JP2014128764A - Device and method for treating oil-containing wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain recycled water with reduced salinity concentration while reducing processing cost with a smaller equipment, with regard to an apparatus for treating oil-containing waste water containing scale components such as oil and Ca salt and sodium chloride. A simple processing device is proposed.
SOLUTION: An oil / water separator that separates and removes oil from wastewater (raw water), a chemical softener that separates and removes Ca by subjecting oil / water separation treated water discharged from the oil / water separation process to chemical softening, and chemical softening Heat treatment between the drain side of the oil-water separator and the incoming side of the chemical softener in a treatment device for oil-containing wastewater, which comprises a desalination device for desalinating the softened water discharged from the device An oil-containing structure comprising a device connected to the oil-water separation treated water discharged from the oil-water separation device, after the temperature of the oil-water separation treated water is raised through the heat exchanger a, and then supplied to the chemical softening device A wastewater treatment device is proposed.
[Selection] Figure 1

Description

  The present invention includes oil, coal, natural gas, shale gas, cold bed methane (CBM), oil sands, surplus oil, and other wastewater containing oil generated during production (referred to as “oil-containing wastewater”). In addition, the present invention relates to a treatment apparatus for oil-containing wastewater discharged from refineries and petrochemical plants, and a method for treating oil-containing wastewater.

  In recent years, with remarkable industrial development, population increase, and urban development in developing countries, needs for energy resources such as oil and natural gas are increasing more and more worldwide. In regions that produce a large amount of oil, coal, natural gas, and the like, there are many regions that lack water resources, and therefore, recycling of oil-containing wastewater that is generated along with these production and production is required. In particular, refineries and oil / coal chemical plants tend to be installed in the vicinity of energy resource production areas, and there is a shortage of water resources required for production and operation management, so there is a strong demand for recycling oil-containing wastewater. .

  On the other hand, oil-containing wastewater that is generated with the production and production of petroleum contains a large amount of sodium chloride, salt such as calcium and magnesium. is necessary.

  Conventionally, as a technique for desalting water containing sodium chloride, a method using a reverse osmosis membrane (RO), a method using electrodialysis (ED), a method using a distillation method, and the like have been performed. In addition, when the salinity concentration is low, ion exchange treatment or the like is also performed.

When RO, ED, or the evaporation method is used, a liquid in which salts such as calcium (Ca), magnesium (Mg), and silica (Si) are concentrated is discharged separately from the desalted treated water. .
If these salts are contained in the water to be treated, components with low solubility, such as calcium carbonate, calcium sulfate, calcium phosphate, magnesium hydroxide, silicate, etc., when concentrated by RO, ED or evaporation methods. Since it insolubilized and deposited and adhered to the surface of the film as a scale, there was a problem that the processing performance of the film was remarkably deteriorated.

  In addition, even when organic components are contained in the water to be treated, it is desalted by adhering to or insolubilizing the membrane such as RO membrane, or by growth on the membrane surface of microorganisms that decompose organic matter etc. Processing performance may be reduced.

  For this reason, about salt water containing an organic substance and a scale component, after removing an organic substance and a scale component previously, desalinating using RO and ED is proposed.

  For example, Patent Document 1 (Japanese Patent Publication No. 7-41243) relates to treatment of organic wastewater containing calcium ions and chlorine ions, and after removing calcium ions as water-insoluble salts, biological treatment is performed to remove organic components. It has been proposed to separate and filter sludge and then desalinate by electrodialysis.

  In Patent Document 2 (US Pat. No. US7815804B2), after deaerating waste water containing oil, organic matter, silica, hardness component, and salt, the hardness component was maintained at a pH of 10.5 or higher with a chemical softening device comprising a multistage tank. A method is proposed in which after separation under conditions, filtration, and subsequent removal of hardness components by ion exchange, followed by RO treatment at pH 10.5 or higher.

  In Patent Document 3 (Japanese Patent No. 3800449), organic wastewater containing high-concentration salts is chemically softened to lower the Ca concentration, and then biological treatment, coagulation sedimentation treatment, sand filtration treatment, microfiltration One or more treatments selected from the group such as treatment, and a treatment consisting of a combination of two or more are performed, then treated with RO, separated into concentrated water and treated water, and the treated water is recovered and concentrated water is electrodialyzed. There has been proposed a method of increasing the recovered amount of desalted treated water by separating it into desalted treated water and concentrated water and returning the treated water to the RO supply side.

Japanese Examined Patent Publication No. 7-41243 US Patent US7815804B2 Japanese Patent No. 3800449

  As a method for treating oil-containing wastewater containing sodium chloride, scale components, etc. in addition to oil, conventionally, many oil removal process facilities and scale component removal process facilities are provided in series, and these steps are repeated. After performing, the processing method which performs a desalination process was made | formed. For this reason, there has been a problem that the processing cost becomes high, such as an increase in equipment and an increase in equipment cost, and an increase in the cost of chemicals used in each process.

  Therefore, the present invention relates to a treatment apparatus and treatment method for oil-containing waste water containing scale components such as oil and Ca salt, and sodium chloride, and it is not necessary to repeat the oil removal step and the scale component removal step, and it is more compact. In this facility, a new oil-containing wastewater treatment method and treatment apparatus capable of obtaining recycled water with reduced salt concentration while reducing treatment costs is proposed.

