Method and system for vertical well salt discharge in moderate and severe saline-alkali land

Abstract

The application provides a method and system for vertical well salt discharge in moderate and severe saline-alkali land, which comprises arranging a plurality of vertical wells in a grid shape or along contour lines in a region to be treated, the depth of the vertical well is 3-10 m, and the distance from the terminal end of the vertical well to the top plate of a deep layer of salt water with a buried depth greater than 50 m is not less than 10 m; the inner diameter of the pipe body of the vertical well is 20-30 cm, the side wall is provided with water seepage holes with a pore size of 1-2 cm and a longitudinal spacing of 20 cm at the corresponding section of the shallow layer of salt water, and the bottom of the pipe body is provided with a filter component; a submersible pump is arranged in the shallow layer of salt water in the vertical well, shallow layer of salt water collected in the well is pumped out and discharged to a regional drainage network; a water level sensor is arranged in the shallow layer of salt water in the vertical well, and the water level sensor is signal-connected with an intelligent control system. The application is driven by a solar power supply system, and realizes green, automatic and efficient operation in a region without power grid coverage.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali land improvement and agricultural water conservancy engineering technology, specifically providing a method and system for vertical well desalination in moderately to severely saline-alkali land. Background Technology

[0002] The key driver of salinization in coastal saline-alkali land is shallow, highly mineralized groundwater. Through capillary action, groundwater carries salts continuously to the surface. After evaporation, the salts accumulate in the topsoil, severely inhibiting crop growth. Traditional remediation methods, such as open ditch drainage, require large land areas, are difficult to maintain, and are prone to siltation. While underground pipe drainage is more effective, it involves large-scale engineering, high investment costs, and is prone to failure in heavy clay soils.

[0003] Coastal saline-alkali land is an important reserve land resource in my country, but its improvement and utilization have long been constrained by high salinity. Moderate to severe saline-alkali land faces the following problems: (1) Strong surface accumulation of salt: strong evaporation causes the bottom salt to continuously accumulate to the surface with capillary water, forming salt crust; (2) Groundwater backflow of salt: the groundwater level is high (usually <1.5m) and the mineralization is high, so salt is very easy to return to the root soil under capillary action; (3) Limited effect of conventional measures: single drainage or covering methods often only treat the symptoms and not the root cause. The salt temporarily moves down after the rainy season or irrigation, but it will rise rapidly in the dry season, and the salt control effect is not lasting.

[0004] Therefore, there is an urgent need for a technology that is easy to construct, low in cost, and capable of "point-to-point" active and rapid pumping of shallow, highly mineralized groundwater to quickly lower the groundwater level in key areas and fundamentally block the upward flow of salt. Summary of the Invention

[0005] To address the aforementioned problems, in a first aspect, this invention provides a method for desalinating moderately to severely saline-alkali land using vertical wells, comprising: arranging multiple vertical wells in a grid pattern or along contour lines in the area to be treated; each vertical well having a tubular structure, a depth of 3-10m, and the distance between the end of the well and the top of a deep saline layer with a burial depth greater than 50m being no less than 10m; the inner diameter of each vertical well tube being 20-30cm, with seepage holes of 1-2cm in diameter and spaced 20cm longitudinally on the sidewalls corresponding to the shallow saline layer; and a filter component sealing the bottom of the tube; installing a submersible pump in the shallow saline layer area within the vertical well to extract the shallow saline water flowing into the well and discharge it into the regional drainage network; installing a water level sensor within the shallow saline layer of the vertical well, the water level sensor being connected to an intelligent control system; and after drainage, reducing the salt content of the 0-1m topsoil layer in the area to be treated to below 3g / kg, achieving a desalination rate ≥50%.

[0006] In one technical solution of the above-mentioned method for draining salt from vertical wells in moderately to severely saline-alkali land, a water pump is triggered to start when the shallow groundwater level is higher than the critical salt return depth of the coastal saline-alkali land, and the water pump is triggered to stop when the shallow groundwater level is lower than the safe root burial depth of the cultivated layer, so that the shallow groundwater level is stably controlled within the range of the critical salt return depth and the safe root burial depth; the critical salt return depth of the coastal saline-alkali land is 1-1.8m, and the safe root burial depth of the cultivated layer is 2.5-3.5m.

