JP2005152806A - Wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment method excellent in both of workability and energy saving properties, capable of realizing the decomposition treatment of wastewater containing a hardly decomposable compound, which must be treated heretofore only by a treatment means for concentrating, drying and solidifying this wastewater to treat the same as industrial waste, at a low cost and markedly excellent in the protection of environment. <P>SOLUTION: This wastewater treatment method includes a critical fluid forming process for pressurizing and heating a reaction fluid to bring the same to a supercritical or sub-critical state and a fluid contact process for bringing the critical fluid obtained in the critical fluid forming process into contact with wastewater containing any one of thiosulfate ions, thiocyanate ions, and hexacyanoferrate ions in a reactor and subjecting the wastewater to reaction treatment using the critical fluid to form a treated fluid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for treating wastewater generated from thermal power generation facilities, gas production facilities, petroleum refining facilities, waste treatment facilities, and the like.

Conventionally, wastewater generated from thermal power generation facilities using fossil fuels such as coal and oil, gas production facilities, oil refining facilities and waste treatment facilities that melt and treat waste such as sludge, Since NO ₂ ⁻ , Fe ²⁺ , sulfides and the like are contained and the chemical oxygen demand (COD) is high, a treatment for removing these substances is necessary when discharged into public water areas. Various methods have been studied as methods for treating these wastewaters.

For example, (Patent Document 1) states that “a flue gas desulfurization effluent discharged from a wet flue gas desulfurization device that absorbs and removes sulfur oxides in combustion exhaust gas such as thermal power generation is brought into contact with activated carbon under a reducing condition and decomposed. A method for treating flue gas desulfurization effluent ”is disclosed.
JP-A-11-267447

However, the above conventional techniques have the following problems.
(1) Since the technology disclosed in (Patent Document 1) brings wastewater into contact with activated carbon, the activated carbon must be replaced every time the activated carbon is deactivated and the decomposition efficiency is lowered, and the replacement frequency is complicated and complicated. There was a problem of lack of workability.
(2) If the effluent contains thiosulfate ion, thiocyanate ion, hexacyanoferrate ion, etc., these cannot be decomposed by activated carbon because of its degradability, and the effluent is collected and heated to evaporate the water. Therefore, it has to be concentrated and dried to be treated as industrial waste, and has a problem that the treatment efficiency is low, the energy saving property is lacking, and the environmental conservation property is lacking.
(3) When the wastewater contains thiosulfate ions, thiosulfate ions can be decomposed into sulfite ions and sulfur under acidic conditions. However, when thiocyanate ions are also contained at the same time, In order to produce harmful gases such as hydrogen cyanide, there is no treatment means other than evaporating moisture under basic conditions, concentrating to dryness and treating it as industrial waste, requiring a lot of treatment equipment and complicated work There was a problem of lack of efficiency.

  The present invention solves the above-mentioned conventional problems, is excellent in workability and energy saving, and also contains a hardly decomposable compound that has so far only been treated as industrial waste after being concentrated to dryness. It is an object of the present invention to provide a wastewater treatment method that can realize decomposition treatment of wastewater at low cost and is extremely excellent in environmental conservation.

In order to solve the above conventional problems, the wastewater treatment method of the present invention has the following configuration.
According to a first aspect of the present invention, there is provided a wastewater treatment method in which a reaction fluid is pressurized and heated to bring the reaction fluid into a supercritical state or a subcritical state, and a critical fluid generation step. The critical fluid obtained in the process and wastewater containing at least one of thiosulfate ion, thiocyanate ion and hexacyanoferrate ion are brought into contact in the reactor, and the wastewater is reacted with the critical fluid and treated. And a fluid contact process for generating a fluid.
With this configuration, the following effects can be obtained.
(1) A wastewater containing at least one of hexacyanoferrate ions such as thiosulfate ion, thiocyanate ion, ferrocyanate ion, ferricyanate ion and a critical fluid such as supercritical water or subcritical water. By bringing them into contact with each other, it is possible to hydrolyze and oxidize and reduce hardly decomposable thiosulfate ions and the like. As a result, until now there was only a processing means to condense and dry it and treat it as industrial waste. However, it is possible to perform decomposition with a simple process, with very few man-hours and processing equipment, and to improve workability and environmental protection. Remarkably excellent in properties.

Here, the waste water, phenol, benzene, organic substances such as toluene, NO 2 ^_-, Fe ^2+, sulfides, industrial wastewater containing heavy metal ions such as sewage, in contact with and penetrate into the landfill landfill waste Wastewater that has a high chemical oxygen demand (COD) such as sludge and leachate leached from the rainwater and wastewater contained in the waste at the final disposal site, and requires treatment of hazardous substances is used. Dilute waste water having a low concentration can also be used. In particular, wastewater generated from coal gasification power generation facilities using fossil fuels such as coal and oil, thermal power generation facilities, gas production facilities, petroleum refining facilities, waste treatment facilities that melt and treat waste such as sludge In particular, in coal gasification power generation equipment and waste treatment facilities that melt and treat waste such as sludge, cooling effluent that cools combustion ash such as coal ash and slag is gasified. It is discharged from washing wastewater that has been washed away from the fuel gas produced, exhaust gas desulfurization wastewater discharged from flue gas desulfurization equipment that absorbs and removes sulfur oxides in combustion exhaust gas, and organic chemical product manufacturing equipment such as acetylene purification equipment. It is suitable for the treatment of cleaning wastewater. These cooling effluents and washing effluents are difficult-to-decompose cyanides, thiosulfate ions, thiocyanate ions, ferrocyanate ions, hexacyanoferrate ions, etc. It is because it contains.

