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

Abstract

The present invention relates to the technical field of seawater desalination, and specifically provides an effect body evaporator, a low-temperature multi-effect distillation seawater desalination system and method. When the steam flow received by the first-effect evaporator in the steam treatment unit of the low-temperature multi-effect distillation seawater desalination system increases, the opening degree of the flexible communication holes in the double-flow channel heat exchange tubes is gradually increased during steam extraction in the steam extraction circulation unit, so that most of the steam entering the heat exchange tubes flows through the main flow channel to the intermediate-effect evaporator; when the steam flow received by the first-effect evaporator decreases, the flexible communication holes are gradually reduced, so that most of the steam entering the heat exchange tubes exchanges heat through the auxiliary flow channel under the action of the steam extraction pressure difference. Thus, the efficient utilization of steam and heat energy recovery in the low-temperature multi-effect distillation seawater desalination system are realized, and at the same time, the outer wall scaling of the heat exchange tubes of the first-effect evaporator caused by relatively unstable steam change conditions can be effectively prevented, and the scaling and cleaning difficulty of the first-effect heat exchange tube bundle are greatly reduced.

Description

Technical Field

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

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

[0003] In the existing low-temperature multi-effect distillation seawater desalination system, the source of motive steam conventionally comes from the fifth extraction and sixth extraction steam of a thermal power plant's steam turbine. After being desuperheated and depressurized, it enters the first-effect evaporator in the low-temperature multi-effect distillation seawater desalination system to exchange heat with seawater. This results in the first-effect evaporator having to withstand the highest heat exchange temperature in the low-temperature multi-effect distillation seawater desalination system. Given the high heat exchange temperature, the relatively unstable steam flow rate changes it faces, and the uneven steam quality caused by steam from different sources, the heat exchange tube bundles of the first-effect evaporator are more likely to have slime deposition and scaling on the outer wall of the heat exchange tube bundles compared to other effect bodies as the operation cycle extends. This causes the amount of steam that allows some seawater to absorb the latent heat of steam released by the condensation of the steam inside the heat exchange tube bundles and vaporize into the next-effect evaporator as secondary steam to gradually decrease. Eventually, the seawater cannot absorb the latent heat of steam released by the condensation of the steam inside the heat exchange tube bundles of the first-effect evaporator and vaporize, ultimately leading to a gradual decrease in the water production efficiency. Summary of the Invention

[0004] In view of the above problems, this application provides an effect body evaporator, a low-temperature multi-effect distillation seawater desalination system and method. Based on the steam flow operation adjustment of the heat exchange tube bundles of the first-effect evaporator, efficient utilization of steam and heat energy recovery are achieved. At the same time, it can effectively prevent the outer wall scaling of the heat exchange tubes of the first-effect evaporator caused by relatively unstable steam quality changes, and greatly reduce the scaling and cleaning difficulty of the first-effect heat exchange tube bundles.

[0005] To achieve the objectives of this application, the following technical solutions are provided in this application:

[0006] In a first aspect, this application provides an effect body evaporator for use in a low-temperature multi-effect distillation seawater desalination system. The effect body evaporator includes: an evaporator housing, an inlet tube sheet and a final-stage end plate disposed at both ends of the evaporator housing, and a plurality of heat exchange tubes disposed on a heat exchange tube support frame inside the evaporator housing.

[0007] The inlet ends of the heat exchange tubes are fixed on the inlet tube sheet, and the outlet ends of the heat exchange tubes are fixed on the outlet tube sheet, and the outlet tube sheet is located at the front end of the last stage end plate; wherein, a gas guiding membrane is provided on the last stage end plate, and reserved channels are densely arranged on the gas guiding membrane, and the reserved channels are in a staggered cross-shaped line slot structure, and the reserved channels are unidirectionally conductive under the action of the steam extraction pressure difference to open the reserved channels in the cut-off flow state and close the reserved channels in the normal operation state of the effect body evaporator;

[0008] Each of the heat exchange tubes includes: an outer tube and an inner tube disposed in the inner cavity of the outer tube along the axial direction; the heat exchange tube is a double-flow heat exchange tube having a main flow channel and an auxiliary flow channel, wherein a main flow channel for conveying steam is formed inside the inner tube, and an auxiliary flow 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 disposed in the auxiliary flow channel, and the spiral fin is fixedly connected to the outer tube and the inner tube;

[0009] A plurality of flexible communication holes are formed in the inner tube wall near the outlet end, and the flexible communication holes are uniformly arranged in the middle and upper middle parts of the side wall of the inner tube, and the flexible communication holes are communicated with the main flow channel;

[0010] A steam flow rate regulating unit is provided near the outlet end of the main flow channel; the steam flow rate regulating unit includes: a steam flow rate regulating flap, and an elastic opening regulating mechanism disposed in the flexible communication hole; the top surface of the steam flow rate regulating flap is perpendicular to the steam flow direction in the main flow channel; the steam flow rate regulating flap is connected to the flexible communication hole through a plurality of traction ropes; one end of each traction rope is fixedly connected to the steam flow rate regulating flap, and the other end is connected to the opening regulating mechanism;

[0011] Wherein, when the steam flow rate in the main flow channel increases, the steam flow impact drives the steam flow rate regulating flap to displace along the steam flow direction, the displacement of the steam flow rate regulating flap drives the traction rope to move, and the traction rope drives the opening of the flexible communication hole to increase based on the opening regulating mechanism. At the same time, the steam opens the reserved channel of the gas guiding membrane, so that the steam is unidirectionally conducted and transmitted to the next effect body evaporator; when the steam flow rate in the main flow channel decreases, the reduced steam flow rate drives the steam flow rate regulating flap to move back along the opposite direction of the steam flow direction, the displacement of the steam flow rate regulating flap drives the opening of the flexible communication hole to decrease, and the reserved channel of the gas guiding membrane is closed, so that the steam completes the return heat exchange in the current effect body evaporator.

[0012] In a possible implementation, a concave ring pipe section is integrally provided at one end of the inner pipe close to the steam outlet along the axial direction; the concave ring pipe section is coaxially arranged with the inner pipe; 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 both 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 pipe; the maximum outer diameters of the first flared portion and the second flared portion are the same as the outer diameter of the inner pipe, and the outer diameter of the horizontal portion is smaller than the outer diameter of the inner pipe; a sliding collar is arranged between the concave ring pipe section and the outer wall, and the sliding collar has an inner tapered hole; the sliding collar can slide axially along the concave ring pipe section between the first flared portion and the second flared portion; the sliding collar is used to unidirectionally block the reverse flow steam in the auxiliary flow channel when the inner inclined surface of the inner tapered hole contacts the outer inclined surface of the second flared section.

