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   First, the division of mining area
The division of mining area mainly depends on industrial reserve distribution, deposit occurrence conditions, water chemical type and water quality distribution characteristics, and is related to mining scale, water quality requirements, engineering geology and hydrogeological conditions.
The deposit conditions and industrial reserves are the basis for the division of mining areas. It determines the size of the mining area, the size of the mining and the length of service. The first mining area should choose a flood-producing area with high exploration level, large industrial reserves, high grade, good storage conditions and sufficient water.
The chemical type of the deposit and the spatial distribution of its water quality play a dominant role in the division of the mining area. In the same salt lake, when the water chemical type and water quality are different in different sections, the mining area should be separately planned. If the ore body is separated by harmful water bodies, it must be mined in sections. In the mining design, the migration speed and migration amount of harmful water bodies should be predicted and taken, and prevention measures should be taken.
The same water chemical type brine, the chemical composition is relatively stable, the water quality index in the mining does not fluctuate, according to the mining scale, should be assigned to a mining area as much as possible to ensure the stability of the salt field process or processing technology control conditions.
The buried depth of the water level and the thickness of the aquifer are also important conditions for the division of the mining area; the sections with the same thickness of the aquifer and the buried depth should be assigned to one mining area as much as possible, so that the same type of halogen-harvesting structures and equipment can be used to facilitate management.
   Second, the brine structure and its choice
The method of halogen extraction includes rationally arranging the mining system and effectively implementing the mining process. The mining system is determined by the order in which the mining work is carried out; the mining process consists of a series of processes; the basic processes are halogen extraction and halogen removal. Different methods of halogen extraction, using different brines, halo-haling structures and corresponding measures (Table 1), according to the geological conditions of the deposit, hydrogeological conditions and mining scale.
Table 1 Mining methods and mining and transporting structures
Deposit type
Mining method
Mining and taking halogen structures
Pump station type
Halogen transport structure
Anti-salt facility
Ground
under
halogen
water
Well mining method
Tube well
Complete tube well
Incomplete tube well
Stationary pumping station
Various material pipes; high and low channels for various materials; mixed halogens for channels and pipes
Pumping and transducing saturated brine with fresh water to prevent salt
Big well
Complete large well
Non-complete large well
Radiation well
Stationary pumping station
Channel mining method
ditch
Complete channel
Non-complete channel
Fixed or barge
Extract saturated brine and add fresh water at the suction port.
Well-canal mixed mining method
Big well and ditches
Complete well + non-complete channel (halogen collection)
Non-complete well + non-complete channel
Fixed or barge
Surface
brine
Fixed halogen extraction structure mining
Stationary pumping station
Same as above
Barge-type halogen structure mining
Barge pump station
When the groundwater level is shallow but the thickness of the aquifer is greater than 10m, or when the water depth of the aquifer is below 10m, the tube well mining is used, and the deep well pump is used to extract the brine. The water level is buried shallow, the aquifer is rich in water, and the water permeability is good. When the thickness is more than 3m, large wells can be used for mining. Radiation wells may be considered when the aquifer has poor water permeability.
The underground brine level is buried close to the surface, and the channel is mined when the thickness of the aquifer is less than 10m. It is advisable to use a complete aquifer with a thickness of less than 5 m, and a non-complete canal and a combination of well and canal for mining of more than 5 m. Generally, the canal is used as a structure for collecting brine and as a structure for taking halogen. Figure 1 shows several typical brine extraction systems for the production of underground brines.
