Seawater desalination plant

Abstract

To improve a recovery rate of fresh water.SOLUTION: A seawater desalination apparatus 100 includes: a mixing part 210 that generates a mixed liquid by mixing seawater and cyclopentane; a generation part 220 that generates a solid-liquid mixture containing cyclopentane hydrate, a crystal chloride and salt water by cooling the mixed liquid to an eutectic temperature of the cyclopentane hydrate and the crystal chloride; and a separation part 410 that separates the solid-liquid mixture into cyclopentane hydrate, crystal chloride and salt water.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a seawater desalination apparatus for desalinating seawater. [Background technology]

[0002] Conventionally, the Multi-Stage Flash (MSF) method has been used as a technology for desalinating seawater. In the Multi-Stage Flash method, the process of heating seawater to evaporate (flash) the water, and then cooling and condensing the evaporated water (steam) is repeated multiple times. For this reason, the Multi-Stage Flash method requires an enormous amount of thermal energy for heating, and also requires an enormous amount of thermal energy to be wasted to the outside through condensation. Therefore, the Multi-Stage Flash method not only requires high heating costs, but is also a factor in global warming.

[0003] Therefore, a reverse osmosis (RO) method has been developed in which high-pressure seawater is passed through a reverse osmosis membrane (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-203258 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the reverse osmosis method, the recovery rate of fresh water is low at about 30%, so there is a demand for the development of technology that can improve the recovery rate of fresh water.

[0006] In view of the above problems, an object of the present invention is to provide a seawater desalination apparatus capable of improving the recovery rate of fresh water. [Means for solving the problem]

[0007] In order to solve the above problems, a seawater desalination apparatus according to the present invention includes a mixing unit that mixes seawater with cyclopentane to produce a mixed liquid, a production unit that cools the mixed liquid to the eutectic temperature of cyclopentane hydrate and crystalline chloride to produce a solid-liquid mixture containing cyclopentane hydrate, crystalline chloride, and salt water, and a separation unit that separates the solid-liquid mixture into cyclopentane hydrate, crystalline chloride, and salt water. a decomposition section for heating the cyclopentane hydrate separated by the separation section to decompose it into cyclopentane and water; Equipped with The production section exchanges heat between the mixed liquid and a refrigerant, and the decomposition section exchanges heat between the refrigerant that has been heat exchanged in the production section and cyclopentane hydrate. do.

[0010] The seawater desalination apparatus may further include a return pump that returns the salt water separated by the separation section to the mixing section. In order to solve the above problems, another seawater desalination apparatus according to the present invention includes a mixing unit that mixes seawater with cyclopentane to produce a mixed liquid, a production unit that cools the mixed liquid to the eutectic temperature of cyclopentane hydrate and crystalline chlorides to produce a solid-liquid mixture containing cyclopentane hydrate, crystalline chlorides, and brine, a separation unit that separates the solid-liquid mixture into cyclopentane hydrate, crystalline chlorides, and brine, and a return pump that returns the brine separated by the separation unit to the mixing unit. Effect of the Invention

[0011] According to the present invention, it is possible to improve the recovery rate of fresh water. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a seawater desalination apparatus. [Diagram 2] FIG. 2 is a diagram illustrating a schematic configuration of a pre-processing unit. [Diagram 3] 2 is a diagram illustrating a schematic configuration of a mixing section, a generating section, and a refrigerant cooling section. FIG. [Figure 4] FIG. 2 is a diagram illustrating a schematic configuration of a separation unit. [Diagram 5] 5 is a cross-sectional view taken along line VV in FIG. 4. [Figure 6] FIG. 2 is a diagram illustrating a schematic configuration of a decomposition unit. [Figure 7] FIG. 2 is a diagram illustrating a schematic configuration of a purification section. [Figure 8] FIG. 1 is a diagram showing the relationship between the sodium chloride concentration in salt water and the formation temperature and freezing temperature of cyclopentane hydrate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to avoid repeated explanations, and elements not directly related to the present invention are not shown.

[0014] [Seawater desalination equipment 100] FIG. 1 is a diagram illustrating a schematic configuration of a seawater desalination apparatus 100. In FIG. 1, solid arrows indicate the flows of seawater, solid-liquid mixture SL, cyclopentane hydrate CH, decomposition water, cyclopentane CP, and circulating salt water J. In FIG. 1, dashed arrows indicate the flow of a refrigerant. As shown in FIG. 1, the seawater desalination apparatus 100 includes a pretreatment section 110, a mixing section 210, a generation section 220, a refrigerant cooling section 310, a separation section 410, a decomposition section 510, a purification section 610, and a central control section 710.

[0015] The pretreatment unit 110 removes impurities from the seawater. The mixer 210 mixes seawater with cyclopentane CP. The refrigerant cooling unit 310 cools the refrigerant. The generator 220 cools the mixture of seawater and cyclopentane CP with a refrigerant to generate cyclopentane hydrate CH and crystalline chlorides. The separator 410 separates cyclopentane hydrate CH and crystalline chlorides from the solid-liquid mixture SL generated by the generator 220. The decomposition unit 510 decomposes cyclopentane hydrate CH into water and cyclopentane CP. The purification unit 610 generates decomposed water (water) obtained by decomposing cyclopentane hydrate CH.

