), etc. Can be given.

By carrying out the hydrothermal oxidation reaction in a state where the value of Z satisfies -0.01≤Z≤ + 0.01, preferably -0.001≤Z≤ + 0.001, the target of the hydrothermal oxidation reaction is Corrosion of the apparatus that occurs when the pH of the treatment liquid is not an appropriate value can be reduced, and the hydrothermal oxidation reaction apparatus can be operated safely and for a long time. In addition, when the waste liquid in which the pH of the treated water after the hydrothermal oxidation reaction is acidic and the waste liquid in which the pH is alkaline are mixed, they function as neutralizing agents, so the amount of neutralizing agent used can be reduced and the cost is low. Can be processed.

The actual pH of the treated water is determined by the influence of elements other than the elements shown in equation (1).
This formula is useful for getting the value. That is, when Z> 0, it is considered that the treated water has a large number of moles of cations such as Na ⁺ and K ⁺ , and the treated water becomes alkaline.
On the other hand, when Z <0, the number of moles of anions such as Cl ⁻ and SO ₄ ²⁻ is large, and the treated water is considered to be acidic.
The case of Z = 0 is considered to be a state in which the cations and anions in the treated water are well balanced, that is, a state close to neutral.

As an example, consider the case of Z = -0.001. In this case, the molar concentration of anions such as Cl ⁻ and SO ₄ ²⁻ is 0.001 mol / L excess,
The estimated pH is about 0.001 mol / L hydrochloric acid added to water, that is, about pH = 3. Similarly, when Z = + 0.001, the molar concentration of cations such as Na ⁺ and K ⁺ is 0.001 mol / L excess, so the estimated pH is about 0.01 mol / L sodium hydroxide added to water. That is, pH = 11.

In addition to the elements represented by the above formula (1), various heavy metal ions, carbonate ions, nitrogen-containing ions (NH 3) are present as ion species present in the treated water of the hydrothermal oxidation reaction.
₄ ⁺ , NO ₂ ⁻ , NO ₃ ^−, etc.), but these are unlikely to be contained, are contained in a small amount, are decomposed under the hydrothermal oxidation reaction, or are contained in the processing fluid. Is an element that moves to the gas side after gas-liquid separation, and in most cases does not significantly affect the neutralization reaction. However, it is considered that the pH value may greatly differ from the approximate value due to these ionic species and other factors. Therefore, even when utilizing the above formula (1), it is desirable to use a means for monitoring the pH of the treated water during treatment and adding a neutralizing agent if necessary.

In some cases, the pH of the treated water may not fall within the appropriate range no matter how the plural liquids to be treated are mixed.
Even in such a case, means for adding the neutralizing agent is necessary. It should be noted that the mixing of a plurality of waste liquids may be usually performed in one storage tank, but if there is some inconvenience (for example, odor is generated, phase separation, solid precipitation, etc.) due to mixing, it is appropriate. They may be mixed at a place (for example, by sending the respective liquids and mixing near the inlet of the reactor).

In the hydrothermal oxidation reaction, the liquid to be treated is introduced into a hydrothermal reactor to oxidize and decompose the substance to be reacted. The hydrothermal reactor is configured to oxidatively decompose a reactant in a supercritical or subcritical state of water in the presence of an oxidant. Here, the hydrothermal oxidation reaction is a reaction of oxidatively decomposing an object to be reacted by an oxidation reaction in the presence of water at high temperature and high pressure in a supercritical or subcritical state and an oxidizing agent. Supercritical state is 374 ℃ or higher, 22MP
The state is a or more. The subcritical state is, for example, 374.
℃ or more, 2.5 MPa or more and less than 22 MPa or 37
A state of less than 4 ° C. and 22 MPa or more, or a state of 374 ° C. or less and less than 22 MPa of high temperature and high pressure close to the critical point.

Such a hydrothermal oxidation reaction is carried out in a hydrothermal reactor in a state where the substance to be reacted is mixed with an oxidant, and these mixtures undergo a hydrothermal oxidation reaction inside the reactor. Air, oxygen, liquid oxygen, ozone, hydrogen peroxide solution, nitric acid, nitrous acid, nitrate, nitrite and the like can be used as the oxidizing agent. The oxidant may be supplied by being mixed with the liquid to be treated, or may be supplied as a multi-layered flow by using a double-tube nozzle as a supply port. If necessary, a catalyst, a neutralizing agent and the like may be added, and these can be mixed with the liquid to be treated or supplied separately to the reactor.

