A method and system for concentrating saline wastewater

Abstract

The present invention discloses a method and system for concentrating saline wastewater. The saline wastewater is sent to a circulation box through a conveying pipeline and then sent to the liquid inlet of a heat exchanger arranged in the inlet flue of a desulfurization tower through a concentrating pump. The water temperature at the outlet of the heat exchanger is controlled at 90°C to 98°C. The saline wastewater that has completed heat exchange and temperature increase is sent to a concentration tower through the liquid outlet of the heat exchanger and a pipeline, and evaporated and concentrated in the concentration tower. The vacuum pump of the concentration tower controls the vacuum degree in the concentration tower to be 63 to 25 kPa by vacuuming. Under this vacuum degree, the boiling point of the wastewater is reduced to 75 to 92°C. Driven by the negative pressure of the concentration tower, the desulfurization slurry in the desulfurization tower enters a buffer water tank through a connecting pipeline until the liquid level pressure difference of the buffer water tank is balanced with the vacuum degree in the concentration tower. The saline wastewater evaporated and concentrated in the desulfurization tower is collected and returned to the circulation box for further circulation and concentration. The present invention realizes efficient evaporation and concentration of saline wastewater while reducing the water consumption of the desulfurization device and realizing timely discharge and concentration of desulfurization tower wastewater.

Description

Technical Field

[0001] The present invention relates to the field of resources and environment, and in particular to a method and system for concentrating saline wastewater. Background Art

[0002] Salt-containing wastewater such as wet desulfurization wastewater and power plant water has always been a difficulty in resource treatment of industrial wastewater. Wet desulfurization is one of the most widely used processes for industrial flue gas purification. In the wet desulfurization washing process, Cl - The enrichment of ions will have a significant negative impact on the operation of the desulfurization system, such as equipment corrosion and decreased desulfurization efficiency of the desulfurizer.

[0003] Cl in desulfurization system - The main sources are coal, desulfurizer and desulfurization equipment supplementary process water. Generally, the chlorine content in coal is 0.1% to 0.3%, the chlorine content in desulfurizer is 0.01%, and the chlorine content in supplementary process water is 100 to 200 mg / L. In order to ensure the continuous and stable operation of the wet desulfurization device, the wet desulfurization device must regularly discharge a certain amount of desulfurization wastewater outside the system to maintain the Cl content in the desulfurization slurry. - The ion concentration is less than 20000mg / L. In addition to the high concentration of Cl - In addition to ions, it also contains a large amount of suspended matter, heavy metal ions, soluble salts, gypsum particles, etc. It is the most difficult industrial wastewater to treat in power plants. It has the characteristics of high salinity, high hardness, complex components, acidity (pH value: 4-6) and strong corrosiveness.

[0004] At the same time, with the popularization of denitrification equipment in coal-fired power plants, the escaped NH3 generated during the flue gas denitrification process enters the wet desulfurization device with the flue gas and is captured and enriched by the acidic absorption liquid, resulting in a high concentration of NH4 in the desulfurization wastewater. + Ions (NH4 in some desulfurization wastewater + The ion concentration even reaches 6000-10000 mg / L), and the high concentration of ammonia nitrogen further increases the hazard of desulfurization wastewater and the difficulty of treatment.

[0005] During the treatment and reuse of saline wastewater such as desulfurization wastewater / power plant reclaimed water, the wastewater needs to be concentrated. Increasing the salt concentration in the wastewater and reducing the volume of wastewater to be treated are the most effective means to reduce the cost of saline wastewater treatment, improve reuse efficiency and reduce wastewater treatment costs.

[0006] Existing wastewater concentration processes include membrane concentration and evaporation concentration. Membrane concentration processes include forward osmosis (FO), electrodialysis (ED), and reverse osmosis (RO). Evaporation concentration processes include flue gas spray technology, flue gas waste heat concentration salt production technology, mechanical vapor recompression (MVR) evaporation crystallization technology, etc. The existing technical difficulties are as follows: (1) The wastewater membrane concentration process has high requirements for wastewater quality. The Ca content in the wastewater is relatively high. 2+ Mg 2+ During the concentration process, ions easily form scale on the membrane surface and block the membrane channel, making it difficult for the membrane concentration device to operate stably. It is necessary to soften the high-salt desulfurization wastewater to remove Ca 2+ Mg 2+ ions, but Ca 2+ Mg 2+ When ions precipitate, the pH range requirements vary greatly, which makes softening difficult. To achieve efficient softening of desulfurization wastewater, the required softening dosage is greatly increased, and the softening cost is high; (2) The evaporation concentration process requires a large amount of heat source to evaporate fresh water, the system is complex, and the investment and operating costs are high. Summary of the Invention

[0007] The present invention provides a method and system for concentrating saline wastewater, which can realize efficient evaporation and concentration of saline wastewater while reducing the operating water consumption of a desulfurization device and realizing timely discharge and concentration of desulfurization tower wastewater.

[0008] A method for concentrating saline wastewater, comprising:

[0009] The salty wastewater is sent to the circulation box through the pipeline, and then sent to the heat exchanger installed in the flue of the desulfurization tower by the concentration pump. The high-temperature flue gas at the desulfurization tower inlet is used to heat the salty wastewater and heat it. By adjusting the flow rate of the salty wastewater in the heat exchanger, the water temperature at the heat exchanger outlet is controlled at 90℃-98℃.