[0007] In one technical solution of the above-mentioned method for draining salt from moderately to severely saline-alkali land using vertical wells, the spacing between the vertical wells is 15-30m. By densely arranging the wells, a regional shallow groundwater level drawdown funnel is quickly formed in the area to be treated. The drawdown funnel covers the shallow saline water layer below the entire cultivated layer in the area to be treated, blocking the path of shallow saline water to migrate to the cultivated layer through capillary action.

[0008] In one technical solution of the above-mentioned method for draining salt from vertical wells in moderately to severely saline-alkali land, the outer side of the filter component is also covered with a bentonite waterproof blanket anti-capillary isolation layer with a thickness of 1-2 cm. The isolation layer is used to block the filter layer from caking caused by shallow saline water entering the filter component through capillary action, while allowing saline water to flow into the vertical well along the concentration gradient.

[0009] In one technical solution of the above-mentioned method for draining salt from vertical wells in moderately to severely saline-alkali land, the filter component consists of, from the inside out, a 0.5-1mm coarse sand layer, a 0.2-0.5mm medium sand layer, a 0.1-0.2mm fine sand layer, and a non-woven fabric layer with a titanium dioxide anti-aging coating sprayed on the outer surface of the fine sand layer.

[0010] In one technical solution of the above-mentioned method for desalination in moderately to severely saline-alkali land using vertical wells, when the porosity of the shallow soil is ≥40%, the thickness of the filter element is adjusted to 8-10cm, and the proportion of fine sand layer is ≥60%; when the porosity of the shallow soil is <40%, the thickness of the filter element is adjusted to 5-8cm, and the proportion of fine sand layer is ≥50%.

[0011] In one technical solution of the above-mentioned method for draining salt from vertical wells in moderately to severely saline-alkali land, the submersible pump and intelligent control system are driven by a solar power supply system; the solar power supply system includes solar panels, batteries and charge / discharge controllers, and is adapted to tidal flat areas in shallow coastal saline-alkali land without power grid coverage.

[0012] In one technical solution of the above-mentioned method for draining salt from vertical wells in moderately to severely saline-alkali land, the pipe body of the vertical well is made of PVC, HDPE or galvanized steel pipe, and the surface of the pipe body is coated with an anti-corrosion coating to resist the moderate corrosion of shallow saline water with a mineralization of 2-15 g / L.

[0013] In one technical solution of the above-mentioned method for draining salt from vertical wells in moderately to severely saline-alkali land, the seepage holes are arranged on the side wall of the vertical well pipe, with 3-4 seepage holes on the same cross-section, so that shallow saline water flows into the vertical well evenly from multiple directions; the water level response cycle of the intelligent control system is ≤1h, which is adapted to the characteristics of frequent water level fluctuations caused by precipitation and evaporation of shallow saline water, and realizes real-time dynamic control of shallow groundwater level.

[0014] Secondly, this invention provides a vertical well desalination system for moderately to severely saline-alkali land, comprising: a vertical well including a pipe body, seepage holes, and a filter component, with a well depth of 3-10m, wherein the termination end of the vertical well is at least 10m away from the top plate of a deep saline aquifer with a burial depth greater than 50m; the inner diameter of the vertical well pipe is 20-30cm, and seepage holes with a diameter of 1-2cm and a longitudinal spacing of 20cm are opened on the side wall in the corresponding section of the shallow saline aquifer; the bottom of the pipe body is sealed with a filter component; a pumping module is set in the shallow saline aquifer area within the vertical well; a water level monitoring and control module includes a water level sensor buried in the shallow saline aquifer and an intelligent control system; a drainage module is connected to the outlet of the pumping module for discharging the pumped shallow saline water; and an energy module is a solar power supply system adapted to scenarios where there is no power grid in shallow saline-alkali land.

[0015] The beneficial effects of the present invention are: (1) Precise and efficient: It directly targets shallow, highly mineralized groundwater for pumping and drainage, which can quickly and accurately lower the water level and curb the upward movement of salt from the source.

[0016] (2) Simple construction and low cost: Compared with underground pipe excavation, vertical shaft drilling is simpler, has less impact on field operations, and requires less pipe material, resulting in lower overall cost.

[0017] (3) Adaptive operation: The automatic control system based on the water level sensor can realize intelligent management according to the dynamics of groundwater, saving water and energy.

[0018] (4) Strong environmental adaptability: Solar power enables it to work stably in remote areas, and it is noiseless and pollution-free.

