AU2012384397A1

AU2012384397A1 - Method and device for treating saline wastewater

Info

Publication number: AU2012384397A1
Application number: AU2012384397A
Authority: AU
Inventors: Shigeo Hatamiya; Ayumi Hatano; Toshiaki Matsuo; Kenji Okishiro; Hiroshi Sasaki; Hiroki Yamamoto
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2012-07-06
Filing date: 2012-07-06
Publication date: 2015-01-29
Anticipated expiration: 2032-07-06
Also published as: AU2012384397B2; JPWO2014006741A1; WO2014006741A1; JP5865495B2

Abstract

The present invention provides a method and device for treating saline wastewater, e.g., accompanying water from gas field drilling, the method and device making it possible to highly efficiently convert the saline wastewater into an effectively utilizable substance in high yield at low cost with reduced environmental burdens. Saline wastewater which contains sodium chloride is concentrated by separating water from the saline wastewater to thereby produce high-concentration saline wastewater. The high-concentration saline wastewater is introduced into the positive-electrode-side chamber of an electrolytic tank which includes a positive electrode and a negative electrode that have been separated by a semipermeable membrane that is permeable to sodium ions, and electrolysis is then conducted to yield sodium hydroxide in the high-concentration saline. This sodium hydroxide is brought into contact with a gas discharged from a gas-turbine power generator or engine power generator which has been disposed in order to obtain electric energy for operating either the plant from which the saline wastewater is discharged or the device for treating the saline wastewater, thereby obtaining an aqueous solution containing sodium carbonate and/or sodium hydrogen carbonate. The sodium carbonate and/or sodium hydrogen carbonate is separated and recovered from this aqueous solution.

Description

1 DESCRIPTION Title of Invention METHOD AND DEVICE FOR TREATING SALINE WASTEWATER 5 Technical Field [0001] The present invention relates to a method and device for treating saline wastewater, and relates more 10 specifically to a treatment device for saline wastewater suitable to a volume reduction treatment of produced water generated in mining an oil field and a gas field, and a treatment method thereof. Background Art 15 [0002] In mining an oil field and a gas field, produced water containing salinity is generated along with oil and natural gas. Normally, the produced water is returned to the well of the oil field and the gas field in most cases to suppress 20 the ground subsidence and so on. However, accompanying increase of steam injection and the like used in mining, the produced water of an amount exceeding the returning amount to the well tends to be generated. With respect to the excessive produced water, it is preferable to bring the 25 eventual generation amount closer to zero without any limit 2 by a treatment from the viewpoint of protection of environment. Further, in seawater desalination also, handling of the concentrated saline water generated in desalinating the seawater becomes a problem. There is also 5 a case that returning the concentrated saline water to the sea causes volatility of environment, and it is preferable to reduce the wastewater containing a salt as much as possible. [0003] 10 Until now, with respect to the treatment of the wastewater containing these salts such as sodium chloride and the like, it has been proposed to reduce the wastewater (saline wastewater) amount by a concentration treatment using a reverse osmosis membrane (RO membrane) and heating 15 (PTL 1 for example) . In PTL 1, the wastewater is evaporated and concentrated, and steam is used which is generated from an exhaust heat recovery boiler that utilizes the exhaust heat of a gas turbine as a heat source used for evaporation and concentration. 20 [0004] On the other hand, in PTL 2, it is described to form soda ash by making carbon dioxide and ammonia react with saline water waste liquid derived from a desalination plant. Also, in PTL 2, the carbon dioxide is obtained from a waste 3 gas flow derived directly or indirectly from a combustion generation source. [0005] Further, in PTLs 3 and 4, as a method for obtaining a 5 crystal of sodium carbonate, it is described to collect a sodium hydroxide aqueous solution by electrolyzing a sodium chloride aqueous solution using membrane type electrolytic cells, and to obtain slurry of a crystal of sodium carbonate by direct contact of the sodium hydroxide aqueous solution 10 and carbon dioxide. Also, in PTLs 3 and 4, it is described that, as the carbon dioxide, carbon dioxide obtained by causing limestone to act on a hydrochloric acid aqueous solution obtained by that chlorine and hydrogen generated by electrolysis are made to react with each other or a flue gas 15 discharged from a thermal-electric combined supply facility is used. Citation List Patent Literature [0006] 20 PTL 1: International Laid-Open No. 2012/008013 PTL 2: Japanese Unexamined Patent Application Publication No. 2012-509237 (International Laid-Open No. 2010/057261) 4 PTL 3: Japanese Unexamined Patent Application Publication No. 2008-532904 (International Laid-Open No. 2006/094982) PTL 4: Japanese Unexamined Patent Application 5 Publication No. 2010-503600 (International Laid-Open No. 2008/031834) Summary of Invention Technical Problems [0007] 10 In PTL 1, the saline wastewater is concentrated, and the amount of the saline wastewater eventually discharged is reduced. However, in order to reduce the waste as much as possible, it is desirable not only to reduce the volume but also to add a devisal of consumption by converting the waste 15 to a valuable object and turning the same into a state easily received by the society or by effectively utilizing the same if possible. [0008] From this viewpoint, in PTL 2, the saline water waste 20 liquid is used for formation of material added with other values (soda ash), and an economical and/or environmental cost can be reduced. However, in PTL 2, a so-called ammonia soda process is used, and ammonia is required for the reaction. When the ammonia soda process is applied to PTL 1 25 for example in which an evaporation and concentration 5 treatment is used for a concentration treatment, the temperature of the concentrated waste liquid is comparatively high, ammonia evaporates and is hard to react. When the concentrated waste liquid is subjected to the 5 reaction after the temperature thereof is lowered, thermal energy of the concentrated waste liquid comes to be wasted and a facility for lowering the temperature is required which is considered to be undesirable. [0009] 10 In PTLs 3 and 4, concentrated saline water is obtained by adding rock salt, a sodium hydroxide aqueous solution is obtained by electrolyzing the concentrated saline water, this sodium hydroxide aqueous solution and carbon dioxide are subjected to gas-liquid contact, and slurry of a crystal 15 of sodium carbonate is obtained. In this method of using electrolysis, it is not necessary to use ammonia for obtaining sodium carbonate as in PTL 2. However, in PTL 3, wastewater such as the produced water generated in mining an oil field and a gas field is not an object. In other words, 20 treatment of saline wastewater is not considered. Also, to add rock salt to the saline wastewater to obtain the concentrated saline water is not realistic. Further, in the saline wastewater such as the produced water, metal ions of magnesium, calcium and the like other than sodium ions and 25 an organic substance are contained, and it is preferable to 6 effectively remove them before the saline wastewater such as the produced water and the like is introduced to an electrolysis vessel. [0010] 5 The present invention has been developed in view of the points described above, and is to provide a method and device for treating saline wastewater capable of converting saline wastewater such as the produced water and the like with high yield and high efficiency to a substance capable 10 of being effectively utilized at a low cost and a low environmental load. Solution to Problem [0011] In order to solve the problems described above, the 15 present invention is configured to separate a water content from saline wastewater containing sodium chloride, thereby to concentrate the saline wastewater and to produce high concentration saline wastewater, to produce the high concentration saline wastewater to the positive electrode 20 side of an electrolysis vessel including a positive electrode and a negative electrode partitioned by a semipermeable membrane that causes sodium ions to permeate therethrough, to form sodium hydroxide in the high concentration saline wastewater by electrolysis, to cause 25 the sodium hydroxide to be in contact with an exhaust gas of 7 a gas turbine generating device or an engine generating device installed in order to obtain electric energy that activates a plant discharging the saline wastewater or a treatment device for the saline wastewater and thereby to 5 obtain an aqueous solution containing sodium carbonate and/or sodium hydrogencarbonate, and to separate and recover the sodium carbonate and/or sodium hydrogencarbonate from the aqueous solution. Advantageous Effects of Invention 10 [0012] According to the present invention, the saline wastewater such as the produced water and the like can be converted to a substance capable of being effectively utilized with a high yield and high efficiency at a low cost 15 and a low environmental load. [0013] Problems, configurations and effects other than those described above will be clarified by description on embodiments below. 20 Brief Description of Drawings [0014] FIG. 1 is a system configuration diagram of a case a treatment device for the saline wastewater of an embodiment of the present invention is applied to a treatment of the 25 produced water of a coal gas field.

8 FIG. 2 is a schematic view showing an example of an electrolysis vessel used for a treatment device for the saline wastewater of the present invention. FIG. 3 is a schematic view showing an example of a C02 5 absorption device used for a treatment device for the saline wastewater of the present invention. FIG. 4 is a system configuration diagram of a treatment device for the saline wastewater in an embodiment of the present invention. 10 FIG. 5 is a system configuration diagram of a treatment device for the saline wastewater in another embodiment of the present invention. FIG. 6 is a system configuration diagram of a treatment device for the saline wastewater in another 15 embodiment of the present invention. FIG. 7 is a system configuration diagram of a treatment device for the saline wastewater in another embodiment of the present invention. FIG. 8 is a system configuration diagram of a 20 treatment device for the saline wastewater in another embodiment of the present invention. FIG. 9 is a perspective view showing an example of an electrolysis vessel used in a treatment device for the saline wastewater of the present invention.

