Supercritical water desalination apparatus and method

Abstract

The application discloses a supercritical water desalination device and method, and belongs to the technical field of desalination. The device is a fluidized bed structure as a whole, and comprises a saltwater distributor arranged in the fluidized bed and used for providing high-temperature saltwater below the critical temperature for the fluidized bed, a heat source arranged in the fluidized bed and located above the saltwater distributor and used for vaporizing the high-temperature saltwater and making the vaporized saltwater reach or be higher than the critical temperature of water, and an overflow weir which is a cylindrical structure, the bottom of the overflow weir surrounds the saltwater distributor, and the top of the overflow weir is higher than the lower end of the heat source. The overflow weir divides the lower part of the fluidized bed into a salt particle forming area and a salt particle overflow area. The device and method can realize internal heating of the desalination device, avoid early desalination of saltwater, automatically discharge salt particles after desalination, and avoid problems caused by a mechanical desalination mode.

Description

Technical Field

[0001] This invention relates to the field of water-salt separation technology, and in particular to a supercritical water desalination device and method applicable to seawater desalination, oxidation treatment of saline organic wastewater and other fields. Background Technology

[0002] Environmental pollution and water scarcity have led to increasing attention being paid to wastewater treatment and water purification technologies. Conventional wastewater treatment methods include physical filtration, biological decomposition, chemical precipitation, and incineration, but these methods are limited in their application to treating high-salt organic wastewater. To address this challenge, supercritical water (SCW) has attracted widespread attention due to its unique properties of extremely low solubility for inorganic substances and extremely high solubility for organic substances. In recent years, the industry has conducted in-depth research on the application of supercritical water, such as the development of supercritical water oxidation technology (SCWO), supercritical water desalination technology (SCWD), and supercritical water gasification (SCWG) hydrogen production technology. However, in the application of SCWO and SCWG technologies, salt deposition problems can easily lead to pipeline blockage and equipment corrosion, resulting in continuous production disruptions.

[0003] To address the salt deposition problem in supercritical water reactions, Chinese patent application CN102642910A discloses a supercritical water oxidation desalination device. The brine is heated in a furnace and then introduced into a hydrocyclone, with a salt storage buffer tank at the bottom. The bottom outlet of the buffer tank connects to a buffer oxidizer, and the lower outlet of the buffer oxidizer connects to an expansion tank, whose lower outlet connects to a salt storage pool. This device achieves efficient and continuous desalination of waste organic matter through the salt storage buffer tank of the hydrocyclone and the salt storage effect of the buffer oxidizer. However, this type of desalination device requires heating the water to above the critical temperature (374°C) before introducing it into the desalination unit, which causes premature desalination of the brine, resulting in salt precipitation at pipes and valves.

[0004] For example, Chinese patent application CN114804423A discloses an online desalination and salt discharge supercritical water oxidation reactor. The reactor has an internal oxidation space for supercritical water oxidation treatment of organic waste. The oxidation space is equipped with a mechanical desalination device, a salt conveying device at the bottom, and a radial filtration device. The mechanical desalination device removes inorganic salts from the oxidation space online to prevent sedimentation, and the bottom salt conveying device enables online salt discharge. While this type of solution allows for online salt discharge without shutdown, desalination is not automatic and requires mechanical desalination or periodic equipment shutdown for water cleaning. Since supercritical water desalination requires a pressure of at least 22.1 MPa and a temperature above 374°C, installing mechanical rotating devices inside the equipment is very difficult, and starting, stopping, and disassembling the equipment can easily damage the heating system and sealing surfaces.

[0005] Therefore, there is an urgent need for a supercritical water desalination device and method that can both prevent premature desalination of brine, which would cause salt precipitation in pipes and valves, and avoid the various problems caused by mechanical desalination.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a supercritical water desalination device and method that can achieve internal heating of the desalination device to avoid premature desalination of brine, and can also automatically discharge the desalinated salt particles to avoid the problems caused by mechanical desalination.