[0013] In a possible implementation, a nozzle inside the pipe is further arranged in the main flow channel, and the nozzle inside the pipe is located on the input side close to the steam flow regulating unit; the nozzle inside the pipe is a tapered port whose inner diameter of the inner pipe gradually contracts to a preset diameter along the steam flow direction, and the nozzle inside the pipe is in fluid communication with the main flow channel located at the front end of the nozzle inside the pipe.

[0014] In a second aspect, the present application provides a low-temperature multi-effect distillation seawater desalination system, including: a steam inlet unit, a steam treatment unit, a steam extraction and circulation unit, a seawater water distribution unit and a temperature reduction unit;

[0015] The steam inlet unit is connected to an external steam source through a steam inlet control valve and is used to provide external heat source steam;

[0016] The steam treatment unit, the output end of the steam inlet unit is connected to the input end of the steam treatment unit, the steam treatment unit includes a first effect evaporator, a plurality of intermediate effect evaporators and a last effect evaporator connected in series in sequence, the first effect evaporator is the effect body evaporator as described above. Wherein, when the steam flow received by the first effect evaporator increases, the opening degree of the flexible communication hole is gradually increased when the steam ejector of the steam extraction and circulation unit extracts steam, so that most of the steam entering the heat exchange tube flows through the main flow channel to the intermediate effect evaporator; when the steam flow received by the first effect evaporator decreases, the flexible communication hole is gradually closed, so that the steam entering the heat exchange tube reduces the amount of steam sucked from the auxiliary pipeline under the action of the steam extraction and circulation unit;

[0017] The steam extraction and circulation unit is fixedly connected to the steam treatment unit. The steam extraction and circulation unit 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 first bypass pipeline, the steam extraction pipeline, and the steam mixing pipeline form the steam extraction operation path of the steam treatment 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. A first steam extraction branch is connected to the steam ejector, and a first steam extraction control valve is installed on the first steam extraction branch. The first temperature and pressure sensor is used to feedback 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 degree of the first steam extraction control valve based on the steam temperature and steam pressure parameters at the first steam control valve.

[0018] The seawater distribution unit is used for spraying and recovering seawater in the steam treatment unit.

[0019] The temperature reduction unit has one end connected to the outlet end of the condensate collection tank of the first effect evaporator, and the other end connected to the middle of the steam mixing pipeline.

[0020] In a possible implementation manner, when the low-temperature multi-effect distillation seawater desalination system is in the steam turbine power 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 for cyclic mixing during steam heat exchange in the steam treatment unit, and then enters the first effect evaporator after the power steam from the steam inlet control valve is cooled, depressurized, and mixed. The target effect evaporator is the determined effect evaporator in the steam treatment unit for the first steam ejector to extract the secondary steam.

[0021] 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 environment data of the corresponding effect evaporator; when the first balance sensor determines that the heat exchange efficiency of the first effect evaporator where it is located 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 wider, so that the gas-permeable film that can conduct heat on 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 assisted to be extracted based on the extraction pipeline, so that it bypasses the first effect evaporator and is forced to enter the second effect evaporator.

[0022] In a possible implementation, 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.

[0023] In a possible implementation, the system further includes a waste heat recovery unit, and 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 exchange the 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 85-95°C hot water into power steam, and make the power steam enter the first effect evaporator through the steam inlet unit; when the low-temperature multi-effect distillation seawater desalination system is in the 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 power steam enters the first effect evaporator through the steam inlet unit, including: the power steam passes through the steam inlet control valve into the back pressure pipeline after being desuperheated and depressurized, and thus directly enters the first effect evaporator to operate in the waste heat recovery mode.

[0024] In a possible implementation, the steam output end of the waste heat recovery unit can be directly connected to the mixed steam 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 the condensate water from the first effect evaporator.

[0025] In a possible implementation, the steam extraction cycle unit further includes a second bypass pipeline, which is connected in parallel with the first bypass pipeline, 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 backup for each other; the second bypass pipeline 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, a second steam extraction branch is connected to the second steam ejector, and a second steam extraction control valve is installed on the second steam extraction branch. The second temperature and pressure sensor is used to feedback 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 degree of the second steam extraction control valve based on the steam temperature and steam pressure parameters at the second steam control valve.

[0026] In a second aspect, the present application provides a method for desalinating seawater by low-temperature multi-effect distillation, which is applied to the low-temperature multi-effect distillation seawater desalination system as described above. The method includes:

[0027] External heat source steam enters the first-effect evaporator of the steam treatment unit through the steam inlet unit;

[0028] When the steam flow received in the heat exchange tubes of the first-effect evaporator increases, gradually increase the opening degree of the flexible communication hole, so that when the steam ejector of the steam extraction cycle unit extracts steam, most of the steam entering the heat exchange tubes flows through the main flow channels of each heat exchange tube to the next intermediate-effect evaporator;

[0029] When the steam flow received in the heat exchange tubes of the first-effect evaporator decreases, gradually decrease the flexible communication hole, so as to reduce the steam flow entering the main flow channel when the steam ejector of the steam extraction cycle unit extracts steam;

[0030] Wherein, the main flow channel and the auxiliary flow channel are coaxially arranged, and the auxiliary flow channel is provided with spiral fins that rotate at intervals.

[0031] In a possible implementation, when the steam ejector of the steam extraction cycle unit extracts steam, making most of the steam entering the heat exchange tubes flow through the main flow channels of each heat exchange tube to the next intermediate-effect evaporator includes: when the steam pressure in the first-effect evaporator is greater than a preset pressure threshold, open the reserved channel on the conductive air film; for each heat exchange tube, the steam passing through the main flow channel is directly and unidirectionally conducted to the next intermediate-effect evaporator.

