Distillation apparatus

Abstract

A distillation apparatus is provided that allows a heat exchanger made of highly heat-conductive metal to be used as a heat exchanger even when raw water contains a volatile a cidic gas. The raw water is sent from a feed-water tank (1) to a heat exchanger (4) through a pump (2) and a pipe (3) and heated in the heat exchanger (4), and is then sent to a membrane module (10) to be subjected to a membrane distillation process. Steam generated on a secondary side of the membrane module (10) is suctioned by an aspirator (50). The aspirator (50) is supplied with an absorbing liquid inside an absorbing liquid tank (90) through a pump (51) and a cooling heat exchanger (70). The heat exchanger (70) is made of metal, such as titanium.

Description

Distillation apparatus

[0001] The present invention relates to a distillation apparatus, and more particularly to a distillation apparatus configured to heat a liquid to be distilled using a heat exchanger, and particularly to a distillation apparatus suitable for use in separating volatile acid gases from an aqueous solution of the volatile acid gases.

[0002] An example of a distillation apparatus configured to heat the liquid to be distilled using a heat exchanger is shown in FIG.

[0003] Raw water (liquid to be distilled) introduced into water supply tank 1 via a supply line (not shown) is sent from water supply tank 1 to heat exchanger 4 via pump 2 and piping 3, heated in heat exchanger 4, and then sent to membrane module 10 via piping 5.

[0004] In this conventional example, the membrane module 10 is a hollow fiber membrane module. In the membrane module 10, a large number of hollow fibers 11 are aligned to form a hollow fiber bundle, which is arranged vertically. The upper and lower ends of the hollow fiber bundle are bound with potting materials 12 and 13.

[0005] The hollow fiber bundle is disposed in a casing 14 of the membrane module 10, with an inlet chamber 15 formed above the upper potting material 12 and an outlet chamber 16 formed below the lower potting material 13. The interior of each hollow fiber 11 communicates with the inlet chamber 15 and the outlet chamber 16, respectively.

[0006] The liquid to be treated from the pipe 5 flows into each hollow fiber 11 (primary side) from the inlet chamber 15, passes through the hollow fibers 11, and flows into the outlet chamber 16, and from the outlet chamber 16 returns to the water supply tank 1 via the pipe 18.

[0007] The secondary side 17 is located outside the hollow fibers 11 within the casing 14 and between the potting materials 12 and 13 .

[0008] The secondary side 17 is connected to a pressure reducing device 9b via a piping (steam piping) 6, a cooled side flow path of the heat exchanger (cooler) 7, a piping 8, a condensate tank 9, and a piping 9a, and the pressure on the secondary side 17 is reduced by the pressure reducing device 9b.

[0009] While the liquid to be treated flows through the hollow fibers 17 (primary side), water in the liquid to be treated permeates the hollow fibers 11, turns into steam, is sucked out from the secondary side 17 into the pipe 6, and is cooled in the heat exchanger 7 to produce condensed water. The condensed water is stored in the condensed water tank 9. The condensed water stored in the condensed water tank 9 is taken out from the bottom of the condensed water tank 9 via an extraction line (not shown). The top of the condensed water tank 9 is connected to a pressure reducing device 9b via a pipe 9a.

[0010] High-temperature water from the heat pump system 19 is passed through the heat source fluid flow path 4 a of the heat exchanger 4 , and low-temperature water from the heat pump system 19 is passed through the heat source fluid flow path 7 a of the heat exchanger 7 .

[0011] The heat pump 20 of the heat pump system 19 has a well-known configuration, and is configured to adiabatically compress a heat medium such as a refrigerant substitute from an evaporator 21 in a compressor 22 to a high temperature and introduce it into a condenser 23, and then introduce the heat medium from the condenser 23 into the evaporator 21 via an expansion valve 24, where it is adiabatically expanded to lower the temperature.

[0012] Water in the hot water tank 30 is passed through the heat transfer tubes 23a provided in the condenser 23 via a pump 31 and a pipe 32, and is heated by heat exchange with the high-temperature heat medium. The heated water is returned to the hot water tank 30 via a pipe 33.

[0013] The high-temperature water in the hot water tank 30 is passed through the heat source fluid flow path 4a of the heat exchanger 4 via a pump 34 and a pipe 35, and heats the raw water by exchanging heat with it. The water, whose temperature has been lowered by the heat exchange with the raw water, is returned to the hot water tank 30 via a pipe 36.