[0008] Another objective of this invention is to provide a supercritical water desalination device and method that allows salt to preferentially deposit in a designated area, thereby protecting the surface of a heat source.

[0009] To achieve the above objectives, according to a first aspect of the present invention, a supercritical water desalination device is provided. The device is an integral fluidized bed structure, comprising: a brine distributor disposed inside the fluidized bed and providing the fluidized bed with high-temperature brine below the critical temperature; a heat source disposed inside the fluidized bed and above the brine distributor, for vaporizing the high-temperature brine and causing the vaporized brine to reach or exceed the critical temperature of water; and an overflow weir, which is a cylindrical structure, with its bottom surrounding the brine distributor and its top higher than the lower end of the heat source; the overflow weir divides the lower part of the fluidized bed into a salt particle formation zone and a salt particle overflow zone.

[0010] Furthermore, in the above technical solution, the upper surface of the brine distributor can be covered with a salt-forming agent layer. The salt-forming agent can be nickel foam or coral stone as the salt-forming carrier, preferably nickel foam.

[0011] Furthermore, in the above technical solution, the heat source can be in the form of a slender column and extend along the axial direction of the fluidized bed, and the outer surface of the heat source is preferably a smooth surface.

[0012] Furthermore, in the above technical solution, the heat source can be an electric heating rod or a tube heat source, and the heating medium in the tube can be high-temperature flue gas or steam, high-temperature molten salt or other high-temperature fluid, with a medium temperature higher than 600°C.

[0013] Furthermore, in the above technical solution, when a tube heat source is used, the inlet and outlet ends of the heating medium can both be located at the top of the fluidized bed, forming a reversible flow of the heating medium inside the tube.

[0014] Furthermore, in the above technical solution, a brine feed pipe is provided at the bottom of the overflow weir. The brine feed pipe is connected to the brine distributor, and the temperature of the saline hot water in the brine feed pipe can be designed to be below 360°C.

[0015] Furthermore, in the above technical solution, a cyclone separator can be provided in the upper part of the fluidized bed to remove the fine salt particles carried by the high-temperature water vapor after desalination.

[0016] Furthermore, in the above technical solution, the salt particle formation zone is the internal area of ​​the cylindrical structure of the overflow weir; the salt particle overflow zone is the annular space between the outer wall of the cylindrical structure of the overflow weir and the inner wall of the fluidized bed.

[0017] According to a second aspect of the present invention, the present invention provides a supercritical water desalination method using the apparatus of any of the foregoing, comprising the following steps: A. Vaporizing and heating saline hot water below the critical temperature in a fluidized bed, wherein the saline vapor is heated to above the critical temperature by a heat source in the fluidized bed; B. The saline vapor above the critical temperature gradually forms salt particles on the surface of the salt-forming agent, the salt particles are in a fluidized state in the salt particle forming zone, and gradually deposit into a salt particle layer; C. When the salt particle layer gradually rises above the upper edge of the overflow weir, the salt particles automatically overflow to the salt particle overflow zone and fall until they reach the bottom of the fluidized bed and are discharged.

[0018] Furthermore, in the above technical solution, the method of the present invention may also include: D, the desalted water vapor undergoes gas-solid separation in the upper part of the fluidized bed to remove the fine salt particles carried in the gas flow, and the water vapor after gas-solid separation leaves the fluidized bed to become fresh water.

[0019] Furthermore, in the above technical solution, the temperature below the critical temperature in step A can specifically be below 360℃; the temperature above the critical temperature can specifically be above 390℃.

[0020] Furthermore, in the above technical solution, the following steps may be included before step A: nitrogen gas is introduced into the fluidized bed to make the internal pressure of the fluidized bed reach the pressure required for supercritical water desalination.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The desalination device of the present invention uses a fluidized bed for desalination. After the salt particles are formed, they are in a fluidized state. Compared with the static salt particles in the prior art, this not only creates better conditions for automatic desalination, but also makes the temperature of the salt particle formation zone more uniform and the desalination efficiency higher.