As the reaction fluid, water, an aqueous solution containing water as a main component, such as an alcohol aqueous solution in which methanol, ethanol, propanol, isopropanol or the like is dissolved in water, or the like is used. This is because the temperature range and pressure range of the critical fluid are high, and the water molecules themselves become nucleophiles due to high temperature and pressure, and many organic substances contained in the wastewater can be decomposed.
It is desirable to use a high-purity fluid as the reaction fluid. This is to prevent corrosion of a heating device or the like used in the critical fluid generation process in which the reaction fluid is made into a high-temperature and high-pressure critical fluid.
In addition, when the density | concentration of a thiosulfate ion, a thiocyanate ion, and a hexacyanoferrate ion is low, waste water can also be used as a reaction fluid. Moreover, the processing fluid after a process can also be used. Thereby, while being able to reduce the quantity of the processing fluid discharged | emitted to a public water area or sent to a water purification apparatus, while being able to reduce the load of a water purification apparatus, constructing | assembling the wastewater treatment system by a closed system it can. The concentration of thiosulfate ions, thiocyanate ions, and hexacyanoferrate ions in the wastewater that can be used as a reaction fluid is preferably a total ion concentration of 200 ppm or less, preferably 50 ppm or less. As the ion concentration becomes higher than 50 ppm, the corrosion of the heating device or the like tends to be remarkable, and the durability of the heating device or the like tends to be lowered. In particular, when the ion concentration is higher than 200 ppm, this tendency becomes remarkable.

  As the critical fluid obtained in the critical fluid generation step, a subcritical fluid or a supercritical fluid in which the reaction fluid is set to a high temperature and a high pressure is used. When the reaction fluid is water, it is heated to a temperature of 200 to 600 ° C. and pressurized to a pressure of 20 to 35 MPa to be in a critical state or a subcritical state.

  As the fluid contact process, any process may be used as long as the critical fluid is diffused into the waste water, and the critical fluid and the waste water are brought into contact with each other by being collided, stirred, or flowed in the reactor. As a result, the wastewater is heated with the critical fluid, and molecules in which the diffusion force due to the thermal kinetic energy is increased due to the supercritical state and the like freely move around in the wastewater to decompose the organic matter in the wastewater.

Next, optimum conditions in the fluid contact process will be described with reference to the drawings.
FIG. 1 is a diagram showing the relationship between water temperature and specific heat capacity at each pressure, FIG. 2 is a diagram showing the relationship between water temperature and density at each pressure, and FIG. 3 is a diagram showing Na under a pressure of 25 MPa. is a diagram showing a relationship between ₂ SO ₄ concentration of temperature and _Na 2 SO ₄ saturated solution. Na ₂ SO ₄ is a product of oxidative decomposition of sodium thiosulfate. 1 to 3 show FJArmellini, JFTester and GTHong: “Precipitation of Sodium Chloride and Sodium Sulfate in Water from Sub- to Supercritical Conditions: 150 to 550 ° C., 100 to 300 bar”: The Journal of Supercritical Fluids, vol. 1994, (7), pp. 147-158, SNRogak and P. Teshima: "Deposition of Sodium Sulfate in a Heated Flow of Supercritical Water": AIChE Journal, vol. 45, (2), pp. 240-247 (1999) The quoted data.

  The temperature of the processing fluid processed in contact with the critical fluid in the fluid contact step is preferably 200 to 500 ° C., preferably 250 to 470 ° C., more preferably 350 to 450 ° C., and the pressure is 20 to 35 MPa. When the pressure is 20 to 35 MPa and the temperature is 350 to 450 ° C., as shown in FIG. 1 and FIG. 2, the amount of increase in specific heat capacity is larger than the amount of decrease in water density. It can be stably maintained at a high temperature, and as shown in (Fig. 3), the solubility of decomposition products such as inorganic salts generated by decomposition of organic substances in the wastewater is remarkably reduced and deposited in the processing fluid. Therefore, wastewater treatment can be easily performed by performing solid-liquid separation.

As the temperature of the processing fluid becomes lower than 350 ° C. (see FIG. 1), the specific heat capacity decreases, so that the temperature of the processing fluid tends to decrease and the decomposition ability tends to decrease. As shown, the solubility of the decomposition products tends to increase, and as the temperature rises above 450 ° C., the specific heat capacity and density decrease and the temperature of the processing fluid tends to decrease as shown in FIGS. Therefore, it is necessary to increase the temperature of the critical fluid in anticipation of a temperature decrease, and there is a tendency to lack energy saving.
When the temperature is lower than 250 ° C., the diffusive power decreases and the decomposition reactivity tends to be poor, and the processing efficiency tends to decrease. As the temperature is higher than 470 ° C., the temperature of the critical fluid increases, so that there is a tendency to lack energy saving. . In particular, when the temperature of the processing fluid is lower than 200 ° C. or higher than 500 ° C., these tendencies become remarkable, which is not preferable.

  Further, as the pressure of the processing fluid becomes lower than 20 MPa, it is difficult to obtain a subcritical phase or supercritical phase, and there is a tendency that the decomposition efficiency of the wastewater is poor and the processing efficiency is lowered, and the pressure is increased as the pressure becomes higher than 35 MPa. This is not preferable because the pressurization pump, the reactor, and the like are enlarged, and the specific heat capacity of water tends to be small and the temperature of the processing fluid tends to become unstable as shown in FIG.

  The volume of the critical fluid that is brought into contact with the wastewater in the fluid contact step depends on the concentration of thiosulfate ions, thiocyanate ions, and hexacyanoferrate ions in the wastewater, but is 1 to 100 times, preferably 1 to 20 times that of the wastewater. Is preferred. As the volume of the critical fluid becomes less than 1 times the volume of the wastewater, it is difficult to raise the temperature of the wastewater to the temperature range of the supercritical region or the subcritical region, which is not preferable. As the volume of the critical fluid exceeds 20 times the volume of the waste water, the amount of the critical fluid increases and the amount of the processing fluid generated by the reaction treatment of the waste water with the critical fluid increases and requires a large processing facility. Is seen. In particular, when it exceeds 100 times, this tendency becomes remarkable, which is not preferable.

