CA2690542C

CA2690542C - Oil-contaminated water reutilization system

Info

Publication number: CA2690542C
Application number: CA 2690542
Authority: CA
Inventors: Akira Mochizuki; Tomoko Shinomura; Norihide Saho; Hisashi Isogami; Ryo Miyake; Tatsuo Fujii; Akio Honji
Original assignee: Hitachi Plant Technologies Ltd
Current assignee: Hitachi Ltd
Priority date: 2007-06-22
Filing date: 2008-06-11
Publication date: 2013-05-28
Anticipated expiration: 2028-06-11
Also published as: WO2009001676A1; MX2009013432A; CA2690542A1; JP5157279B2; JP2009000656A

Abstract

An oil-contaminated water reutilization system designed to purify any oil-contaminated water occurring at oil production and reutilize the same.
The oil-contaminated water reutilization system has the following characteristics. Any oil-contaminated water (W1) occurring at oil production is subjected to flocculation magnetic separation by means of a flocculation magnetic separator (10) to thereby obtain a preliminary purified water (W2) free from the oil-contamination components contained in the oil-contaminated water (W1). From the obtained preliminary purified water (W2), any water-soluble organic matter dissolved in the oil-contaminated water (W1) is removed by a COD removing unit (30) adapted to carry out ozonolysis to thereby obtain a COD treated water (W3). Further, the COD treated water (W3) is distilled by means of a solar heat distiller (50) so as to remove salt contents, thereby obtaining reusable purified water (w4).

Description

DESCRIPTION

OIL-CONTAMINATED WATER REUTILIZATION SYSTEM

Technical Field [0001]
The present invention relates to an oil-contaminated water reutilization system capable of clarifying the oil-contaminated water generated in the process of petroleum production, and ensuring reuse of the purified water.

Background Art [0002]
In almost all the petroleum production sites, water flooding method is used to increase the pressure of petroleum reservoir using hydraulic water. In the initial phase of production, only petroleum can be produced, but the percentage of water (oil-contaminated water) produced is increased with the lapse of time.

[0003]
An increase in the percentage of oil-contaminated water reduces the amount of petroleum produced, due to the flow rate in the pipeline. This makes it necessary to clarify and discard the oil-contaminated water at the production site.

[0004]
To solve the aforementioned problems, for example, the Patent Document 1 discloses a solid/liquid separation apparatus that can be applied as a clarifier to remove the solid contaminants such as oil-contaminated components contained in the oil-contaminated water. In the solid/liquid separation apparatus disclosed in the Patent Document 1, a finer wire net or a mesh knitted with polymeric fiber is used as a water-permeating filter membrane. Magnetic flocks are generated by adding coagulant and magnetic powder to the oil-contaminated water containing the contaminant particles as substances to be separated.
This magnetic flock is separated by the water-permeating filter membrane, and the magnetic flocks separated by the water-permeating filter membrane are sucked and collected by magnetism generated by a magnetic field generating device, thereby these flocks are recovered as highly concentrated sludge.

[0005]
The Patent Document 2 discloses a technique of filtering oil-contaminated water by a porous membrane.
The technique disclosed in the Patent Document 2 uses a porous membrane having a pore size of 0.1 m or less, and adjusts the angle of contact between the oil-contaminated water and porous membrane, thereby the oil-contaminated water can be effectively filtered.

[0006]
Patent Document 1: Japanese Patent Application Laid-open No. 2002-273261 (see Paragraph 0010 and Fig.
1) Patent Document 2: Japanese Patent Application Laid-open No. Hei 09 (1997)-234353 (see Paragraph 0008) Disclosure of the Invention Problems to be solved by the Invention [0007]
The technique disclosed on the Patent Documents 1 and 2 clarify the oil-contaminated water by removing the solid contaminants therefrom.

[0008]
The major petroleum production site, however, is located in the Middle East wherein there is a small amount of annual precipitation, and water constitutes the valuable natural resource. Thus, there is an intense demand for reuse of purified water that is produced by clarification of the oil-contaminated water.

[0009]
In the purified water generated by the technique having been disclosed so far, solid suspended matter such as oil-contaminated components, or solid contaminants such as algae, fungi and microbes can be removed, but water soluble organic substances or salts dissolved in the oil-contaminated water cannot be removed. Thus, this technique involves problems in that the purified water generated by the technique cannot be purified up to the level of permitting reuse.