[0014] Water in a cold water tank 40 is passed through a heat transfer tube 21a provided in the evaporator 21 via a pump 41 and a pipe 42, and is cooled by heat exchange with the low-temperature heat medium. The cooled water, which has become low-temperature water, is returned to the cold water tank 40 via a pipe 43.

[0015] The low-temperature water in the tank 40 is passed through the heat source fluid flow path 7a of the heat exchanger 7 via a pump 44 and a pipe 45, and exchanges heat with the steam to cool it. The water, whose temperature has increased by the heat exchange with the steam, is returned to the cold water tank 40 via a pipe 46.

[0016] Japanese Patent Laid-Open No. 3-52627 Japanese Patent Laid-Open No. 2019-158173

[0017] When the water to be distilled (raw water) is an aqueous solution of a volatile acidic gas such as hydrochloric acid or hydrofluoric acid and the volatile acidic gas is recovered by passing it through a membrane module, the heat exchanger 7 comes into contact with a highly concentrated corrosive acid. For this reason, heat exchangers made of synthetic resins (e.g., fluororesins) with excellent corrosion resistance are used as the heat exchanger 7. However, because synthetic resins have low thermal conductivity, it has been necessary to use large heat exchangers with a large heat exchange area as the heat exchanger 7. Furthermore, heat exchangers made of synthetic resins are expensive.

[0018] An object of the present invention is to provide a distillation apparatus that can use a metal heat exchanger with high thermal conductivity as a heat exchanger even when the raw water contains volatile acidic gases.

[0019] The present invention has the following gist.

[0020] [1] A distillation apparatus comprising a still into which a liquid to be distilled is introduced, an aspirator or ejector for sucking vapor generated in the still, a tank into which the outflow water of the aspirator or ejector flows, a path for delivering the water in the tank to the working fluid inlet of the aspirator or ejector, and a heat exchanger for cooling provided in the path.

[0021] [2] The distillation apparatus of [1], further comprising: a water quality measuring means for measuring the quality of the water in the tank or the water circulating between the tank and the aspirator or ejector; and a discharge means for discharging a portion of the water when the water quality measured by the water quality measuring means exceeds a specified value.

[0022] [3] The distillation apparatus according to [2], wherein the water is an aqueous solution of an acid, and the water quality is electrical conductivity or resistivity.

[0023] [4] The distillation apparatus according to any one of [1] to [3], wherein the heat exchanger is made of a highly corrosion-resistant metal.

[0024] [5] The distillation apparatus according to [4], wherein the highly corrosion-resistant metal is titanium, a titanium alloy, or Hastelloy.

[0025] [6] The distillation apparatus according to any one of [1] to [5], wherein the distiller is a membrane distiller.

[0026] [7] The distillation apparatus according to any one of [1] to [6], further comprising a means for replenishing the tank with water.

[0027] In the distillation apparatus of the present invention, steam generated in the distiller is sucked in by an aspirator or ejector. Because the steam dissolves in the water effluent from the aspirator or ejector, even if the steam contains acidic gases, the acid concentration in the effluent is low. Therefore, even if a metal heat exchanger is used in the path that transports the effluent from the tank to the aspirator or ejector as a working fluid, it is protected from corrosion over the long term. This metal heat exchanger has good heat exchange characteristics and is significantly smaller than a synthetic resin heat exchanger.

[0028] In one aspect of the present invention, when the acid concentration of water as a working fluid becomes higher than a predetermined value, a portion of the water is discharged and new water is added.

[0029] 1 is a diagram showing the configuration of a distillation apparatus according to an embodiment of the present invention;

[0030] Hereinafter, an embodiment will be described with reference to FIG.

[0031] The raw water (liquid to be distilled) introduced into the water supply tank 1 via the supply line 1F is sent from the water supply tank 1 to the heat exchanger 4 via the pump 2 and the piping 3, where it is heated and then sent to the membrane module 10 via the piping 5.

[0032] The membrane module 10 is a hollow fiber membrane module. In the membrane module 10, a large number of hollow fibers 11 are aligned to form a hollow fiber bundle, which is arranged vertically. The upper and lower ends of the hollow fiber bundle are bound with potting materials 12 and 13.