The invention according to claim 2 of the present invention is the wastewater treatment method according to claim 1, wherein the reaction fluid contains at least one of thiosulfate ions, thiocyanate ions, and hexacyanoferrate ions. It has the structure which is the waste_water | drain which contains or does not contain in low concentration.
With this configuration, in addition to the operation obtained in the first aspect, the following operation can be obtained.
(1) Treatment of these wastewaters by using industrial wastewater such as phenol, benzene, toluene, etc., NO ₂ ⁻ , Fe ²⁺ , sulfides, heavy metal ions, etc., and wastewater such as sewage as reaction fluids. The treatment can be performed simultaneously with the treatment of thiosulfate ion, thiocyanate ion, and hexacyanoferrate ion, and the treatment efficiency can be increased.

Here, as drainage, in addition to what has been described in claim 1, precipitation, drainage from other devices, and the like can be used.
As the concentration of thiosulfate ion, thiocyanate ion and hexacyanoferrate ion in the waste water, the total ion concentration is 200 ppm or less, preferably 50 ppm or less. As the ion concentration becomes higher than 50 ppm, the corrosion of the heating device or the like tends to be remarkable and the durability tends to be lowered. In particular, when the ion concentration is higher than 200 ppm, this tendency becomes remarkable, which is not preferable.

Invention of Claim 3 of this invention is a wastewater treatment method of Claim 1 or 2, Comprising: In the said fluid contact process, it has the structure provided with the waste_water | drain pressurization process which pressurizes the said waste_water | drain. ing.
With this configuration, in addition to the operation obtained in the first or second aspect, the following operation can be obtained.
(1) Since the waste water pressurization process which pressurizes waste water is provided, the pressure of the critical fluid which contacted the waste water within the reactor can be maintained, and the reaction processing efficiency can be increased.
(2) The wastewater is heated to a high temperature only after it joins the critical fluid, and at the same time, the harmful substances in the system are decomposed, so even if the wastewater is corrosive, the reactor is corrosive. The exposure time to the environment can be shortened and the durability of the reactor can be increased.

The drainage is pressurized to substantially the same pressure as the critical fluid in the drainage pressurization step.
If the corrosiveness of the wastewater is poor, the wastewater can be heated as needed in the wastewater pressurization process, but if the wastewater is corrosive, the corrosiveness becomes stronger by heating, etc. This is not preferable because the corrosion of the apparatus becomes remarkable and the durability of the apparatus is lowered. In the drainage pressurizing step, the pressure is increased to substantially the same pressure as the critical fluid.

Invention of Claim 4 of this invention is a processing method of the waste_water | drain of any one of Claim 1 thru | or 3, Comprising: The said critical fluid and the said waste_water | drain were made to contact in the said fluid contact process. It has the structure provided with the holding process which hold | maintains the temperature and pressure of a reactor.
According to this configuration, in addition to the action obtained in any one of claims 1 to 3, the following action is obtained.
(1) Since it is equipped with a holding process, the reaction fluid can be completely carried out by maintaining the processing fluid generated by contact between the critical fluid and the waste water in a supercritical state or a subcritical state for a long time. Can be increased.

  Here, as a holding process, what hold | maintains the temperature of a reactor at 200-500 degreeC, Preferably it is 250-450 degreeC, More preferably, it is the range of 350-400 degreeC, and a pressure is the range of 20-35 MPa. In the same manner as described in the first aspect, this is to maintain the ability to decompose the hardly decomposable substance in the wastewater by the critical fluid.

  The holding time is suitably from 0.1 to 60 minutes, preferably from 1 to 30 minutes. As the retention time becomes shorter than 1 minute, depending on the type of the hardly decomposable substance, there is a tendency to show that the decomposition process becomes incomplete. As the retention time becomes longer than 30 minutes, the wastewater treatment time becomes longer. There is a tendency for efficiency to decrease. In particular, when the time is shorter than 0.1 minutes or longer than 60 minutes, these tendencies are remarkable, so that neither is preferable.

Invention of Claim 5 of this invention is a waste-water-treatment method of any one of Claims 1 thru | or 4, Comprising: The pH adjuster is added to the said waste_water | drain, and pH of the said waste_water | drain is 7-13 preferably. Has a configuration with a pH adjustment step of adjusting to 10-12.
With this configuration, in addition to the action obtained in any one of claims 1 to 4, the following action is obtained.
(1) Since a pH adjusting step for adjusting the pH of the waste water to 7 to 13, preferably 10 to 12, is provided, no harmful gas such as hydrogen cyanide is generated even when the waste water contains thiocyanate ions. In addition to being excellent in safety, it is also excellent in safety and environmental conservation.
(2) Since a pH adjustment step is provided, even when an acidic substance such as sulfuric acid is generated as a decomposition product in the processing fluid, it can be changed from substantially neutral to basic, and corrosion of metallic materials in the reactor can be prevented. This can increase the durability of the reactor.

Here, as a pH adjuster, 1 or more types of alkali agents, such as NaOH and KOH, are used.
As an addition amount of a pH adjuster, 2-5 equivalent times with respect to the ionic species made into object, Preferably 2.5-5 equivalent times is used. As the amount added is less than 2.5 equivalent times, the treatment fluid tends to be acidic and corrosivity tends to increase. In particular, when the amount is less than 2 equivalent times, this tendency becomes remarkable, which is not preferable. In addition, as the number of equivalents exceeds 5 equivalents, basic salts are likely to precipitate in the treatment fluid, which may cause clogging of the reactor and the like, and the metal material of the reactor tends to corrode in the high-temperature alkaline aqueous solution. It is not preferable.

  As the pH of the wastewater in the pH adjustment step becomes smaller than 10, depending on the type of harmful substances in the wastewater, hydrogen cyanide and the like when the treatment fluid is likely to be acidic and corrosive, and the wastewater contains thiocyanate ions. As the pH becomes higher than 12, a basic salt precipitates in the processing fluid, which may cause clogging of the reactor or the like, and the metallic material of the reactor is a high-temperature alkaline aqueous solution. There is a tendency to corrode easily. In particular, when the pH is smaller than 7 or larger than 13, these tendencies are remarkable, so that neither is preferable.