[0016] The central control unit 710 is composed of a semiconductor integrated circuit including a CPU (Central Processing Unit). The central control unit 710 reads out programs and parameters for operating the CPU itself from a ROM (Read Only Memory). The central control unit 710 manages and controls the entire seawater desalination apparatus 100 in cooperation with programs, a RAM (Random Access Memory) as a work area, and other electronic circuits.

[0017] The pretreatment section 110, the mixing section 210, the production section 220, the refrigerant cooling section 310, the separation section 410, the decomposition section 510, and the purification section 610 will be described in detail below.

[0018] [Preprocessing unit 110] Fig. 2 is a diagram illustrating a schematic configuration of the pre-treatment unit 110. In Fig. 2, solid arrows indicate the flows of seawater and fresh water.

[0019] As shown in FIG. 2, the pretreatment section 110 includes a rough purification section 112 , a seawater booster pump 114 , a reverse osmosis membrane filter 116 , a clean water purification section 118 , and a seawater supply pipe 120 .

[0020] The rough purification unit 112 removes impurities from the seawater (for example, at a temperature between 2° C. and 28° C.) and sterilizes the seawater. The rough purification unit 112 is composed of, for example, a filter and a germicidal lamp.

[0021] The suction side of the seawater boost pump 114 is connected to the rough purification section 112. The discharge side of the seawater boost pump 114 is connected to the reverse osmosis membrane filter 116. The seawater boost pump 114 boosts the pressure of the seawater from which impurities have been removed and which has been sterilized by the rough purification section 112, and guides the seawater to the reverse osmosis membrane filter 116.

[0022] The reverse osmosis membrane filter 116 recovers a portion of the fresh water from the seawater (approximately 30% of the seawater guided from the seawater boost pump 114). The recovered fresh water is guided to the water purification section 118. The water purification section 118 purifies the fresh water. The purified fresh water is used as drinking water or the like.

[0023] Meanwhile, in the reverse osmosis membrane filter 116, the seawater from which some of the fresh water has been recovered (approximately 70% of the seawater guided from the seawater boost pump 114) is guided to the mixing section 210 through a seawater supply pipe 120. The seawater supply pipe 120 is a pipe that connects the reverse osmosis membrane filter 116 and the mixing section 210. A safety valve 124 and a flow rate adjustment valve 126 are provided in the seawater supply pipe 120.

[0024] [Mixing section 210] Fig. 3 is a diagram illustrating a schematic configuration of the mixing section 210, the generation section 220, and the refrigerant cooling section 310. In Fig. 3, solid arrows indicate the flows of seawater, solid-liquid mixture SL, cyclopentane hydrate CH, cyclopentane CP, and circulating salt water J. In Fig. 3, dashed arrows indicate the flow of the refrigerant.

[0025] 3, seawater is guided from the pretreatment section 110 to the mixing section 210 through the seawater supply pipe 120. Cyclopentane CP is guided from the separation section 410 to the mixing section 210 through the guest supply pipe 432. Circulating salt water J is guided from the separation section 410 to the mixing section 210 through the circulating salt water supply pipe 442.

[0026] The mixer 210 mixes (liquid-liquid mixes) seawater, cyclopentane CP, and circulating salt water J. The mixer 210 is, for example, a spiral line mixer (a mixer that rotates with the flow of a fluid to agitate the fluid). The mixer 210 first mixes seawater introduced from the seawater supply pipe 120 with cyclopentane CP introduced from a separation unit 410 described below. Thereafter, the mixer 210 mixes the mixed liquid (emulsion) of seawater and cyclopentane CP with the circulating salt water J.

[0027] In the mixer 210, the mixed solution of seawater and cyclopentane CP is mixed with circulating salt water J (−13.4° C.), and the mixed solution of seawater and cyclopentane CP is cooled by the circulating salt water J. This causes the hydrate production reaction to proceed, and the water in the seawater is taken in as crystal water, producing cyclopentane hydrate CH.

[0028] The mixer 210 includes a foaming device made of sintered metal or ceramic. The foaming device sprays cyclopentane CP into seawater as droplets with a particle size of about 10 μm. Cyclopentane CP is insoluble in water. Therefore, the hydrate formation reaction between cyclopentane CP and water (seawater) proceeds at the liquid-liquid interface. Therefore, by using the foaming device to spray cyclopentane CP into seawater as droplets with a particle size of about 10 μm, the contact area between cyclopentane CP and seawater can be increased, and the hydrate formation reaction can be promoted.

[0029] In addition, the hydrate formation reaction is an exothermic reaction. Therefore, by increasing the contact area between the cyclopentane CP and seawater using the bubbler, the reaction heat can be efficiently removed. This makes it possible to accelerate the hydrate formation reaction.

[0030] Also, if the particle size of cyclopentane CP is too small, the cyclopentane CP particles will undergo the Tyndall phenomenon due to hydrogen bonds of the water surrounding the cyclopentane CP particles, resulting in an emulsion, which will hinder contact with new seawater and slow down the reaction rate. Therefore, by making the particle size of cyclopentane CP about 10 μm, the occurrence of the Tyndall phenomenon can be suppressed. This makes it possible to avoid a situation in which the contact between cyclopentane CP and new seawater is hindered. Also, if the particle size of cyclopentane CP is made too small, that is, the diameter of the foaming device's nozzle hole is made too small, the injection pressure of cyclopentane CP into the foaming device will increase, and the energy required for pressurization will increase. Therefore, by making the particle size of cyclopentane CP about 10 μm, the injection pressure into the foaming device can be lowered, making it possible to reduce the energy required for pressurization.

