WO2022222452A1

WO2022222452A1 - Zero-discharge and resource recycling process for seawater desalination

Info

Publication number: WO2022222452A1
Application number: PCT/CN2021/131417
Authority: WO
Inventors: 叶伟炳; 谭润宇
Original assignee: 广东闻扬环境科技有限公司
Priority date: 2021-04-23
Filing date: 2021-11-18
Publication date: 2022-10-27
Also published as: CN113105058A

Abstract

The present application relates to a zero-discharge and resource recycling process for seawater desalination. The process comprises the following steps: a seawater pretreatment step, involving: removing impurities in seawater to obtain pretreated seawater; a seawater concentration step, involving: concentrating the pretreated seawater obtained from the seawater pretreatment step to obtain a concentrated solution, in which the content of heavy metal elements is not higher than 0.5 mg/kg, the content of silicon dioxide is not higher than 5 mg/kg, and the content of multivalent ions is not higher than 1 mg/kg; and a product preparation step, comprising at least one of the following steps: a salt making step, involving: concentrating and separating the concentrated solution to obtain solid sodium chloride, and an alkali and hydrogen preparation step, involving: softening the concentrated solution, then carrying out electrolysis to obtain a sodium hydroxide solution, hydrogen and chlorine. The method can achieve zero discharge of seawater by utilizing the concentrated solution, and sodium chloride, sodium hydroxide, hydrogen, and chlorine can be directly prepared from seawater.

Description

Seawater desalination zero discharge and resource recycling process

technical field

The present application relates to the technical field of seawater utilization, in particular to zero-discharge seawater desalination and resource recovery and utilization processes.

Background technique

Seawater is a very complex multi-component aqueous solution. Seawater contains abundant resources, and the stock of seawater is very huge, accounting for 96.5% of the global water reserve. It is of great significance for the utilization of seawater.

With the development of science and technology, people's use of seawater technology has been continuously improved. In traditional technology, when people use seawater, they first use membrane technology to desalinate seawater to obtain fresh water, and the remaining concentrated liquid will be re-discharged into seawater, which cannot achieve zero discharge of concentrated liquid. In addition, if this part of the concentrated solution is recovered to prepare solid sodium chloride, a large amount of different kinds of medicaments need to be added to remove various impurity ions in the concentrated solution.

However, the above method is not easy to remove impurities in the concentrated solution, and there are many types of chemicals used. The production process of the above-mentioned seawater utilization method for making alkali is relatively complicated, and the cost is relatively high, and it is impossible to perform better resource recovery and utilization of seawater.

SUMMARY OF THE INVENTION

According to various embodiments of the present application, a seawater desalination zero-discharge and resource recycling process is provided, comprising the following steps:

The seawater pretreatment step removes impurities in seawater to obtain pretreated seawater;

In the seawater concentration step, the pretreated seawater obtained in the seawater pretreatment step is concentrated to obtain a concentrated solution; in the concentrated solution: the content of each heavy metal element is not higher than 0.5 mg/kg; the content of silicon dioxide is not higher than 5 mg/kg kg; the content of each multivalent ion is not higher than 1mg/kg;

Product preparation steps: including at least one of the following steps:

Salt-making step: the concentrated solution is concentrated and separated to obtain solid sodium chloride;

In the step of making alkali and hydrogen, the concentrated solution is softened, and after softening, electrolysis is performed, and after electrolysis, sodium hydroxide solution, hydrogen and chlorine gas are obtained.

In one embodiment, the seawater pretreatment step includes the following steps:

In the step of electro-precipitation, electro-precipitation is performed on the pretreated seawater, and the first pretreated seawater is obtained after filtering;

Ultrafiltration step, the first pretreated seawater is subjected to ultrafiltration to obtain the second pretreated seawater;

In the nanofiltration step, the second pretreated seawater is subjected to nanofiltration to obtain the third pretreated seawater.