[0010] The vacuum pump in the concentration tower controls the vacuum degree in the concentration tower to -63 to -25 kPa by pumping vacuum. Under this vacuum degree, the boiling point of wastewater is 75°C to 92°C. The saline wastewater that has completed heat exchange and temperature increase is sent from the liquid outlet of the heat exchanger through connecting pipes to the liquid distribution layer and heat exchange grid in the concentration tower. The saline wastewater, atomized by the liquid distribution layer, evaporates and cools rapidly under the negative pressure environment of the concentration tower, and forms a liquid film on the surface of the heat exchange grid for further heat exchange and evaporation.

[0011] After two stages of evaporation and concentration, the wastewater is collected by the liquid distribution layer and the heat exchange grid surface and then returned to the circulation box through the pipeline for cyclic heating and evaporation concentration. When the saline wastewater in the circulation box is concentrated to the set concentration, it is discharged to the crystallization unit. This achieves the low-cost and high-efficiency concentration of the power plant's saline wastewater using the wet desulfurization device.

[0012] After the water vapor that has completed evaporation in the concentration tower and the circulation box is pressurized at the outlet of the corresponding vacuum pump, part of the evaporated steam generates condensed water to form a steam-water mixture, which is sent through pipelines to the desuperheater and humidifier located in the inlet flue of the desulfurization tower and downstream of the heat exchanger. It is sprayed by the injection head in the desuperheater and humidifier and mixed with the flue gas entering the desulfurization tower, thereby reducing the temperature of the flue gas entering the desulfurization tower, increasing the humidity of the flue gas, and reducing the amount of evaporated water in the wet desulfurization process.

[0013] Optionally, the bottom of the concentrating tower is connected to the desulfurization slurry pool in the desulfurization tower through a pipeline, and a desulfurization slurry buffer water tank connected to the circulation box is provided on the connecting pipeline; under the push of the negative pressure of the vacuum pump on the top of the circulation box, the desulfurization slurry in the desulfurization slurry pool enters the desulfurization slurry buffer water tank through the liquid inlet at the bottom of the desulfurization slurry buffer water tank and the connecting pipeline of the desulfurization slurry pool at a flow rate of 0.05m / s-0.20m / s, and the clear desulfurization slurry after precipitation in the desulfurization slurry buffer water tank is transported to the circulation box through the pipeline.

[0014] Optionally, the salt-containing wastewater is power plant water, desulfurization gypsum filtrate, and desulfurization slurry clear liquid with a salt content of less than 2.5%, and the salt content of the circulating concentrated wastewater in the circulation box is 7%-12%. Unless otherwise specified, the salt content in the present invention refers to the mass percentage content.

[0015] Optionally, the water and desulfurization gypsum filtrate from the power plant are transported to the circulation box by pipeline, and the desulfurization slurry clear liquid is transported by overflow negative pressure.

[0016] Optionally, the saline wastewater is evaporated in two stages in a concentration tower through a liquid distribution layer and a heat exchange grid, and the liquid distribution layer is located above the heat exchange grid; in the first stage: the saline wastewater entering the liquid distribution layer is controlled to be atomized into droplets with an average particle size of 20μm to 80μm through an atomizing nozzle under a pressure of 0.07MPa to 0.15MPa, and the evaporation surface area of ​​the saline wastewater in a negative pressure environment is increased by liquid distribution atomization; in the second stage: the concentrated wastewater droplets that have completed the atomization evaporation of the liquid distribution layer fall onto the surface of the heat exchange grid under the action of gravity, forming a stable liquid film on the surface of the heat exchange grid, and further exchange heat with the high-temperature saline wastewater flowing in the heat exchange grid to increase the temperature, thereby increasing the evaporation temperature, evaporation time and evaporation area of ​​the saline wastewater.

[0017] Optionally, the slurry in the desulfurization slurry pool is pumped to the washing layer through the desulfurization pump for reverse washing with the inlet flue gas. The chloride ions and heavy metal components in the flue gas continue to accumulate in the desulfurization slurry pool. When the chloride ions in the desulfurization slurry pool accumulate to the point where wastewater needs to be discharged, the circulation box vacuum pump is turned on, and the pipeline valve connecting the side wall of the buffer water tank and the circulation box is opened to introduce the desulfurization wastewater that has completed precipitation in the buffer water tank into the circulation box, thereby completing the discharge and concentration of the wastewater in the desulfurization tower.

[0018] The present invention also provides a salt-containing wastewater concentration system, comprising a desulfurization tower, a concentration tower, a concentration tower vacuum pump, a circulation box, a concentration pump and a buffer water tank. The bottom of the desulfurization tower is a desulfurization slurry pool. A flue gas inlet is provided on the tower wall of the desulfurization tower. The flue gas inlet is connected to an inlet flue, and a heat extractor is provided in the inlet flue.

[0019] The bottom liquid inlet of the buffer water tank is connected to the desulfurization slurry pool through a pipeline, the top liquid outlet of the buffer water tank is connected to the bottom air inlet of the concentration tower through a pipeline, and the top exhaust port of the concentration tower is connected to the air inlet of the vacuum pump of the concentration tower through a pipeline;

[0020] The liquid inlet of the concentration pump is connected to the liquid outlet of the circulation box through a pipeline. The liquid outlet of the concentration pump is connected to the liquid inlet of the heat exchanger and the concentrated brine crystallization unit through pipelines respectively. The liquid outlet of the heat exchanger is connected to the concentration tower through a pipeline.