[0032] The low-temperature multi-effect distillation seawater desalination system provided by the present application, in view of the different steam flow rates received by the first-effect evaporator and their changing conditions, 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. Based on the displacement of the steam flow rate adjusting flap of the steam flow rate adjusting unit in the double-channel heat exchange tube bundle, the steam flow rate condition is determined, and the transportation of the steam is adjusted under different steam flow rate conditions, thereby realizing the redistribution of the steam. Under high flow rate conditions, the steam is sucked in from the inner flow channel, and the remaining small amount of steam enters the auxiliary flow channel provided with spiral fins. The steam in the auxiliary flow channel is easily condensed and collected, reducing the steam temperature of the heat exchange tube bundle, realizing the efficient utilization of steam and heat energy recovery. At the same time, by controlling the steam circulation flow rate distribution ratio, the temperature of the heat exchange tube bundle can be delayed below the scaling temperature, effectively preventing the outer wall scaling of the heat exchange tubes of the first-effect evaporator caused by the relatively unstable steam change conditions, and greatly reducing the 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 by the present application reduces the opening degree of the inner flow channel through the flexible communication hole of the steam flow rate adjusting unit under low flow rate conditions, so that the steam mainly circulates through the auxiliary flow channel for heat exchange, improving the heat exchange efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The 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;

[0034] Figure 1 It is a schematic operation plan view of the thermocompression-low temperature multi-effect distillation seawater desalination system provided by the embodiment of the present application;

[0035] Figure 2 It is a schematic architecture view of the low-temperature multi-effect distillation seawater desalination system provided by the embodiment of the present application;

[0036] Figure 3a It is a schematic end face view inside the effect body evaporator provided by the embodiment of the present application;

[0037] Figure 3b provided by the embodiment of the present application Figure 3a Schematic structural view of the derivable ventilation membrane with partial enlargement at A;

[0038] Figure 4a It is a schematic plan view of the double-channel heat exchange tube provided by the embodiment of the present application;

[0039] Figure 4b It is a schematic three-dimensional structure view of the double-channel heat exchange tube provided by the embodiment of the present application;

[0040] Figure 4c It is a schematic three-dimensional structure view of the steam flow rate adjusting unit in the double-channel heat exchange tube provided by the embodiment of the present application;

[0041] Figure 4d It is a three-dimensional structural schematic diagram of the steam flow regulating unit provided by the embodiment of the present application;

[0042] Figure 5a It is an implementation structural schematic diagram of the double-channel heat exchange tube provided by the embodiment of the present application;

[0043] Figure 5b It is an implementation structural schematic diagram of the double-channel heat exchange tube provided by the embodiment of the present application;

[0044] Figure 6 It is a cross-sectional schematic diagram in the auxiliary flow channel of the double-channel heat exchange tube provided by the embodiment of the present application;

[0045] Figure 7 It is an implementation structural schematic diagram of the double-channel heat exchange tube provided by the embodiment of the present application;

[0046] Figure 8 It is an optional plan schematic diagram of the low-temperature multi-effect distillation seawater desalination system provided by the embodiment of the present application;

[0047] Figure 9 It is an optional plan schematic diagram of the low-temperature multi-effect distillation seawater desalination system provided by the embodiment of the present application;

[0048] Figure 10 It is a flow schematic diagram of the low-temperature multi-effect distillation seawater desalination method provided by the embodiment of the present application.

[0049] Reference numerals:

[0050] 1, the first-effect evaporator; 2, the first steam inlet control valve; 3, the first steam control valve; 4, the second steam control valve; 5, the back pressure control valve; 6, the thermal expansion joint; 7, the first steam ejector; 8, the second steam ejector; 9, the first bypass control valve; 10, the second bypass control valve; 11, the vacuum breaker valve; 12, the second steam inlet control valve; 13, the first steam extraction control valve; 14, the second steam extraction control valve; 15, the recovery control valve; 16, the balance sensor; 17, the first temperature and pressure sensor; 18, the second temperature and pressure sensor; 19, the third temperature and pressure sensor; 20, the fourth temperature and pressure sensor; 21, the bypass sensor; 22, the indirect heat exchange device; 23, the flash evaporation device; 24, the water inlet control valve; 25, the back pressure pipeline; 26, the steam extraction pipeline; 27, the first bypass pipeline; 28, the second bypass pipeline; 29, the mixed steam pipeline; 201, the steam inlet unit; 202, the steam treatment unit; 203, the steam extraction circulation unit; 204, the water distribution unit; 205, the temperature reduction unit; 301, the outer pipe; 302, the inner pipe; 303, the flexible communication hole; 304, the nozzle inside the pipe; 401, the concave ring pipe section; 402, the spiral fin; 403, the outlet end; 601, the first straight pipe wall; 602, the first inclined pipe wall; 603, the second straight pipe wall; 604, the second inclined pipe wall; 605, the third straight pipe wall. Detailed implementation manners

[0051] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the accompanying drawings in the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the protection scope of the present application.

[0052] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features; in the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0053] The low-temperature multi-effect distillation (MED) seawater desalination system is a thermal seawater desalination production process with many commercial cases at present. It connects a series of effect evaporators containing spray tube bundles and heat exchange tube bundles in series. The motive steam flows inside the heat exchange tube bundles. At the same time, the feed seawater is sprayed through the spray tube bundles onto the outer wall of the heat exchange tube bundles and evenly distributed from top to bottom. Part of the seawater absorbs the latent heat of vaporization released by the condensation of the steam inside the heat exchange tube bundles and vaporizes into secondary steam and enters the next effect evaporator, making the evaporation temperature of the latter effect lower than that of the previous effect, so as to obtain desalinated water several times the amount of steam. This evaporation and condensation process is repeated along a series of effect evaporators until the steam in the last effect is introduced into the condenser and completely condensed. Figure 1 is a schematic operation plan view of the thermo vapor compression-low temperature multi-effect distillation (TVC-MED) seawater desalination system. TVC-MED is an efficient seawater desalination technology developed based on traditional MED. As Figure 1 shown, its working principle is based on traditional MED. It uses a thermo-compressor to compress the secondary steam generated by the evaporator and then recycle it as heating steam. Among them, the feed seawater enters the evaporator after pretreatment and flows in the form of a thin film in each effect evaporator, absorbs the latent heat of vaporization and evaporates. The generated secondary steam is mixed and compressed with 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.

