CN108990452A - A kind of replacement of coupling water table aquifer salt-fresh water and Leaching and desalinization device - Google Patents

Abstract

The invention discloses a salty and fresh water replacement and leaching desalination device coupled with a submarine layer, which comprises a field desalination component, a brine treatment component and a rainwater collection wetland. Field desalination components include several desalination units, water inlet parts and drainage parts, each desalination unit includes desalination unit outline, water inlet branch parts and partition partitions; brine treatment components include sedimentation tanks, overflow weirs, ecological corridors and filtration Pipes; rainwater collection wetlands include impermeable layers, sumps, distribution wells, perforated connecting pipes and porous media for water storage. On the one hand, the present invention changes the groundwater in saline-alkali land, and gradually desalinizes the groundwater through several cycles; The rainwater added to the circulation of the underground aquifer, thus fundamentally solve the desalination problem of coastal saline-alkali land.

Description

A device for replacing brackish and fresh water and leaching and desalting in coupled aquifers

technical field

The invention relates to the field of saline-alkali land irrigation, in particular to a device for replacing salty and fresh water in a submerged layer and leaching and desalting.

Background technique

Coastal tidal flats are an important reserve land resource in our country and an effective measure to solve the contradiction between man and land in our country.

The biggest limiting factor for the development of coastal tidal flats is the severe salinization of the land, which makes it difficult to realize large-scale reclamation and planting and other agricultural activities. The main cause of land salinization is serious groundwater salinization, specifically as follows.

1. When the rainy season comes, the underground phreatic water level rises, bringing salt water to the soil surface. When the phreatic water level drops, the salt will be adsorbed on solid particles and stay in the soil.

2. Evaporation of the land surface intensifies the loss of water on the soil surface, resulting in more serious salt analysis, which remains on the land surface.

3. Capillary salt return is also a cause of land salinization that cannot be ignored.

Through the above analysis, the main problem of land salinization is serious soil phreatic salinization. How to reduce the degree of soil phreatic salinization will fundamentally solve the desalination problem of coastal saline-alkali land.

Contents of the invention

The technical problem to be solved by the present invention is to provide a coupling submerged layer salty and fresh water replacement and leaching desalination device for the above-mentioned deficiencies in the prior art. The groundwater in the alkaline land is changed, and the groundwater is gradually desalinated through several cycles; on the other hand, the method of brackish water and rainwater irrigation is used, which not only saves the precious freshwater resources in the coastal area, but also makes full use of the collected rainwater to add to the underground water. In the circulation of layers, thus, fundamentally solve the desalination problem of coastal saline-alkali land.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A device for replacing salty and fresh water in a coupled aquifer and leaching and desalting, including a field desalination component, a brine treatment component and a rainwater collection wetland.

Field desalination components include several desalination units, water inlet components and drainage components.

The number of desalination units is equal to the number of field plots, and each desalination unit includes a desalination unit profile, water inlet branch parts and partition partitions; wherein, the desalination unit profile is the profile of the corresponding field plot, including the horizontal profile and vertical profile. contour.

The water inlet components include the main water inlet canal, the water inlet branch canal, the fresh water pump and several in-situ pumping wells.

The water inlet branch components include water inlet pipes, brackish water pumps, constant head wells and water intake gates.

Drainage components include main drainage canals, branch drainage canals and hidden salt drainage pipes.

The arrangement direction of the salt discharge buried pipe is parallel to the direction of the water inlet pipe, and each salt discharge buried pipe is equidistantly buried within the range of 0.8m-1.2m underground of the lateral outline of the desalination unit.

The water inlet pipe is arranged on the surface of the field plot in the middle of the two adjacent salt discharge hidden pipes, and the water inlet end of the water inlet pipe is connected with the in-situ pumping well through the brackish water pump.

The in-situ pumping wells are set at the middle junction of two adjacent desalination units on the left and right, and are located on the axis of the corresponding inlet branch canals. Fresh water lift pump.

On the surface of the field plot between the two adjacent salt drainage pipes, with the drainage pipe as the center, several partition partitions are equidistantly arranged.

The height of the partition partition gradually decreases from the side of the water inlet pipe to both ends, and the maximum height of the partition partition is not higher than the height of the outline of the desalination unit.

The drainage branch canal is perpendicular to the salt drainage pipe, and is adjacent to the vertical profile of the desalination unit away from the in-situ pumping well; one end of each salt drainage pipe is connected to the drainage branch canal, and the other end is closed; each drainage branch canal Both are connected to the main drainage canal.