[0021] Optionally, the desulfurization tower is provided with a desulfurization slurry pool, a flue gas inlet, several washing layers, several demisting layers and a flue gas outlet in sequence from bottom to top; the inlet of the desulfurization pump is connected to the desulfurization slurry pool through a pipeline, and the outlet of the desulfurization pump is connected to the liquid inlet of each washing layer through a pipeline.

[0022] The concentration tower is used for evaporation and concentration of saline wastewater. The vacuum pump of the concentration tower creates a vacuum negative pressure state for the concentration tower cavity by pumping air, lowering the boiling point of the saline wastewater, thereby achieving rapid evaporation of the wastewater entering the concentration tower. As a preferred method: the vacuum degree in the concentration tower is controlled to be -63~-25kPa (the boiling point of wastewater is 75℃~92℃); the buffer water tank and connecting pipelines are used to maintain the negative pressure of the concentration tower, the precipitation of desulfurization slurry and the discharge of saline wastewater from the desulfurization tower. Under the action of the negative pressure in the concentration tower, the desulfurization slurry in the desulfurization slurry pool is sucked back to the buffer water tank through the pipeline, and the particulate matter in the desulfurization slurry is precipitated in the buffer water tank and returned to the desulfurization slurry pool along the pipeline; the loop formed between the circulation box, the heat collector and the evaporation and concentration device in the concentration tower is used to extract heat from the flue gas, solving the heat source problem of evaporation and concentration in the concentration tower.

[0023] Optionally, a liquid guide, a heat exchange grid and a liquid distribution layer are sequentially arranged in the concentration tower from bottom to top; the liquid guide is used to collect wastewater after evaporation and concentration; and the liquid outlet of the liquid guide is connected to the circulation box through a pipeline.

[0024] Preferably, the liquid distribution layer includes a connecting pipeline and a plurality of atomizing nozzles evenly installed on the connecting pipeline, which are used to atomize and distribute the salt-containing wastewater after heat exchange and temperature increase to increase the evaporation area of ​​the wastewater.

[0025] As a preference, the nozzle atomization pressure is controlled to be 0.07MPa to 0.15MPa, and the average atomized particle size of the wastewater is 20μm to 80μm.

[0026] Preferably, the heat exchange tube grid is a multi-layer acid-resistant alloy steel smooth tube structure, which is used to distribute and heat the salt-containing wastewater that has completed atomization evaporation, and to increase the evaporation time and evaporation surface area of ​​the wastewater.

[0027] As a preference, the flow rate of saline wastewater on the surface of the liquid distribution grid is controlled at 100L-500L / m 2 ·h.

[0028] Preferably, the liquid guide comprises several layers of liquid guide grooves with V-shaped cross sections, which are used to recover the concentrated liquid that has completed atomization evaporation of the liquid distribution layer and evaporation on the surface of the heat exchange tube grid and to introduce the concentrated liquid into the circulation box.

[0029] Optionally, a demisting layer is provided in the concentration tower and above the liquid distribution layer, and the demisting layer is provided with a cleaning atomization layer, and the liquid inlet of the cleaning atomization layer is connected to the demineralized water replenishment pipeline.

[0030] Optionally, the cleaning atomization layer includes connecting pipes and atomizing nozzles, which are used to dissolve and clean crystalline particles formed on the wall of the concentration tower and the surface of the demisting layer during the evaporation process of the salt-containing wastewater, so as to avoid scaling and clogging of the concentration tower.

[0031] Most preferably, the concentration tower is provided with an air inlet, a liquid guide, a heat exchange tube grid, a liquid distribution layer, a cleaning atomization layer, a demisting layer and an exhaust port in sequence from bottom to top.

[0032] Optionally, a circulation box vacuum pump is also included; an overflow port is also provided on the side wall of the desulfurization slurry buffer water tank, the overflow port is connected to the circulation box through a pipeline, and the exhaust port of the circulation box is connected to the air inlet of the circulation box vacuum pump through a pipeline.

[0033] When the chloride ion concentration in the desulfurization tower slurry pool is too high and wastewater needs to be discharged, turn on the circulation box vacuum pump to suck the clear liquid in the buffer water tank into the circulation box.

[0034] Optionally, the desulfurization slurry buffer water tank includes a tank body, the liquid inlet provided at the bottom of the tank body, the liquid outlet provided at the top of the tank body, and an overflow port and a saline wastewater inlet provided on the side wall of the tank body. Further optionally, the buffer water tank is a cylindrical hollow cylindrical structure.

[0035] The buffer water tank and connecting pipelines are used to maintain the negative pressure of the concentration tower, the precipitation of desulfurization slurry and the discharge of salt-containing wastewater from the desulfurization tower. Under the action of the negative pressure in the concentration tower, the desulfurization slurry in the desulfurization slurry pool is sucked back into the buffer water tank through the pipeline, and the particulate matter in the desulfurization slurry is precipitated in the buffer water tank and returned to the desulfurization slurry pool along the pipeline; when the chloride ion concentration in the desulfurization tower slurry pool is too high and wastewater needs to be discharged, the circulation box vacuum pump is turned on to suck the clear liquid in the buffer water tank into the circulation box.

[0036] Optionally, the height of the desulfurization slurry buffer water tank is 1.5m-3.0m, and the height between the bottom of the desulfurization slurry buffer water tank and the liquid level of the desulfurization slurry pool is 3.0m-5.0m; when discharging wastewater, the desulfurization slurry flow rate in the pipeline connecting the buffer water tank and the desulfurization slurry pool is 0.05m / s-0.20m / s.