[0019] (5) Easy to maintain: A single shaft or water pump failure does not affect the operation of the entire system and is easy to repair and replace. Attached Figure Description

[0020] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Furthermore, similar numbers in the drawings are used to denote similar components, wherein: Figure 1 This is a schematic diagram of the structure of a vertical shaft pipe body according to an embodiment of the present invention; Figure 2This is a comparison diagram of groundwater level changes under the method of this invention and without any measures, according to an embodiment of the present invention. Detailed Implementation

[0021] Some embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0022] Example 1 This invention provides a method for draining salt from vertical wells in moderately to severely saline-alkali land, comprising the following steps: Step S1: In the area to be treated, multiple vertical shafts 1 are laid out in a grid pattern or along contour lines. The vertical shaft 1 is a tubular structure with a depth of 3-10m, and the distance between the end of the vertical shaft 1 and the top plate of the deep saline aquifer with a burial depth greater than 50m is not less than 10m. The inner diameter of the vertical shaft 1 is 20-30cm, and the side wall has seepage holes with a diameter of 1-2cm and a longitudinal spacing of 20cm in the corresponding section of the shallow saline aquifer. The bottom of the pipe is covered with a filter component.

[0023] In this embodiment, the layout of the shafts 1 can be flexibly selected according to the terrain of the area to be treated. A grid-like layout is suitable for flat areas with moderate to severe saline-alkali soil, with a grid spacing of 10-50m (the higher the degree of salinization, the smaller the spacing; for example, in extremely severe saline-alkali areas with a salt content >8g / kg, the spacing is 10-20m). A layout along contour lines is suitable for sloping saline-alkali areas, with a shaft spacing of 20-60m along the contour line direction and 15-40m perpendicular to the contour line direction, which can reduce the impact of soil erosion on the salt drainage effect. For the tubular structure of shaft 1, PVC pipes or corrosion-resistant cement pipes are preferred to be used to adapt to the high-salt and high-alkali soil environment of saline-alkali land. The well depth of 3-10m should be matched with the burial depth of the shallow saline water layer (for example, if the burial depth of the shallow saline water layer is 4m, the well depth should be 5-6m to ensure that the core area of ​​the shallow saline water layer is covered). The termination end should be set at least 10m away from the top plate of the deep saline water layer to avoid disturbing the deep saline water during the pumping process and causing secondary soil salinization.

[0024] The inner diameter of the vertical shaft pipe is 20-30cm, which can be adjusted according to the pumping flow rate: a 30cm inner diameter is selected for high-flow, rapid salt drainage, while a 20cm inner diameter is selected for low-flow, refined salt drainage. The seepage holes corresponding to the shallow saline water layer have a diameter of 1-2cm to effectively prevent soil particles from entering the pipe and causing blockage. The longitudinal spacing of 20cm ensures that the shallow saline water flows evenly from different heights within the pipe. Seepage holes can also be added at a circumferential spacing of 10-15cm to further improve seepage efficiency. The filter components can be a filter layer or a filter screen.

[0025] Step S2: Install a submersible pump 2 in the shallow saline water layer area inside the shaft 1 to pump out the shallow saline water flowing into the shaft and discharge it into the regional drainage network.

[0026] In this embodiment, the submersible pump 2 is adapted to the inner diameter of the vertical shaft 1 and the salt discharge requirements. It is selected as a salt-resistant and corrosion-resistant type with a flow rate of 1-5 m³ / h and a head of 8-15 m, which can be dynamically adjusted according to the water volume of the shallow saline layer. Before the pumped shallow saline water is discharged to the regional drainage network, a simple sedimentation tank with a volume of 1-2 m³ can be added to settle the silt in the water before discharge, so as to avoid clogging of the drainage network. The regional drainage network needs to be set with a drainage slope of ≥0.5% to ensure that the saline water is discharged smoothly from the treatment area and to prevent local water accumulation and salt backflow.

[0027] Step S3: Install a water level sensor in the shallow saline water layer inside the vertical shaft 1. The water level sensor is connected to the intelligent control system 3. After pumping, the salt content of the topsoil in the 0-1m layer of the area to be treated is reduced to below 3g / kg, and the desalination rate is ≥50%.