Dingshuitou wells are equidistantly arranged on the central axis of the drainage branch canal, and the bottom of Dingshuitou wells runs through the underground water layer of the entire field plot.

The brine treatment components include sedimentation tank, overflow weir, ecological corridor and filter pipe; the outlet end of the main drainage channel extends into the sedimentation tank, the overflow weir is set in the middle and upper part of the sedimentation tank on the side of the ecological corridor, and one end of the filter pipe is connected to the ecological corridor. The permeable layers of the corridors are connected, and the filter pipes are filled with filter particles.

The rainwater collection wetland includes an impermeable layer, a sump, a water distribution well, a perforated connecting pipe, and a porous medium for water storage; The anti-seepage geomembrane is laid; the water distribution wells are evenly arranged in the water storage porous medium, one end of the perforated connecting pipe is connected with the water outlet end of the filter pipe, the middle part of the perforated connecting pipe is connected with all the water distribution wells, and the tail end of the perforated connecting pipe is connected with the collection The pools are connected; the sump is connected with the water inlet end of the water inlet main canal.

The water distribution well is also communicated with each constant head water well in the desalination unit through a communication pipe.

A salinity sensor is set on the overflow weir, and a salt discharge hole is set on the sedimentation tank.

The outlet end of the main drainage channel is provided with a flow rate control pump.

From top to bottom, the field plot includes humus layer, mixed layer and original soil layer. The mixed layer is a mixture of admixture and surface saline-alkali soil.

The admixture is sand, gravel and sawdust, and the admixture is evenly mixed with the surface saline-alkali soil by means of deep plowing; the humus layer includes straw and sawdust.

Tidal flat plants are planted on the water storage porous medium.

The diameter of the hidden salt drainage pipe is 15-25cm, and a circle of gravel is laid around the hidden salt drainage pipe.

Each desalination unit is equipped with five constant head wells, the top elevation of the constant head wells is 50-100cm lower than that of the distribution wells, and valves are installed on the connecting pipes connecting the constant head wells and the distribution wells.

On the surface of the field plot between two adjacent salt drainage pipes, six partition partitions are arranged equidistantly. The six partition partitions are symmetrically distributed on both sides of the water inlet pipe, and the three partition partitions located on one side of the water inlet pipe The boards are counted from the side of the water inlet pipe, and the heights are 15cm, 10cm and 5cm respectively.

A gravel filter layer is laid at the bottom of the ecological corridor, and salt-resistant plants are planted on the gravel filter layer.

The present invention has following beneficial effects:

1. Desalination of saline-alkali land by using in-situ brackish underground water in saline-alkali land not only saves precious underground freshwater resources in coastal areas, but also produces a good salt washing effect and saves investment in fresh water pipelines.

2. While the in-situ pumping well pumps groundwater to desalinate the saline-alkali land, the fixed-head well is used to supplement fresh water to the underground aquifer, and the water exchange treatment of the underground aquifer is completed with high efficiency, reducing the salinity of the groundwater in the saline-alkali land, and fundamentally solving the problem Groundwater backsalt and surface soil salt accumulation.

3. Adopt brackish water and rainwater wheel irrigation to improve the desalination efficiency of saline-alkali land.

4. The fresh water supplemented by the Dingshuitou well is rainwater collected from tidal flats, which effectively saves groundwater and fresh water resources in coastal areas.

5. The surface of the desalinated saline-alkali land adopts the method of partition irrigation, forming a large driving water head inside the saline-alkali land, and forming a small driving water head near the position of the salt discharge hidden pipe, which improves the desalination efficiency of the saline-alkali land.

6. Add admixture to the surface of the soil layer, and do deep plowing and uniform treatment to increase the permeability coefficient of the surface soil, increase the desalination efficiency, and provide carbon sources and humus for later planting.

7. After the desalination canal system completes the desalination task, the field plot can also be used as an irrigation and drainage system for the farmland during the later planting process, which can satisfy the irrigation and drainage of the farmland, and also realize the recycling of the irrigation water in the coastal area, increasing the Irrigation water use efficiency.

8. This design also has a numerical simulation result, which proves that the salinity of underground water can be effectively reduced by exchanging brackish and fresh water.

Description of drawings

Fig. 1 shows a structural schematic diagram of a device for replacing salty and fresh water in a submerged layer and leaching and desalting in accordance with the present invention.

Fig. 2 shows a schematic cross-section A-A in Fig. 1 .

Fig. 3 shows a schematic cross-sectional view of B-B in Fig. 1 .

Figure 4 shows an enlarged schematic view of two adjacent desalination units.