[0037] Optionally, a dehumidifier for injecting a steam-water mixture into the inlet flue gas is provided in the inlet flue and downstream of the heat exchanger, and the air outlet of the concentration tower vacuum pump and the air outlet of the circulation box vacuum pump are connected to the air inlet of the dehumidifier through pipelines.

[0038] Preferably, the dehumidifier includes a connecting pipeline and a plurality of injection heads evenly installed on the connecting pipeline, which are used to inject the evaporated steam from the concentration tower and the circulation box to mix with the flue gas entering the desulfurization tower, thereby reducing the temperature of the flue gas entering the desulfurization tower and increasing the humidity of the flue gas.

[0039] Optionally, regulating valves are provided on the connecting pipelines between the desulfurization slurry pool and the bottom liquid inlet of the desulfurization slurry buffer water tank, the overflow port on the side wall of the desulfurization slurry buffer water tank and the circulation box, the liquid outlet of the heat exchanger and the liquid inlet of the heat exchange tube grid, the liquid outlet of the heat exchanger and the liquid inlet of the liquid distribution layer, the air outlet of the vacuum pump of the concentration tower and the air inlet of the desuperheater and humidifier, and the air outlet of the vacuum pump of the circulation box and the air inlet of the desuperheater and humidifier.

[0040] Optionally, the heat collector is a metal bare tube structure, which is used to exchange heat and heat the saline wastewater in the circulation box.

[0041] Preferably, the temperature of the saline wastewater at the outlet of the heat exchanger is controlled to be 90°C-98°C.

[0042] The low-temperature salt-containing wastewater in the circulation box is sent to the inside of the heat exchanger through a concentration pump, and is indirectly heat-exchanged with the high-temperature flue gas entering the desulfurization tower. The salt-containing wastewater that has completed the heat exchange and temperature increase is sent to the heat exchange tube grid and the liquid distribution layer through the liquid outlet of the heat exchanger.

[0043] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0044] (1) The present invention provides a solution for the efficient and low-cost concentration of saline wastewater: a vacuum pump is provided at the outlet of the concentration tower to evacuate the concentration tower and reduce the boiling point of the wastewater; a heat collector is provided at the inlet flue of the desulfurization tower to heat the saline wastewater and increase its temperature; the liquid layer spraying and atomization is combined to increase the evaporation area; the heat exchange tube grid is used for heating to increase the evaporation temperature and evaporation time of the wastewater; the evaporated steam-water mixture is used to reduce the temperature and humidify the flue gas entering the desulfurization tower, thereby achieving efficient evaporation and concentration of the saline wastewater and reducing the water consumption of the desulfurization device during operation.

[0045] (2) The present invention provides a solution for the switchable discharge and concentration treatment of desulfurization pulp pool wastewater: a buffer water tank is set at the bottom of the concentration tower, and the height difference between the buffer water tank and the liquid level of the desulfurization pulp pool is used to stabilize the vacuum degree in the concentration tower. By controlling the slurry flow rate of the pipeline connecting the bottom of the buffer water tank and the desulfurization pulp pool, the sedimentation effect of the slurry entering the buffer water tank is improved, and the timely discharge and concentration of the desulfurization tower wastewater can be achieved according to the chloride ion concentration of the desulfurization pulp pool. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a process flow chart of the present invention.

[0047] The reference numerals shown in the figures are as follows:

[0048] 1-Desulfurization tower 2-Desulfurization slurry pool 3-Desulfurization pump

[0049] 4-Inlet flue 5-Washing layer 6-Desulfurization tower demisting layer

[0050] 7-Flue gas outlet 8-Heat extractor 9-Desuperheater and humidifier

[0051] 10-concentration tower 11-liquid guide 12-heat exchange tube grid

[0052] 13-Liquid distribution layer 14-Cleaning atomization layer 15-Concentration tower demisting layer

[0053] 16- Vacuum gauge 17- Concentration tower vacuum pump 18- Desulfurization slurry buffer water tank

[0054] 19-Circulation box 20-Concentration pump 21-Circulation box vacuum pump 22-Regulating valve DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0057] In the present invention, on the one hand, a vacuum pump is provided at the outlet of the concentration tower to evacuate the concentration tower and reduce the boiling point of the wastewater. A heat collector is provided at the inlet flue of the desulfurization tower to heat the saline wastewater and increase its temperature. The evaporation area is increased by spraying and atomizing the liquid layer. The heat exchange grid is used to heat and increase the evaporation temperature and evaporation time of the wastewater. In the preferred embodiment, the evaporated steam-water mixture can also be used to cool and humidify the flue gas entering the desulfurization tower, thereby achieving efficient evaporation and concentration of the saline wastewater while reducing the water consumption of the desulfurization device. On the other hand, a desulfurization slurry buffer water tank is provided at the bottom of the concentration tower. The height difference between the desulfurization slurry buffer water tank and the desulfurization slurry pool stabilizes the vacuum degree in the concentration tower. The slurry flow rate in the pipeline connecting the bottom of the desulfurization slurry buffer water tank and the desulfurization slurry pool is controlled to improve the precipitation effect of the slurry entering the desulfurization slurry buffer water tank. In the preferred embodiment, the desulfurization tower wastewater can be discharged and concentrated in a timely manner according to the chloride ion concentration in the desulfurization slurry pool.

