AU2013202562B2 - Apparatus for recovering sodium hydrogen carbonate and method for recovering the same - Google Patents

Abstract

An evaporation concentrator concentrates underground water. A carbon dioxide gas absorption crystallizer crystallizes sodium hydrogen carbonate to deposit crystals thereof by making carbon dioxide gas contact the concentrated underground 5 water. The carbon dioxide gas generated in the evaporation concentrator is introduced into the concentrated underground water in the carbon dioxide gas absorption crystallizer to increase the recovery ratio of the sodium hydrogen carbonate. -o >, 0, Cu (.0 c0 4-J 4,J - L L o &.) a - 4-J -d 0)) c (Dcu o o (. -0 >.. E Co C C 4- CD 0) U) L 6 ~ > C, 0

Description

P100/011 Reguation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Apparatus for recovering sodium hydrogen carbonate and method for recovering the same The following statement is a full description of this invention, including the best method of performing it known to us: APPARATUS FOR RECOVERING SODIUM HYDROGEN CARBONATE AND METHOD FOR RECOVERING THE SAME TECHNICAL FIELD 5 [ 1 ] The invention relates to apparatuses and methods for recovering sodium hydrogen carbonate contained in underground water, more particularly to apparatuses and methods suitably used to recover sodium hydrogen carbonate contained in underground water, for example, associated water generated when gases, such as coal seam gas, are collected. 10 BACKGROUND OF THE ART [ 2 ] In recent years, there are growing uses of coal seam gas that can be collected from coal seams. However, a great quantity of associated water generated when the coal seam gas is collected, and the associated water contains substances 15 such as sodium chloride, sodium hydrogen carbonate, and sodium carbonate. [ 3 ] The associated water thus containing salts cannot be used as irrigation water or discharged into rivers. Conventionally, the associated water is subjected to treatments; for example, the associated water is temporarily kept in an evaporation pond to be reduced in volume by spontaneous evaporation. 20 [ 4 ] To launch such an evaporation pond system, however, it is necessary to secure a large area of land to keep the associated water for spontaneous evaporation. [ 5 ] The Patent Reference 1 W02012/008013 discloses a concentration apparatus invented to largely reduce an installed capacity as compared to the evaporation pond system. To this end, the concentration apparatus is structurally 25 characterized in that a desalting device using a reverse osmosis membrane and a concentrator using the evaporation technique are used in combination. [ 6 ] The concentration apparatus disclosed in the Patent Reference 1 succeeds in reducing the volume of associated water while also succeeding in considerably reducing the installed capacity. A problem with the apparatus is that the 30 concentrated water having a reduced volume is difficult to be treated. Though it is 1 desirable in order to solve the problem that effective soda components contained in the concentrated water be separated and recovered, the Patent Reference 1 fails to disclose any technique for separately recovering the soda components. [ 7 ] The object of the present invention is to provide an apparatus and/or 5 method to recover sodium hydrogen carbonate that is a soda component contained in underground water such as associated water. [ 8 ] Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment, or any form of suggestion, that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this 10 prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. [ 9 ] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude other additives, components, integers or 15 steps. SUMMARY OF INVENTION [ 10 ] 1) A sodium hydrogen carbonate recovery apparatus according to an aspect of the invention is an apparatus for recovering sodium hydrogen carbonate 20 from underground water containing at least the sodium hydrogen carbonate, sodium carbonate, and sodium chloride. The apparatus includes an evaporation concentrator for concentrating the underground water, and a carbon dioxide gas absorption crystallizer for depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water concentrated by the evaporation concentrator contact 25 carbon dioxide gas, wherein the carbon dioxide gas generated in the evaporation concentrator is introduced into the concentrated underground water in the carbon dioxide gas absorption crystallizer. [ 11 ] To deposit crystals of the sodium hydrogen carbonate from the evaporated and concentrated underground water using the carbon dioxide gas absorption 30 crystallizer, the recovery apparatus according to the invention introduces the carbon 2 1000139088 dioxide gas generated in the evaporation concentrator into the concentrated underground water in the carbon dioxide gas absorption crystallizer and makes the carbon dioxide gas contact the concentrated underground water. This facilitates the formation of hydrogen carbonate ions in the concentrated underground water, thereby 5 improving the recovery ratio of the sodium hydrogen carbonate. [ 12 ] 2) Preferably, the recovery apparatus according to the invention further includes a reverse osmosis membrane concentrator for separating the underground water to be supplied to and concentrated by the evaporation concentrator into permeated water and membrane-concentrated water, wherein the 10 membrane-concentrated