Fig. 5 shows a schematic diagram of the M-M section in Fig. 4 .

Figure 6 shows a schematic diagram of the layout of constant head wells.

Figure 7 shows the isoline change map of the concentration field of the aquifer during the brackish-fresh water replacement process of the aquifer.

Figure 8 shows the isoline change map of the groundwater salinity field 2m below the surface.

Including:

10. Desalination unit;

11. Desalination unit profile;

121. Inlet main canal; 122. Inlet branch canal; 123. Fresh water pump; 124. In-situ pumping well; 125. Brackish water pump; 126. Inlet pipe;

13. Partition partition;

141. Drainage main canal; 142. Drainage branch canal; 143. Salt drainage pipe; 144. Gravel layer;

15. Field plot; 151. Humus layer; 152. Mixed layer; 153. Original soil layer;

21. Sedimentation tank; 211. Flow rate control pump; 212. Salt discharge hole;

22. Overflow weir; 23. Ecological corridor; 231. Gravel filter layer; 24. Filter pipe;

30. Rainwater harvesting wetlands;

31. Impermeable layer; 32. Collecting pool; 33. Water distribution well; 34. Perforated connecting pipe; 35. Porous medium for water storage;

40. Ground elevation.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific preferred embodiments.

As shown in FIG. 1 , a coupled aquifer salty and fresh water replacement and leaching desalination device, that is, an irrigation and drainage system, includes a field desalination component, a brine treatment component and a rainwater collection wetland 30 .

The field desalination assembly includes several desalination units 10, water inlet components and drainage components.

The number of desalination units is equal to the number of field plots. In Figure 1, the field desalination components include several desalination units in the horizontal and vertical directions, as shown in bold black boxes. In this application, the horizontal direction is also referred to as the left-right direction, and the vertical direction is also referred to as the longitudinal direction or the front-rear direction.

Each desalination unit comprises a desalination unit profile 11 , an inlet branch part and partition partitions 13 .

The outline of the desalination unit is the outline corresponding to the field plot, including the horizontal outline and the vertical outline.

As shown in FIG. 1 and FIG. 4 , the water inlet components include a main water inlet channel 121 , a water inlet branch channel 122 , a fresh water pump 123 and several in-situ pumping wells 124 .

The drainage components include a main drainage channel 141 , a branch drainage channel 142 and an underground salt discharge pipe 143 .

The arrangement direction of the salt discharge buried pipe is parallel to the direction of the water inlet pipe, and each salt discharge buried pipe is equidistantly buried within the range of 0.8m-1.2m underground of the lateral outline of the desalination unit. Each hidden salt discharge pipe runs through two adjacent field plots, that is, two adjacent field plots share a set of salt discharge concealed pipes.

The diameter of the hidden salt drainage pipe is preferably 15-25 cm, and a circle of crushed stone layer 144 as shown in FIG. 5 is preferably laid around the hidden salt drainage pipe. The role of the gravel layer is to speed up the drainage efficiency and prevent the blockage of the salt drainage pipe.

As shown in FIG. 1 and FIG. 4 , the water inlet branch components include a water inlet pipe 126 , a brackish water pump 125 , a constant head well 127 and a water intake gate 128 .

The water inlet pipe is arranged on the surface of the field plot in the middle of the two adjacent salt discharge concealed pipes, and is parallel to the salt discharge concealed pipe; the water inlet end of the water inlet pipe is connected to the in-situ pumping well through a brackish water pump.

The in-situ pumping wells are set at the middle junction of two adjacent desalination units on the left and right, and are located on the axis of the corresponding inlet branch canals. The fresh water pump, that is, the two desalination units share one in-situ pumping well, so as to ensure that it can provide flood irrigation water for the left and right desalination units.

On the surface of the field plot between two adjacent salt-discharging concealed pipes at the front and back, several partition partitions 13 are equidistantly arranged with the drainage pipe as the center.

The height of the partition partition gradually decreases from the side of the water inlet pipe to both ends, and the maximum height of the partition partition is not higher than the height of the outline of the desalination unit.

As shown in Figure 5, on the surface of the field plot between two adjacent salt drainage pipes, it is preferable to equidistantly arrange six partition partitions, and the six partition partitions are symmetrically distributed on both sides of the water inlet pipe. The three partition partitions on one side of the water pipe are counted from the side of the water inlet pipe, and the heights are 15cm, 10cm and 5cm respectively.