[0023] 2) The present invention places the heat source inside the desalination device, which avoids the need to heat the brine to a critical temperature (374°C) or higher before it is introduced into the desalination device, as is required in the prior art, which causes the brine to be desalinated in advance, resulting in salt precipitation and blockage at the pipes and valves;

[0024] 3) By using fluidized salt particles and an overflow weir, this invention can achieve overflow and automatic salt discharge after sufficient salt particles are deposited. The device can operate in a stable state of material balance without the need for mechanical desalination facilities with moving parts, and there is no need for periodic shutdowns for cleaning. It is suitable for large-scale industrial applications.

[0025] 4) Through the inventors’ experimental research, it was found that both coral stone and nickel foam are good salt-forming carriers. Nickel foam is lighter and more durable. The amount of inorganic salt loaded per unit mass of material (15wt%) is much higher than that of coral stone (3wt%). Therefore, nickel foam is preferred as a salt-forming agent. By using the salt-forming agent, salt can be formed on the surface of the salt-forming agent first, making the salt-forming area more fixed and effectively avoiding a large amount of salt formation on the outer surface of the heat source.

[0026] 5) In order to minimize the deposition of salt on the surface of the heat source, the heat source is designed as a slender column extending along the axial direction of the fluidized bed. The smooth surface of the outer surface of the heat source can be used to effectively prevent salt particles from adhering and growing on the surface of the heat source.

[0027] 6) The present invention can effectively remove fine salt particles carried by high-temperature water vapor after desalination by providing a cyclone separator in the upper part of the fluidized bed.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other objects, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the internal structure of the supercritical water desalination device of the present invention.

[0030] Figure 2 This is a schematic diagram of the supercritical water desalination method of the present invention.

[0031] Explanation of key figure labels:

[0032] 1-Brine distributor, 2-Tube heat source, 3-Overflow weir, 4-Cyclone separator, 41-Fine salt particle outlet, 42-Water vapor outlet pipe;

[0033] 100-Fluidized bed, 101-Fluidized bed wall, 102-Brine feed pipe, 103-Heating medium inlet pipe, 104-Heating medium outlet pipe, 105-Salt discharge pipe. Detailed Implementation

[0034] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0035] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0036] In this document, for ease of description, spatial relative terms such as “below,” “under,” “down,” “above,” “above,” “upper,” etc., are used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that spatial relative terms are intended to encompass different orientations of an object in use or operation, in addition to those depicted in the figures. For example, if an object in the figure is flipped, an element described as “below” or “under” another element or feature would be oriented “above” that element or feature. Thus, the exemplary term “below” can encompass both the downward and upward orientations. An object may also have other orientations (rotated 90 degrees or other orientations), and the spatial relative terms used herein should be interpreted accordingly.

[0037] In this document, the terms "first," "second," etc., are used to distinguish two different elements or parts, and are not used to define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0038] This invention utilizes the characteristic of water's slight solubility for inorganic salts under supercritical conditions to obtain fresh water with a salt content below 0.1 g / L, far below the 1 g / L standard for tap water. Applications include seawater desalination and oxidation treatment of saline organic wastewater. The supercritical water desalination device of this invention features internal heating and automatic salt particle discharge, meeting the requirements of large flow rates, long operating times, and harsh conditions in industrial wastewater treatment.

[0039] Example 1

[0040] like Figure 1As shown, this embodiment provides a supercritical water desalination device, which is a fluidized bed 100 structure, including at least a brine distributor 1, a heat source 2, and an overflow weir 3. The brine distributor 1 is located inside the fluidized bed 100 and provides the fluidized bed with high-temperature brine below the critical temperature. Further, the brine distributor can be a flat nozzle type or a cap type. The heat source 2 is located inside the fluidized bed 100 and above the brine distributor 1, used to vaporize the high-temperature brine and make the vaporized brine above the critical temperature of water. The overflow weir 3 is a cylindrical structure, with its bottom surrounding the brine distributor 1 and its top higher than the lower end of the heat source 2; the overflow weir 3 divides the lower part of the fluidized bed into a salt particle formation zone and a salt particle overflow zone. Specifically, the salt particle formation zone is the internal area of ​​the cylindrical structure of the overflow weir 3; the salt particle overflow zone is the annular space between the outer wall of the cylindrical structure of the overflow weir 3 and the inner wall of the fluidized bed.

