Effect body evaporator and low-temperature multi-effect distillation seawater desalination system and method

Abstract

The invention relates to the technical field of seawater desalination, and particularly provides an effect body evaporator, a low-temperature multi-effect distillation seawater desalination system and a low-temperature multi-effect distillation seawater desalination method. When the steam extraction circulating unit extracts steam, the opening degree of a flexible communicating hole in the double-flow-channel heat exchange pipe is gradually increased, so that most of steam entering the heat exchange pipe flows to an intermediate-effect evaporator through a main flow channel; and under the condition that the flow of the steam received by the first-effect evaporator is reduced, the flexible communication hole is gradually reduced, so that most of the steam entering the heat exchange pipe is subjected to heat exchange through the auxiliary flow channel under the action of the steam extraction pressure difference, and therefore, efficient utilization and heat energy recovery of the steam in the low-temperature multi-effect distillation seawater desalination system are realized, and the energy consumption is reduced. And meanwhile, scaling of the outer wall of the heat exchange tube of the first-effect evaporator due to the fact that the heat exchange tube bears the relatively unstable steam change condition can be effectively prevented, and scaling and cleaning difficulty of the first-effect heat exchange tube bundle are greatly reduced.

Description

Technical Field

[0001] The present application relates to the technical field of seawater desalination, and in particular to an effect evaporator, a low-temperature multi-effect distillation seawater desalination system and a method. Background Art

[0002] The low-temperature multi-effect seawater desalination device is a series of effect evaporators containing spray tube bundles and heat exchange tube bundles connected in series. The heat exchange process mainly distributes the feed water and seawater evenly on the outer surface of the heat exchange tube bundle inside the effect evaporator through the spray tube bundle. The seawater on the outer surface of the tube bundle absorbs the latent heat of steam and vaporizes. The steam on the inner wall of the tube bundle condenses into fresh water when it is cooled. After multiple evaporation and condensation in the device, desalinated water many times the amount of steam is obtained.

[0003] In the existing low-temperature multi-effect distillation seawater desalination system, the power steam source is conventionally from the fifth and sixth extraction steam of the steam turbine of the thermal power plant. After being cooled and reduced in pressure, it enters the first-effect evaporator in the low-temperature multi-effect distillation seawater desalination system for heat exchange with seawater. This causes the first-effect evaporator to withstand the highest heat exchange temperature in the low-temperature multi-effect distillation seawater desalination system. In view of the high heat exchange temperature, the relatively unstable steam flow change condition faced, and the uneven steam quality caused by steam from different sources, the heat exchange tube bundle of the first-effect evaporator is more prone to mud accumulation and scaling on the outer wall of the heat exchange tube bundle as the operation cycle is extended than other effects. This causes part of the seawater to absorb the steam latent heat released by the condensation of steam inside the heat exchange tube bundle and vaporize to enter the next effect evaporator to become secondary steam. The amount of steam gradually decreases, and even the seawater cannot absorb the steam latent heat released by the condensation of steam inside the heat exchange tube bundle of the first-effect evaporator and vaporizes, which ultimately leads to a gradual decrease in water production efficiency. Summary of the invention

[0004] In response to the above problems, the present application provides a first-effect evaporator, a low-temperature multi-effect distillation seawater desalination system and a method, which adjusts the steam flow operation based on the heat exchange tube bundle of the first-effect evaporator to achieve efficient steam utilization and heat energy recovery. At the same time, it can effectively prevent the outer wall scaling of the heat exchange tube of the first-effect evaporator due to the relatively unstable steam quality changes, thereby greatly reducing the scaling and cleaning difficulty of the first-effect heat exchange tube bundle.

[0005] To achieve the purpose of this application, this application provides the following technical solutions: In a first aspect, the present application provides an effect evaporator, which is applied to a low-temperature multi-effect distillation seawater desalination system, wherein the effect evaporator comprises: an evaporator shell, an inlet tube sheet and a final end plate arranged at both ends of the evaporator shell, and a plurality of heat exchange tubes arranged on a heat exchange tube support frame inside the evaporator shell; The inlet end of each heat exchange tube is fixed on the inlet tube sheet, and the outlet end of the heat exchange tube is fixed on the outlet tube sheet, and the outlet tube sheet is located at the front end of the final end plate; wherein, a conductive air membrane is provided on the final end plate, and densely arranged reserved channels are opened on the conductive air membrane, and the reserved channels are in a staggered cross-shaped seam structure, and the reserved channels are unidirectionally conducted under the action of the extraction steam pressure difference, so as to open the reserved channels in the isolation flow state, and close the reserved channels in the normal effect evaporator operation state; Each of the heat exchange tubes comprises: an outer tube and an inner tube arranged in the inner cavity of the outer tube in the axial direction; the heat exchange tube is a double-channel heat exchange tube having a main channel and an auxiliary channel, wherein a main channel for conveying steam is formed inside the inner tube, and an auxiliary channel for steam is formed between the inner wall of the outer tube and the outer wall of the inner tube; a spiral fin extending axially along the outer wall of the inner tube is arranged in the auxiliary channel, and the spiral fin is fixedly connected to the outer tube and the inner tube; A plurality of flexible communication holes are provided on the inner tube wall near the outlet end, the flexible communication holes are evenly arranged in the middle and upper middle parts of the side wall of the inner tube, and the flexible communication holes are connected with the main flow channel; The main channel is provided with a steam flow regulating unit near the outlet end; the steam flow regulating unit comprises: a steam flow regulating paddle, and an elastic opening regulating mechanism arranged in the flexible connecting hole; the top surface of the steam flow regulating paddle is perpendicular to the steam flow direction in the main channel; the steam flow regulating paddle is connected to the flexible connecting hole through a plurality of traction ropes; one end of each traction rope is fixedly connected to the steam flow regulating paddle, and the other end is connected to the opening regulating mechanism; Among them, when the steam flow in the main channel increases, the steam flow impact drives the steam flow regulating paddle to move in the direction of steam flow, and the displacement of the steam flow regulating paddle drives the traction rope to move. The traction rope drives the opening of the flexible connecting hole to increase based on the opening adjustment mechanism. At the same time, the steam opens the reserved channel of the conductive air membrane, so that the steam is unidirectionally transmitted to the next effect evaporator; when the steam flow in the main channel decreases, the reduced steam flow drives the steam flow regulating paddle to move back in the opposite direction of the steam flow direction, and the displacement of the steam flow regulating paddle drives the reduction of the opening of the flexible connecting hole, and the reserved channel of the conductive air membrane is closed, so that the steam completes the return heat exchange in the current effect evaporator.

[0006] In a possible implementation, a concave ring pipe section is integrally provided at one end of the inner tube axially close to the steam outlet; the concave ring pipe section is coaxially arranged with the inner tube; the concave ring pipe section includes a first flared portion, a horizontal portion and a second flared portion; the first flared portion and the second flared portion are respectively located at two ends of the horizontal portion and are symmetrically arranged; the first flared portion is located on one side of the horizontal portion close to the outlet end of the inner tube; the maximum outer diameters of the first flared portion and the second flared portion are the same as the outer diameter of the inner tube, and the outer diameter of the horizontal portion is smaller than the outer diameter of the inner tube; a sliding ring is provided between the concave ring pipe section and the outer wall, and the sliding ring has an inner tapered hole; the sliding ring can slide between the first flared portion and the second flared portion along the axial direction of the concave ring pipe section; the sliding ring is used to unidirectionally block the counterflow steam of the auxiliary flow channel when the inner inclined surface of the inner tapered hole contacts the outer inclined surface of the second flared portion.

[0007] In a possible implementation, an in-tube nozzle is also provided in the main channel, and the in-tube nozzle is located near the input side of the steam flow regulating unit; the in-tube nozzle is a tapered mouth that gradually shrinks from the inner diameter of the inner tube to a preset diameter along the steam flow direction, and the in-tube nozzle is connected to the main channel fluid located at the front end of the in-tube nozzle.

[0008] In a second aspect, the present application provides a low-temperature multi-effect distillation seawater desalination system, comprising: a steam inlet unit, a steam processing unit, a steam extraction circulation unit, a seawater distribution unit, and a temperature reduction unit; The steam inlet unit is connected to an external steam source through a steam inlet control valve to provide steam from an external heat source; A steam processing unit, wherein the output end of the steam inlet unit is connected to the input end of the steam processing unit, and the steam processing unit comprises a first-effect evaporator, a plurality of intermediate-effect evaporators and a final-effect evaporator connected in series in sequence, wherein the first-effect evaporator is the effect body evaporator as described above, wherein, when the steam flow rate received by the first-effect evaporator increases, the opening of the flexible connecting hole is gradually increased when the steam ejector of the steam extraction circulation unit extracts steam, so that most of the steam entering the heat exchange tube flows to the intermediate-effect evaporator through the main channel; when the steam flow rate received by the first-effect evaporator decreases, the flexible connecting hole is gradually closed, so that the steam entering the heat exchange tube reduces the amount of steam absorbed from the auxiliary pipeline under the action of the steam extraction circulation unit; An extraction circulation unit is fixedly connected to the steam processing unit, the extraction circulation unit comprises an extraction pipeline, a mixing steam pipeline and a first bypass pipeline, the input end of the extraction pipeline is independently connected to each effect evaporator, and a recovery control valve is installed between each effect evaporator and the extraction pipeline, and the output end of the extraction pipeline is connected to the first bypass pipeline; the first bypass pipeline, the extraction pipeline and the mixing steam pipeline form an extraction operation passage of the steam processing unit; the first bypass pipeline is sequentially installed with a first steam control valve, a first temperature and pressure sensor, and the steam ejector along the steam inlet direction, the steam ejector is connected to a first extraction branch, the first extraction control valve is installed on the first extraction branch, and the first temperature and pressure sensor is used to feed back the steam temperature and steam pressure parameters at the first steam control valve to the control unit, so that the control unit adjusts the opening of the first extraction control valve based on the steam temperature and steam pressure parameters at the first steam control valve; A seawater distribution unit, used for spraying and recovering seawater on the steam treatment unit; A cooling unit, one end of which is connected to the outlet of the condensate collecting tank of the first-effect evaporator, and the other end of which is connected to the middle of the steam mixing pipeline.