9 FIG. 10 is a top view of the electrolysis vessel shown in FIG. 9. FIG. 11 is a perspective view showing another example of an electrolysis vessel used in a treatment device for the 5 saline wastewater of the present invention. FIG. 12 is a perspective view showing another example of an electrolysis vessel used in a treatment device for the saline wastewater of the present invention. FIG. 13 is a perspective view showing another example 10 of an electrolysis vessel used in a treatment device for the saline wastewater of the present invention. Description of Embodiments [0015] Below, embodiments of the present invention will be 15 described using the drawings. [0016] First, how the present invention has been developed will be described. [0017] 20 As described above, in order to reduce the waste as much as possible, it is preferable not only to reduce the volume but also to convert the waste to a valuable object. In order to be converted to a valuable object, it can be conceived for example to reduce the volume of the saline 25 wastewater to solid salt, and to refine the same thereafter 10 and to convert the same to a common salt. However, when the manufacturing cost is compared to that of an ordinary common salt, in terms that various impurities removing steps are required, to manufacture the common salt from the saline 5 wastewater is extremely disadvantageous economically. Further, there is also a physiological sense of rejection in eating and drinking a product recovered from the wastes. From such viewpoint, it is preferable to convert the saline wastewater that is the waste to a product utilized in a 10 style with a low load on the environment including human health by a method as close as possible to a common manufacturing process with a high yield and high efficiency. [0018] Therefore, the present inventors considered to form 15 sodium hydrogencarbonate (sodium bicarbonate, NaHCO3) or sodium carbonate (Na2CO3) by obtaining sodium hydroxide (caustic soda) by electrolyzing the saline wastewater and causing carbon dioxide to react with the same by aeration and the like. 20 [0019] In the produced water and the like generated in mining an oil field and a gas field, metal ions of magnesium, calcium and the like other than sodium ions and organic substances are contained, and it is preferable to remove 25 them effectively before the saline wastewater such as the 11 produced water and the like is introduced to the electrolysis vessel. [0020] The solubility of the salt of magnesium, calcium and 5 the like of the alkaline earth metal is lower compared to a sodium salt. Therefore, it was considered to precipitate the salt of magnesium, calcium and the like of the alkaline earth metal by concentrating the saline wastewater and to allow to be separated from the saline wastewater before 10 being introduced to the electrolysis vessel. Further, with respect to the organic substances also, it was considered to be allowed to be separated utilizing salting out. Thus, by concentration treatment of the saline wastewater, the saline wastewater can be made a treatment liquid that is rich in a 15 sodium salt suitable to obtain caustic soda from the saline wastewater by an electrolytic treatment. [0021] Also, in a plant discharging the saline wastewater (for example a mining plant of an oil field and a gas field), 20 electric energy is necessary, and a gas turbine generating device is often installed. Therefore, it was conceived that, when the gas turbine exhaust gas of the gas turbine generating device was used as carbon dioxide used in forming sodium hydrogencarbonate (sodium bicarbonate, NaHCO3) or 25 sodium carbonate (Na2CO3), the gas turbine exhaust gas could 12 be utilized also for fixing carbon dioxide contained in the exhaust gas, leading to reduction of the equipment cost of the saline wastewater treatment device. Further, because enormous DC current is required also for the treatment 5 device for the saline wastewater, it is also possible to install a gas turbine generating device and an engine generating device for obtaining electric energy of the treatment device for the saline wastewater, and to use the exhaust gas thereof as carbon dioxide used for reaction of 10 carbonation of caustic soda. [0022] Thus, the salt having a higher value can be preferentially produced in the saline wastewater treatment, and the salt content in the saline wastewater eventually 15 discharged can be minimized. Also, because the electric power used for the treatment device for the saline wastewater is covered, the carbon dioxide amount discharged from a generating device using a fossil-derived fuel can be reduced and so on, and the impact on environment can be 20 reduced. Further, by performing the concentration treatment of the saline wastewater utilizing the heat derived from the exhaust gas of a generating device and so on, the efficiency as the entire system can be improved. [0023] 13 Next, using a treatment system for the produced water generated in mining an oil field and a gas field which is an appropriate application example of a method and device for treating saline wastewater of the present invention, the 5 summary of the embodiment of the present invention will be described including various devisal points, and the system configuration example of the treatment device for the saline wastewater will be thereafter described in detail. [0024] 10 FIG. 1 is a system configuration diagram of a case a treatment device for the saline wastewater of an embodiment of the present invention is applied to a treatment of the produced water of a coal gas field. [0025] 15 The present treatment system is composed of an RO membrane system for treating the saline wastewater that is the produced water in mining a gas field, a system for obtaining the fresh water by a multi-effect distillation (MED) system, an electric power/heat supply system for 20 generating electric energy, steam and the like for driving these systems, an electrolysis/volume reduction system for treating high concentration saline wastewater generated in the MED system and obtaining a valuable salt such as sodium carbonate, sodium hydrogencarbonate and the like, and a 25 chlorine refining/liquefaction system for treating a 14 chlorine gas generated by electrolysis. The electric power/heat supply system also generates electric energy required for the mining plant of the gas field. [0026] 5 In FIG. 1, 101 is a gas field, 102 is a gas treatment device, 103 is a water supply pump, 104 is a strainer, 105 is a pretreatment device such as a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane) and the like, 106 is a pressurized air tank, 107 is an alkali 10 supply tank, 108 is an acid supply tank, 109 is a neutralization tank, 110 is a high pressure water pump, 111 is an RO membrane desalination device, 112 is a chemical cleaning/discharge treatment device, 113 is a pressure energy recovery device, 114 is a surface back washing device 15 (blower), 115 is a product gas supply blower, 116 is an MED device, 117 is a heat exchanger, 118 is a radiator unit, 119 and 120 are ejectors, 121 is a gas turbine, 122 is a generator, 123 is an exhaust heat recovery boiler, 124, 125 and 126 are liquid feed pumps, 127 is a 20 transformer/converter, 128 is an electrolysis vessel, 129 is a scrubber, 130 is a powder separator, 131 and 132 are liquid feed pumps, 133 is a C02 absorption device, 134 is a powder separator, 135 is a sodium carbonate vessel, 136 is a heat exchange type cooler, 137 is a gas/liquid separator, 25 138 is a dryer, 139 is a concentrated sulfuric acid vessel, 15 140, 141 and 142 are liquid feed pumps, 143 is a sulfuric acid concentration vessel, 144 is a chlorine gas liquefaction device, 145 is a liquid feed pump, 146 is a liquefied chlorine vessel, 147 is a steam turbine, 148 is a 5 generator, and 152 is a liquid feed pump. [0027] Natural gas mined from the gas field 101 is refined by the gas treatment device 102, and is thereafter fed by the product gas supply blower 115. Also, the produced water 10 gushing from the gas field 101 along with the natural gas mined is pumped by the water supply pump 103 and is introduced to the RO membrane system. [0028] In the RO membrane system, in order to reduce a load 15 to the RO membrane, first, impurities of a solid matter are removed from the produced water by the strainer 104. Thereafter, in the pretreatment device 105, impurities of a fine solid matter are removed from the produced water. As the pretreatment device 105, the MF membrane, the UF 20 membrane, or a combination of the both is used. In the pretreatment device 105, the rise of the pressure difference between before and after the membrane is monitored (illustration of the pressure gage is omitted), when the pressure difference rises beyond a set value, the water 25 supply pump 103 is stopped, valves are opened and closed 16 properly, and membrane cleaning is performed. For example, high pressure air is blown in from the surface back washing device (blower) 114, and the membrane is cleaned. Also, according to the necessity, backwashing of the membrane by 5 high pressure air blow from the pressurized air tank 106 and washing of the membrane surface with chemicals using an alkaline solution (caustic soda) from the alkali supply tank 107 and an acid from the acid supply tank 108 are performed. The acid and alkali used in washing with chemicals are 10 neutralized, are added with a reducing agent according to the necessity to be treated, and thereafter the waste liquid is recovered to the neutralization tank 109. The waste liquid recovered is discharged thereafter. [0029] 15 The produced water having passed through the pretreatment device 105 is fed to the RO membrane desalination device 111 by the high pressure water pump 110, fresh water is produced, and the salt portion is concentrated in the remaining liquid. In the RO membrane 20 desalination device 111 also, membrane surface cleaning using the acid and reducing agent is performed according to the necessity, and the wastewater thereof is fed to and treated in the chemical cleaning/discharge treatment device 112. Also, the fresh water discharged from the RO membrane 25 desalination device 111 is sent to the outside of the system, 17 energy of the concentrated water is recovered through the pressure energy recovery device 113, and the concentrated water is fed to the MED system as supply raw water. [0030] 5 In the MED system of the present embodiment, as the steam used for heating the supply raw water from the RO membrane desalination device 111, steam derived from the steam generated by the exhaust heat recovery boiler 123 that is steam after working in the steam turbine 147 (discharged 10 steam) is used. [0031] Also, in the MED system of the present embodiment, a part of the concentrated water discharged from the RO membrane desalination device 111 (supply raw water) is 15 directly fed to the MED device 116, and a part of the remaining portion is heated using a part of the discharged steam from the steam turbine 147 and is fed to the MED device 116. This heating is performed so that a part of the discharged steam is supplied to the heat exchanger 117 20 through the ejector 119, and the supply raw water goes through the heat exchanger 117. [0032] A part of the supply raw water in the MED device 116 is drawn in by the ejector 120 where a part of the 25 discharged steam from the steam turbine flows, is heated by 18 mixing with the steam, and returns thereafter to the MED device 116. At that time, the pressure inside the MED device 116 is reduced than the atmospheric pressure by drawing in by the steam flow, and it becomes easy that the 5 supply raw water inside the MED device evaporates. The steam generated inside the MED device 116 is cooled by the radiator unit 118 to become distilled water (fresh water), a part thereof is fed by the liquid feed pump 126 as the supply water to outside the system, and a part of the 10 remaining portion is fed to a boiler of the exhaust heat recovery boiler 123 by the liquid feed pump 124 as the supply water. Also, the produced water concentrated by evaporation (concentrated wastewater) is fed to the electrolysis vessel 128 by the liquid feed pump 125. 15 Further, with respect to concentration of the produced water by evaporation, although a device applied with the multi effect distillation method is most preferable, a distillation and concentration device other than that is also applicable. 20 [0033] In the present embodiment, concentration of the produced water is performed by the RO system and the MED system. By concentration of them, a salt of magnesium, calcium and the like of the alkaline earth metal having low 25 solubility contained in the produced water precipitates.

19 Further, the organic substances contained in the produced water also salt out. Thus, those becoming impurities in obtaining caustic soda become separable from the saline wastewater before the saline wastewater (produced water) is 5 introduced to the electrolysis vessel. Also, it is preferable to arrange a filter that captures precipitated impurities between the MED device and the electrolysis vessel although it is not illustrated. By subjecting the saline wastewater to a concentration treatment thus, the 10 saline wastewater can be made a suitable treatment liquid rich in sodium salt for the electrolytic treatment. [0034] The concentrated wastewater from the MED device 116 is supplied to the electrolysis vessel 128 of the 15 electrolysis/volume reduction system and is electrolyzed. An outline of the electrolysis vessel 128 used in the present embodiment will be described using FIG. 2. The electrolysis vessel 128 has a structure in which the positive electrode side cell and the negative electrode side 20 cell are partitioned by a semipermeable membrane 150, and the potential difference between both electrodes is controlled to approximately 3-5 V for example. The concentrated wastewater from the MED device 116 is supplied to the positive electrode side cell of the electrolysis 25 vessel 128.