  The present invention provides an oil / water separation device for separating and removing oil from waste water (raw water) containing oil, Ca salt and sodium chloride, and oil / water separation treated water discharged from the oil / water separation step by subjecting the oil / water to a chemical softening treatment. In the oil-containing wastewater treatment apparatus comprising: a chemical softening device that separates and removes Ca contained in the separation treated water; and a desalination device that desalinates the softened treatment water discharged from the chemical softening device. A heat exchanger A is connected between the waste water side of the apparatus and the incoming water side of the chemical softening device, and the temperature of the oil / water separation treated water discharged from the oil / water separator is passed through the heat exchanger A. An oil-containing wastewater treatment apparatus having a structure for supplying the chemical softening apparatus after the increase in the pressure is proposed.

  The present invention also includes an oil / water separation step of separating and removing oil from waste water (raw water) containing oil, Ca salt and sodium chloride, and chemical softening treatment of the oil / water separation treated water discharged from the oil / water separation step. In a method for treating oil-containing wastewater, comprising: a chemical softening treatment step for separating and removing Ca contained in the separation treated water; and a desalination treatment step for desalting the softening treatment water discharged from the chemical softening treatment step. Proposed is a method for treating oil-containing wastewater, characterized in that after the oil-water separation treated water discharged from the oil-water separation step is heated to raise the temperature of the oil-water separation treated water, chemical softening treatment is performed.

  According to the method and apparatus for treating oil-containing wastewater proposed by the present invention, it is not necessary to repeat the oil removal step and the scale component removal step, and the treatment is performed with smaller equipment and with reduced processing costs. Recycled water with reduced salt concentration can be obtained at low cost. Therefore, for example, in crude oil production or crude oil refining, it can be suitably used as water used for oil desalting, recycled water used for rig drilling injection, washing water in flue gas or desulfurization processes, and the like.

It is process drawing for demonstrating an example of the processing apparatus and processing method of the oil containing waste water which concern on this invention. It is process drawing for demonstrating the other example of the processing apparatus and processing method of the oil containing waste_water | drain which concerns on this invention. It is process drawing for demonstrating the further another example of the processing apparatus and processing method of the oil containing waste_water | drain which concerns on this invention. It is process drawing for demonstrating the further another example of the processing apparatus and processing method of the oil containing waste_water | drain which concerns on this invention. It is process drawing for demonstrating the further another example of the processing apparatus and processing method of the oil containing waste_water | drain which concerns on this invention. It is the figure which showed the structural example of the slurry circulation type high-speed coagulation sedimentation basin. It is the figure which showed the structural example of the sludge blanket type | mold high-speed coagulation sedimentation basin. It is the figure which showed the process example in the case of performing ED process after RO membrane process in a desalination process. It is the figure which showed the process example in the case of performing RO membrane process after ED process in a desalination process. FIG. 6 is a graph showing the relationship between pH after reaction for 24 hours and ion concentrations of Ca ²⁺ and Mg ²⁺ as a result of Test 2. FIG. 6 is a graph showing the relationship between the pH during chemical softening reaction and the soluble CODcr concentration as a result of Test 2. FIG.

  Next, the present invention will be described based on examples of embodiments of the present invention. However, the present invention is not limited to the embodiment described below.

<This wastewater treatment method>
As shown in FIG. 1, the wastewater treatment method according to an example of this embodiment (referred to as “the wastewater treatment method”) separates and removes oil from wastewater (raw water) 1 containing oil, Ca salt, and sodium chloride. Oil-water separation process, chemical-softening treatment of oil-water separation treated water discharged from the oil-water separation process to separate and remove Ca contained in the oil-water separation treated water, and softening discharged from the chemical softening treatment In the method for treating oil-containing wastewater, the method includes a desalination treatment step of demineralizing the treatment water 7 to obtain a desalination treatment water 2 (shown as treatment water 2 in the figure) and a concentrate 6. A method for treating oil-containing wastewater, characterized in that after the discharged oil-water separation treated water is heated to raise the temperature of the oil-water separation treated water, chemical softening treatment is performed.

<This wastewater treatment equipment>
As an example of a treatment apparatus for carrying out the present wastewater treatment method (referred to as “the present wastewater treatment apparatus”), an oil-containing wastewater provided with an oil / water separation device 3, a chemical softening device 4, and a desalination device 5. An oil-containing wastewater treatment apparatus having a configuration in which a heat exchanger A is disposed between the drainage side of the oil / water separator 3 and the incoming water side of the chemical softening device 4. be able to. However, the treatment apparatus for carrying out this waste water treatment method is not limited to this waste water treatment apparatus.

<Raw water>
The raw water (treated water) 1 to be treated by this treatment method is water containing oil, scale components such as Ca salt, and salt such as sodium chloride. However, other components such as organic substances, surfactants, and other components may be included.

Examples of preferable raw water (treated water) to be treated by this treatment method include the production and production of petroleum, coal, natural gas, shale gas, cold bed methane (CBM), oil sand, surreal oil, etc. Oil-containing wastewater discharged from oil refineries and petrochemical plants.
Among them, waste water from a desalter (referred to as “disalter waste water”) is particularly preferable as the water to be treated in the present treatment method in that the effect of the present invention can be most effectively enjoyed.
The water temperature of such a disalter drainage is generally 60 to 80 ° C.

  As treated water (raw water) of the present wastewater treatment method, wastewater having a salt concentration of 2,000 to 40,000 mg / L is preferable from the viewpoint that the effects of the present invention can be effectively obtained, and in particular, 20,000 mg / LL. The following drainage is preferred.

