Device and method for recycling saline wastewater

Abstract

The present invention relates to the field of wastewater treatment technology, and in particular to a device and method for recycling saline wastewater. The saline wastewater recycling device provided by the present invention comprises a hot wastewater circulation unit, a membrane assembly and a condensed water circulation unit connected in sequence. The present invention utilizes the factory's own heat source to heat the saline wastewater, and the heated saline wastewater is transported to the membrane assembly together with the cold water provided by the condensed water circulation unit, wherein the hot saline wastewater enters the hot side chamber, and the cold water enters the cold side chamber. Under the action of the temperature difference between the hot and cold sides, the hot saline wastewater is concentrated into a saline wastewater concentrate; the cyclone fluidized bed can serve as both a crystallizer and a sedimentation tank, which can remove a large amount of SS in the wastewater, and can also use the remaining SS to act as a seed crystal to accelerate the precipitation of salt in the saline wastewater concentrate, and use a heat exchanger to control different temperatures, and use a membrane assembly to control the degree of wastewater concentration to achieve the purpose of separating and precipitating crystals, thereby realizing the recycling of different crystals.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a device and method for recycling saline wastewater. Background Art

[0002] In 2019, the total discharge of industrial wastewater in my country was about 19.6 billion tons, but the overall reuse rate was below 10%. High-salt wastewater accounted for more than 16% of industrial wastewater, mainly from the pillar industries of the national economy such as electricity, chemical industry, printing and dyeing, and steel. In view of the complex water quality components, diverse types of pollutants, and large fluctuations in water quality and quantity of high-salt wastewater, existing treatment technologies often combine multiple processes, with a long process flow, and upstream equipment has a restraining effect on subsequent links. The overall operation coordination is difficult, and the equipment of each unit is frequently overhauled and maintained, which seriously restricts the stable operation of the entire process and the effective removal of pollutants.

[0003] At present, the devices and processes for treating saline wastewater are relatively complex and have high energy consumption. For example, Chinese patent CN105198148A discloses a saline wastewater treatment process, which mainly includes pretreatment, evaporation, crystallization, carbonization and other processes. The process requires pretreatment of the wastewater, and the process is complex. In addition, the evaporation and carbonization processes consume a large amount of electrical energy and are costly. Chinese patent CN102583862A discloses a saline wastewater treatment system, which includes a grid, a regulating tank, a flotation unit, a composite separation unit, an ion exchange unit, a WLRO ultrafiltration unit, a WLRO ordinary reverse osmosis membrane treatment unit, a WLAO electrolytic oxidation unit, a low-temperature evaporation crystallization unit, a sludge treatment unit, etc. The treatment device is large and complex, and the cost is high, which limits its large-scale application. The existing high-salinity wastewater treatment technology has an investment cost of between 1 and 2 million yuan per ton of water, and the operating cost remains high, which cannot meet the current water treatment industry's actual needs for efficient, low-cost, zero-emission wastewater treatment. Therefore, it is particularly important to design a new wastewater treatment technology with good treatment effect and low investment and operating costs. Summary of the invention

[0004] The purpose of the present invention is to provide a salt-containing wastewater recycling device. The device provided by the present invention is simple, can utilize the factory's own heat source to treat wastewater, reduces production costs, realizes low-cost zero-emission treatment of wastewater, and is suitable for promotion and application.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a salt-containing wastewater recycling device, comprising a hot wastewater circulation unit 2, a membrane module 1 and a condensed water circulation unit 3 connected in sequence;

[0007] The membrane assembly 1 comprises a hydrophobic microporous membrane, a hot side cavity and a cold side cavity arranged on both sides of the hydrophobic microporous membrane;

[0008] The hot wastewater circulation unit 2 includes a cyclone fluidized bed 2-2 and a heating heat exchanger 2-4 connected in sequence; the water outlet of the heating heat exchanger 2-4 is connected to the water inlet of the hot side chamber; the water outlet of the hot side chamber is connected to the water inlet of the cyclone fluidized bed 2-2;

[0009] The condensate circulation unit 3 includes a condensate tank 3-1 and a cold water tank 3-3 which are connected in sequence; the water outlet of the cold water tank 3-3 is connected to the water inlet of the cold side chamber; the water outlet of the cold side chamber is connected to the water inlet of the condensate tank 3-1.