The hydrothermal reactor used in the present invention is made of a heat-resistant and pressure-resistant material and is formed in a cylindrical reactor arranged substantially vertically so as to carry out the hydrothermal oxidation reaction in a supercritical or subcritical state. It If the reaction heat alone does not reach the supercritical or subcritical state, an external heating means can be provided. The reactor may have a cylindrical shape, an elliptic shape, or a polygonal shape, and the lower end portion may have a cone shape.
When a hydrothermal oxidation reaction is carried out in a supercritical or subcritical state by such a hydrothermal oxidation reactor, the substance to be reacted is oxidized by an oxidant and finally decomposed into water and carbon dioxide, or is hydrolyzed to a low level. The substance is polymerized and the inorganic substance is separated in a solid or molten state. The reaction product, after separating the solid, cooled,
The pressure is reduced and the gas and liquid are separated.

As the above-mentioned hydrothermal reactor, the one conventionally used for the hydrothermal oxidation reaction can be used as it is, but as shown in JP-A-11-156186, a mixture accompanied by a backflow at the upper part is used. A mixed flow of the liquid to be treated and the oxidant is supplied in a downward flow from a supply device provided in the upper part of the reaction zone and a substantially vertical reactor forming a plug flow reaction zone in the lower part. There is a structure in which a mixed flow with backflow is formed in the mixed reaction zone to carry out the hydrothermal oxidation reaction, and a parallel downward plug flow is formed in the lower plug flow reaction area to carry out the additional hydrothermal oxidation reaction. preferable.

The material of the hydrothermal reactor is not limited, but is preferably a corrosion resistant material such as Hastelloy, Inconel or stainless steel. The hydrothermal reactor is preferably provided with a corrosion resistant liner. The corrosion-resistant liner is not particularly limited, and a corrosion-resistant liner having a gap between the corrosion-resistant liner and the pressure load wall as disclosed in JP-A-11-156186 can be used.

The hydrothermal reactor may be provided with cooling means for cooling the reaction mixture before it is discharged from the outlet. The cooling means is not particularly limited, but water can be introduced into the reactor to cool it, and the inorganic salt can be dissolved to accelerate its discharge. Further, water containing an acid or an alkali may be introduced into the reactor and cooled to neutralize the alkali or the acid. When the adherence of solids is significant, a mechanical removal device for removing solids adhering to the inner wall of the reactor can be provided. The mechanical removing device for removing solids is not particularly limited, but a substantially cylindrical scraper including a notched window portion disclosed in JP-A-11-156186 is suitable.

Separation means may be provided for separating solids in the reaction fluid discharged from the hydrothermal reactor. In particular,
Inorganic salts are not dissolved in the reaction fluid in the supercritical state but are contained as a solid, so that the treated water can be easily reused by separating the insolubilized inorganic substances. The solid matter separating means is not particularly limited, and a container having an inlet for introducing the reaction fluid from the hydrothermal reactor and an outlet for discharging the fluid from which the solid has been removed, and the reaction fluid disposed in the container to the reaction fluid. A means provided with a means for removing and discharging the contained solid can be used. In addition, a means for solid separation or gas-liquid separation can be included in the cooling and depressurizing steps.

The means for starting the reaction by the hydrothermal reactor is not particularly limited. Usually, the reactor is preheated to around a predetermined reaction temperature at the start of the reaction. Preheating can be carried out by providing a heating device in the reactor or by introducing water or air heated in the liquid to be treated and / or the oxidant supply passage. Also, normally, supplying water and an oxidant to the reactor,
It is pressurized to a predetermined pressure by a pressure adjusting valve that is usually provided. After the temperature and pressure are adjusted to predetermined values, a fluid containing the liquid to be treated is supplied to start the hydrothermal oxidation reaction. The reaction product decomposes due to the reaction, and heat of reaction is generated. When a mixing reaction zone with backflow is provided above the hydrothermal reactor, the temperature of the fluid rises because the reactant, oxidant, reactor contents, etc. are sufficiently mixed by the mixing action with backflow. To do.
The reactant to be supplied thereby rapidly starts the hydrothermal oxidation reaction, and the stable reaction is continued. The reaction fluid moves downward in the reactor, continuously reacts in the plug flow reaction region, and is then discharged from the discharge port. The length: diameter ratio of the reactor is preferably 1: 1 to 100: 1.

