JP3499782B2 - Method and apparatus for removing trace organic compounds in water - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method and an apparatus for removing a trace amount of organic compounds dissolved in groundwater or the like.

[0002]

2. Description of the Related Art Environmental protection has become a major issue. For example, organic solvents used in degreasing materials for dry cleaning, cleaning solutions for electronic and metal industries, etc. often contain organic compounds that are harmful to the human body, and are usually discharged after being subjected to some detoxification treatment. It However, it can be said that it will be discharged untreated, and it may pollute soil and groundwater. Examples of organic compounds regarded as harmful substances include benzene and organic chlorine compounds (eg, trichloroethylene, tetrachloroethylene, trichloroethane, carbon tetrachloride), and many of them have environmental standards announced by the Environmental Agency. As a method of removing this kind of organic compound in groundwater, conventionally, an adsorption method with activated carbon, a decomposition / reduction treatment method with a catalyst, a decomposition treatment method with ultraviolet rays, a decomposition treatment method with microorganisms, etc. have been proposed.

The activated carbon adsorption method is a method in which ground water is brought into contact with activated carbon having a large surface area by, for example, granulation and the organic compounds in the ground water are adsorbed by the activated carbon to be removed, and a high removal rate can be obtained. It takes time and effort to regenerate and replace the activated carbon, and it has disadvantages such as high running cost. Further, it is unavoidable that the removal rate changes with time. In the decomposition / reduction treatment method using a catalyst, an organic compound extracted in a gas phase is brought into contact with a specific oxidative decomposition catalyst or the like to make it harmless (see, for example, JP-A-8-693). Similar to the adsorption method, it takes time and money to replace the catalyst, and the removal rate changes due to deterioration of the catalyst.

The decomposition treatment method using ultraviolet rays decomposes organic compounds by using ultraviolet rays and a photocatalyst, but has a drawback of high cost. A method for decomposing a microorganism is to decompose a specific organic compound by a specific microorganism (see, for example, JP-A-2-92).
No. 274, etc.), it is not possible to expect a high treatment effect for substances such as groundwater that may contain many kinds of organic compounds.

As another method, a treatment method has been proposed in which an organic chlorine compound is extracted in a gas phase from water containing the organic chlorine compound and is brought into contact with oil so that the organic chlorine compound is absorbed by the oil. (See JP-A-5-50096). By evaporating the oil that has absorbed the organic chlorine compound to remove the organic chlorine compound, the oil can be reused, continuous operation becomes possible, and there is an advantage that running costs can be reduced, such as the need for oil replacement. However, there is a disadvantage that many additional facilities such as a heating means for oil and a means for recovering the evaporated organic chlorine compound are required.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art,
Its purpose is to enable continuous operation for a long time while maintaining a high removal rate, and because it does not require parts replacement, the running cost is low, and since many additional equipment is not required, the device is compact. An object of the present invention is to provide a method and a device for removing a trace amount of organic compounds in water that can be converted into water.

[0007]

According to the present invention, the above object is basically to extract an organic compound from a water containing a trace amount of the organic compound into a gas phase, and burn the extracted organic compound with air. A method for removing a trace amount of organic compounds in water, and means for pumping water containing trace organic compounds, means for extracting an organic compound from the pumped water into a gas phase,
And a means for burning the extracted gas together with air, the apparatus for removing a trace amount of organic compounds in water.

According to the present invention, a trace amount of an organic compound contained in groundwater or the like is extracted into the gas phase by bringing it into contact with a gas (for example, air). The gas containing the extracted organic compound is mixed with a fuel such as city gas and subjected to combustion to achieve complete decomposition of the organic compound. For example, in the case of a compound containing only carbon and hydrogen, C-H + air → CO ₂ + H ₂ O Example: benzene C ₆ H ₆ + 7.5O ₂ → 6CO ₂ + 3H ₂ O

In the case of a compound containing carbon, hydrogen, and halogen (X), C—H—X + air + H ₂ O → CO ₂ + HX Example: trichlorethylene C ₂ HCl ₃ + 1.5O ₂ + H ₂ O → 2CO ₂ + 3HC
Example: tetrachloroethylene C ₂ HCl ₄ + O ₂ + 2H ₂ O → 2CO ₂ + 4HCl

In the case of a compound containing carbon, hydrogen, and nitrogen, C—H—N + air + H ₂ O → CO ₂ + H ₂ O + NOx Example: pyridine C ₅ H ₁₁ N + 6.75O ₂ → 5CO ₂ + 2.5H ₂ O +
Decomposes like NO 2.

Depending on the type of organic compound contained in groundwater, if it is an organic compound containing only carbon and hydrogen as described above, the by-product in the combustion exhaust gas produced by combustion is carbon dioxide gas. And water, and the flue gas can be released to the atmosphere as it is. Treated groundwater from which organic compounds have been removed can be discarded as waste water.