water separated by the reverse osmosis membrane concentrator is supplied to the evaporation concentrator as the underground water to be concentrated. [ 13 ] The underground water is concentrated by membrane filtration in the reverse osmosis membrane concentrator and then evaporated to be further 15 concentrated by the evaporation concentrator. The apparatus thus configured can efficiently concentrate the underground water. [ 14 ] 3) A sodium hydrogen carbonate recovery apparatus according to another aspect of the invention is an apparatus for recovering sodium hydrogen carbonate from underground water containing at least the sodium hydrogen carbonate, 20 sodium carbonate, and sodium chloride. The apparatus includes an evaporation concentrator for concentrating the underground water, a carbon dioxide gas absorption crystallizer for depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water concentrated by the evaporation concentrator contact carbon dioxide gas, and a reverse osmosis membrane 25 concentrator for separating the underground water to be supplied to and concentrated by the evaporation concentrator into permeated water and membrane-concentrated water, wherein the carbon dioxide gas contained in the permeated water separated by the reverse osmosis membrane concentrator is collected and introduced into the concentrated underground water in the carbon dioxide gas absorption crystallizer, and 30 the membrane-concentrated water separated by the reverse osmosis membrane 3 1000139088 concentrator is supplied to the evaporation concentrator as the underground water to be concentrated. 15 ] The underground water to be supplied as raw water to the sodium hydrogen carbonate recovery apparatus contains a large quantity of carbonate ions. 5 Accordingly, the permeated water separated by the reverse osmosis membrane concentrator provided before the evaporation concentrator contains a large quantity of carbon dioxide gas. The carbon dioxide gas can be collected from the permeated water by, for example, a vacuum degassing apparatus. [ 16 1 To deposit crystals of the sodium hydrogen carbonate from the evaporated 10 and concentrated underground water using the carbon dioxide gas absorption crystallizer, the recovery apparatus according to the invention collects the carbon dioxide gas contained in the permeated water separated by the reverse osmosis membrane concentrator and introduces the collected carbon dioxide gas into the concentrated underground water in the carbon dioxide gas absorption crystallizer, 15 making the carbon dioxide gas contact the concentrated underground water. This facilitates the formation of hydrogen carbonate ions in the concentrated underground water, thereby improving the recovery ratio of the sodium hydrogen carbonate. [ 17 ] The underground water is concentrated by membrane filtration in the reverse osmosis membrane concentrator and then evaporated to be further 20 concentrated by the evaporation concentrator. The apparatus thus configured can efficiently concentrate the underground water. [ 18 ] 4) Preferably, the recovery apparatus according to the invention further includes a heat recovery device for preheating the underground water to be supplied to and concentrated by the evaporation concentrator using heat of the concentrated 25 underground water concentrated by the evaporation concentrator. { 19 ] The concentrated underground water already concentrated by the evaporation concentrator is at high temperatures. The underground water, before being supplied to the evaporation concentrator to be concentrated, is preheated with the heat of the hot underground water already concentrated. It improves the energy 30 efficiency to thus recover the heat of the concentrated underground water. The 4 1000139088 concentrated underground water is cooled down to lower temperatures, and the solubility of the sodium hydrogen carbonate is decreased. As a result, the recovery ratio of crystals of the sodium hydrogen carbonate is improved. The concentrated underground water discharged from the heat recovery device may be further cooled 5 down by chilled water from a chiller. [ 20 1 5) According to yet another aspect of the invention, the underground water is associated water discharged from coal seams along with the carbon dioxide gas. [ 21 ] The associated water discharged from coal seams along with the carbon 10 dioxide gas has a pH value in the range of 8 to 9, approximately. The apparatus according to the aspect of the invention can recover the sodium hydrogen carbonate contained in the associated water without adjusting the pH value of the associated water. [ 22 1 6) A sodium hydrogen carbonate recovery method according to an 15 aspect of the invention is a method for recovering sodium hydrogen carbonate from underground water containing at least the sodium hydrogen carbonate, sodium carbonate, and sodium chloride. The method includes steps of: concentrating the underground water by evaporation; and depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water concentrated by 20 evaporation in the concentrating step contact carbon dioxide gas, wherein the depositing step introduces the carbon dioxide gas generated in the concentrating step into the concentrated underground water. [ 23 ] To deposit crystals of the sodium hydrogen carbonate from the evaporated and concentrated underground water, the recovery method according to the invention 25 collects the carbon dioxide gas generated when the underground water is concentrated by evaporation and introduces the collected carbon dioxide gas into the concentrated underground water. This facilitates the formation of hydrogen carbonate ions in the concentrated underground water, thereby improving the recovery ratio of the sodium hydrogen carbonate. 