[0031] As described above, the mixer 210 mixes the circulating salt water J with the mixed solution of seawater and cyclopentane CP. This makes it possible to suppress the rapid generation of cyclopentane hydrate CH in the mixed solution of seawater and cyclopentane CP. This makes it possible to prevent the holes in the bubble-forming device from being blocked by cyclopentane hydrate CH. The temperature of the mixed solution of seawater and cyclopentane CP is estimated to be about 4°C even in winter. Therefore, the holes in the bubble-forming device are not blocked by cyclopentane hydrate CH even in winter.

[0032] The amount of cyclopentane CP led from the separation section 410 is set to an amount in which 90% to 95% of the water in the seawater that can become cyclopentane hydrate CH is taken up (converted) into cyclopentane hydrate CH as crystal water. This makes it possible to prevent the mixing section 210, the solid-liquid mixture supply pipe 212, the production section 220, and the solid-liquid mixture delivery pipe 222 from being clogged with cyclopentane hydrate CH.

[0033] In addition, the amount of the circulating salt water J led from the separation section 410 is about eight times that of the seawater led from the pretreatment section 110. In the generation section 220 described later, when the solid-liquid mixture SL produced in the mixing section 210 is cooled, cyclopentane hydrate CH is rapidly produced. Then, the water in the solid-liquid mixture SL decreases and the concentration of sodium chloride (NaCl) increases. When the concentration of sodium chloride reaches a eutectic concentration (for example, 23.8 mass%), sodium chloride dihydrate (NaCl·2H2O, crystalline chloride) precipitates. Therefore, by making the amount of the circulating salt water J about eight times that of seawater, the amount of solids (cyclopentane hydrate CH and sodium chloride dihydrate) produced in the generation section 220 can be made 10 mass% or less. This makes it possible to prevent the solid-liquid mixture delivery pipe 222 from being clogged.

[0034] [Generation unit 220] The production section 220 cools the solid-liquid mixture SL introduced from the mixing section 210 through the solid-liquid mixture supply pipe 212 to the eutectic temperature (for example, −13.4° C.) of cyclopentane hydrate CH and crystalline chlorides. In this embodiment, the production section 220 is a heat exchanger that exchanges heat between the solid-liquid mixture SL and a refrigerant. The production section 220 cools the solid-liquid mixture SL and heats the refrigerant. The hydrate production reaction in the solid-liquid mixture SL is further promoted by being cooled by the production section 220. As a result, cyclopentane hydrate CH is further produced in the production section 220. The solid-liquid mixture SL containing cyclopentane hydrate CH, crystalline chlorides, and eutectic concentration salt water produced by the production section 220 is led to the separation section 410 through the solid-liquid mixture delivery pipe 222.

[0035] [Refrigerant cooling section 310] The refrigerant cooling unit 310 includes a buffer tank 320 , a refrigerant compressor 330 , a cooler 340 , and a buffer tank 350 .

[0036] The buffer tank 320 is connected to the generation unit 220 through a refrigerant return pipe 322. In addition, the buffer tank 320 is connected to the separation unit 410 through a refrigerant return pipe 324. The buffer tank 320 stores the gaseous refrigerant guided from the generation unit 220 through the refrigerant return pipe 322, and the gaseous refrigerant guided from the separation unit 410 through the refrigerant return pipe 324. By including the buffer tank 320, the refrigerant cooling unit 310 can suppress fluctuations in the suction pressure and the suction amount of the refrigerant compressor 330.

[0037] The suction side of the refrigerant compressor 330 is connected to the buffer tank 320. The discharge side of the refrigerant compressor 330 is connected to the cooler 340 and the decomposition unit 510. The refrigerant compressor 330 increases the pressure of the refrigerant. The refrigerant compressed by the refrigerant compressor 330 is guided to the cooler 340 and the decomposition unit 510.

[0038] The cooler 340 cools and condenses the refrigerant pressurized by the refrigerant compressor 330. The cooler 340 is configured, for example, by an air-cooling device or a water-cooling device.

[0039] The buffer tank 350 stores the refrigerant (liquid) condensed by the cooler 340 and the refrigerant (liquid) condensed in the decomposition unit 510. By including the buffer tank 350, the refrigerant cooling unit 310 can absorb pulsations (fluctuations in flow rate and pressure) of the refrigerant (liquid).

[0040] The refrigerant supply pipe 360 ​​connects the discharge side of the refrigerant compressor 330 and the decomposition section 510 (decomposition heat exchanger 522). A flow rate control valve 362 is provided in the refrigerant supply pipe 360. The central control unit 710 adjusts the opening degree of the flow rate control valve 362 so that cyclopentane hydrate CH is decomposed by the refrigerant passing through the decomposition heat exchanger 522 of the decomposition section 510 described later. The refrigerant return pipe 364 connects the decomposition section 510 and the buffer tank 350.

[0041] The refrigerant supply pipe 370 connects the buffer tank 350 and the production unit 220. A flow rate control valve 372 is provided in the refrigerant supply pipe 370. The central control unit 710 adjusts the opening degree of the flow rate control valve 372 so that the temperature of the solid-liquid mixture SL in the production unit 220 becomes the eutectic temperature.