The reaction fluid leaving the hydrothermal reactor is separated into solids, then cooled and decompressed to be separated into gas and liquid. When liquid is produced by cooling in the reactor, the liquid can be separated together with the solid at the stage of leaving the reactor, and further cooling and gas-liquid separation can be performed if necessary. The finally produced water, gas, and solid are directly recovered as energy, reused as a substance, or directly or additionally treated and disposed of.

In the present invention, the balance of the elements contained in the liquid to be treated is adjusted by a method such as mixing a plurality of waste liquids so as to satisfy the above condition, so that the amount of the neutralizing agent used can be saved. It becomes possible to perform the treatment while suppressing the corrosion of the reactor. INDUSTRIAL APPLICABILITY The present invention is useful as a simple and inexpensive corrosion inhibition method in actual hydrothermal oxidation reaction.

[0027]

EFFECTS OF THE INVENTION In the hydrothermal oxidation reaction method of the present invention, since the hydrothermal oxidation reaction is carried out in a specific state in which the relationship of the content of each element contained in the liquid to be treated is specified, It is possible to reduce the amount of the neutralizing agent used and to operate at low cost, while reducing the corrosion of the steel to enable safe and long-term operation.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of a hydrothermal oxidation reaction apparatus of an embodiment for carrying out the hydrothermal oxidation reaction method of the present invention, wherein 1 is a mixing tank, 2 is a hydrothermal reactor, 3 is an oxidizer tank, and 5 is gas-liquid. It is a separator.

The hydrothermal oxidation reaction process by the apparatus of FIG. 1 is performed as follows. First, the waste liquid A is introduced into the mixing tank 1 from the system passage 11 and the waste liquid B is introduced from the system passage 12 to mix them.
Prepare 3. In this case, Z represented by the above equation (1)
Are mixed so as to satisfy the value of −0.01 ≦ Z ≦ + 0.01.

The mixed waste liquid 13 is sent by the high-pressure pump P1 through the system 14 to the supply device 2a of the hydrothermal reactor 2, where the oxidant (eg air, sent from the oxidizer tank 3 by the high-pressure pump P2 is sent through the system 15). (Hydrogen peroxide water), and the mixed flow is supplied to the hydrothermal reactor 2 in a downward flow to perform a hydrothermal oxidation reaction. In the hydrothermal reactor 2, a preheater (not shown) provided in the system passage 14 or 15 at the start of the reaction performs heating to perform a hydrothermal oxidation reaction while maintaining a supercritical or subcritical state.

The mixed flow supplied from the supply device 2a forms a mixed reaction zone accompanied by a backflow in the upper part of the hydrothermal reactor 2, oxidative decomposition of the reaction product containing organic substances is carried out, and the turbulent flow is eliminated in the lower part. Then, a plug flow reaction zone is formed and an additional reaction is carried out. Since the mixed waste liquid 13 processed in the hydrothermal reactor 2 is adjusted so that the value of Z satisfies −0.01 ≦ Z ≦ + 0.01, corrosion of the hydrothermal reactor 2 is suppressed. .

The reaction fluid of the hydrothermal reactor 2 is introduced into the cooler 19 from the system passage 16, cooled by the cooling water supplied from the cooling water passage 21, and introduced into the gas-liquid separator 5 from the system passage 22 to be vaporized. The liquid is separated, the gas is discharged from the gas discharge path 23 through the valve V1, and the treated water is discharged from the liquid discharge path 24 through the valve V2. The treated water obtained is of high quality in which organic substances, ammonia, and other substances to be reacted are decomposed, and can be recovered and used.

Although two types of waste liquids A and B are mixed in FIG. 1, three or more types of waste liquids can be mixed. It is also possible to add a pH adjusting agent such as acid or alkali. A compressor may be used instead of the pump P2.

[0034]

EXAMPLES Example 1 1) Determination of Mixing Ratio of Plural Waste Liquids The method of determining the mixing ratio will be described taking three kinds of waste liquids shown in Table 1 as examples.

[Table 1] It is expected that the waste liquid A and the waste liquid C in Table 1 will be acidic when the hydrothermal oxidation reaction is performed, and the waste liquid B will be alkaline. Therefore, waste liquid A
Alternatively, by distributing the waste liquid B to the waste liquid C and mixing them,
The calculation was performed by the above mathematical formula (1) so that the elemental balance of the mixed waste liquid would be appropriate. As a result, it was found that the element balance becomes appropriate when mixed in the ratios shown in Table 2.