In one embodiment, in the electroprecipitation step, the current density is set in the range of 40A/m ² -60A/m ² .

In one embodiment, in the ultrafiltration step, the pore size of the ultrafiltration membrane is selected from 0.005 μm to 0.1 μm.

In one embodiment, in the nanofiltration step, the pressure difference of nanofiltration is set in the range of 0.1MPa-0.5MPa.

In one embodiment, in the seawater concentration step, evaporative concentration is selected, and the mass percentage concentration range of the concentrated solution after concentration is 26%-40.7%.

In one embodiment, in the seawater concentration step, at least one of the MED evaporation system, the MVR evaporation system or the MED-TC evaporation system is used for evaporation and concentration.

In one embodiment, in the step of making alkali and hydrogen, a double alkali method is used to perform softening treatment.

In one embodiment, in the step of producing alkali and hydrogen, during the electrolysis process, the current density is set to be 3.4KA/m ² -4.0KA/m ² and the voltage is 2.45V-3.3V.

In one of the embodiments, the seawater recovery step is also included:

The remaining electrolyte in the alkali production and hydrogen step is added to a dechlorination agent to obtain a recovered sodium chloride solution; the recovered sodium chloride solution is passed into the seawater pretreatment step for utilization.

The details of one or more embodiments of the application are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the present application will become apparent from the description, drawings and claims.

Description of drawings

In order to better describe and illustrate the embodiments and/or examples of those applications disclosed herein, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the drawings should not be considered to limit the scope of any of the disclosed applications, the presently described embodiments and/or examples, and the best mode of those applications presently understood.

1 is a flowchart of a zero-discharge and resource recycling process for seawater desalination provided by an embodiment of the application;

2 is a flow chart of a zero-discharge and resource recycling process for seawater desalination provided by another embodiment of the application;

Fig. 3 is the flow chart of a kind of seawater desalination zero discharge and resource recovery and utilization process provided by an embodiment of the application (recovering sodium chloride solution and carrying out step S11 to utilize);

FIG. 4 is a flow chart of a seawater desalination zero-discharge and resource recovery and utilization process provided by an embodiment of the application (recovering the sodium chloride solution and performing step S12 for utilization).

Detailed ways

In order to make the above objects, features and advantages of the present application more clearly understood, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Back, Left, Right, Vertical, Horizontal, Top, Bottom, Inner, Outer, Clockwise, Counterclockwise, Axial , "radial", "circumferential" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the application and simplifying the description, rather than indicating or implying the indicated device or Elements must have a particular orientation, be constructed and operate in a particular orientation and are therefore not to be construed as limitations on this application.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In the description of the present application, "plurality" means at least two, such as two, three, etc., unless expressly and specifically defined otherwise.

In this application, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between the two elements, unless otherwise specified limit. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

In this application, unless otherwise expressly stated and defined, a first feature "on" or "under" a second feature may be in direct contact with the first and second features, or indirectly through an intermediary between the first and second features touch. Also, the first feature being "above", "over" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly or obliquely below the second feature, or simply means that the first feature has a lower level than the second feature.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or an intervening element may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for the purpose of illustration only and do not represent the only embodiment.

Referring to FIG. 1 , FIG. 1 is a flowchart of a zero-discharge and resource recovery and utilization process for seawater desalination according to an embodiment of the present application. An embodiment of the present application provides a seawater desalination zero-emission and resource recycling process, comprising the following steps:

S10, the seawater pretreatment step. Remove impurities from seawater.

Specifically, in some embodiments, step S10 may include the following steps:

S11, the step of electroprecipitation. Pass the seawater through the electric sedimentation device, so that the iron salts and aluminum salts in the seawater are co-precipitated. Precipitation separation is carried out after electric sedimentation, and the first pretreated seawater is obtained after separation.