[0054] In the existing systems and devices related to MED seawater desalination, the source of motive steam usually comes from the fifth and sixth extraction steam of the steam turbine in a thermal power plant. After being desuperheated and depressurized, 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 bear 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 bundles in it are more likely to deposit slime and scale on the outer wall of the heat exchange tube bundles compared with other effects as the operation cycle extends. This leads to a gradual decrease in the amount of steam that part of the seawater absorbs the latent heat of vaporization released by the condensation of the steam inside the heat exchange tube bundles and vaporizes into the next effect evaporator as secondary steam. Even the seawater cannot absorb the latent heat of vaporization released by the condensation of the steam inside the heat exchange tube bundles of the first effect evaporator and vaporize, ultimately resulting in a gradual decrease in the water production efficiency.

[0055] At the same time, in the existing TVC-MED seawater desalination system, the source of motive steam is single, the waste heat recovery efficiency is not high, the extraction steam flow rate of the system device is unstable, and the adjustable precision and comprehensive utilization efficiency are relatively low.

[0056] 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.

[0057] Example 1

[0058] 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;

[0059] 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;

[0060] 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.

[0061] 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 in the figure, 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 flow channel for steam formed inside the inner tube 302, and an auxiliary flow channel formed between the inner wall of the outer tube 301 and the outer wall of the inner tube 302; one end of the inner tube close to the steam outlet along the axial direction is integrally provided with a concave ring tube section 401, and the concave ring tube section 401 is coaxially arranged with the inner tube 302; a spiral fin 402 extending axially along the outer wall of the inner tube 302 is arranged inside the auxiliary flow channel, and the fins extend at intervals, and the outer tube 301 is supported around the inner tube 302 through the spiral fin 402; a plurality of flexible communication holes 303 are opened on the inner tube wall near the outlet end 403, the flexible communication holes 303 are uniformly arranged on the side wall of the inner tube 302, and the flexible communication holes 303 are communicated with the main flow channel; as a feasible implementation manner, a nozzle inside the tube 304 is arranged in the front section (i.e., the input side) of the main flow channel close to the steam flow rate regulating unit; the nozzle inside the tube 304 is a conical opening that gradually contracts to a preset diameter along the steam flow direction, and the nozzle inside the tube 304 is in fluid communication with the main flow channel located at the front end of the nozzle inside the tube 304, so as to further converge and increase the steam flow rate at the conical opening through the nozzle inside the tube 304. At the same time, a vacuum suction chamber is formed in the main flow channel section where the conical outlet is located, so that the opening degree of the flexible communication hole 303 is convenient to adjust. Exemplarily, the conical outlet is circular, and the preset diameter is 1 / 4-1 / 2 of the inner tube diameter. Figure 4a The direction of the black arrow in the figure is the steam flow direction.

[0062] A steam flow rate regulating unit is provided at the steam outlet end 403 of the main flow channel, such as Figure 4c , 4d As shown in the figure, the steam flow rate regulating unit includes: a steam flow rate regulating flap, an opening degree regulating mechanism arranged in the flexible communication hole 303, and a traction rope for realizing traction connection between the steam flow rate regulating flap and the flexible communication hole; wherein, an elastic opening degree regulating mechanism is arranged in each flexible communication hole 303, and the opening degree regulating mechanism includes a plurality of closing fans, and the plurality of closing fans are arranged in a lapping manner, so that the flexible communication hole forms a closed state in the static state; a cross-shaped or cross-shaped intersection is formed at the joint of the plurality of closing fans, and this intersection is used to adjust the opening degree of the flexible communication hole; at the same time, a plurality of the flexible communication holes are uniformly arranged in the upper middle part and the lower middle part of the inner tube side wall in the same longitudinal direction (a fixed distance from the heat exchange tube outlet end) perpendicular to the inner tube axis, excluding the bottom side wall (refer to Figure 4c the connection point of the traction rope in the figure, and the direction is fixed; it should be noted that Figure 4aThe flexible communication holes below the side wall of the inner tube are used to schematically show the connection relationship of the towing ropes on a plane, and the heat exchange tube turns to a fixed direction during the use of the evaporator); the flexible communication holes 303 communicate with the main flow channel, and a double-sealing structure is adopted at the connection between the flexible communication holes 303 and the inner tube 302 to ensure that steam leakage does not occur during the adjustment process; the steam flow rate adjusting flap is located in the inner cavity of the inner tube 302, and the top surface thereof is perpendicular to the steam flow direction in the main flow channel. The steam flow rate adjusting flap is connected to the flexible communication holes 303 through a plurality of towing ropes, and the opening degree adjusting mechanism is used to elastically control the opening degree of the intersection with the towing ropes; as a feasible implementation manner, in each flexible communication hole 303, on each closing fan at the intersection, an opening degree towing wire is connected, and a plurality of opening degree towing wires converge and are connected to one end of the towing rope, and the other end of the towing rope is fixedly connected to the steam flow rate adjusting flap at the corresponding position of the steam flow rate adjusting flap (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;.

[0063] The steam extraction and circulation unit 203 is fixedly connected to each effect evaporator of the steam treatment unit 202. The steam extraction and 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, the first bypass pipeline, the steam extraction pipeline, and the steam mixing pipeline form the steam extraction operation path of the steam treatment unit 202. Among them, the first bypass pipeline 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 one in the embodiment of the present application) along the steam inlet direction. A first steam extraction branch is connected to the first steam ejector, and a first steam extraction control valve is installed on the first steam extraction branch. The first temperature and pressure sensor is used to feedback 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 degree of the first steam extraction control valve based on the steam temperature and steam pressure parameters at the first steam control valve.

[0064] The seawater water distribution unit 204 is used for spraying seawater on the steam treatment unit 202.

[0065] The temperature reduction unit 205, one end of the temperature reduction unit 205 is connected to the outlet end of the condensate collection tank of the first effect evaporator, and the other end of the temperature reduction unit 205 is connected to the middle of the steam mixing pipeline.

[0066] In the embodiment of the present application, the area of the steam flow regulating flap 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 cycle unit 203 extracts steam, the increase in the steam flow in the main flow channel causes the steam flow regulating flap to displace along the steam flow direction, and the tilting angle at the lower part of the steam flow regulating flap increases. This displacement drives the opening regulating mechanism at the center of the flexible communication hole to generate a corresponding displacement through the traction rope, thereby increasing the opening of the flexible communication hole 303, so that most of the steam entering the heat exchange tube flows through the main flow channel to the intermediate-effect evaporator; 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 flap decreases (returns), and at the same time drives the opening regulating mechanism to displace less (return), so that the opening of the flexible communication hole 303 decreases accordingly, thereby reducing the amount of steam sucked from the auxiliary flow channel when the steam ejector of the steam extraction cycle unit 203 extracts steam, so that the steam can be fully heat-exchanged through the auxiliary flow channel. Here, when the change range of the steam flow received by the first-effect evaporator is small, the slight displacement generated by the steam flow regulating flap correspondingly will not change the opening of the flexible communication hole 303. It should be noted that considering the application cost, in this embodiment of the present application, only double-flow heat exchange tubes are used in the first-effect evaporator on site, and there is no limitation in actual implementation, and it can be extended to the intermediate-effect evaporator to adapt to a wider working range.