[0042] The refrigerant supply pipe 380 connects the buffer tank 350 and the separation unit 410. A flow rate control valve 382 is provided in the refrigerant supply pipe 380. The central control unit 710 adjusts the opening degree of the flow rate control valve 382 so that the temperature of the solid-liquid mixture SL in a solid-liquid separator 412 of the separation unit 410 described below becomes a eutectic temperature (for example, −13.4° C.).

[0043] [Separation section 410] Fig. 4 is a diagram illustrating a schematic configuration of the separation unit 410. In Fig. 4, solid arrows indicate the flows of the solid-liquid mixture SL, cyclopentane CP, circulating salt water J, cyclopentane hydrate CH, and crystalline chlorides. In Fig. 4, dashed arrows indicate the flows of the refrigerant. In Fig. 4, the dashed line indicates the interface between the salt water and cyclopentane CP, the one-dot chain line indicates the interface between cyclopentane hydrate CH and cyclopentane CP, and the two-dot chain line indicates the interface between cyclopentane CP and the gas phase (air).

[0044] As shown in FIG. 4, the separation section 410 includes a solid-liquid separator 412, a heat exchanger 420, a dehydrator 422, a dryer 424, a circulation pump 430, a return pump 440, an entrained liquid separator 450, a deliquifier 460, and a guest supply section 470.

[0045] The solid-liquid separator 412 is a cylindrical container. A jetting part 414 and a partition plate 416 are provided inside the solid-liquid separator 412. The jetting part 414 jets cyclopentane CP. The partition plate 416 separates cyclopentane hydrate CH from the solid-liquid mixture SL.

[0046] Fig. 5 is a cross-sectional view taken along line VV in Fig. 4. In Fig. 5, the ejection part 414 is omitted for ease of understanding.

[0047] As shown in FIG. 5, the partition plate 416 has a bottom surface portion 416a, a front surface portion 416b, and two side surfaces 416c. The bottom surface portion 416a is a plate that protrudes horizontally from the side wall of the solid-liquid separator 412 into the solid-liquid separator 412. The bottom surface portion 416a is located above the interface between salt water and cyclopentane CP (shown by a broken line in FIG. 4), which will be described later. The front surface portion 416b is a plate that extends vertically upward from the tip of the bottom surface portion 416a. The side surface portion 416c is a plate that is continuous with the bottom surface portion 416a, the front surface portion 416b, and the inner wall of the solid-liquid separator 412. Therefore, in the solid-liquid separator 412, a partition space S is formed that is surrounded by the bottom surface portion 416a, the front surface portion 416b, the side surface portion 416c, and the inner wall of the solid-liquid separator 412.

[0048] Although the details will be described later, the cyclopentane hydrate CH floats up in the salt water in the solid-liquid separator 412. The floating cyclopentane hydrate CH overflows the upper ends of the front surface portion 416b and the side surface portion 416c and is guided to the partition space S. The cyclopentane hydrate CH guided to the partition space S is guided to the associated liquid separator 450 described later through a discharge port formed in the inner wall of the solid-liquid separator 412 that constitutes the partition space S.

[0049] Returning to Fig. 4, a gas trap 418 is connected to the upper part of the solid-liquid separator 412. The gas trap 418 exhausts air guided from the solid-liquid separator 412 and supplies air to the solid-liquid separator 412 to maintain the pressure inside the solid-liquid separator 412 at atmospheric pressure (approximately 0.1 MPa). The configuration including the gas trap 418 makes it possible to maintain the pressure inside the solid-liquid separator 412 at atmospheric pressure regardless of the temperature difference between day and night and fluctuations in atmospheric pressure.

[0050] In addition, the solid-liquid mixture delivery pipe 222 connects the generation section 220 to the space between the jetting section 414 and the partition plate 416 in the solid-liquid separator 412. Therefore, the solid-liquid mixture SL guided from the generation section 220 is supplied to the space between the jetting section 414 and the partition plate 416 in the solid-liquid separator 412.

[0051] The heat exchanger 420 cools the solid-liquid mixture SL in the solid-liquid separator 412 to a eutectic temperature (for example, −13.4° C.). A refrigerant supply pipe 380 and a refrigerant return pipe 324 are connected to the heat exchanger 420. The heat exchanger 420 exchanges heat between the refrigerant guided from the refrigerant cooling unit 310 and the solid-liquid mixture SL to cool the solid-liquid mixture SL. This further promotes the hydrate production reaction in the solid-liquid separator 412. Then, when the temperature of the solid-liquid mixture SL reaches the eutectic temperature (for example, −13.4° C.), the concentration of sodium chloride in the salt water contained in the solid-liquid mixture SL reaches the eutectic concentration (for example, 23.8 mass%), and crystalline chloride precipitates.

[0052] In the solid-liquid separator 412, the solid-liquid mixture SL is separated into cyclopentane hydrate CH, crystalline chlorides, salt water, and cyclopentane CP based on the difference in specific gravity. Specifically, the specific gravity of cyclopentane CP is 0.75. The specific gravity of cyclopentane hydrate CH is 0.95. The specific gravity of salt water is 1.20. The specific gravity of crystalline chlorides is 1.69. Therefore, in the solid-liquid separator 412, cyclopentane hydrate CH floats to the interface between the salt water and cyclopentane CP (indicated by the broken line in FIG. 4), and the crystalline chlorides sink into the salt water. Note that about 70% of the cyclopentane hydrate CH is located in the cyclopentane CP layer, and about 30% is located in the salt water. The solid-liquid separator 412 is designed so that the residence time of cyclopentane hydrate CH is long enough to sufficiently separate cyclopentane hydrate CH and cyclopentane CP in the solid-liquid separator 412.