[0010]
Thus, the object of the present invention is to provide an oil-contaminated water reutilization system capable of clarifying the oil-contaminated water generated in the process of petroleum production and ensuring the reuse of the purified water.

ak 02690542 2012-08-21 - 4a -Means for Solving the Problems [0010a]
Certain exemplary embodiments can provide an oil-contaminated water reutilization system comprising: a treated water generation device for generating treated water by removing oil-contaminated component as a substance to be removed, from oil-contaminated water generated in the process of petroleum production; a COD removing device for removing water-soluble organic substance as the substance to be removed, from the treated water generated by the treated water generation device; and a salt removing device for removing salt as the substance to be removed, by adding heat to the treated water from which the water-soluble organic substance has been removed by the COD removing device, thereby purified water is obtained, wherein the salt removing device is a membrane still which is structured in such a way that a duct through which the treated heated water runs and another duct through which a coolant runs contact each other through a hydrophobic porous membrane having pores of a size to permit passage of water molecule as steam.

[0011]
To solve the aforementioned problems, the oil-contaminated water reutilization system of the present invention clarifies the oil-contaminated water using a treated water generation device and COD removing device, and distills the purified water using a salt removing device, thereby purified water is obtained.

Advantages of the Invention [0012]
According to the present invention, an oil-contaminated water reutilization system capable of clarifying the oil-contaminated water generated in the process of petroleum production and ensuring the reuse of the purified water can be provided.

Brief Description of the Drawings [0013]
Fig. 1 shows a schematic structure of an oil-contaminated water reutilization system relating to an embodiment of the present invention;
Fig. 2 shows an embodiment of the magnetic coagulation separator in the oil-contaminated water reutilization system shown in Fig. 1;
Fig. 3 shows an embodiment of the COD removing device in the oil-contaminated water reutilization system shown in Fig. 1;
Fig. 4 shows an embodiment of the solar heat still in the oil-contaminated water reutilization system shown in Fig. 1;
Fig. 5 shows an embodiment of the membrane still in the oil-contaminated water reutilization system shown in Fig. 1; and Fig. 6 is a schematic diagram representing a Jatropha cultivation field.

Description of Reference Numerals [0014]
1. Oil-contaminated water reutilization system 10. Magnetic coagulation separator (treated water generation means) 16. Coagulation reservoir (magnetic flock generation means) 20. Rotary cylinder (magnetic separation means) 21. Magnetic field generation device (magnetic separation means) 30. COD removing device (COD removing means) 32. Ozone generator =
33. Activated carbon treatment reservoir 50. Solar heat still (salt removing means) 51. Heater 53. Coolant reservoir 54. Coagulant reservoir Wl. Oil-contaminated water W2. Primary purified water (treated water) W3. COD treated water W4. Purified water (useful water) Wc. Coolant 4 * CA 02690542 2009-12-10 Pl. Vegetation cultivation plant Best Mode for Carrying Out the Invention [0015]
<<Overview of oil-contaminated water reutilization system>>
The oil-contaminated water reutilization system of the embodiment in the present invention is installed in a petroleum production plant for generating petroleum using the hydraulic pressure in water flooding method, and is used to separate and remove the substances to be removed, such as solid contaminants or water-soluble organic substance such as oil-contaminated components contained in the oil-contaminated water generated in the process of petroleum production. The following describes the oil-contaminated water reutilization system of the embodiment in the present invention:

[0016]
The oil-contaminated water generated in the process of petroleum production includes solid suspended matter such as oil-contaminated components;
solid contaminants such as algae, fungi and microbes;
water soluble organic substances dissolved in the oil-contaminated water; and substance to be removed such as salts. Clarification by distillation is preferably used to completely remove the substance to be removed from the oil-contaminated water and to clarify it to the level of reuse. However, if the water containing water soluble organic substance is distilled, water soluble organic substances are deposited on the duct of the heater provided on the still in the process of distillation, and the duct will be clogged in some cases. Further, although clogging can be avoided, the organic substance deposited inside the duct will block the flow inside the duct and will reduce heat transfer efficiency. Further, the distilled water obtained by distillation may contain water soluble organic substances. Thus, the water with the water soluble organic substance dissolved therein cannot be used as it is.

[0017]
To solve this problem in the present embodiment salt is removed after the solid contaminants and the water soluble organic substance have been removed from the oil-contaminated water.

Embodiment 1 [0018]
Fig. 1 is a drawing to show a schematic structure of an oil-contaminated water reutilization system relating to an embodiment of the present invention. In Fig. 1, the oil-contaminated water reutilization system 1 includes;
a magnetic coagulation separator 10 (treated water generation means) for coagulating and separating the solid suspended matter such as oil-contaminated components, or solid contaminants such as algae, fungi and microbes contained in the oil-contaminated water W1 generated in the process of petroleum production at the petroleum production site;
a COD removing device (COD removing means) 30 for removing the water soluble organic substance dissolved in the primary purified water (treated water) W2 from which the solid contaminants have been removed by the magnetic coagulation separator 10, thereby the COD
(Chemical Oxygen Demand) is reduced; and a solar heat still 50 (salt removing means) which uses solar heat to distill the COD treated water W3 from which the water soluble organic substance has been removed by the COD removing device 30, and which generates purified water (useful water) by removing the salt dissolved therein.