[0058] The following is a detailed description of the specific implementation method:

[0059] like Figure 1 The salt-containing wastewater concentration system shown includes a desulfurization tower 1, a desulfurization pump 3, a concentration tower 10, a concentration tower vacuum pump 17, a desulfurization slurry buffer water tank 18, a circulation box 19, a concentration pump 20, a circulation box vacuum pump 21, connecting pipelines and regulating valves 22 installed on each pipeline.

[0060] The desulfurization tower 1 can be a wet spray tower. A desulfurization slurry tank 2, several washing layers 5, and several desulfurization tower demisting layers 6 are arranged in sequence from bottom to top within the tower body. A flue gas outlet 7 is provided on the side wall of the tower body, located between the desulfurization slurry tank and the bottom washing layer. A flue gas outlet 7 is also provided at the top of the tower body. The inlet of the desulfurization pump 3 is connected to the desulfurization slurry tank 2 via a pipeline, and the outlet of the desulfurization pump 3 is connected to the liquid inlet of each washing layer 5 via a pipeline, so that the desulfurization slurry circulates and sprays within the desulfurization tower 1. The flue gas inlet of the desulfurization tower 1 is located on the tower wall between the desulfurization slurry tank and the bottom washing layer. The flue gas inlet is connected to the inlet flue 4. A heat collector 8 and a desuperheater and humidifier are arranged in sequence within the inlet flue 4 along the flue gas flow direction.

[0061] The concentration tower 10 includes a closed tower body, an air inlet is provided at the bottom of the tower body, an air outlet is provided at the top of the tower body, and the tower body is provided with a liquid guide 11, a heat exchange tube grid 12, a liquid distribution layer 13, a cleaning atomization layer 14 and a concentration tower demisting layer 15 from bottom to top. A vacuum gauge 16 is provided on the tower body. The desulfurization slurry buffer water tank 18 includes a box body. In the embodiment shown in the figure, the box body is arranged below the concentration tower 10, a liquid inlet is provided at the bottom of the box body, and a liquid outlet is provided at the top of the box body. The circulation box 19 includes a closed pool body, a liquid outlet is provided at the bottom of the pool body, a reflux port and an exhaust port are provided at the top of the circulation box, and a saline wastewater inlet and a desulfurization slurry clear liquid inlet are respectively provided on the side wall. The saline wastewater inlet is connected to the saline wastewater conveying pipeline.

[0062] The bottom liquid inlet of the desulfurization slurry buffer water tank 11 is connected to the desulfurization slurry pool 2 through a pipeline, the top liquid outlet of the desulfurization slurry buffer water tank 11 is connected to the bottom air inlet of the concentration tower 10 through a pipeline, and the top exhaust port of the concentration tower 10 is connected to the air inlet of the concentration tower vacuum pump 17 through a pipeline; the liquid inlet of the concentration pump 20 is connected to the liquid outlet of the circulation box 19 through a pipeline, and the liquid outlet of the concentration pump 20 is connected to the liquid inlet of the heat exchanger 8 and the concentrated brine crystallization unit (not shown in the figure) through pipelines respectively, and the liquid outlet of the heat exchanger 8 is connected to the heat exchange tube grid 12 and the liquid distribution layer 13 in the concentration tower 10 through pipelines.

[0063] The heat exchanger 8 is used to heat the saline wastewater in the circulation box 19. The low-temperature saline wastewater in the circulation box 19 is sent to the inside of the heat exchanger 8 through a concentration pump, and is indirectly heat exchanged with the high-temperature flue gas entering the desulfurization tower. The saline wastewater that has completed the heat exchange and temperature increase is sent to the heat exchange tube grid 12 and the liquid distribution layer 13 through the liquid outlet of the heat exchanger 8. Preferably, the temperature of the saline wastewater at the liquid outlet of the heat exchanger is controlled to be 90°C-98°C. As a specific embodiment of the structure of the heat exchanger 8, the heat exchanger can adopt a metal smooth tube structure, and is preferably installed in the inlet flue with the axial direction of the metal tube perpendicular to the axial direction of the inlet flue.

[0064] The liquid distribution layer 12 is used to atomize and distribute the salt-containing wastewater after heat exchange and temperature increase, thereby increasing the evaporation area of ​​the wastewater. As a specific embodiment of the liquid distribution layer 12, the liquid distribution layer includes a connecting pipe and a plurality of atomizing nozzles evenly installed on the connecting pipe. Preferably, the nozzle atomizing pressure is controlled to be 0.07MPa~0.15MPa, and the average atomized particle size of the wastewater is 20μm~80μm.

[0065] The heat exchange grid 13 is used to distribute and heat the salty wastewater after atomization and evaporation, and to increase the evaporation time and evaporation surface area of ​​the wastewater. As a specific embodiment of the heat exchange grid 13, the heat exchange grid 13 is a multi-layer acid-resistant alloy steel smooth tube structure. As an optimal method, the flow rate of salty wastewater on the surface of the distribution grid is controlled at 100L-500L / m 2 ·h.

[0066] The liquid guide 11 is used to recover the concentrated liquid that has completed the atomization evaporation of the liquid distribution layer and the evaporation on the surface of the heat exchange tube grid and introduce the concentrated liquid into the circulation box. As a specific embodiment of the liquid guide 11, the liquid guide 11 includes several layers of liquid guide grooves with a V-shaped cross-section.