The setting of partition partitions can adopt the method of partition irrigation and salt discharge, that is, the middle part of the two salt discharge hidden pipes is irrigated first, and then gradually expands to both sides through overflow, and finally the entire surface of the desalinated land has complete water storage . According to the arrangement of the present invention, the surface of the desalinated land is divided into three different water level zones through partition partitions, and the water levels from the inside to both sides are 15cm, 10cm, and 5cm in sequence.

The drainage branch canal is perpendicular to the salt drainage pipe, and is adjacent to the vertical profile of the desalination unit away from the in-situ pumping well; one end of each salt drainage pipe is connected to the drainage branch canal, and the other end is closed; each drainage branch canal Both are connected to the main drainage canal.

Each desalination unit is preferably equipped with five constant head wells, which are equidistantly arranged on the central axis of the drainage branch canal, and the bottom of the constant head wells are connected to the underground water layer of the field plot.

As shown in FIG. 5 , the field plot preferably includes a humus layer 151 , a mixed layer 152 and an original soil layer 153 from top to bottom, and the mixed layer is preferably a mixture of admixture and surface saline-alkali soil. Cover straw to provide carbon source and reduce soil evaporation.

The admixture is preferably sand, gravel and sawdust, etc., and the admixture is preferably mixed evenly with the surface saline-alkali soil by means of deep plowing; the humus layer preferably includes straw and sawdust. The addition of admixtures is to improve the permeability of topsoil and provide carbon source.

The brine treatment component includes a sedimentation tank 21 , an overflow weir 22 , an ecological corridor 23 and a filter pipe 24 .

The water outlet end of the main drainage canal extends into the sedimentation tank, and the water outlet end of the main drainage canal is preferably provided with a flow rate control pump 211 .

As shown in Figure 2, the overflow weir is set in the middle and upper part of the sedimentation tank located on the side of the ecological corridor, the overflow weir is preferably provided with a salinity sensor, and the sedimentation tank is provided with a salt discharge hole 212.

As shown in FIG. 3 , a gravel filter layer 231 is preferably laid on the bottom of the ecological corridor, and salt-resistant plants are preferably planted on the gravel filter layer.

One end of the filter pipe is connected with the seepage layer of the ecological corridor, and the filter pipe is filled with filter particles.

The rainwater collection wetland includes an impermeable layer 31 , a sump 32 , a water distribution well 33 , a perforated connecting pipe 34 and a water storage porous medium 35 . The impermeable layer is laid underground in the excavation, the water storage porous medium is laid above the water impermeable layer, and an anti-seepage geomembrane is laid around the water storage porous medium, and tidal flat plants are planted on the water storage porous medium.

The water distribution wells are evenly arranged in the water storage porous medium, one end of the perforated connecting pipe is connected with the water outlet end of the filter pipe, the middle part of the perforated connecting pipe is connected with all the water distribution wells, and the tail end of the perforated connecting pipe is connected with the sump; The water inlet end of the main water inlet channel is connected.

As shown in Figure 6, the water distribution well is also connected to each constant head water well in the desalination unit through a connecting pipe. Valves are preferably arranged on the communicating pipes between them.

A tidal flat desalination method coupled with water circulation, comprising the following steps.

Step 1, layout of irrigation and drainage system and desalination unit: According to the topography and landform of coastal saline-alkali land, it is assumed that the direction parallel to the sea boundary is the horizontal direction, and the direction perpendicular to the sea boundary is the vertical direction; the main water inlet canal and the main drainage canal are respectively parallel to the sea boundary , based on the layout direction of the main water inlet and drainage canals, the entire tidal flat irrigation and drainage system is arranged, that is, the irrigation and drainage system can be arranged along the sea boundary for a length of 5-10 km, and several desalination units are embedded in the entire irrigation and drainage system. The horizontal dimension of the unit is set between 100-200m, and the longitudinal (or vertical) dimension of the desalination unit is set between 20-40m.

Step 2. Drill in-situ pumping wells: the in-situ pumping wells are arranged on the axis of the inlet branch channel. The flow rate of the in-situ pumping wells should be set according to the size of the desalination unit. One in-situ pumping well can provide flooding for two adjacent desalination units on the left and right. Irrigation source.

Step 3. Arranging constant head wells: The constant head wells are arranged on the axis of the drainage branch canal. Each desalination unit corresponds to five constant head wells. The spacing is determined according to the size of the pumping unit. The constant head wells are connected to the distribution wells through connecting pipes. The top elevation of the water distribution well is 50-100cm higher than the top elevation of the constant head water well, ensuring that the water level of the constant head water well is not lower than the top elevation of the salt discharge concealed pipe, preferably 0-1m higher than the top elevation of the salt discharge concealed pipe.