[0019]
Various forms of method can be considered to use the purified water W4 generated by the oil-contaminated water reutilization system 1 described above. The present embodiment gives an example of using it as the vegetation cultivation water in a vegetation cultivation plant Pl.

[0020]
The oil-contaminated water W1 generated in the process of petroleum production is put into the magnetic coagulation separator 10, and solid contaminants are removed by the coagulation and separation using magnetism. To be more specific, the magnetic coagulation separator 10 removes the solid contaminants from the oil-contaminated water W1 to generate primary purified water W2. This primary purified water W2 has the primary purified water W2 in which the solid contaminants has been removed, but contains water soluble organic substance or salt dissolved therein.

[0021]
In the meantime, the solid contaminants having been removed are separated as sludge and are treated in a sludge treatment facility 60. The sludge includes the heavy metals contained in the oil-contaminated water Wl, and treatment agents such as the coagulant or magnetite added by the magnetic coagulation separator 10. Accordingly, they are separated and collected by the sludge treatment facility 60 and are reused if they can. If they are to be discarded, they are further subjected to treatment (e.g., detoxification) and are discarded after that.

[0022]
The primary purified water W2 generated by the magnetic coagulation separator 10 is put into the COD
removing device 30. The water soluble organic substance dissolved in the primary purified water W2 is removed by the COD removing device 30 using the process of oxidation by ozone, thereby the COD level of the primary purified water W2 is reduced, and the COD treated water W3 is generated.

[0023]
It should be noted that part of the primary purified water W2 can be discharged into rivers.

[0024]
The primary purified water W2 put into the COD
removing device 30 may contain the salt dissolved therein. Incidentally, in the oil field along the coast, as well as the oil field located several tens of kilometers inland from the coastline, the oil-contaminated water W1 may contain about 1% salt.
However, the salt as inorganic substance is not removed by the COD removing device 30. Thus, the COD
treated water W3 generated by the COD removing device 30 may contain salt dissolved therein.

[0025]
The cultivation water having a salt concentration of about 1% is known to give a fatal influence to the vegetation, although it depends on the type of the vegetation to be cultivated. Thus, the COD treated water W3 generated by the COD removing device 30 of the present embodiment cannot be used to cultivate vegetation.

[0026]
However, since the COD treated water W3 has its water soluble organic substance removed, it can be distilled by distillation means. Thus, the COD treated water W3 generated by the COD removing device 30 is put into the solar heat still 50 and is distilled, thereby salt can be removed.

[0027]
The COD treated water W3 put into the solar heat still 50 is heated by the heater using solar heat and is distilled in the solar heat still 50. The purified water W4 is generated by the solar heat still 50 using the distilled water obtained by distillation.

[0028]

= 0 CA 02690542 2009-12-10 The salt dissolved in the COD treated water W3 is deposited as salt S in the process of distillation by the solar heat still 50. Accordingly, it can be stored in a storage reservoir, for example, and can be brought to the treatment site by a truck or other appropriate means.

[0029]
Solid contaminants, water soluble organic substance and salt are removed from the purified water W4 generated by the solar heat still 50. Thus, the purified water W4 can be used for a great variety of applications.

[0030]
In Fig. 1, the purified water W4 generated by the oil-contaminated water reutilization system 1 is used for the vegetation cultivation plant P1 for cultivating the vegetation for biofuel (e.g., Jatropha), for example. In a biofuel production plant and others, the biofuel can be produced from the vegetation such as Jatropha cultivated at the vegetation cultivation plant Pl. As described above, the purified water W4 generated from the oil-contaminated water W1 by the oil-contaminated water reutilization system 1 of the present embodiment can be used (or reused) to produce the biofuel.