[0028] In this embodiment, the water level sensor in step S3 is a salt-resistant submersible level gauge with a measurement accuracy of ±1cm. Its deployment depth dynamically matches the water level of the shallow saline layer. Real-time water level data is transmitted to the intelligent control system 3 (such as a PLC control cabinet) via a 485 bus. The intelligent control system 3 can preset water level thresholds (e.g., when the shallow saline layer water level is lower than the lower edge of the seepage hole in the vertical well 1), automatically starting and stopping the submersible pump 2 to achieve unmanned intelligent pumping. The treatment target after pumping is that the salt content of the 0-1m topsoil layer is reduced to below 3g / kg, with a desalination rate ≥50%.

[0029] Of course, the specific implementation methods mentioned above are not limited to the situations listed above: the pipe of the vertical shaft 1 can also be made of fiberglass, which has better corrosion resistance; the diameter and spacing of the seepage holes can be adjusted according to the soil particle size; the submersible pump 2 can be equipped with a frequency conversion control module to dynamically adjust the pumping flow rate according to the water level; the water level sensor can also be paired with a salinity sensor to synchronously monitor the salinity of the saline water in the well.

[0030] In one embodiment, the water pump is triggered to start when the shallow groundwater level is higher than the critical salt return depth of the coastal saline-alkali land, and to stop when the shallow groundwater level is lower than the safe root burial depth of the cultivated layer, so that the shallow groundwater level is stably controlled within the range of the critical salt return depth and the safe root burial depth; the critical salt return depth of the coastal saline-alkali land is 1-1.8m, and the safe root burial depth of the cultivated layer is 2.5-3.5m.

[0031] In this embodiment, real-time monitoring of the shallow groundwater level is accomplished by a salt-resistant submersible water level sensor deployed in the shallow saline aquifer within shaft 1. When the shallow groundwater level in the coastal saline-alkali land rises to the 1-1.8m range, soil capillary action will transport the saline water upwards to the 0-1m topsoil layer, causing salinization in the topsoil. At this time, starting submersible pump 2 to pump out the saline water can quickly lower the groundwater level and block the salinization path. The specific value of the critical salinization depth can be adjusted according to the soil texture. For example, clay soils have strong capillary action and are prone to salinization, so the value is 1-1.3m; sandy soils have weak capillary action, so the value is 1.5-1.8m.

[0032] Maintaining the water level stably within the range of 1-1.8m to 2.5-3.5m prevents both excessively high water levels leading to salt backflow and excessively low water levels causing water shortages. The intelligent control system 3 can preset upper and lower water level thresholds (e.g., upper limit 1.5m, lower limit 3m), and, in conjunction with the submersible pump 2 using the variable frequency control module, achieves precise regulation: increasing the pumping flow rate when the water level approaches the upper limit and decreasing the flow rate when it approaches the lower limit, rather than directly starting and stopping the pump, reduces the wear and tear from frequent pump operations and improves water level stability.

[0033] Of course, the specific implementation methods mentioned above are not limited to the situations listed above: the critical salt return burial depth and the safe root burial depth can be dynamically adjusted in combination with annual precipitation and initial soil salinity; a 5-10 minute delay mechanism can be added to the water pump triggering logic to avoid frequent start-stop due to short-term water level fluctuations; the water level range can also be adjusted according to the crop growth stage (e.g., the root system is shallow during the seedling stage, so the safe root burial depth is 2.5-2.8m, and during the mature stage, it is 3-3.5m). Those skilled in the art can flexibly set the parameters according to the crops planted and soil conditions in coastal saline-alkali land.

[0034] In one embodiment, the vertical shafts 1 are spaced 15-30m apart, and the dense arrangement of shafts quickly forms a regional shallow groundwater level drawdown cone in the area to be treated; the drawdown cone covers the shallow saline water layer below the entire cultivated layer in the area to be treated, blocking the path of shallow saline water to migrate to the cultivated layer through capillary action.

[0035] In this embodiment, the spacing of the vertical shafts from 115 to 30 meters needs to be adapted to the degree of salinization of the area to be treated: for severely saline-alkali land, the spacing is 15 to 20 meters due to the high risk of salt return, and the formation speed of the sinkhole is accelerated by denser wells; for moderately saline-alkali land, the spacing is 20 to 30 meters, which reduces the engineering cost while ensuring the salt removal effect.

[0036] The sinkhole must completely cover the shallow saline water layer below the cultivated layer in the area to be treated. The lowest water level should be controlled within the safe root burial depth of the cultivated layer (2.5-3.5m) and the overall water level should be lower than the critical salt return burial depth of coastal saline-alkali land (1-1.8m).