Step 4. Arrange the hidden salt drainage pipe: the buried salt drainage pipe is equidistantly buried within the range of 0.8m-1.2m underground in the lateral outline of the desalination unit, and is perpendicular to the axial direction of the branch drainage channel. The diameter of the salt drainage hidden pipe is 15-25cm , the distance between the underground salt drainage pipes corresponds to the size of the selected desalination unit, and the distance is between 20-40m.

Step 5, field plot leveling: first add the admixture to the surface saline-alkali soil, the admixture includes sand, gravel and sawdust, and use deep plowing to mix the admixture with the surface saline-alkali soil evenly and level off. A mixed layer is formed; then, a humus layer is covered on the surface of the mixed layer, and the humus layer includes straw or sawdust, etc.; therefore, the field plot is divided into a humus layer, a mixed layer and an original soil layer from top to bottom. The thickness of the humus layer and the mixed layer is preferably 5 cm, 50-100 cm, respectively.

Step 6, salt washing with brackish water: use the in-situ pumping well to pump the brackish water in the in-situ subsurface layer of the saline-alkali land to irrigate and wash the field plots, and keep the field irrigation depth at 5-15cm; The fixed-head wells replenish fresh water to the in-situ underground aquifer, thereby exchanging brackish-fresh water for the in-situ groundwater in the saline-alkali land.

Step 7, brackish water washing and salt drainage: use the hidden salt discharge pipe to discharge the rinsing brine to the sedimentation tank for sedimentation. The fresh salt water in the upper part of the sedimentation tank flows into the ecological corridor through the overflow weir, and is filtered by the ecological corridor and then passes through the filter layer. Then it is recycled to the sump through the perforated connecting pipe to recover the reclaimed water.

The overflow weir is preferably equipped with a salinity sensor for monitoring the salt concentration of the recovered water flowing through the overflow weir; when the salt concentration is detected to be greater than 3‰, the overflow weir is closed, the salt discharge hole on the sedimentation tank is opened, and the return The water is discarded; when the salt concentration is detected to be not lower than 3‰, the overflow weir is opened again, the salt discharge hole is closed, and the return water is recovered.

In addition, the top elevation of the overflow weir is preferably 1.5-2m higher than the bottom elevation of the sedimentation tank.

Step 8, Rainwater collection: Rainwater flows to the surface of the rainwater collection wetland, and after being filtered by tidal flat plants and water storage porous media, it enters water distribution wells, fixed head wells and sump tanks, and becomes natural fresh water.

The rainwater collection wetland is arranged on the side close to the sea boundary, and the top elevation of the rainwater collection wetland is slightly lower than the elevation of the coastal zone in the adjacent area, so it is easy for the rainwater to flow to the rainwater collection wetland. prevent seawater intrusion.

In addition, there are ridges formed by excavated land around the rainwater collection wetland, and the height of the ridge is 20cm, and the water storage of the rainwater collection wetland is surrounded by geomembrane to prevent seepage, so as to prevent the salt water in the aquifer from flowing backward into the rainwater collection wetland.

The width of the rainwater collection wetland is 5-7m, and the length corresponds to the length of the irrigation and drainage system; tidal flat plants are planted on the rainwater collection wetland.

Step 9, washing salt with fresh water: In the flat water season, use the underground brackish water to irrigate and wash the salt for 48 hours, then stop using the brackish water to wash the salt; then, the water intake gate is opened, and the fresh water pump works, and the fresh water in the sump is sequentially passed through the inlet The water main canal, water inlet branch canal and water inlet pipe are washed with fresh water and salt for 6 hours; in the wet season, in accordance with the weather forecast, before the rainfall, use the underground brackish water to irrigate and wash the salt. When the rainfall reaches the predetermined level, the optimal irrigation is 48 hours, then stop pumping brackish water and use rainwater to wash the salt.

Step 10, fresh water washing and salt drainage: follow the method of step 7 to drain water and form recycled reclaimed water. When the salt concentration is detected to be greater than 3‰, the overflow weir is closed, the salt discharge hole on the sedimentation tank is opened, and the return water is discarded; when the salt concentration is detected to be not lower than 3‰, the overflow weir is opened again, and the salt discharge hole is closed. Carry out backwater recovery.

Step 11, brine washing cycle: repeat steps 6 to 10 to form a brine washing cycle.

The present invention has following beneficial effects:

1. The present invention can complete the task of irrigation and drainage during the early desalination development of tidal flat saline-alkali land.

2. The present invention can effectively reduce the waste of water resources in the tidal flat desalination process and increase the water utilization efficiency.