20 [0035] When water containing sodium chloride is electrolyzed, caustic soda, chlorine and hydrogen are formed as the electrolytic chemical reaction shown in the expression (1) 5 and the expression (2) below. More specifically, in this reaction, chlorine ions are oxidized in a positive electrode 151, become chlorine molecules (gas), and are discharged from the upper part of the positive electrode side cell, and remaining sodium ions pass through the semipermeable 10 membrane 150, and move to the negative electrode side cell of the electrolysis vessel 128. On the other hand, on a negative electrode 153 side, hydrogen ions are reduced, become hydrogen molecules (gas) formed and are discharged from the upper part of the negative positive electrode side 15 cell, and remaining hydroxide ions form sodium hydroxide (caustic soda) along with sodium ions. 2NaCl - 2Na m + 2Cl - 2Na+ + C1 2 + 2e ... (1) 2H 2 0 + 2e - 2OH+ + H 2 ... (2) In this reaction, because the electric charges having 20 a mol amount same as that of the caustic soda formation amount become necessary, when the reaction is performed in a large scale continuously, enormous DC current becomes necessary. [0036] 21 The sodium ions and the hydroxide ions formed in the electrolysis vessel 128 are discharged from the electrolysis vessel as a caustic soda aqueous solution, and are supplied to the C02 absorption device 133 by the liquid feed pump 132. 5 [0037] Further, depending on the gas field, there is also a case sodium hydrogencarbonate and sodium carbonate: e.g. carbonate ions and bicarbonate ions are contained in the produced water. When carbonate ions and bicarbonate ions 10 are contained in the concentrated wastewater of the produced water, unless the potential difference is made a value significantly larger than the value described above, these ions are not affected, and chlorine ions are oxidized. When the chlorine ions are less and the carbonate ions and the 15 bicarbonate ions are contained much in the concentrated wastewater of the produced water and so on, in the positive electrode side cell, the chlorine ions are removed by electrolysis, and the carbonate ions and the bicarbonate ions (sodium hydrogencarbonate and sodium carbonate) come to 20 remain. In the present embodiment, the wastewater removed of the chlorine ions (electrolyzed water) is fed to the negative electrode side cell of the electrolysis vessel 128 by the liquid feed pump 152 after a predetermined treatment has been performed (for example after presence/absence of 25 the chlorine ions has been confirmed and heating treatment 22 and the like has been performed when the chlorine ions have not been detected yet) according to the necessity. Thus, sodium hydrogencarbonate and sodium carbonate can be obtained with high purity. Further, although the water 5 level is liable to drop by electrolysis of water on the negative electrode side, the water level of the negative electrode side can be maintained without supplementing electrolyzed water from the outside. [0038] 10 The chlorine gas having been discharged from the upper part of the positive electrode side cell of the electrolysis vessel 128 is fed to the chlorine refining/liquefaction system. Because the chlorine gas contains moisture and is highly corrosive, it is preferable that gas feeding pipes 15 are made of corrosion resistant material such as a glass lining material and the like. [0039] With respect to the chlorine gas discharged from the electrolysis vessel 128 and containing moisture, majority of 20 the moisture is condensed by being cooled to approximately 0-15 0 C by the heat exchange type cooler 136. By passing through the gas/liquid separator 137 in this state, the condensed water is removed. The choline gas having passed through the gas/liquid separator 137 is fed to the dryer 138. 25 The dryer 138 is an aeration vessel to concentrated sulfuric 23 acid for example, and a trace of moisture remaining in the chlorine gas is thereby removed. To the dryer 138, concentrated sulfuric acid is supplied from the concentrated sulfuric acid vessel 139 by the liquid feed pump 140. 5 Sulfuric acid having absorbed the moisture of the chlorine gas is sent to the sulfuric acid concentration vessel 143 by the liquid feed pump 141. The sulfuric acid concentration vessel 143 is a heating device for example, and regenerates concentrated sulfuric acid by heating and evaporating the 10 moisture. The concentrated sulfuric acid regenerated is recovered to the concentrated sulfuric acid vessel 139 by the liquid feed pump 142. Dry chlorine gas discharged from the dryer 138 is sent to the chlorine gas liquefaction device 144 and is liquefied. The chlorine gas liquefaction 15 device 144 is composed of a cooling device, a compressor, or a combination of the both for example. In the case of the cooling device, by cooling the chlorine gas to the liquefaction temperature of chlorine (-35'C) or below, the chlorine gas can be liquefied alone. Liquefied chlorine 20 discharged from the chlorine gas liquefaction device 144 is sent to the liquefied chlorine vessel 146 by the liquid feed pump 145 and is stored therein. The liquefied chlorine is utilized as a raw material for useful products such as hydrochloric acid, sodium hypochlorite, calcium hypochlorite, 25 vinyl chloride monomer and the like.

24 [0040] Because the hydrogen gas generated in the negative electrode side cell of the electrolysis vessel is a combustible gas, sufficient exhaust and to secure safety are 5 important so that the hydrogen gas does not stay within the electrolysis vessel. In the present embodiment, the hydrogen gas is sent to a combustor of the gas turbine 121, and is used as a part of the fuel. Thus, there is an advantage that the fuel supplied to the gas turbine is 10 reduced. [0041] Electric energy for driving respective systems and steam supplied to the MED system are obtained from an electric power/supply system. In the present embodiment, 15 the electric power/supply system is composed of the gas turbine 121, the generator 122 driven by the gas turbine, the exhaust heat recovery boiler 113 generating steam utilizing the exhaust gas of the gas turbine, the steam turbine 147 driven using steam from the exhaust heat 20 recovery boiler, and the generator 148 driven by the steam turbine. [0042] To the combustor of the gas turbine 121, a part of a product gas refined in the gas treatment device 102 is 25 supplied as fuel. Further, the hydrogen gas generated in 25 the electrolysis vessel 128 is also supplied to the combustor as fuel, and is effectively utilized. Although a part of the product gas and the hydrogen gas generated in the electrolysis vessel are used as the fuel for the gas 5 turbine in the example of FIG. 1, it is also possible to use various kinds of liquid fuel and gas fuel supplied from outside the system. Also, instead of the gas turbine 121 for the generator 122, other internal combustion engines such as a gas engine, diesel engine and the like may be used. 10 [0043] The temperature of a combustion exhaust gas formed in the combustor of the gas turbine 121 is as high as 1,000 1,600'C. The exhaust heat recovery boiler 123 introduces this combustion exhaust gas, heats the boiler supply water 15 sent from the liquid feed pump 124, and generates steam. This steam is supplied to the steam turbine 147 as a working medium, and rotatively drives the steam turbine. When the demand of steam in the system is less and an excessive amount of steam is produced by the exhaust heat recovery 20 boiler 123, electric power generation by the steam turbine 147 leads to effective utilization of the exhaust heat which is effective. Also, the MED device 116 described above can be operated without any problem even with the steam of comparatively low pressure, and therefore is not affected by 25 whether the steam turbine 147 is installed or not.

26 [0044] Electric energy generated by the generators 122 and 148 is supplied to various pumps such as the water supply pump 103, the high pressure water pump 110 and the like as 5 well as the electrolysis vessel 128 and the like. To the electrolysis vessel 128, electric energy is supplied after being converted to a DC voltage suitable to electrolysis by the transformer/converter 127. [0045] 10 In a case a large volume of distilled water is required to be produced, there is a case water supply for driving the steam turbine is hardly be secured. In such a case and so on, according to the necessity, it is also possible not to arrange the steam turbine 147 and the 15 generator 148. In this case, to the MED device 116, steam from the exhaust heat recovery boiler comes to be directly supplied through the ejectors 119 and 120. [0046] The exhaust gas discharged from the exhaust heat 20 recovery boiler 123 is used for carbonation of a caustic soda aqueous solution from the electrolysis vessel 128 in the C02 absorption device 133 described below. The temperature of the exhaust gas discharged from the exhaust heat recovery boiler 123 is lowered to approximately 150 25 200 0 C. In the present embodiment, first, the exhaust gas 27 from the exhaust heat recovery boiler 123 is sent to the scrubber 129. The scrubber 129 is for removing SOx and NOx component contained in the exhaust gas, sending the exhaust gas having been removed of the SOx and NOx component to the 5 C02 absorption device 133, and thereby reducing mixing of impurities to sodium bicarbonate and sodium carbonate formed in the C02 absorption device 133. [0047] To the scrubber 129, a part of the electrolyzed water 10 (caustic soda aqueous solution) formed in the negative electrode side cell of the electrolysis vessel 128 is sent by the liquid feed pump 131. The caustic soda aqueous solution is sprayed into the scrubber 129 to which the exhaust gas from the exhaust heat recovery boiler 123 has 15 been introduced, and gas/liquid contact of the caustic soda aqueous solution and the exhaust gas (aeration of the exhaust gas to the caustic soda aqueous solution) is performed. By reaction of the alkaline content such as the caustic soda and the like in the electrolyzed water with the 20 SOx and NOx component contained in the exhaust gas, these are removed from the exhaust gas. More specifically, the alkaline content in the electrolyzed water preferentially reacts with the SOx and NOx component that is a strong acid component in the combustion exhaust gas rather than reacting 25 with CO 2 that is a weak acid component, and salt is formed.