The invention according to claim 6 of the present invention is the wastewater treatment method according to any one of claims 1 to 5, wherein oxidation is performed by adding an oxidizing agent to the treatment fluid generated in the fluid contact step. It has the structure provided with the agent addition process.
With this configuration, in addition to the action obtained in any one of claims 1 to 5, the following action is obtained.
(1) Since an oxidizing agent addition step for adding an oxidizing agent to the processing fluid is provided, the durability of the reactor is increased by making the oxidation-reduction potential of the processing fluid the oxidation side and making the metal material of the reactor difficult to be brittle. In addition, the oxidative decomposition of the waste water can be advanced.

Here, as an oxidizing agent used in the oxidizing agent addition step, hydrogen peroxide, oxygen gas, air, nitrogen tetrachloride gas, ozone gas, sodium metaperiodate, potassium dichromate, potassium permanganate, anhydrous chromic acid Any one or more of hypochlorous acid, hydrogen peroxide and the like can be used.
As addition amount of an oxidizing agent, 2-5 equivalent times with respect to the ionic species made into object, Preferably 2.5-5 equivalent times is used. As the amount added becomes less than 2.5 equivalents, the oxidation-reduction potential of the treatment fluid is less likely to be acidic, and base embrittlement tends to occur. In particular, when the amount is less than 2 equivalents, this tendency becomes significant, which is not preferable. . Moreover, since the consumption of an oxidizing agent increases and the waste water treatment expense tends to increase as it becomes more than 5 equivalent times, it is not preferable.

  The oxidant is preferably added to the processing fluid. This is because, when added to the wastewater, in the fluid contact process in which the wastewater and the critical fluid are brought into contact with each other, the oxidant is decomposed simultaneously with the contact with the critical fluid, and the effect as the oxidant cannot be exhibited. Therefore, it is preferable to add the oxidizing agent to the processing fluid in which the waste water is subjected to the reaction processing with the critical fluid.

By adjusting the amount of oxidizing agent added to the processing fluid, the oxidation-reduction potential of the processing fluid can be adjusted.
The oxidation-reduction potential of the processing fluid is preferably adjusted to −300 to +700 mV, preferably −200 to +500 mV. As the oxidation-reduction potential is on the reduction side from -200 mV, the critical fluid tends to easily embrittle the metal material such as the reactor, and as it becomes more acidic than +500 mV, the critical fluid corrodes the metal material such as the reactor. As a result, the amount of oxidant added to the treatment fluid increases and the wastewater treatment cost tends to increase. In particular, when the oxidation-reduction potential is on the reduction side from −300 mV or on the oxidation side from +700 mV, these tendencies tend to be remarkable, and neither is preferable.

The invention according to claim 7 of the present invention is the wastewater treatment method according to any one of claims 1 to 6, wherein the wastewater is generated when coal is gasified to produce fuel gas. The cooling water which cooled the wastes, such as coal ash and slag, and / or the washing | cleaning waste_water | drain which wash | cleaned the said fuel gas are included.
With this configuration, in addition to the action obtained in any one of claims 1 to 6, the following action is obtained.
(1) Cooling water that cools coal ash and slag generated during coal gasification, and cleaning wastewater that cleans fuel gas contain thiosulfate ions, thiocyanate ions, hexacyanoferrate ions, etc. Until now, there was only a treatment means by concentrating to dryness and treating it as industrial waste. However, by mixing or merging with a critical fluid, it is possible to hydrolyze and oxidize the hardly decomposable thiosulfate ions and the like, and to be remarkably excellent in workability and environmental conservation.

An eighth aspect of the present invention is the wastewater treatment method according to any one of the first to seventh aspects, wherein the critical fluid is generated at a coal gasification power plant or a thermal power plant. The high-temperature high-pressure water.
With this configuration, in addition to the action obtained in any one of claims 1 to 7, the following action is obtained.
(1) Since drainage treatment can be performed in a coal gasification power plant or a thermal power plant in which cooling water that cools slag, etc. or cleaning waste water that is washed with fuel gas is generated, it is not necessary to transport waste water, which is efficient.
(2) It is excellent in energy efficiency because it can produce high-temperature and high-pressure water in the critical state by effectively using the thermal energy of steam and auxiliary steam for driving steam turbines in coal gasification power plants and thermal power plants. . Moreover, the wastewater treatment system by a closed system can be constructed | assembled by reusing the processing fluid which processed the wastewater as a reaction fluid.

As described above, according to the wastewater treatment method of the present invention, the following advantageous effects can be obtained.
According to the invention of claim 1,
(1) Refractory thiosulfuric acid by contacting waste water containing at least one of thiosulfate ion, thiocyanate ion and hexacyanoferrate ion with a critical fluid such as supercritical water or subcritical water. Since ions and the like can be decomposed by hydrolysis and oxidation-reduction, until now there was only a processing means to concentrate and dry and process as industrial waste, but it was a simple process and very few man-hours, It is possible to provide a treatment method of waste water that can be decomposed by a treatment facility, is remarkably excellent in workability and environmental conservation, can be discharged into a public water area, and is remarkably excellent in environmental conservation.

According to invention of Claim 2, in addition to the effect of Claim 1,
(1) Treatment of these wastewaters by using industrial wastewater such as phenol, benzene, toluene, etc., NO ₂ ⁻ , Fe ²⁺ , sulfides, heavy metal ions, etc., and wastewater such as sewage as reaction fluids. It can be performed simultaneously with the treatment of thiosulfate ions, thiocyanate ions, and hexacyanoferrate ions, and a wastewater treatment method that provides high treatment efficiency can be provided.