<Oil water separation process>
In the oil / water separation step, oil contained in the waste water (raw water) is separated and removed to obtain oil / water separation treated water, and the sludge is discharged through a waste mud pipe.

As an oil-water separation method, a method usually used as a method for separating oil from water to be treated, for example, a method using a stationary levitation separation device such as API or CPI, a method of levitation separation by injecting gas, etc. Can be adopted. However, it is also possible to employ other methods used for oil separation.
According to such an oil-water separation method, floating organic substances can be separated and removed simultaneously with the oil.

(apparatus)
A raw water supply pipe is connected to the water inlet side of the oil / water separator 3, and an oil / water separation treated water circulation pipe is connected to the drain side. The waste water (raw water) is supplied to the oil / water separator 3 through the raw water supply pipe, and oil and floating organic substances contained in the waste water (raw water) are separated and removed, and discharged as oil-water separation treated water.

As the oil / water separator 3, a static levitation separator such as API or CPI, or a device such as DAF (Disolved Air Flotation) or IGF (Induced Gas Flotation) that levitates and separates by adding a gas or a flocculant is used. it can.
When the dispersible oil content contained in the waste water is large, it is preferable to provide a device such as a core racer or a nut shell filter after the device.

(Oil-water separation treated water)
In the oil / water separation step, it is preferable that the oil concentration and the SS concentration of the discharged oil / water separation treated water are both reduced to 50 mg / L or less, particularly 30 mg / L or less.

<Chemical softening process>
In the chemical softening treatment step, the oil / water separation treated water discharged from the oil / water separation step is chemically softened to separate and remove scale components such as Ca contained in the oil / water separation treated water, and then discharged as the softened treatment water 7. .

  As a method of chemical softening treatment, an alkali agent, carbon dioxide or carbonate, or both of them are added to oil-water separation treated water which is treated water, and Ca salt and Mg salt contained in the treated water. Such scale components are insolubilized and separated and removed, and the scale components contained in the water to be treated are separated and removed.

Here, examples of the alkaline agent include lime (Ca (OH) ₂ ), caustic soda (NaOH), caustic potash (KOH), and the like.
On the other hand, carbonic acid includes injection of carbon dioxide gas or flue gas of a combustion furnace, and examples of carbonate include soda ash (Na ₂ CO ₃ ).

Since the Ca salt and Mg salt contained in the water to be treated are insolubilized by the following chemical softening reaction, the insolubilized material may be separated into solid and liquid.
CO ₂ : CO ₂ + Ca (OH) ₂ = CaCO ₃ ↓ + H ₂ O
Ca: Ca (HCO ₃ ) ₂ + Ca (OH) ₂ = 2CaCO ₃ ↓ + 2H ₂ O
Ca: CaSO ₄ + Na ₂ CO ₃ = CaCO ₃ ↓ + Na ₂ SO ₄
Ca: CaCl ₂ + Na ₂ CO ₃ = CaCO ₃ ↓ + 2NaCl
Mg: Mg (HCO ₃ ) ₂ + 2Ca (OH) ₂ = Mg (OH) ₂ ↓ + 2CaCO ₃ ↓ + 2H ₂ O
Mg: MgSO ₄ + Ca (OH) ₂ = Mg (OH) ₂ ↓ + CaSO ₄
Mg: MgCl ₂ + Ca (OH) ₂ = Mg (OH) ₂ ↓ + CaCl ₂ ↓
Mg: MgSO ₄ + 2NaOH = Mg (OH) ₂ ↓ + Na ₂ SO ₄
Mg: MgCl ₂ + 2NaOH = Mg (OH) ₂ ↓ + 2NaCl

When the oil-water separation treated water contains a large amount of magnesium, for example, when the magnesium concentration in the oil-water separation treated water is 30 mg / L or more, especially caustic soda (NaOH) is used as lime (Ca (OH) ₂ ) or sodium carbonate (Na _2). It is preferable to add it together with CO ₃ ). By adding caustic soda, the amount of Ca ions to be added can be reduced, so that the amount of calcium carbonate that is insolubilized can be suppressed, and the amount of waste generated can be reduced.

(PH adjustment)
In the chemical softening treatment step, an alkaline agent such as lime (Ca (OH) ₂ ), soda ash (Na ₂ CO ₃ ), caustic soda (NaOH) or a carbonate or both thereof is added to adjust the pH of the water to be treated. Above all, it is preferable to adjust to 9 or more. On the other hand, if the pH is raised too much, ultrafine crystals can be formed in an instant, or crystals may adhere to the reaction vessel wall surface, leading to clogging. Therefore, it is preferable to keep the pH at 10.5 or less. . In addition, the chemical softening equipment has also been shown to incorporate some organic substances into the insolubilized material during the insolubilization reaction in the chemical softening process, and the effect is that the higher the pH, the lower the amount of uptake. From the viewpoint of removing organic substances in the chemical softening step, the pH is preferably 10.5 or less.

  In the chemical softening treatment, an inorganic flocculant or a polymer flocculant or both of them may be added in order to enhance the sedimentation property of the insolubilized material.

