A method and system for treating desulfurization wastewater

Abstract

The application provides a desulfurization wastewater treatment method and a treatment system. The treatment method can simplify the zero emission process flow and reduce the treatment cost of the desulfurization wastewater. The treatment method comprises the following steps: 1) sending the desulfurization wastewater into a dewatering machine for dewatering; 2) sending the dewatering machine effluent into a tubular membrane treatment unit to remove the suspended solids in the dewatering machine effluent; 3) sending the tubular membrane effluent into a nanofiltration unit for nanofiltration separation to obtain nanofiltration concentrated water and nanofiltration product water; 4) dividing the nanofiltration concentrated water into a first nanofiltration concentrated water and a second nanofiltration concentrated water; returning the first nanofiltration concentrated water to the desulfurization tower to make calcium ions and sulfate ions in the desulfurization tower generate calcium sulfate; sending the second nanofiltration concentrated water into a softening unit to remove magnesium ions, heavy metals and silicon dioxide therein, and obtaining miscellaneous salts and filter press effluent after treatment by a filter press, and returning the filter press effluent to the desulfurization tower.

Description

TECHNICAL FIELD

[0001] The present application relates to a desulfurization wastewater treatment technology, in particular to a desulfurization wastewater treatment method and system. BACKGROUND

[0002] Most coal-fired power plants in China use limestone wet desulfurization technology to remove SO2 in flue gas. The desulfurization wastewater generated during operation is one of the most difficult wastewater to treat in coal-fired power plants due to its complex composition, high hardness, high suspended solids content, and multiple types of pollutants. Currently, the main method for treating desulfurization wastewater in China is chemical precipitation (three-tank system), which mainly removes heavy metals and suspended solids and other impurities in wastewater. However, the treated water has high salt content, which can cause secondary pollution if directly discharged. With the further strengthening of environmental protection requirements in China, it is urgent to develop a deep zero-emission treatment process for desulfurization wastewater.

[0003] Currently, almost all desulfurization wastewater zero-emission processes treat the effluent from the three-tank system. Since the three-tank system includes neutralization, flocculation and sedimentation, and pressure filtration, the process is complex and requires high maintenance costs for power plants. In recent years, power plants have begun to implement desulfurization wastewater zero-emission processes, which include softening, flocculation and clarification processes, resulting in a long and complex desulfurization wastewater zero-emission process. Some functions are repeated with the three-tank system, and multiple types of chemicals are added in large quantities, resulting in high costs for the entire desulfurization wastewater zero-emission process. In addition, after removing heavy metals and suspended solids from desulfurization wastewater using the three-tank system, the wastewater still contains a large amount of calcium and magnesium ions. The zero-emission process uses chemical softening to remove these easily scaling ions. The commonly used softening process for desulfurization wastewater at home and abroad is the caustic soda and soda ash softening process, and the lime and soda ash softening process. This process is mature, stable, and can remove all hardness in wastewater, but the cost of chemicals required is high, and the process is complex, resulting in high operating and maintenance costs for desulfurization wastewater zero-emission.

[0004] Therefore, for the desulfurization wastewater zero-emission process, it is urgent to innovate and develop technology in terms of reducing the cost of the process system and simplifying the process.

[0005] The domestic invention patent application CN 110563166A discloses a resourceful pretreatment method for desulfurization wastewater in coal-fired power plants. The process steps are as follows: desulfurization wastewater (three-tank effluent) is first sent to a pre-sedimentation tank, calcium oxide and a flocculant are added, and the effluent is discharged into a magnesium removal tank; magnesium removal agent and dispersant are added to the magnesium removal tank, and the effluent flows into a pre-sulfur removal tank; pre-sulfur removal agent is added to the pre-sulfur removal tank, and the effluent flows into a deep sulfur removal tank; deep sulfur removal agent is added to the deep sulfur removal tank, and the effluent flows into a calcium removal tank; calcium removal agent is added to the calcium removal tank for calcium removal treatment, the precipitate is sent to a desulfurization tower as a desulfurization agent, and the effluent is used as the influent for subsequent treatment in the downstream membrane method zero-emission process.

[0006] The domestic invention patent application CN105481157A discloses a flue gas waste heat evaporation desulfurization wastewater zero discharge treatment method, and the process steps are as follows: the water from the triple box is first subjected to softening, flocculation and clarification by a double alkali method pretreatment, then the clarified liquid is subjected to desalination concentration reduction by a membrane process, the obtained desalted water can be recycled, and the concentrated liquid is sent into a flue gas bypass evaporation tower for evaporation by using boiler flue gas waste heat, gaseous water vapor is condensed and recovered in a desulfurization absorption tower along with flue gas, and the crystalline substance is discharged along with fly ash.