Figure 1 Several brine extraction systems for underground brine production
A-row well group layout system; b-row well group arrangement system; c-well combination combined with halogen arrangement system
1-halogen well; 2-pressure pipeline; 3-pump station; 4-halogenation tank; 5-channel
For surface brine mining, fixed or stern (floating) halogen structures are generally used. Figure 2 shows several typical brine extraction systems for the exploitation of surface brines. The inclined trough type halogen-distributing system a is suitable for shallow lake water. It is used to build a chute to deepen the bottom of the lake, and to build a fixed pumping station to extract brine. The mining of the Dabusu-alka lake in Jilin Province is to use this arrangement system. The diversion channel brine extraction system b is suitable for the unsaturated brine, which is saturated by channel evaporation and then supplied to the salt field. The dam-type brine extraction system c is suitable for silt at the bottom of the lake and can be used to build a salt field by separating the lake bay from the dam. The stern-type mining system d is suitable for the conditions where the pumping station cannot be built at the bottom of the lake and the water level of the lake is large. The barge is made constant by the barge, and is not affected by the fluctuation of the lake.
Figure 2 Several brine extraction systems for mining surface brines
A-choline-type halogen-harvesting system; b-channel drainage system; c-bar-type brine-harvesting system; d-barge-type halogen-laying system
1-water diversion trough; 2-halide well; 3-pump station; 4-halogen pipe; 5-halogen storage channel;
6-barge; 7-floating tube; 8-dam; 9-salt field; 10-channel; 11-halogen
   Third, the determination of basic process parameters
(1) Calculation of water inflow
The water inflow of different brine-harvesting structures is listed in Table 2.
Table 2 Calculation of water consumption of different brine-harvesting structures
Table 2 Calculation of water consumption of different brine-harvesting structures (continued)
(II) Determination of structural parameters of tube wells
1, filter length
The length of the filter is determined according to the thickness of the halogen-containing layer, the amount of water inflow, and the vertical distribution characteristics of the chemical composition of the brine. When the thickness of the halogen-containing layer is not large and the water quality of the brine in the vertical direction changes uniformly, the length of the filter is equal to the thickness of the halogen-containing layer; when the chemical composition of the brine is vertically differentiated, the water quality requirement is met, and the length is determined according to the calculation of the halogen. . However, it should be noted that the mixing of the brine in different parts of the well changes with time, and the liquid-solid conversion by the halogen is more complicated. Therefore, in addition to the calculation of the filter to determine the length of the filter, it should also be field test.
2, filter effective porosity
There are many types of filters, and the salt lake brine mining uses a tangled wire and a net filter.
Their effective porosity is calculated as follows:
In the formula:
--aqueous layer water supply;
Ρ-filter skeleton porosity.
In the formula:
d 1 , d 2 - the width of the rib and the diameter of the entanglement;
m 1 , m 2 - the center distance of the backing bars and the center distance of the adjacent winding wires;
N-package porosity.
   Fourth, the use and prevention of liquid-solid conversion
Under the mining conditions, the underground brine seepage field, water chemical field and thermodynamic conditions all change, and the equilibrium relationship between liquid and solid is destroyed. To establish a new balance, liquid-solid conversion of dissolved salt and salt is produced.
Liquid-solid conversion is of great significance in liquid mining. Because each salt lake brine has specific water chemistry types and water and salt system characteristics. Through phase diagram analysis, the law of evaporation and precipitation of brine can be mastered under certain conditions, so that the water chemistry and water quality division of the deposit can be determined according to the salt precipitation stage of the brine; the deposit and water quality index of the deposit can be determined to achieve reasonable development and utilization. Salting of equipment and formations in mining can also be controlled in advance.
(1) Determination of the quality index of intercrystalline brine
Taking the brine of the Chaer Khan section of the Chaerhan Salt Lake as an example, the following is a statistical analysis of the water chemical analysis of the intergranular brine in the Chaerhan section, plotted on K + , Na + , Mg +2 /Cl - -H 2 O On the 25 °C phase diagram of the element system, all points are located in the NaCl phase region (Fig. 3). It can be seen from the figure that any point of isothermal evaporation, before the NaCl and KCl, KCl, MgCl 2 · 6H 2 O, MgCl 2 · 6H 2 O co-saturation line, the ratio of MgCl 2 / KCl is constant, so it is a measure The quality of brine is of great significance. According to statistical analysis, the specific gravity of brine increases, the value of MgCl 2 /KCl increases, and the position increases on the phase diagram. According to the aquifer water supply and water volume, the brine components are mixed with different concentration limits. The new composition points are marked on the map. For example, P 1 is the composition point of the whole section brine and halogen; P2 is the specific gravity of more than 1.2 brine. The composition point after halogenation; according to calculation, the brine of MgCl 2 /KCl<30 accounts for more than 66% of the total. From the mining point of view, determine the reserves index of the deposit, the specific gravity of the brine is 1.21 ~ 1.30, MgCl 2 / KCl = 30. The mining index is set to be 1.255~1.28, and MgCl 2 /KCl=17 is suitable. Of course, the final determination of water quality indicators requires a comprehensive comparison of the technology and economy.