In step S11, the distance between adjacent electrode plates of the electroprecipitation device is set to be 1 cm-5 cm, such as 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, and the like. Pass seawater through the gap between the above electrode plates. At the same time, the electrode plates are all supplied with pulse current. The current density is controlled within the range of 40A/m ² -60A/m ² , for example, the current density is 40A/m ² , 45A/m ² , 50A/m ² , 55A/m ² , 60A/m ² and the like. It should be noted here that when the current density is less than 40A/m ² , the impurity removal efficiency is low. When the current density is greater than 40A/m ² , the electrode plate is easily passivated, reducing the impurity removal rate. In addition, in the electroprecipitation device, the electrode plate can be made of graphite, titanium, iron-aluminum alloy or stainless steel material, but it is not limited to the electrode plate made of the above materials.

Under the action of electric current, iron salts and aluminum salts in seawater undergo redox reactions to form precipitates that adhere to the electrode plates. When the current direction of the pulse current is changed, the precipitate is separated from the electrode plate for easy separation.

After the electroprecipitation treatment is completed, a filter is used to filter the sediment produced in the seawater, so as to separate the sediment from the seawater, thereby obtaining the first pretreated seawater. In some embodiments, the filter may be a security filter. The filtration precision of the security filter can be 1μm, and other filters with the same or similar filtration precision can also be used.

S12, ultrafiltration step. Ultrafiltration is performed on the first pretreated seawater to remove fine precipitation in the first pretreated seawater to obtain the second pretreated seawater.

In some embodiments, ultrafiltration membrane separation equipment with models of SFP-2860, SFP-2880 and IP-77 can be selected for ultrafiltration, but it is not limited to the ultrafiltration membrane separation equipment of the above models. Among them, the pore size of the ultrafiltration membrane in the ultrafiltration membrane separation equipment can be selected between 0.005μm-0.1μm, such as 0.005μm, 0.01μm, 0.02μm, 0.03μm, 0.04μm, 0.05μm, 0.08μm, 0.1μm, etc. , 0.03 μm in this embodiment. The first pretreated seawater is passed through an ultrafiltration membrane separation device to remove fine precipitates in the first pretreated seawater. After the ultrafiltration is completed, the effective recovery rate of the ultrafiltration membrane is 90%-95%.

S13, the nanofiltration step. The second pretreated seawater is subjected to nanofiltration treatment to remove dissolved salts and organic matter with a molecular weight of about 200-400 in the second pretreated seawater to obtain the third pretreated seawater.

In step S13, the models of nanofiltration machines that can be selected are NF-90, NF-270, NF-400, XC-N, etc., but not limited to the above-mentioned models, depending on the quality of seawater in different regions and the grade of membrane It depends on the number of designs. For example, for seawater with high salinity, for example, the salinity is about 50,000 mg/L, in order to reduce the energy consumption of the system and improve the service life of the membrane system, the recovery rate is designed to be relatively low. Another example is seawater with low salinity, for example, the salinity is about 28,000 mg/L, and its recovery rate is designed to be relatively high. During nanofiltration, the pressure difference between the two ends of the nanofiltration membrane can range from 0.1MPa to 0.5MPa. 0.5MPa, etc. In this embodiment, 0.25Mpa is selected.

After the completion of nanofiltration, the retention capacity of soluble salts is 20%-98%. The removal rate of monovalent anion salt solution is lower than that of high-valent anion salt solution. In some embodiments, the removal rate of sodium chloride and calcium chloride is 20%-80%, and the removal rate of magnesium sulfate and sodium sulfate is 90%-98%. The molecular weight of the retained organics is approximately 200-400.

It should be noted here that: in step S12, the ultrafiltration process can be repeated, that is, the number of ultrafiltration processes can be one or more. In step S13, the nanofiltration process can also be repeated, that is to say, the number of nanofiltration processes can be one or more.

The seawater is pretreated through the above-mentioned electro-sedimentation step-ultrafiltration step-nanofiltration step. The obtained pretreated seawater, that is, the third pretreated seawater, contains less impurity ions.

S20, the seawater concentration step. The third pretreated seawater is concentrated to obtain a concentrated solution.