[0007] The domestic invention patent application CN107892427A discloses a coal-fired power plant desulfurization wastewater zero discharge treatment system and method, and the process steps are as follows: after the desulfurization wastewater is subjected to deep pretreatment by two-stage lime and sodium carbonate clarifiers, the wastewater is concentrated in an electrodialysis system, the concentrated wastewater is subjected to spray drying in a spray drying tower, and the wastewater is atomized into fine droplets by a high-speed atomizer and then subjected to sufficient heat exchange with flue gas in a flue gas waste heat exchanger, so that the desulfurization wastewater is instantaneously dried by using flue gas waste heat, and most of the solid substances generated by evaporation are discharged from the discharge port at the bottom of the spray drying tower.

[0008] The domestic invention patent application CN110563166A discloses a resourceful pretreatment method for desulfurization wastewater of a coal-fired power plant, and the process steps are as follows: the desulfurization wastewater is first sent into a pre-sedimentation tank, calcium oxide and a flocculant are added, and the effluent is discharged into a magnesium removal tank; a magnesium removal agent and a dispersing agent are added into the magnesium removal tank, the effluent flows into a pre-desulfurization tank; a pre-desulfurization agent is added into the pre-desulfurization tank, the effluent flows into a deep desulfurization tank; a deep desulfurization agent is added into the deep desulfurization tank, the effluent flows into a calcium removal tank; a calcium removal agent is added into the calcium removal tank for calcium removal treatment, the precipitate is sent into a desulfurization tower as a desulfurization agent, and the effluent is used as the influent of a downstream membrane method zero discharge process for subsequent treatment. By using the method, the triple box effluent is softened by adding a magnesium removal agent and a calcium removal agent, and the softened effluent is sent to the downstream membrane method zero discharge process. The process flow is long and complex, a large number of chemicals are added, and the calcium ion concentration in the wastewater is sharply increased due to the addition of lime, which further leads to an increase in the amount of calcium removal agent used in the subsequent process. Since the market prices of the calcium removal agent and the magnesium removal agent are relatively high, the treatment cost of the process is relatively high. SUMMARY

[0009] Therefore, the present application provides a desulfurization wastewater treatment method and a treatment system.

[0010] In order to achieve the above object, the present application provides the following technical solutions.

[0011] In one aspect, the present application provides a desulfurization wastewater treatment method, which comprises the following steps:

[0012] 1) sending desulfurization wastewater discharged from a desulfurization tower into a dewatering machine to dewater, to obtain gypsum and dewatering machine effluent;

[0013] 2) sending the dewatering machine effluent into a tubular membrane treatment unit to remove suspended solids in the dewatering machine effluent, to obtain tubular membrane effluent in which the suspended solids are removed;

[0014] 3) sending the tubular membrane effluent into a nanofiltration unit for nanofiltration separation, to obtain nanofiltration concentrated water rich in divalent ions and nanofiltration product water rich in monovalent ions;

[0015] 4) splitting the nanofiltration concentrated water into a first nanofiltration concentrated water and a second nanofiltration concentrated water;

[0016] returning the first nanofiltration concentrated water to the desulfurization tower, so that calcium ions and sulfate ions in the desulfurization tower generate calcium sulfate;

[0017] sending the second nanofiltration concentrated water into a softening unit to remove magnesium ions, heavy metals and silicon dioxide therein, and obtaining miscellaneous salts and filter press effluent after treatment by a filter press, and returning the filter press effluent to the desulfurization tower.

[0018] In some embodiments, the supersaturation degree of calcium sulfate in the nanofiltration concentrated water reaches 200%-400%.

[0019] In some embodiments, the amount of the first nanofiltration concentrated water returned to the desulfurization tower is greater than the amount of the second nanofiltration concentrated water sent into the softening unit; preferably, the volume flow rate of the first nanofiltration concentrated water is 75%-90% of the total volume flow rate of the nanofiltration concentrated water, and the volume flow rate of the second nanofiltration concentrated water is 10-25% of the total volume flow rate of the nanofiltration concentrated water.

[0020] In some embodiments, in step 2), the tubular membrane treatment unit comprises a concentration tank and a tubular membrane filter, the dewatering machine effluent is sent into the concentration tank and then into the tubular membrane filter to filter, to obtain concentrated water containing suspended solids and tubular membrane effluent in which the suspended solids are removed, the concentrated water containing suspended solids is returned to the concentration tank to mix with the dewatering machine effluent, and the tubular membrane effluent is sent into the nanofiltration unit; when the solid content of water in the concentration tank reaches a preset solid content, it is returned to the desulfurization tower; preferably, the preset solid content is 2wt%-5wt%.