28 The salt content formed is evaporated and dried by heating caused by contact with the exhaust gas to become a solid state, and is sent to the powder separator 130 through the flow of the exhaust gas. Here, after the salt content is 5 separated and removed from the exhaust gas, the exhaust gas is sent to the C02 absorption device 133. The salt content having been separated and removed is discharged from the powder separator 130 as a mixed salt according to the necessity. The powder separator 130 is a bag filter, 10 cyclone and the like. [0048] Thus, by treating the exhaust gas before being supplied to the C02 absorption device 133, mixing of sodium sulfate, sodium nitrate and the like into sodium bicarbonate 15 and sodium carbonate which are the final products as the impurities is reduced, and the sodium bicarbonate and sodium carbonate come to have a form easily utilized as the material of glass and the like. Also, with respect to the scrubber 129 and the powder separator 130, when the strong 20 acid component of SOx and NOx is less in the exhaust gas, because the impurities to the final product becomes less, arrangement thereof may be omitted. Further, with respect to spraying into the scrubber 129, instead of the alkaline electrolyzed water from the electrolysis vessel 128, a 29 liquid such as amine and the like and water supplied from outside the system may be used. [0049] Next, the C02 absorption device 133 of the 5 electrolysis/volume reduction system will be described. In the C02 absorption device 133, the caustic soda aqueous solution from the electrolysis vessel 128 is aerated to the exhaust gas derived from the combustion exhaust gas of the gas turbine, carbon dioxide contained in the exhaust gas is 10 made to be absorbed by the caustic soda aqueous solution and is made to react with caustic soda, thereby sodium hydrogencarbonate (sodium bicarbonate, NaHCO3) or sodium carbonate (Na2CO3) is formed, and carbon dioxide contained in the exhaust gas is fixed thereby. 15 [0050] An outline of the C02 absorption device 133 used in the present embodiment will be described using FIG. 3. In the C02 absorption device 133, the exhaust gas sent from the powder separator 130 is supplied to the inside through a 20 supply port 154. To the C02 absorption device 133 to which the exhaust gas has been introduced, the caustic soda aqueous solution (alkaline electrolyzed water) having been sent from the electrolysis vessel 128 through the liquid feed pump 132 is sprayed through spray nozzles 155. By 25 reaction of the alkaline content of the electrolyzed water 30 with CO 2 contained in the exhaust gas, a salt is formed and is removed from the exhaust gas. [0051] When the exhaust gas is to be aerated to the caustic 5 soda aqueous solution by spraying, the formation ratio of sodium bicarbonate and sodium carbonate depends on the carbon dioxide gas content in the gas. More specifically, in the case of the caustic soda, a salt formed in the reaction with CO 2 differs according to the CO 2 content in 10 the exhaust gas, formation of sodium bicarbonate becomes dominant when the CO 2 content exceeds far beyond 5%, and formation of sodium carbonate becomes dominant when the CO 2 content is significantly less than 5%. When the CO 2 content is around 5%, the salt becomes a mixture of the both. 15 Therefore, by changing the CO 2 content in the exhaust gas, the objected final product (sodium bicarbonate or sodium carbonate and so on) can be obtained. Because the content of carbon dioxide contained in the combustion exhaust gas of the gas turbine 121 is low (approximately 2%), when the 20 content of carbon dioxide of the exhaust gas supplied to the C02 absorption device 133 is to be increased, a method of adding CO 2 gas to the combustion exhaust gas is conceivable for example. In the present embodiment, the accompanying gas separated and removed from the product gas when natural 25 gas mined from the gas field 101 is refined in the gas 31 treatment device 102 and containing CO 2 gas is made to join the exhaust gas from the exhaust heat recovery boiler 123, and the exhaust gas is supplied to the scrubber 129. The content of carbon dioxide can be adjusted by that the CO 2 5 gas content of a proper amount is separated and recovered from the accompanying gas by the gas treatment device 102 and is mixed with the exhaust gas. Also, to mix the accompanying gas with the exhaust gas serves also from the viewpoint of adjusting (for example reducing) the 10 temperature of the exhaust gas. Further, as another method for increasing the content of carbon dioxide contained in the exhaust gas, for example, it is conceivable to use an engine generating device such as a gas engine, diesel engine and the like instead of the gas turbine 121 and to utilize 15 the exhaust gas thereof (the CO 2 content is approximately 10%) . Also, for the feature that the CO 2 content in the gas is changed in order to obtain the objected final product (sodium bicarbonate or sodium carbonate and so on), the exhaust gas of the gas turbine is not the must, and the CO 2 20 content in the gas may be changed using the accompanying gas and the like from the gas field as described above. [0052] The salt content formed by the C02 absorption device 133 is evaporated and dried by heating by contact with the 25 exhaust gas to become a solid state. The salt content of a 32 solid state passes through a mist separator 160 on a flow of the exhaust gas, is thereby removed of a trace of the remaining water content, and is thereafter sent to the powder separator 134. Also, the temperature of the exhaust 5 gas lowers by heat exchanging with the alkaline solution (caustic soda aqueous solution) sprayed from the spray nozzles 155, and the content of carbon dioxide also lowers. In the powder separator 134, the salt content of a solid state is separated and removed from the exhaust gas, and is 10 thereafter sent to the sodium carbonate vessel 135 as a final product. With respect to the powder separator 134, similarly to the powder separator 130, a bag filter, ceramic filter, cyclone and the like are used. Out of the alkaline solution sprayed from the spray nozzles 155, that remained 15 as a liquid phase without being evaporated and dried or the liquid removed by the mist separator 160 flows down to a pool 156 and is reserved there. This returns to the spray nozzles 155 through a valve 158 by a pump 157, and is sprayed again. When the pool 156 is to be drained in 20 stopping operation of the plant and so on, a valve 159 is opened for discharging. From the powder separator 134, the exhaust gas of a state that the temperature lowers and the carbon dioxide content reduces is discharged to outside the system. 25 [0053] 33 By a treatment in the C02 absorption device 133, the water content of the concentrated wastewater derived from the produced water is evaporated and removed by effectively utilizing the thermal energy of the exhaust gas, and the 5 volume of the wastewater can be significantly reduced. Also, the soda content formed from sodium chloride contained in the concentrated wastewater derived from the produced water combines with carbon dioxide of the exhaust gas and is fixed, thereby the waste can be converted to a valuable object that 10 can be utilized for industrial use and is easily acceptable which serves also to prevention of global warming. With respect to the latter, by converting the saline wastewater to an aqueous solution of caustic soda, the amount of dissolving and absorbing carbon dioxide increases compared 15 to an aqueous solution of sodium chloride which serves to reduction of the discharge amount of carbon dioxide. [0054] Further, although it will be described in detail in an embodiment described below, with respect to the method of 20 aerating the caustic soda aqueous solution to the exhaust gas, there are a method for performing direct aeration in the electrolysis vessel, a method for aerating the caustic soda aqueous solution discharged from the electrolysis vessel, a method for spraying the caustic soda aqueous 34 solution discharged from the electrolysis vessel to the exhaust gas, and so on. [0055] When direct aeration in the electrolysis vessel is 5 performed and aeration to the caustic soda aqueous solution discharged from the electrolysis vessel is performed, because the temperature of the reaction liquid rises due to the heat of electrolysis and the exhaust gas, the solubility of NaHCO3 and Na2CO3 increases, and there is an advantage 10 that sodium bicarbonate or sodium carbonate can be recovered as a solution. When direct aeration in the electrolysis vessel is performed, it is preferable that the temperature is approximately 50-70'C in order to reduce evaporation of the water content from the reaction liquid from the 15 viewpoint of reducing the moisture contained in the chlorine gas. With respect to a method of aeration to the alkaline solution discharged from the electrolysis vessel, for example, there is a method of using an ejector and drawing in and dissolving the exhaust gas by a negative pressure 20 accompanying the flow velocity of the solution and narrowing of the flow passage, and so on. [0056] Also, when aeration is to be performed to an alkaline solution, it is necessary to lower the temperature of the 25 exhaust gas which normally is approximately 150-200'C to a 35 temperature at which the alkaline solution does not boil beforehand. The reason is that, when the exhaust gas is directly introduced, the exhaust gas may dry rapidly and a solid body may deposit within the system. Also, until a 5 process of making a final product state (drying/solidification), it is preferable to be liquid in order to facilitate transportation. From this viewpoint, the temperature of the exhaust gas is to be lowered to approximately 80-100'C for example. From the viewpoint of 10 effectively utilizing thermal energy of the exhaust gas, for example, the water content of the carbonated solution is to be evaporated and removed by the exhaust heat of the exhaust gas to dry NaHCO3 and Na2CO3. Thus, the final product can be made recoverable as a solid body utilizing the heat of 15 the exhaust gas. At that time, what evaporates is not only free water, and crystal water of NaHCO3 and Na2CO3 also can become devolatilizable. With respect to a concrete method for recovering the thermal energy of the exhaust gas, for example, there are a method for spraying a solution after 20 absorbing a carbon dioxide gas into the exhaust gas for evaporation and drying, a method for executing recovery through a heat exchanger, and so on. Also, when Na2CO3 that is a raw material of glass is assumed as a final product, it is preferable that the crystal water has been removed from 36 the viewpoint of safety in a step under a high temperature in manufacturing glass. [0057] Next, several configuration examples of the treatment 5 device for saline wastewater of the present invention will be described using FIG. 4-FIG. 8. <System configuration example 1> FIG. 4 shows the system configuration 1 of the treatment device for saline wastewater. In the present 10 configuration example, only an MED (evaporation concentration device) 2 is installed as the concentration device for saline wastewater, however, as described above, an RO membrane system may be combined, and the RO membrane system may be used also instead of the MED (evaporation 15 concentration device) 2. Further, only a gas turbine 12 is installed as the electric power/heat supply system, however, as described above, an exhaust heat recovery boiler and a steam turbine may be also installed. [0058] 20 As shown in FIG. 4, in the present configuration example, saline wastewater 41 is supplied to the MED (evaporation concentration device) 2, is concentrated and purified here, and is separated into fresh water 30 and high concentration saline wastewater 28. Although it is not 25 illustrated, it is preferable to install a filter for 37 removing a calcium salt and the like precipitated by concentration in the MED (evaporation concentration device) 2 between the MED (evaporation concentration device) 2 and an electrolysis vessel 14. Further, it is also possible to 5 supply the separated fresh water 30 as make-up water that maintains the water level on the negative electrode side of the electrolysis vessel. [0059] The high concentration saline wastewater 28 is 10 supplied to the electrolysis vessel 14 through a pump 7. At this time, the electric power for operating the MED (evaporation concentration device) 2 is electric energy 23 supplied from a generator 24 driven by the gas turbine 12. The number of units of the gas turbine 12 and the generator 15 24 may be increased to 2 units or more according to the necessity when the power is of shortage and so on. Also, by arranging plural units of the gas turbine thus, utilization as a backup for a failure is possible. [0060] 20 As described above, the high concentration saline wastewater 28 from the MED (evaporation concentration device) 2 is supplied to the positive electrode chamber of the electrolysis vessel 14. In the positive electrode chamber and the negative electrode chamber, a water level 25 meter (+) 3 and a water level meter (-) 4 for measuring the 38 water level as well as a salt concentration meter (+) 5 and a salt concentration meter (-) 6 for measuring the salt concentration are installed respectively, and the measured values measured by these water level meter (+) 3 and water 5 level meter (-) 4 as well as salt concentration meter (+) 5 and salt concentration meter (-) 6 are inputted to a calculation device 1. Also, an ammeter 51 for measuring the current of the positive electrode and the negative electrode of the positive electrode chamber and the negative electrode 10 chamber as well as a voltmeter 52 for measuring the voltage are installed, the current and voltage measured by these ammeter 51 and voltmeter 52 are inputted to the calculation device 1, and the application amount of the electric power required for electrolysis is controlled based on these 15 measured values. [0061] In the electrolysis vessel 14, the high concentration saline wastewater 28 of the positive electrode chamber is electrolyzed by the current flowing from electrodes inserted 20 in the positive electrode chamber and the negative electrode chamber, and is converted to high concentration saline water 29 and a sodium hydroxide aqueous solution 26. [0062] A chlorine gas 18 generated in the positive electrode 25 chamber at the time of electrolysis in the electrolysis 39 vessel 14 is supplied to a cooler 8, and is separated into water vapor and salts by a mist separator 9 and is washed after being cooled by the cooler 8. Thereafter, the chlorine gas 18 is dried in a drying column 10 to which a 5 concentrated sulfuric acid 19 is supplied, is thereafter cooled and pressurized in a cooler 11, and is stored in a tank as liquefied chlorine 21. The concentrated sulfuric acid used in the drying column 10 is discharged as a waste sulfuric acid 20, and is subjected to a required treatment 10 for reusing. Hydrogen generated in the negative electrode chamber at the time of electrolysis in the electrolysis vessel 14 is supplied to the gas turbine 12 as fuel. The high concentration saline water 29 discharged from the positive electrode chamber of the electrolysis vessel 14 is 15 supplied to the MED (evaporation concentration device) 2 again through the pump 7, and is concentrated along with the saline wastewater 41. [0063] On the other hand, the sodium hydroxide aqueous 20 solution 26 discharged from the negative electrode chamber of the electrolysis vessel 14 is supplied to a carbonation vessel 32 (C02 absorption device) that is a reaction vessel by the pump 7, and is sprayed within this carbonation vessel 32 to be converted to fine droplets, and the surface area 25 thereof is increased. To the carbonation vessel 32 in such 40 state, an exhaust gas 25 containing carbon dioxide is supplied from the gas turbine 12 by a blower 33 through a heat exchanger 13, and the sodium hydroxide aqueous solution 26 and the exhaust gas 25 containing carbon dioxide are made 5 to be in contact with each other. Thus, the sodium hydroxide aqueous solution 26 and carbon dioxide in the exhaust gas 25 react with each other to become an aqueous solution containing sodium hydrogencarbonate or sodium hydrogencarbonate and sodium carbonate. 10 [0064] The aqueous solution containing sodium hydrogencarbonate obtained in the carbonating vessel 32 is supplied to a centrifugal separation mechanism 17 that is a recovery device, and sodium hydrogencarbonate is recovered 15 in the centrifugal separation mechanism 17 and is stored in a tank as sodium hydrogencarbonate 27. Here, sodium hydrogencarbonate in the aqueous solution is precipitated utilizing low saturation solubility of sodium hydrogencarbonate, and sodium hydrogencarbonate precipitated 20 in the centrifugal separation mechanism 17 is separated from the aqueous solution. [0065] Further, it is also possible to heat the sodium hydrogencarbonate aqueous solution formed in the carbonation 25 vessel 32 at 150-200 0 C by the exhaust heat of the exhaust 41 gas and the like, to thereby cause dehydration and decarbonation reaction, and to convert the same to a solid body of sodium carbonate. Particularly, in the present system configuration, because the exhaust heat recovery 5 boiler in FIG. 1 is not installed, the temperature of the exhaust gas of the gas turbine is high. When the exhaust gas is used for carbonation of caustic soda, because it is preferable that the exhaust gas of the gas turbine is supplied to the carbonation vessel 32 after being cooled, it 10 is preferable to supply the exhaust gas to the carbonation vessel 32 after the exhaust gas is used for evaporation and drying of the sodium hydrogencarbonate aqueous solution and the temperature of the exhaust gas is lowered. [0066] 15 Further, in the present embodiment, although the carbonate is left in a state of an aqueous solution in the carbonation vessel 32, it is also possible to evaporate and dry the carbonate by the heat of the exhaust gas in the carbonation vessel 32 as done in the system shown in FIG. 1. 20 [0067] Also, the sodium carbonate aqueous solution and/or the sodium hydrogencarbonate aqueous solution 34 not recovered by the centrifugal separation mechanism 17 is heated by the heat exchanger 13, and is supplied to the negative electrode 25 chamber of the electrolysis vessel 14 through the pump 7.