[0067] As a feasible implementation manner, refer to Figure 5a As shown, the number of flexible communication holes is 3, which are respectively located at the left end, right end and upper end of the tangential inner tube; refer to Figure 5b As shown, the number of flexible communication holes is 4, which are respectively located at the left end, right end, upper left end and upper right end symmetric to the upper left end of the tangential inner tube. As a feasible implementation manner, flexible lines crossing in a cross or a cross with a middle dot are arranged inside the flexible communication hole 303, and the traction rope is fixed in the middle of each line segment after crossing. When increasing the opening of the flexible communication hole, the traction rope drives the flexible line to generate a corresponding displacement, so that the flexible communication hole bulges forward, increasing the steam flow outlet. Among them, to reduce the influence of the resistance of steam regulation in the pipeline, the thicknesses of the steam flow regulating flap and the flexible line are controlled.

[0068] In the embodiment of the present application, the inner diameter of the main steam flow channel is d, and the inner diameter of the heat exchange tube bundle is D. The distance between every two adjacent fin segments needs to satisfy 0.5d to 1.5d; the fin height is 0 to (D - d) / 2: the ratio of the main flow channel to the auxiliary flow channel in terms of diameter is distributed between 1 and 4. Exemplarily, when the distance between two adjacent fin segments is close to 0.5d, the heat exchange effect of the auxiliary flow channel is better; in the case where the steam flow rate faced by the evaporator is mostly large, the distance between two adjacent fin segments is close to 1.5d, which is conducive to extracting steam into the main flow channel, and then entering the next-stage evaporator after mixing. Specific parameters can be designed / regulated according to actual situations.

[0069] In the embodiment of the present application, with reference to Figure 7 As shown, the height of the spiral fins (i.e., the spiral fins 402) in the auxiliary flow channel on the outer wall of the inner tube is the largest at the upper-middle part of the auxiliary flow channel (completely connected to the inner wall of the outer tube), and the smallest at the lower-middle part of the auxiliary flow channel (gradually separating from the inner wall of the outer tube more and more downward in the vertical direction). This enhances the overall stability of the heat exchange tube structure. At the same time, considering the pressure change and gravity influence during the steam flow process, the accumulation of condensate water at the bottom of the fins is avoided, thereby protecting the stress state of the heat exchange tube during application. The heat-exchanged condensate water is deposited at the bottom of the auxiliary flow channel under the influence of gravity distribution, and is collected and processed through a specific collection structure to avoid the deposition of condensate water inside the heat exchange tube. In the embodiment of the present application, the heat exchange tube can adopt a split assembly form for on-line splicing, and the overall penetration is achieved through internal and external rotating threads. A rubber O-ring is arranged on the thread sealing surface to prevent seawater from seeping into the inside of the heat exchange tube.

[0070] In the embodiment of the present application, an annular concave pipe section 401 is integrally provided at the outlet end of the inner tube 302 along the axial direction close to the steam outlet. The annular concave pipe section 401 is coaxially arranged with the inner tube 302. The annular concave pipe 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 both 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 annular concave pipe section is the same as the wall thickness of the inner tube. Exemplarily, with reference to Figure 6As shown in the figure, a pipe section protruding towards the axis of the inner pipe is coaxially arranged near the axial end 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. The diameter of the pipe section is smaller than that of the inner pipe. A one-way slider unit is arranged on the second inclined pipe wall 604. The one-way slider unit is arranged in a wedge-shaped space formed by the outer pipe wall corresponding to the second inclined pipe wall 604 on the second inclined pipe wall 604, and is used to prevent reverse flow of steam at the outlet position of the auxiliary flow channel when the ejector extracts steam.

[0071] As a feasible implementation manner, a sliding collar is arranged between the concave ring pipe section 401 and the outer wall. The sliding collar has an inner tapered hole. The sliding collar can slide axially along the concave ring pipe section between the first flared portion and the second flared portion. The sliding collar is used to unidirectionally block the reverse flow of steam in the auxiliary flow channel when the inner inclined surface of the inner tapered hole contacts the outer inclined surface of the second flared section.

[0072] As a feasible implementation manner, referring to Figure 6 As shown in the figure, the one-way slider unit here can be a sharp-angle circular cone structure. Its edge contact surfaces are parallel to the second inclined pipe wall 604 in the auxiliary flow channel and the inner wall of the outer pipe respectively. During the process of fluid diffusion to both sides when the fluid in the auxiliary flow channel passes through, and when the main flow channel extracts the steam in the auxiliary flow channel through the steam extraction circulation unit 203, the one-way slider unit slides reversely to close the flow channel, preventing reverse flow of steam at the outlet position of the auxiliary flow channel.

[0073] In the embodiment of the present application, the effect body evaporator further includes: a spray pipe, spray nozzles, a demister, a fresh water collection pipeline, a brine collection pipe, and a fresh water collection tank. Among them, the spray pipe bundle is arranged at the top inside the effect body evaporator. A plurality of heat exchange pipes are arranged in parallel below the spray pipe bundle. A plurality of spray nozzles are installed on the spray pipe bundle. The spray nozzles are evenly and symmetrically arranged on the spray pipe bundle. The bottom plane of the spray nozzles is parallel to the plane where the heat exchange pipes are arranged, ensuring that the incoming seawater is evenly distributed to the outer wall of the heat exchange pipe bundle through the spray nozzles. A gas-conducting membrane is arranged at the end plate at the end of the effect body evaporator. There is a certain interval between the end plate and the outlet pipe plate for the steam at the outlet end to perform return heat exchange when the steam flow rate cannot break through the gas-conducting membrane.