= CA 02690542 2009-12-10 [0031]
The following describes the components constituting the oil-contaminated water reutilization system 1:
<<Magnetic coagulation separator>>
Fig. 2 shows an embodiment of the magnetic coagulation separator in the oil-contaminated water reutilization system shown in Fig. 1. In Fig. 2, the oil-contaminated water W1 containing the oil-contaminated component is fed into the raw water oil tank 12 by a pump P, and is stored therein. In the raw water oil tank 12, the oil-contaminated water W1 is stirred by the stirrer 12a which is driven by the motor M. Oil in the oil-contaminated water W1 having been stirred spreads in a thin layer around the liquid level, and is emulsified and dispersed in water at the same time. In the magnetic coagulation separator 10, the pipe running from the raw water oil tank 12 is provided with a recirculating path 14 that allows the oil to go back to the raw water oil tank 12 through the in-line mixer 13. The in-line mixer 13 is operated so that the oil is recirculated inside the recirculating path 14, thereby the oil in water inside the raw water oil tank 12 is sufficiently emulsified.
The in-line mixer 13 and recirculating path 14 constituting the recirculation system are operated for a predetermined period of time and the oil in the oil-contaminated water W1 is emulsified. After that, the in-line mixer 13 is stopped and the raw water valve 15 is opened.

[0032]
It should be noted that a reservoir type emulsion generation method has been shown, but it is also possible to use the continuous type API (American Petroleum Institute), PPI (Parallel Plate Interceptor) or CPI (Coagulated Plate Interceptor) type oil separation method or the method wherein the oil layer is removed using a cyclone, and only the emulsified oil-contaminated water W1 is fed to the coagulation reservoir 16.

[0033]
The aforementioned arrangement allows the oil-contaminated water W1 including the emulsified oil to flow into the coagulation reservoir 16. If the oil-contaminated water W1 contains small solids of such as mud, sand or salt, these solids together with liquid are fed into the coagulation reservoir 16. Further, oil may adsorb onto the solids, although this depends on the type of solids.

[0034]

Coagulants as iron or aluminum salts as exemplified by ferric sulfate, ferrous chloride or polyaluminum chloride are put in the coagulation reservoir 16, and are stirred by the stirrer 16a which is driven by the motor M, so that coagulation occurs.
In this case, if magnetic particles (magnetic components) such as magnetite (ferroso-ferric oxide) are added at the same time, the emulsified particles of oil, solid contaminants and magnetic particles under water are coagulated to form a flock (magnetic flock) having a size of a few hundred micrometers through a few millimeters (the water forming a flock in the coagulation reservoir 16 will be hereinafter referred to as "interim treated water"). Thus, the coagulation reservoir 16 serves as a magnetic flock generating means.

[0035]
If sufficient emulsification cannot be achieved by the recirculating path 14, uniform formation of the flock cannot be performed. This will cause excessive input of the coagulant, and will generate an increased amount of sludge. Further, the oil layer which has not absorbed on the flock flowed to downstream side and being contained in the waste water, so that the separator installed on the downstream side will be contaminated with oil. Moreover, in the reaction of coagulation, the coagulant is generally acidic, and therefore, alkali such as sodium hydroxide is preferably put therein to adjust the pH value. Further, the strength of flock can be increased by putting high molecular polymer in the process of coagulation. This interim treated water is placed into the separator 17.

[0036]
The separator 17 incorporates a rotary filtration film 18 provided with an aperture having a size of approximately several micrometers through several tens of micrometers. Thus, the liquid is filtrated by the filtration film and the primary purified water W2 can be obtained inside the rotary filtration film 18. The flock deposited on the rotary filtration film 18 is separated by the cleaning water using the clarifier 19, and is dropped in the vicinity of a rotary cylinder 20 (magnetic separation means). A magnetic field generation device 21 (magnetic separation means) using a permanent magnet, superconducting bulk magnet, or electromagnet is installed inside the rotary cylinder 20. The flock is attracted by the magnetism of the magnetic field generation device 21 and is scraped off by a sludge collection plate 22 along the surface of the rotary cylinder 20. The flock is then stored into a sludge tank 23. Scraping off by the sludge collection plate 22 is carried out in the atmosphere, not under water. Thus, a certain amount of water falls down, thereby a sludge of smaller water content is obtained.

[0037]
The aforementioned procedure reduces the cost for the treatment of sludge, and permits combustion to be carried out without adding much fuel, depending on the circumstances. The flock mainly composed of oil has a light specific gravity and floats on water in many cases. However, its specific gravity may be increased by the influence of solid contaminants under water or the amount of coagulant, and some flocks sink under water. Thus, it is difficult to ensure highly efficient removal of the flock from water by the difference in specific gravity. By contrast, separation by magnetism ensures easy and highly efficient removal of the flock.

[0038]
Further, the boron contained in the oil-contaminated water W1 can be removed and the concentration of boron in the oil-contaminated water W1 can be reduced by using the aluminum compound such as aluminum sulfate is used as a coagulant. If the ' CA 02690542 2009-12-10 water containing much boron is used to cultivate vegetation, the vegetation is known to be adversely affected. Thus, it is preferred not to use water containing much boron for the purpose of cultivating vegetation.