[0010] Preferably, the hydrophobic microporous membrane has a thickness of 30 to 450 μm, a pore size of 0.03 to 0.5 μm, and a porosity of 40 to 80%.

[0011] Preferably, the hot wastewater circulation unit further comprises a cooling heat exchanger 2-5, and the water outlet of the hot side chamber is connected to the water inlet of the cyclone fluidized bed 2-2 via the cooling heat exchanger 2-5.

[0012] Preferably, the hot wastewater circulation unit further comprises a water storage tank 2-1, and a water outlet of the water storage tank 2-1 is connected to a water inlet of the cyclone fluidized bed 2-2.

[0013] Preferably, the hot wastewater circulation unit further comprises a liquid tank 2-3, the water inlet of the liquid tank 2-3 is connected to the water outlet of the cyclone fluidized bed 2-2, and the water outlet of the liquid tank 2-3 is connected to the water inlet of the heating heat exchanger 2-4.

[0014] Preferably, the condensed water circulation unit further includes a cooling water tank 3-2 connected to the condensed water tank 3-1 and the cold water tank 3-3.

[0015] The present invention also provides a method for recycling saline wastewater based on the device described in the above technical solution, comprising the following steps:

[0016] The saline wastewater is transported to the cyclone fluidized bed 2-2 for precipitation to obtain pretreated saline wastewater;

[0017] The pretreated saline wastewater is transported to the heating heat exchanger 2-4 and heated by the factory's own heat source to obtain hot saline wastewater;

[0018] The hot saline wastewater is transported to the hot side chamber of the membrane module 1, and the cold water in the cold water tank 3-3 is transported to the cold side chamber of the membrane module 1, so as to obtain a saline wastewater concentrate in the hot side chamber and condensed water in the cold side chamber;

[0019] The concentrated salt-containing wastewater is transported from the hot side chamber to the cyclone fluidized bed 2-2 for crystallization to obtain crystalline salt;

[0020] The condensed water is transported from the cold side chamber to the condensed water tank 3 - 1 for reuse.

[0021] Preferably, the saline wastewater is wastewater with a total salt content of more than 1% by mass.

[0022] Preferably, the heat source for heating is the factory's own heat source.

[0023] Preferably, the temperature difference between the hot saline wastewater and the cold water is 30-50°C.

[0024] The present invention provides a saline wastewater recycling device, comprising a hot wastewater circulation unit 2, a membrane assembly 1 and a condensed water circulation unit 3 connected in sequence. In the hot wastewater circulation unit 2, the present invention utilizes a factory's own heat source to heat the saline wastewater, and the heated saline wastewater and the cold water provided by the condensed water circulation unit 3 are transported to the membrane assembly 1 together, wherein the hot saline wastewater enters a hot side chamber, and the cold water enters a cold side chamber. Under the action of the temperature difference between the hot and cold sides, with the vapor pressure difference as a driving force, the water vapor in the wastewater in the hot side chamber passes through a hydrophobic microporous membrane of the membrane assembly and enters the cold side chamber to be condensed, and the hot saline wastewater is concentrated into a saline wastewater concentrate; the cyclone fluidized bed can serve as both a crystallizer and a sedimentation tank, can remove a large amount of SS in the wastewater, and can accelerate the precipitation of salt in the saline wastewater concentrate by utilizing the remaining SS to act as a crystal seed, and utilizes a heat exchanger to control different temperatures and utilizes the membrane assembly to control the concentration degree of the wastewater to achieve the purpose of separating and precipitating crystals, thereby realizing the recycling of different crystals. The device provided by the present invention has reasonable design and simple structure, can utilize the factory's own heat source to treat wastewater, reduces the cost of wastewater treatment, realizes low-cost zero-discharge treatment of wastewater, and is suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of the salt-containing wastewater recycling device in an embodiment of the present invention; wherein 1 is a membrane assembly, 2 is a hot wastewater circulation unit, 2-1 is a water storage tank, 2-2 is a cyclone fluidized bed, 2-3 is a liquid tank, 2-4 is a heating heat exchanger, 2-5 is a cooling heat exchanger, 3 is a condensate water circulation unit, 3-1 is a condensate water tank, 3-2 is a cooling water tank, and 3-3 is a cold water tank. DETAILED DESCRIPTION