30 [24] 7) A sodium hydrogen carbonate recovery method according to another 5 1000139088 aspect of the invention is a method for recovering sodium hydrogen carbonate from underground water containing at least the sodium hydrogen carbonate, sodium carbonate, and sodium chloride. The method includes steps of: separating the underground water into permeated water and membrane-concentrated water using a 5 reverse osmosis membrane; obtaining concentrated underground water by further concentrating the membrane-concentrated water by evaporation; and depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water contact carbon dioxide gas, wherein the depositing step collects the carbon dioxide gas contained in the permeated water separated through the reverse osmosis 10 membrane and introduces the collected carbon dioxide gas into the concentrated underground water. [ 25 ] To deposit crystals of the sodium hydrogen carbonate from the evaporated and concentrated underground water, the recovery method according to the invention collects the carbon dioxide gas contained in the permeated water separated through 15 the reverse osmosis membrane and introduces the collected carbon dioxide gas into the concentrated underground water. This facilitates the formation of hydrogen carbonate ions in the concentrated underground water, thereby improving the recovery ratio of the sodium hydrogen carbonate. 20 EFFECT OF THE INVENTION [ 26 ] According to the invention, in order to deposit crystals of the sodium hydrogen carbonate from the evaporated and concentrated underground water using the carbon dioxide gas absorption crystallizer, the carbon dioxide gas generated in the evaporation concentrator or the carbon dioxide gas contained in the permeated water 25 separated by the reverse osmosis membrane concentrator is introduced into the concentrated underground water. This facilitates the formation of hydrogen carbonate ions in the concentrated underground water, thereby improving the recovery ratio of the sodium hydrogen carbonate. 30 BRIEF DESCRIPTION OF THE DRAWINGS 6 1000139088 [ 27 ] Fig. 1 is a block diagram illustrating an overall structure of a recovery apparatus according to an embodiment of the invention. Fig. 2 is a structural drawing of an evaporation concentrator illustrated in Fig. 1. 5 Fig. 3 is a schematic structural drawing of a heat recovery device illustrated in Fig. 1. Fig. 4 is a structural drawing of a carbon dioxide gas absorption crystallizer illustrated in Fig. 1. 1o EMBODIMENTS OF THE INVENTION [ 28 ] An embodiment of the invention is hereinafter described in detail referring to the accompanied drawings. [ 29 ] Fig. I is a block diagram illustrating an overall structure of a sodium hydrogen carbonate recovery apparatus according to an embodiment of the invention. 15 [ 30 ] In a recovery apparatus I according to the embodiment, underground water, such as a large quantity of associated water generated when coal seam gas is collected from coal seams, is used as raw water. The recovery apparatus 1 recovers sodium hydrogen carbonate contained in the raw water. [ 31 ] The raw water, such as underground water, supplied to the recovery 20 apparatus 1 contains sodium chloride, sodium hydrogen carbonate, and sodium carbonate as its major components. The recovery apparatus I recovers the sodium hydrogen carbonate contained in the raw water. The pH value of the raw water is about 8 to 9. Therefore, it is unnecessary to adjust the pH value of the raw water. [ 32 1 The recovery apparatus 1 includes a reverse osmosis membrane 25 concentrator 2, a heat recovery device 3, an evaporation concentrator 4, a carbon dioxide gas absorption crystallizer 5, and a solid-liquid separator 6. The reverse osmosis membrane concentrator 2 separates the raw water, such as underground water, into permeated water (fresh water) and non-permeated water (membrane-concentrated water). The heat recovery device 3 preheats the membrane-concentrated water 30 (non-permeated water) concentrated by membrane filtration in the reverse osmosis 7 1000139088 membrane concentrator 2 as described later. The membrane-concentrated water preheated by the heat recovery device 3 is supplied to the evaporation concentrator 4 as the underground water to be evaporated and concentrated. This underground water, not yet concentrated, is evaporated and thereby concentrated by the 5 evaporation concentrator to such an extent that is almost saturated or supersaturated with carbonate. The concentrated underground water is then supplied to the heat recovery device 3. The carbon dioxide gas absorption crystallizer 5 makes the concentrated underground water from which heat has been recovered by the heat recovery device 3 contact carbon dioxide gas, thereby depositing crystals of the 10 sodium hydrogen carbonate. The solid-liquid separator 6 separates the deposited crystals of the sodium hydrogen carbonate obtained by the carbon dioxide gas absorption crystallizer 5. As described later, the carbon dioxide gas generated in the evaporation concentrator 4 is introduced into the carbon dioxide gas absorption crystallizer 5. 