42 When the temperature of the aqueous solution in the electrolysis vessel 14 is controlled to approximately 60'C for example, the aqueous solution is heated to approximately 60 0 C by the heat exchanger 13. Although the water level of 5 the negative electrode chamber tends to lower by electrolysis of water, the water level is maintained by supplying the electrolyzed water (sodium carbonate aqueous solution and/or sodium hydrogencarbonate aqueous solution 34). Also, because the supply water is not pure water but 10 electrolyzed water, electrolysis in the electrolysis vessel is performed efficiently. [0068] With such configuration, by converting the saline wastewater to sodium hydroxide by electrolysis and making 15 this sodium hydroxide and carbon dioxide react with each other, the efficiency in forming sodium hydrogencarbonate (sodium bicarbonate) and/or sodium carbonate can be improved. [0069] Therefore, by the present embodiment, such effect is 20 obtained that sodium chloride can be converted to a substance capable of being effectively utilized with a high yield and high efficiency not only at a low cost but also at a low environmental load. Also, the salt having a higher value can be preferentially produced in the saline 25 wastewater treatment, and the salt content in the saline 43 wastewater can be minimized. Further, the carbon dioxide amount discharged from a gas turbine using a fossil-derived fuel installed for covering the power used for the present facility can be reduced, the temperature of the wastewater 5 can be lowered, and the impact on environment can be reduced. [0070] Also, in the present embodiment, it is configured that the aqueous solution of sodium hydroxide is sprayed in the carbonation vessel 32 and is converted to fine droplets and 10 that the surface area is increased to allow to be in contact with the exhaust gas, and therefore conversion to sodium hydrogencarbonate or sodium carbonate with high efficiency is possible. <System configuration example 2> 15 FIG. 5 shows a system configuration 2 of a treatment device for the saline wastewater. The present configuration example is configured that, instead of eliminating the carbonation vessel 32 in the system configuration example 1 shown in FIG. 4, a CO 2 blow-in unit 16 for the exhaust gas 20 25 is connected to the negative electrode side of the electrolysis vessel 14, the exhaust gas 25 is directly introduced into the negative electrode chamber of the electrolysis vessel 14, and sodium hydroxide formed by electrolysis is converted to sodium hydrogencarbonate or 25 sodium carbonate. In other words, it is configured that 44 electrolysis and carbonation are performed in a same electrolysis vessel. Thus, a mechanism for making the exhaust gas be in contact with the wastewater after electrolysis becomes unnecessary. 5 [0071] Further, in the present system, the aqueous solution containing sodium hydrogencarbonate or sodium carbonate from the electrolysis vessel 14 is supplied to a cooling precipitation vessel 15. In the aqueous solution containing 10 sodium hydrogencarbonate and the like, by being cooled in the cooling precipitation vessel 15 (for example approximately 5'C), sodium hydrogencarbonate with low saturation solubility is precipitated. A crystal of sodium hydrogencarbonate is recovered in the centrifugal separation 15 mechanism 17 that is a recovery device, and is stored in a tank as the sodium hydrogencarbonate 27. Other points are the same as those of the system configuration shown in FIG. 4, and description thereof will be omitted. Also, in FIG. 5, it is preferable actually to install the centrifugal 20 separation mechanism 17 right below the cooling precipitation vessel 15. <System configuration example 3> FIG. 6 shows a system configuration 3 of a treatment device for saline wastewater. In the present configuration 25 example, the CO 2 blow-in unit 16 for the exhaust gas 25 in 45 the system configuration example 2 shown in FIG. 5 is connected to the cooling precipitation vessel 15 instead of the negative electrode side of the electrolysis vessel 14, and the exhaust gas is supplied to the cooling precipitation 5 vessel 15. To the cooling precipitation vessel 15, the sodium hydroxide aqueous solution 26 discharged from the negative electrode chamber of the electrolysis vessel 14 is supplied, and the exhaust gas is supplied from the CO 2 blow in unit 16. The sodium hydroxide aqueous solution 26 10 supplied from the electrolysis vessel 14 and carbon dioxide in the exhaust gas 25 introduced from the CO 2 blow-in unit 16 react with each other to form a sodium hydrogencarbonate aqueous solution which is precipitated as the crystal of sodium hydrogencarbonate by being cooled in the cooling 15 precipitation vessel 15. The crystal of sodium hydrogencarbonate is separated from a mixture aqueous solution of sodium carbonate and sodium hydrogencarbonate in the centrifugal separation mechanism 17 that is a recovery device, and is stored in a tank as the sodium 20 hydrogencarbonate 27. [0072] Also, in the present system, it is configured that the wastewater on the positive electrode side after electrolysis is fed to the negative electrode side also. This method is 25 effective when the concentration of sodium carbonate and 46 sodium hydrogencarbonate in the saline wastewater is higher than the concentration of sodium chloride. [0073] More specifically, as described above, in electrolysis, 5 the carbonate ions are not affected and chlorine ions are oxidized in the positive electrode, which results in that majority of sodium chloride is converted to sodium hydroxide. When there is a difference in the concentration of the sodium ion between the positive electrode and the negative 10 electrode, the sodium ions move to the electrode side of low concentration. Therefore, when the concentration of sodium carbonate and sodium hydrogencarbonate on the positive electrode side is higher than the concentration of sodium chloride, even if all amount of sodium chloride is 15 electrolyzed, the concentration of the sodium ion on the positive electrode side can exceed the concentration of the sodium ion on the negative electrode side. [0074] Therefore, by electrolyzing sodium chloride on the 20 positive electrode side almost completely, the positive electrode side can be made sodium carbonate and sodium hydrogencarbonate, and it becomes possible to feed the wastewater on the positive electrode side after electrolysis to the negative electrode side. Thus, although the water 25 level in the negative electrode chamber tends to lower by 47 electrolysis of water, by supplying the positive electrode side wastewater (electrolyzed water), the water level is maintained. Also, because the supply water is not pure water but electrolyzed water, electrolysis in the 5 electrolysis vessel is performed efficiently. [0075] Further, in the present embodiment, a chlorine ion concentration meter (+) 31 measuring the chlorine ion concentration of the positive electrode chamber of the 10 electrolysis vessel 14 is provided, and it is configured that the measured data of the chlorine ion concentration of the positive electrode chamber are inputted to the calculation device 1. Also, when the chlorine ion remains on the positive electrode side, if the chlorine ion is fed 15 to the negative electrode side, hypochlorous acid is formed, and therefore electrolysis is performed so that the chlorine ion becomes a detection limit value for example. [0076] Other points are the same as those of the system 20 configurations shown in FIG. 4 and FIG. 5, and description thereof will be omitted. <System configuration example 4> FIG. 7 shows a system configuration 4 of a treatment device for saline wastewater. In the present configuration 25 example, a line for feeding the wastewater on the positive 48 electrode side after electrolysis also to the negative electrode side to the system configuration example 2 shown in FIG. 5 as the system configuration example 3 shown in FIG. 6. Other points are the same as those of the system 5 configurations shown in FIG. 4 and FIG. 5, and description thereof will be omitted. <System configuration example 5> FIG. 8 shows a system configuration 5 of a treatment device for the saline wastewater. In the present 10 configuration example, a line for feeding the wastewater of the positive electrode side after electrolysis also to the negative electrode side in the system configuration example 3 shown in FIG. 6 is omitted. Other points are the same as those of the system configurations shown in FIG. 4 and FIG. 15 6, and description thereof will be omitted. <Configuration example of electrolysis vessel> An example of an electrolysis vessel employed in an embodiment of the present example is shown in FIG. 9 and FIG. 10. FIG. 10 is a top view of the electrolysis vessel shown 20 in FIG. 9. In these drawings, 200 is an electrolysis cell forming the electrolysis vessel, 201 is a positive electrode chamber, 202 is a negative electrode chamber, 203 is high concentration saline water filled in the positive electrode chamber 201, 204 is negative electrode electrolyzed water 25 filled in the negative electrode chamber 202, 205 is a 49 positive electrode, 206 is a negative electrode, 207 is a temperature sensor for the positive electrode chamber 201, 207' is a temperature sensor for the negative electrode chamber 202, 208 is a salt concentration sensor for the 5 positive electrode chamber 201, 208' is a salt concentration sensor for the negative electrode chamber 202, 209 is a chlorine gas, 210 is a recovery port for the chlorine gas, 211 is a discharge port for a hydrogen gas, 212 is an introduction port for negative electrode electrolyzed water, 10 213 is an introduction port for high concentration saline water, 214 is a hydrogen gas, 215 is a discharge port for the negative electrode electrolyzed water, 216 is a discharge port for positive electrode high concentration saline water, 217 is a water level gage for the positive 15 electrode chamber, 218 is a water level gage for the negative electrode chamber, 219 is a positive electrode terminal, 220 is a negative electrode terminal, and 221 is an ion exchange membrane. [0077] 20 Also, the positive electrode chamber 201 and the negative electrode chamber 202 are installed so as to be adjacent to each other only through the ion exchange membrane 221, the positive electrode 205 and the negative electrode 206 are laid adjacently to the ion exchange 25 membrane 221 inside the positive electrode chamber 201 and 50 the negative electrode chamber 202 respectively and in parallel with the ion exchange membrane 221. In the positive electrode 205 and the negative electrode 206, the positive electrode terminal 219 and the negative electrode 5 terminal 220 for each are arranged. For the positive electrode 205 and the negative electrode 206, a plate of copper, platinum, gold, iridium oxide and the like is preferable, and it may be netlike installed on a current collector. Also, it is preferable that the positive 10 electrode 205 and the negative electrode 206 are installed closest possible to the ion exchange membrane 221 in order to minimize a loss by resistance at the time of electrolysis. [0078] For the ion exchange membrane 221, a semipermeable 15 membrane that allows positive ions of sodium and the like to selectively permeate therethrough is used. By this membrane, although the sodium ion moves from the positive electrode to the negative electrode side, the chloride ion and the hydroxide ion cannot permeate this membrane, therefore 20 chlorine is accumulated in the positive electrode chamber, and sodium hydroxide is accumulated in the negative electrode chamber. When this ion exchange membrane 221 is not present for the time being, the chloride ion formed in the positive electrode and the hydroxide ion, the sodium ion 51 react with each other to form sodium hypochlorite and the like which is not preferable. [0079] In the positive electrode chamber 201, the 5 introduction port 213 for introducing the high concentration saline water 203 and the discharge port 216 are arranged, and inflow/drainage of the high concentration saline water 203 is performed. Also, in the negative electrode chamber 202, the introduction port 212 for introducing the negative 10 electrode electrolyzed water 204 and the discharge port 215 are arranged, and inflow/drainage of the negative electrode electrolyzed water 204 is performed. Here, the negative electrode electrolyzed water 204 is introduced for performing electrolysis with low resistance, and is saline 15 water containing much sodium ions and the like. [0080] Also, the recovery port 210 for recovering the chlorine gas 209 generated by electrolysis is arranged in the positive electrode chamber 201, and the recovery port 20 211 for recovering the hydrogen gas 214 generated by electrolysis is arranged in the negative electrode chamber 202. [0081] Further, in the positive electrode chamber 201 and the 25 negative electrode chamber 202, the temperature sensors 207, 52 207', the salt concentration sensors 208, 208', and the water level gages 217, 217' are arranged respectively. The temperature, salt concentration and water level measured by them are transferred to the calculation device 1 shown in 5 the system configuration examples 1 to 5 as data. [0082] In the electrolysis vessel 14 thus configured, when an electric field is generated between the positive electrode 205 and the negative electrode 206, an electric current is 10 generated with the ion exchange membrane 221 in between, the sodium ions flow from the positive electrode 205 side to the negative electrode 206 side, an electrochemical reaction of the above expression (1) and expression (2) are caused in respective electrodes, chlorine is generated on the positive 15 electrode 205 side, hydrogen is generated in the negative electrode 206 side, and sodium hydroxide is formed simultaneously and is accumulated in the negative electrode electrolyzed water 204 inside the negative electrode chamber 202. 20 [0083] With respect to the electrolysis cell 200, in order to efficiently electrolyzing the high concentration saline water 203 caused to pass thereinto, it is preferable that the volume thereof relative to the electrodes is configured 25 to be small, and, in order to gain the volume of the 53 treatment liquid, it is preferable to perform electrical field with the electrolysis cell 200 being installed by plural number of units in parallel. [0084] 5 In FIG. 11, another example of the electrolysis vessel is shown. The example shown in the drawing is an electrolysis vessel for obtaining sodium hydrogencarbonate or sodium carbonate by aerating the exhaust gas 25 containing carbon dioxide from the gas turbine 12 into the 10 negative electrode chamber 202, and making sodium hydroxide formed in the negative electrode electrolyzed water 204 inside the negative electrode chamber 202 and carbon dioxide react with each other inside the negative electrode chamber 202. Also, in FIG. 11, 222 is an introduction port for 15 carbon dioxide, and 223 is a blowoff port for carbon dioxide. [0085] By using the electrolysis cell 200 shown in FIG. 11, carbon dioxide is made to directly react with sodium hydroxide formed on the negative electrode side, and it 20 becomes possible to form sodium carbonate and sodium hydrogencarbonate. [0086] In FIG. 12, a still other example of an electrolysis vessel is shown. The example shown in the drawing shows an 25 electrolysis vessel formed by arraying the electrolysis cell 54 200 shown in FIG. 9 and FIG. 10 by plural number of units in parallel. [0087] In FIG. 12, 200 is the electrolysis cell, 224 is a 5 recovery pipe for recovering hydrogen generated in the negative electrode chambers of respective electrolysis cells, 225 is a recovery pipe for recovering chlorine generated in the positive electrode chambers of respective electrolysis cells 200, 226 is an introduction pipe for the negative 10 electrode electrolyzed water 204, 227 is an introduction pipe for high concentration saline wastewater introduced to the positive electrode chamber, 228 is a discharge pipe for the negative electrode electrolyzed water 204, and 229 is a discharge pipe for high concentration saline wastewater of 15 the positive electrode chamber. [0088] In FIG. 12, an example of a case the electrolysis cell 200 shown in FIG. 9 is connected by 8 cells in parallel is shown, however, the number of units of the cell in parallel 20 is not limited to it, and an electrolysis vessel with a large capacity such as 80 cells-100 cells also can be formed. [0089] In the example shown in FIG. 12, the recovery pipe 224 for hydrogen is a pipe connecting the recovery ports 211 25 arranged in the negative electrode chambers of respective 55 electrolysis cells 200 in parallel, and hydrogen is supplied again as fuel for the gas turbine 12 and is exhausted by the power of a blower and the like not illustrated according to the necessity. 5 [0090] The recovery pipe 225 for chlorine is a pipe for connecting the recovery ports 210 for the chlorine gas arranged in the positive electrode chambers of respective electrolysis cells 200 in parallel, and the chlorine gas is 10 introduced to a chlorine treatment unit composed of the coolers 8, 11, the mist separator 9, and the drying column 10 shown in FIG. 4 to FIG. 8, becomes the liquid chlorine 21 and is eventually took out as a valuable object. The chlorine gas is exhausted by the power of a blower and the 15 like not illustrated according to the necessity. [0091] Also, through the introduction pipe 226 for the negative electrode electrolyzed water 204 introduced to the negative electrode and the introduction pipe 227 for the 20 high concentration saline wastewater introduced to the positive electrode, these liquids are supplied to the electrolysis cells 200 by the power of liquid feed pumps and the like arranged separately. Further, the negative electrode electrolyzed water 204 is fed to sodium carbonate 25 or sodium hydrogencarbonate recovery unit by the power of 56 liquid feed pumps and the like arranged separately through the discharge pipe 228 for the negative electrode electrolyzed water 204, and the high concentration saline water 203 is introduced to the MED (evaporation 5 concentration device) 2 or the negative electrode chamber 202 through the discharge pipe 229 for the high concentration saline wastewater of the positive electrode. [0092] In FIG. 13, a still other example of an electrolysis 10 vessel is shown. The example shown in the drawing shows an electrolysis vessel formed by arraying the electrolysis cell 200 having a mechanism for aerating carbon dioxide shown in FIG. 11 by plural number of units in parallel. [0093] 15 In FIG. 13, 230 is an introduction pipe for the exhaust gas 25 containing carbon dioxide. This introduction pipe 230 is a pipe for connecting the introduction ports 222 for carbon dioxide of respective electrolysis cells 200 to each other in parallel, and the exhaust gas 25 is introduced 20 using the power of a blower and the like not illustrated according to the necessity. [0094] When aeration of carbon dioxide shown in FIG. 11 and FIG. 13 is to be performed inside the negative electrode 25 chamber, nitrogen, oxygen, moisture, and carbon dioxide not 57 yet reacted contained in the exhaust gas 25 are introduced into the negative electrode and are sent from the recovery pipe 224 for hydrogen to the gas turbine 12 along with hydrogen that is fuel, however, even when these gasses may 5 have been mixed, problems do not occur in combustion in the gas turbine. <Application example> Below, with respect to a case the treatment device for saline wastewater of the embodiment of the present invention 10 was applied to a treatment of the produced water discharged from a gas field, material balance calculation, electric power balance calculation, heat balance calculation and the like were performed, and the effect of the embodiment of the present invention was confirmed. Also, the present 15 invention is not limited to them. <Application example 1> A case of treating the produced water discharged from a certain gas field A in the system shown in FIG. 1 and FIG. 4 will be described. 20 [0095] By causing the produced water to pass through the RO membrane system and the MED system, high concentration saline wastewater that has been concentrated is obtained. The concentration of the positive ion species and the 58 negative ion species of this high concentration saline wastewater is as described below. Positive ion species Na 59,000 mg/L 5 Other positive ions 700 mg/L or less Negative ion species Cl 77,200 mg/L