[0037] Of course, the specific implementation methods mentioned above are not limited to the situations listed above: the spacing can be fine-tuned according to the soil texture. For example, in clay soils with strong capillary action and rapid salt return, the spacing is 15-20m; in sandy soils with weak capillary action, the spacing is 25-30m; the formation rate of the sinkhole can be adjusted by adjusting the pumping flow rate of submersible pump 2. For example, in severely saline-alkali land, the flow rate can be adjusted to 3-5m³ / h, and in moderately saline-alkali land, it can be adjusted to 1-3m³ / h to speed up or slow down the process; the coverage area of ​​the sinkhole can also be monitored in real time through a distributed water level sensor network. If a local area is not covered, a mobile vertical shaft 1 can be temporarily added for supplementary drainage.

[0038] In one embodiment, the outer side of the filter element is also covered with a bentonite waterproof blanket anti-capillary barrier layer with a thickness of 1-2 cm. The barrier layer is used to prevent shallow saline water from entering the filter element through capillary action and causing filter layer caking, while allowing saline water to flow into the vertical well 1 along the concentration gradient.

[0039] In this embodiment, clay soil has strong capillary action, which easily carries fine soil particles to penetrate, so a 2cm thick waterproof blanket is selected to enhance the isolation effect; sandy soil has weak capillary action, so a 1cm thick blanket is sufficient, ensuring the isolation effect while reducing resistance to the inflow of saline water. The waterproof blanket uses sodium-based bentonite as the core filler, with an outer composite non-woven / woven fabric as the protective layer.

[0040] Of course, the specific implementation methods mentioned above are not limited to the situations listed above: the bentonite waterproof blanket can be replaced with a polymer composite anti-capillary membrane with a thickness of 0.8-1.5mm, which is suitable for extremely high salt and high alkalinity soil environments; the thickness of the isolation layer can be adjusted according to the soil salinity (e.g., 2cm for extremely severely saline-alkali land with a salinity of >10g / kg, and 1.5cm for severely saline-alkali land with a salinity of 5-10g / kg); stainless steel buckles can also be added to the seams of the covering to further improve the sealing performance.

[0041] In one embodiment, the filter element consists of, from the inside out, a 0.5-1mm coarse sand layer, a 0.2-0.5mm medium sand layer, a 0.1-0.2mm fine sand layer, and a non-woven fabric layer with a titanium dioxide anti-aging coating sprayed on the outer surface of the fine sand layer.

[0042] In one embodiment, when the porosity of the shallow soil is ≥40%, the thickness of the filter element is adjusted to 8-10cm, and the proportion of the fine sand layer is ≥60%; when the porosity of the shallow soil is <40%, the thickness of the filter element is adjusted to 5-8cm, and the proportion of the fine sand layer is ≥50%.

[0043] In one embodiment, the submersible pump 2 and the intelligent control system 3 are driven by a solar power supply system 4; the solar power supply system 4 includes solar panels, batteries and charge / discharge controllers, and is adapted to shallow coastal saline-alkali tidal flats without power grid coverage.

[0044] In one embodiment, the pipe body of the shaft 1 is made of PVC, HDPE or galvanized steel pipe, and the surface of the pipe body is coated with an anti-corrosion coating to resist the moderate corrosion of shallow saline water with a mineralization of 2-15 g / L.

[0045] In one embodiment, the seepage holes are arranged on the side wall of the shaft 1 pipe body, and the number of seepage holes on the same cross section is 3-4, so that shallow saline water flows into the shaft 1 evenly from multiple directions. The intelligent control system 3 has a water level response cycle of ≤1h, which is adapted to the characteristics of shallow saline water where water level fluctuates frequently due to precipitation and evaporation, and realizes real-time dynamic control of shallow groundwater level.

[0046] Example 2 This invention provides a vertical well desalination system for moderately to severely saline-alkali land, comprising: a vertical well 1 including a pipe body, seepage holes, and a filter component, with a well depth of 3-10m, wherein the termination end of the vertical well 1 is at least 10m away from the top plate of a deep saline aquifer with a burial depth greater than 50m; the inner diameter of the pipe body of the vertical well 1 is 20-30cm, and seepage holes with a diameter of 1-2cm and a longitudinal spacing of 20cm are opened on the side wall in the corresponding section of the shallow saline aquifer; the bottom of the pipe body is sealed with a filter component; a pumping module is set in the shallow saline aquifer area within the vertical well 1; a water level monitoring and control module includes a water level sensor buried in the shallow saline aquifer and an intelligent control system 3; a drainage module is connected to the outlet of the pumping module for discharging the pumped shallow saline water; and an energy module is a solar power supply system 4, adapted to scenarios where there is no power grid in shallow saline-alkali land.