[0053] Thus, the floating cyclopentane hydrate CH flows over the partition plate 416 and is guided to the entrained liquid separator 450. As described above, the bottom surface 416a of the partition plate 416 is provided above the interface between the salt water and the cyclopentane CP. Therefore, the cyclopentane hydrate CH that flows over the partition plate 416 is accompanied by almost no salt water, but by cyclopentane CP. This makes it possible to reduce the sodium chloride concentration in the water generated in the subsequent decomposition section 510.

[0054] Meanwhile, the precipitated crystalline chloride is dehydrated by the dehydrator 422. The crystalline chloride dehydrated by the dehydrator 422 is dried by the dryer 424. Meanwhile, the salt water generated by the dehydrator 422 is guided to an accumulator 456, which will be described later. The crystalline chloride (sodium chloride) dried by the dryer 424 is shipped as a product.

[0055] Furthermore, a flow rate adjustment valve 426 is provided in the pipe connecting the dehydrator 422 and the accumulator 456. The central control unit 710 adjusts the opening degree of the flow rate adjustment valve 426 so as to maintain the dehydration efficiency of the dehydrator 422.

[0056] Moreover, the cyclopentane CP separated by flotation in the solid-liquid separator 412 is returned to the mixing section 210 and the jetting section 414 by the circulation pump 430 .

[0057] The suction side of the circulation pump 430 is connected to the upper side of the partition plate 416 in the solid-liquid separator 412. The discharge side of the circulation pump 430 is connected to a guest supply pipe 432. The guest supply pipe 432 is a pipe that connects the circulation pump 430 and the mixer 210. The guest supply pipe 432 is provided with a flow control valve 434. The central control unit 710 adjusts the aperture of the flow control valve 434 so that the amount of cyclopentane CP introduced to the mixer 210 is an amount in which 90% or more and 95% or less of the water in seawater that can become cyclopentane hydrate CH is taken into cyclopentane hydrate CH as crystal water.

[0058] The guest circulation pipe 436 is a pipe that connects the portion between the flow rate control valve 434 and the mixer 210 in the guest supply pipe 432 and the jetting portion 414. The guest circulation pipe 436 is provided with a flow rate control valve 438. The central control unit 710 adjusts the aperture of the flow rate control valve 438 so that the amount of cyclopentane CP introduced to the solid-liquid separator 412 is an amount in which 5% to 10% of the water in the seawater that can become cyclopentane hydrate CH is taken into cyclopentane hydrate CH as crystal water. In other words, the cyclopentane CP introduced from the jetting portion 414 can convert almost all (100%) of the water in the seawater that can become cyclopentane hydrate CH into cyclopentane hydrate CH. The central control unit 710 may adjust the aperture of the flow rate control valve 434 and the flow rate control valve 438 so that the amount of freshwater is a target amount set in the purification unit 610 described later.

[0059] Furthermore, salt water (for example, at −13.4° C.) separated in the solid-liquid separator 412 is returned to the mixing section 210 by a return pump 440. The suction side of the return pump 440 is connected to a lower side of the ejection section 414 in the solid-liquid separator 412. The discharge side of the return pump 440 is connected to a circulating salt water supply pipe 442. The circulating salt water supply pipe 442 is a pipe that connects the return pump 440 and the mixing section 210. The circulating salt water supply pipe 442 is provided with a flow rate control valve 444. The central control section 710 adjusts the opening of the flow rate control valve 444 so that the amount of salt water (circulating salt water J) introduced to the mixing section 210 is about eight times the amount of seawater.

[0060] Cyclopentane hydrate CH, and trace amounts of cyclopentane CP and salt water that are accompanied by the cyclopentane hydrate CH are introduced to the associated liquid separator 450. The associated liquid separator 450 separates the cyclopentane hydrate CH, cyclopentane CP, and salt water by the difference in specific gravity.

[0061] In the entrained liquid separator 450, cyclopentane CP rises to the upper layer and accumulates there. A mixture of cyclopentane hydrate CH and free liquid forms a middle layer. The free liquid is a mixture of salt water and cyclopentane CP. The salt water accumulates in the lower layer.

[0062] The guest return pipe 452 is a pipe that connects the upper part of the entrained liquid separator 450 to the upper part of the interface (indicated by a two-dot chain line in FIG. 4) between cyclopentane CP and air in the solid-liquid separator 412. Cyclopentane CP constituting the upper layer of the entrained liquid separator 450 is pushed up to the middle and lower layers due to the difference in specific gravity, and is automatically returned to the gas phase of the solid-liquid separator 412 through the guest return pipe 452.

[0063] Cyclopentane hydrate CH forming a middle layer in the entrained liquid separator 450 rises and is sandwiched between the liquid levels of the lower layer, and is sucked into the deliquor 460, which will be described later.

[0064] The salt water forming the lower layer in the entrained liquid separator 450 is sucked by the retained water discharge pump 454 and returned to the mixer 210 through the circulating salt water supply pipe 442. An accumulator 456 is provided between the entrained liquid separator 450 and the retained water discharge pump 454. The accumulator 456 separates the salt water and cyclopentane CP based on the specific gravity difference. For this reason, the retained water discharge pump 454 returns the salt water separated by the accumulator 456 to the mixer 210. The cyclopentane CP separated by the accumulator 456 is returned to the solid-liquid separator 412 through the guest return pipe 452.