CO

3 181 mg/L

HCO

3 23,000 mg/L 10 Other negative ions 700 mg/L or less Also, COD is 300 mg/L or less. [0096] From the above, other than water, the high concentration saline wastewater is mainly of a material 15 including sodium chloride (128,000 mg/L: 12.8 g (0.22 mol) in 1 L), sodium carbonate (247 mg/L: 0.247 g (0.0032 mol) in 1 L), and sodium hydrogencarbonate (32,000 mg/L: 32 g (0.38 mol) in 1 L) . In other words, this produced water is saline waste water lean in sodium chloride and rich in carbonate. 20 [0097] This saline wastewater is fed to the positive electrode chamber of the electrolysis cell shown in FIG. 9, a sodium carbonate aqueous solution of 60,000 mg/L is fed to the negative electrode chamber, and electrolysis is 25 performed. 60,000 mg/L of the sodium carbonate aqueous 59 solution is the concentration of the electrolyzed water after passing through the centrifugal separation mechanism shown in FIG. 4. The inside dimension of the positive electrode side and the negative electrode side of the 5 electrolysis cell is 1 mXl mX0.01 m for the both, and the volume is 10 L. The water temperature at the time of feeding for the both was made 70 0 C. [0098] Here, by electricity supply of the voltage of 3 V and 10 the amperage of 60 ampere, electrolysis is performed. Bubbles of the chlorine gas are generated from the positive electrode, and electrolysis proceeds. Although the sodium ions of the positive electrode chamber move to the negative electrode chamber and the sodium ion concentration of the 15 positive electrode chamber lowers accompanying progress of electrolysis, because the difference in the sodium ion concentration between the positive electrode chamber and the negative electrode chamber is 3% or more by a sodium ion concentration adjustment mechanism, the high concentration 20 saline wastewater is made to flow in making this state a steady state, and stable operation state is maintained. At this time, the high concentration saline water of sodium chloride of 90,000 mg/L is discharged from the positive electrode chamber through the discharge port, and is fed to 25 the evaporation concentration device again. It is shown 60 that sodium of an amount equivalent to sodium chloride of 38,000 g/L moves to the negative electrode chamber accompanying it. [0099] 5 Accompanying it, the sodium ion concentration of the negative electrode chamber becomes 72,000 mg/L. This corresponds to increase of sodium ion by 12,000 mg/L compared to initial 60,000 mg/L, which shows that sodium hydroxide of 21,000 mg/L is formed in the negative electrode 10 chamber. This solution is fed to the carbonation layer 32 shown in FIG. 4 using the pump 7, and is sprayed in a spray state. The exhaust gas 25 of the gas turbine 12 is blown in to there, sodium hydroxide is converted to sodium carbonate, is crystallized, and is recovered as the powder of the 15 sodium hydrogencarbonate 27. [0100] The exhaust gas composition used in the present application example is shown below. Exhaust gas composition 20 N2: 70.0% 02: 13.0% C02: 3.4% H20: 11.0% Ar: 0.9% 25 Others: 11.7% 61 The temperature of the gas immediately after being discharged from the gas turbine 12 is 330 0 C. Although this gas is fed to the carbonation layer 32 through the heat exchanger 13, the temperature after passing through the heat 5 exchanger is 180 0 C. Because the concentration of carbon dioxide is 0.01% or more, the operation state becomes a normal state. Sodium carbonate recoverable then is 5.5 kg when the liquid feed amount of the high concentration saline wastewater fed to the electrolysis vessel is 100 L. 10 [0101] It was prospected that sodium carbonate of 473 kg could be recovered when the electrolysis cells were arranged in parallel by 86 cells as shown in FIG. 12 and a treatment of 8,600 L was performed. 15 <Application example 2> A case of treating the produced water discharged from a certain gas field in the system shown in FIG. 1 and FIG. 4 will be described. [0102] 20 By causing the produced water to pass through the RO membrane system and the MED system, concentrated high concentration saline wastewater is obtained. The concentration of the positive ion species and the negative ion species of this high concentration saline wastewater is 25 as described below.