[0026] The present invention provides a salt-containing wastewater recycling device, comprising a hot wastewater circulation unit 2, a membrane module 1 and a condensed water circulation unit 3 connected in sequence;

[0027] The saline wastewater recycling device provided by the present invention includes a membrane assembly 1 for concentrating saline wastewater. In the present invention, the membrane assembly 1 includes a hydrophobic microporous membrane, a hot side chamber and a cold side chamber arranged on both sides of the hydrophobic microporous membrane. In the present invention, the material of the hydrophobic microporous membrane is preferably PP, PTFE or PVDF; the thickness of the hydrophobic microporous membrane is preferably 30 to 450 μm, more preferably 100 to 230 μm; the pore size of the hydrophobic microporous membrane is preferably 0.03 to 0.5 μm, more preferably 0.1 to 0.3 μm; the porosity of the hydrophobic microporous membrane is preferably 40 to 80%. The present invention utilizes a hydrophobic microporous membrane to allow water vapor in the hot side chamber to enter the cold side chamber, while ensuring that the salt in the hot side chamber does not enter the cold side chamber, thereby achieving the concentration of the saline wastewater in the hot side chamber.

[0028] The saline wastewater recycling device provided by the present invention comprises a hot wastewater circulation unit 2 connected to the hot side chamber of the membrane module 1, which is used for precipitating, heating, concentrating and crystallizing the saline wastewater. In the present invention, the hot wastewater circulation unit 2 comprises a cyclone fluidized bed 2-2 and a heating heat exchanger 2-4 connected in sequence; the water outlet of the heating heat exchanger 2-4 is connected to the water inlet of the hot side chamber; the water outlet of the hot side chamber is connected to the water inlet of the cyclone fluidized bed 2-2.

[0029] The present invention has no special limitation on the structure of the cyclone fluidized bed 2-2, and a cyclone fluidized bed 2-2 known to those skilled in the art can be used. In a specific embodiment of the present invention, the cyclone fluidized bed 2-2 includes a barrel and a conical barrel at the bottom, and the barrel is preferably a cylinder; the water inlet and the water outlet of the cyclone fluidized bed 2-2 are arranged on the side wall of the barrel, the water inlet is arranged opposite to the water outlet, and the horizontal height of the water inlet is less than the horizontal height of the water outlet. In a specific embodiment of the present invention, the saline wastewater enters the cyclone fluidized bed 2-2 along a tangent, rotates slowly and naturally in the cyclone fluidized bed 2-2, removes a large amount of suspended particles (SS) in the saline wastewater, and obtains pretreated saline wastewater, which flows out of the cyclone fluidized bed 2-2 along a tangent; in addition, the saline wastewater concentrate concentrated by the membrane assembly 1 is crystallized in the cyclone fluidized bed 2-2, and the clear liquid after crystallization flows out of the cyclone fluidized bed 2-2 along a tangent, and the crystallized salt is discharged through the cone barrel of the cyclone fluidized bed 2-2 for recycling. In the present invention, the separation of crystallized salt is achieved by segmented precipitation using different solubility of crystals. In the present invention, the cyclone fluidized bed 2-2 is used in conjunction with the membrane assembly 1, and is used as both a crystallizer and a sedimentation tank. The present invention does not specifically limit the specific use parameters of the cyclone fluidized bed 2-2, and is usually specifically adjusted according to the different types of salts contained in the wastewater.