[0065] A flow control valve 458 is provided in the pipe connecting the accompanied liquid separator 450 and the accumulator 456. The central control unit 710 adjusts the opening of the flow control valve 458 so that the interface between the lower layer and the middle layer in the accompanied liquid separator 450 is maintained at a predetermined position.

[0066] The deliquifier 460 sucks the middle layer (cyclopentane hydrate CH) from the associated liquid separator 450 and deliquifies it. The deliquifier 460 reduces the associated liquid to 30 mass % or less, for example. The cyclopentane hydrate CH deliquified by the deliquifier 460 is guided to the decomposition section 510. Meanwhile, the associated liquid (cyclopentane CP and salt water) generated by the deliquifier 460 is returned to the associated liquid separator 450. A flow rate control valve 462 is provided between the deliquifier 460 and the associated liquid separator 450. The central control unit 710 adjusts the opening degree of the flow rate control valve 462 so as to maintain the deliquification efficiency of the deliquifier 460.

[0067] The guest supply unit 470 guides cyclopentane CP to the solid-liquid separator 412. The guest supply unit 470 includes a nitrogen cylinder 472, a tank 474, and a guest supply pipe 478. The nitrogen cylinder 472 stores nitrogen. The tank 474 stores cyclopentane CP. A safety valve 476 is provided on the pipe connecting the nitrogen cylinder 472 and the tank 474. In addition, a vent valve (not shown) is provided in the tank 474. The guest supply pipe 478 connects the tank 474 and the guest return pipe 452.

[0068] The nitrogen stored in the nitrogen cylinder 472 is led to a tank 474. The nitrogen led to the tank 474 pushes cyclopentane CP in the tank 474 to a guest supply pipe 478. Then, the cyclopentane CP is led to the solid-liquid separator 412 through the guest supply pipe 478 and the guest return pipe 452.

[0069] In addition, a flow rate control valve 480 is provided in the guest supply pipe 478. The central control unit 710 adjusts the opening degree of the flow rate control valve 480 so that the interface between cyclopentane CP and air in the solid-liquid separator 412 is maintained at a predetermined position.

[0070] [Disassembly section 510] The decomposition unit 510 heats the cyclopentane hydrate CH separated by the separation unit 410 to decompose it into cyclopentane CP and water. FIG. 6 is a diagram illustrating a schematic configuration of the decomposition unit 510. In FIG. 6, solid arrows indicate the flows of cyclopentane hydrate CH, the solid-liquid mixture, cyclopentane CP, and decomposed water. In FIG. 6, dashed arrows indicate the flow of the refrigerant. In FIG. 6, the dashed line indicates the interface between the water and cyclopentane CP, and the dashed-dotted line indicates the interface between cyclopentane CP and the gas phase (air).

[0071] As shown in FIG. 6, the decomposition section 510 includes a heat exchange tube 512 , a decomposer 520 , a recovery pump 530 , and an adsorption tower 540 .

[0072] The heat exchange tube 512 is a pipe that connects the deliquifier 460 of the separation section 410 and the decomposer 520. The heat exchange tube 512 exchanges heat between the cyclopentane hydrate CH led from the deliquifier 460 of the separation section 410 and the refrigerant led from the refrigerant cooling section 310. The heat exchange tube 512 is, for example, a double tube. The cyclopentane hydrate CH passes through the inner tube of the heat exchange tube 512. The refrigerant led from the refrigerant cooling section 310 through the refrigerant supply tube 360 ​​passes through the outer tube of the heat exchange tube 512. Due to the configuration including the heat exchange tube 512, a part of the cyclopentane hydrate CH is decomposed to generate water (decomposition water). As a result, the decomposition water functions as a lubricating liquid, and the cyclopentane hydrate CH can be easily transferred from the deliquifier 460 to the decomposer 520.

[0073] The decomposer 520 is a cylindrical container. A decomposition heat exchanger 522 is provided inside the decomposer 520. The decomposition heat exchanger 522 exchanges heat between the cyclopentane hydrate CH in the decomposer 520 and the refrigerant that is guided from the refrigerant cooling unit 310 and passes through a heat exchange tube 512. The decomposition heat exchanger 522 heats the cyclopentane hydrate CH by the heat of condensation of the refrigerant.

[0074] The refrigerant from which heat has been removed (cooled) is temporarily stored in a liquid trap 366 and then returned to the buffer tank 350 through a refrigerant return pipe 364 .

[0075] On the other hand, cyclopentane hydrate CH heated by the refrigerant is decomposed into cyclopentane CP and water (decomposition water). As described above, the specific gravity of cyclopentane CP is smaller than that of water. Therefore, in the decomposer 520, cyclopentane CP rises to form an upper layer, and the decomposition water sinks to form a lower layer.

[0076] In addition, a gas trap 524 is connected to the upper part of the cracker 520. The gas trap 524 exhausts the air guided from the cracker 520 and supplies air to the cracker 520 to maintain the pressure inside the cracker 520 at atmospheric pressure (about 0.1 MPa). The configuration including the gas trap 524 makes it possible to maintain the pressure inside the cracker 520 at atmospheric pressure regardless of the temperature difference between day and night and fluctuations in atmospheric pressure.

[0077] The decomposition water remaining in the lower layer of the decomposer 520 is guided to the purification section 610. Meanwhile, the cyclopentane CP remaining in the upper layer of the decomposer 520 is guided to the adsorption tower 540 by the recovery pump 530.