[0033] The hollow fiber bundle is disposed in a casing 14 of the membrane module 10, with an inlet chamber 15 formed above the upper potting material 12 and an outlet chamber 16 formed below the lower potting material 13. The interior of each hollow fiber 11 communicates with the inlet chamber 15 and the outlet chamber 16, respectively.

[0034] The liquid to be treated from the pipe 5 flows into each hollow fiber 11 (primary side) from the inlet chamber 15, passes through the hollow fibers 11, and flows into the outlet chamber 16, and from the outlet chamber 16 returns to the water supply tank 1 via the pipe 18.

[0035] The secondary side 17 is located outside the hollow fibers 11 within the casing 14 and between the potting materials 12 and 13 .

[0036] The secondary side 17 is connected to a suction part 50 a of an aspirator 50 via a pipe (steam pipe) 6 , and the secondary side 17 is decompressed by the aspirator 50 .

[0037] While the liquid to be treated flows through the hollow fibers 17 (primary side), the water in the liquid to be treated permeates the hollow fibers 11, turns into steam, and is sucked out from the secondary side 17 through the piping 6 to the aspirator 50, producing an absorbing liquid that has absorbed the steam.

[0038] The absorbing liquid in the absorbing liquid tank 90 is introduced into the working fluid inlet 50b of the aspirator 50 via the pump 51, the piping 52, the cooled fluid flow path 71 of the highly corrosion-resistant metal heat exchanger 70, and the piping 54. The outflow water from the outlet 50c of the aspirator 50 returns to the absorbing liquid tank 90 via the piping 55.

[0039] A pipe 57 branches off from the pipe 52, and a valve 58 is provided on the pipe 57. An electric conductivity meter 59 is provided in the absorption liquid tank 90.

[0040] High-temperature water from the hot water tank 30 of the heat pump system 19 is circulated through the heat source fluid flow path 4a of the heat exchanger 4 via pipes 35 and 36. Low-temperature water from the cold water tank 40 of the heat pump system 19 is circulated through the heat source fluid flow path 72 of the heat exchanger 70 via pipes 45 and 46.

[0041] The heat pump 20 of the heat pump system 19 is configured to adiabatically compress a heat medium such as a refrigerant substitute from an evaporator 21 in a compressor 22 to a high temperature and introduce it into a condenser 23, and then introduce the heat medium from the condenser 23 into the evaporator 21 via an expansion valve 24, where it is adiabatically expanded to lower the temperature.

[0042] Water in the hot water tank 30 is passed through the heat transfer tubes 23a provided in the condenser 23 via a pump 31 and a pipe 32, and is heated by heat exchange with the high-temperature heat medium. The heated water is returned to the hot water tank 30 via a pipe 33.

[0043] The high-temperature water in the hot water tank 30 is passed through the heat source fluid flow path 4a of the heat exchanger 4 via a pump 34 and a pipe 35, and heats the raw water by exchanging heat with it. The water, whose temperature has been lowered by the heat exchange with the raw water, is returned to the hot water tank 30 via a pipe 36.

[0044] Water in a cold water tank 40 is passed through a heat transfer tube 21a provided in the evaporator 21 via a pump 41 and a pipe 42, and is cooled by heat exchange with the low-temperature heat medium. The cooled water, which has become low-temperature water, is returned to the cold water tank 40 via a pipe 43.

[0045] The low-temperature water in this tank 40 is passed through a heat source fluid flow path 72 of a heat exchanger 70 via a pump 44 and a pipe 45, and exchanges heat with the absorbing liquid flowing through a cooled fluid flow path 71 to cool it. The water, whose temperature has increased by heat exchange with the absorbing liquid, is returned to the cold water tank 40 via a pipe 46.

[0046] Make-up water can be introduced into the absorption liquid tank 90 via a make-up water line 56. Prior to starting operation of the distillation apparatus, a predetermined amount of water is supplied to the absorption liquid tank 90 from the make-up water line 56 and stored therein.

[0047] As described above, the end of the pipe 6 for sucking the secondary side 17 of the membrane module 10 is connected to the suction part 50a of the aspirator 50. The absorption liquid in the absorption liquid tank 90 is circulated and passed to the aspirator 50 via the pump 51, the pipe 52, the metal heat exchanger 70, and the pipes 54 and 55.