(Chemical softening device 4)
An oil / water separation treated water distribution pipe is connected to the water inlet side of the chemical softening apparatus 4 via a heat exchange device A, and a softened treated water distribution pipe is connected to the drain side. The oil / water separation treated water is supplied to the chemical softening device 4 through the oil / water separation treated water circulation pipe through the heat exchange device A, and after being softened by the chemical softening device 4, the softened treated water 7 is passed through the softening treated water circulation pipe. Discharged.

The chemical softening device 4 should just be provided with the normal chemical softening processing tank.
Especially, it is preferable that it is a chemical softening apparatus provided with the chemical softening processing tank provided with the function which can circulate the slurry containing an insolubilized material.
That is, insoluble materials and crystals of CaCO ₃ and Mg (OH) ₂ usually have a very small particle size, so the sedimentation rate is low. However, by rapidly mixing with an alkali agent and soda ash, and circulating the insolubilized slurry of CaCO ₃ or Mg (OH) ₂ , the density of the slurry and the particle size of the crystal increase, and the sedimentation property is increased. A good slurry of CaCO ₃ or Mg (OH) ₂ can be formed. Therefore, it is preferable that the chemical softening device 4 includes a chemical softening treatment tank having a function of circulating the slurry containing the insolubilized material.

As a chemical softening treatment tank equipped with such a slurry circulation function, for example, an apparatus equipped with a slurry circulation type high-speed coagulation sedimentation basin used in coagulation sedimentation can be cited as a preferred apparatus example (FIG. 6).
Moreover, the apparatus provided with the sludge bran type slurry circulation type high-speed coagulation sedimentation basin shown in FIG. 7 can also be illustrated as a preferable apparatus. This apparatus is preferable in that a relatively clear treated water can be obtained because fine insoluble matter is trapped by the blanket.

A twin reactor described in Japanese Patent No. 4101506 can also be used. When this twin reactor is used, a CaCO ₃ crystallite with good sedimentation is prepared by making a seed crystal of CaCO ₃ in the second reaction tank and returning the seed crystal to the first reactor to react with the influent water. Can be obtained.
If such a twin reactor is used, since the hardness component can be removed to a low concentration level in a reaction tank residence time of a few tens of minutes, it can be processed more efficiently.

In addition, as shown in FIG. 3, a scale deposition tank is provided on the drain side of the chemical softening treatment tank, and a flat plate or corrugated plate (scale deposition plate) is detachably installed in the scale deposition tank. The softening-treated water 7 may be rectified by contacting the scale depositing plate. Thus, the softening treatment water 7 that is rectified in contact with the scale deposition plate, can be deposited scale components of CaCO ₃ or Mg (OH) ₂ scale deposition plate (Figure 3). The scale of CaCO ₃ or Mg (OH) ₂ adhering to the scale deposit plate can be easily removed by removing it and periodically washing it with acid or the like.
The discharged water from the chemical softening treatment process has Ca and Mg removed in the softening process, but since it is dissolved in a saturated or slightly supersaturated state, the insolubilization reaction proceeds slowly thereafter, and slightly in the piping line etc. There is also a risk that the scale will occur. Therefore, it is preferable to remove the scale components such as CaCO ₃ and Mg (OH) ₂ by contacting the softened water 7 with these plates in this manner and attaching them to the scale deposition plates.

Moreover, you may make it provide a filter in the waste_water | drain side of a chemical softening processing tank.
That is, some SS may flow out into the effluent of the chemical softening process. Since these SS components also cause clogging in the desalting process, it is preferable to remove them using a filter when a large amount of SS components are discharged.
As the filter, a sand filtration, a cartridge filter, or a membrane separation device such as MF or UF can be used.

Furthermore, as shown in FIG. 4, an ion exchange softening device equipped with an anion exchanger is installed on the drain side of the chemical softening device 4 to remove Ca ions and Mg ions remaining after chemical softening. May be.
In this way, part of the effluent from the chemical softening treatment step is passed through an ion exchange softening device, and the treated water is mixed with the remaining effluent from the chemical softening treatment step, so that the desalted concentrated liquid 6 is deposited in scale. The amount of water passing through the ion exchange softening device can be minimized. Alternatively, the removal rate can be kept low by increasing the water flow rate (SV), and the equipment can be made compact.

(Water temperature adjustment)
In the chemical softening treatment step, it is preferable to increase the temperature of the water to be treated from the viewpoint of increasing the efficiency of the chemical softening treatment. In other words, it is preferable to adjust so as to increase the water temperature in the chemical softening treatment tank.
For example, it is preferable that the oil / water separation treated water discharged from the oil / water separation step is heated to increase the temperature of the oil / water separation treatment water and then supplied to the chemical softening treatment step.

The higher the water temperature, the lower the solubility of Ca salt and Mg salt. Therefore, the dissolution concentration of Ca and Mg can be lowered by chemical softening reaction under high temperature conditions. This effect is achieved by setting the temperature at the time of the reaction when the oil / water separation treated water discharged from the oil / water separation step is brought into contact with an alkali agent or carbonate agent to 50 ° C. or higher, desirably 80 ° C. or higher. The effect can be further enjoyed.
On the other hand, the higher the pH is, the lower the solubility of Ca salt and Mg salt is. However, under the condition of high temperature, the decreasing rate of dissolved concentration starts to decrease at pH 6.5 or higher, and becomes almost constant at pH 9 or higher. Tend.
On the other hand, when SiO ₂ is included as a scale component, Si has a characteristic that, as opposed to Ca and Mg, Si is more easily dissolved as the temperature is higher, and more easily dissolved as the pH is higher. However, when Mg is insolubilized as Mg (OH) ₂ ↓, a phenomenon that Si is taken in together is observed, and the soluble residual Si concentration is also reduced as CaCO ₃ and Mg (OH) ₂ are insolubilized. Can do.
Further, when the Mg ion concentration in the water to be treated is small, the Si concentration can be greatly reduced by adding a magnesium compound such as MgO or MgCl ₂ .