[0078] The suction side of the recovery pump 530 is connected to the residence position of the upper layer in the decomposer 520. The discharge side of the recovery pump 530 is connected to the adsorption tower 540.

[0079] The adsorption tower 540 adsorbs and removes trace amounts of impurities contained in the cyclopentane CP. The cyclopentane CP from which the impurities have been removed by the adsorption tower 540 is returned to the upper layer of the entrained liquid separator 450.

[0080] [Refining Department 610] Fig. 7 is a diagram illustrating a schematic configuration of the purification section 610. In Fig. 7, solid arrows indicate the flow of water.

[0081] As shown in FIG. 7, the purification section 610 includes a decomposition water boost pump 612 , a reverse osmosis membrane filter 620 , and a clean water purification section 622 .

[0082] The decomposition water boost pump 612 boosts the pressure of the decomposition water (water) generated in the decomposition heat exchanger 522 of the decomposition section 510 and guides it to the reverse osmosis membrane filter 620. The suction side of the decomposition water boost pump 612 is connected to the bottom of the decomposition heat exchanger 522. The discharge side of the decomposition water boost pump 612 is connected to the reverse osmosis membrane filter 620.

[0083] The reverse osmosis membrane filter 620 recovers fresh water with a salinity of 100 ppm or less from the decomposed water. The recovered fresh water (for example, about 88% of the seawater led to the mixer 210) is led to the water purification unit 622. The water purification unit 622 purifies the fresh water. The purified fresh water is used as drinking water or the like.

[0084] Meanwhile, in the reverse osmosis membrane filter 620, a part of the decomposed water from which fresh water has been recovered is returned to the solid-liquid separator 412 of the separation section 410 through the three-way valve 624. In addition, the remainder of the decomposed water from which fresh water has been recovered is discharged to the outside through the three-way valve 624.

[0085] [Startup method] Next, a method for starting up the seawater desalination apparatus 100 will be described. First, the central control unit 710 drives the seawater boost pump 114 of the pretreatment unit 110 to fill the solid-liquid separator 412 with seawater (raw material). Then, when the seawater is filled up to a position slightly below the outlet of the cyclopentane hydrate CH in the solid-liquid separator 412, the central control unit 710 stops driving the seawater boost pump 114. Then, the central control unit 710 drives the return pump 440 to circulate the seawater in the solid-liquid separator 412. In addition, the central control unit 710 drives the guest supply unit 470 to supply cyclopentane CP to the solid-liquid separator 412, and drives the circulation pump 430 to supply cyclopentane CP to the mixer 210.

[0086] Next, the central control unit 710 drives the refrigerant cooling unit 310. The central control unit 710 controls the refrigerant cooling unit 310 so that cyclopentane hydrate CH is precipitated at a constant rate in the production unit 220, that is, so that the sodium chloride concentration in the saltwater increases at a constant rate.

[0087] Then, when the temperature of the circulating salt water J (the temperature in the solid-liquid separator 412) reaches the eutectic temperature (-13.4°C) and the sodium chloride concentration of the circulating salt water J (the sodium chloride concentration of the salt water in the solid-liquid separator 412) reaches 23.8 mass %, the central control unit 710 starts the seawater boost pump 114 and switches to normal operation. The central control unit 710 also switches the refrigerant cooling unit 310, the circulation pump 430, and the return pump 440 to normal operation.

[0088] As described above, the seawater desalination apparatus 100 according to this embodiment can convert almost all of the seawater into freshwater by generating cyclopentane hydrate CH from seawater and decomposing the cyclopentane hydrate CH. Therefore, the seawater desalination apparatus 100 can improve the recovery rate of freshwater compared to a technology that employs only reverse osmosis. Therefore, the seawater desalination apparatus 100 can achieve zero emissions. In addition, the seawater desalination apparatus 100 can achieve almost zero liquid discharge (ZLD).

[0089] As described above, the seawater desalination apparatus 100 includes the mixing section 210, the production section 220, the refrigerant cooling section 310, and the separation section 410, and cools seawater and cyclopentane CP to produce cyclopentane hydrate CH and crystalline chloride in parallel. FIG. 8 is a diagram showing the relationship between the sodium chloride concentration in saltwater and the production temperature and freezing temperature of cyclopentane hydrate CH. In FIG. 8, the horizontal axis indicates the sodium chloride concentration [wt% (mass%)] in saltwater. In FIG. 8, the vertical axis indicates temperature [°C]. In FIG. 8, the solid line indicates the production temperature of cyclopentane hydrate CH, the dashed line indicates the freezing temperature, and the dashed line indicates the saturated solubility of sodium chloride. That is, the intersection of the solid line and the dashed line is the eutectic point (eutectic temperature) of cyclopentane hydrate CH and sodium chloride dihydrate, and the intersection of the dashed line and the dashed line is the eutectic point (eutectic temperature) of ice and sodium chloride dihydrate.

[0090] 8, regardless of the sodium chloride concentration, the production temperature of cyclopentane hydrate CH hydrate is higher than the freezing temperature (freezing point). Therefore, in the mixer 210, the production section 220, and the separation section 410, cyclopentane hydrate CH is produced in preference to freezing.

[0091] In addition, since the production temperature of cyclopentane hydrate (CH hydrate) is higher than the freezing temperature, the seawater desalination plant 100 can reduce the cooling load of the refrigerant by the refrigerant cooling unit 310, as compared to the case of freezing seawater.