15 [ 33 ] The reverse osmosis membrane concentrator 2 is supplied with the raw water (underground water) already subjected pretreatments performed by a pretreatment device not illustrated in the drawings. An example of the pretreatments is the removal of ions that produce poor solubility salts such as calcium, magnesium, barium, and strontium. The raw water is separated into permeated water and 20 non-permeated water by the reverse osmosis membrane concentrator 2. The permeated water is utilized as fresh water, and the membrane-concentrated water (non-permeated water) concentrated by membrane filtration is supplied to the heat recovery device 3 and preheated therein. The membrane-concentrated water preheated by the heat recovery device 3 is supplied to the evaporation concentrator 4 2. as the underground water to be concentrated by evaporation. [ 34 ] The evaporation concentrator 4 according to the present embodiment is a horizontal tube falling film evaporator of double effect type illustrated in Fig. 2. The evaporation concentrator 4 is not limited to a double-effect evaporator and may be a single-effect evaporator or a multi-effect evaporator with three or more effects. 30 The evaporation concentrator may be a mechanical recompression evaporator that 8 1000139088 uses no heating steam. [ 35 ] The evaporation concentrator 4 includes a first-effect evaporator 7 and a second-effect evaporator 8. The evaporators 7 and 8 are respectively equipped with a large number of heat transfer pipes 7a and 8a. The heat transfer pipes 7a and 8a 5 are respectively arranged substantially in parallel in upper sections of the evaporators 7 and 8. The evaporators 7 and 8 are further provided with circulation pipelines 31 and 32. The circulation pipelines 31 and 32 are configured to draw in and circulate the underground water supplied to lower sections of the evaporators 7 and 8 so as to spray the underground water onto outer surfaces of the heat transfer pipes 7a and 8a. 1o In the circulation pipelines 31 and 32, first and second circulation pumps 9 and 10 are respectively installed. [ 36 ] The membrane-concentrated water preheated by the heat recovery device 3 is carried through a feed pipeline 11 and supplied to a lower section of the first-effect evaporator 7 as the underground water to be concentrated by evaporation. The 15 underground water in the first-effect evaporator 7 is partly circulated as described above. The remainder of the underground water is carried through a pipeline 12 and supplied to a lower section of the second-effect evaporator 8. [ 37 ] One ends of the heat transfer pipes 7a and 8a of the evaporators 7 and 8 are communicated with inlet-side headers 7b and 8b. The other ends of the heat transfer 20 pipes 7a and 8a are communicated with outlet-side headers 7c and 8c. [ 38 ] A part of vapor from the second-effect evaporator 8 is suctioned and compressed by a vapor ejector 14 driven by vapor supplied through a vapor duct 13 from a heat source not illustrated in the drawings such as a boiler. The vapor suctioned and compressed by the vapor ejector 14 is carried through a vapor duct 15 25 and supplied to the inlet-side header 7b of the first-effect evaporator 7. The supplied vapor is used as a heat source to evaporate the underground water in the first-effect evaporator 7. The vapor generated in the first-effect evaporator 7 is carried through a vapor duct 16 and supplied to the inlet-side header 8b of the second-effect evaporator 8. The supplied vapor is used as a heat source to evaporate the 30 underground water in the second-effect evaporator 8. 9 1000139088 [ 39 ] The vapor generated in the second-effect evaporator 8 is partly supplied to the vapor ejector 14. The remainder of the vapor is supplied to a condenser 17 through a branch duct 27. The vapor supplied to the condenser 17 is cooled down and condensed. The condensed water is discharged by a condensed water pump 30. 5 The condenser 17 is connected to a vacuum pump 29 provided for pressure reduction of the evaporators 7 and 8. [ 40 ] In the evaporation concentrator 4, the membrane-concentrated water supplied from the heat recovery device 3 to the first-effect evaporator 7 through the feed pipeline 11 is heated and evaporated to be concentrated. The concentrated 10 underground water concentrated in the first-effect evaporator 7 is carried to the second-effect evaporator 8 and further heated and evaporated to be concentrated. 41 ] Normally, the first-effect evaporator 7 is operated at temperatures from 100*C to 60*C, and the second-effect evaporator 8 is operated at temperatures slightly lower than the operating temperatures of the first-effect evaporator 7. According to 15 the present embodiment, the concentrated underground water concentrated in the first-effect evaporator 7 has a temperature about 68*C, and the concentrated underground water concentrated in the second-effect evaporator 8 has a temperature about 65*C. [ 42 ] The concentrated underground water concentrated in the second-effect 20 evaporator 8 is partly circulated through the circulation pipeline 32, while the remainder of the concentrated underground water is supplied to the heat recovery device 3. The heat recovery device 3 recovers heat of the supplied concentrated underground water by exchanging heat with the membrane-concentrated water from the reverse osmosis membrane concentrator 2. 