[0047] Furthermore, the side wall of the shaft 1 is provided with several seepage holes 5; the outside of the seepage holes 5 is covered with a filter material layer 6, which is used to block soil particles from entering the shaft and prevent the seepage holes from becoming blocked.

[0048] Reference Figure 1 and Figure 2 This embodiment was implemented in a heavily saline-alkali area along the coast of Jiangsu Province. The groundwater level in this area is 0.6-1.0 meters deep, and the groundwater salinity is 15 g / L.

[0049] The vertical well salt removal system of the present invention includes: A PVC pipe with an inner diameter of 25cm and a length of 1.5 meters is used. 1.5cm diameter holes are drilled every 20cm from top to bottom on the side wall of the pipe as drainage holes. The bottom of the pipe is sealed with a 100-mesh nylon filter screen and secured with clamps.

[0050] A small submersible pump 2 with a power of 0.75KW and a flow rate of 5 m³ / h is placed at the bottom of the vertical shaft 1.

[0051] Water level monitoring and control module: includes a water level sensor and an intelligent controller. The controller has a preset water level threshold of 0.8 meters from the ground surface (meaning the groundwater level must be controlled below 80 cm).

[0052] Drainage module: DN50 PE hose is used to lead the pumped water to the open drainage ditch at the edge of the field.

[0053] Energy module: consists of a 0.4KW solar panel, a 100Ah battery pack and a charge / discharge controller.

[0054] The implementation steps are as follows: Step 1: Use a drilling rig to drill holes with a diameter of 30cm and a depth of 1.5m at the planned points (20m apart); Step 2: Vertically place the assembled shaft 1 into the hole, and backfill the space between shaft 1 and the hole wall with coarse sand as a filter layer; Step 3: Place the submersible pump 2 and water level sensor at the bottom of the well, and connect the drain pipe and circuit. Step 4: Install solar panels and smart controller, and complete system debugging; Step 5: Automatic System Operation: When the water level exceeds -0.8 meters (below the ground surface), the water pump automatically starts pumping water; when the water level drops to -1.0 meters, the water pump stops. After three months of operation and observation, in the area where the method of this invention was implemented, the groundwater level remained stable at less than 2.0 meters below the surface, and the salinity of the topsoil layer (0-20cm) decreased from 0.7% to 0.3%. In contrast, in the control area (without measures), the groundwater level could rise to 0.5 meters in sunny weather with strong evaporation, and the salinity of the topsoil layer remained above 0.6%. Figure 2 The method of the present invention clearly demonstrates that it can effectively maintain groundwater at a low level.

[0055] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the original technical features, and the technical solutions resulting from these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for draining salt from vertical wells in moderately to severely saline-alkali land, characterized in that, include: Multiple vertical shafts are laid out in a grid pattern or along contour lines in the area to be treated. The vertical shafts are tubular structures with a depth of 3-10m, and the distance between the end of the vertical shaft and the top of the deep saline aquifer with a burial depth greater than 50m is not less than 10m. The inner diameter of the vertical shaft pipe is 20-30cm, and the sidewalls have seepage holes with a diameter of 1-2cm and a longitudinal spacing of 20cm in the corresponding section of the shallow saline aquifer. The bottom of the pipe is covered with a filter component. Submersible pumps are installed in the shallow saline water layer area inside the vertical shaft to extract the shallow saline water flowing into the shaft and discharge it into the regional drainage network. A water level sensor is installed in the shallow saline aquifer inside the vertical shaft, and the water level sensor is connected to the intelligent control system. After pumping, the salinity of the topsoil layer (0-1m) in the area to be treated is reduced to below 3g / kg, with a desalination rate of ≥50%. When the shallow groundwater level is higher than the critical salt return depth of the coastal saline-alkali land, the water pump is triggered to start. When the shallow groundwater level is lower than the safe root burial depth of the cultivated layer, the water pump is triggered to stop, so that the shallow groundwater level is stably controlled within the range of critical salt return depth and safe root burial depth. The critical salinization depth of the coastal saline-alkali land is 1-1.8m, and the safe burial depth of the cultivated root system is 2.5-3.5m. The vertical shafts are spaced 15-30m apart, and the dense arrangement of shafts quickly forms a regional shallow groundwater level drawdown funnel in the area to be treated. The drop funnel covers the shallow saline water layer below the entire cultivated layer in the area to be treated, blocking the path of shallow saline water to migrate to the cultivated layer through capillary action. The outer side of the filter element is also covered with a bentonite waterproof blanket anti-capillary isolation layer with a thickness of 1-2 cm. The isolation layer is used to prevent shallow saline water from entering the filter element through capillary action and causing filter layer caking, while allowing saline water to flow into the vertical well along the concentration gradient.