[0039]
Especially in the dry land such as the Middle East, the amount of boron in the soil tends to be made excessive by dry weather, and the growth of vegetation is known to be often impaired by the excessive amount of boron. Thus, the water used for cultivation of vegetation in a particularly dry area is preferred to contain less boron. For example, in the case of Jatropha, use of water containing boron having a concentration 4 ppm or more is known to give a fatal influence to the vegetation.

[0040]
The magnetic coagulation separator 10 of the present embodiment can be used to remove the boron when the solid contaminants as oil-contaminated components are removed, thereby the concentration of boron contained in the oil-contaminated water W1 can be reduced. Thus, the conditions (the type and amount of the aluminum compound used in the coagulation reservoir 16, and time of stirring) of the magnetic coagulation separator 10 are set in such a way that the concentration of boron will be less than 4 ppm.
Then the purified water W4 used in the oil-contaminated water reutilization system 1 can be used in the Jatropha cultivation plant P1, as shown in Fig.
1.

[0041]
The permissible concentration of boron is known to differ according to the type of the vegetation to be cultivated, and environmental conditions for cultivation (soil and meteorological conditions). The amount of the boron to be removed by the magnetic coagulation separator 10 can be set as appropriate. In the oil-contaminated water reutilization system 1 of the present embodiment, the concentration of boron can be set over a wide range, for example, by appropriate setting of the type and amount of the aluminum compound, and time of stirring, as described above.

[0042]
Further, boron can also be removed by distillation in the subsequent treatment. This arrangement ensures a further reduction in the concentration of boron, and provides the water (purified water W4) suitable for cultivation of vegetation in a dry land.

[0043]

A permanent magnet or electromagnet can be effectively used as the magnet of the magnetic coagulation separator 10. However, a high level of magnetism can be provided by a small-sized separator if a superconducting bulk member -- a high-temperature superconducting bulk in particular -- is used. In this case, if the high-temperature superconducting bulk is cooled by conduction using a small-sized refrigerator such as a GM (Gifford McMahon) refrigerator or pulse tube refrigerator, there is no need of replenishing the coolant such as liquid helium or liquid nitrogen.
This arrangement ensures excellent maneuverability.

[0044]
The oil-contaminated water reutilization system 1 of the present embodiment (Fig. 1) has a magnetic coagulation separator 10 of the aforementioned structure, and is capable of producing a primary purified water W2 by removing the solid contaminants from oil-contaminated water Wl.

[0045]
In the present invention, an example has been taken from the magnetic coagulation separation as a method of removing the oil-contaminated component and solid contaminants. The same advantages as those of the present embodiment can also be obtained by using other coagulation separation methods wherein, instead of the magnetic particle (magnetic component), sand particles or pressurized air is used in the process of coagulation, and separation is made by sedimentation, flotation or cyclone.
<<COD removing device>>
In the present embodiment, the COD removing device using the process of ozone degradation and activated carbon adsorption is employed as the COD removing means for removing the water soluble organic substance dissolved in the primary purified water W2. Fig. 3 shows an embodiment of the COD removing device in the oil-contaminated water reutilization system shown in Fig. 1. As shown in Fig. 3, the COD removing device 30 contains a ozone treatment reservoir 31 for storing the primary purified water W2 generated by the magnetic coagulation separator 10; a ozone generator 32 for supplying ozone to the ozone treatment reservoir 31; and an activated carbon treatment reservoir 33 filled with activated carbon 33a.

[0046]
There is no particular restriction to the ozone generator 32. For example, one of the methods preferably used is the method (silent discharge method) wherein AC high voltage is applied between two * CA 02690542 2009-12-10 electrodes sandwiching air and dielectric in-between, and electrical discharge is caused, thereby oxygen is made into ozone by the energy of discharge plasma.

[0047]
As shown in Fig. 3, the primary purified water W2 generated by the magnetic coagulation separator 10 is put into the ozone treatment reservoir 31 and is stored therein. The ozone treatment reservoir 31 is supplied with the ozone generated in the ozone generator 32. Since ozone has a very high level of acidity, it oxidizes the water soluble organic substance dissolved in the primary purified water W2 stored in the ozone treatment reservoir 31 and degrades it into a biodegradable substance (easily biodegradable substance).

[0048]
The primary purified water W2 obtained by degradation of the organic substance by the biodegradable substance in the ozone treatment reservoir 31 is put into the activated carbon treatment reservoir 33 filled with activated carbon 33a.

[0049]
In the activated carbon treatment reservoir 33, the biodegradable substance contained in the primary purified water W2 is subjected to biodegradation by the microbe deposited on the surface of the activated carbon 33a. At the same time, the water soluble organic substance remaining in the primary purified water W2 is removed by adsorption.