According to invention of Claim 3, in addition to the effect of Claim 1 or 2,
(1) Since a waste water pressurizing step for pressurizing waste water is provided, a waste water treatment method capable of maintaining the pressure of the critical fluid in contact with the waste water in the reactor and increasing the reaction treatment efficiency is provided. can do.
(2) The wastewater is heated to a high temperature only after it joins the critical fluid, and at the same time, the harmful substances in the system are decomposed, so even if the wastewater is corrosive, the reactor is corrosive. It is possible to provide a wastewater treatment method capable of shortening the exposure time to the environment and enhancing the durability of the reactor.

According to the invention of claim 4, in addition to the effect of any one of claims 1 to 3,
(1) Since it is equipped with a holding process, the reaction fluid can be completely carried out by maintaining the processing fluid generated by contact between the critical fluid and the waste water in a supercritical state or a subcritical state for a long time. It is possible to provide a wastewater treatment method capable of increasing the pressure.

According to invention of Claim 5, in addition to the effect of any one of Claims 1 to 4,
(1) Since a pH adjusting step for adjusting the pH of the waste water to 7 to 13, preferably 10 to 12, is provided, no harmful gas such as hydrogen cyanide is generated even when the waste water contains thiocyanate ions. It is possible to provide a wastewater treatment method which is excellent in safety, excellent in safety and environmentally safe.
(2) Since a pH adjustment step is provided, even when an acidic substance such as sulfuric acid is generated as a decomposition product in the processing fluid, it can be changed from substantially neutral to basic, and corrosion of metallic materials in the reactor can be prevented. It is possible to provide a wastewater treatment method that can prevent and increase the durability of the reactor.

According to invention of Claim 6, in addition to the effect of any one of Claims 1 to 5,
(1) Since an oxidizing agent addition step for adding an oxidizing agent to the processing fluid is provided, the durability of the reactor is increased by making the oxidation-reduction potential of the processing fluid the oxidation side and making the metal material of the reactor difficult to be brittle. In addition, it is possible to provide a wastewater treatment method capable of promoting oxidative decomposition of wastewater.

According to the invention described in claim 7, in addition to the effect of any one of claims 1 to 6,
(1) Cooling water that cools coal ash and slag generated during coal gasification, and cleaning wastewater that cleans fuel gas contain thiosulfate ions, thiocyanate ions, hexacyanoferrate ions, etc. Until now, there was only a processing means to condense and dry it and treat it as industrial waste, but by mixing or joining it with a critical fluid, it decomposes and decomposes refractory thiosulfate ions etc. by hydrolysis and oxidation reduction Therefore, it is possible to provide a wastewater treatment method remarkably excellent in workability and environmental conservation.

According to the invention described in claim 8, in addition to the effect of any one of claims 1 to 7,
(1) Since wastewater treatment can be performed in coal gasification power plants and thermal power plants that generate cooling water that cools slag, etc., or cleaning wastewater that is washed with fuel gas, it is not necessary to transport wastewater and is efficient and energy-saving It is possible to provide an excellent wastewater treatment method.
(2) Since the heat energy of steam and auxiliary steam for driving steam turbines in coal gasification power plants and thermal power plants can be used effectively, high-temperature and high-pressure water in the critical state can be produced. An excellent wastewater treatment method can be provided. Moreover, the wastewater processing method which can construct | assemble the wastewater treatment system by a closed system can be provided by reusing the processing fluid which processed the wastewater as a reaction fluid.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 4 is a system configuration diagram of the reaction apparatus according to Embodiment 1 of the present invention.
In FIG. 4, 1 is a reaction apparatus in the first embodiment, 2 is a reaction fluid such as water or an aqueous alcohol solution, 3 is a reaction fluid tank for storing the reaction fluid 2, and 4 is introduced by the reaction fluid 2 in the reaction fluid tank 3. The critical fluid supply path 5 is an on-off valve disposed in the critical fluid supply path 4, and 6 is disposed in the critical fluid supply path 4 on the downstream side of the on-off valve 5, and the reaction fluid 2 is placed in the supercritical region or subcritical state. A first pressurizing device that pressurizes the pressure region, 7 is a check valve disposed in the critical fluid supply path 4 on the downstream side of the first pressurizing device 5, and 8 is a critical pressure on the downstream side of the check valve 7. A first heating device 9 is disposed in the fluid supply path 4 and heats the reaction fluid 2 to a temperature range of the supercritical region or the subcritical region. The formed critical fluid supply port. The reaction fluid 2 is changed to a supercritical fluid or a subcritical fluid (hereinafter referred to as critical fluid) in a supercritical state or a subcritical state by the first pressurizing device 6 and the first heating device 8, and the reactor is supplied from the critical fluid supply port 9. Supplied to the upper part 22.

10 _organics, ^NO 2 -, ^{Fe 2+,} sulfides, industrial containing heavy metal ions like waste water, sewage, chemical oxygen demand, such as sludge (COD) waste water requiring high processing, coal, fossil oil such as Drainage generated from coal gasification power generation equipment using fuel, thermal power generation equipment, waste treatment equipment that melts and treats waste such as sludge, 11 is a drainage tank for storing wastewater 10, and 12 is a drainage tank 11 The drainage supply path into which the drainage 10 is introduced, 13 is an on-off valve disposed in the drainage supply path 12, 14 is disposed in the drainage supply path 12 downstream of the on-off valve 13, and the drainage 10 is placed in the supercritical region or A second pressurizing device that pressurizes the pressure region in the subcritical region, 15 is a check valve disposed in the drainage supply passage 12 on the downstream side of the second pressurization device 14, and 16 is a downstream portion of the drainage supply passage 12. Drain supply port connected and formed in the reactor upper part 22 described later A.
17 is a pH adjusting agent such as an aqueous solution of an alkaline agent such as NaOH or KOH, 18 is a pH adjusting agent tank in which the pH adjusting agent 17 is stored, 19 is connected to the pH adjusting agent tank 18, and the other end is opened and closed. A pH adjusting agent supply path 20 connected to the drainage supply path 12 on the upstream side of the second pressurizing device 14 on the downstream side of the valve 13 is introduced into the pH adjusting agent supply path 19. Open / close valve. The drainage 10 is pressurized under a pressure condition in which a pH adjusting agent 17 is added as necessary to adjust the pH to 7 to 13 and preferably 10 to 12 and to be in a supercritical state or a subcritical state by the second pressurizing device 14. Then, it is supplied from the waste water supply port 16 to the reactor upper part 22.