[0092] As described above, the mixing section 210, the production section 220, and the separation section 410 are maintained at the eutectic temperature of cyclopentane hydrate CH and crystalline chlorides. Therefore, the seawater desalination apparatus 100 can produce cyclopentane hydrate CH and crystalline chlorides in parallel.

[0093] As described above, the seawater desalination apparatus 100 includes the seawater boost pump 114, the mixer 210, the generator 220, the separator 410, the decomposer 510, and the purifier 610. This enables the seawater desalination apparatus 100 to continuously produce fresh water and salt.

[0094] As described above, cyclopentane CP is insoluble in water. Therefore, the decomposer 520 can easily separate cyclopentane CP from the decomposition water. Furthermore, since cyclopentane CP and the decomposition water can be separated only by the difference in specific gravity, the seawater desalination plant 100 can make the internal pressure of the decomposer 520 below atmospheric pressure. Similarly, since cyclopentane CP, cyclopentane hydrate CH, and salt water can be separated only by the difference in specific gravity, the seawater desalination plant 100 can make the internal pressure of the solid-liquid separator 412 below atmospheric pressure.

[0095] In addition, since cyclopentane CP is insoluble in water, the seawater desalination plant 100 can prevent cyclopentane CP from being dissolved in the decomposed water. This enables the seawater desalination plant 100 to convert the decomposed water into safe drinking water.

[0096] As described above, the seawater desalination plant 100 includes the refrigerant cooling unit 310 and the decomposition heat exchanger 522. This allows the refrigerant to be cooled by cyclopentane hydrate CH. This makes it possible to reduce the energy required to remove the heat of reaction of cyclopentane hydrate CH. Furthermore, the decomposition unit 510 can decompose cyclopentane hydrate CH using the heat of the refrigerant. This allows the seawater desalination plant 100 to reduce the thermal energy required for decomposing cyclopentane hydrate CH.

[0097] As described above, the seawater desalination plant 100 includes the return pump 440. This enables the seawater desalination plant 100 to improve the recovery rate of crystallized chlorides and decomposed water.

[0098] Although the preferred embodiment of the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can think of various modifications or alterations within the scope of the claims, and it is understood that these also naturally belong to the technical scope of the present invention.

[0099] For example, in the above embodiment, the pretreatment unit 110 is provided with the reverse osmosis membrane filter 116. However, the reverse osmosis membrane filter 116 is not an essential component. If the reverse osmosis membrane filter 116 is not provided, the discharge pressure of the seawater boost pump 114 will be about 0.3 MPaG, which is lower than the case where the reverse osmosis membrane filter 116 is provided.

[0100] In the above embodiment, the generation unit 220 cools the mixed liquid by the refrigerant cooled by the decomposition heat exchanger 522 exchanging heat with cyclopentane hydrate CH. However, the decomposition of cyclopentane hydrate CH and the cooling of the mixed liquid may be performed by different heat media or devices. For example, the decomposition of cyclopentane hydrate CH may be performed by heat exchange with the combustion exhaust gas. Furthermore, the cooling of the mixed liquid may be performed by heat exchange with LNG.

[0101] In the above embodiment, the seawater desalination plant 100 includes the return pump 440. However, the return pump 440 is not an essential component.

[0102] In the above embodiment, the separation unit 410 (solid-liquid separator 412) separates the solid-liquid mixture SL into cyclopentane hydrate CH, crystalline chlorides, salt water, and cyclopentane CP based on the difference in specific gravity. However, the separation unit 410 (solid-liquid separator 412) may be configured with a centrifuge. That is, the separation unit 410 (solid-liquid separator 412) may centrifuge the solid-liquid mixture SL into cyclopentane hydrate CH, crystalline chlorides, salt water, and cyclopentane CP. This makes it possible to install the seawater desalination apparatus 100 inside a ship, etc. [Explanation of symbols]

[0103] 100 Seawater desalination equipment 210 Mixing section 220 Generation part 410 Separation section 440 Return Pump 510 Disassembly section

Claims

1. a mixing section for mixing seawater and cyclopentane to generate a mixed liquid; a generating unit that generates a solid-liquid mixture containing cyclopentane hydrate, the crystalline chloride, and salt water by cooling the mixed liquid to a eutectic temperature of cyclopentane hydrate and the crystalline chloride; A separation section that separates the solid-liquid mixture into the cyclopentane hydrate, the crystalline chloride, and the salt water; a decomposition section for heating the cyclopentane hydrate separated by the separation section to decompose it into cyclopentane and water; Equipped with The generating unit exchanges heat between the mixed liquid and a refrigerant, The decomposition section is a seawater desalination apparatus that exchanges heat between the refrigerant that has been heat exchanged in the production section and the cyclopentane hydrate.

2. The seawater desalination apparatus according to claim 1 , further comprising a return pump that returns the salt water separated by the separation section to the mixing section.

3. a mixing section for mixing seawater and cyclopentane to generate a mixed liquid; a generating unit that generates a solid-liquid mixture containing cyclopentane hydrate, the crystalline chloride, and salt water by cooling the mixed liquid to a eutectic temperature of cyclopentane hydrate and the crystalline chloride; A separation section that separates the solid-liquid mixture into the cyclopentane hydrate, the crystalline chloride, and the salt water; A return pump that returns the salt water separated by the separation section to the mixing section; A seawater desalination device comprising:

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