[0030] As an embodiment of the present invention, the hot wastewater circulation unit 2 also includes a cooling heat exchanger 2-5, and the water outlet of the hot side chamber is connected to the water inlet of the cyclone fluidized bed 2-2 through the cooling heat exchanger 2-5. The present invention has no special limitation on the specific structure of the cooling heat exchanger 2-5, and a heat exchanger well known to those skilled in the art can be used. In the present invention, when the solubility difference of the salts in the saline wastewater at the same temperature is more than 3 times, and the segmented crystallization can be controlled by controlling the concentration ratio, the water outlet of the hot side chamber is directly connected to the water inlet of the cyclone fluidized bed 2-2; when the solubility difference of the salts in the saline wastewater at the same temperature is not large (the solubility difference is less than 2 times) but the difference is large at different temperatures, the temperature can be controlled while controlling the concentration ratio to perform segmented crystallization of the crystals, that is, some crystallized salts are precipitated at the current temperature, and then another part of the crystallized salts are precipitated after cooling through the cooling heat exchanger 2-5. In a specific embodiment of the present invention, the solubility of different salts in saline wastewater at different temperatures is used to precipitate crystalline salts. A three-way valve is installed on the outlet pipe of the hot side chamber of the membrane module 1. When it is necessary to control the precipitation of crystalline salts by cooling, the three-way valve is controlled to allow the saline wastewater concentrate to flow to the cooling heat exchanger 2-5 and then enter the cyclone fluidized bed 2-2 after being cooled to the required temperature, and then crystallize and discharge the crystalline salt for comprehensive utilization. In a specific embodiment of the present invention, the cold source of the cooling heat exchanger 2-5 is preferably provided by a cooling device.

[0031] In the present invention, the hot wastewater circulation unit 2 includes a heating heat exchanger 2-4 connected to the outlet of the cyclone fluidized bed 2-2, and the pre-treated saline wastewater discharged from the cyclone fluidized bed 2-2 is heated by the factory's own heat source. The present invention does not specifically limit the specific structure of the heating heat exchanger 2-4, and a heat exchanger well known to those skilled in the art can be used. In the present invention, the heat exchange mode of the heating heat exchanger 2-4 preferably includes liquid-liquid heat exchange or gas-liquid heat exchange. In a specific embodiment of the present invention, gas-liquid heat exchange is preferably used to heat the pre-treated saline wastewater using the flue gas waste heat of thermal power plants, steel plants, coking plants, waste incineration power plants and other factories, which is more energy-saving and environmentally friendly and has extremely high heat exchange efficiency. In a specific embodiment of the present invention, liquid-liquid heat exchange is preferably applied to factories with available hot water. When the hot water temperature is sufficient, the pre-treated saline wastewater can be directly heated. When the hot water temperature is insufficient, the hot water is heated to the required temperature before the pre-treated saline wastewater is heated, which can save energy. In a specific embodiment of the present invention, the pretreated saline wastewater and flue gas / hot water are countercurrently exchanged in the heating heat exchanger 2-4.

[0032] As an embodiment of the present invention, the hot wastewater circulation unit 2 further includes a water tank 2-1, and the water outlet of the water tank 2-1 is connected to the water inlet of the cyclone fluidized bed 2-2. In the present invention, the water tank 2-1 is used to hold the saline wastewater to be treated and control the flow rate of the saline wastewater entering the cyclone fluidized bed 2-2. The present invention has no special restrictions on the structure and size of the water tank 2-1, and the water tank 2-1 known to those skilled in the art can be used.

[0033] As an embodiment of the present invention, the hot wastewater circulation unit 2 further includes a liquid tank 2-3, the water inlet of the liquid tank 2-3 is connected to the water outlet of the cyclone fluidized bed 2-2, and the water outlet of the liquid tank 2-3 is connected to the water inlet of the heating heat exchanger 2-4. The present invention has no special limitation on the structure and size of the liquid tank 2-3, and the liquid tank 2-3 known to those skilled in the art can be used.