As described above, in the case of an organic compound containing nitrogen in addition to carbon and hydrogen, N as a by-product in the combustion exhaust gas.
Ox is included. Since the amount of organic compounds contained in groundwater to be treated is essentially trace and NOx as a by-product is also trace, it is possible to release flue gas as it is to the atmosphere, but if necessary, two-stage combustion It is also possible to use a conventionally known NOx treatment such as a method. Treated groundwater from which organic compounds have been removed may be discarded as it is as wastewater.

In the case of an organic compound containing halogen (eg, trichloroethylene, tetrachloroethylene, trichloroethane, carbon tetrachloride, etc.), hydrogen halide (HX: eg HCl as a by-product in the combustion exhaust gas is used. ) And other acidic substances are included, it is not always preferable to release them to the atmosphere as they are. Therefore, in a preferred embodiment of the present invention, the combustion exhaust gas obtained by burning the extracted organic compound is allowed to pass through the scrubber, where an acidic substance such as HX is absorbed to make the combustion exhaust gas harmless and then released to the atmosphere. I am trying to do it.

The form of the scrubber may be appropriately selected according to the type of by-products after combustion, and may be of a spray type or the like, but in the normal groundwater treatment, water and combustion exhaust gas are used. It is sufficient to use the form of contact. When the combustion exhaust gas comes into contact with water, acidic substances such as HX are absorbed by the water, and the combustion exhaust gas is rendered harmless.
The use of water after aeration treatment to separate organic compounds as the treated water in the scrubber is a preferable mode because the configuration of the apparatus and the circulation cycle can be simplified. Although the treated water discharged from the scrubber contains a trace amount of an acidic substance such as HX, its concentration is usually low, so there is no problem in discharging it as it is. If the pH of the treated water is expected to be out of the standard discharge range for sewage, the treated water is discharged after passing through a conventionally known ordinary neutralization device.

Any means can be used to extract the organic compound into the gas phase from the groundwater pumped up using a vacuum pump or the like.
The conventionally known aeration treatment devices such as shower type and bubble type are particularly effective from the viewpoint of ease of use. At that time, preferably, the pumped water is heated in order to enhance the extraction efficiency in the aeration treatment device. Although the heating means is optional, in order to improve the thermal efficiency of the entire apparatus, it is a preferable embodiment to perform heat exchange between the pumped water and the flue gas in which the extracted organic compound is burned. .
By such heat exchange treatment, the gas-liquid separation speed can be increased, and as a result, the liquid layer tank (for example, in the aeration processor) can be downsized, and the blower that sends air to the aeration processor. The capacity of can be downsized, and the entire device can be downsized.

There is no particular limitation on the combustion fuel for burning the organic compound extracted from groundwater with air.
It is optional such as gas fuel, liquid fuel, and solid fuel. However, considering that it is necessary to expose the entire amount of air in which the organic compound is dispersed to the combustion field in a short time, it is preferable to use a gas fuel, and city gas is used as a combustion fuel because it is easily available. Use is recommended. Further, when using a liquid fuel or a solid fuel, it is recommended to atomize (atomize) it by an appropriate means and use it in a gas state.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an entire apparatus for removing a trace amount of organic compounds in water according to the present invention. A suction pump 2 is arranged in the middle of the pumping pipe 1 that reaches the groundwater W, and the pumped groundwater W passes through the heat exchanger 3 and is sent to the aeration processor 4. The pumping pipe 1 may be arranged not only in groundwater but also in an appropriate water channel such as a drainage channel from a factory where organic compounds are considered to be mixed.

In this example, the aeration processing unit 4 is an aeration process by aeration, and the ground water W pumped up is put into the aeration processing unit 4 from above, and the air from the blower 5 is blown from below. The groundwater W comes into contact with the blown air, and if the groundwater contains an organic compound such as an organic chlorine compound,
Following the aeration process, organic compounds are expelled from the water,
Extracted into the air.

The air containing the extracted organic compound exits the aeration processor 4 and passes through the pipe line 6 to reach the burner 7. The pipeline 6 has a branch pipe 8 from which fuel such as city gas is supplied. The premixture of the air containing the extracted organic compounds and the city gas as the fuel is burned in the burner 7. Premixed combustion facilitates ensuring that all of the air participates in combustion. The amount of fuel to be supplied is an amount that allows complete combustion to proceed in consideration of the flow rate of air containing organic compounds.

Upon combustion, the extracted organic compound is completely decomposed, and carbon dioxide gas, water,
Change to nitrogen oxides, hydrogen halides, etc. Usually, organic compounds dissolved in groundwater are unspecified substances,
It cannot be denied that it contains nitrides and halogen compounds. Therefore, in this example, the total amount of the combustion exhaust gas after combustion is sent to the scrubber 9 to prevent the release of hydrogen halide (HX) and the like into the atmosphere, and the NOx is converted into nitric acid by dissolving it in water, for example. By applying
Prevents its release into the atmosphere.

Further, since the combustion exhaust gas has a high heat energy, the heat energy is also effectively utilized. That is, the combustion exhaust gas from the burner 7 is supplied to the conduit 10
After passing through the heat exchanger 3, heat is exchanged with the groundwater W pumped by the pump 2 and the temperature of the groundwater W is raised (usually 100 ° C. or lower). By heating the groundwater W by this heat exchange, the gas-liquid separation speed in the aeration treatment device 4 can be increased, and as a result, the aeration treatment device 4 can be downsized, and the aeration treatment device 4 can be further reduced. The capacity of the blower 5 that sends in air can also be reduced, and the overall size of the device can be reduced.