[0050]
As described above, in the COD removing device 30 of the present embodiment, the water soluble organic substance dissolved in the primary purified water W2 is subjected to oxidative degradation by ozone. At the same time, the biodegradable substance generated by oxidative degradation is subjected to biodegradation by the microbe deposited on the activated coal, thereby the primary purified water W2 is purified, and the COD treated water W3 is obtained.

[0051]
Since ozone is generated from oxygen, the water subsequent to the process of clarification (COD
treated water W3) contains no remaining impurities.
Further, since ozone is formed from the oxygen omnipresent in the atmosphere, a required amount of ozone can be obtained at a desired time. For this reason, the present embodiment uses the COD removing device 30 which is based on the principle of ozone degradation. Further, when the biodegradable substance generated by ozone degradation is subjected to biodegradation, the remaining water soluble organic substance is removed by adsorption. Thus, the activated coal adsorption process is used in the COD
removing device 30. However, the COD removing means is not restricted to the COD removing device 30 which uses the process of ozone degradation and activated coal adsorption. In addition to the process of ozone degradation and activated coal adsorption, the process of Fenton treatment and electrolysis are conventionally known as the art of removing the water soluble organic substance dissolved in the oil-contaminated water and clarifying the water. These processes can be used as the COD removing means. These processes can be used independently or two or more of them can be used in combination.

[0052]
The COD treated water W3 obtained in the aforementioned procedure does not include any water soluble organic substance. Accordingly, even if distilled by distillation means, there is no possibility of a water soluble organic substance being deposited or remaining in the generated distilled water. Further, the solid contaminants are removed by the magnetic coagulation separator 10 (Fig. 2). Thus, even if the COD treated water W3 is distilled by distillation means, there is no possibility of ducts of the heater of the distillation means being clogged with solid contaminants or water soluble organic substances. The COD treated water W3 of the present embodiment can be further purified by he distillation means and the salt is removed.

[0053]
However, in the COD removing device 30 of Fig. 3, the activated carbon 33a is used as the adsorbent.
Without the present invention being restricted thereto, zeolite can be used, for example. Further, in the COD
removing device 30 of Fig. 3, biodegradation is carried out in the activated carbon treatment reservoir 33. Without the present invention being restricted thereto, an apparatus different from the activated carbon treatment reservoir 33 can be used.
<<Solar heat still>>
In the present embodiment, the COD treated water W3 (Fig. 3) generated by the COD removing device 30 is distilled by a distillation means, and purified water W4 (Fig. 1) with salts removed is obtained. A solar still having a heater using solar heat is used as the distillation means for distilling the COD treated water W3. The solar heat still shown in Fig. 4 is conventionally known. Fig. 4 shows an embodiment of the solar heat still.

[0054]
As shown in Fig. 4, the COD treated water W3 generated by the COD removing device 30 is led to the heater 51 of the solar heat still 50 by the pump P, and is heated by the solar heat. The heater 51 is arranged in such a way that the duct through which the COD treated water W3 runs will expand parallel to the surface exposure to the sun. The COD treated water W3 running through the duct is heated by the solar heat applied to the duct. In this case, the solar heat absorbing efficiency is improved by using the duct with black or other color that easily absorbs the solar heat, and this contributes to efficient heating of the COD treated water W3. Further, the heat transfer efficiency is enhanced by reducing the wall thickness of the duct, and the efficient heating of the COD treated water W3 flowing inside is also ensured. The heating efficiency is also improved by expanding the duct to the greatest possible extent with reference to the surface exposed to the sun. To minimize the pressure loss of the running water, the duct diameter is preferably increased, and the number of bends is preferably minimized.

[0055]
The COD treated water W3 is sprayed into the coolant reservoir 53 by the sprinkler 52, and the sprayed COD treated water W3 is evaporated by the heat exchange with air in the coolant reservoir 53, thereby steam ST is produced. It should be noted that there is no particular restriction to the sprinkler 52, if it has a function of spraying the COD treated water W3 by the rotation of the fan (not illustrated).

[0056]
In the coolant reservoir 53, the COD treated water W3 is cooled by the latent heat produced by evaporation. The COD treated water W3 that is not evaporated is stored in the coolant reservoir 53 as coolant.

[0057]
The COD treated water W3 having been converted into steam ST by evaporation is put into a coagulant reservoir 54. In the coagulant reservoir 54, the COD
treated water W3 cooled by the coolant reservoir 53 is recirculated as coolant Wc. The steam SP put into the coagulant reservoir 54 is cooled by the coolant Wc and is condensed, thereby purified water W4 is produced.
The COD treated water W3 having cooled the steam ST is fed back to the coolant reservoir 53.