[0034] The salt-containing wastewater recycling device provided by the present invention includes a condensate circulation unit 3 connected to the cold side chamber of the membrane assembly 1, which is used to provide cold water to the cold side chamber and recycle the condensate. In the present invention, the condensate circulation unit 3 includes a condensate tank 3-1 and a cold water tank 3-3 connected in sequence; the water outlet of the cold water tank 3-3 is connected to the water inlet of the cold side chamber; the water outlet of the cold side chamber is connected to the water inlet of the condensate tank 3-1. In the present invention, the condensate tank 3-1 is used to collect condensate discharged from the cold side chamber; the cold water tank 3-3 is used to store cold water and control the amount of cold water entering the cold side chamber. The present invention has no special restrictions on the structure and size of the condensate tank 3-1 and the cold water tank 3-3, and the condensate tank 3-1 and the cold water tank 3-3 known to those skilled in the art can be used.

[0035] As an embodiment of the present invention, the condensing water circulation unit 3 also includes a cooling water tank 3-2 connected to the condensing water tank 3-1 and the cold water tank 3-3. As an embodiment of the present invention, the inlet and outlet water pumps of the cooling water tank 3-2 adopt an intermittent working mode: when the water in the condensing water tank 3-1 accumulates to the upper limit of the condensing water tank 3-1, the water in the condensing water tank 3-1 is pumped into the cooling water tank 3-2 to be cooled to room temperature and stored; when the water in the cold water tank 3-3 is reduced to the lower limit of the tank body, the water stored in the cooling water tank 3-2 is pumped to the cold water tank 3-3 to replenish its water.

[0036] The salt-containing wastewater recycling device provided by the present invention is as follows Figure 1As shown, it includes a hot wastewater circulation unit 2, a membrane assembly 1 and a condensed water circulation unit 3 connected in sequence; the membrane assembly 1 includes a hydrophobic microporous membrane, a hot side cavity and a cold side cavity arranged on both sides of the hydrophobic microporous membrane; the hot wastewater circulation unit 2 includes a water storage tank 2-1, a cyclone fluidized bed 2-2, a liquid tank 2-3 and a heating heat exchanger 2-4 connected in sequence; the water outlet of the heating heat exchanger 2-4 is connected to the water inlet of the hot side cavity; the hot side The water outlet of the cavity is directly connected to the water inlet of the cyclone fluidized bed 2-2 or is connected to the water inlet of the cyclone fluidized bed 2-2 via the cooling heat exchanger 2-5; the condensed water circulation unit 3 includes a condensed water tank 3-1, a cooling water tank 3-2 and a cold water tank 3-3 connected in sequence; the water outlet of the cold water tank 3-3 is connected to the water inlet of the cold side cavity; the water outlet of the cold side cavity is connected to the water inlet of the condensed water tank 3-1.

[0037] When the device provided by the present invention is used to treat saline wastewater, there is no need to set up special pretreatment facilities to pretreat the saline wastewater. The saline wastewater can be directly concentrated and crystallized, which greatly reduces the operating cost of the system; the device provided by the present invention can use the factory's own heat source to heat the saline wastewater, thereby reducing the treatment cost; in addition, the device provided by the present invention can realize the segmented crystallization of salts in the saline wastewater, thereby achieving the purpose of recovering different crystallized salts, realizing low-cost zero-emission treatment of saline wastewater, and can achieve complete resource utilization of the saline wastewater.

[0038] The present invention also provides a method for recycling saline wastewater based on the device described in the above technical solution, comprising the following steps:

[0039] The saline wastewater is transported to the cyclone fluidized bed 2-2 for precipitation to obtain pretreated saline wastewater;

[0040] The pretreated saline wastewater is transported to the heating heat exchanger 2-4 for heating to obtain hot saline wastewater;

[0041] The hot saline wastewater is transported to the hot side chamber of the membrane assembly 1, and the cold water is transported to the cold side chamber of the membrane assembly 1. Under the action of the temperature difference between the hot and cold sides, with the vapor pressure difference as the driving force, the water vapor in the wastewater in the hot side chamber passes through the hydrophobic microporous membrane of the membrane assembly and enters the cold side chamber to be condensed, and the hot saline wastewater is concentrated into a saline wastewater concentrate. The hot saline wastewater is concentrated to obtain a saline wastewater concentrate and condensed water;

[0042] The concentrated salt-containing wastewater solution is transported to the cyclone fluidized bed 2-2 for crystallization to obtain crystalline salt;

[0043] The condensed water is transported to the condensed water tank 3-1 for reuse.