[0067] The liquid inlet of the cleaning atomization layer 14 is connected to the desalted water replenishment pipeline, which is used to dissolve and clean the crystal particles formed on the walls of the concentration tower and the surface of the demisting layer during the evaporation of the salt-containing wastewater, thereby preventing scaling and clogging of the concentration tower. As a specific embodiment of the cleaning atomization layer, the cleaning atomization layer includes a connecting pipeline and an atomizing nozzle.

[0068] The demisting layer 15 of the concentration tower can be a conventional demisting device.

[0069] The concentrator is used to evaporate and concentrate saline wastewater. The concentrator's vacuum pump creates a negative vacuum in the concentrator cavity by pumping air, lowering the boiling point of the saline wastewater and enabling rapid evaporation of the wastewater entering the concentrator. Preferably, the vacuum level in the concentrator is controlled between -63 and -25 kPa (wastewater boiling point 75°C to 92°C).

[0070] The desulfurization slurry buffer water tank 18 and its connecting pipelines are used to maintain negative pressure in the concentrator, settle the desulfurization slurry, and discharge saline wastewater from the desulfurization tower. Under the negative pressure in the concentrator, the desulfurization slurry in the desulfurization slurry tank 2 is sucked back into the desulfurization slurry buffer water tank 18 through the pipeline. Particulate matter in the desulfurization slurry settles in the desulfurization slurry buffer water tank and returns to the desulfurization slurry tank along the pipeline. Preferably, the height of the desulfurization slurry buffer water tank is 1.5m-3.0m, and the height between the bottom of the desulfurization slurry buffer water tank and the liquid level of the desulfurization slurry tank is 3.0m-5.0m.

[0071] In order to facilitate the discharge of desulfurization wastewater from the desulfurization system, in a preferred embodiment, an overflow port is further provided on the side wall of the desulfurization slurry buffer water tank. Preferably, the desulfurization slurry buffer water tank is a cylindrical hollow cylinder structure. The overflow port of the desulfurization slurry buffer water tank is connected to the circulation box 19 through a pipeline, and the top exhaust port of the circulation box 19 is connected to the air inlet of the circulation box vacuum pump 21 through a pipeline. The desulfurization slurry clear liquid in the desulfurization slurry buffer tank is transported to the circulation box through negative pressure overflow. When the chloride ion concentration in the desulfurization tower slurry pool 2 is too high and wastewater needs to be discharged, the circulation box vacuum pump 21 is turned on to suck the clear liquid in the desulfurization slurry buffer water tank into the circulation box 19. When the wastewater is discharged, the desulfurization slurry flow rate in the pipeline connecting the desulfurization slurry buffer water tank and the desulfurization slurry pool is 0.05m / s-0.20m / s.

[0072] In a preferred embodiment, a dehumidifier 9 for injecting a steam-water mixture into the inlet flue gas is provided in the inlet flue 4 and downstream of the heat collector 8. The outlet of the concentrator vacuum pump 17 is connected to the air inlet of the dehumidifier through a pipeline, and the outlet of the circulation box vacuum pump 219 is also connected to the air inlet of the dehumidifier through a pipeline. The dehumidifier 9 is used to mix the evaporated steam from the concentrator and the circulation box with the steam and water formed by the condensed water, and then inject it to mix with the flue gas entering the desulfurization tower, thereby reducing the temperature of the flue gas entering the desulfurization tower and increasing the humidity of the flue gas. As a specific embodiment of the dehumidifier, the dehumidifier includes a connecting pipeline and a plurality of injection heads evenly installed on the connecting pipeline.

[0073] In order to facilitate the control of each process pipeline, regulating valves 22 are provided on the connecting pipeline between the desulfurization slurry pool and the bottom liquid inlet of the desulfurization slurry buffer water tank, the connecting pipeline between the overflow outlet of the side wall of the desulfurization slurry buffer water tank and the circulation box, the connecting pipeline between the liquid outlet of the heat exchanger and the liquid inlet of the heat exchange tube grid, the connecting pipeline between the liquid outlet of the heat exchanger and the liquid inlet of the liquid distribution layer, the connecting pipeline between the vacuum pump outlet of the concentration tower and the air inlet of the desuperheater and humidifier, and the connecting pipeline between the vacuum pump outlet of the circulation box and the air inlet of the desuperheater and humidifier.

[0074] Use Figure 1 The system shown in the figure performs a method for concentrating saline wastewater, including:

[0075] (1) The power plant water or desulfurization gypsum filtrate with a salt content of less than 2.5% is sent to the circulation box through the transmission pipeline, and then sent to the heat exchanger inlet located in the flue of the desulfurization tower through the concentration pump. By adjusting the wastewater flow rate in the heat exchanger, the water temperature of the heat exchanger outlet is controlled at 90℃-98℃. The salty wastewater that has completed the heat exchange and temperature increase is sent to the heat exchange tube grid and liquid distribution layer in the concentration tower through the heat exchanger outlet through the pipeline;

[0076] (2) The vacuum pump of the concentration tower controls the vacuum degree in the concentration tower to -63~-25kPa by vacuuming. Under this vacuum degree, the boiling point of the wastewater is reduced to 75℃~92℃. Driven by the negative pressure of the concentration tower, the desulfurization slurry in the desulfurization slurry pool of the desulfurization tower enters the desulfurization slurry buffer water tank through the liquid inlet at the bottom of the desulfurization slurry buffer water tank and the connecting pipeline of the desulfurization slurry pool at a flow rate of 0.05m / s-0.20m / s until the liquid level pressure difference of the desulfurization slurry buffer water tank is balanced with the vacuum degree in the concentration tower;