62 Positive ion species Na 23,000 mg/L Other positive ions 100 mg/L or less Negative ion species 5 Cl 7,100 mg/L

CO

3 1,500 mg/L

HCO

3 46,000 mg/L Other negative ions 100 mg/L or less Also, COD was 100 mg/L or less. 10 [0103] From the above, other than water, the high concentration saline wastewater is mainly of a material including sodium chloride (11,700 mg/L: 11.7 g (0.2 mol) in 1 L), sodium carbonate (5,300 mg/L: 5.3 g (0.05 mol) in 1 L), 15 and sodium hydrogencarbonate (59,000 mg/L: 59 g (0.7 mol) in 1 L). In other words, this produced water is also saline wastewater lean in sodium chloride and rich in carbonate. [0104] This saline wastewater is fed to the positive 20 electrode of the electrolysis vessel shown in FIG. 9, a sodium carbonate aqueous solution of 0.5 wt% is fed to the negative electrode side, and electrolysis is performed. The inside dimension of the positive electrode side and the negative electrode side of the electrolysis vessel is 1 mXl 25 mXO.01 m for the both, and the volume is 10 L. The water 63 temperature at the time of feeding for the both was made 70 0 C. [0105] Here, by electricity supply of the voltage of 3 V and 5 the amperage of 5.9 ampere, electrolysis is performed. Bubbles of the chlorine gas are generated from the positive electrode, and the electrolysis proceeds. Although the sodium ions on the positive electrode side move to the negative electrode side and the sodium ion concentration on 10 the positive electrode side lowers accompanying progress of the electrolysis, after 10 hours, the bubbles are not generated any more, and the Cl concentration on the positive electrode side becomes the detection limit or less. The Na concentration also lowers by 4,600 mg/L, and it can be 15 determined that the electrolysis of sodium chloride in the positive electrode side has almost completed. [0106] On the other hand, the negative electrode side becomes strong basic. Further, bubbles of the hydrogen gas are 20 generated from the negative electrode, and it becomes that generation of the bubbles cannot be confirmed after 10 hours. The aqueous solution on the negative electrode side is discharged, and the combustion exhaust gas is made to be in contact therewith in the carbonation vessel. Thereafter, 25 the aqueous solution is heated and dried at 150-200 0 C, and a 64 white solid body (156 g) is obtained. This solid body is sodium carbonate. Out of it, by deducting 50 g which is a portion of sodium carbonate of 0.5 wt% having been dissolved in the aqueous solution beforehand, sodium carbonate of 106 5 g is obtained by the electrolysis and contact of the combustion exhaust gas. [0107] In the meantime, by the electrolysis, in the aqueous solution on the positive electrode side, sodium chloride 10 almost disappears, and sodium carbonate and sodium hydrogencarbonate become main components. Therefore, by heating and drying it also at 150-200 0 C, the decarbonation and dehydration reaction of sodium hydrogencarbonate also proceeds, and sodium hydrogencarbonate changes to sodium 15 carbonate after heating. Eventually, sodium carbonate (425 g) is obtained. [0108] From the above, by treating the saline wastewater of 10 L, it becomes possible to obtain sodium carbonate of 531 20 g in total of the positive electrode and the negative electrode. [0109] It was prospected that, by applying the electrolysis vessel of FIG. 9 to the system in which the electrolysis 25 vessels were arrayed in parallel as shown in FIG. 12, the 65 amount of sodium carbonate obtained by drying respective electrolysis vessel aqueous solutions after the electrolysis would become approximately 420 g. Therefore, also in the case plural units of the electrolysis vessel are arrayed in 5 parallel, sodium carbonate can be obtained. <Application example 3> Similarly to the application example 2, in the electrolysis vessel shown in FIG. 11, the saline wastewater is fed to the positive electrode, 10 L of the sodium 10 carbonate aqueous solution of 0.5 wt% is fed to the negative electrode, and electrolysis is performed. At that time, the combustion exhaust gas is introduced to the negative electrode. After 10 hours, the Cl concentration on the positive electrode side becomes the detection limit or less. 15 The Na concentration also lowers by 4,600 mg/L, and it can be determined that the electrolysis of sodium chloride has almost completed. [0110] After the aqueous solution on the negative electrode 20 side has been discharged, the aqueous solution is heated and dried at 150-200'C, and a white solid body (156 g) is obtained. This solid body is sodium carbonate. Out of it, by deducting 50 g which is a portion of sodium carbonate of 0.5 wt% having been dissolved in the aqueous solution 66 beforehand, sodium carbonate of 106 g can be obtained by the electrolysis and contact of the combustion exhaust gas. [0111] Similarly to the application example 2, by heating and 5 drying the aqueous solution on the positive electrode side also, sodium carbonate (425 g) is obtained. [0112] From the above, it was prospected that, even when the combustion exhaust gas was blown in at the time of the 10 electrolysis, by treating the saline wastewater of 10L, sodium carbonate of 531 g would be obtained in total of the positive electrode and the negative electrode. [0113] The method for treating saline wastewater of the 15 present invention can be summarized as follows. (1) A method for treating saline wastewater including a first step for concentrating the saline wastewater by separating the water content from the saline wastewater containing sodium chloride and producing high concentration 20 saline wastewater, a second step for producing or generating electricity and steam required for performing this concentration by energy obtained by combusting a fossil fuel, a third step for feeding the high concentration saline wastewater to the positive electrode side of an electrolysis 25 vessel including a positive electrode and a negative 67 electrode partitioned by a semipermeable membrane that causes sodium ions to permeate therethrough and forming sodium hydroxide in high concentration saline water by electrolysis, a fourth step for causing the sodium hydroxide 5 to be in contact with an exhaust gas generated by combusting the fossil fuel in the second step and thereby obtaining an aqueous solution containing sodium carbonate and/or sodium hydrogencarbonate, a fifth step for separating and recovering sodium carbonate and/or sodium hydrogencarbonate 10 having been generated from the aqueous solution containing sodium carbonate and/or sodium hydrogencarbonate, and a sixth step for recovering gas containing chlorine generated from the positive electrode of the electrolysis vessel and gas containing hydrogen generated from the negative 15 electrode. (2) The method for treating saline wastewater according to (1) in which the step for concentrating the saline wastewater is performed first by a reverse osmosis device and then by an evaporation column method successively. 20 (3) The method for treating saline wastewater according to (1) in which the step for concentrating the saline wastewater is performed only by an evaporation column method. (4) The method for treating saline wastewater according to any one of (1)-(3) in which a step for removing suspended 68 matter in the saline wastewater is performed before the step for concentrating the saline wastewater. (5) The method for treating saline wastewater according to any one of (1)-(4) in which the step for causing the saline 5 wastewater to be in contact with the exhaust gas after the electrolysis is performed by a method of introducing the exhaust gas to the negative electrode side of the electrolysis vessel. (6) The method for treating saline wastewater according to 10 any one of (1)-(4) in which the step for causing the saline wastewater to be in contact with the exhaust gas after the electrolysis is performed in such a manner that the contact occurs after the saline wastewater is moved from the electrolysis vessel to a mechanism for causing the exhaust 15 gas to be in contact with the saline wastewater. (7) The method for treating saline wastewater according to any one of (1)-(4) and (6) in which the step for causing the saline wastewater to be in contact with the exhaust gas after the electrolysis is performed in such a manner that 20 the saline wastewater is moved from the electrolysis vessel to a mechanism for causing the exhaust gas to be in contact with the saline wastewater, is thereafter converted to droplets, and is made to be in contact with the exhaust gas. (8) The method for treating saline wastewater according to 25 any one of (1)-(7) in which sodium carbonate and/or sodium 69 hydrogencarbonate is recovered by heating and drying an aqueous solution containing sodium carbonate and/or sodium hydrogencarbonate in the step for recovering sodium carbonate and/or sodium hydrogencarbonate. 5 (9) The method for treating saline wastewater according to any one of (1)-(7) in which sodium carbonate and/or sodium hydrogencarbonate is precipitated by cooling an aqueous solution containing sodium carbonate and/or sodium hydrogencarbonate and is recovered in the step for 10 recovering sodium carbonate and/or sodium hydrogencarbonate. (10) The method for treating saline wastewater according to any one of (1)-(7) in which sodium carbonate and/or sodium hydrogencarbonate is precipitated by cooling an aqueous solution containing sodium carbonate and/or sodium 15 hydrogencarbonate and is recovered, a residual liquid is thereafter returned to the negative electrode side of the electrolysis chamber in the step for recovering sodium carbonate and/or sodium hydrogencarbonate. (11) A method for treating saline wastewater that utilizes 20 a hydrogen gas generated from the positive electrode of the electrolysis vessel or a mixed gas of a hydrogen gas and an exhaust gas introduced to the electrode after a fossil fuel is combusted as fuel for generating energy. (12) A saline wastewater treatment device including a 25 concentration device that concentrates saline wastewater 70 containing sodium chloride, a generating device that produces or generates electricity and steam required for performing this concentration by combusting a fossil fuel, and an electrolysis vessel that electrolyzes the saline 5 wastewater, in which the electrolysis vessel includes a positive electrode chamber, a negative electrode chamber, and a semipermeable membrane that separates them, with the semipermeable membrane causing sodium ions to pass therethrough, a mechanism of feeding the saline wastewater 10 to the positive electrode chamber is provided, a mechanism of feeding an aqueous solution of sodium hydroxide or sodium carbonate to a negative electrode is provided, a mechanism of recovering a chlorine gas generated in electrolysis on the positive electrode side is provided, a mechanism of 15 recovering a hydrogen gas generated in electrolysis on the negative electrode side is provided, a mechanism of introducing an exhaust gas generating by combustion of the fossil fuel to the negative electrode is provided, a mechanism of discharging aqueous solutions from the positive 20 electrode and negative electrode sides after introduction is provided, a mechanism of heating and drying the aqueous solution discharged from the negative electrode is provided, and a mechanism of recovering a solid body formed after drying is provided.