[0044] The present invention transports saline wastewater to a cyclone fluidized bed 2-2 for precipitation to obtain pretreated saline wastewater. In the present invention, the saline wastewater is wastewater with a total salt content of at least 1% by mass. In the present invention, the salt in the saline wastewater preferably includes one or more of calcium sulfate, magnesium sulfate, calcium chloride, magnesium chloride, sodium sulfate and sodium chloride. In the precipitation process of the present invention, most of the SS in the saline wastewater is removed, and the clear liquid enters the membrane assembly 1 from the outlet of the cyclone fluidized bed 2-2 to avoid crystallization of salts on the surface of the hydrophobic microporous membrane of the membrane assembly 1, resulting in a decrease in membrane flux caused by clogging of the membrane pores; and in the subsequent crystallization, the remaining SS in the cyclone fluidized bed 2-2 can be used as a seed to accelerate the precipitation of crystalline salt.

[0045] In a specific embodiment of the present invention, it is preferred that the saline wastewater is first introduced into the water storage tank 2-1, and then introduced into the cyclone fluidized bed 2-2 after being transferred through the water storage tank 2-1.

[0046] After obtaining the pretreated saline wastewater, the present invention transports the pretreated saline wastewater to the heating heat exchanger 2-4 for heating to obtain hot saline wastewater. In the present invention, the heat source for heating is preferably waste heat from factory flue gas or waste heat from hot water. In the present invention, the temperature of the hot saline wastewater is preferably 60-70°C. The present invention controls the temperature of the hot saline wastewater within the above range, which can not only meet the membrane flux requirements during distillation of the membrane assembly 1, but also avoid the problem of excessive cost caused by heating the wastewater to a high temperature.

[0047] In a specific embodiment of the present invention, the pretreated saline wastewater preferably first enters the liquid tank 2-3 and then is transported to the heating heat exchanger 2-4, and the amount of water entering the heating heat exchanger 2-4 is adjusted.

[0048] After obtaining the hot saline wastewater, the present invention transports the hot saline wastewater to the hot side chamber of the membrane module 1, transports the cold water to the cold side chamber of the membrane module 1, and concentrates the hot saline wastewater to obtain saline wastewater concentrate and condensed water. In the present invention, the temperature of the cold water is preferably 20 to 30° C., more preferably 25° C. In a specific embodiment of the present invention, the cold water comes from tap water, which can eliminate the energy consumption of cooling equipment and minimize the operating cost.

[0049] In the present invention, the temperature of the hot saline wastewater and the temperature of the cold water ensure a temperature difference of 30 to 50°C to meet the temperature difference requirements of the hot and cold sides. The present invention limits the temperature difference of the hot and cold sides to 30 to 50°C to ensure the vapor pressure difference of the hot and cold sides of the membrane assembly 1. At this time, the water vapor in the hot saline wastewater enters the cold side cavity through the membrane pores of the hydrophobic microporous membrane of the membrane assembly 1 and is condensed and recycled. The hot saline wastewater is concentrated to obtain a saline wastewater concentrate. The present invention achieves the purpose of segmented crystallization by controlling the concentration degree of the saline wastewater, and realizes the separation and recycling of different crystallized salts.

[0050] After obtaining the saline wastewater concentrate, the present invention transports the saline wastewater concentrate to a cyclone fluidized bed 2-2 for crystallization to obtain crystalline salt. In the present invention, when the solubility difference of the salts in the saline wastewater concentrate is large at the same temperature (the solubility difference is more than 3 times), and the segmented crystallization can be controlled simply by controlling the concentration ratio, the saline wastewater concentrate is directly transported to the cyclone fluidized bed 2-2 for crystallization; when the solubility difference of the salts in the saline wastewater concentrate is not large at the same temperature (the solubility difference is less than 2 times) but is large at different temperatures, it is preferred to first cool the saline wastewater concentrate through a cooling heat exchanger 2-5 and then transport it to the cyclone fluidized bed 2-2 for crystallization.