25 [ 43 ] In the evaporation concentrator 4, carbon dioxide gas (C0 2 ) is generated during the concentration process by evaporation. The evaporation concentrator 4 collects and supplies the generated carbon dioxide gas to the carbon dioxide gas absorption crystallizer 5. More specifically, a mixed gas of vapor and carbon dioxide gas is supplied to the condenser 17 through the branch duct 27 diverging from 3D a vapor duct 28 in an upper section of the second-effect evaporator 8. The mixed 10 1000139088 gas supplied to the condenser 17 is cooled down so that associated vapor is removed therefrom. The mixed gas, after the associated vapor is removed therefrom, is supplied to the carbon dioxide gas absorption crystallizer 5 through the vacuum pump 29 which is a water-seal vacuum pump. 5 [ 44 ] As schematically illustrated in Fig. 3, a multi-stage flash evaporator, for example, a seven-stage flash evaporator constitutes the heat recovery device 3 according to the present embodiment. The heat recovery device 3 includes evaporation chambers 31 - 37 reduced in pressure. The evaporation chambers 31 - 37 respectively have, in their lower sections, openings 3 1 a - 3 7 a for the concentrated 10 underground water to pass through. The heat recovery device 3 continuously introduces the concentrated underground water concentrated by the evaporation concentrator 4 and flash-evaporates the concentrated underground water that is introduced to. At the same time, the heat recovery device 3 cools down the evaporated vapor using the membrane-concentrated water at low temperatures carried 15 from the reverse osmosis membrane concentrator 2 through a preheat pipeline 18 in an upper section of the heat recovery device 3. As a result of ongoing heat exchange thus performed between the concentrated underground water at high temperatures and the membrane-concentrated water at low temperatures, heat of the hot concentrated underground water is recovered and used to preheat the membrane-concentrated water. 20 Then, the preheated membrane-concentrated water is supplied to the evaporation concentrator 4. [ 45 ] The temperature of the concentrated underground water supplied from the second-effect evaporator 8 of the evaporation concentrator 4 to the heat recovery device 3 is about 65*C. After repeatedly performing the flash evaporation in the 25 heat recovery device 3 and preheating the membrane-concentrated water from the reverse osmosis membrane concentrator 2, the temperature of the concentrated underground water is lowered to about 40*C. [ 46 ] The heat recovery of the underground water concentrated by the evaporation concentrator 4 ensures a higher degree of energy efficiency. 30 [47 ] In place of the flash evaporator, a heat exchanger may be used as the heat 11 1000139088 recovery device 3. According to the present embodiment, the flash evaporator is used as the heat recovery device 3 due to the following disadvantages of the heat exchanger. One of the disadvantages is; crystals are deposited on a heating surface as the concentrated underground water saturated or supersaturated with carbonate is 5 cooled down. The other disadvantage is; the raw water contains silica, resulting in a high silica density in the concentrated underground water concentrated by the evaporation concentrator 4, and the heat exchanger effectiveness is degraded by silica scales attached to a heat exchange surface as the concentrated underground water is cooled down to lower temperatures. 10 [ 48 ] The carbon dioxide gas absorption crystallizer 5 according to the present embodiment is a jacket cooling crystallizer. [ 49 ] As illustrated in Fig. 4, the carbon dioxide gas absorption crystallizer 5 has a jacket 19a in a peripheral portion of a crystallizer 19 for depositing crystals. The carbon dioxide gas absorption crystallizer 5 feeds chilled water from a chiller not 15 illustrated in the drawings into the jacket 19a to cool down the concentrated underground water in the crystallizer 19 on contact with a wall surface of the crystallizer 19. In this manner, the concentrated underground water in the crystallizer 19 is cooled down to 15'C to 20*C and stays in the temperature range. [ 50 ] The crystallizer 19 has an upper section formed in a tubular shape and a 20 lower section formed in a conical shape for classification. The concentrated underground water cooled down to lower temperatures by the heat recovery device 3 is supplied to the lower section through a feed pipeline 22. [ 51 ] A slurry containing deposited crystals of the sodium hydrogen carbonate is recovered from a bottom section of the crystallizer 19. A part of the recovered 25 slurry is supplied to the solid-liquid separator 6, while the remainder of the recovered slurry is suctioned by an ejector 25 and further mixed with the carbon dioxide gas generated in the evaporation concentrator 4 by the ejector 25. The slurry mixed with the carbon dioxide gas by the ejector 25 is introduced into the bottom section of the crystallizer 19. 30 [52 ] The concentrated underground water is agitated in the crystallizer 19, and 12 1000139088 the carbon dioxide gas forming micro air bubbles in all over the crystallizer 19 is finally dissolved in the concentrated underground water. This somewhat lowers the pH value of the concentrated underground water, leading to a lower content of carbonate ions (C0 3 ) in the concentrated underground water. Because of the lower 5 pH value resulting in a lower content of sodium carbonate (Na 2