[0041] The supercritical water desalination device in this embodiment adopts a fluidized bed structure. After the salt particles are formed, they are in a fluidized state. Compared with the static salt particles in the prior art, this not only creates better conditions for automatic desalination, but also makes the temperature of the salt particle formation zone more uniform and the desalination efficiency higher. In this embodiment, the heat source is set inside the desalination device, avoiding the need to heat the brine to above the critical temperature (374°C) before it is introduced into the desalination device, which causes premature desalination and salt precipitation blockage in the pipes and valves. In this embodiment, through the fluidized salt particles and the overflow weir, sufficient salt particles can be deposited to achieve overflow and automatic salt discharge. The device can operate in a stable material balance state without the need for mechanical desalination facilities with moving parts, and there is no need for periodic shutdown for cleaning. It is suitable for large-scale industrial applications.

[0042] Furthermore, the upper surface of the brine distributor can be covered with a salt-forming agent layer. Preferably, but not limitingly, the salt-forming agent uses nickel foam or coral stone as the salt-forming carrier, with nickel foam being preferred. The inventors have discovered that due to the high surface temperature of the heat source 2 (the heating medium of this invention is designed to operate at temperatures above 600°C), salt deposition is highly likely to occur on the heat source surface. To address this issue, this embodiment employs a method of covering the surface of the brine distributor 1 with a layer of salt-forming agent, allowing salt to first deposit on the surface of the salt-forming agent and then gradually form salt particles. Experimental studies have shown that both coral stone and nickel foam are good salt-forming carriers, but nickel foam is lighter and more durable, and the amount of inorganic salt loaded per unit mass of material (15 wt%) is significantly higher than that of coral stone (3 wt%). Therefore, nickel foam is preferred as the salt-forming agent. To minimize salt deposition on the surface of the heat source 2, the heat source 2 is designed as a slender column extending along the fluidized bed axis. The outer surface of the heat source 2 is preferably smooth, without pits or grooves, making it difficult for salt particles to adhere and grow on the heat source surface.

[0043] Further as Figure 1 As shown, the heat source can be an electric heating rod or a tube heat source 2. The heating medium in the tube is high-temperature flue gas or steam, high-temperature molten salt, or other high-temperature fluid, with a medium temperature higher than 600°C. In this embodiment, a tube heat source is preferred. The inlet pipe 103 and outlet pipe 104 of the heating medium in the tube heat source 2 are both located at the top of the fluidized bed 100, forming a reversible flow of the heating medium within the pipe. The heating medium continuously flows in and out, ensuring the required heating temperature within the fluidized bed. This invention introduces a high-temperature heat source into the desalination device, providing the heat required for the heating, vaporization, and further heating of the saline wastewater. It is assumed that the average temperature of the desalination device is 390°C, operating at 22.9 MPa. Since the technical concept of this invention addresses the problem of "salt buildup in valves and pipelines caused by premature desalination," it is necessary to control the inlet temperature of the saline hot water below the critical temperature (i.e., below 374°C). If the inlet temperature of the saline hot water is 350°C, since the water is in a liquid state at this temperature, its enthalpy is 1632 kJ / kg. The water in the device is all superheated steam with an enthalpy of 2586 kJ / kg and a constant pressure heat capacity of 13.1 kJ / kg·°C. The temperature of the water vapor obtained after the liquid water at the inlet vaporizes is 277.2°C, which is 73°C lower than the inlet temperature. Therefore, it is necessary to utilize the tube heat source 2 inside the desalination device to raise the temperature to achieve the required heat. Further... Figure 1 As shown, the bottom of the overflow weir 3 is provided with a brine inlet pipe 102, which is connected to the brine distributor 1. In this embodiment, the temperature of the salt-containing hot water in the brine inlet pipe 102 is controlled below 360°C, thereby effectively avoiding premature desalination of the brine and the problem of salt precipitation and blockage at the pipes and valves.