[0009] In a possible implementation, when the low-temperature multi-effect distillation seawater desalination system is in a turbine powered steam operation mode, the back pressure control valve on the back pressure pipeline is closed, and the steam inlet control valve, the first steam control valve, the first steam extraction control valve, and the recovery control valve are opened; the control unit controls the first steam ejector to extract secondary steam from the target effect evaporator when the steam treatment unit performs steam heat exchange, and then circulates and mixes the secondary steam with the power steam from the steam inlet control valve to enter the first effect evaporator after cooling and reducing the pressure; the target effect evaporator is the determined effect evaporator in the steam treatment unit for the first steam ejector to extract the secondary steam.

[0010] In a possible implementation, a balance sensor is installed on each of the effect evaporators, and the balance sensor is used to monitor the internal environmental data of the corresponding effect evaporator; when the first balance sensor determines that the heat exchange efficiency of the first effect evaporator is lower than the heat exchange threshold, and the second balance sensor determines that the heat exchange efficiency of the next second effect evaporator relative to the first effect evaporator is normal, the recovery control valve on the first effect evaporator is closed, and the recovery control valve on the second effect evaporator is opened, so that the conductive air membrane of the heat exchange tube bundle of the first effect evaporator is opened, and the secondary steam generated by the previous effect evaporator relative to the first effect evaporator is auxiliary extracted based on the steam extraction pipeline, so that it passes through the first effect evaporator and is forced to enter the second effect evaporator.

[0011] In a possible implementation, the balance sensor includes at least a temperature difference sensor, a pressure difference sensor and a pressure balance chamber; the temperature difference sensor is used to monitor the temperature data of the secondary steam generated by the first-effect evaporator and the evaporator of the previous effect of the first-effect evaporator; the pressure difference sensor is used to monitor the pressure data of the secondary steam generated by the first-effect evaporator and the evaporator of the previous effect of the first-effect evaporator; the pressure balance chamber is used to correct the pressure of the secondary steam generated by the first-effect evaporator in real time based on the atmospheric pressure.

[0012] In a possible implementation, the system also includes a waste heat recovery unit, which includes an indirect heat exchange device and a flash evaporation device; the indirect heat exchange device is used to indirectly exchange waste hot water into hot water at 85-95°C, and the flash evaporation device is connected to the first-effect evaporator, and is used to flash the hot water at 85-95°C into motive steam, and allow the motive steam to enter the first-effect evaporator through the steam inlet unit; when the low-temperature multi-effect distillation seawater desalination system is in a waste heat recovery operation mode, the steam inlet control valve and the back pressure control valve are opened, and the first steam control valve is closed; the motive steam enters the first-effect evaporator through the steam inlet unit, including: the motive steam enters the back pressure pipeline through the steam inlet control valve after being cooled and reduced in pressure, thereby directly entering the first-effect evaporator to operate in a waste heat recovery mode.

[0013] In a possible embodiment, the steam output end of the waste heat recovery unit can be directly connected to the steam mixing pipeline for mixing with the external heat source steam and the secondary steam extracted by the first steam ejector. One end of the waste heat recovery unit is connected to the first effect evaporator for receiving condensate from the first effect evaporator.

[0014] In a possible implementation, the steam extraction circulation unit also includes a second bypass line, which is connected in parallel with the first bypass line, and the output end of the steam extraction line is also connected to the second bypass line; the second bypass line and the first bypass line are backup for each other; the second bypass line is sequentially installed with a second steam control valve, a second temperature and pressure sensor, and a second steam ejector along the steam inlet direction, the second steam ejector is connected to a second steam extraction branch, and a second steam extraction control valve is installed on the second steam extraction branch, and the second temperature and pressure sensor is used to feed back the steam temperature and steam pressure parameters at the second steam control valve to the control unit, so that the control unit adjusts the opening of the second steam extraction control valve based on the steam temperature and steam pressure parameters at the second steam control valve.

[0015] In a second aspect, the present application provides a low-temperature multi-effect distillation seawater desalination method, which is applied to the above low-temperature multi-effect distillation seawater desalination system, and the method comprises: The external heat source steam enters the first-effect evaporator of the steam treatment unit through the steam inlet unit; When the steam flow rate received in the heat exchange tube of the first-effect evaporator increases, the opening of the flexible connecting hole is gradually increased so that when the steam ejector of the steam extraction circulation unit extracts steam, most of the steam entering the heat exchange tube flows through the main flow channel of each heat exchange tube to the next intermediate-effect evaporator; When the steam flow rate received in the heat exchange tube of the first-effect evaporator decreases, the flexible connecting hole is gradually reduced to reduce the steam flow rate entering the main channel when the steam ejector of the steam extraction circulation unit extracts steam; The main flow channel and the auxiliary flow channel are coaxially arranged, and spiral fins rotating at intervals are arranged in the auxiliary flow channel.

[0016] In a possible implementation, when the steam ejector of the steam extraction circulation unit extracts steam, most of the steam entering the heat exchange tube flows through the main flow channel of each heat exchange tube to the next intermediate effect evaporator, including: when the steam pressure in the first effect evaporator is greater than a preset pressure threshold, opening the reserved channel on the conductive air membrane; for each heat exchange tube, the steam passing through the main flow channel is directly unidirectionally conducted to the next intermediate effect evaporator.

[0017] The low-temperature multi-effect distillation seawater desalination system provided by the present application targets different steam flow rates and their changing conditions received by the first-effect evaporator. When the double-channel heat exchange tube is working, the steam from the inlet of the first-effect evaporator enters the double-channel heat exchange tube, and the steam flow condition is determined based on the displacement of the steam flow regulating paddle of the steam flow regulating unit in the double-channel heat exchange tube bundle, and the steam transportation is adjusted under different steam flow conditions, thereby realizing the redistribution of steam; under high flow conditions, steam is sucked in from the inner channel, and the remaining small amount of steam enters the auxiliary channel provided with spiral fins. The steam in the auxiliary channel is easily condensed and collected, thereby reducing the steam temperature of the heat exchange tube bundle, realizing efficient utilization of steam and heat energy recovery, and at the same time, by controlling the steam circulation flow distribution ratio, the temperature of the heat exchange tube bundle can be delayed to be below the scaling temperature, so as to effectively prevent scaling of the outer wall of the heat exchange tube of the first-effect evaporator due to relatively unstable steam changes, thereby greatly reducing scaling and cleaning difficulty of the first-effect heat exchange tube bundle. At the same time, the low-temperature multi-effect distillation seawater desalination system provided in the present application reduces the opening of the inner flow channel through the flexible connecting hole of the steam flow regulating unit under low flow conditions, so that the steam mainly circulates through the auxiliary flow channel for heat exchange, thereby improving the heat exchange efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide a further understanding of the present application and form a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation to the present application. Figure 1 A schematic diagram of the operation of a thermal compression-low temperature multi-effect distillation seawater desalination system provided in an embodiment of the present application; Figure 2 A schematic diagram of the architecture of a low-temperature multi-effect distillation seawater desalination system provided in an embodiment of the present application; Figure 3a A schematic diagram of the end surface inside the effect evaporator provided in an embodiment of the present application; Figure 3b Provided for the embodiments of this application Figure 3a A schematic diagram of the structure of the conductive air membrane with a local enlargement at A; Figure 4a A schematic diagram of the planar structure of a double-channel heat exchange tube provided in an embodiment of the present application; Figure 4b A schematic diagram of the three-dimensional structure of a double-channel heat exchange tube provided in an embodiment of the present application; Figure 4c A schematic diagram of the three-dimensional structure of a steam flow regulating unit provided in an embodiment of the present application in a double-channel heat exchange tube; Figure 4d A schematic diagram of the three-dimensional structure of a steam flow regulating unit provided in an embodiment of the present application; Figure 5a A schematic diagram of an implementation structure of a double-channel heat exchange tube provided in an embodiment of the present application; Figure 5b A schematic diagram of an implementation structure of a double-channel heat exchange tube provided in an embodiment of the present application; Figure 6 A schematic cross-sectional view of the auxiliary flow channel of the dual-flow channel heat exchange tube provided in an embodiment of the present application; Figure 7 A schematic diagram of an implementation structure of a double-channel heat exchange tube provided in an embodiment of the present application; Figure 8 An optional plan view of a low-temperature multi-effect distillation seawater desalination system provided in an embodiment of the present application; Fig. 9 An optional plan view of a low-temperature multi-effect distillation seawater desalination system provided in an embodiment of the present application; Fig.10 A schematic flow chart of the low-temperature multi-effect distillation seawater desalination method provided in an embodiment of the present application.