[0077] (3) The salt-containing wastewater entering the liquid distribution layer is atomized into droplets with an average particle size of 20μm to 80μm at a pressure of 0.07MPa to 0.15MPa by the atomizing nozzle, and the outlet water temperature is higher than the boiling point of the corresponding vacuum degree in the concentration tower, so that the salt-containing wastewater can be quickly evaporated and cooled; the concentrated wastewater droplets that have completed the atomization and evaporation of the liquid distribution layer fall onto the surface of the heat exchange tube grid under the action of gravity, and further exchange heat with the high-temperature salt-containing wastewater flowing in the heat exchange tube grid to increase temperature and evaporate; the concentrated wastewater that has completed the two-stage evaporation of the liquid distribution layer and the heat exchange tube grid enters the circulation box through the liquid guide to continue circulating and concentrating, and the salt content of the wastewater in the circulation box is controlled at 7% to 12% by discharging concentrated water and replenishing water;

[0078] (4) In the desulfurization tower, the slurry in the desulfurization slurry pool is pumped to the washing layer by the desulfurization pump for reverse washing with the flue gas entering the tower. The chloride ions and heavy metal components in the flue gas are continuously accumulated in the desulfurization slurry pool. When the chloride ions in the desulfurization slurry pool accumulate to the point where wastewater needs to be discharged, the circulation box vacuum pump is turned on, and the pipeline valve connecting the side wall of the desulfurization slurry buffer water tank and the circulation box is opened to introduce the desulfurization wastewater that has completed precipitation in the desulfurization slurry buffer water tank into the circulation box, completing the discharge and concentration of the wastewater in the desulfurization tower;

[0079] (5) After the water vapor that has completed evaporation in the concentration tower and the circulation box is pressurized at the outlet of the vacuum pump, part of the evaporated steam generates condensed water to form a steam-water mixture, which is sent through pipelines to the dehumidifier located in the flue at the inlet of the desulfurization tower and downstream of the heat exchanger. The mixture is sprayed by the nozzle in the dehumidifier and mixed with the flue gas entering the desulfurization tower, thereby reducing the temperature of the flue gas entering the desulfurization tower and increasing the humidity of the flue gas, thereby reducing the flue gas volume and the gas velocity in the tower, and reducing the evaporation of water in the desulfurization process.

[0080] The above (1) to (5) are numbered only for the convenience of description. The concentration method of the present invention does not necessarily have to be carried out in the order of the above (1) to (5). After the system is running stably, except that the vacuum pump of the circulation box is only turned on when the desulfurization wastewater needs to be discharged, the other steps are basically carried out simultaneously.

[0081] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for concentrating saline wastewater, characterized in that: It is carried out based on a saline wastewater concentration system, which includes a desulfurization tower, a concentration tower, a concentration tower vacuum pump, a circulation box, a concentration pump, a desulfurization slurry buffer water tank and a circulation box vacuum pump; The saline wastewater concentration method comprises: The salty wastewater is sent to the circulation box through the pipeline, and then sent to the heat exchanger installed in the flue of the desulfurization tower by the concentration pump. The high-temperature flue gas at the desulfurization tower inlet is used to heat the salty wastewater and heat it. By adjusting the flow rate of the salty wastewater in the heat exchanger, the water temperature at the heat exchanger outlet is controlled at 90℃-98℃. The bottom of the thickening tower is connected to the desulfurization slurry pool in the desulfurization tower through a pipeline, and a desulfurization slurry buffer water tank connected to the circulation box is provided on the connecting pipeline. The bottom of the desulfurization slurry buffer water tank is 3.0 m-5.0 m above the liquid level of the desulfurization slurry pool. The vacuum pump of the thickening tower controls the vacuum degree in the thickening tower to be -63~-25 kPa by vacuuming. The boiling point of the wastewater at this vacuum degree is 75°C~92°C. Driven by the negative pressure of the thickening tower, the desulfurization slurry in the desulfurization slurry pool of the desulfurization tower enters the desulfurization slurry buffer water tank through the liquid inlet at the bottom of the desulfurization slurry buffer water tank and the connecting pipeline of the desulfurization slurry pool at a flow rate of 0.05 m / s-0.20 m / s until the liquid level pressure difference of the desulfurization slurry buffer water tank is balanced with the vacuum degree in the thickening tower. The salty wastewater that has completed heat exchange and temperature increase is sent from the liquid outlet of the heat exchanger through connecting pipes to the liquid distribution layer and heat exchange grid in the concentration tower. The salty wastewater, after being atomized by the liquid distribution layer, evaporates and cools down rapidly under the negative pressure environment of the concentration tower, and forms a liquid film on the surface of the heat exchange grid for further heat exchange and evaporation. After two-stage evaporation and concentration on the liquid distribution layer and the heat exchange grid surface, the wastewater is collected by the liquid guide and returned to the circulation box through the pipeline for cyclic heating and evaporation concentration; when the salt-containing wastewater in the circulation box is concentrated to the set concentration, it is discharged to the crystallization unit; After the water vapor that has completed evaporation in the concentration tower and the circulation box is pressurized at the outlet of the corresponding vacuum pump, part of the evaporated steam generates condensed water to form a steam-water mixture, which is sent through pipelines to the desuperheater and humidifier located in the inlet flue of the desulfurization tower and downstream of the heat exchanger. It is sprayed by the injection head in the desuperheater and humidifier and mixed with the flue gas entering the desulfurization tower, thereby reducing the temperature of the flue gas entering the desulfurization tower, increasing the humidity of the flue gas, and reducing the amount of evaporated water in the wet desulfurization process.