  From the above viewpoint, the water temperature in the chemical softening treatment tank is preferably adjusted to 40 ° C. or higher, particularly 50 ° C. or higher, and particularly preferably 80 ° C. or higher. At that time, the pH is preferably adjusted to 6.5 to 10.5, particularly pH 8.5 or more or pH 10.5 or less, and particularly preferably pH 9.0 or more or pH 10.5 or less.

The heating means for the oil / water separation treated water is optional.
For example, a heat exchanger A is disposed between the drain side of the oil / water separation treatment device and the water inlet side of the chemical softening device 4, that is, an intermediate portion of the oil / water separation treatment water flow pipe, and performs heat exchange with a high-temperature heat medium. Can raise the temperature of the oil-separated treated water (FIG. 1).

As an example, the accompanying water discharged along with oil and gas production, the disolter drainage, and the like generally have a temperature of 60 ° C. or higher, so that the drainage of the oil-water separator 3 as shown in FIG. A heat exchanger A is connected between the side of the chemical softening device 4 and a water inlet side of the chemical softening device 4, a drainage (raw water) introduction pipe for introducing drainage (raw water) is connected to the heat exchanger A, and Waste water (raw water) can be used as a heat medium (indicated as a high-temperature heat source in the figure).
Thus, if waste water (raw water) is used as a heat medium source (shown as a high-temperature heat source in the figure) of the heat exchanger A, heat can be supplied more economically and effectively. Moreover, since the heat of the waste water is taken away through the heat exchanger A, there is also an advantage that raw water having a lowered water temperature can be supplied to the oil / water separation step. As a result, in the oil / water separation step, the fluidity and solubility of the oil component are reduced, and the advantages of collecting and facilitating oil separation in the oil / water separation step are brought about, and the advantage that oil removal in the oil / water separation step is facilitated Will bring.
For example, when waste water (raw water) at 65 to 70 ° C. is first flowed into the next chemical softening device 4 through an API device having a residence time of 5 hours, heat is released by the API device. Will drop to 50-55 ° C. At this time, if the raw water is used as a heat medium source of the heat exchanger A, the water temperature of the oil / water separation treated water can be increased by 5 to 15 ° C. to 60 to 65 ° C., and the heat of the heat exchanger I The water temperature of the raw water used as the medium source drops by 5 to 10 ° C. to 55 to 60 ° C.

Moreover, the water temperature in the chemical softening treatment tank can be further increased by blowing steam directly into the pipe immediately before flowing into the chemical softening treatment process or into the reaction tank. According to this method, it is possible to bring about an advantage that the reaction vessel temperature control in the chemical softening treatment process is facilitated by the amount of steam injected.
In this case, it is preferable that the alkali agent or soda ash is injected immediately before the influent water comes into contact with the steam and the temperature rises or immediately after the temperature rises and is rapidly mixed. Thereby, the chemical softening reaction at higher temperatures can be more effectively promoted. This method is effective for removing Si particularly when a large amount of Si is contained.

(Softened water)
The softened water 7 discharged from the chemical softening treatment step preferably has a Ca concentration of 35 mg / L or less, more preferably 15 mg / L or less. The Mg concentration is preferably 10 mg / L or less, more preferably 4 mg / L or less.

<Desalination process>
In the desalting treatment step, the softening treatment water 7 discharged from the chemical softening treatment step is desalted to separate and remove the salts contained in the softening treatment water 7, and the desalination treatment water 2 (in the figure) The treated water 2 is displayed) and the concentrated liquid 6 is discharged.

  As a desalting treatment method employed in the desalting treatment step, for example, an electrodialysis method (ED), a reverse osmosis membrane method (RO), a distillation method, or the like can be used. Among them, when the temperature is lowered before the desalting process, it is preferable to apply the ED or RO process because the thermal efficiency is lowered in the distillation method.

The RO membrane treatment is a method of separating the RO concentrated water and the RO membrane treated water by applying a mechanical pressure equal to or higher than the osmotic pressure to the salt water in the chamber partitioned by the RO membrane and passing the RO membrane.
It is known that the efficiency of RO membrane treatment is improved when the salt concentration is low.

In the ED treatment, a large number of cation exchange membranes and anion exchange membranes are alternately arranged between the anode and the cathode, and salt is removed through the ion exchange membrane by passing a salt water through voltage. The dilution chamber and the concentration chamber in which salts are concentrated are alternately formed. This is a method of obtaining concentrated water having a high concentration of salt and treated water having a low concentration by sending most of the raw water to the dilution water side and a small amount to the concentration side while circulating the water in the concentration chamber and dilution chamber.
In ED treatment, since heating and pressurization are not performed and the operation pressure is low, it is known to use for desalination from brine and further concentration and recovery of salts from concentrated brine.