3. It can make the field plots and rainwater collection wetlands form a complete water cycle process, and can effectively reduce the soil salinity content in the field area.

4. The salinity treatment component can recover a part of the saline-alkali water and add it to the water cycle again, reducing the water rejection rate.

5. Rainwater collection wetlands can filter rainwater and improve the quality of stored fresh water. At the same time, tidal flat halophytes are planted on the surface of rainwater collection wetlands, which can absorb tidal flat salt, help protect the tidal flat environment, and alleviate water head loss caused by the development of tidal flat saline-alkali land.

6. The rainwater collection wetland is located on the offshore side, which can resist the seawater intrusion of part of the unconfined aquifer, and ensure the backflow of seawater caused by the development of groundwater in the tidal flat saline-alkali land. (For example, when pumping wells in the coastal zone, it will cause seawater intrusion, which will cause permanent damage to the groundwater in the coastal zone)

In view of the above effects, the present invention adopts the following two preferred implementation cases for illustration.

Case Study 1

It demonstrates the efficiency of reducing the salinity of groundwater in saline-alkaline submerged layers by the salty-fresh water exchange designed in the present invention, and simulates the salt water concentration distribution map in the aquifer after the salty-fresh water exchange by means of numerical simulation.

The numerical simulation was carried out using the Groundwater Vistas software package, and the MODFLOW module was used to simulate the flow field and the MT3D module was used to simulate the solute transport.

To simulate the movement of solutes in unconfined aquifers, select the size of the typical saline-alkali land desalination unit treated by the present invention, and set the length, width and height of the desalination unit (hereinafter referred to as the model) to be 200m×40m×10m respectively, and the length, width and height are discrete The spacing is 1m, 1m, 0.5m, and the total number of discrete elements in the model is 160,000. The model is a homogeneous and isotropic seepage field, the permeability coefficient K=10m/d, the porosity of the seepage field n=0.35, the water release coefficient s=0.01, the longitudinal dispersion coefficient (following the flow direction) D _L =2m, and the transverse dispersion coefficient The coefficient D _T and the vertical diffusion coefficient D _V are both 0.2m, and the initial concentration of groundwater in the aquifer is 10kg/m ³ . The total duration of the model simulation is 45 days, the time step of simulating flow field is 1d, and the time step of simulating solute transport is 0.2d.

The above discretization distance is a technical term for numerical simulation calculations, mainly referring to the need to discretize the entire desalination unit and turn it into small elements one by one when using the model to calculate the water level and salt content of the block model of the "desalination unit". Calculation, through discretization, can make the calculation result closer to the actual situation. Discretization is to turn a large block into a small block, which increases the calculation accuracy and makes the calculation closer to the real situation.

Here, 1m, 1m, and 0.5m refer to the minimum distance divided in the three directions of length, width, and height, and the discrete elements are how many small blocks the desalination unit is divided into.

As shown in Figure 7, what is displayed is the contour change map of the groundwater concentration field at the section where the pumping well is located. Since the model is symmetrical in the length direction, only the simulation results on the left side are drawn. X represents the length direction, Z represents the depth direction, the origin of the coordinates is located at the groundwater water table (due to the gentle slope of the coastal zone, it is assumed that the ground water table is horizontal), the fixed head well is located on the X=0m axis, and the in-situ pumping well is located at X=100m On the axis, the unit of the contour line is kg/m ³ . It can be seen from Figure 7 that from 5 days to 45 days, the high-concentration contour has been shifting to the right. This is because the left boundary is a constant head water well, and the right boundary is an in-situ pumping well. While pumping groundwater, the constant head well on the left continuously replenishes fresh water to the aquifer, causing the high-concentration contour to move to the right, thereby gradually reducing the salinity of the groundwater in the aquifer. It can also be seen from Fig. 7 that when the model runs to 45 days, the 2kg/ ^m3 contour line has almost reached around the pumping well, showing that the method can quickly exchange salt and fresh water for groundwater, showing that the invention can quickly Reduce groundwater salinity in saline-alkali aquifers.

Case Study 2

It proves that zonal irrigation increases desalination efficiency more than non-zonal irrigation, and uses numerical simulation to simulate the desalination process of saline-alkali soil. At the same time, it also proves that brackish water has a good effect on desalination of saline-alkali soil irrigation.

The groundwater Vistas software package was used for numerical simulation, and the MODFLOW module was used to simulate the flow field and the MT3D module was used to simulate the solute transport.