In some embodiments, the concentration is evaporative concentration. In the evaporation process, at least one of the following evaporation systems can be used, such as MED evaporation system, MVR evaporation system or MED-TC evaporation system. It is also possible to combine different systems, such as using MED evaporation and concentration system combined with MVR evaporation and crystallization system for evaporation.

In some embodiments, an MVR evaporation system is used, and step S20 is described by taking this embodiment as an example.

The MVR evaporation system may include a heating chamber, a separation chamber and a concentrate cooler.

Wherein, the heating chamber includes a transfer pump for pumping the third pretreated seawater into the heater, a heat exchanger for preheating the third pretreated seawater, so that the preheated third pretreated seawater and the forced circulating liquid A mixed circulation pipeline, a forced circulation pump for splitting the mixed third pretreated seawater (ie, circulating liquid), and a plurality of heat exchange tubes that can accommodate and heat the split circulating liquid.

The separation chamber is used for concentrating the circulating liquid heated by the heat exchange tube. The pressure in the separation chamber is lower than the heat exchange tube, so the circulating liquid enters the separation chamber for flash evaporation to complete the concentration. During flash evaporation, water, concentrate and high temperature steam are produced.

The concentrate cooler is used to cool the concentrate to room temperature.

In the process of concentrating the seawater, the third pretreated seawater is transported to the heat exchanger by the transfer pump. The high temperature water vapor is compressed by the compressor and enters the heating chamber, and in the heat exchanger, the third pretreated seawater is preheated using the aforementioned high temperature water vapor. This method can recover a large amount of energy in the high-temperature water vapor, so that the temperature of the third pretreated seawater can be raised close to the boiling point temperature. At the same time, the temperature of the distilled water discharged from the separation chamber can be lowered.

The third pre-treated seawater reaches the circulation pipeline after preheating, and is mixed with the forced circulating liquid to form a circulating liquid. It should be noted here that the "forced circulating liquid" refers to: after the third pretreated seawater is heated by the heat exchange tube and flashed in the separation chamber, because the concentration of the concentrated liquid left after flashing does not meet the concentration requirements, The concentrate returned to the circulation line. That is to say, when the third pretreated seawater is concentrated in the separation chamber, if the concentration of the concentrated solution cannot meet the technological requirements, that is, the ion concentration of the concentrated solution is less than the specified ion concentration of the concentrated solution that can be released, then this part of the concentrated solution is used as the Force the circulating liquid to return to the circulating pipeline for circulation until the concentrated liquid is concentrated in the separation chamber and the concentration of the concentrated liquid reaches the technological requirements, and the concentrated liquid is discharged from the system.

The circulating liquid is divided into each heat exchange tube through a forced circulating pump. In some embodiments, the flow velocity of the liquid in the heat exchange tube can be controlled to be 1.5m/s-3.5m/s, such as 1.5m/s, 2.0m/s, 2.5m/s, 3.0m/s, 3.5m/s, etc. . When the liquid flow rate of the heat exchange tube is in the above range, the heating efficiency can be ensured, and the fouling probability can be reduced, so as not to affect the heat exchange efficiency. When the circulating liquid flows from the heat exchange tube at a high speed, the circulating liquid is heated by the heat generated by the condensation of the steam outside the heat exchange tube. By controlling the pressure in the tube to be higher than the saturated vapor pressure at this temperature, the circulating liquid will not boil in the heat exchange tube, so that the circulating liquid will not evaporate in the heat exchange tube.

The heated circulating liquid flows out from the heater to the low-pressure separation chamber. Due to the sudden drop in the pressure of the separation chamber, the high-temperature circulating liquid flashes here, and the evaporation temperature is between 60°C and 90°C. The seawater is concentrated to obtain a concentrate and distilled water. After the concentration of the concentrated liquid reaches the concentration requirements, it is drawn out from the outlet of the forced circulation pump and enters the concentrated liquid cooler for concentration.