2. The method according to claim 1, characterized in that, The filter element consists of, from the inside out, a 0.5-1mm coarse sand layer, a 0.2-0.5mm medium sand layer, a 0.1-0.2mm fine sand layer, and a non-woven fabric layer with a titanium dioxide anti-aging coating sprayed on the outer surface of the fine sand layer.

3. The method according to claim 2, characterized in that, When the porosity of the shallow soil is ≥40%, the thickness of the filter element is adjusted to 8-10cm, and the proportion of fine sand layer is ≥60%; when the porosity of the shallow soil is <40%, the thickness of the filter element is adjusted to 5-8cm, and the proportion of fine sand layer is ≥50%.

4. The method according to claim 1, characterized in that, The submersible pump and intelligent control system are driven by a solar power system, which includes solar panels, batteries and charge / discharge controllers, and is suitable for shallow coastal saline-alkali tidal flats without power grid coverage.

5. The method according to claim 1, characterized in that, The shaft is made of PVC, HDPE or galvanized steel pipe, and the surface of the pipe is coated with an anti-corrosion coating to resist the moderate corrosion of shallow saline water with a mineralization of 2-15 g / L.

6. The method according to claim 1, characterized in that, The seepage holes are arranged on the side wall of the vertical shaft pipe, with 3-4 seepage holes on the same cross section, so that shallow saline water flows into the vertical shaft evenly from multiple directions. The intelligent control system has a water level response cycle of ≤1h, which is suitable for the frequent water level fluctuations of shallow saline water affected by precipitation and evaporation, and realizes real-time dynamic control of shallow groundwater level.

7. A vertical well desalination system for moderately to severely saline-alkali land, characterized in that, include: The vertical shaft includes a pipe body, seepage holes, and a filter component. The shaft depth is 3-10m. The distance between the end of the vertical shaft and the top plate of the deep saline aquifer with a burial depth greater than 50m is not less than 10m. The inner diameter of the vertical shaft pipe is 20-30cm. Seepage holes with a diameter of 1-2cm and a longitudinal spacing of 20cm are opened on the side wall in the corresponding section of the shallow saline aquifer. The bottom of the pipe body is covered with a filter component. The pumping module is installed in the shallow saline water layer area inside the vertical shaft; The water level monitoring and control module includes a water level sensor buried in a shallow saline layer and an intelligent control system. The drainage module is connected to the outlet of the pumping module and is used to discharge the pumped shallow saline water. The energy module is designed for solar power systems and is suitable for shallow saline-alkali land without power grids. When the shallow groundwater level is higher than the critical salt return depth of the coastal saline-alkali land, the water pump is triggered to start. When the shallow groundwater level is lower than the safe root burial depth of the cultivated layer, the water pump is triggered to stop, so that the shallow groundwater level is stably controlled within the range of critical salt return depth and safe root burial depth. The critical salinization depth of the coastal saline-alkali land is 1-1.8m, and the safe burial depth of the cultivated root system is 2.5-3.5m. The vertical shafts are spaced 15-30m apart, and the dense arrangement of shafts quickly forms a regional shallow groundwater level drawdown funnel in the area to be treated. The drop funnel covers the shallow saline water layer below the entire cultivated layer in the area to be treated, blocking the path of shallow saline water to migrate to the cultivated layer through capillary action. The outer side of the filter element is also covered with a bentonite waterproof blanket anti-capillary isolation layer with a thickness of 1-2 cm. The isolation layer is used to prevent shallow saline water from entering the filter element through capillary action and causing filter layer caking, while allowing saline water to flow into the vertical well along the concentration gradient.

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