[0074] In the embodiment of the present application, the steam extraction cycle unit 203 further includes a second bypass pipeline, which is connected in parallel with the first bypass pipeline, 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 backup to each other; the second bypass pipeline 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. A second steam extraction branch is connected to the second steam ejector, and a second steam extraction control valve (steam extraction control valve two) is installed on the second steam extraction branch. The second temperature and pressure sensor is used to feedback 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 degree of the second steam extraction control valve based on the steam temperature and steam pressure parameters at the second steam control valve.

[0075] In the low-temperature multi-effect distillation seawater desalination system according to the embodiment of the present application, in view of the different steam flow rates received by the first-effect evaporator and their change conditions, the operation is adjusted by adjusting the displacement of the steam flow regulation flap of the steam flow regulation unit in the double-flow heat exchange tube bundle, so that the steam is sucked into the inner flow channel under high-flow conditions, and the remaining small amount of steam enters the auxiliary flow channel provided with spiral fins. The steam in the auxiliary flow channel is easily condensed and collected, reducing the steam temperature of the heat exchange tube bundle, realizing the efficient utilization of steam and heat energy recovery. At the same time, it can effectively prevent the outer wall of the heat exchange tubes of the first-effect evaporator from scaling due to the relatively unstable steam change conditions, and greatly reduce the scaling and cleaning difficulty of the first-effect heat exchange tube bundle.

[0076] Embodiment 2

[0077] Based on the foregoing embodiments, the embodiment of the present application provides a low-temperature multi-effect distillation seawater desalination system, in which a gas-permeable membrane can be used to isolate the current-effect evaporator when the heat exchange efficiency of the current-effect evaporator is relatively low, and open the reserved channel to enable the one-way conduction and transmission of the secondary steam to the next-effect evaporator in the isolated flow state.

[0078] In the embodiments of the present application, the working principles of the heat-conducting and air-permeable membrane in the normal multiple-effect operation state and the blocked flow state are as follows: 1) During the heat exchange process of the normal multiple-effect operation of the effect body evaporator (without the low-efficiency effect body evaporator), the secondary steam from the previous effect body evaporator first passes through the demister of the previous effect body evaporator to filter out the moisture and salts carried in the secondary steam, enters the first channel of the heat exchange tube bundle of the effect body evaporator where it is located (located at the lower part of the heat exchange tube bundle, accounting for 80-90% of the total amount of the heat exchange tube bundle), and is condensed after heat exchange. Part of the steam that is not fully condensed is blocked by the heat-conducting and air-permeable membrane of the support partition and turns back into 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 amount of the heat exchange tube bundle) for heat exchange and then condensation. The steam that still remains uncondensed will have its monitoring data fed back to the control device (control unit) by the balance sensor; the control device controls the recovery control valve, the steam extraction control valve, and enters the steam ejector to enter the first-effect body evaporator again with the motive steam, and conducts the cyclic waste heat recovery control process, so as to obtain the condensed water and secondary steam of the excess motive steam volume, effectively improving the water production ratio and water production of the low-temperature multiple-effect distillation seawater desalination system. Here, the heat exchange tubes in the first channel of the heat exchange tube bundle are all double-channel heat exchange tubes.

[0079] 2) In the blocked flow state (when there is at least one low-efficiency effect body evaporator in the steam treatment unit), the heat-conducting and air-permeable membrane of the support partition is in the open state. Furthermore, the secondary steam from the previous effect body evaporator first passes through the demister of the previous effect body evaporator to filter out the moisture and salts 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 degree of the recovery control valve of the next effect body evaporator according to the feedback data. At the same time, it closes the recovery control valve of the low-efficiency effect body evaporator where it is located, and under the action of the steam extraction control valve, increases the extraction amount of the secondary steam of the next effect body evaporator, so that it enters the steam ejector and enters the first-effect body evaporator again with the motive steam; so that the steam entering the first channel and the second channel of the heat exchange tube bundle of the low-efficiency effect body evaporator where it is located, under the negative pressure state of the steam extraction of the next effect body evaporator, directly enters the first channel of the heat exchange tube bundle of the next effect body evaporator through the open state of the heat-conducting and air-permeable membrane of the support partition for heat exchange and then condensation. Part of the steam that is not fully condensed is blocked by the heat-conducting and air-permeable membrane of the support partition and turns back into the second channel of the heat exchange tube bundle for repeated heat exchange and condensation process. Here, for the specific schematic diagrams of the first channel, the second channel of the heat exchange tube bundle and the distillation flow, please refer to the Chinese patent with the application number 202110349602.8.

[0080] In this way, by adjusting the operation based on the displacement of the steam flow regulating flap of the steam flow regulating unit in the double-flow heat exchange tube bundle, the steam is sucked into the inner flow path under high-flow conditions, and the remaining small amount of steam enters the auxiliary flow path provided with spiral fins inside. The steam in the auxiliary flow path is easily condensed and collected, and it will not cause the temperature of the first-effect evaporator to be too high and lead to scaling. The secondary steam and part of the primary steam after heat exchange and evaporation respectively enter the second-effect evaporator through the one-way conductive air film. At this time, the steam temperature is low and the salt content of the concentrated seawater is low, and the scaling phenomenon of the heat exchange tube bundle is fully alleviated.

[0081] Embodiment 3

[0082] Based on the foregoing embodiments, an embodiment of the present application provides a low-temperature multi-effect distillation seawater desalination system. Figure 8 The schematic plan view of the low-temperature multi-effect distillation seawater desalination system according to the embodiment of the present application is shown. Refer to Figure 8 As shown, the low-temperature multi-effect distillation seawater desalination system according to the embodiment of the present application includes a steam inlet control valve 1, a back pressure pipeline 25, a steam extraction pipeline 26, a bypass pipeline 1 27, a bypass pipeline 2 28, and a steam mixing pipeline 29. Among them, the steam inlet control valve 1 is connected to an external steam source through a steam inlet pipeline. The steam mixing pipeline 29 is in series with the steam inlet pipeline. The bypass pipeline 1 27 and the bypass pipeline 2 28 are connected in parallel with the back pressure pipeline 25. The end of the steam mixing pipeline 29 is connected to the heat exchange tube bundle of the first-effect evaporator (the first-effect evaporator 1). The output end of the first-effect evaporator is successively connected in series with multiple effect evaporators, and a balance sensor 16 is installed on each effect evaporator. The balance sensor 16 is used to monitor and feedback the internal environment data (temperature and pressure data of the secondary steam) of the corresponding effect evaporator in real time. The input end of the steam extraction pipeline 26 is independently connected to each effect evaporator, and a recovery control valve 15 is installed between each effect evaporator and the steam extraction pipeline 26. The output end of the steam extraction pipeline 26 is simultaneously connected to the bypass pipeline 1 27 and the bypass pipeline 2 28. Among them, the back pressure pipeline 25 and the steam mixing pipeline 29 form a back pressure operation path of the effect evaporator, and the bypass pipeline 1 27, the bypass pipeline 2 28, the steam extraction pipeline 26, and the steam mixing pipeline 29 form a steam extraction operation path of the effect evaporator. Valves and sensors for adjusting precision are installed on both the back pressure operation path and the steam extraction operation path, and the valves and sensors are controlled and connected to the control devices of the bypass pipeline 1 27 and the bypass pipeline 2 28.