[0058]
In the solar heat still 50 of the aforementioned structure, the COD treated water W3 is fed into the heater 51 by the pump P. The temperature of the COD
treated water W3 is raised 10 through 20 C by exposure to the sun through the heater 51, and is sprayed into the coolant reservoir 53 by the sprinkler 52. In the coolant reservoir 53, the COD treated water W3 with the temperature having been raised is evaporated by heat exchange with air, and the COD treated water W3 is cooled by the latent heat resulting from this evaporation, whereas the air is heated. The steam ST
having been evaporated in the coolant reservoir 53 is fed to the coagulant reservoir 54 and is cooled and condensed by the COD treated water W3 cooled by the coolant reservoir 53. The steam ST having been evaporated in the coolant reservoir 53 and having been fed to the coagulant reservoir 54 has the temperature higher by about 10 C than the COD treated water W3 cooled by the coolant reservoir 53 and fed to the coagulant reservoir 54. Thus, in the coagulant reservoir 54, part of the steam ST is cooled and condensed, thereby purified water W4 is produced.

[0059]
In the solar heat still 50 shown in Fig. 4, the COD treated water W3 is heated by the heater 51 using the solar heat and is further evaporated and condensed, thereby purified water W4 is obtained. Thus, the electric power for getting the purified water W4 is restricted only to the power of the pump P and sprinkler 52. The purified water W4 is obtained with the minimum power by making the maximum use of the solar heat as natural energy. Thus, the COD treated water W3 is distilled, and purified water W4 is obtained at a reduced cost. At the same time, the discharge of carbon dioxide can be reduced. Thus, this arrangement ensures production of a system friendly to global environment.

[0060]
As shown in Fig. 4, a solar heat still 50 provided with a coolant reservoir 53 and coagulant reservoir 54 is used as the distillation means in the present embodiment. Without the present invention being restricted thereto, a membrane still using a hydrophobic porous membrane is a known example to which the present invention is applicable.

[0061]
Fig. 5 shows an embodiment of the membrane still in the oil-contaminated water reutilization system shown in Fig. 1. As shown in Fig. 5, the membrane still 55 is structured in such a way that the duct through which the COD treated heated water W3 runs and the duct through which the coolant Wc runs contact each other through the hydrophobic porous membrane 56.

[0062]
The hydrophobic porous membrane 56 has a great number of fine pores having a size that permits passage of the water molecule as steam, and is capable of separating water as liquid (COD treated water W3) from the steam as gas. The steam having passes through the hydrophobic porous membrane 56 is cooled and condensed by the coolant Wc, thereby purified water W4 is produced. As shown in Fig. 5, a space wherein purified water W4 is condensed may be provided between the hydrophobic porous membrane 56 and the ducts through which coolant Wc run.

[0063]
As shown in Fig. 5, even when the membrane still 55 is used, solar heat can be used to heat the COD
treated water W3.

[0064]
Since the COD is removed by the COD removing device 30 (Fig. 3), heat transfer efficiency is not reduced in the phase of heating, or the hydrophobic porous membrane 56 is not clogged, even when the membrane still 55 is used.

[0065]
As described above, the solar heat still 50 using the solar heat is employed as the distillation means.
This arrangement reduces the load on the global environment. Thus, the COD treated water W3 can be distilled to get the purified water W4 that has been purified by distillation. Further, since COD is removed by the COD removing device 30 (Fig. 3), effective use of solar heat can be ensured without heat transfer efficiency being reduced.

[0066]
The salt removing means is not restricted to the solar heat still 50 (Fig. 4) and membrane still 55 (Fig. 5). The conventionally known technique of clarifying the water containing salt is exemplified by the reverse osmosis membrane method and freezing method, which can be used as the salt removing means of the present embodiment.

[0067]
As described above, in the present embodiment, the oil-contaminated water generated in the process of petroleum production is distilled and purified in the final phase. The purified water produced is clear water that hardly contains a solid contaminant, water soluble organic substance or salt as the substance to be removed. This arrangement ensures the purified water to be used over an extensive range. Further, in the magnetic coagulation separator 10 (Fig. 1), aluminum compound is added as a coagulant to achieve coagulation and separation, as described above, thereby boron is removed from the oil-contaminated water W1 (Fig. 1), and the concentration of boron is reduced.

[0068]
As described above, the magnetic coagulation separator 10 carries out coagulation and separation using the coagulant, thereby removing boron. This arrangement increases the degree of freedom in the selection of devices in the succeeding process.