CO

3 ), crystallization of the sodium carbonate is prevented from happening in the concentrated underground water. [ 53 ] The carbon dioxide gas generated in the evaporation concentrator 4 is collected and introduced into the crystallizer 19. The introduced carbon dioxide gas 10 dissolves in the concentrated underground water, creating new hydrogen carbonate ions (HC0 3 ~). This increases the recovery ratio of the sodium hydrogen carbonate. [ 54 ] The slurry containing the sodium hydrogen carbonate crystals and recovered from the bottom section of the crystallizer 19 is supplied to the solid-liquid separator 6 illustrated in Fig. 1. 15 [ 55 ] Examples of the solid-liquid separator 6 are a centrifugal separator and a rotary vacuum filter. The solid-liquid separator 6 separates and recovers the sodium hydrogen carbonate crystals. As illustrated in Fig. 1, a part of filtrate generated then is blown out of the system, while the remainder of the filtrate is returned to and mixed with the membrane-concentrated water (non-permeated water) from the reverse 20 osmosis membrane concentrator 2. The membrane-concentrated water (non-permeated water) mixed with the filtrate is supplied to the heat recovery device 3. 56 ] Table I shows a composition of the underground water from which the sodium hydrogen carbonate was recovered by the recovery apparatus 1 according to 25 the present embodiment. 13 1000139088 [57] Table I membrane-concentrated item unit underground water water by reverse osmosis membrane concentrator rate of flow m 3 /h 140 26 pH --- 8.5 8.8 Na mg/L 4,300 23,000 Cl mg/L 1,150 6,100