[0019] Reference numerals: 1. First-effect evaporator; 2. Steam inlet control valve 1; 3. Steam control valve 1; 4. Steam control valve 2; 5. Back pressure control valve; 6. Thermal expansion joint; 7. Steam ejector 1; 8. Steam ejector 2; 9. Bypass control valve 1; 10. Bypass control valve 2; 11. Vacuum breaker valve; 12. Steam inlet control valve 2; 13. Steam extraction control valve 1; 14. Steam extraction control valve 2; 15. Recovery control valve; 16. Balance sensor; 17. Temperature and pressure sensor 1; 18. Temperature and pressure sensor 2; 19. Temperature and pressure sensor 3; 20. Temperature and pressure sensor 4; 21. Bypass sensor; 22. Indirect heat exchange device; 23. Flash evaporation device; 24. Water inlet control valve ; 25, back pressure pipeline; 26, extraction pipeline; 27, bypass pipeline one; 28, bypass pipeline two; 29, steam mixing pipeline; 201, steam inlet unit; 202, steam treatment unit; 203, extraction circulation unit; 204, water distribution unit; 205, cooling unit; 301, outer tube; 302, inner tube; 303, flexible connecting hole; 304, nozzle in tube; 401, concave ring tube section; 402, spiral fin; 403, outlet end; 601, first straight tube wall; 602, first inclined tube wall; 603, second straight tube wall; 604, second inclined tube wall; 605, third straight tube wall. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of this application, unless otherwise specified, "plurality" means two or more.

[0022] The low-temperature multi-effect distillation (MED) seawater desalination system is a thermal seawater desalination production process with many commercial cases. It connects a series of effect evaporators containing spray tube bundles and heat exchange tube bundles in series. The power steam circulates inside the heat exchange tube bundle. At the same time, the feed water and seawater are sprayed from the spray tube bundle to the outer wall of the heat exchange tube bundle and evenly distributed from top to bottom. Part of the seawater absorbs the steam latent heat released by the condensation of steam inside the heat exchange tube bundle and vaporizes into secondary steam to enter the next effect evaporator, making the evaporation temperature of the next effect lower than that of the previous effect, thereby obtaining a desalinated water process with multiple times the amount of steam. This evaporation and condensation process is repeated along a series of effect evaporators until the steam of the last effect is introduced into the condenser and completely condensed. Figure 1 This is a schematic diagram of the operation of the Thermo Vapor Compression Multi Effect Distillation (TVC-MED) system. TVC-MED is a highly efficient seawater desalination technology developed based on traditional MED. Figure 1 As shown in the figure, its working principle is to use a hot compressor to compress the secondary steam generated by the evaporator on the basis of traditional MED, and then recycle it as heating steam; wherein, the feed water and seawater enter the evaporator after pretreatment, flow in the form of a thin film in each effect evaporator, absorb the latent heat of steam and evaporate, and the generated secondary steam is mixed and compressed with the high-pressure steam through a vacuum ejector, so that the secondary steam is recycled between the first effect and each intermediate effect, reducing the demand for high-quality steam from the outside.

[0023] In the existing systems and devices involving MED seawater desalination, the power steam source is conventionally from the fifth and sixth extraction steam of the steam turbine of the thermal power plant. After being cooled and reduced in pressure, it enters the first-effect evaporator in the low-temperature multi-effect distillation seawater desalination system to exchange heat with seawater. This causes the first-effect evaporator to withstand the highest heat exchange temperature in the low-temperature multi-effect distillation seawater desalination system. Due to the high heat exchange temperature of the first-effect evaporator, the heat exchange tube bundle therein is more prone to mud accumulation and scaling on the outer wall of the heat exchange tube bundle as the operation cycle is extended than other effects. This causes part of the seawater to absorb the steam latent heat released by the condensation of steam inside the heat exchange tube bundle and vaporize to enter the next effect evaporator to become secondary steam. The amount of steam gradually decreases, and even the seawater cannot absorb the steam latent heat released by the condensation of steam inside the heat exchange tube bundle of the first-effect evaporator and vaporizes, which ultimately leads to a gradual decrease in water production efficiency.

[0024] At the same time, the existing TVC-MED seawater desalination system has a single source of power steam, low waste heat recovery efficiency, unstable steam extraction flow rate, and low adjustable accuracy and comprehensive utilization efficiency.

[0025] In order to solve the above technical problems, the present invention proposes the following technical solutions and corresponding embodiments. Figures 1 to 10 The illustrated embodiments describe the technical solution of the present invention.

[0026] Example 1 Figure 2 The schematic diagram of the architecture of the low-temperature multi-effect distillation seawater desalination system according to an embodiment of the present application is shown, the system includes a steam inlet unit 201, a steam processing unit 202, a steam extraction circulation unit 203, a water distribution unit 204 and a temperature reduction unit 205; The steam inlet unit 201 is connected to an external steam source and is used to provide external heat source steam for the low-temperature multi-effect distillation seawater desalination system; The steam treatment unit 202, whose input end is connected to the output end of the steam inlet unit 201, is used to realize multiple heat exchange evaporation of the feed water and seawater; the steam treatment unit 202 includes a plurality of effect evaporators connected in series in sequence, and the plurality of effect evaporators are a first effect evaporator, a plurality of intermediate effect evaporators and a final effect evaporator. The feed water and seawater flow in the form of a thin film on the surface of the heat exchange tubes in each effect evaporator in sequence, and evaporate by absorbing the latent heat of the steam in the heat exchange tubes to form fresh water; in the steam treatment unit 202, the inlet ends of the plurality of heat exchange tubes in each effect evaporator are fixed to the inlet tube sheet at one end of the evaporator shell, and the outlet ends of the plurality of heat exchange tubes are fixed to the outlet tube sheet at the other end of the evaporator shell, and the outlet tube sheet is provided with a conductive gas film (refer to Figure 3a , Figure 3b As shown), the conductive air membrane is provided with densely staggered reserved channels, the reserved channels are in a staggered M-shaped seam structure, the reserved channels are densely arranged, and the reserved channels are unidirectionally conductive under the action of the extraction pressure difference, so that the reserved channels are opened in the isolation flow state to play the role of forward conductive steam output, and the reserved channels are closed in the normal multi-effect operation state to play the role of steam return heat exchange baffle (when the effect evaporator is in normal operation, the internal pressure of the effect evaporator is stable, and the steam emitted by seawater evaporation cannot break through the reserved channels on the conductive air membrane, and the conductive air membrane plays the role of steam return heat exchange baffle); wherein, the opening of the reserved channels forms a convex structure on one side of the conductive air membrane, and the convex structure makes the steam break through the reserved channels directional (it is easy to break through in the forward convex direction and difficult to break through in the reverse convex direction), so that the reserved channels can have unidirectional conductive ability under the action of the extraction pressure difference.

[0027] Among them, the heat exchange tubes in the first-effect evaporator are all double-channel heat exchange tubes, such as Figure 4a , Figure 4bAs shown, the double-channel heat exchange tube includes: an outer tube 301, an inner tube 302 located in the inner cavity of the outer tube 301, a main steam channel formed inside the inner tube 302, and an auxiliary channel formed between the inner wall of the outer tube 301 and the outer wall of the inner tube 302; the inner tube is integrally provided with a concave ring tube section 401 at one end close to the steam outlet in the axial direction, and the concave ring tube section 401 is coaxially arranged with the inner tube 302; the auxiliary channel is provided with spiral fins 402 extending axially along the outer wall of the inner tube 302, and the fins extend at intervals, and the outer tube 301 is supported on the periphery of the inner tube 302 through the spiral fins 402; a fin 403 is opened on the inner tube wall close to the outlet end There are several flexible connecting holes 303, which are evenly arranged on the side wall of the inner tube 302, and the flexible connecting holes 303 are connected to the main channel; as a feasible implementation, an in-tube nozzle 304 is arranged in the main channel near the front section (i.e., the input side) of the steam flow regulating unit; the in-tube nozzle 304 is a tapered mouth that gradually shrinks to a preset diameter along the steam flow direction, and the in-tube nozzle 304 is connected to the main channel fluid located at the front end of the in-tube nozzle 304, so as to further converge through the in-tube nozzle 304 to increase the steam flow rate at the tapered mouth, and at the same time, the steam forms a vacuum suction chamber in the main channel section where the tapered outlet is located, so that the opening of the flexible connecting hole 303 is easy to adjust. Exemplarily, the tapered outlet is circular, and the preset diameter is 1 / 4-1 / 2 of the inner tube diameter. Figure 4a The black arrow in the figure indicates the steam flow direction.