[0069]
Further, as described above, the excessive amount of boron is detrimental to vegetation. Especially in the dry land, the amount of boron tends to increase even if much boron is not included. This may hinder the growth of vegetation. Accordingly, it is preferred not to use the water containing boron for cultivation of vegetation. Boron is removed from the purified water W4 generated by the oil-contaminated water reutilization system 1 in the present embodiment, and the concentration of boron contained therein is very low. Accordingly, the purified water W4 can be used for cultivation of the vegetation.

[0070]
In the present embodiment, as shown in Fig. 1, the purified water W4 generated in the oil-contaminated water W1 is used in a vegetation cultivation plant Pl, especially in the Jatropha cultivation plant Pl. A
biofuel can be produced from by the oil content extracted from the seed of Jatropha, and Jatropha itself is not an edible plant. Thus, differently from corn or sugar cane, Jatropha can be produced only for the purpose of production of biofuel without adversely affecting the supply of food. For this reason, the amount of cultivation of Jatropha is expected to increase. Further, a relatively small amount of water is required for cultivation. Jatropha can be cultivated with comparative ease in a dry land of very small precipitation as in the Middle East as a petroleum production area.

[0071]
Fig. 6 is a schematic diagram representing a Jatropha cultivation field (Photo for reference only).
As shown in Fig. 6, Jatropha Ja can be cultivated at intervals about 2.5 meters (2 through 3 meters). About 1600 pieces of Jatropha Jo can be cultivated on the Jatropha cultivation field 70 of one hectare. If 1600 pieces of Jatropha Ja is cultivated on the Jatropha cultivation field 70 of one hectare, about 2.5 through 12 tons of seeds is expected to be yielded six years after start of cultivation. About 0.71 through 3.4 kL
of biofuels can be yielded from this amount of seeds.
To be more specific, an annual production of 0.71 through 3.4 kL of biofuels can be gained from the Jatropha cultivation field 70 of one hectare.

[0072]
It should be noted that such Jatropha cultivation fields 70 are integrated to form a vegetation cultivation plant P1 (Fig. 1) made up of vast Jatropha cultivation fields 70. Thus, biofuels are produced from the Jatropha Ja produced in the vegetation cultivation plant Pl.

[0073]
As described above, the Jatropha Ja is highly resistant to dry climate. However, 2500 m3 of water is required for the Jatropha cultivation field 70 of one hectare for cultivation of 1600 pieces of Jatrophas Ja.
This is equivalent to annual precipitation of 250 mm.

[0074]
This annual precipitation is several times greater than that in the Middle East as the major petroleum production site (e.g., 5 through 6 times greater than that of Oman registering about 40 through 50 mm).
Accordingly, the precipitation in the Middle East is not sufficient to provide the amount of water required to cultivate Jatropha Ja.

[0075]
In the present embodiment, the purified water produced from the oil-contaminated water generated in the petroleum production is used for the production of Jatropha Ja, thereby Jatropha Ja can be cultivated even on the Middle East characterized by very small precipitation. Biofuels are produced from Jatropha Ja, and this arrangement provides a new energy resource supply source. In addition to these excellent advantages, the present embodiment provides an excellent effect of contributing to afforestation of the desert.

Claims

1. An oil-contaminated water reutilization system comprising:
a treated water generation device for generating treated water by removing oil-contaminated component as a substance to be removed, from oil-contaminated water generated in the process of petroleum production;
a COD removing device for removing water-soluble organic substance as the substance to be removed, from the treated water generated by the treated water generation device; and a salt removing device for removing salt as the substance to be removed, by adding heat to the treated water from which the water-soluble organic substance has been removed by the COD removing device, thereby purified water is obtained, wherein the salt removing device is a membrane still which is structured in such a way that a duct through which the treated heated water runs and another duct through which a coolant runs contact each other through a hydrophobic porous membrane having pores of a size to permit passage of water molecule as steam.

2. The oil-contaminated water reutilization system according to Claim 1, wherein the treated water generation device comprises:
a magnetic flock generation device for generating a magnetic flock by adding to the oil-contaminated water a coagulant and magnetic component for coagulating the oil-contaminated component; and a magnetic separation device for sucking and collecting the generated magnetic flock by magnetic force.

3. The oil-contaminated water reutilization system according to Claim 1 or Claim 2, wherein the COD removing device removes the COD by using any one of an ozone degradation, a Fenton processing, an electrolysis and an activated carbon adsorption.

4. The oil-contaminated water reutilization system according to any one of Claim 1 to Claim 3, wherein the salt removing device is for heating the treated water by using solar heat.

5. The oil-contaminated water reutilization system according to any one of Claim 1 to Claim 4, wherein the treated water with the salt having been removed therefrom is used to cultivate plants.