[0048] When the water in the water supply tank 1 is an aqueous solution of a volatile acidic gas such as hydrochloric acid or hydrofluoric acid, the pump 51 is operated to pass the water through the aspirator 50, generating negative pressure, which causes the acidic gas to be sucked from the secondary side 17 of the membrane module 10 into the pipe 6. This acidic gas dissolves in the water flowing through the aspirator 50 and flows into the absorbent tank 90 as an acidic aqueous solution. Therefore, as operation continues, the acid concentration of the aqueous solution in the absorbent tank 90 gradually increases.

[0049] When the electrical conductivity detected by the electrical conductivity meter 59 provided in the absorption liquid tank 90 becomes higher than a predetermined value, the valve 58 is opened, a portion of the absorption liquid is discharged from the system through the piping 57, and makeup water is supplied to the absorption liquid tank 90 from the makeup water line 56 instead.

[0050] In this embodiment, as described above, the acidic aqueous solution in the absorbent tank 90 flows through the cooled fluid flow path 71 of the heat exchanger 70, and therefore the heat exchanger 70 is made of a highly corrosion-resistant metal. Furthermore, when the electrical conductivity of the liquid in the absorbent tank 90 becomes higher than a predetermined value, the valve 58 is opened to discharge the highly concentrated acidic aqueous solution from the pipe 57 to the outside of the system, and instead makeup water is introduced into the absorbent tank 90 from the makeup water line 56. This prevents the heat exchanger 70 from corroding over a long period of time, allowing stable operation.

[0051] Suitable highly corrosion-resistant metals for forming the heat exchanger 70 include titanium, titanium alloys, and hastelloy, among other highly corrosion-resistant metals or alloys.

[0052] The thermal conductivities of titanium, Hastelloy C, and polytetrafluoroethylene are as follows: Titanium: 21.9 w / (m·k) Hastelloy C: 11.1 w / (m·k) Polytetrafluoroethylene: 0.24 w / (m·k)

[0053] As described above, the thermal conductivity of titanium and Hastelloy is significantly higher than that of polytetrafluoroethylene, so that it is possible to use a small heat exchanger 70 with a small heat exchange area.

[0054] Although an aspirator is used in FIG. 1, an ejector may also be used.

[0055] The above embodiment is merely an example of the present invention, and the present invention may be embodied in other forms. For example, although an electrical conductivity meter is used in the above embodiment, various sensors capable of detecting the acid concentration in water, such as a resistivity meter or a pH meter, may be used.

[0056] In the above embodiment, the electrical conductivity meter is provided in the absorption liquid tank 90, but it may be provided in other locations such as the pipes 52 and 54.

[0057] In the above embodiment, a membrane distiller having a membrane module 10 and a water supply tank 1 is installed, but other distillers may also be used.

[0058] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2020-157300, filed on September 18, 2020, and is incorporated by reference in its entirety.

[0059] 1 Water supply tank 4, 7, 70 Heat exchanger 9 Condensate tank 19 Heat pump system 20 Heat pump 21 Evaporator 22 Compressor 23 Condenser 24 Expansion valve 30 Hot water tank 40 Cold water tank 50 Aspirator 59 Electrical conductivity meter 90 Absorption liquid tank

Claims

1. A distillation apparatus comprising: a still into which a liquid to be distilled is introduced; an aspirator or ejector for sucking in vapor generated in the still; a tank into which the outflow water of the aspirator or ejector flows; a path for sending the water in the tank to the working fluid inlet of the aspirator or ejector; and a heat exchanger for cooling provided in the path.

2. The distillation apparatus of claim 1, further comprising a water quality measuring means for measuring the quality of the water in the tank or the water circulating between the tank and the aspirator or ejector, and a discharge means for discharging a portion of the water when the water quality measured by the water quality measuring means exceeds a specified value.

3. The distillation apparatus of claim 2, wherein the water is an aqueous solution of an acid, and the water quality is determined by electrical conductivity or resistivity.

4. The distillation apparatus according to any one of claims 1 to 3, wherein the heat exchanger is made of a highly corrosion-resistant metal.

5. The distillation apparatus of claim 4, wherein said highly corrosion-resistant metal is titanium, a titanium alloy, or Hastelloy.

6. The distillation apparatus according to any one of claims 1 to 5, wherein the distiller is a membrane distiller.

7. The distillation apparatus according to any one of claims 1 to 6, further comprising means for replenishing said tank with water.