It should be noted here that the concentration requirement of the concentrated solution may be: the mass percentage concentration of the concentrated solution is 26%-40.7%. The aforementioned concentration requirement is that when the concentration of the concentrated solution reaches 26%-40.7%, the concentrated solution can be discharged from the evaporation system for further processing, and if the above concentration requirement is not met, the cyclic evaporation will continue.

Compared with ordinary atmospheric evaporation (evaporation temperature is 95℃-100℃), the MVR evaporation system uses a lower temperature for evaporation, and the high-temperature water vapor generated after evaporation can be compressed by the compressor and re-entered The heating chamber is used as a heat source to maintain the third pretreated seawater in a boiling state, and the high temperature water vapor itself condenses into water. The waste water vapor in the ordinary atmospheric evaporation is fully utilized, and the thermal efficiency is improved.

After concentration, the concentrate can be tested. In the test results, the content of heavy metal elements is not higher than 0.5mg/kg; the content of silicon dioxide is not higher than 5mg/kg; the content of multivalent ions is not higher than 1mg/kg. The heavy metal elements may include Hg, Ba, Mn, Ni, Pb, and Sr; the multivalent ions may include Fe2+, Fe3+.

S30, the product preparation step. Include at least one of the following steps:

Sa, salt making step. Continue to concentrate the concentrated solution obtained in step S20, where the equipment used for concentration is a centrifuge, and the centrifuge is used to separate the concentrated solution to obtain solid sodium chloride and centrifugal mother liquor. The solid sodium chloride is shipped out to obtain the product.

It should be noted here that the centrifugation mother liquor remaining after centrifugation may be subjected to step S20 to continue to concentrate.

Sb, alkali production and hydrogen production steps:

Sb1: softening step. The concentrated solution obtained in step S20 is softened to remove residual calcium and magnesium ions therein.

Step Sb1 can be softened by the following two methods:

Method 1: Double alkali softening.

The concentrated solution obtained in step S20 is detected. According to the content of calcium and magnesium ions in the detected concentrate, an appropriate amount of sodium hydroxide and sodium carbonate are added to generate magnesium hydroxide and calcium carbonate precipitation. Remove calcium and magnesium ions from the concentrate to obtain a softened concentrate. Preferably, feeding can be performed according to the ratio of X Mg ²⁺ : Y NaOH=3:10, A Ca ²⁺ : B Na ₂ CO ₃ =20:53. Wherein, X represents the amount of magnesium ions in the concentrated solution, Y represents the amount of sodium hydroxide that needs to be added, A represents the amount of calcium ions in the concentrated solution, and B represents the amount of sodium carbonate that needs to be added. . At the same time, flocculants PAC and/or PAM can be added, and the content of flocculants can be added according to the amount of sedimentation, or other types of flocculants can be selected. Adding a flocculant can make the smaller particles generated by the softening reaction adsorb to obtain larger particles, which is convenient for sedimentation. The mixed solution was stirred evenly and then settled. Compressed air can be used for stirring, or a stirring motor can be used for stirring or other stirring methods.

Method 2: Lime softening method.

The concentrated solution obtained in step S20 is detected. According to the amount of calcium and magnesium ions in the detected concentrate, lime and sodium carbonate are added to form magnesium hydroxide and calcium carbonate precipitation, and the calcium and magnesium ions in the concentrate are removed to obtain a softened concentrate. Optionally, feeding can be performed according to the ratio of Mg ²⁺ :Ca(OH) ₂ =12:37; Ca ²⁺ :Na ₂ CO ₃ =20:53. Similarly, flocculant can be added as described in Method 1, so it will not be repeated here.

In this embodiment, in step Sb1, the first method is adopted, that is, the double-alkali method is used to soften and remove calcium and magnesium ions, which can reduce the amount of sodium carbonate.