[0044] Further as Figure 1 As shown, a cyclone separator 4 is provided at the upper part of the fluidized bed 100 to remove fine salt particles carried by the high-temperature steam after desalination. Specifically, the cyclone separator 4 has a fine salt particle outlet 41 at the bottom and a steam outlet pipe 42 at the top. After desalination, the high-temperature steam enters the cyclone separator 4 from the upper part of the fluidized bed, removes the fine salt particles carried by the airflow, and then leaves the desalination device through the steam outlet pipe 42.

[0045] Example 2

[0046] like Figure 1 , 2 As shown, this embodiment provides a supercritical water desalination method, which uses the apparatus in Embodiment 1 and includes the following steps:

[0047] Step S101: Nitrogen gas is introduced into the fluidized bed to bring the internal pressure of the fluidized bed up to the pressure required for supercritical water desalination. Specifically, the required pressure inside the fluidized bed is 23 MPa.

[0048] Step S102 involves vaporizing and heating saline hot water at a temperature below the critical temperature within a fluidized bed. The saline vapor is then heated to a temperature above the critical temperature by a heat source within the fluidized bed. Specifically, preferably but not limitingly, the temperature below the critical temperature in this step is below 360°C; the temperature above the critical temperature is above 390°C. For example, when high-temperature molten salt is used as the heating medium for the tube heat source, molten salt at 600°C is introduced into the desalination device (i.e., the fluidized bed) through the heating medium inlet pipe. The molten salt flows into the tubes of the heat source, reaches the bottom, and then flows back out through the heating medium outlet pipe. After the temperature and pressure within the fluidized bed stabilize, saline hot water at 350°C is introduced through the brine feed pipe. The brine is heated by the heat source after passing through a distributor, causing it to vaporize and change from a liquid to a gaseous state. The steam is further heated by the heat source, raising its temperature to 390°C, thus entering a supercritical state.

[0049] In step S103, brine vapor at a temperature above the critical temperature gradually forms salt particles on the surface of the salt-forming agent. These salt particles are in a fluidized state within the salt particle formation zone and gradually deposit as a salt layer. Specifically, this invention utilizes an overflow weir with a cylindrical structure within the fluidized bed, creating a salt particle formation zone in a fluidized state inside the cylindrical structure. Furthermore, before the desalination device operates, some salt-forming agent is pre-placed on the upper surface of the brine distributor, allowing salt to preferentially crystallize and deposit on the salt-forming agent, thus protecting the heat source surface. Within the salt particle formation zone, as desalination continues, the number of salt particles in the fluidized bed continuously increases, and the bed layer continuously rises.

[0050] In step S104, when the salt layer gradually rises to a height above the upper edge of the cylindrical structure of the overflow weir, the salt particles automatically overflow to the salt overflow area and fall until they reach the bottom of the fluidized bed and are discharged. Specifically, a salt discharge pipe 105 is provided at the bottom of the fluidized bed 100. The salt discharge pipe 105 is connected to the salt overflow area, and the salt particles falling from the salt overflow area can be directly discharged from the salt discharge pipe 105, thereby realizing automatic salt discharge (without the intervention of mechanical salt discharge facilities).

[0051] In step S105, the desalinated water vapor undergoes gas-solid separation in the upper part of the fluidized bed to remove the fine salt particles carried in the gas flow. The water vapor after gas-solid separation leaves the fluidized bed and becomes fresh water.