2. The method for concentrating saline wastewater according to claim 1, wherein The saline wastewater is power plant reclaimed water, desulfurization gypsum filtrate and desulfurization slurry clear liquid with a salt content of less than 2.5%, and the salt content of the concentrated wastewater circulating in the circulation box is 7%-12%.

3. The method for concentrating saline wastewater according to claim 2, wherein: The water and desulfurization gypsum filtrate of the power plant are transported to the circulation box by pipeline, and the desulfurization slurry clear liquid is transported by overflow negative pressure.

4. The method for concentrating saline wastewater according to claim 1, wherein The saline wastewater is evaporated in two stages in the concentration tower through the liquid distribution layer and the heat exchange tube grid, and the liquid distribution layer is located above the heat exchange tube grid; First stage: The saline wastewater entering the liquid distribution layer is controlled to be atomized into droplets with an average particle size of 20μm to 80μm through the atomizing nozzle at a pressure of 0.07MPa to 0.15MPa. The evaporation surface area of ​​the saline wastewater in the negative pressure environment is increased through liquid distribution atomization; Second stage: The concentrated wastewater droplets that have completed the atomization and evaporation of the liquid layer fall onto the surface of the heat exchange grid under the action of gravity, forming a stable liquid film on the surface of the heat exchange grid, and further exchange heat with the high-temperature saline wastewater flowing in the heat exchange grid to increase the evaporation temperature, evaporation time and evaporation area of ​​the saline wastewater.

5. A saline wastewater concentration system, characterized in that: It includes a desulfurization tower, a concentration tower, a concentration tower vacuum pump, a circulation box, a concentration pump, a desulfurization slurry buffer water tank and a circulation box vacuum pump. The bottom of the desulfurization tower is a desulfurization slurry pool. A flue gas inlet is provided on the side wall of the desulfurization tower. The flue gas inlet is connected to the inlet flue. A heat collector is provided in the inlet flue. A desuperheater and humidifier for injecting a steam-water mixture into the inlet flue gas is provided in the inlet flue and downstream of the heat collector. The air outlet of the concentration tower vacuum pump and the air outlet of the circulation box vacuum pump are both connected to the air inlet of the desuperheater and humidifier through pipelines. The bottom of the desulfurization slurry buffer water tank is 3.0 m to 5.0 m above the liquid level of the desulfurization slurry pool; the bottom liquid inlet of the desulfurization slurry buffer water tank is connected to the desulfurization slurry pool through a pipeline, and the top liquid outlet of the desulfurization slurry buffer water tank is connected to the bottom air inlet of the concentration tower through a pipeline. An overflow port is also provided on the side wall of the desulfurization slurry buffer water tank, and the overflow port is connected to the circulation box through a pipeline. The exhaust port of the circulation box is connected to the air inlet of the circulation box vacuum pump through a pipeline, and the top exhaust port of the concentration tower is connected to the air inlet of the concentration tower vacuum pump through a pipeline. The liquid inlet of the concentration pump is connected to the liquid outlet of the circulation box through a pipeline, the liquid outlet of the concentration pump is connected to the liquid inlet of the heat exchanger and the concentrated brine crystallization unit through pipelines respectively, and the liquid outlet of the heat exchanger is connected to the concentration tower through a pipeline; a liquid guide, a heat exchange tube grid and a liquid distribution layer are arranged in sequence from bottom to top in the concentration tower; the liquid guide is used to collect wastewater after evaporation and concentration; the liquid outlet of the liquid guide is connected to the circulation box through a pipeline.

6. The saline wastewater concentration system according to claim 5, characterized in that: The liquid distribution layer includes a connecting pipeline and several atomizing nozzles evenly installed on the connecting pipeline, which are used to atomize and distribute the salt-containing wastewater after heat exchange and increase the evaporation area of ​​the wastewater; the nozzle atomization pressure is controlled to be 0.07MPa~0.15MPa, and the average atomized particle size of the wastewater is 20μm~80μm.

7. The saline wastewater concentration system according to claim 5, characterized in that: The heat exchange grid is a multi-layer acid-resistant alloy steel smooth tube structure, which is used to distribute and heat the salt-containing wastewater after atomization and evaporation, and to increase the evaporation time and evaporation surface area of ​​the wastewater; the flow rate of salt-containing wastewater on the surface of the distribution grid is controlled at 100L-500L / m 2 ·h.

8. The saline wastewater concentration system according to claim 5, characterized in that: The liquid guide comprises several layers of liquid guide grooves with V-shaped cross sections, which are used to recover the concentrated liquid after atomization evaporation of the liquid distribution layer and evaporation on the surface of the heat exchange tube grid and to introduce the concentrated liquid into the circulation box.

9. The saline wastewater concentration system according to claim 5, characterized in that: The height of the desulfurization slurry buffer water tank is 1.5 m-3.0 m.

10. The saline wastewater concentration system according to claim 5, characterized in that: The desuperheating and humidifying device comprises a connecting pipeline and a plurality of spray heads evenly installed on the connecting pipeline.

Images