Figure 3 brine composition map
(2) Water quality division of the deposit
According to the analysis data of the borehole water sample, the isoline map of the intergranular brine (Fig. 4) and the contour map of the MgCl 2 /KCl level and the profile are shown (Fig. 5). The phase diagram is determined Water Partition: specific gravity 1.21 ~ 1.245, MgCl 2 / KCl <7.75 ( point E in FIG. 3) to rock salt - sylvite precipitate segment brine; specific gravity 1.243 ~ 1.292, MgCl 2 /KCl=7.7~30 It is the brine of the stone salt-halogenite precipitation; the specific gravity is >1.275, and the MgCl 2 /KCl>30 is the brine of the stone salt-carnallite- picochlorite precipitation section. The mining area is delineated according to the water quality requirements. In the mining area, according to the thickness of the aquifer, the depth of burial, and the differentiation of water quality, the type of the structure of the brine is determined, and the mining project is arranged.
Fig. 4 Equivalent diagram of brine specific gravity (°Be) in the Chaerhan section
Figure 5 Distribution of brine water quality in the Chaer Khan section
1-stone salt-potassium salt stage brine; 2-stone salt-halogenite stage brine; 3-stone salt-carnallite-magnesium chloride stage brine;
4-salt lake boundary; 5-brass water chemical system boundary; 6-MgCl 2 /KCl ratio contour
(3) Salt formation and its prevention
In the intergranular brine mining, different water brines are mixed under certain conditions. Due to the same ion effect, the halogenated salt is formed, so that the formation and the mining and halogen conveying equipment are salted, which affects normal production.
There are many ways to prevent and cure salt in equipment. It is divided into four categories: chemical method, physical method, mechanical desalting method and fresh water method. Among them, mechanical desalination belongs to the rule. At present, foreign data reports are only used for pipelines, and the impeller and blades of the pump are difficult to implement. Add chemical agents to prevent salt, and foreign countries add a molecular formula:
R-CO-N-CH 2 CH 2 SO 4 M
|
R 1
The mixture of taurine and alkali metal phosphate, to prevent oil brine salting. Alkylene potassium ferricyanide inhibiting effect salting had done at Salt Lake intergranular brine extraction test, good results, but expensive, economically unreasonable. Experiments have shown that ultrasonic, electric, magnetic fields and various hydrophobic coatings have the ability to prevent salt formation, but due to the complexity of equipment and power consumption, engineering applications are limited. At present, the United States and China's salt lake mining are used to add salt water to prevent salt.
In the process of mining intergranular brine, a method of adding a certain amount of fresh water to prevent salt formation in the pumping and halogen conveying process equipment is to introduce a fresh water pipe in a parallel suction pipe in the well or the channel, and a water spray ring is arranged under the suction port. Figure 6 shows the fresh water installation when the tank is used for mining. Adding fresh water to prevent salt formation has the advantages of simple process facilities, low cost, no toxicity and good effect.
Figure 6 Add fresh water device
1- fresh water storage tank; 2-valve; 3-flow meter; 4-plus fresh water pipe; 5-water spray ring; 6-tip
The fresh water rate is related to the brine concentration, chemical composition and water quality differentiation. It can be calculated according to the salt absorption rate during liquid extraction or by experiment.