[0021] In some embodiments, in step 4), calcium hydroxide and organic sulfur are added in the softening unit to remove magnesium ions, heavy metals and silicon dioxide in the second nanofiltration concentrated water; preferably, the amount of calcium hydroxide is determined according to the pH in the softening unit reaching 11-11.5; preferably, the amount of organic sulfur is 5-10 ppm.

[0022] And / or, the dewatering machine in step 1) is a vacuum belt dewatering machine.

[0023] In some embodiments, the process further comprises the steps of: feeding the nanofiltration product water obtained in step 3) into a membrane concentration unit to concentrate to obtain membrane concentration product water and membrane concentration concentrated water as reclaimed water; and feeding the membrane concentration concentrated water into a solidification unit to obtain sodium chloride.

[0024] The present application also provides a treatment system for treating desulfurization wastewater from a desulfurization tower, the treatment system comprising:

[0025] a dewatering machine for receiving and dewatering the desulfurization wastewater discharged from the desulfurization tower to obtain gypsum and dewatering machine effluent;

[0026] a tubular membrane treatment unit for receiving the dewatering machine effluent from the dewatering machine and removing suspended solids in the dewatering machine effluent to obtain tubular membrane effluent with the suspended solids removed;

[0027] a nanofiltration unit for receiving the tubular membrane effluent and performing nanofiltration separation thereon to obtain nanofiltration concentrated water rich in divalent ions and nanofiltration product water rich in monovalent ions; the nanofiltration unit being connected to the desulfurization tower to return part of the nanofiltration concentrated water to the desulfurization tower;

[0028] a softening unit for receiving part of the nanofiltration concentrated water from the nanofiltration unit and removing magnesium ions, heavy metals and silicon dioxide therefrom;

[0029] a filter press for performing filter pressing on the feed liquid obtained by the treatment in the softening unit to obtain miscellaneous salts and filter press effluent; the filter press being connected to the desulfurization tower to return the filter press effluent to the desulfurization tower;

[0030] Preferably, the treatment system further comprises a membrane concentration unit and a solidification unit, wherein the membrane concentration unit is used to concentrate the nanofiltration product water from the nanofiltration unit to obtain membrane concentration product water and membrane concentration concentrated water; and the solidification unit is used to solidify the membrane concentration concentrated water to obtain sodium chloride.

[0031] In some embodiments, the tubular membrane treatment unit comprises a concentration tank and a tubular membrane filter;

[0032] the concentration tank being connected to the dewatering machine to receive the dewatering machine effluent;

[0033] The water inlet of the tubular membrane filter is connected with the concentration tank to receive water from the concentration tank; the concentrated water outlet of the tubular membrane filter is connected with the concentration tank to return the concentrated water containing suspended solids obtained by the tubular membrane filter to the concentration tank and mix with the water outlet of the dewatering machine; and the water outlet of the tubular membrane filter is connected with the nanofiltration unit to send the tubular membrane water outlet obtained by the tubular membrane filter to the nanofiltration unit.

[0034] In some embodiments, the concentration tank is further connected with the desulfurization tower to return the water in the concentration tank to the desulfurization tower when the solid content of the water in the concentration tank reaches a preset solid content.

[0035] In some embodiments, the treatment system is used to implement the treatment method described above.

[0036] The technical solution provided by the present application has the following beneficial effects:

[0037] The desulfurization wastewater treatment method provided by the present application does not need to use the traditional triple-tank system, reduces the investment cost and maintenance cost of the triple-tank system, and through the ingenious integration of the dewatering machine, the nanofiltration unit, the softening unit and the filter press and the arrangement of the specific material flow, not only the traditional triple-tank system is not needed, but also the coagulation and clarification system is not needed in the treatment process, which greatly simplifies the zero-emission treatment process of the desulfurization wastewater, reduces the dosing link and the dosing amount, and greatly reduces the system operation cost. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 FIG. 1 is a schematic diagram of a treatment system for treating desulfurization wastewater from a desulfurization tower according to an embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to facilitate the understanding of the present application, the present application will be further described below in conjunction with examples. It should be understood that the following examples are only for better understanding of the present application, and do not mean that the present application is limited to the following examples only.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0041] The present application provides a desulfurization wastewater treatment method, mainly comprising the following steps:

[0042] 1) sending the desulfurization wastewater discharged from the desulfurization tower into the dewatering machine to dewater, to obtain gypsum and dewatering machine water;

[0043] 2) sending the dewatering machine effluent into a tubular membrane treatment unit to remove suspended solids in the dewatering machine effluent, to obtain tubular membrane effluent with suspended solids removed;

[0044] 3) sending the tubular membrane effluent into a nanofiltration unit for nanofiltration separation, to obtain nanofiltration concentrated water rich in divalent ions and nanofiltration product water rich in monovalent ions;

[0045] 4) splitting the nanofiltration concentrated water into a first nanofiltration concentrated water and a second nanofiltration concentrated water;

[0046] returning the first nanofiltration concentrated water to the desulfurization tower, so that calcium ions and sulfate ions in the desulfurization tower generate calcium sulfate;

[0047] sending the second nanofiltration concentrated water into a softening unit to remove magnesium ions, heavy metals and silicon dioxide therein, and obtaining miscellaneous salts and filter press effluent after pressure filter treatment, and returning the filter press effluent to the desulfurization tower.

[0048] In some embodiments, the supersaturation degree of calcium sulfate in the nanofiltration concentrated water reaches 200%-400%.

[0049] The nanofiltration unit can specifically adopt a conventional nanofiltration device capable of separating monovalent and divalent salts in the technical field.

[0050] In the treatment method of the present application, most of the nanofiltration concentrated water is returned to the desulfurization tower as the first nanofiltration concentrated water, and only a small amount of the nanofiltration concentrated water is sent to the softening unit as the second nanofiltration concentrated water, i.e., the amount of the first nanofiltration concentrated water returned to the desulfurization tower is greater than the amount of the second nanofiltration concentrated water sent to the softening unit. In the present application, most of the nanofiltration concentrated water is returned to the desulfurization tower, so that the calcium ions and the sulfate ions in the desulfurization wastewater in the desulfurization tower can spontaneously generate calcium sulfate. In the present application, a part of the nanofiltration concentrated water is branched off as the second nanofiltration concentrated water and sent to the softening unit for treatment, which can avoid the enrichment of impurities such as magnesium ions, heavy metals and silicon in the system caused by returning all the nanofiltration concentrated water to the desulfurization tower. In addition, in the present application, only a part of the nanofiltration concentrated water, especially a small amount of the nanofiltration concentrated water, is sent to the softening unit for treatment, so that the amount of the medicament required to be added in the softening unit is greatly reduced, which is beneficial to reducing the cost of the medicament, and at the same time, the small amount of water treated by the softening system is helpful to reducing the investment of the softening system. In some embodiments, the volume flow rate of the first nanofiltration concentrated water accounts for 75%-90%, for example, 80%-90% of the total volume flow rate of the nanofiltration concentrated water, and the volume flow rate of the second nanofiltration concentrated water accounts for 10-25% of the total volume flow rate of the nanofiltration concentrated water. With the preferred return ratio of the nanofiltration concentrated water, not only can the spontaneous generation of calcium sulfate from calcium ions and sulfate ions in the desulfurization tower be promoted, but also the treatment amount of the softening unit can be greatly reduced, the device size and the investment cost of the softening unit can be reduced, and the amount of the medicament added in the softening unit can be saved. By returning the nanofiltration concentrated water to the desulfurization tower, calcium sulfate can be easily generated spontaneously from calcium ions and sulfate ions in the desulfurization tower, so that the addition of sodium carbonate or sodium sulfate in the system can be greatly reduced.

[0051] In some embodiments, in step 2), the tubular membrane treatment unit comprises a concentration tank and a tubular membrane filter, the water outlet of the dehydrator is sent to the concentration tank, and then enters the tubular membrane filter to obtain concentrated water containing suspended solids and tubular membrane water outlet without suspended solids, the concentrated water containing suspended solids is returned to the concentration tank to mix with the water outlet of the dehydrator, and the tubular membrane water outlet is sent to the nanofiltration unit. During the treatment of the desulfurization wastewater, the tubular membrane filter will intercept the suspended solids, which will gradually increase the solid content of the water in the concentration tank. When the solid content of the water in the concentration tank reaches the preset solid content, it is returned to the desulfurization tower. In some embodiments, when the solid content of the water in the concentration tank reaches 2wt%-5wt%, it is returned to the desulfurization tower.