Further, for example, as shown in FIGS. 8 and 9, ED processing and RO membrane processing may be performed in combination.
For example, as shown in FIG. 8, when the RO membrane treatment is performed first, if the salt concentration of the water to be treated is high, the osmotic pressure increases and the operating pressure on the RO membrane increases. In this case, the salt concentration of the RO membrane treatment feed water can be increased by sending the RO membrane concentrated water to the ED treatment and mixing the treated water desalted in the ED treatment with the RO membrane treatment feed water. As a result, the operation can be performed without significantly increasing the operation pressure at the RO membrane, and the recovery rate of the desalted water in the RO membrane treatment can be increased. Moreover, if the concentrated liquid discharged | emitted from ED process returns to the inflow side of the chemical softening apparatus 4, and it makes it a chemical softening process with oil-water separation process water, the discharge | emission amount of the concentrated liquid 6 can be reduced.
On the other hand, for example, as shown in FIG. 9, when the ED treatment is performed first, since the treated water of the RO membrane treatment is only ED treated water, the salt concentration of the treated water of the RO membrane treatment is also low. The water recovery rate in the RO membrane treatment can be increased. In this case, if the concentrated liquid discharged from the ED process and the concentrated liquid discharged from the RO process are both returned to the water entering side of the chemical softening device 4 and subjected to chemical softening treatment together with oil-water separation treated water, The discharge amount of the liquid 6 can be reduced. At this time, a part of the concentrated liquid discharged from the RO process may be returned to the incoming side of the ED process.
Further, instead of the RO membrane treatment, an NF membrane treatment may be performed.

(Desalination device 5)
A softened treated water circulation pipe is connected to the incoming side of the desalting apparatus 5, and a desalted treated water discharge pipe and a concentrated liquid discharge pipe are connected to the drain side. The softened treated water 7 is supplied to the desalinating device 5 through the softened treated water circulation pipe, and after desalting is performed in the desalted device 5, the desalted treated water 2 is discharged through the desalted treated water discharge pipe, and the concentrated liquid The concentrate 6 is discharged through the discharge pipe.

As an example of the configuration of the desalination apparatus 5, for example, an RO concentrated water supply pipe and an RO membrane treated water discharge pipe are connected to the drain side of the RO membrane processing apparatus, and the RO concentrated water supply pipe is connected to the ED processing apparatus. An example of a configuration in which an ED treated water supply pipe and an ED concentrated water supply pipe are connected to the drainage side can be given.
At this time, for example, the ED treated water supply pipe is connected to the RO membrane treatment inflow pipe, the ED concentrated water supply pipe is connected to the incoming side of the chemical softening device 4, and the ED concentrated water is returned to the incoming side of the chemical softening process. You may do it.

Further, as another configuration example of the desalination apparatus 5, an ED treated water supply pipe and an ED concentrated water supply pipe are connected to the drain side of the ED apparatus, and the ED treated water supply pipe is connected to the RO membrane treatment apparatus. A configuration example in which an RO concentrated water supply pipe and an RO membrane treated water discharge pipe are connected to the drain side of the membrane treatment apparatus can be given.
At this time, the RO concentrated water supply pipe may be connected to the inflow pipe of the ED device, or connected to the incoming side of the chemical softening device 4 so that the RO treated water is returned to the incoming side of the chemical softening treatment step. May be. Further, the ED concentrated water supply pipe may be returned to the incoming water side of the chemical softening process.
Furthermore, instead of the RO membrane device, an NF membrane treatment device can be installed.

(Demineralized water)
The salt concentration required for desalted water varies depending on the purpose of use, but when the salt concentration (TDS) of the raw water is 2,000 to 40,000 mg / L, about 98% of salt is removed by the RO membrane one-stage treatment. Rate is obtained. Therefore, the TDS of the desalted water is about 40 to 800 mg / L. On the other hand, in the ED treatment, an arbitrary desalination treatment can be obtained by changing the amount of water circulating in the dilution chamber and concentrated water and the amount of current depending on the required water quality of the salinity in the reuse, but the desalination rate is about 98% at the maximum. is there. Therefore, when reusing as cooling tower cooling water or boiler water, it is preferable to perform further desalting treatment or desalting with an ion exchange resin as necessary. On the other hand, it can be applied to RO / ED single-stage treatment as wastewater treatment water in Desalter's Make UP and Refinery.

<Adjustment of water to be treated (softened water) in the desalination process>
The water to be treated in the desalting process, that is, the softened water 7 is preferably lowered in water temperature or adjusted in pH from the viewpoint of increasing the treatment efficiency in the desalting process. That is, it is preferable that the water temperature or pH of the softened water 7 discharged from the chemical softening process is adjusted and then supplied to the desalting process.

(Adjusting the temperature of softened water)
The width of decrease in the water temperature of the softened treated water 7 is 5 ° C. or higher, desirably 10 ° C. or higher. However, it is preferable to determine how much the water temperature should be lowered under conditions that do not cause precipitation of scale or the like on the concentrated water side. Moreover, it is necessary to consider the heat resistance of the membrane material of ED and RO used for a desalting process. For example, when it is necessary to use the film material at 40 ° C. or lower, it is necessary to lower the temperature.
Since the scale components of CaCO ₃ and Mg (OH) ₂ increase in solubility and become less likely to cause scale as the temperature is lower, they adhere to the membrane surface due to scale generation or deposition on the concentrated water side in the next desalting process. Is suppressed, and stable operation is possible.