Reference numeral 21 denotes a reactor whose inner wall surface is formed in a vertically long cylindrical shape and is formed substantially vertically. Reference numeral 22 is an upper part of the reactor formed on the upper side of the reactor 21 and provided with a critical fluid supply port 9 and a drainage supply port 16. , 23 is a confluence portion of the reactor upper part 22 where the critical fluid supplied from the critical fluid supply port 9 collides with the waste water supplied from the drainage supply port 16, and 24 is a confluence part 23 of the reactor upper part 22. A reactor lower portion 25, which is disposed below and communicates with the reactor upper portion 22, is a reactor bottom portion having a funnel shape at the bottom of the reactor lower portion 24.
Reference numeral 26 denotes a second heating device that is disposed outside the reactor 21 (reactor upper part 22, reactor lower part 24, reactor bottom part 25) and heats the reactor 21 to a predetermined temperature.

27 is an oxidizing agent in the form of an aqueous solution such as hydrogen peroxide, 28 is an oxidizing agent tank in which the oxidizing agent 27 is stored, 29 is an oxidizing agent supply path into which the oxidizing agent 27 in the oxidizing agent tank 28 is introduced, and 30 is an oxidizing agent. The on-off valve 31 provided in the supply passage 29 is a third pressurization provided in the oxidant supply passage 29 downstream of the on-off valve 30 to pressurize the oxidant 27 to the supercritical region or subcritical region pressure region. 32, a check valve disposed in the oxidant supply path 29 on the downstream side of the third pressurizing apparatus 31, and 32a, a lower part of the reactor below the merging section 23, to which the downstream part of the oxidant supply path 29 is connected. 22 is an oxidant supply port formed at 22.
In addition, when using gaseous forms, such as oxygen gas and air, as an oxidizing agent, the pressure vessel etc. which were filled with the oxidizing agent instead of the oxidizing agent tank 28 are used.

  Reference numeral 33 denotes a processing fluid discharge path connected to the reactor bottom 25, and the processing fluid generated by processing the waste water in the reactor 21 with the critical fluid is discharged from the reactor 21. 34 is a cooling device disposed in the processing fluid discharge passage 33 for cooling the processing fluid, and 35 is disposed in the processing fluid discharge passage 33 on the downstream side of the cooling device 34 and is a solid such as an inorganic salt which is a decomposition product from the processing fluid. A solid-liquid separation device that separates an object, 36 is a gas-liquid separation device disposed in a processing fluid discharge passage 33 on the downstream side of the solid-liquid separation device 35, and 37 is a vapor discharge connected to an upper portion of the gas-liquid separation device 36. , 38 is a pressure reducing device such as a pressure reducing valve or orifice disposed in the vapor discharge path 37, 39 is a liquid discharge path connected to the lower part of the gas-liquid separator 36, and a processing fluid flows, and 40 is arranged in the liquid discharge path 39. A pressure reducing device such as a pressure reducing valve provided.

A wastewater treatment method using the reactor according to Embodiment 1 configured as described above will be described.
First, the first heating device 8 and the second heating device 26 of the reaction apparatus 1 are heated to a predetermined temperature, the predetermined reaction fluid 2 is stored in the reaction fluid tank 3, and the drainage 10 is stored in the drain tank 11. Next, in the critical fluid supply path 4, when the on-off valve 5 is opened and the first pressurizing device 6 is driven, the reaction fluid 2 is introduced into the critical fluid supply path 4, and the reaction fluid 2 is supercritical or subcritical. Pressurized to the pressure range of the region. Further, the first heating device 8 is heated to the temperature range of the supercritical region or the subcritical region to generate a critical fluid, and the generated critical fluid travels through the critical fluid supply path 4 toward the critical fluid supply port 9. (End of critical fluid generation process)
On the other hand, in the drainage supply path 12, the on-off valve 13 is opened to supply drainage 10 to the drainage supply path 12.
At this time, if necessary, the on-off valve 20 is opened and the pH adjusting agent 17 is added to the waste water 10 to adjust the pH of the waste water to 7 to 13, preferably 10 to 12. (End of pH adjustment step) The pH of the wastewater can be measured with a pH meter (not shown) disposed in the drainage supply passage 12 upstream of the second pressurizing device 14 on the downstream side of the pH adjusting agent supply passage 19. it can. In addition, the pH of the treatment fluid can be measured by a pH meter (not shown) disposed in the treatment fluid discharge path 33 and the liquid discharge path 39, and the pH of the waste water can be adjusted based on the measured pH.
Next, when the second pressurizing device 14 is driven to pressurize the drainage 10 to the supercritical region or the subcritical region of the reaction fluid 2, the pressurized drainage 10 passes through the drainage channel 12 to the drainage supply port. Head to 16. (End of drainage pressurization process)

The critical fluid in the critical fluid supply path 4 toward the critical fluid supply port 9 and the wastewater in the drainage supply path 12 toward the drainage supply port 16 are the upper part of the reactor 21 of the reactor 21 heated by the second heating device 26. Two fluids supplied from the critical fluid supply port 9 and the drainage supply port 16 to the merging portion 23 of 22 collide with each other, and come into contact with each other. The two fluids joined at the junction 23 form a downward flow that descends the reactor upper part 22, and the waste water reacts with the critical fluid in the downward flow of the junction 23 and the reactor 21 to generate a processing fluid. (End of fluid contact process)
At this time, if necessary, the on-off valve 30 is opened, and the oxidant 27 is added to the processing fluid in the reactor lower part 24 from the oxidant supply port 32a formed in the upper part of the reactor lower part 24. (Oxidant addition step) The oxidation-reduction potential of the processing fluid is -300 to +700 mV, preferably -200 to +500 mV. The oxidation-reduction potential of the processing fluid can be measured by an oxidation-reduction potentiometer (not shown) disposed in the processing fluid discharge path 33 and the liquid discharge path 39. The amount of the oxidizing agent added based on this can be adjusted.