In the above two methods, after the reaction is completed, the concentrated solution after the above reaction needs to be placed in a sedimentation tank for precipitation separation. The precipitation time can be 20min-2h, and the precipitation time can be appropriately adjusted according to the amount of water. For example, when the water volume is small, the sedimentation time can be 20min-30min; when the water volume is large, the settling time can be 1h-2h.

After sedimentation, the supernatant liquid and the mud at the bottom of the sedimentation tank are obtained. The mud can be separated from mud and water by a mud water separator. The filtrate obtained after being separated by a mud-water separator is filtered together with the supernatant to obtain a softened concentrate. After testing, the total amount of Ca and Mg in the concentrate is less than 0.02 mg/L. The dehydrated dry mud can be transported to landfill.

The content of impurities in the concentrate after softening meets the standards shown in Table 1:

Table 1

As can be seen from Table 1, using the seawater desalination zero discharge and resource recycling method shown in this application, in the front-end processing process, that is, after completing steps S10 and S20, the content of heavy metal elements can be made not higher than 0.5mg/kg, The content of silica is not higher than 5mg/kg, and the content of multivalent ions is not higher than 1mg/kg. And after the softening process, the total content of calcium and magnesium may not exceed 0.02 mg/kg.

Sb2: Electrolysis step. The softened concentrate can be electrolyzed by means of ion membrane electrolysis.

In some embodiments, ionic membrane electrolysis is performed using an ion electrolysis cell. The softened concentrate is passed into the ion electrolytic cell for electrolysis, and the current density can be set to be 3.4KA/m ² -4.0KA/m ² , and the voltage can be set to 2.45V-3.3V. The ion electrolysis reaction formula is as follows:

NaCl+H ₂ O=NaOH+Cl ₂ +H ₂

At the anode of the ion electrolytic cell, NaCl is electrolyzed into Na ⁺ and Cl ^- , Na ⁺ migrates to the cathode chamber through a selective cation membrane under the action of electric charge, and the remaining Cl ^- generates chlorine gas under the action of anode electrolysis. The obtained chlorine can be used to obtain hydrogen chloride in subsequent reactions. The H ₂ O in the cathode chamber is ionized into H ⁺ combined with OH ^- , OH ^- and Na ⁺ to generate sodium hydroxide, and H ⁺ generates hydrogen, which can be used as hydrogen fuel.

When the concentration of the generated sodium hydroxide solution is about 30%, the sodium hydroxide solution is discharged from the ion electrolytic cell to obtain a sodium hydroxide solution. Since there are few impurities in the concentrated solution before electrolysis, after electrolysis, a sodium hydroxide solution with less impurities and higher quality can be obtained. The remaining electrolyte in the ion electrolytic cell can be recycled.

In some embodiments, after step S20 is completed, only step Sa may be performed to obtain solid sodium chloride. In some embodiments, after step S20 is completed, only step Sb may be performed to obtain a sodium hydroxide solution with a concentration of about 30% and hydrogen gas. In some embodiments, the concentrated solution obtained after step S20 is completed may be subjected to step Sa with a part of the concentrated solution and step Sb with another part of the concentrated solution to obtain solid sodium chloride, sodium hydroxide solution with a concentration of about 30% and hydrogen gas . In the actual production and preparation process, the amount of the concentrated solution participating in the step Sa and the step Sb can be adjusted according to the actual situation.

In some embodiments, the seawater recovery step is also included:

S40, the seawater recovery step. The electrolyte solution remaining in the Sb2 step is added to the dechlorination agent, in some embodiments, the electrolyte solution is a sodium chloride solution with a concentration of about 20%-24%. Sodium bisulfite can be used as a chlorine removal agent. To absorb the residual chlorine in the electrolyte. In some embodiments, as shown in Figure 2, hydrogen chloride can also be introduced in this process, and the recovered sodium chloride solution can be obtained after the reaction, and sulfuric acid can also be generated at the same time to increase the product type.