71 (13) The saline wastewater treatment device according to (12) in which the concentration device for the saline wastewater is a system performed by a reverse osmosis device and then by an evaporation column successively. 5 (14) The saline wastewater treatment device according to (12) in which the concentration device for the saline wastewater is a system performed by an evaporation column. (15) The saline wastewater treatment device according to any one of (12)-(14) in which a step for removing suspended 10 matter in the saline wastewater in a stage before the concentration device for the saline wastewater is included. (16) A saline wastewater treatment device in which an aqueous solution is discharged from the negative electrode side after electrolysis in the electrolysis vessel and is 15 thereafter made to be in contact with carbonate. (17) A saline wastewater treatment device in which, when an aqueous solution is discharged from the negative electrode after electrolysis in the electrolysis vessel and is thereafter made to be in contact with carbonate, the contact 20 to the carbonate takes place in a state the aqueous solution is sprayed and converted to droplets. (18) The saline wastewater treatment device according to any one of (12)-(15) including a centrifugal separation mechanism for cooling the aqueous solution discharged from 25 the negative electrode and recovering a solid body formed.

72 (19) The saline wastewater treatment device according to any one of (12)-(18) including a mechanism that feeds the aqueous solution discharged from the positive electrode to the negative electrode. 5 (20) The saline wastewater treatment device according to any one of (12)-(15), (18) and (19) including a control mechanism that sends a mixed gas of a hydrogen gas generated on the negative electrode side and an exhaust gas introduced as fuel for the generating device. 10 [0114] Also, the present invention is not limited to the embodiments described above, and various alterations are included therein. For example, the embodiments described above were described in detail for easy understanding of the 15 present invention, and the present invention is not necessarily limited to those having all configurations described. Further, a part of the configuration of an embodiment can be substituted to a configuration of another embodiment, and it is also possible to add a configuration 20 of another embodiment to a configuration of an embodiment. Furthermore, with respect to a part of each embodiment, it is possible to effect addition of other configurations, deletion, and replacement. [0115] 73 Also, with respect to the flow of the water and steam, heat exchanging and the like, those considered to be necessary for explanation have been shown, and all flows of the water and steam, heat exchanging and the like of the 5 plant have not necessarily been shown. Actually, in order to improve the thermal efficiency and the like of the plant, the flow of the water and steam, heat exchanging and the like are devised variously. Reference Signs List 10 [0116] 1.. .calculation device, 2 ...MED (evaporation concentration device), 3 water level gage (+), 4 water level gage (-), 15 5 --salt concentration meter (+) 6 - - salt concentration meter (-), 7 - --pump, 8, 11 - -cooler, 9 --mist separator, 20 10 - -drying column, 12, 121 - -gas turbine, 13, 117 - - heat exchanger, 14, 128 --electrolysis vessel, 15 ... cooling precipitation vessel, 25 16 - -- CO 2 blow-in unit, 74 17 ... centrifugal separation mechanism, 18, 209 - chlorine gas, 19 ... concentrated sulfuric acid, 20 ... exhaust sulfuric acid, 5 21 - liquid chlorine, 22 - hydrogen gas, 23 ... electric energy, 24, 122, 148 - -generator, 25 ... exhaust gas, 10 26 ... sodium hydrogencarbonate aqueous solution, 27 ... sodium carbonate, 28.. .high concentration saline wastewater, 29.. .high concentration saline water, 30 ... fresh water, 15 31 .-chlorine ion concentration meter (+), 32 ... carbonation vessel, 33 -. - blower, 34 ... sodium carbonate aqueous solution, 41 ... saline wastewater, 20 51 ... ammeter, 52 - --voltmeter, 101 - gas field, 102 - gas treatment device, 103 - water suction pump, 25 104 - strainer, 75 105 pretreatment device, 106 pressurized air tank, 107 - alkali supply tank, 108 acid supply tank, 5 109 - neutralization tank, 110 high pressure water pump, 111 - RO membrane desalination device, 112 - chemical cleaning/discharge treatment device, 113 pressure energy recovery device, 10 114 back wash device, 115 product gas supply blower, 116 MED device, 118.. .radiator unit, 119, 120.. .ejector, 15 123 exhaust heat recovery boiler, 124, 125, 126, 131, 132, 140, 141, 142, 145 - liquid feed pump, 127 --transformer, 129 --scrubber, 20 130, 134 --powder separator, 133 -.- C0 2 absorption device, 135 sodium carbonate vessel, 136 heat exchange type cooler, 137 - gas/liquid separator, 25 138 --dryer, 76 139 concentrated sulfuric acid vessel, 143 - sulfuric acid concentration vessel, 144 - chlorine gas liquefaction device, 146 - liquefied chlorine vessel, 5 147 - steam turbine, 200 - electrolysis cell, 201 positive electrode chamber, 202 negative electrode chamber, 203 high concentration saline water filled in 10 positive electrode chamber, 204 negative electrode electrolyzed water, 205 positive electrode, 206 negative electrode, 207 - temperature sensor for positive electrode 15 chamber, 207' ---temperature sensor for negative electrode chamber, 208 ... salt concentration sensor for positive electrode chamber, 20 208' - --salt concentration sensor for negative electrode chamber, 210.. .recovery port for chlorine gas, 211.. .recovery port for hydrogen gas, 212 ... introduction port for negative electrode 25 electrolyzed water, 77 213 ... introduction port for high concentration saline water, 214 - hydrogen gas, 215 discharge port for negative electrode 5 electrolyzed water, 216 discharge port for positive electrode high concentration saline water, 217 water level gage for positive electrode chamber, 218 water level gage for negative electrode chamber, 10 219 positive electrode terminal, 220 negative electrode terminal, 221 * ion exchange membrane, 222 ... introduction port for carbon dioxide, 223 - blowoff port for carbon dioxide, 15 224 recovery pipe recovering hydrogen generated in negative electrode chamber, 225 recovery pipe recovering chlorine generated in positive electrode chamber, 226 --introduction pipe for negative electrode 20 electrolyzed water, 227 ... introduction pipe for high concentration saline wastewater introduced to positive electrode chamber, 228 discharge pipe for electrolyzed water of negative electrode chamber, 78 229 discharge pipe for high concentration saline wastewater of positive electrode chamber, 230 ... introduction pipe for exhaust gas

Claims

1. A method for treating saline wastewater, comprising the steps of: 5 separating a water content from saline wastewater containing sodium chloride, thereby concentrating the saline wastewater and producing high concentration saline wastewater; feeding the high concentration saline wastewater to a 10 positive electrode side of an electrolysis vessel including a positive electrode and a negative electrode partitioned by a semipermeable membrane that causes sodium ions to permeate therethrough; forming sodium hydroxide in the high concentration 15 saline wastewater by electrolysis; causing the sodium hydroxide to be in contact with an exhaust gas of a gas turbine generating device or an engine generating device installed in order to obtain electric energy that activates a plant discharging the saline 20 wastewater or a treatment device for the saline wastewater and thereby obtaining an aqueous solution containing sodium carbonate and/or sodium hydrogencarbonate; and separating and recovering the sodium carbonate and/or sodium hydrogencarbonate from the aqueous solution. 80

2. The method for treating saline wastewater according to claim 1, wherein a solid body formed in concentrating the saline wastewater is removed before the high concentration saline 5 wastewater is fed to the electrolysis vessel.

3. A saline wastewater treatment device that treats saline wastewater containing sodium chloride, comprising: a concentration device that concentrates the saline wastewater by separating a water content from the saline 10 wastewater; an electrolysis vessel that has a positive electrode and a negative electrode partitioned by a semipermeable membrane that causes sodium ions to permeate therethrough, and electrolyzes sodium chloride in the saline wastewater; 15 a supply pipe for high concentration saline wastewater arranged between a discharge port for the high concentration saline wastewater produced in the concentration device and the positive electrode side of the electrolysis vessel; a carbonation vessel that introduces an exhaust gas of 20 a gas turbine generating device or an engine generating device installed in order to obtain electric energy that activates a plant discharging the saline wastewater or a saline wastewater treatment device, and carbonates a salt in an aqueous solution; 81 a supply pipe for the aqueous solution arranged between a discharge port for the aqueous solution on the negative electrode side of the electrolysis vessel and the carbonation vessel; and 5 a recovery device for carbonate formed in the carbonation vessel.

4. A saline wastewater treatment device that treats saline wastewater containing sodium chloride, comprising: a concentration device that concentrates the saline 10 wastewater by separating a water content from the saline wastewater; an electrolysis vessel that has a positive electrode and a negative electrode partitioned by a semipermeable membrane that causes sodium ions to permeate therethrough, 15 and electrolyzes sodium chloride in the saline wastewater; a supply pipe for high concentration saline wastewater arranged between a discharge port for the high concentration saline wastewater produced in the concentration device and the positive electrode side of the electrolysis vessel; 20 a supply pipe that introduces an exhaust gas of a gas turbine generating device or an engine generating device installed in order to obtain electric energy that activates a plant discharging the saline wastewater or a saline wastewater treatment device to the negative electrode side 25 of the electrolysis vessel; and 82 a recovery device for carbonate formed on the negative electrode side of the electrolysis vessel.

5. The saline wastewater treatment device according to claim 3 or 4, wherein 5 the concentration device is a concentration device by an evaporation method, and uses an exhaust gas of the gas turbine generating device or the engine generating device or heat derived from the exhaust gas as a heat source.

6. The saline wastewater treatment device according to 10 claim 3 or 4 further comprising a cooling device for an aqueous solution containing the carbonate.

7. The saline wastewater treatment device according to claim 6 further comprising a centrifugal separator that separates the aqueous solution containing the carbonate 15 precipitated by the cooling device into a crystal of the carbonate and an aqueous solution.

8. The saline wastewater treatment device according to claim 6 further comprising a pipe that supplies the aqueous solution from which the carbonate precipitated by the 20 cooling device has been separated to the negative electrode side of the electrolysis vessel.

9. The saline wastewater treatment device according to claim 8, wherein a heating device for an aqueous solution is arranged 25 in the middle of the pipe that supplies the aqueous solution 83 from which the carbonate has been separated to the negative electrode side of the electrolysis vessel.

10. The saline wastewater treatment device according to claim 3 or 4, wherein 5 a device that removes NOx or SOx contained in the exhaust gas is arranged in the middle of a supply pipe for an exhaust gas of the gas turbine generating device or the engine generating device.

11. The saline wastewater treatment device according to 10 claim 3 or 4, wherein a cooling device for the exhaust gas is arranged in the middle of the supply pipe for an exhaust gas of the gas turbine generating device or the engine generating device.

12. The saline wastewater treatment device according to 15 claim 11, wherein the cooling device performs cooling by heating and drying an aqueous solution containing the carbonate.

13. The saline wastewater treatment device according to claim 3 or 4, wherein 20 a mechanism that adjusts the carbon dioxide concentration in the exhaust gas is arranged in the middle of the supply pipe for the exhaust gas of the gas turbine generating device or the engine generating device. 84

14. The saline wastewater treatment device according to claim 3 further comprising a spray device that sprays the aqueous solution into the carbonation vessel.

15. The saline wastewater treatment device according to 5 claim 3 or 4 further comprising a pipe that supplies a hydrogen gas generated on the negative electrode side of the electrolysis vessel to the gas turbine generating device or the engine generating device.