[0028] The main channel is provided with a steam flow regulating unit near the steam outlet end 403, such as Figure 4c , 4d As shown, the steam flow regulating unit includes: a steam flow regulating paddle, an opening regulating mechanism arranged in the flexible connecting hole 303, and a traction rope for realizing traction connection between the steam flow regulating paddle and the flexible connecting hole; wherein, an elastic opening regulating mechanism is arranged in each flexible connecting hole 303, and the opening regulating mechanism includes a plurality of closing fans, and the plurality of closing fans are overlapped and arranged to make the flexible connecting hole form a closed state in a static state; a cross-shaped or M-shaped intersection is formed at the junction of the plurality of closing fans, and the intersection is used to adjust the opening of the flexible connecting hole; at the same time, a plurality of the flexible connecting holes are evenly arranged in the middle and upper parts and the middle and lower parts of the inner tube side wall in the same longitudinal direction perpendicular to the axial direction of the inner tube (at a fixed distance from the outlet end of the heat exchange tube), excluding the bottom side wall (reference Figure 4c The traction rope connection point in the middle is fixed in direction; it should be noted that Figure 4aThe flexible connecting hole below the side wall of the inner tube is used to illustrate the connection relationship of the traction rope on the plane, and the heat exchange tube turns to a fixed direction during the use of the evaporator); the flexible connecting hole 303 is connected to the main channel, and the connection between the flexible connecting hole 303 and the inner tube 302 adopts a double sealing structure to ensure that no steam leakage occurs during the adjustment process; the steam flow regulating paddle is located in the inner cavity of the inner tube 302, and its top surface is perpendicular to the steam flow direction in the main channel. The steam flow regulating paddle is connected to the flexible connecting hole 303 through a plurality of traction ropes, and the opening adjustment mechanism is used to elastically control the opening of the intersection with the traction rope; as a feasible implementation method, in each flexible connecting hole 303, an opening traction line is connected to each closing fan at the intersection, and multiple opening traction lines converge and are connected to one end of the traction rope, and the other end of the traction rope is fixedly connected to the steam flow regulating paddle at the corresponding position of the steam flow regulating paddle (it should be noted that the number of closing fans and intersections is not specifically limited here).In the embodiment of the present application, when the steam flow in the main channel increases or decreases, the opening adjustment mechanism is correspondingly driven by the traction rope to change its displacement when the steam flow regulating paddle changes its displacement, thereby adjusting the opening of the flexible connecting hole 303, so that the steam extraction circulation unit 203 can adjust the steam flow between the main channel and the auxiliary channel of each heat exchange tube when extracting steam; wherein, when the steam flow in the main channel increases, the internal pressure of the first-effect evaporator increases, and the steam flow forms a higher flow rate at the conical outlet through the nozzle 304 in the tube; at the same time, when the steam When the steam is ejected at high speed through the nozzle 304 in the tube, the increase in fluid velocity will cause the pressure to decrease, and a low-pressure vacuum suction area will be formed near the conical mouth (near the flexible connecting hole 303); thereby, the vacuum suction area is connected to the flexible connecting hole 303, and the amount of steam sucked from the auxiliary flow channel is increased based on the pressure difference on both sides of the flexible connecting hole 303; at the same time, the displacement of the steam flow regulating paddle increases due to the high-speed fluid at the conical outlet, which further drives the increase in the opening of the flexible connecting hole 303, and the reserved channel for the conductive air film (and the extraction circulation unit 2) is opened based on the pressure inside the first-effect evaporator. 03 extracts the steam inside the next-effect evaporator, thereby generating a negative pressure difference inside the first-effect evaporator), so that the steam in the first-effect is unidirectionally transmitted to the next-effect evaporator quickly; when the steam flow in the main channel decreases, the flow rate of the steam flow through the nozzle in the tube at the conical outlet is reduced, and the pressure difference on both sides of the flexible connecting hole 303 is reduced, gradually reducing the suction amount of the main channel from the auxiliary channel, and at the same time, the displacement of the steam flow regulating paddle is reduced, reducing / resetting the opening of the flexible connecting hole, so that the steam flowing through the auxiliary channel can increase the residence time in the auxiliary channel, thereby improving the heat exchange area and heat exchange efficiency. rate, and at the same time, due to the stable pressure inside the first-effect evaporator, the steam cannot break through the reserved channel of the staggered M-shaped seam structure on the conductive air membrane. At this time, the reserved channel of the conductive air membrane is closed, so that the steam can return to exchange heat in the current effect evaporator; wherein, the traction rope is made of high-strength, corrosion-resistant, and high-temperature resistant steel wire or synthetic fiber material to ensure long-term stable operation under harsh working conditions; the flexible connecting hole 303 is made of high-temperature resistant and wear-resistant flexible material, such as high-temperature silicone rubber or Teflon coating material; and the flexible connecting hole 303 adopts a double sealing structure to ensure that no steam leakage occurs during the adjustment process;. The steam extraction circulation unit 203 is fixedly connected to each effect evaporator of the steam treatment unit 202. The steam extraction circulation unit 203 includes a steam extraction pipeline, a steam mixing pipeline and a first bypass pipeline. The input end of the steam extraction pipeline is independently connected to each effect evaporator, and a recovery control valve is installed between each effect evaporator and the steam extraction pipeline. The output end of the steam extraction pipeline is connected to the first bypass pipeline; the output end of the first bypass pipeline is connected to the steam mixing pipeline, and the output end of the steam mixing pipeline is connected to the heat exchange tube bundle of the first effect evaporator; the steam inlet unit 201 and the first bypass pipeline, the steam extraction pipeline and the steam mixing pipeline form a first effect evaporator. The steam extraction operation passage of the steam processing unit 202; wherein, the first bypass line is sequentially installed with a first steam control valve, a first temperature and pressure sensor, and a first steam ejector (corresponding to the steam ejector / steam ejector 1 in the embodiment of the present application) along the steam inlet direction, the first steam ejector is connected to a first steam extraction branch, the first steam extraction branch is installed with a first steam extraction control valve, the first temperature and pressure sensor is used to feed back the steam temperature and steam pressure parameters at the first steam control valve to the control unit, so that the control unit adjusts the opening of the first steam extraction control valve based on the steam temperature and steam pressure parameters at the first steam control valve; A seawater distribution unit 204, used for spraying seawater on the steam processing unit 202; A cooling unit 205, one end of which is connected to the outlet of the condensate collecting tank of the first-effect evaporator, and the other end of which is connected to the middle of the mixed steam pipeline.

[0029] In the embodiment of the present application, the area of ​​the steam flow regulating paddle is 1 / 2-2 / 3 of the area of ​​the inner tube ring. When the steam flow received by the first-effect evaporator increases, when the steam ejector of the steam extraction circulation unit 203 extracts steam, the steam flow in the main channel increases, causing the steam flow regulating paddle to displace along the steam flow direction, and the inclination angle of the lower part of the steam flow regulating paddle increases. This displacement drives the opening adjustment mechanism in the center of the flexible connecting hole to produce a corresponding displacement through the traction rope, thereby increasing the opening of the flexible connecting hole 303, so that most of the steam entering the heat exchange tube flows to the intermediate effect evaporator through the main channel; when the steam flow received by the first-effect evaporator changes from a large flow to a small flow, the displacement of the steam flow regulating paddle decreases (restores), and at the same time drives the displacement of the opening adjustment mechanism to be smaller (restores), so that the opening of the flexible connecting hole 303 decreases accordingly, thereby reducing the amount of steam absorbed from the auxiliary channel when the steam ejector of the steam extraction circulation unit 203 extracts steam, so that the steam can be fully exchanged through the auxiliary channel. Here, when the steam flow rate received by the first-effect evaporator changes slightly, the slight displacement of the steam flow regulating paddle will not change the opening of the flexible connecting hole 303. It should be noted that, considering the application cost, the present application only uses a double-channel heat exchange tube in the first-effect evaporator on site in this embodiment, and there is no restriction on this in actual implementation, and it can be extended to the intermediate-effect evaporator to adapt to a wider range of working conditions.

[0030] As a feasible implementation method, refer to Figure 5a As shown, the number of flexible connecting holes is 3, which are located at the left end, right end and upper end of the tangential inner tube respectively; Figure 5b There are 4 flexible connecting holes, which are located at the left end, right end, upper left end and upper right end symmetrical to the upper left end of the tangential inner tube. As a feasible implementation, a cross or cross-shaped flexible line is arranged inside the flexible connecting hole 303, and the traction rope is fixed in the middle of each line segment after the intersection. When the opening of the flexible connecting hole is increased, the traction rope drives the flexible line to produce a corresponding displacement, so that the flexible connecting hole is convex in the forward direction, increasing the flow outlet of the steam. In order to reduce the resistance effect of steam regulation in the pipeline, the thickness of the steam flow regulating paddle and the flexible line is controlled.