The recovered sodium chloride solution is subjected to step S10 for recycling, optionally, the recovered sodium chloride solution can be subjected to step S13, and the multivalent ions are intercepted by the nanofiltration membrane and then continue to evaporate. Compared with carrying out step S11 (as shown in Figure 3) to reclaiming sodium chloride solution, namely processing reclaiming sodium chloride solution through electro-precipitation, ultrafiltration and nanofiltration process; or carrying out step S12 to reclaiming sodium chloride solution (as shown in Figure 4), namely, the recovery of sodium chloride solution is processed through ultrafiltration and nanofiltration processes. Only carrying out the S13 step to recover the sodium chloride solution can reduce the waste of resources.

Taking a certain seawater desalination process with zero discharge and resource recycling as an example, the mass of seawater treated is 1 ton, of which the concentration of sodium chloride is about 3%, and the proportion of impurity ions is about 0.5%. When carrying out zero discharge of seawater desalination and resource recycling according to the method shown in the present application, in step S30, only step Sa is used to generate solid sodium chloride, the quality of the sodium chloride is about 30kg, and the quality of fresh water is about 30kg. is 965kg.

Taking a certain seawater desalination process with zero discharge and resource recycling as an example, the mass of seawater treated is 1 ton, of which the concentration of sodium chloride is about 3%, and the proportion of impurity ions is about 0.5%. When performing zero discharge of seawater desalination and resource recovery and utilization according to the method shown in this application, before step S30, the obtained sodium chloride solution with a concentration of 30% is about 100 kg. In step S30, using only step Sb, about 22.7 kg of 30% sodium hydroxide solution and about 0.14 kg of hydrogen gas were obtained.

According to the method in the related art, taking a certain seawater desalination zero discharge and resource recycling process as an example, the quality of the seawater treated is 1 ton, the sodium chloride concentration is about 3%, and the proportion of impurity ions is about 0.5%. The seawater is directly concentrated to obtain fresh water. According to the calculation of 8% of the highest concentration of the concentrated liquid in the current related technology, the discharged unusable concentrated liquid is about 375kg.

It can be seen from the above three sets of data that the use of the seawater desalination zero-discharge and resource recovery and utilization methods shown in this application can greatly reduce the discharge of concentrated liquid in the process of seawater utilization, and achieve zero discharge of concentrated liquid. In addition, more fresh water is obtained. At the same time, it can realize the direct production of salt, alkali, hydrogen and chlorine from seawater, so as to obtain more resources.

The above seawater desalination zero-discharge and resource recovery and utilization methods have at least the following technical effects:

Through the seawater pretreatment step, the heavy metal ions, silica and multivalent ions in the seawater are separated to obtain relatively clean seawater. The pretreated seawater is then subjected to a seawater concentration step. In the seawater concentration step, fresh water is obtained, and a concentrated solution of sodium chloride solution with a concentration of about 30% can be obtained, and the concentrated solution has less impurities. It is easier to use in subsequent use. If sodium chloride solution is required, this part of the concentrate can be used directly. If solid sodium chloride is desired, this part of the sodium chloride solution can be evaporated to obtain solid sodium chloride. Moreover, in the process of preparing solid sodium chloride, compared with the related art, the addition of chemical reagents is greatly reduced, and the cost of reagents is reduced. If it is necessary to obtain sodium hydroxide solution, this part of the concentrated solution can be softened and then electrolyzed to obtain hydrogen and chlorine gas while obtaining sodium hydroxide solution. The residual low-concentration sodium chloride solution after electrolysis can be recycled in combination with chlorine gas. Correspondingly, it is also possible to directly prepare sodium chloride solution, solid sodium chloride, sodium hydroxide solution, hydrogen and chlorine gas by using seawater as raw material in one production line. Hydrogen can further be made into hydrogen fuel, and chlorine can further be made into hydrogen chloride.