The cooling means of the softening process water 7 is arbitrary.
For example, as shown in FIG. 2, a heat exchanger B is arranged between the drain side of the chemical softening device 4 and the incoming water side of the desalination device 5, that is, in the middle portion of the softened treated water circulation pipe, The temperature of the softened water 7 can be lowered by exchanging heat with the water.
In cooling the softened treated water 7, desalted treated water (membrane permeated water) can be used as a cooling medium for cooling. When the cooling effect is small at the temperature of the permeated water, the water temperature can be sufficiently lowered by passing the desalted water (membrane permeated water) through a chiller or the like to further lower the temperature and supplying it to the heat exchanger B. Desalinated water (membrane permeated water) has the advantage of easy maintenance of chillers and heat exchangers because of its good water quality.

(PH adjustment of softened water 7)
In the desalting process, the desalted desalted water (membrane permeated water) 2 is collected, while the scale component is concentrated in the concentrated liquid 6. Therefore, it is preferable to obtain and set the relationship between the recovery rate at which precipitation is unlikely to occur and the water temperature from the concentration of Ca ions and Mg ions in the concentrate 6. However, when the treated water is reused, it is also desirable to increase the recovery rate as much as possible. Therefore, it may happen that a sufficient recovery rate cannot be obtained only by lowering the water temperature. In this case, deposition of CaCO ₃ and Mg (OH) ₂ can be prevented by adding an acid to the influent water in the desalting treatment step and lowering the pH. That is, the deposition of CaCO ₃ or Mg (OH) ₂ is less likely to occur because the lower the pH, the lower the CO ₃ ²⁻ ions and OH ^{2 −} ions, thus increasing the recovery rate of desalted water (membrane permeated water). In some cases, this can be achieved by adjusting the water temperature and / or pH drop.

From such a viewpoint, the pH of the softened water 7 is preferably adjusted to 6 to 10, particularly 7 or more, or 9.5 or less, and then supplied to the desalting process. However, when hydrogen sulfide is dissolved in raw water and softened water 7 at a high concentration, if the pH of the softened water 7 is lower than 8, hydrogen sulfide comes out as a gas body on the gas phase side. In this case, it is preferable to adjust the pH of the softened water 7 to 8 or higher, desirably 8.5 or higher.
Moreover, the scale deposition of the concentrate 6 can also be suppressed by adding a scale inhibitor to the influent water in the desalting process.

  Since the scale generation conditions differ depending on the properties of the wastewater, an optimal process can be determined in consideration of safety and economics by conducting tests in which the pH and the addition amount of the scale inhibitor are changed simultaneously with the water temperature.

<Washing>
Part of the oil and organic matter can be removed by the chemical softening treatment step, but when the raw water contains a large amount of a surfactant, the RO membrane is particularly contaminated. In this case, as shown in FIG. 4, it is preferable to provide an activated carbon adsorption tank or the like before the desalting treatment step to adsorb and remove these surfactants.
Even when the surfactant is not included, some organic matter remains in the softened water 7, so that a concentrated organic gel layer is formed on the surface of the RO or ED membrane, resulting in a desalting effect or desalting. Since the amount of salt treated water (membrane permeated water) decreases, the gel layer needs to be washed.

In the conventional process, a means for restoring the desalting performance by performing membrane cleaning of RO or ED using a chemical cleaning solution to which acid, alkali or the like is added once every several months has been a conventional method. However, there is a problem that the processing cost is increased.
Therefore, in the present invention, when a large amount of organic matter is contained in the water to be treated, the desalinized water is passed to the incoming side of the desalinating process, and the gel layer formed on the RO or ED membrane surface is periodically added. A method of cleaning is proposed.

  Specifically, as shown in FIG. 5, a three-way valve is provided on the upstream side of the pump that supplies the softened water 7 to the desalinator 5, that is, in the middle of the softened water supply pipe, and the desalted water is discharged. By connecting a demineralized water supply pipe branched from the pipe to the three-way valve, the supply of the softened water 7 to the demineralization process is temporarily stopped, and the demineralized water (membrane permeated water) ) Can be passed through the inlet of the desalting process. At the same time, by opening the pressure regulating valve on the concentrate side of the desalting process and lowering the pressure, the flow rate on the inflow side of the desalting process can be increased, and the generated gel layer can be washed out. This washing drainage water is preferably returned before or after the chemical softening treatment step in order to increase the recovery rate.

  The frequency of washing the inflow side of the desalting treatment process using the desalting treatment water (membrane permeate) in the desalting treatment process depends on the formation of the gel layer, but at least once / day to several tens of times / It is preferable to carry out the frequency of the day.

  The washing time is preferably several minutes / times to sufficient / times.

When the organic substance concentration is high, the cleaning effect can be enhanced by adding an alkali such as caustic soda (NaOH) to the cleaning liquid and cleaning the film.
In the case of adding an alkali agent, the cleaning waste water is returned to the chemical softening treatment step, thereby resulting in a merit of reducing the supply of the alkaline agent in the chemical softening treatment step.
In the case of adding an alkaline agent, it is preferable from the viewpoint of preventing scale formation that the alkaline agent is added after first passing through the desalted filtrate and the addition of the alkaline agent is stopped before washing is stopped.

<Explanation of terms>
In the present invention, when expressed as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably Y”, with the meaning of “X to Y” unless otherwise specified. It means “smaller”.
Further, in the present invention, when expressed as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and “Y or less” (Y is an arbitrary number). ) Includes the meaning of “preferably smaller than Y” unless otherwise specified.

  Hereinafter, test results related to the present invention will be described.