The flue gas discharged from the heat exchanger 3 flows into the scrubber 9 through the pipe 11. In this example, the scrubber 9 is of a form in which water and combustion exhaust gas are brought into contact with each other, and as the treated water Wa, the groundwater W after the treatment in which the organic compound is separated in the exhibitor 4 is taken in through the pipe 12. . The groundwater after the treatment comes into contact with the combustion exhaust gas in the scrubber 9, takes in an acidic substance (hydrogen halide, etc.) in the combustion exhaust gas, and renders the combustion exhaust gas harmless. The detoxified combustion exhaust gas is released from the scrubber 9 to the atmosphere.

The treated water Wa in the scrubber 9 is highly likely to contain a trace amount of an acidic substance such as hydrogen halide. However, since the concentration is usually low, there is no problem if it is discharged into the ground as sewage. If the pH of the treated water is expected to be out of the discharge standard value range for sewage, it is discharged after passing through a conventionally known ordinary neutralization device (not shown).

In the above example, groundwater is taken as the one to be treated, but it is also possible to suck the water impregnated in the soil by an appropriate means and use it as the treated water. As described above, the treated water may be directly taken in from the drainage channel of the factory waste liquid. Also, the heat exchanger 3
Although the aeration treatment device 4 and the aeration treatment device 4 are separately provided and connected to each other by a pipeline, the heat exchanger 3 can be incorporated in the aeration treatment device 4 (not shown), and the apparatus can be made more compact. it can.

Further, in the above explanation, it was explained that the total amount of the combustion exhaust gas from the burner 7 passes through the heat exchanger 3, but as shown in the figure, the bypass passage 12 and the flow control valve 13 are provided in the pipe passage 10. May be provided so that the flow rate of the combustion exhaust gas to the heat exchanger 3 can be controlled. By doing so, the heat balance balance can be made variable, whereby the temperature rise of the pumped water is adjusted, the pumped water boils in the aeration processor 4, and the steam containing the organic compounds contains steam. It is possible to reliably avoid a situation in which the fuel is mixed, and as a result, combustion in the burner 7 becomes disordered (for example, incomplete combustion).

[0026]

As described above, according to the present invention, it is possible to properly treat the organic compounds contained in groundwater and the like, and there is no need to replace activated carbon as compared with the conventional method. Therefore, maintenance-free operation can be performed for a long time, the apparatus can be simplified and downsized, and the running cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an entire apparatus for removing a trace amount of organic compounds in water according to the present invention.

[Explanation of symbols]

W ... Groundwater, 2 ... Pumping pump, 3 ... Heat exchanger, 4 ...
Aeration processor, 5 ... Blower, 7 ... Burner, 8 ... Fuel gas introduction line, 9 ... Scrubber

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-48-53560 (JP, A) JP-A-62-4489 (JP, A) JP-A-8-81890 (JP, A) JP-A-8- 243544 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F23G ^7/ 00-7/06 C02F 1/20 C02F 1/58

Claims (5)

(57) [Claims] 1. Water-containing trace organic compounds are aged and then aerated to extract the organic compounds into a gas phase, and the extracted organic compounds are burnt together with air to become trace organic compounds in water.
A method for removing a compound, which comprises the combustion exhaust gas obtained by burning the extracted organic compound and
A step of exchanging heat with water containing a large amount of organic compounds and a scrubbing of the flue gas produced by burning the extracted organic compounds.
The method for removing a trace amount of organic compounds in water , further comprising the step of releasing the compound into the air after passing through the bar . 2. The method for removing a trace amount of organic compounds in water according to claim 1, wherein water after aeration treatment to separate organic compounds is used as the treated water in the scrubber. 3. Combustion of burning extracted organic compounds
Heat exchange between exhaust gas and water containing the trace organic compounds
As a pre-step of the process, the flow of flue gas involved in heat exchange
The method of claim 1, further comprising the step of controlling the quantity.
The method for removing trace organic compounds in water according to 1 or 2 . 4. A means for drawing up water containing a trace amount of organic compounds, a heat exchange means for heating the drawn water by heat exchange, and heat.
A means for blowing air to the pumped water heated by the exchange means to extract an organic compound contained in the pumped water into a gas phase, a means for burning the extracted organic compound with air, and a combustion exhaust gas from the combustion means. For the heat exchange means
An apparatus for removing a trace amount of organic compounds in water, which comprises at least a means for introducing and a means for bringing a combustion exhaust gas from the combustion means into contact with water to dissolve a water-soluble substance in the combustion exhaust gas in water. 5. The combustion exhaust gas from the combustion means is used for the heat exchange.
The means for introducing into the heat exchange means further flows into the heat exchange means.
And a means for controlling the amount of combustion exhaust gas.
The trace amount organic compound removing device in water according to claim 4 .