[0031] In the embodiment of the present application, the inner diameter of the main steam flow channel is d, the inner diameter of the heat exchange tube bundle is D, and the spacing between each two adjacent fins must meet 0.5d~1.5d; the fin height is 0~(Dd) / 2: the ratio of the main flow channel and the auxiliary flow channel in diameter is distributed in 1~4. For example, the closer the spacing between two adjacent fins is to 0.5d, the better the heat exchange effect of the auxiliary flow channel; when the steam flow rate faced by the evaporator is mostly large, the spacing between two adjacent fins is close to 1.5d, which is conducive to extracting steam to the main flow channel, so that it can be mixed and enter the next effect evaporator. The specific parameters can be designed / adjusted according to the actual situation.

[0032] In the examples of this application, refer to Figure 7 As shown, the height of the spiral fins (i.e., spiral fins 402) in the auxiliary flow channel on the outer wall of the inner tube is the largest in the middle and upper part of the auxiliary flow channel (completely connected to the inner wall of the outer tube), and the height is the smallest in the middle and lower part of the auxiliary flow channel (gradually separated from the inner wall of the outer tube as it goes down in the vertical direction), thereby enhancing the overall stability of the heat exchange tube structure. At the same time, considering the pressure changes and gravity effects during the steam flow process, the accumulation of condensed water at the bottom of the fins is avoided, thereby protecting the application stress state of the heat exchange tube. The condensed water that has undergone heat exchange is affected by the gravity distribution and deposited at the bottom of the auxiliary flow channel. It is collected and processed by a specific collection structure to avoid the deposition of condensed water inside the heat exchange tube. In an embodiment of the present application, the heat exchange tube can be spliced ​​online in a split assembly form, and the overall penetration is achieved by rotating the internal and external threads. A rubber O-ring is set on the thread sealing surface to prevent seawater from penetrating into the interior of the heat exchange tube.

[0033] In the embodiment of the present application, the inner tube 302 is integrally provided with a concave ring section 401 at the outlet end axially close to the steam outlet, and the concave ring section 401 is coaxially arranged with the inner tube 302, and the concave ring section 401 includes a first flared portion, a horizontal portion, and a second flared portion; the first flared portion and the second flared portion are respectively located at the two ends of the horizontal portion and are symmetrically arranged; the first flared portion is located on one side of the horizontal portion close to the outlet end of the inner tube; the maximum outer diameters of the first flared portion and the second flared portion are the same as the outer diameter of the inner tube, and the outer diameter of the horizontal portion is smaller than the outer diameter of the inner tube; the wall thickness of the concave ring section is the same as the wall thickness of the inner tube. Exemplarily, refer to Figure 6As shown, a pipe section protruding toward the axis of the inner pipe is coaxially arranged near the axial end position of the inner pipe, forming a first straight pipe wall 601, a first inclined pipe wall 602, a second straight pipe wall 603, a second inclined pipe wall 604 and a third straight pipe wall 605 on the inner pipe, and the diameter of the pipe section is smaller than the diameter of the inner pipe; a one-way slider unit is arranged on the second inclined pipe wall 604, and the one-way slider unit is arranged on the second inclined pipe wall 604 in a wedge-shaped space formed by the outer pipe wall corresponding to the second inclined pipe wall 604, so as to avoid reverse backflow of steam at the outlet position of the auxiliary flow channel when the ejector is extracting steam.

[0034] As a feasible implementation mode, a sliding ring is arranged between the concave ring pipe section 401 and the outer wall, and the sliding ring has an inner tapered hole; the sliding ring can slide along the axial direction of the concave ring pipe section between the first flared portion and the second flared portion; the sliding ring is used for unidirectionally blocking the counterflow steam of the auxiliary flow channel when the inner inclined surface of the inner tapered hole contacts the outer inclined surface of the second flared section.

[0035] As a feasible implementation method, refer to Figure 6 As shown, the one-way slider unit here can be a pointed circular cone structure, and its edge contact surfaces are parallel to the second inclined tube wall 604 in the auxiliary flow channel and the inner wall of the outer tube respectively. The auxiliary flow channel fluid diffuses to both sides through the process fluid, and the main flow channel extracts the auxiliary flow channel steam through the steam extraction circulation unit 203. The one-way slider unit slides in the opposite direction to close the flow channel to avoid reverse backflow of steam at the outlet position of the auxiliary flow channel.

[0036] In an embodiment of the present application, the effect evaporator further includes: a spray pipe, a spray nozzle, a demister, a fresh water collection pipeline, a salt water collection pipe, and a fresh water collection box; wherein, the spray tube bundle is arranged at the top of the effect evaporator, a plurality of heat exchange tubes are arranged in parallel at the lower part of the spray tube bundle, a plurality of spray nozzles are installed on the spray tube bundle, the spray nozzles are evenly and symmetrically arranged on the spray tube bundle, the bottom plane of the spray nozzle is parallel to the plane where the heat exchange tubes are arranged, so as to ensure that the feed seawater is evenly distributed to the outer wall of the heat exchange tube bundle through the spray nozzle, and the conductive air membrane is arranged on the final end plate at the end face of the effect evaporator, and a certain interval is provided between the final end plate and the outlet tube plate, so that the steam at the outlet end can be returned for heat exchange when the steam flow cannot break through the conductive air membrane.

[0037] In an embodiment of the present application, the steam extraction circulation unit 203 also includes a second bypass line, which is connected in parallel with the first bypass line, and the output end of the steam extraction line is also connected to the second bypass line; the second bypass line and the first bypass line are backup for each other; the second bypass line is sequentially installed with a second steam control valve (steam control valve two), a second temperature and pressure sensor (temperature and pressure sensor three), and a second steam ejector (steam ejector two) along the steam inlet direction, the second steam ejector is connected to a second steam extraction branch, and a second steam extraction control valve (steam control valve two) is installed on the second steam extraction branch, and the second temperature and pressure sensor is used to feed back the steam temperature and steam pressure parameters at the second steam control valve to the control unit, so that the control unit adjusts the opening of the second steam extraction control valve based on the steam temperature and steam pressure parameters at the second steam control valve.

[0038] The low-temperature multi-effect distillation seawater desalination system of the embodiment of the present application is designed to adjust the operation of the first-effect evaporator by displacing the steam flow regulating paddle based on the steam flow regulating unit in the double-channel heat exchange tube bundle according to the different steam flow rates and their changing conditions received by the first-effect evaporator, so that the steam is sucked into the inner channel under high flow conditions, and the remaining small amount of steam enters the auxiliary channel provided with spiral fins. The steam in the auxiliary channel is easily condensed and collected, thereby reducing the steam temperature of the heat exchange tube bundle and achieving efficient utilization of steam and heat energy recovery. At the same time, it can effectively prevent the heat exchange tubes of the first-effect evaporator from scaling on the outer wall due to relatively unstable steam changes, thereby greatly reducing scaling and cleaning difficulty of the first-effect heat exchange tube bundle.

[0039] Example 2 Based on the aforementioned embodiments, the embodiments of the present application provide a low-temperature multi-effect distillation seawater desalination system, wherein a conductive air membrane can be used to isolate the current effect evaporator when the heat exchange efficiency of the current effect evaporator is low, and open the reserved channel in the isolated flow state to allow the secondary steam to be unidirectionally transmitted to the next effect evaporator.

[0040] In the embodiment of the present application, the working principle of the conductive air film in the normal multi-effect operation state and the isolation flow state is as follows: 1) During the normal multi-effect operation heat exchange process of the effect evaporator (without the low-efficiency effect evaporator), the secondary steam from the previous effect evaporator first passes through the demister of the previous effect evaporator to filter out the moisture and salt carried in the secondary steam, and enters the first channel of the heat exchange tube bundle of the effect evaporator (located in the lower part of the heat exchange tube bundle, accounting for 80-90% of the total heat exchange tube bundle) for heat exchange and condensation. Some of the steam that is not fully condensed is conductively supported by the supporting partition. Under the blocking effect of the gas film, it returns to the second channel of the heat exchange tube bundle (located at the upper part of the heat exchange tube bundle, accounting for 10-20% of the total heat exchange tube bundle) for heat exchange and condensation. The steam that has not yet condensed will be fed back to the control device (control unit) through the monitoring data of the balance sensor; the control device controls the recovery control valve, the steam extraction control valve, and the steam ejector to enter the first effect evaporator with the power steam for the second time to carry out the cyclic waste heat recovery control process, thereby obtaining condensed water and secondary steam of the excess power steam, effectively improving the water production ratio and water production of the low-temperature multi-effect distillation desalination system. Here, the heat exchange tubes in the first channel of the heat exchange tube bundle are all double-flow heat exchange tubes.

[0041] 2) In the cut-off flow state (there is at least one low-efficiency evaporator in the steam treatment unit), the supporting baffle can conduct the air film in the open state, and then the secondary steam from the previous evaporator first passes through the demister of the previous evaporator to filter out the moisture and salt carried in the secondary steam. The monitoring data of each effect balance sensor is fed back to the control device, and the control device automatically controls the opening of the recovery control valve of the next evaporator according to the feedback data, and at the same time closes the recovery control valve of the low-efficiency evaporator, and increases the opening of the next evaporator under the action of the extraction control valve. The secondary steam extraction of the first-effect evaporator allows it to enter the steam ejector and re-enter the first-effect evaporator with the power steam; the steam entering the first channel and the second channel of the heat exchange tube bundle of the low-efficiency evaporator is directly entered into the first channel of the heat exchange tube bundle of the next-effect evaporator through the open state of the conductive air film of the support baffle under the negative pressure state of the next-effect evaporator for heat exchange and condensation, and part of the steam that is not fully condensed is blocked by the conductive air film of the support baffle and returns to the second channel of the heat exchange tube bundle to repeat the heat exchange and condensation process. Here, please refer to the Chinese patent application number 202110349602.8 for the first channel, the second channel and the distillation flow diagram of the heat exchange tube bundle.