The processing fluid is further subjected to a reaction process in the reactor upper part 22 and the reactor lower part 24 which are kept warm by the second heating device 26. Further, since the reactor bottom 25 is formed in a funnel shape, the residence time of the processing fluid in the reactor 21 can be lengthened, and unreacted components are decomposed in the reactor upper part 22 and the reactor lower part 24. Processed (the holding step).
The processing fluid processed in the reactor 21 is discharged out of the reactor 21 through a processing fluid discharge path 33 connected to the reactor bottom 25.
After the processing fluid in the processing fluid discharge passage 33 is cooled by the cooling device 34, solids such as unreacted material are separated by the solid-liquid separation device 35. Further, the processing fluid is gas-liquid separated by the gas-liquid separation device 36, the gas is discharged from the vapor discharge passage 37 through the decompression device 38 to the atmosphere and the exhaust gas treatment device (not shown), and one liquid is decompressed from the liquid discharge passage 39. The pressure is reduced through the device 40, and after neutralization or the like is performed as necessary, it is discharged into a public water area or sent to a water purification device (not shown) equipped with a biological treatment tank or the like. Further, it is reused as a reaction fluid as necessary.

According to the wastewater treatment method using the reaction apparatus in the first embodiment as described above, the following effects are obtained.
(1) Since the critical fluid in the supercritical state or the subcritical state is combined with the pressurized wastewater to perform the reaction treatment, the wastewater can be treated continuously, and it is excellent in workability and energy saving.
(2) Since the wastewater is heated to a high temperature in the joining portion 23 only after joining the critical fluid, and harmful substances in the wastewater are decomposed at the same time as being heated, even if the wastewater is corrosive, The time during which the reactor 21 is exposed to the corrosive environment can be shortened, and the durability of the reactor 21 can be enhanced.
(3) Since a holding process is provided, the processing fluid generated by contact between the critical fluid and the waste water can be retained in a supercritical state or a subcritical state, and the reaction process can be performed completely, thereby increasing the reaction efficiency. be able to. Unreacted components can also be decomposed in the reactor upper part 22 and the reactor lower part 24, and the efficiency of the waste water decomposition reaction can be increased.
(4) Since a pH adjusting step for adjusting the pH of the waste water to 7 to 13, preferably 10 to 12, is provided, even when the waste water contains thiocyanate ion, no harmful gas such as hydrogen cyanide is generated and workability And environmental conservation.
(5) Since a pH adjustment step is provided, even when an acidic substance such as sulfuric acid is generated as a decomposition product in the processing fluid, it can be neutralized almost neutrally, and the metal material of the reactor 21 is corroded. It is difficult to increase the durability of the reactor 21.
(6) Since an oxidizing agent addition step of adding an oxidizing agent to the processing fluid is provided, the durability of the reactor 21 is reduced by making the oxidation-reduction potential of the processing fluid the oxidation side and making the metal material of the reactor 21 difficult to be embrittled. And the oxidative decomposition of the waste water can be advanced.

Hereinafter, the present invention will be specifically described by way of examples. The present invention is not limited to these examples.
(Example 1)
Predetermined amounts of sodium thiosulfate, sodium thiocyanate, and potassium ferrocyanide were dissolved in ion-exchanged water to prepare wastewater samples of Experimental Examples 1-14. A predetermined amount of sodium hydroxide as a pH adjuster was added to each drainage sample to adjust the pH to 11.3-12.6. Next, pressurize ion-exchanged water as a reaction fluid to various pressures and heat it to create a critical fluid in the supercritical or subcritical state, and pressurize to the same pressure as each critical fluid. Each wastewater sample was mixed in a stainless steel reactor to prepare a treatment fluid. The mixing time was 20 seconds.
Here, the amount of the critical fluid was set to 10 times the amount of the drainage sample. During this period, the temperature and pressure of the reactor were maintained under the same conditions as the temperature and pressure of the critical fluid. After the reactor was depressurized and the processing fluid was cooled, the processing fluid was analyzed.
In Experimental Examples 4, 9, and 12, hydrogen peroxide water as an oxidant was added twice as much as each ionic species to the processing fluid in the reactor immediately after mixing the critical fluid and the drainage sample.
The target ionic species of the wastewater sample in Experimental Examples 1 to 14, the processing conditions (processing fluid temperature, pressure, holding time, presence / absence of oxidizing agent), the concentration of each ionic species of the draining sample and the processing fluid, COD, pH, processing fluid (Table 1) summarizes the sulfate ion concentration, ion decomposition rate, COD decomposition rate, and reactor corrosion state.
The ion decomposition rate is calculated using a formula of (100 (%) − (target ion concentration in treatment fluid ÷ target ion concentration in wastewater sample) × 100), and the COD decomposition rate is , (100 (%) − (COD of processing fluid ÷ COD of drainage sample) × 100).

The evaluation of the state of corrosion in (Table 1) is a visual inspection of the external appearance of the reactor. The case where the discoloration or erosion due to the corrosion is hardly observed is ◯, the case where it is easily recognized is △, the remarkable Those in which discoloration, erosion, etc. were observed were represented as x.
In Experimental Examples 1 to 10, the concentration of sulfate ions in the processing fluid is measured because it is assumed that sodium thiosulfate, sodium thiocyanate, and potassium ferrocyanide are decomposed by the oxidation reaction shown in (Chemical Formula 1). This is because it can be inferred that in a wastewater sample in which sodium thiosulfate and sodium thiocyanate are dissolved, the decomposition progresses as the concentration of sulfate ions in the treatment fluid increases. In (Chemical Formula 1), (Formula 1) represents an oxidation reaction of sodium thiosulfate, (Formula 2) represents an oxidation reaction of sodium thiocyanate, and (Formula 3) represents an oxidation reaction of potassium ferrocyanide.