To simulate the salt migration law in the desalination process of saline-alkali land, the size of the desalination unit is selected as 20m×0.1m×2m. The middle section between the pipes is distributed symmetrically, so only half of the size is selected for simulation, namely 10m, so the length, width and height of the simulation model are set to 10m×0.1m×2m respectively, and the discrete intervals are 0.1m, 0.1m and 0.05 m, so the total number of discrete elements in the model is 4,000. Since the law of salt movement in the desalination unit along the direction of the salt discharge underground pipe is similar, the model size can be set to 0.1m along the direction of the salt discharge underground pipe. In addition, since the desalination process only focuses on the salt migration law of the surface soil, only the range from the surface soil to two meters underground is selected.

The model is a homogeneous and isotropic seepage field, the permeability coefficient K=10m/d, the porosity of the seepage field n=0.35, the water release coefficient s=0.01, the longitudinal dispersion coefficient (following the flow direction) D _L =2m, and the transverse dispersion coefficient The coefficient D _T and the vertical diffusion coefficient D _V are both 0.2m, and the initial concentration of groundwater in the aquifer is 10kg/m ³ . The total duration of the model simulation is 10 days, the time step of simulating flow field is 1d, and the time step of simulating solute transport is 0.2d.

In this simulation process, two irrigation methods will be set up for comparison, one is the traditional irrigation and desalination method, which applies a 10cm high driving water head on the surface of the model (that is, maintains a 10cm high water storage on the surface of the desalination land during irrigation desalination), and the other is the method of the present invention. The proposed zonal irrigation and salt discharge method is to irrigate the middle part of the two salt discharge hidden pipes first, and then gradually expand to both sides through the overflow method, and finally the entire surface of the desalinated land has complete water storage. According to the arrangement of the present invention, the surface of the desalinated land is divided into three different water level zones through partition partitions, and the water levels from the inside to both sides are 15cm, 10cm, and 5cm in sequence. The model selects half of the desalinated land for simulation, so the water levels from right to left are 15cm, 10cm, and 5cm. To simulate the desalination effect of brackish water, the leaching water applied to the surface of the desalted land during the simulation process is brackish water with a constant concentration of 2.5kg/m ³ . At the same time, set up a salt drainage pipe at an elevation of 1m on the left boundary of the model.

As shown in Figure 8, the left half of the figure is the traditional irrigation desalination method, and the right half is the partition irrigation desalination method. The curve in Fig. 8 represents the contour line, and the unit is kg/m ³ .

In Fig. 8, the salt migration results of the surface soil under two different irrigation methods are shown. X represents the length direction, Z represents the depth direction, and the coordinate origin is located on the ground. The left side is the salt migration result of the traditional irrigation desalination method, and the right side is the salt migration result of the partition irrigation desalination method provided by the present invention, and the unit of the contour line is kg/m ³ . Since the desalination method of zonal irrigation gradually expands from the inside through the overflow method to both sides, and finally the entire surface of the desalinated land has complete water storage, but the time of this process is relatively short, and it can be ignored compared with the scale of the sky. consider.

From the simulation results from the first day to the tenth day, the salinity contours of the two irrigation methods have been retreating downwards, indicating that brackish water irrigation has a good effect on the desalination of saline-alkali soil. In addition, comparing the concentration contour distribution maps on both sides, it can be found that the desalination method of partition irrigation is more efficient and effective than the traditional desalination method. In the traditional irrigation desalination method, starting from the sixth day, the position of the 4kg/m ³ contour Almost no change, but the position of the 4kg/ ^m3 isoline of the divisional irrigation desalination method still retreats downward, and the desalination effect is better in the middle area of the two salt drainage underground pipes.

The preferred embodiments of the present invention have been described in detail above, however, the present invention is not limited to the specific details in the above embodiments, and is within the scope of the technical concept of the present invention.

Claims (10)