<Test 1>
The oil-containing wastewater as the water to be treated was subjected to oil separation treatment by a CPI device to separate and remove the oil and organic matter, thereby obtaining oil-water separation treated water (see Table 1 below for components and the like). Next, the temperature of the oil / water separation treated water is adjusted to 30 ° C., 50 ° C., 80 ° C. or 105 ° C. using a thermostatic bath, and the chemicals shown in the table (lime alone, lime + sodium carbonate, or lime + sodium carbonate) + Caustic soda) is added at a rate of 0.2% by mass with respect to 1 kg of raw water, and the oil-water separation treated water is chemically softened to insolubilize Ca and Mg, and filtered with filter paper after 2 hours. The amount of each component was measured, and the measurement results are shown in Table 1.
In addition, the addition ratio (mass) of each material in lime + sodium carbonate is lime: sodium carbonate = 1: 1, and the addition ratio of each material in lime + sodium carbonate + caustic soda is lime: sodium carbonate: caustic soda = 1. 1: 0.5.
The heating at 105 ° C. was performed under pressure using a sealed container.

As the reaction temperature of oil-water separation treated water, which is the water to be treated in the softening treatment process, is increased, except for the removal behavior of Ca when lime alone is added, the temperature of any of lime + sodium carbonate, lime + sodium carbonate + caustic soda It has been found that the effect of removing Ca and Mg, which are scale components, increases with the increase of. On the other hand, in the case of addition of lime alone, the Ca concentration clearly decreased due to the addition of lime, but a tendency to slightly deteriorate the removal effect at 50 ° C. or higher was also observed.
The reason is not clear, but it has been found that the removal effect of Ca and Mg can be increased by adding sodium carbonate and caustic soda together with lime and increasing the reaction temperature.
Moreover, the tendency for Mg removal rate to increase somewhat by addition of caustic soda was also recognized.
On the other hand, with regard to Si, although the removal effect is low up to 50 ° C., it was confirmed that when the water temperature of the oil-water separation treated water was 80 ° C. or higher, it was removed simultaneously with Ca and Mg.

<Test 2>
Sodium carbonate was added at a rate of 0.2 (w / v%) to 1 L of oil-containing wastewater treated in Test 1, and the pH was adjusted with hydrochloric acid or caustic soda and stirred. The filter paper was filtered after 24 hours, and the Ca ²⁺ , Mg ²⁺ and CODcr of the filtered water were measured. The results are shown in FIGS.
In the long-time reaction, the Ca ²⁺ ion concentration increased from the pH of the oil-containing wastewater, began to decrease from pH 6.0, and became almost insoluble at pH 8 or higher. Further, the ion concentration of Mg ²⁺ began to decrease from about 6.5, and was almost insolubilized at pH 8 or higher like Ca.
On the other hand, the organic substance concentration tended to be low at low pH and high at 10 or more.

Claims (8)

An oil / water separator for separating and removing oil from wastewater (raw water) containing oil, Ca salt and sodium chloride;
A chemical softening device that performs chemical softening treatment on the oil-water separation treated water discharged from the oil-water separation step to separate and remove Ca contained in the oil-water separation treated water;
In a treatment apparatus for oil-containing wastewater, comprising a desalination apparatus for desalinating softened water discharged from a chemical softening apparatus,
A heat exchanger (i) is connected between the drain side of the oil / water separator and the incoming side of the chemical softening device, and the oil / water separation treated water discharged from the oil / water separator is passed through the heat exchanger (i). An apparatus for treating oil-containing wastewater having a structure for supplying water to the chemical softening apparatus after increasing the temperature of water.   A heat exchanger (B) is connected between the drain side of the chemical softening device and the incoming water side of the desalination device, and the softened water discharged from the chemical softening device is passed through the heat exchanger (B). The processing apparatus of the oil containing waste water of Claim 1 provided with the structure supplied to this desalination apparatus after reducing the water temperature of water.   The waste water treatment according to claim 1 or 2, wherein a raw water supply pipe for introducing waste water (raw water) is connected to the heat exchanger (i), and the waste water (raw water) is used as a heat medium of the heat exchanger (i). apparatus.   The heat exchanger B and a drain side of the desalinator are connected, and the desalted water discharged from the desalter is used as a cooling medium for the heat exchanger B. The oil-containing waste water treatment apparatus as described. Oil / water separation process for separating and removing oil from waste water (raw water) containing oil, Ca salt and sodium chloride, and oil / water separation treated water discharged from the oil / water separation process are chemically softened and included in the oil / water separation treated water In a method for treating oil-containing wastewater, comprising: a chemical softening treatment step for separating and removing Ca, and a desalting treatment step for desalting softening treatment water discharged from the chemical softening treatment step,
A method for treating oil-containing wastewater, comprising heating the oil-water separation treated water discharged from the oil-water separation step to increase the temperature of the oil-water separation treated water and then subjecting the oil to water.   6. The method of treating oil-containing wastewater according to claim 5, wherein the desalination treatment is performed after cooling the softened water discharged from the chemical softening treatment step and lowering the water temperature of the softened water.   The method for treating oil-containing wastewater according to claim 5 or 6, wherein wastewater (raw water) is used as a heat medium for heating the oil-water separation treated water. The method for treating oil-containing wastewater according to any one of claims 5 to 7, wherein the desalted water discharged from the desalting treatment step is used as a cooling medium for cooling the softened water.

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