[0035]

[Table 2]

2) Hydrothermal Oxidation Reaction Test of Mixed Waste Liquid A mixed waste liquid X or Y of Table 2 was subjected to a hydrothermal oxidation reaction test with the apparatus shown in FIG. The mixed waste liquid preheated to 300 ° C. and the oxidizer (35% hydrogen peroxide solution) were mixed in front of the reactor, and the mixture was supplied into the reactor through a nozzle (tube diameter 1 mmφ). An external heater was attached to the reactor, and the reaction conditions were adjusted to 650 ° C. and 24 MPa. A test rod (1.6 mmφ) for corrosion evaluation is attached in the reactor. Water and an oxidizing agent were supplied to the reactor, and the inside of the reactor was adjusted by heating with an external heater so that the reaction temperature was set. When the reaction temperature reached the set value, the water and the mixed waste liquid were gradually switched to carry out the hydrothermal oxidation reaction in the supercritical or subcritical state of water. The reaction was continued for 4 hours after the water and the mixed waste liquid were completely switched, the mixed waste liquid was gradually switched to water, and then the heater was turned off to end the test. In order to minimize corrosion during cooling, the reactor was cooled by flowing only air after turning off the heater. After the test, the test rod was taken out and several sections were observed to determine the maximum corrosion depth. The results are shown in Table 3.

Comparative Example 1 The oxidative decomposition test of the waste liquids A, B and C by a single hydrothermal oxidation reaction was carried out in the same manner as in Example 1. The results are shown in Table 3.

[0038]

[Table 3]

From the results shown in Table 3, in the decomposition test of the mixed waste liquid X or Y in which the element balance was taken into consideration, no significant corrosion was observed on the test rod in the reactor. On the other hand, in the waste liquid A and the waste liquid C in which the acid component in the treated water is excessive, the progress of corrosion is observed in HC-276, and in the waste liquid B in which the alkaline component is excessive, the progress of corrosion is caused by HC-276 and titanium. Was observed.

[Brief description of drawings]

FIG. 1 is a system diagram of a hydrothermal oxidation reaction apparatus of an embodiment for carrying out the hydrothermal oxidation reaction method of the present invention.

[Explanation of symbols] 1 mixing tank 2 Hydrothermal reactor 3 oxidizer tank 5 gas-liquid separator 11, 12, 14, 15, 16, 22 Route 13 Mixed waste liquid 19 Cooler 21 Cooling channel 23 Gas discharge path 24 Liquid discharge path

   ─────────────────────────────────────────────────── ─── Continued front page    (71) Applicant 598124412             General Atomix Incorporated             Itted             United States of America California Sun             Diego General Atomics Co             3550 (72) Inventor Hiroshi Obuse             Kurita, 3-4-3 Nishi-Shinjuku, Shinjuku-ku, Tokyo             Industry Co., Ltd. F term (reference) 4D050 AA13 AB11 BB01 BB02 BB08                       BB09 BC01 BC02 BD02 BD06                       CA20                 4D059 AA05 BC02 BC03 BJ00 DA43                       DA44 DA47 DA70 EB20

Claims (2)

[Claims] 1. A hydrothermal oxidation reaction method for oxidizing a reaction target substance contained in a liquid to be treated in a supercritical or subcritical state of water, which is a relation of contents of respective elements contained in the liquid to be treated. The value of Z represented by the following mathematical expression (1) is −0.01 ≦ Z ≦ +
A hydrothermal oxidation reaction method in which a hydrothermal oxidation reaction is carried out in a state of satisfying 0.01. [Equation 1] (In the formula (1), [Na], [K], [Mg], and [C]
a], [F], [Cl], [Br], [P] and [S] are molar concentrations (mol) of each atom contained in the liquid to be treated.
/ L). ) 2. A hydrothermal oxidation reaction method for oxidizing a reaction target substance contained in a liquid to be treated in a supercritical or subcritical state of water, which is a relation of contents of respective elements contained in the liquid to be treated. The value of Z represented by the following mathematical expression (1) is −0.01 ≦ Z ≦ +
A hydrothermal oxidation reaction method in which two or more kinds of liquids to be treated are mixed so as to satisfy 0.01 and a hydrothermal oxidation reaction is performed. [Equation 2] (In the formula (1), [Na], [K], [Mg], and [C]
a], [F], [Cl], [Br], [P] and [S] are molar concentrations (mol) of each atom contained in the liquid to be treated.
/ L). )