[0051] In the present invention, the cyclone fluidized bed 2-2 acts as a sedimentation tank to remove SS in the wastewater, which occurs in the early stage of saline wastewater treatment; the cyclone fluidized bed 2-2 acts as a crystallization tank to crystallize in the late stage of saline wastewater treatment, at which time the saline wastewater has been concentrated to a certain extent, and the SS in the saline wastewater has been precipitated and completely removed.

[0052] After obtaining the condensed water, the present invention transports the condensed water to the condensed water tank 3-1 for reuse. In the present invention, it is preferred to first pump the water in the condensed water tank 3-1 into the cooling water tank 3-2 to prevent the temperature from rising during the cold water circulation and reduce the condensation effect; then pump the cooling water in the cooling water tank 3-2 into the cold water tank 3-3 to replenish the water in the cold water tank 3-3.

[0053] In the present invention, the conductivity of the condensed water is below 100 μS / m, and can be used as factory process feed water. The water contained in the crystals discharged from the bottom of the cyclone fluidized bed can be naturally evaporated to obtain dry crystals, or heated and evaporated to obtain dry crystals. The entire system achieves zero wastewater discharge treatment.

[0054] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1

[0056] Taking the desulfurization waste liquid of a coking plant as an example, the saline wastewater (salt content is 5000-20000 mg / L) is transported to the cyclone fluidized bed 2-2 through the water storage tank 2-1 for precipitation to obtain pretreated saline wastewater; the pretreated saline wastewater is transported to the heating heat exchanger 2-4 through the liquid tank 2-3 for heating to obtain hot saline wastewater at 60-70°C; the hot saline wastewater is transported to the hot side chamber of the membrane assembly 1, and tap water at 25°C is transported to the cold side chamber of the membrane assembly 1. The temperature difference between the hot and cold sides is used to allow the water vapor in the hot saline wastewater to enter the cold side chamber through the membrane pores of the hydrophobic microporous membrane to obtain condensed water. At the same time, the hot saline wastewater is concentrated to obtain a saline wastewater concentrate; the hot saline wastewater concentrate is transported to a cyclone fluidized bed 2-2 for crystallization, and after ammonium thiosulfate crystals are discharged from the bottom, the hot saline wastewater concentrate is further concentrated to precipitate ammonium sulfate crystals, and after the crystals are discharged from the bottom of the cyclone fluidized bed, the hot saline wastewater concentrate is further concentrated to precipitate ammonium thiocyanate crystals, thereby achieving zero-emission treatment and resource utilization of desulfurization waste liquid; the condensed water is transported to a condensation water tank 3-1, and then transported to a cold water tank via a cooling water tank 3-2, and the water in the cold water tank is transported to the cold side chamber of the membrane assembly 1, thereby achieving recycling of the condensed water.