From (Table 1), it became clear that the decomposition reaction of harmful substances in the wastewater sample proceeds because the COD decomposition rate increases as the temperature and pressure of the processing fluid increase. It was also revealed that a high ion decomposition rate of 99% or higher can be obtained when the temperature is 400 ° C. or higher and the pressure is 20 MPa or higher.
In addition, since the concentration of sulfate ions in the processing fluid is increased by adding the oxidizing agent, it is clear that the decomposition reaction proceeds more than in the case of no addition. Further, since the corrosion of the reactor is not recognized so much by adding the oxidant, it is clear that the metal material of the reactor can be hardly made brittle and the durability of the reactor can be improved.
Moreover, since the pH adjuster is added to the wastewater sample to adjust the pH of the wastewater sample to 7 to 13, even when an acidic substance such as sulfuric acid is generated in the processing fluid as a decomposition product, the pH is 8.3 to 12.4. It became clear that it was possible to change from a neutral to basic.

(Example 2)
Next, an example in which wastewater treatment is performed using the reaction apparatus described in Embodiment 1 will be described.
FIG. 5 is a graph showing the relationship between the temperature at the bottom of the reactor and the ion decomposition rate in the reactor of the first embodiment.
A sample obtained by dissolving sodium thiosulfate in ion-exchanged water so that the S ₂ O ₃ ²⁻ concentration was 1000 ppm was prepared as a drainage sample. The wastewater sample (25 ° C.) was pressurized to 25 MPa and supplied from the wastewater supply port to the junction of the reactor. At the same time, the ion-exchanged water was heated to 400 ° C. and a critical fluid pressurized to 25 MPa was supplied from the critical fluid supply port to the junction of the reactor, and the two fluids collided to contact and merge. The ratio of the critical fluid flow rate to the drainage sample flow rate was 185: 20.
FIG. 5 shows that the ion decomposition rate tends to increase as the temperature at the lower part of the reactor increases, and it is clear that a high ion decomposition rate of 80% or higher can be obtained at 360 ° C. or higher.

  The present invention relates to a method for treating wastewater generated from thermal power generation equipment, gas production equipment, petroleum refining equipment, waste treatment equipment, etc., and is excellent in workability and energy saving, and has been concentrated and dried until now. It is possible to provide a wastewater treatment method that can realize a decomposition treatment of wastewater containing a hardly decomposable compound that has only been treated as an industrial waste at a low cost and is extremely excellent in environmental conservation.

Diagram showing the relationship between water temperature and specific heat capacity at each pressure Diagram showing the relationship between water temperature and density at each pressure Shows the relationship between the concentration of temperature and _Na 2 SO ₄ of a saturated aqueous _Na 2 SO ₄ solution at a pressure of 25MPa System configuration diagram of reaction apparatus in embodiment 1 The figure which showed the relationship between the temperature of the lower part of a reactor in the reaction apparatus of Embodiment 1, and an ion decomposition rate

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction apparatus 2 Reaction fluid 3 Reaction fluid tank 4 Critical fluid supply path 5 On-off valve 6 1st pressurization apparatus 7 Check valve 8 1st heating apparatus 9 Critical fluid supply port 10 Drain 11 Drain tank 12 Drain supply path 13 On-off valve DESCRIPTION OF SYMBOLS 14 2nd pressurization apparatus 15 Check valve 16 Drain supply port 17 pH adjuster 18 pH adjuster tank 19 pH adjuster supply path 20 On-off valve 21 Reactor 22 Reactor upper part 23 Merge part 24 Reactor lower part 25 Reactor bottom part 26 Second Heating Device 27 Oxidant 28 Oxidant Tank 29 Oxidant Supply Path 30 On-off Valve 31 Third Pressurizer 32 Check Valve 32a Oxidant Supply Port 33 Processing Fluid Discharge Path 34 Cooling Device 35 Solid-Liquid Separator 36 Gas Liquid separator 37 Vapor discharge path 38 Pressure reducing device 39 Liquid discharge path 40 Pressure reducing apparatus

Claims (8)

  A critical fluid generating step of pressurizing and heating the reaction fluid to bring the reaction fluid into a supercritical or subcritical critical state, and the critical fluid, thiosulfate ions, and thiocyanate ions obtained in the critical fluid generating step. A fluid contact step of contacting a wastewater containing at least one of hexacyanoferrate ions in a reactor and reacting the wastewater with the critical fluid to generate a treatment fluid. Characterized wastewater treatment method.   The wastewater treatment method according to claim 1, wherein the reaction fluid is wastewater containing or not containing at least one of thiosulfate ions, thiocyanate ions, and hexacyanoferrate ions at a low concentration. .   The wastewater treatment method according to claim 1 or 2, further comprising a wastewater pressurizing step for pressurizing the wastewater in the fluid contact step.   The holding step of holding the temperature and pressure of the reactor in which the critical fluid and the waste water are brought into contact with each other in the fluid contact step is provided. Wastewater treatment method.   The wastewater according to any one of claims 1 to 4, further comprising a pH adjustment step of adjusting a pH of the wastewater to 7 to 13, preferably 10 to 12, by adding a pH adjusting agent to the wastewater. Processing method.   The wastewater treatment method according to any one of claims 1 to 5, further comprising an oxidant addition step of adding an oxidant to the treatment fluid generated in the fluid contact step.   The waste water is cooling water obtained by cooling waste such as coal ash and slag generated when gasifying coal to generate fuel gas, and / or washing waste water obtained by washing the fuel gas. The wastewater treatment method according to any one of claims 1 to 6.   The wastewater treatment method according to any one of claims 1 to 7, wherein the critical fluid is high-temperature high-pressure water generated in a coal gasification power plant or a thermal power plant.

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