[0052] This method embodiment 2 achieves the same technical effect as the device embodiment 1. That is, by introducing a high-temperature heat source into the desalination device, the heat required for the saline wastewater to heat up, vaporize, and continue to heat up after vaporization can be provided, effectively preventing premature desalination of brine and causing salt precipitation blockage at pipes and valves; through the setting of salt particle formation zone and overflow zone, after sufficient salt particles are deposited, overflow and automatic salt discharge can be achieved, eliminating the need for mechanical desalination facilities and enabling the fluidized bed to maintain a stable operating state of material balance, which is suitable for large-scale industrial applications; by adopting a fluidized operation mode, the salt particles are in a fluidized state during the formation process. Compared with the static salt particles in the prior art, this is not only conducive to the stable operation of the fluidized bed by automatic salt discharge, but also more conducive to the uniform temperature of the salt particle formation zone.

[0053] The foregoing description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. Any simple modifications, equivalent changes, and alterations made to the foregoing exemplary embodiments should fall within the scope of protection of the present invention.

Claims

1. A supercritical water desalination device, characterized in that, The device is an overall fluidized bed structure. Nitrogen gas is introduced into the fluidized bed to raise the internal pressure to the level required for supercritical water desalination. The device includes: A brine distributor is disposed inside the fluidized bed and provides the fluidized bed with high-temperature brine below the critical temperature; the upper surface of the brine distributor is covered with a salt-forming agent layer, wherein the salt-forming agent is nickel foam. A heat source, disposed inside the fluidized bed and above the brine distributor, is used to vaporize the high-temperature brine and bring the vaporized brine to or above the critical temperature of water. The heat source is a slender column extending axially along the fluidized bed, and its outer surface is smooth. The heat source is either an electric heating rod or a tube heat source. When a tube heat source is used, both the inlet and outlet ends of the heating medium are located at the top of the fluidized bed, forming a reversible flow of the heating medium within the tubes. An overflow weir, which is a cylindrical structure, surrounds the brine distributor at its bottom and extends above the lower end of the heat source at its top. The overflow weir divides the lower part of the fluidized bed into a salt particle formation zone and a salt particle overflow zone. The salt particle formation zone is the internal area of ​​the cylindrical structure of the overflow weir. The salt particle overflow zone is the annular space between the outer wall of the cylindrical structure of the overflow weir and the inner wall of the fluidized bed. A cyclone separator, located in the upper part of the fluidized bed, is used to remove fine salt particles carried by the high-temperature water vapor after desalination.

2. The supercritical water desalination device according to claim 1, characterized in that, The heating medium in the tube is high-temperature flue gas or steam, high-temperature molten salt or other high-temperature fluid, and the medium temperature is higher than 600°C.

3. The supercritical water desalination device according to claim 1, characterized in that, The bottom of the overflow weir is equipped with a brine inlet pipe, which is connected to the brine distributor. The temperature of the salt-containing hot water in the brine inlet pipe is below 360°C.

4. A supercritical water desalination method, characterized in that, Using the apparatus according to any one of claims 1 to 3, the steps include: A. In a fluidized bed, saline hot water below the critical temperature is vaporized and heated, and the saline vapor is heated to above the critical temperature by a heat source in the fluidized bed. B. Salt vapor containing salt water at a temperature above the critical temperature gradually forms salt particles on the surface of the salt-forming agent. The salt particles are in a fluidized state within the salt particle formation zone and gradually deposit as a salt particle layer. C. When the salt layer gradually rises above the upper edge of the overflow weir, the salt particles automatically overflow to the salt overflow area and fall until they reach the bottom of the fluidized bed and are discharged. Before step A, the following steps are also included: nitrogen gas is introduced into the fluidized bed to make the internal pressure of the fluidized bed reach the pressure required for supercritical water desalination.

5. The supercritical water desalination method according to claim 4, characterized in that, The method further includes: D. After desalination, the water vapor undergoes gas-solid separation in the upper part of the fluidized bed to remove the fine salt particles carried in the gas flow. The water vapor after gas-solid separation leaves the fluidized bed and becomes fresh water.

6. The supercritical water desalination method according to claim 4, characterized in that, In step A, "below the critical temperature" specifically means below 360°C; "above the critical temperature" specifically means above 390°C.

Images