[0083] Refer to Figure 8, a temperature and pressure sensor 17 is installed in the steam inlet direction of the first steam inlet control valve 2. The temperature and pressure sensor 17 is used to feedback the monitored pressure data of the steam system to the control device. The control device controls the load state of the seawater desalination system according to the data feedback by the temperature and pressure sensor 17 and automatically adjusts the opening degree of the first steam inlet control valve 2. A back pressure control valve 5 and a fourth temperature and pressure sensor 20 are sequentially installed on the back pressure pipeline 25 along the steam inlet direction. The fourth temperature and pressure sensor 20 feedbacks 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 degree of the back pressure control valve 5.

[0084] Referring to Figure 8 , a first bypass pipeline 27 is sequentially installed with a first steam control valve 3 (the first steam control valve), a second temperature and pressure sensor 18 (the first temperature and pressure sensor), and a first steam ejector 7 (the steam ejector) along the steam inlet direction. A first steam extraction branch is connected to the first steam ejector 7, and the first steam extraction branch is connected to the steam extraction pipeline 26. A first steam extraction control valve 13 is installed on the first steam extraction branch. The second temperature and pressure sensor 18 feedbacks the steam temperature and pressure parameters at the first steam control valve 3 to the control device. The control device assists in adjusting the opening degree of the first steam control valve 3 and controls the opening degree of the first steam extraction control valve 13 to control the steam extraction amount of the first steam ejector 7 from the steam extraction pipeline 26. In the embodiment of the present application, the second bypass pipeline 28 has the same structure and function as the first bypass pipeline 27, and the two bypass pipelines complement each other. The second bypass pipeline 28 is the same as the above-mentioned first bypass pipeline 27 and will not be described in detail here.

[0085] Taking the first bypass pipeline 27 as an example, a thermal expansion joint 6 is also installed on the first bypass pipeline 27. The thermal expansion joints 6 are respectively arranged at the steam inlet and outlet positions of the first steam ejector 7. The first bypass pipeline 27 also includes a first buffer branch, and the first buffer branch is connected in parallel with the thermal expansion joint 6. The first buffer branch is sequentially installed with a first bypass control valve 9 and a bypass sensor 21 along the steam inlet direction; the thermal expansion joint 6 can balance the pipeline expansion allowance caused by thermal expansion and contraction during the start-up or shutdown of the pipeline, and avoid long-term stress damage.

[0086] A vacuum breaker 11 is installed on the steam mixing pipeline 29. The vacuum breaker 11 is located at the inlet end of the first effect evaporator 1. The vacuum breaker 11 is regulated by the control device. When the first steam inlet control valve 2 is closed, it can quickly break the internal vacuum state of the low-temperature multi-effect seawater desalination system and restore it to atmospheric pressure. That is, during the shutdown of the seawater desalination system (when the first steam inlet control valve 2 is closed), the vacuum breaker 11 can quickly supply air to the steam mixing pipeline 29 to break the internal vacuum state of the low-temperature multi-effect seawater desalination system and restore the vacuum state to atmospheric pressure.

[0087] 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 incoming hot water is indirectly heated to hot water at 85-95 °C, and then enters the heat exchange tube bundle inside the first-effect evaporator 1 through the flash evaporation device 23. The steam generated after heat exchange with seawater enters the subsequent effect bodies as secondary steam. The condensed water enters the waste heat recovery unit through the inlet control valve 24 and is heat-exchanged with the indirect heat exchange device 22 again to be converted 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 output from the steam output (flash evaporation device 23) end of the waste heat recovery unit.

[0088] In the embodiment of the present application, the low-temperature multi-effect distillation seawater desalination system includes a waste heat recovery operation mode and a steam turbine operation mode based on the waste heat recovery unit for actual application selection; the steam turbine operation mode is the same as the system in Embodiment 1 above, and the steam turbine steam entering the system operates through the steam extraction circulation unit; in the waste heat recovery mode, refer to Figure 8 , Figure 9 As shown, the power steam pressure from the waste heat recovery unit is lower than 0.12 MPa, and the temperature is lower than 100 °C (85-90 °C) after vacuum extraction, and it can be directly connected to the steam inlet of the first-effect evaporator through the back pressure pipeline; when the power steam pressure from the waste heat recovery unit is between 0.12 MPa and 0.40 Mpa, the power steam operates in the system through the steam extraction circulation unit. During operation, the steam extraction circulation unit extracts the excess secondary steam and adds it to the first effect through the steam mixing pipeline; at the same time, through the steam flow distribution of the double-flow channel of the first effect or the double-flow channel heat exchange tubes of the first few effects, the steam temperature in the heat exchange tubes can be reduced to a certain extent.

[0089] Based on this, the low-temperature multi-effect distillation seawater desalination system in the embodiment of the present application can achieve comprehensive optimization of the power steam source and waste heat recovery, can adjust the heat source according to the power steam heat source state and the generator set state, and increases the flexibility of the system.

[0090] In the embodiment of the present application, a one-way conductive air-permeable membrane is provided at the end of the heat exchange tube bundle of each effect evaporator in the low-temperature multi-effect distillation seawater desalination system. The one-way conductive air-permeable membrane is in a closed state under normal operating conditions 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 where it is located is reduced, when the balance sensor and the control device of the subsequent effect evaporator of the effect evaporator where it is located perform steam extraction regulation through the recovery control valve, the one-way conductive air-permeable membrane of the low-efficiency effect evaporator where it is located is opened, the recovery control valve of the low-efficiency effect evaporator where it is located is closed, and the recovery control valve of the subsequent effect evaporator is opened wide. The steam extraction ability of the steam ejector is used to assist in extracting the secondary steam generated by the previous effect evaporator, so that part of the secondary steam bypasses the effect evaporator where it is located that cannot achieve efficient heat exchange, and the secondary steam is forced to enter the subsequent effect evaporator for repeated desalinated water production.