[0057] Example 2

[0058] Taking the desulfurization wastewater from a thermal power plant as an example, the saline wastewater (the salt content is preferably 30,000 to 40,000 mg / L) is transported to the cyclone fluidized bed 2-2 through the water storage tank 2-1 for precipitation to obtain pretreated saline wastewater; the pretreated saline wastewater is transported to the heating heat exchanger 2-4 through the liquid tank 2-3 for heating to obtain hot saline wastewater at 60 to 70°C; the hot saline wastewater is transported to the hot side chamber of the membrane assembly 1, and tap water at 25°C is transported to the cold side chamber of the membrane assembly 1. The temperature difference between the hot and cold sides is used to allow the water vapor in the hot saline wastewater to enter the cold side chamber through the membrane pores of the hydrophobic microporous membrane to obtain condensed water, and the hot saline wastewater is concentrated to obtain a saline wastewater concentrate; the hot saline wastewater concentrate is first After the calcium sulfate crystals with the smallest solubility at 60-70°C are precipitated by the cyclic concentration treatment of the cyclone fluidized bed 2-2-membrane assembly 1-cyclone fluidized bed 2-2, they are discharged from the bottom of the cyclone fluidized bed, and the concentration is continued until the sodium chloride crystals with smaller solubility at 60-70°C are precipitated, and the crystals are discharged from the bottom of the cyclone fluidized bed, and then the cyclone fluidized bed 2-2-membrane assembly 1-cooling heat exchanger 2-5-cyclone fluidized bed 2-2 is carried out for cooling and crystallization to obtain sodium sulfate crystals with smaller solubility at 10-20°C and the crystals are discharged from the bottom of the cyclone fluidized bed; the condensed water is transported to the condensation water tank 3-1, and then transported to the cold water tank through the cooling water tank 3-2, and the water in the cold water tank is transported to the cold side chamber of the membrane assembly 1 to realize the recycling of the condensed water.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recycling saline wastewater, characterized in that: The method is carried out by using a saline wastewater recycling device, wherein the saline wastewater recycling device comprises a hot wastewater circulation unit (2), a membrane module (1) and a condensed water circulation unit (3) which are connected in sequence; The membrane assembly (1) comprises a hydrophobic microporous membrane, a hot side cavity and a cold side cavity arranged on both sides of the hydrophobic microporous membrane; The hot wastewater circulation unit (2) comprises a cyclone fluidized bed (2-2) and a heating heat exchanger (2-4) connected in sequence; the water outlet of the heating heat exchanger (2-4) is connected to the water inlet of the hot side chamber; the water outlet of the hot side chamber is connected to the water inlet of the cyclone fluidized bed (2-2); The condensed water circulation unit (3) comprises a condensed water tank (3-1) and a cold water tank (3-3) which are connected in sequence; the water outlet of the cold water tank (3-3) is connected to the water inlet of the cold side chamber; the water outlet of the cold side chamber is connected to the water inlet of the condensed water tank (3-1); The following steps are involved: The saline wastewater is transported to a cyclonic fluidized bed (2-2) for precipitation to obtain pretreated saline wastewater; The pretreated saline wastewater is transported to a heating heat exchanger (2-4) and heated using the factory's own heat source to obtain hot saline wastewater; The hot saline wastewater is transported to the hot side chamber of the membrane module (1), and the cold water in the cold water tank (3-3) is transported to the cold side chamber of the membrane module (1), thereby obtaining a saline wastewater concentrate in the hot side chamber and obtaining condensed water in the cold side chamber; The concentrated salt-containing wastewater is transported from the hot side chamber to a cyclonic fluidized bed (2-2) for crystallization to obtain crystalline salt; The condensed water is transported from the cold side chamber to the condensed water tank (3-1) for reuse.

2. The method for recycling saline wastewater according to claim 1, characterized in that: The hydrophobic microporous membrane has a thickness of 30 to 450 μm, a pore size of 0.03 to 0.5 μm, and a porosity of 40 to 80%.

3. The method for recycling saline wastewater according to claim 1, characterized in that: The hot wastewater circulation unit also includes a cooling heat exchanger (2-5), and the water outlet of the hot side chamber is connected to the water inlet of the cyclone fluidized bed (2-2) via the cooling heat exchanger (2-5).

4. The method for recycling saline wastewater according to claim 1 or 3, characterized in that: The hot wastewater circulation unit also includes a water storage tank (2-1), and a water outlet of the water storage tank (2-1) is connected to a water inlet of the cyclone fluidized bed (2-2).

5. The method for recycling saline wastewater according to claim 1 or 3, characterized in that: The hot wastewater circulation unit also includes a liquid tank (2-3), the water inlet of the liquid tank (2-3) is connected to the water outlet of the cyclone fluidized bed (2-2), and the water outlet of the liquid tank (2-3) is connected to the water inlet of the heating heat exchanger (2-4).

6. The method for recycling saline wastewater according to claim 1, characterized in that: The condensed water circulation unit further comprises a cooling water tank (3-2) connected to the condensed water tank (3-1) and the cold water tank (3-3).

7. The method for recycling saline wastewater according to claim 1, characterized in that: The saline wastewater is wastewater with a total salt content of more than 1% by mass.

8. The method for recycling saline wastewater according to claim 1, characterized in that: The heat source for the heating is the factory's own heat source.

9. The method for recycling saline wastewater according to claim 1, characterized in that: The temperature difference between the hot saline wastewater and the cold water is 30-50°C.

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