HCO

3 mg/L 6,300 34,000

CO

3 mg/L 1,300 6,900 total alkalinity mg/L 7,700 40,950 Table 1 also shows a composition of the underground water concentrated by membrane filtration in the reverse osmosis membrane concentrator 2 (membrane-concentrated water). 5 [ 58 ] The membrane-concentrated water concentrated by membrane filtration in the reverse osmosis membrane concentrator 2 and having the composition shown in Table I was evaporated and thereby concentrated by the evaporation concentrator 4. Table 2 shows a composition of the circulated liquid (filtrate) from the solid-liquid separator 6 that is the concentrated underground water collected from the carbon 10 dioxide gas absorption crystallizer 5. [ 59 ] The rate of flow of the membrane-concentrated water having the composition shown in Table I was 26 m 3 /h, and the rate of flow of the circulated liquid from the solid-liquid separator 6 was 3 m 3 /h. The evaporation capacity of the evaporation concentrator 4 was 23 t/h. The supplied membrane-concentrated water 15 was concentrated about six times. In the second-effect evaporator 8 of the evaporation concentrator, the sodium hydrogen carbonate crystals were generated in the quantity of 640 kg (7.6 kmol/h), and the concentrated underground water was collected and removed in the quantity of 3.7 t/h. [ 60 ] The carbon dioxide gas in the quantity of 56 kg/h was generated from the 20 concentrated underground water in the evaporation concentrator 4 and discharged 14 1000139088 through the outlet of the vacuum pump 29. [61] Table 2 concentrated underground item unit water by cooling crystallizer rate of flow m 3 /h 3 temperature *C 15 pH --- _10.2 Na mg/L 130,000 CI mg/L 92,000

HCO

3 mg/L 68,000

CO

3 mg/L 68,000 Further, a crystalline matter of the sodium hydrogen carbonate was obtained in the dry weight of 405 kg/h (4.8 kmol/h) by the solid-liquid separator 6 from the 5 concentrated underground water from which the sodium hydrogen carbonate crystals had been removed by the second-effect evaporator 8 of the evaporation concentrator. [ 62 1 The underground water contains the following soda components as shown in Table 1. [63 ] HCO 3 : 6,300 mg/L, 6.3/61 = 0.1 mol/L 10 C0 3 : 1300 mg/L, 1.3/60 = 0.022 mol/ Total: 0.122 mol/L, that is 0.122 kmol/m 3 As shown in Table 1, the rate of flow of the underground water supplied as the raw water was 140 m 3 /h. Therefore, 0.122 kmol*140m 3 = 17.1 kmol, resulting in the recovery ratio of (7.6+4.8)/17.1 = 73%. 15 [ 64 1 The apparatus according to the present embodiment succeeded in recovering the sodium hydrogen carbonate by the recovery ratio of more than 70%. [ 65 ] The underground water described in the embodiment is associated water generated when the coal seam gas is collected. The underground water may be other kinds of underground water containing sodium chloride, sodium hydrogen carbonate, 20 and sodium carbonate. [ 66 ] The evaporation concentrator is configured to deposit crystals using the 15 1000139088 second-effect evaporator. An evaporation concentration crystallizer may be separately provided in a stage subsequent to the evaporation concentrator so that crystals are not generated in the evaporation concentrator. [ 67 ] The carbon dioxide gas absorption crystallizer 5 according to the 5 embodiment is a jacket cooling crystallizer using a chiller. The carbon dioxide gas absorption crystallizer 5 may be a conventional cooling tower device where the temperature range from 35*C to 40*C is obtained. The cooling method is not necessarily limited to the jacket cooling method. For example, a cooling pipe may be provided in the crystallizer or a crystallizer differently configured may be used. 10 [ 68 ] According to the embodiment, the carbon dioxide gas generated in the evaporation concentrator is introduced into the carbon dioxide gas absorption crystallizer to make contact with the concentrated underground water. According to another embodiment of the invention, the carbon dioxide gas contained in the permeated water separated by the reverse osmosis membrane concentrator may be 15 collected by a vacuum degassing device and so on and introduced into the carbon dioxide gas absorption crystallizer to make contact with the concentrated underground water. According to yet another embodiment of the invention, the carbon dioxide gas generated in the evaporation concentrator and the carbon dioxide gas collected from the permeated water may be both introduced into the carbon dioxide gas 20 absorption crystallizer. DESCRIPTION OF REFERENCE SYMBOLS [ 69 ] 2 reverse osmosis membrane concentrator 25 3 heat recovery device 4 evaporation concentrator 5 carbon dioxide gas absorption crystallizer 6 solid-liquid separator 7 first-effect evaporator 30 8 second-effect evaporator 16 1000139088 19 crystallizer 17