1. A coupling submerged brackish and fresh water replacement and leaching desalination device is characterized in that: it includes field desalination components, brine treatment components and rainwater collection wetlands; Field desalination components include several desalination units, water inlet components and drainage components; The number of desalination units is equal to the number of field plots, and each desalination unit includes a desalination unit profile, water inlet branch parts and partition partitions; wherein, the desalination unit profile is the profile of the corresponding field plot, including the horizontal profile and vertical profile. contour; The water inlet components include main water inlet canal, water inlet branch canal, fresh water pump and several in-situ pumping wells; Water inlet branch components include water inlet pipes, brackish water pumps, constant head wells and water intake gates; Drainage components include main drainage canals, branch drainage canals and hidden salt drainage pipes; The arrangement direction of the salt discharge buried pipe is parallel to the direction of the water inlet pipe, and each salt discharge buried pipe is equidistantly buried within the range of 0.8m-1.2m underground of the lateral outline of the desalination unit; The water inlet pipe is set on the surface of the field plot in the middle of the two adjacent salt drainage pipes, and the water inlet end of the water inlet pipe is connected to the in-situ pumping well through the brackish water pump; The in-situ pumping wells are set at the middle junction of two adjacent desalination units on the left and right, and are located on the axis of the corresponding inlet branch canals. fresh water pumps; On the surface of the field plot between two adjacent salt drainage pipes, with the drainage pipe as the center, several partition partitions are equidistantly arranged; The height of the partition partition gradually decreases from the side of the water inlet pipe to both ends, and the maximum height of the partition partition is not higher than the height of the outline of the desalination unit; The drainage branch canal is perpendicular to the salt drainage pipe, and is adjacent to the vertical profile of the desalination unit away from the in-situ pumping well; one end of each salt drainage pipe is connected to the drainage branch canal, and the other end is closed; each drainage branch canal are all connected to the main drainage channel; Dingshuitou wells are equidistantly arranged on the central axis of the drainage branch canal, and the bottom of Dingshuitou wells runs through the underground water layer of the entire field plot; The brine treatment components include sedimentation tank, overflow weir, ecological corridor and filter pipe; the outlet end of the main drainage channel extends into the sedimentation tank, the overflow weir is set in the middle and upper part of the sedimentation tank on the side of the ecological corridor, and one end of the filter pipe is connected to the ecological corridor. The seepage layer of the corridor is connected, and the filter pipe is filled with filter particles; The rainwater collection wetland includes an impermeable layer, a sump, a water distribution well, a perforated connecting pipe, and a porous medium for water storage; The anti-seepage geomembrane is laid; the water distribution wells are evenly arranged in the water storage porous medium, one end of the perforated connecting pipe is connected with the water outlet end of the filter pipe, the middle part of the perforated connecting pipe is connected with all the water distribution wells, and the tail end of the perforated connecting pipe is connected with the collection The pool is connected; the sump is connected with the water inlet of the main water inlet; The water distribution well is also communicated with each constant head water well in the desalination unit through a communication pipe. 2. The salty and fresh water replacement and leaching desalination device coupled with submerged layer according to claim 1, characterized in that: a salinity sensor is set on the overflow weir, and a salt discharge hole is set on the sedimentation tank. 3. The salty and fresh water replacement and leaching desalination device coupled with submerged layer according to claim 1, characterized in that: the outlet end of the main drainage channel is provided with a flow rate control pump. 4. The salty and fresh water replacement and leaching and desalination device for coupling aquiferous layer according to claim 1, characterized in that: the field plot comprises humus layer, mixed layer and original soil layer successively from top to bottom, and the mixed layer is blended The mixture of materials and surface saline-alkali soil. 5. The salty and fresh water replacement and leaching desalination device for coupled submerged layer according to claim 4, characterized in that: the admixture is sand, gravel and sawdust, and the admixture is evenly mixed with the surface saline-alkali soil by means of deep plowing ; The humus layer includes straw and sawdust. 6. The salty and fresh water replacement and leaching desalination device coupled with submerged layer according to claim 1, characterized in that tidal flat plants are planted on the water storage porous medium. 7. The salty and fresh water replacement and leaching desalination device coupled with submerged layer according to claim 1, characterized in that: the diameter of the hidden salt discharge pipe is 15-25 cm, and a circle of gravel is laid around the hidden salt discharge pipe. 8. The salty and fresh water replacement and leaching desalination device for coupled submerged layer according to claim 1, characterized in that: each desalination unit is equipped with five constant head water wells, and the top elevation of the water distribution wells is 50-50- 100cm, and there is a valve on the connecting pipe connecting the fixed head water well and the water distribution well. 9. The coupling submerged brackish and fresh water replacement and leaching desalination device according to claim 1, characterized in that: on the surface of the field plot between the front and rear adjacent two salt drainage pipes, six partitions are equidistantly arranged Partition boards, six partition partitions are symmetrically distributed on both sides of the water inlet pipe, and the three partition partitions located on one side of the water inlet pipe are counted from the side of the water inlet pipe, and the heights are 15cm, 10cm and 5cm respectively. 10. The salty and fresh water replacement and leaching desalination device for coupled submerged layer according to claim 1, characterized in that: a gravel filter layer is laid on the bottom of the ecological corridor, and salt-resistant plants are planted on the gravel filter layer.