The method of obtaining the minimum fresh water rate by evaporation test is to add excess fresh water to the equipment to prevent salt from being formed when the halogen is extracted, and to sample and evaporate at the outlet of the pipeline to measure the amount of water loss when the crystallites appear. The amount of water loss is actually the amount of fresh water added. . According to this, the minimum fresh water rate for preventing salt formation of the device can be obtained. The evaporation test method was used in the CK829 drilling of the Chaerhan Salt Lake CK829. The fresh water rate was 0.4%-1.0%.
   5. Anti-corrosion of halogen-harvesting structures
Brine and brine vapors, salt layers and saline soils have strong chemical and electrochemical corrosion effects on metals. Therefore, adequate attention should be paid to the problems of pumping, halogen transport, water supply equipment and pipeline corrosion protection.
There are three types of anti-corrosion methods: anti-corrosion materials, anti-corrosion coatings, and cathodic protection; sometimes several methods can be used simultaneously.
Corrosion of pipe wells is closely related to the chemical composition of well materials and brines. Ordinary bricks and cement mortars are not suitable for use as well wall masonry materials in salt lake areas. Because brines are immersed in concrete surfaces or holes, salt crystals are precipitated due to evaporation or temperature changes, resulting in volume expansion, which is destroyed by internal stress. Therefore, depending on the type of water, alumina cement, sulfate-resistant cement, pozzolan cement and magnesium cement can be used.
When selecting the well pipe and water filter material, according to the chemical composition and pH value of the brine, high-silicon cast iron pipe, ordinary cast iron pipe, corrosion-resistant low-carbon alloy steel pipe and corrosion-resistant non-metallic material pipe, such as glass steel pipe and hard polychlorination, are respectively selected. vinyl tube and the like; filter tubes wrapping material should not use lead wires, preference should be given nylon, glass fiber reinforced plastic wire and stainless steel wire.
There are many anti-corrosion coatings, which have significant effects on protecting well pipes, halogens and water pipes. They can be selected according to the composition of brine and pH value. For example, phenol “酉-based†(representing a word) resin is resistant to chemical corrosion; Acid resistance; Furan resin has good acid and alkali resistance; asphalt is water, moisture, acid and alkali resistant; epoxy asphalt paint is good for cast iron pipe.
The cathode is the most economical and effective reliable method to prevent electrochemical corrosion and extend the life of the pipeline. Cathodic protection can be applied by an impressed current method or a sacrificial anode method (Fig. 7). In the former, an external DC power source is used to pass the anode, and a constant current is applied to the protected metal pipe. The cathode is polarized to reduce or prevent corrosion. In the latter, a metal with a more negative potential is connected to the protected metal pipe as an anode, and the protected metal forms a large battery in the electrolyte solution, and the metal with a negative potential continuously loses electrons, and a current flows into the protected body. The protected body is polarized into a cathode for protection purposes.
Figure 7 Principle of cathodic protection against corrosion
E-electron flow direction; i-current flow direction
For example, the first phase project of Qinghai Potash Fertilizer Plant supplies water from Golmud to the Lake District. The soil geological structure and hydrogeological conditions of the pipeline more than 60 kilometers are complicated. There are pebble belts, reeds, swamps, light salted areas and heavy salt areas. And cross the river twice, the measured soil resistivity along the line, the pebble zone is 1000 ~ 2000 Ω / m, the reed swamp zone is 20 ~ 50 Ω / m, the saline soil zone is 0.5 ~ 20 Ω / m, from the soil resistivity, Saline soil is a strong corrosion zone, reed marsh section is a strong corrosion zone, and the cobble section is a lightly corrosive zone.
In the pipeline material, from the instrument well outside the pump room of the water source to the lake area, ordinary water supply cast iron pipe, spiral electric welded steel pipe and hard polyvinyl chloride pipe are selected respectively (Fig. 8).