[0091] In the embodiment of the present application, during the normal heat exchange process of the effect evaporator (that is, when it is judged that the heat exchange efficiency of the effect evaporator where it is located does not decrease), 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 inside the heat exchange tube bundle of the effect evaporator where it is located for heat exchange and then condenses. Part of the secondary steam that is not fully condensed is blocked by the conductive air-permeable membrane and returns to the second channel inside the heat exchange tube bundle for heat exchange and then condenses. After the above treatment, the uncondensed secondary steam is fed back to the control device through the monitoring data of the balance sensor. The control device controls the recovery control valve, the steam extraction control valve 13, and the steam extraction control valve 14 of the effect evaporator where it is located so that they enter the steam ejector 7 and the steam ejector 8 respectively and enter the first effect evaporator again with the motive steam for the cyclic waste heat recovery control process.

[0092] In the embodiment of the present application, when the heat exchanger evaporator in the current effect is in a blocked flow state (that is, when it is determined that the heat transfer efficiency of the heat exchanger evaporator in the current effect is reduced), the secondary steam from the previous effect heat exchanger evaporator first passes through the demister of the previous effect heat exchanger evaporator to filter out the moisture and salts carried in the secondary steam. The monitoring data of the balance sensors corresponding to each effect heat exchanger evaporator are fed back to the control device, and the control device automatically controls the opening degree of the recovery control valve of the next effect heat exchanger evaporator according to the received monitoring data. At the same time, the recovery control valve of the heat exchanger evaporator in the current effect is closed, and under the combined action of the steam extraction control valve 13 and the steam extraction control valve 14, the extraction amount of the secondary steam of the next effect heat exchanger evaporator is increased, and it enters the steam ejector 1 7 and the steam ejector 2 8 respectively and then enters the internal part of the first effect heat exchanger evaporator again along with the motive steam; among them, the secondary steam entering the first channel and the second channel of the heat exchange tube bundle of the heat exchanger evaporator in the current effect, under the negative pressure state of the steam extraction of the next effect heat exchanger evaporator, directly enters the internal part of the first channel of the heat exchange tube bundle of the next effect heat exchanger evaporator through the gas-permeable membrane for heat exchange and then condenses. Part of the secondary steam that is not fully condensed is blocked by the gas-permeable membrane of the heat exchanger evaporator in this effect and turns back into the internal part of the second channel of the heat exchange tube bundle for repeated heat exchange and condensation process.

[0093] It should be noted that the steam extraction amount of the steam ejector 1 7 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 2 8 is jointly adjusted according to the steam extraction control valve 14 and the recovery control valve. The steam ejector 1 7 and the steam ejector 2 8 are used to extract the secondary steam of the heat exchanger evaporator in the current effect into the first effect heat exchanger evaporator, and to extract the secondary steam of the heat exchanger evaporator to promote the reflux of the concentrated brine flash tank and the product flash tank into the heat exchanger evaporator.

[0094] In this way, the present application utilizes the dual operation modes of the motive steam heat source state and the waste heat recovery flash evaporation system. The operation modes are flexible and diverse, and the heat source can be adjusted according to the motive steam heat source state and the generator set state, making the range of the operation power and efficiency adjustment modes of the system wider.

[0095] Embodiment 4

[0096] Based on the foregoing embodiments, the embodiment of the present application provides a method for desalinating seawater by low-temperature multi-effect distillation based on a double-flow channel heat exchange tube, including the following steps S801 to S803:

[0097] Step S801, the external heat source steam enters the first effect evaporator of the steam treatment unit through the steam inlet unit.

[0098] Step S802: When the steam flow rate received in the heat exchange tubes of the first-effect evaporator increases, gradually increase the opening degree of the flexible communication hole, so that when the steam ejector of the steam extraction cycle unit extracts steam, most of the steam entering the heat exchange tubes flows through the main flow path of each heat exchange tube and goes to the next intermediate-effect evaporator.

[0099] Step S803: When the steam flow rate received in the heat exchange tubes of the first-effect evaporator decreases, gradually decrease the flexible communication hole, so that when the steam ejector of the steam extraction cycle unit extracts steam, the steam entering the heat exchange tubes turns to flow through the auxiliary flow paths in each heat exchange tube for heat exchange; wherein, the main flow path and the auxiliary flow path are coaxially arranged, and the auxiliary flow path is provided with spiral fins that rotate at intervals.

[0100] Thus, it is possible to achieve an all-round optimization and improvement of the waste heat recovery of the seawater desalination system, thereby increasing the water production and the water production ratio of the seawater desalination system.

[0101] In particular, according to the embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, the embodiments of the present invention include a computer program product that includes a computer program carried on a computer-readable storage medium, and the computer program contains program codes for executing the methods shown in the flowcharts. In such an embodiment, the computer program can be downloaded and installed from the network through the 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.

[0102] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. The present application is not limited to the exact structures that have been described above and illustrated in the drawings, and it cannot be determined that the specific implementation of the present application is only limited to these descriptions. For those of ordinary skill in the technical field to which the present application belongs, without departing from the concept of the present application, various changes and deformations made should be regarded as belonging to the protection scope of the present application.

[0103] The flowcharts and block diagrams in the drawings illustrate the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the above-mentioned module, program segment, or part of code contains one or more executable instructions for implementing the specified logical function.

[0104] In several embodiments provided by 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 illustrative. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods. For example, 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 displayed or discussed coupling or direct coupling or communication connection between each other can be an indirect coupling or communication connection through some interfaces, modules, or units, and can be in electrical, mechanical, or other forms.

[0105] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit them. The present application is not limited to the exact structures already described and illustrated in the drawings, and it cannot be considered that the specific implementation of the present application is only limited to these descriptions. For those of ordinary skill in the technical field to which the present application belongs, without departing from the concept of the present application, various changes and deformations made should be regarded as belonging 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 backflow 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 a first steam ejector along the steam inlet direction, the first 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 also includes 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.

8. The low-temperature multi-effect distillation seawater desalination system according to claim 4, characterized in that: 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 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 motive steam, and allow the motive 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 channel is directly unidirectionally conducted to the next intermediate effect evaporator.

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