[0042] In this way, operation adjustment is performed by displacing the steam flow regulating paddle of the steam flow regulating unit in the double-channel heat exchange tube bundle, so that steam is sucked into the inner channel under high flow conditions, and the remaining small amount of steam enters the auxiliary channel with spiral fins inside. The steam in the auxiliary channel is easily condensed and collected, and will not cause the first-effect evaporator to have too high a temperature and cause scaling. The secondary steam and part of the primary steam evaporated by heat exchange enter the second-effect evaporator through the one-way conductive air membrane respectively. At this time, the steam temperature is relatively low, and the salt content of the concentrated seawater is low, so the scaling phenomenon of the heat exchange tube bundle is fully alleviated.

[0043] Example 3 Based on the above embodiments, the present application provides a low-temperature multi-effect distillation seawater desalination system. Figure 8 A schematic plan view of a low-temperature multi-effect distillation seawater desalination system according to an embodiment of the present application is shown. Figure 8 As shown, the low-temperature multi-effect distillation seawater desalination system of the embodiment of the present application includes a steam inlet control valve 2, a back pressure pipeline 25, a steam extraction pipeline 26, a bypass pipeline 1 27, a bypass pipeline 28, and a mixed steam pipeline 29; wherein, the steam inlet control valve 2 is connected to an external steam source through a steam inlet pipeline, the mixed steam pipeline 29 and the steam inlet pipeline are connected in series, the bypass pipeline 1 27 and the bypass pipeline 28 are connected in parallel with the back pressure pipeline 25, and the end of the mixed steam pipeline 29 is connected to the heat exchange tube bundle of the first effect evaporator (first effect evaporator 1), and the output end of the first effect evaporator is connected in series with a plurality of effect evaporators in sequence, and each effect evaporator is installed with a balance sensor 16, which is used to monitor and feedback the corresponding effect evaporator in real time. Internal environmental data (temperature and pressure data of secondary steam), the input end of the extraction pipeline 26 is independently connected to each effect evaporator, and a recovery control valve 15 is installed between each effect evaporator and the extraction pipeline 26, and the output end of the extraction pipeline 26 is connected to the bypass pipeline 1 27 and the bypass pipeline 2 28 at the same time; wherein, the back pressure pipeline 25 and the mixed steam pipeline 29 form the back pressure operation passage of the effect evaporator, the bypass pipeline 1 27, the bypass pipeline 28, the extraction pipeline 26 and the mixed steam pipeline 29 form the extraction operation passage of the effect evaporator, and valves and sensors for adjusting accuracy are installed on the back pressure operation passage and the extraction operation passage, and the valves and sensors are controllably connected to the control devices of the bypass pipeline 1 27 and the bypass pipeline 28.

[0044] Reference Figure 8A temperature and pressure sensor 17 is installed in the steam inlet direction of the steam inlet control valve 2. The temperature and pressure sensor 17 is used to feed back the steam system monitoring pressure data to the control device. The control device controls the load state of the seawater desalination system according to the data fed back by the temperature and pressure sensor 17, and automatically adjusts the opening of the steam inlet control valve 2. The back pressure pipeline 25 is sequentially installed with a back pressure control valve 5 and a temperature and pressure sensor 20 along the steam inlet direction. The temperature and pressure sensor 20 feeds back the steam temperature and pressure parameters at the back pressure control valve 5 to the control device, and the control device assists in adjusting the opening of the back pressure control valve 5.

[0045] Reference Figure 8 , the bypass line 27 is sequentially installed with a steam control valve 3 (first steam control valve), a temperature and pressure sensor 2 18 (first temperature and pressure sensor), and a steam ejector 7 (steam ejector) along the steam inlet direction, the steam ejector 7 is connected with a steam extraction branch line 1, the steam extraction branch line 1 is connected to the steam extraction pipeline 26, the steam extraction branch line 1 is installed with a steam extraction control valve 13, the temperature and pressure sensor 2 18 feeds back the steam temperature and pressure parameters at the steam control valve 3 to the control device, the control device assists in adjusting the opening of the steam control valve 3, and controls the opening of the steam extraction control valve 13 to control the steam extraction amount of the steam ejector 7 from the steam extraction pipeline 26. In the embodiment of the present application, the bypass line 28 has the same structure and function as the bypass line 27, the two sets of bypass pipes complement each other, the bypass line 28 is the same as the above-mentioned bypass line 27, and will not be repeated here.

[0046] Taking the bypass line 27 as an example, a thermal expansion joint 6 is also installed on the bypass line 27, and the thermal expansion joint 6 is respectively arranged at the steam inlet and steam outlet positions of the steam ejector 7. The bypass line 27 also includes a buffer branch 1, and the buffer branch 1 is connected in parallel with the thermal expansion joint 6. The buffer branch 1 is sequentially installed with a bypass control valve 9 and a bypass sensor 21 along the steam inlet direction; the thermal expansion joint 6 can balance the expansion and contraction margin of the pipeline caused by thermal expansion and contraction during the startup or shutdown of the pipeline, thereby avoiding long-term stress damage.

[0047] A vacuum breaker valve 11 is installed on the mixed steam pipeline 29. The vacuum breaker valve 11 is located at the inlet end of the first-effect evaporator 1. The vacuum breaker valve 11 is regulated by the control device. When the steam inlet control valve 2 is closed, the vacuum state inside the low-temperature multi-effect seawater desalination system can be quickly destroyed and restored to atmospheric pressure. That is, during the shutdown of the seawater desalination system (the steam inlet control valve 2 is closed), the vacuum breaker valve 11 can quickly supply air to the mixed steam pipeline 29, destroy the vacuum state inside the low-temperature multi-effect seawater desalination system, and restore the vacuum state to atmospheric pressure.

[0048] In the embodiment of the present application, the low-temperature multi-effect distillation seawater desalination system includes a waste heat recovery unit, which includes a flash evaporation device 23 and an indirect heat exchanger 22. The flash evaporation device 23 is connected to the first-effect evaporator 1. The hot water is indirectly heat-exchanged to 85-95 degrees Celsius hot water, and then enters the heat exchange tube bundle of the first-effect evaporator 1 through the flash evaporation device 23. The steam generated after heat exchange with seawater enters the subsequent effect body as secondary steam. The condensed condensate enters the waste heat recovery unit through the water inlet control valve 24 and is again heat-exchanged with the indirect heat exchanger 22 to convert into steam. In the embodiment of the present application, the external steam source of the low-temperature multi-effect distillation seawater desalination system is the steam from the steam output (flash evaporation device 23) end of the waste heat recovery unit.

[0049] In the embodiment of the present application, the low-temperature multi-effect distillation seawater desalination system includes a waste heat recovery operation mode based on the waste heat recovery unit and a steam turbine steam operation mode for practical application selection; the steam turbine steam operation mode is the same as the system in the above embodiment 1, and the steam turbine steam entering the system is operated through the steam extraction circulation unit; in the waste heat recovery mode, refer to Figure 8 , Fig. 9 As shown, the motive steam pressure from the waste heat recovery unit is lower than 0.12MPa, and the temperature is lower than 100℃ (85-90℃) after vacuuming, and can be directly connected to the steam inlet of the first-effect evaporator through the back pressure pipeline; when the motive steam pressure from the waste heat recovery unit is at 0.12MPa-0.40Mpa, the motive steam runs in the system through the steam extraction circulation unit, and during the operation, the excess secondary steam is extracted by the steam extraction circulation unit and added to the first effect through the steam mixing pipeline; at the same time, through the steam flow distribution of the double-flow channel heat exchange tube of the first effect or the double-flow channel heat exchange tube of the first effects, the steam temperature in the heat exchange tube can be reduced to a certain extent.

[0050] Based on this, the low-temperature multi-effect distillation seawater desalination system of the embodiment of the present application can achieve comprehensive optimization of the power steam source and waste heat recovery, and can adjust the heat source according to the power steam heat source status and the generator set status, thereby increasing the flexibility of the system.

[0051] In the embodiment of the present application, a one-way conductive air membrane is provided at the end of the heat exchange tube bundle of each effect evaporator of the low-temperature multi-effect distillation desalination system. The one-way conductive air membrane is in a closed state under normal operation and serves as a steam return heat exchange baffle. In the embodiment of the present application, the control device judges the heat exchange efficiency of the corresponding effect evaporator according to the balance sensor arranged on each effect evaporator. When it is judged that the heat exchange efficiency of the effect evaporator is reduced, when the balance sensor and the control device of the next effect evaporator of the effect evaporator perform steam extraction control through the recovery control valve, the one-way conductive air membrane of the low-efficiency effect evaporator is opened, and the recovery control valve of the low-efficiency effect evaporator is closed, and the recovery control valve of the next effect evaporator is opened, and the steam extraction capacity of the steam ejector is used to assist in extracting the secondary steam generated by the previous effect evaporator, so that the secondary steam part passes over the effect evaporator where the efficient heat exchange cannot be achieved, so that the secondary steam is forced to enter the next effect evaporator for repeated desalination of water.