Figure 8 Water pipeline plan
1-West water source pump house; 2-PVC pipe 2-ф355×16.9mm; 3-steel pipe ф529×8mm;
4-tank; 5-check piece; 6-test column; 7-sacrificial anode group
The outer anticorrosion of spiral welded steel pipe is a joint anticorrosive layer of epoxy coal tar pitch and chlorosulfonated polyethylene. The outer surface of the steel pipe is strictly rust-removed. To achieve China's hull descaling standard b 1 level. The epoxy coal tar pitch anti-corrosion coating is selected from the structural reinforcement grade. The structure is a primer, four coats, three layers of glass cloth wound between the coatings, and the total thickness is not less than 0.7 mm. The protective layer of chlorosulfonated polyethylene has two primers and six top coats with a total thickness of about 130 mm. The anti-corrosion in the pipeline is sprayed with cement mortar, and the coating thickness is 6mm. The inner surface of the pipe before spraying should also be strictly rust-proof (up to b 1 level).
The steel pipe adopts epoxy coal tar pitch, chlorosulfonated polyethylene combined with external anticorrosion and anticorrosion in cement mortar, and is also supplemented by cathodic protection measures to control the electric corrosion of underground pipelines. According to the principle of simple management and low operating costs, the project uses zinc- aluminum- cadmium alloy sacrificial anode method for protection. The length of the protected pipeline is 42.18km, and 115 sets of sacrificial anodes are arranged on the whole line, with 1 to 6 sets in each group. Each group is grouped in unequal distances, and the length of the protection pipeline is 100-400m.
   6. Water quality and quantity forecasting and monitoring
(1) Monitoring
The monitoring is to periodically measure the quality of the external brine in the mining area, the change of water volume and the harmful water bodies and pollution sources in the mining area, in order to grasp the degree of water quality change, so as to take measures to prevent the water quality from deteriorating. The monitoring method is to establish a monitoring station.
The monitoring stations are fixed and mobile, and are managed by special personnel. The number and layout of monitoring stations shall be subject to changes in water quality and water volume.
The monitoring project is based on the type of brine deposit and the requirements for water quality and water volume. Generally include: hydrology, meteorology, such as flow, flow rate, flow direction, water level, temperature; physical properties of water, such as specific gravity, water temperature, color, turbidity, odor, pH, etc.; water chemical composition and harmful impurities.
The monitoring methods include sampling analysis and direct measurement. The former is indoor sampling and then analyzed indoors; the latter is directly monitored by various sensors on the spot, and the collected data is processed by computer.
The timely monitoring of monitoring data is to grasp the changes in water quality and quantity of water, to identify the law of change, to forecast future trends, to guide production, and to organize monitoring data, including:
1. Draw a graph of water quality and water level as a function of time as shown in Figure 9.
Figure 9 Water quality and water level changes measured by brine extraction in the Chaerhan Salt Lake channel
2. Draw a water quality distribution map, that is, the concentration distribution of specific ions or compounds on the flat and cross-section. It can be expressed by the concentration contour.
3. Draw a water quality related diagram as shown in Figure 10.
Figure 10 brine water quality map
Draw a composition diagram of the brine water quality. There are many ways to express:
1. The isothermal phase diagram of the water and salt system is used;
2, using a comprehensive histogram, that is, the cations are listed in the order of K + , Na + , Mg + 2 , Ca + 2 on the left side of Cl - , SO 4 -2 , HCO 3 - histogram to form a comprehensive histogram;
3. Water quality map;
4. Water chemical concentration map;
5. Water chemical classification map.
(2) Forecast
The forecast is to use the obtained hydrogeological data, water chemical distribution law and brine dynamic monitoring data to establish a mathematical model to solve the future brine level, water volume, water quality and liquid-solid conversion trend, and guide the brine.
In underground brine mining, the prediction method of water level and water quantity is mainly to calculate the change value of future mining years by solving the groundwater equilibrium equation. The methods for solving the groundwater equilibrium equation include water balance calculation method, numerical simulation method and electric network simulation method. The dynamic prediction of water quality in underground brine mining is mainly based on the law of conservation of mass. Due to the complexity of the mathematical model, it is still in the research stage in China.