By adopting the above-mentioned process method, zero discharge of concentrated solution of seawater recovery and treatment can be realized to a large extent, and in the process of obtaining fresh water, substances such as solid sodium chloride, sodium hydroxide, hydrogen gas and chlorine gas are prepared, which is very beneficial to the resources of seawater. The recovery rate is large, and seawater can be directly used for salt production, alkali production and hydrogen production, and the amount of salt production, alkali production and hydrogen production can be flexibly adjusted. Improve the utilization rate of seawater resources to a large extent.

In addition, in this application, although the input cost of seawater pretreatment in the early stage may be high, because it can simultaneously produce a large amount of sodium chloride, sodium hydroxide and hydrogen, its net profit is relatively high, and the technical prospect is good.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present application, and the descriptions thereof are relatively specific and detailed, but should not be construed as a limitation on the scope of the patent application. It should be noted that, for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims

A seawater desalination zero-discharge and resource recovery and utilization process is characterized in that, comprising the following steps:

The seawater pretreatment step removes impurities in seawater to obtain pretreated seawater;

In the seawater concentration step, the pretreated seawater obtained in the seawater pretreatment step is concentrated to obtain a concentrated solution; in the concentrated solution: the content of each heavy metal element is not higher than 0.5 mg/kg; the content of silicon dioxide is not higher than 5 mg/kg kg; the content of each multivalent ion is not higher than 1mg/kg;

Product preparation steps: including at least one of the following steps:

Salt-making step: the concentrated solution is concentrated and separated to obtain solid sodium chloride;

In the step of making alkali and hydrogen, the concentrated solution is softened, and after softening, electrolysis is performed, and after electrolysis, sodium hydroxide solution, hydrogen and chlorine gas are obtained.
The seawater desalination zero-discharge and resource recycling process according to claim 1, wherein the seawater pretreatment step comprises the following steps:

In the step of electro-precipitation, electro-precipitation is performed on the pretreated seawater, and the first pretreated seawater is obtained after filtering;

Ultrafiltration step, the first pretreated seawater is subjected to ultrafiltration to obtain the second pretreated seawater;

In the nanofiltration step, the second pretreated seawater is subjected to nanofiltration to obtain the third pretreated seawater.
The seawater desalination zero-discharge and resource recovery and utilization process according to claim 2, wherein, in the electric sedimentation step, the current density is set in the range of 40A/m 2 -60A/m 2 .
The seawater desalination zero-discharge and resource recycling process according to claim 2, wherein, in the ultrafiltration step, the ultrafiltration membrane pore size is selected from 0.005 μm to 0.1 μm.
The seawater desalination zero-discharge and resource recycling process according to claim 2, wherein, in the nanofiltration step, the nanofiltration pressure difference is set in the range of 0.1MPa-0.5MPa.
The seawater desalination zero-discharge and resource recovery and utilization process according to claim 1, characterized in that, in the seawater concentration step, evaporative concentration is selected, and the concentration range of the concentrated liquid mass percentage after concentration is 26%-40.7%.
The seawater desalination zero-discharge and resource recovery and utilization process according to claim 6, wherein in the seawater concentration step, at least one evaporation system in the MED evaporation system, the MVR evaporation system or the MED-TC evaporation system is used to carry out the process. Concentrated by evaporation.
The seawater desalination zero-emission and resource recovery and utilization process according to claim 1, wherein, in the steps of making soda and hydrogen, a double-alkali method is used for softening treatment.
The seawater desalination zero-emission and resource recovery and utilization process according to claim 1, wherein in the step of making soda and hydrogen, in the electrolysis process, the current density is set to be 3.4K A/m 2 -4.0K A/m 2 , the voltage is 2.45V-3.3V.
The seawater desalination zero discharge and resource recovery and utilization process according to claim 1, is characterized in that, also comprises seawater recovery step:

Adding a chlorine remover to the remaining electrolyte in the alkali-making and hydrogen steps to obtain a reclaimed sodium chloride solution;

The reclaimed sodium chloride solution is passed into the seawater pretreatment step for utilization.