Claims (7)

1. An apparatus for recovering sodium hydrogen carbonate from underground water containing at least the sodium hydrogen carbonate, sodium carbonate, and sodium chloride, the apparatus comprising: 5 an evaporation concentrator for concentrating the underground water; and a carbon dioxide gas absorption crystallizer for depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water concentrated by the evaporation concentrator contact carbon dioxide gas, wherein the carbon dioxide gas generated in the evaporation concentrator is 10 introduced into the concentrated underground water in the carbon dioxide gas absorption crystallizer.

2. The apparatus for recovering sodium hydrogen carbonate as claimed in claim 1, further comprising a reverse osmosis membrane concentrator for separating the underground water to be supplied to and concentrated by the evaporation concentrator 15 into permeated water and membrane-concentrated water, wherein the membrane-concentrated water separated by the reverse osmosis membrane concentrator is supplied to the evaporation concentrator as the underground water to be concentrated.

3. An apparatus for recovering sodium hydrogen carbonate from underground 20 water containing at least the sodium hydrogen carbonate, sodium carbonate, and sodium chloride, the apparatus comprising: an evaporation concentrator for concentrating the underground water; a carbon dioxide gas absorption crystallizer for depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water 25 concentrated by the evaporation concentrator contact carbon dioxide gas; and a reverse osmosis membrane concentrator for separating the underground water to be supplied to and concentrated by the evaporation concentrator into permeated water and membrane-concentrated water, wherein the carbon dioxide gas contained in the permeated water separated by the 30 reverse osmosis membrane concentrator is collected and introduced into the 18 1000139088 concentrated underground water in the carbon dioxide gas absorption crystallizer, and the membrane-concentrated water separated by the reverse osmosis membrane concentrator is supplied to the evaporation concentrator as the underground water to be concentrated. 5

4. The apparatus for recovering sodium hydrogen carbonate as claimed in claims 1 through 3, further comprising a heat recovery device for preheating the underground water to be supplied to and concentrated by the evaporation concentrator using heat of the concentrated underground water concentrated by the evaporation concentrator. 10

5. The apparatus for recovering sodium hydrogen carbonate as claimed in claims I through 4, wherein the underground water is associated water discharged from coal seams along with the carbon dioxide gas.

6. A method for recovering sodium hydrogen carbonate from underground 15 water containing at least the sodium hydrogen carbonate, sodium carbonate, and sodium chloride, the method comprising steps of: concentrating the underground water by evaporation; and depositing crystals of the sodium hydrogen carbonate by making the concentrated underground water concentrated by evaporation in the concentrating step 20 contact carbon dioxide gas, wherein the depositing step introduces the carbon dioxide gas generated in the concentrating step into the concentrated underground water.

7. A method for recovering sodium hydrogen carbonate from underground water containing at least the sodium hydrogen carbonate, sodium carbonate, and 25 sodium chloride, the method comprising steps of: separating the underground water into permeated water and membrane-concentrated water using a reverse osmosis membrane; obtaining concentrated underground water by further concentrating the membrane-concentrated water by evaporation; and 30 depositing crystals of the sodium hydrogen carbonate by making the 19 1000139088 evaporated and concentrated underground water contact carbon dioxide gas, wherein the depositing step collects the carbon dioxide gas contained in the permeated water separated through the reverse osmosis membrane and introduces the collected carbon dioxide gas into the concentrated underground water. 20