[0052] In the embodiment of the present application, during the normal heat exchange process of the effect evaporator (that is, when it is determined that the heat exchange efficiency of the effect evaporator is not reduced), the secondary steam from the previous effect evaporator first passes through the demister of the previous effect evaporator to filter out the moisture and salt carried in the secondary steam, and then enters the first channel of the heat exchange tube bundle of the effect evaporator for heat exchange and condensation. Some of the secondary steam that is not fully condensed returns to the second channel of the heat exchange tube bundle under the blocking effect of the conductive air film for heat exchange and condensation. After the above treatment, the secondary steam that has not yet condensed will be fed back to the control device through the monitoring data of the balance sensor, and the control device controls the recovery control valve, steam extraction control valve 13, and steam extraction control valve 2 14 of the effect evaporator to make them enter the steam ejector 1 7 and steam ejector 2 8 respectively and enter the first effect evaporator again with the power steam to perform the cyclic waste heat recovery control process.

[0053] In the embodiment of the present application, when the evaporator of the current effect is in a cut-off flow state (i.e., when it is determined that the heat exchange efficiency of the evaporator of the current effect is reduced), the secondary steam from the evaporator of the previous effect first passes through the demister of the evaporator of the previous effect to filter out the moisture and salt carried in the secondary steam, and the monitoring data of the balance sensor corresponding to each effect evaporator is fed back to the control device, which automatically controls the opening of the recovery control valve of the next effect evaporator according to the received monitoring data, and at the same time closes the recovery control valve of the evaporator of the current effect, and connects the extraction control valve 13 and the extraction control valve 14. Under the cooperative effect, the secondary steam extraction amount of the next-effect evaporator is increased, so that it enters the steam ejector 1 7 and the steam ejector 2 8 respectively and enters the first-effect evaporator again with the power steam; wherein, the secondary steam entering the first channel and the second channel of the heat exchange tube bundle of the evaporator of the current effect directly enters the first channel of the heat exchange tube bundle of the evaporator of the next effect through the conductive air membrane under the negative pressure state of the steam extraction of the next-effect evaporator for heat exchange and then condensation, and part of the secondary steam that is not fully condensed returns to the second channel of the heat exchange tube bundle under the blocking effect of the conductive air membrane of the evaporator of this effect to repeat the heat exchange and condensation process.

[0054] It should be noted that the steam extraction amount of the steam ejector 17 of the present application is jointly adjusted according to the steam extraction control valve 13 and the recovery control valve, and the steam extraction amount of the steam ejector 28 is jointly adjusted according to the steam extraction control valve 2 14 and the recovery control valve. The steam ejector 17 and the steam ejector 28 are used to extract the secondary steam of the effect evaporator into the first effect evaporator, and to extract the secondary steam of the effect evaporator to promote the reflux of the brine flash tank and the product flash tank into the effect evaporator.

[0055] In this way, the present application utilizes the dual operation modes of the power steam heat source state and the waste heat recovery flash evaporation system, and the operation mode is flexible and diverse. The heat source can be adjusted according to the power steam heat source state and the generator set state, making the system's operating power and efficiency adjustment mode range wider.

[0056] Example 4 Based on the above embodiments, the present application provides a low-temperature multi-effect distillation seawater desalination method based on a double-channel heat exchange tube, comprising the following steps S801 to S803: Step S801: External heat source steam enters the first-effect evaporator of the steam processing unit through the steam inlet unit.

[0057] Step S802: When the steam flow rate received in the heat exchange tube of the first-effect evaporator increases, gradually increase the opening of the flexible connecting hole so that most of the steam entering the heat exchange tube when the steam ejector of the steam extraction circulation unit extracts steam flows through the main flow channel of each heat exchange tube to the next intermediate-effect evaporator.

[0058] Step S803, when the steam flow rate received in the heat exchange tube of the first-effect evaporator decreases, gradually reduce the size of the flexible connecting hole so that the steam entering the heat exchange tube when the steam ejector of the steam extraction circulation unit extracts steam is diverted to the auxiliary flow channel in each heat exchange tube for heat exchange; wherein the main flow channel and the auxiliary flow channel are coaxially arranged, and spiral fins rotating at intervals are provided in the auxiliary flow channel.

[0059] As a result, it is possible to achieve all-round optimization and improvement of waste heat recovery in the seawater desalination system, thereby increasing the water output and water production ratio of the seawater desalination system.

[0060] In particular, according to an embodiment of the present invention, the process described above with reference to the flowchart can be implemented as a computer software program. For example, an embodiment of the present invention includes a computer program product, which includes a computer program carried on a computer-readable storage medium, and the computer program contains program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication part, and / or installed from a removable medium. When the computer program is executed by a central processing unit (CPU), the above-mentioned functions defined in the system of the present application are executed.

[0061] The above embodiments are only used to illustrate the technical solution of the present application, but not to limit it. The present application is not limited to the exact structure described above and illustrated in the accompanying drawings, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, various changes and modifications made without departing from the concept of the present application should be deemed to belong to the protection scope of the present application.

[0062] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present invention. In this regard, each box in the flowchart or block diagram may represent a module, a program segment, or a part of the code, which includes one or more executable instructions for implementing the specified logical functions.

[0063] In the several embodiments provided in the present application, it should be understood that the disclosed systems, modules and methods can be implemented in other ways. For example, the module embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, modules or units, which can be electrical, mechanical or other forms.

[0064] The above embodiments are only used to illustrate the technical solution of the present application, but not to limit it. The present application is not limited to the exact structure described above and illustrated in the accompanying drawings, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, various changes and modifications made without departing from the concept of the present application should be deemed to belong to the protection scope of the present application.

Claims

1. An effect evaporator, applied to a low-temperature multi-effect distillation seawater desalination system, characterized in that: The evaporator comprises: an evaporator shell, an inlet tube sheet and a final end plate arranged at both ends of the evaporator shell, and a plurality of heat exchange tubes arranged on a heat exchange tube support frame inside the evaporator shell; The inlet end of each heat exchange tube is fixed on the inlet tube sheet, and the outlet end of the heat exchange tube is fixed on the outlet tube sheet, and the outlet tube sheet is located at the front end of the final end plate; wherein, a conductive air membrane is provided on the final end plate, and densely arranged reserved channels are opened on the conductive air membrane, and the reserved channels are in a staggered cross-shaped seam structure, and the reserved channels are unidirectionally conducted under the action of the extraction steam pressure difference, so as to open the reserved channels in the isolation flow state, and close the reserved channels in the normal effect evaporator operation state; Each of the heat exchange tubes comprises: an outer tube and an inner tube arranged in the inner cavity of the outer tube in the axial direction; the heat exchange tube is a double-channel heat exchange tube having a main channel and an auxiliary channel, wherein a main channel for conveying steam is formed inside the inner tube, and an auxiliary channel for steam is formed between the inner wall of the outer tube and the outer wall of the inner tube; a spiral fin extending axially along the outer wall of the inner tube is arranged in the auxiliary channel, and the spiral fin is fixedly connected to the outer tube and the inner tube; A plurality of flexible communication holes are provided on the inner tube wall near the outlet end, the flexible communication holes are evenly arranged in the middle and upper middle parts of the side wall of the inner tube, and the flexible communication holes are connected with the main flow channel; The main channel is provided with a steam flow regulating unit near the outlet end; the steam flow regulating unit comprises: a steam flow regulating paddle, and an elastic opening regulating mechanism arranged in the flexible connecting hole; the top surface of the steam flow regulating paddle is perpendicular to the steam flow direction in the main channel; the steam flow regulating paddle is connected to the flexible connecting hole through a plurality of traction ropes; one end of each traction rope is fixedly connected to the steam flow regulating paddle, and the other end is connected to the opening regulating mechanism; Among them, when the steam flow in the main channel increases, the displacement of the steam flow regulating paddle drives the movement of the traction rope, and the traction rope drives the opening of the flexible connecting hole to increase based on the opening regulating mechanism. At the same time, the steam opens the reserved channel of the conductive air membrane, so that the steam is unidirectionally transmitted to the next effect evaporator; when the steam flow in the main channel decreases, the displacement of the steam flow regulating paddle drives the reduction of the opening of the flexible connecting hole, and the reserved channel of the conductive air membrane is closed, so that the steam completes the return heat exchange in the current effect evaporator.

2. The effect evaporator according to claim 1, characterized in that: A concave ring pipe section is integrally provided at one end of the inner tube close to the steam outlet in the axial direction; the concave ring pipe section is coaxially arranged with the inner tube; the concave ring pipe section comprises a first flared portion, a horizontal portion and a second flared portion; the first flared portion and the second flared portion are respectively located at two ends of the horizontal portion and are symmetrically arranged; the first flared portion is located on one side of the horizontal portion close to the outlet end of the inner tube; the maximum outer diameters of the first flared portion and the second flared portion are the same as the outer diameter of the inner tube, and the outer diameter of the horizontal portion is smaller than the outer diameter of the inner tube; A sliding ring is provided between the concave ring pipe section and the outer wall, and the sliding ring has an inner tapered hole; the sliding ring can slide along the axial direction of the concave ring pipe section between the first flared portion and the second flared portion; the sliding ring is used for unidirectionally blocking the counterflow steam of the auxiliary flow channel when the inner inclined surface of the inner tapered hole contacts the outer inclined surface of the second flared portion.

3. The effect evaporator according to claim 1, characterized in that: An in-tube nozzle is also provided in the main channel, and the in-tube nozzle is located near the input side of the steam flow regulating unit; the in-tube nozzle is a tapered mouth that gradually shrinks from the inner diameter of the inner tube to a preset diameter along the steam flow direction.

4. A low-temperature multi-effect distillation seawater desalination system, characterized in that: include: Steam inlet unit, steam treatment unit, steam extraction circulation unit, seawater distribution unit and temperature reduction unit; The steam inlet unit is connected to an external steam source through a steam inlet control valve to provide steam from an external heat source; A steam processing unit, wherein the output end of the steam inlet unit is connected to the input end of the steam processing unit, and the steam processing unit comprises a first-effect evaporator, a plurality of intermediate-effect evaporators and a final-effect evaporator connected in series in sequence, wherein the first-effect evaporator is an effect body evaporator as claimed in any one of claims 1 to 3, wherein, when the steam flow rate received by the first-effect evaporator increases, the opening of the flexible connecting hole is gradually increased when the steam ejector of the steam extraction circulation unit extracts steam, so that most of the steam entering the heat exchange tube flows to the intermediate-effect evaporator through the main channel; when the steam flow rate received by the first-effect evaporator decreases, the flexible connecting hole is gradually closed, so that the steam entering the heat exchange tube reduces the amount of steam absorbed from the auxiliary pipeline under the action of the steam extraction circulation unit; An extraction circulation unit is fixedly connected to the steam processing unit, the extraction circulation unit comprises an extraction pipeline, a mixing steam pipeline and a first bypass pipeline, the input end of the extraction pipeline is independently connected to each effect evaporator, and a recovery control valve is installed between each effect evaporator and the extraction pipeline, and the output end of the extraction pipeline is connected to the first bypass pipeline; the first bypass pipeline, the extraction pipeline and the mixing steam pipeline form an extraction operation passage of the steam processing unit; the first bypass pipeline is sequentially installed with a first steam control valve, a first temperature and pressure sensor, and the steam ejector along the steam inlet direction, the steam ejector is connected to a first extraction branch, the first extraction control valve is installed on the first extraction branch, and the first temperature and pressure sensor is used to feed back the steam temperature and steam pressure parameters at the first steam control valve to the control unit, so that the control unit adjusts the opening of the first extraction control valve based on the steam temperature and steam pressure parameters at the first steam control valve; A seawater distribution unit, used for spraying and recovering seawater on the steam treatment unit; A cooling unit, one end of which is connected to the outlet of the condensate collecting tank of the first-effect evaporator, and the other end of which is connected to the middle of the steam mixing pipeline.

5. The low-temperature multi-effect distillation seawater desalination system according to claim 4, characterized in that: When the low-temperature multi-effect distillation seawater desalination system is in the state of being supplied with power steam, the steam inlet control valve, the first steam control valve, the first steam extraction control valve, and the recovery control valve of the target effect evaporator are opened; The control unit controls the first steam ejector to extract secondary steam from the target effect evaporator based on the parameters of the motive steam when the steam heat exchange is performed in the steam processing unit, and then circulates and mixes the secondary steam with the motive steam from the steam inlet control valve to enter the first effect evaporator after the secondary steam is reduced in temperature and pressure; The target effect evaporator is an effect evaporator determined by a control unit from the steam processing unit for the first steam ejector to extract the secondary steam.

6. The low-temperature multi-effect distillation seawater desalination system according to claim 5, characterized in that: A balance sensor is installed on each of the effect evaporators, and the balance sensor is used to monitor the internal environmental data of the corresponding effect evaporator; When the first balance sensor determines that the heat exchange efficiency of the first-effect evaporator is lower than the heat exchange threshold, and the second balance sensor determines that the heat exchange efficiency of the second-effect evaporator next to the first-effect evaporator is normal, the recovery control valve on the first-effect evaporator is closed, and the recovery control valve on the second-effect evaporator is opened, so that the conductive air membrane of the heat exchange tube bundle of the first-effect evaporator is opened, and the secondary steam generated by the previous-effect evaporator of the first-effect evaporator is auxiliary extracted based on the steam extraction pipeline, so that the secondary steam passes through the first-effect evaporator and is forced to enter the second-effect evaporator; The balance sensor at least includes a temperature difference sensor, a pressure difference sensor and a pressure balance chamber; The temperature difference sensor is used to monitor the temperature data of the secondary steam generated by the first-effect evaporator and the previous-effect evaporator of the first-effect evaporator; The pressure difference sensor is used to monitor the pressure data of the secondary steam generated by the first-effect evaporator and the previous-effect evaporator of the first-effect evaporator; The pressure balance chamber is used to correct the pressure of the secondary steam generated by the first-effect evaporator in real time based on the atmospheric pressure.

7. The low-temperature multi-effect distillation seawater desalination system according to claim 4, characterized in that: The system further comprises a waste heat recovery unit, a steam output end of the waste heat recovery unit is connected to the steam mixing pipeline for mixing with the external heat source steam and the secondary steam extracted by the first steam ejector, and one end of the waste heat recovery unit is connected to the first effect evaporator for receiving condensed water from the first effect evaporator; The waste heat recovery unit includes an indirect heat exchange device and a flash evaporation device; the indirect heat exchange device is used to indirectly heat the waste hot water into hot water at 85-95°C, and the flash evaporation device is connected to the first-effect evaporator to flash the hot water at 85-95°C into power steam, and allow the power steam to enter the first-effect evaporator through the steam inlet unit.

8. The low-temperature multi-effect distillation seawater desalination system according to claim 7, characterized in that: The steam output end of the waste heat recovery unit is connected to the steam inlet unit to serve as another external steam source, and one end of the waste heat recovery unit is connected to the first effect evaporator to receive condensed water from the first effect evaporator; The waste heat recovery unit includes an indirect heat exchange device and a flash evaporation device; the indirect heat exchange device is used to indirectly heat the waste hot water into hot water at 85-95°C, and the flash evaporation device is connected to the first-effect evaporator to flash the hot water at 85-95°C into power steam, and allow the power steam to enter the first-effect evaporator through the steam inlet unit.

9. The low-temperature multi-effect distillation seawater desalination system according to any one of claims 4 to 8, characterized in that: The steam extraction circulation unit further includes a second bypass pipeline, the second bypass pipeline and the first bypass pipeline are connected in parallel, and the output end of the steam extraction pipeline is also connected to the second bypass pipeline; the second bypass pipeline and the first bypass pipeline are standby for each other; A second steam control valve, a second temperature and pressure sensor, and a second steam ejector are sequentially installed on the second bypass line along the steam inlet direction; the second steam ejector is connected to a second steam extraction branch, and a second steam extraction control valve is installed on the second steam extraction branch; the second temperature and pressure sensor is used to feed back steam temperature and steam pressure parameters at the second steam control valve to a control unit, so that the control unit adjusts the opening of the second steam extraction control valve based on the steam temperature and steam pressure parameters at the second steam control valve.

10. A low-temperature multi-effect distillation seawater desalination method, applied to the system of any one of claims 4 to 9, characterized in that: The method comprises: The external heat source steam enters the first-effect evaporator of the steam treatment unit through the steam inlet unit; When the steam flow rate received in the heat exchange tube of the first-effect evaporator increases, the opening of the flexible connecting hole is gradually increased so that when the steam ejector of the steam extraction circulation unit extracts steam, most of the steam entering the heat exchange tube flows to the next intermediate-effect evaporator through the main flow channel of each heat exchange tube; When the steam flow rate received in the heat exchange tube of the first-effect evaporator decreases, the flexible connecting hole is gradually reduced to reduce the steam flow rate entering the main channel when the steam ejector of the steam extraction circulation unit extracts steam; The main flow channel and the auxiliary flow channel are coaxially arranged, and spiral fins rotating at intervals are arranged in the auxiliary flow channel.

11. The low-temperature multi-effect distillation seawater desalination method according to claim 10, characterized in that: When the steam ejector of the steam extraction circulation unit extracts steam, most of the steam entering the heat exchange tube flows through the main flow channel of each heat exchange tube to the next intermediate effect evaporator, including: When the steam pressure in the first-effect evaporator is greater than a preset pressure threshold, opening the reserved channel on the conductive air membrane; For each of the heat exchange tubes, the steam passing through the main flow channel is directly unidirectionally conducted to the next intermediate effect evaporator.

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