[0052] In some embodiments, in step 4), calcium hydroxide and organic sulfur are added in the softening unit to remove magnesium ions, heavy metals, and silicon dioxide, etc. from the second stream of nanofiltration concentrated water; the suspension obtained after the treatment of the softening unit is filtered by a filter press to obtain a sludge containing impurity salt, and the water (i.e. filtrate) discharged from the filter press is returned to the desulfurization tower. Preferably, the amount of calcium hydroxide added is determined according to the pH value of the softening unit, which is 11-11.5. In some embodiments, the amount of organic sulfur added is 5-10 ppm, for example, 6 ppm, 8 ppm, etc. The preferred amount of addition can achieve a better removal effect of magnesium ions, heavy metals, and silicon dioxide, etc. Organic sulfur can be obtained by commercial purchase, for example, but not limited to, organic sulfur TMT-15 (for example, available from Guangzhou Lanquan Environmental Protection Technology Co., Ltd., etc.), TMT-55 (for example, available from Hubei Jingdi Technology Co., Ltd., etc.), etc.

[0053] In some embodiments, the dewatering machine in step 1) preferably uses a vacuum belt dewatering machine.

[0054] In some embodiments, the treatment method of the present application further comprises the following steps: sending the nanofiltration product water obtained in step 3) into a membrane concentration unit to concentrate to obtain membrane concentration product water as reclaimed water and membrane concentration concentrated water; and sending the membrane concentration concentrated water into a solidification unit for solidification to obtain sodium chloride. The solidification can be performed by evaporation, crystallization, etc., for example, the solidification can be performed by using an MVR crystallizer or a multi-effect evaporator. The condensed water obtained from the solidification unit can be used as reclaimed water. In some embodiments, the main component of the nanofiltration product water is sodium chloride, and the mass concentration is about 10-15 g / L. After the treatment of the membrane concentration unit, the concentration of the membrane concentration concentrated water reaches, for example, more than 140 g / L. The membrane concentration unit can be a commonly used membrane concentration device in the art, for example, it can be a reverse osmosis device, specifically, a high-salt reverse osmosis device, a DTRO reverse osmosis device, an EDRO reverse osmosis device, etc.

[0055] The above treatment method provided by the present application is particularly suitable for treating desulfurization wastewater discharged from a desulfurization tower of a coal-fired power plant.

[0056] The method for treating desulfurization wastewater provided by the application has a simple process flow. The method does not need to use a traditional triple-tank system. The desulfurization wastewater discharged from the desulfurization tower is dewatered by a dewatering machine, and then the suspended solids are removed by a tubular membrane. The divalent salt separation is performed by a nanofiltration unit, the hardness in the wastewater is removed, and the nanofiltration product water rich in monovalent salt is recovered downstream to obtain sodium chloride. Part (a small amount) of the nanofiltration concentrated water is sent to a softening unit to remove magnesium ions, heavy metals and silicon dioxide. Part (a large amount) of the nanofiltration concentrated water is refluxed to the desulfurization tower again. Calcium ions and sulfate ions in the desulfurization tower spontaneously produce calcium sulfate. Through the ingenious integration of multiple treatment units and the ingenious arrangement of the treatment flow, the water resources in the desulfurization wastewater can be recycled and utilized, the treatment process is greatly simplified, the equipment investment is reduced, the addition of reagents is reduced, and the reagent investment is reduced.

[0057] The application further provides a treatment system for treating desulfurization wastewater from a desulfurization tower. The treatment system is particularly suitable for implementing the above-mentioned method for treating desulfurization wastewater provided by the application. The treatment system provided by the application mainly comprises:

[0058] a dewatering machine, configured to receive and dewater the desulfurization wastewater discharged from the desulfurization tower to obtain gypsum and dewatering machine effluent;

[0059] a tubular membrane treatment unit, configured to receive the dewatering machine effluent from the dewatering machine and remove the suspended solids in the dewatering machine effluent to obtain tubular membrane effluent in which the suspended solids are removed;

[0060] a nanofiltration unit, configured to receive the tubular membrane effluent and perform nanofiltration separation thereon to obtain nanofiltration concentrated water rich in divalent ions and nanofiltration product water rich in monovalent ions; the nanofiltration unit is connected to the desulfurization tower to reflux part of the nanofiltration concentrated water to the desulfurization tower;

[0061] a softening unit, configured to receive part of the nanofiltration concentrated water from the nanofiltration unit and remove magnesium ions, heavy metals and silicon dioxide therefrom;

[0062] a filter press, configured to perform filter pressing on the slurry treated in the softening unit to obtain miscellaneous salt and filter press effluent; the filter press is connected to the desulfurization tower to return the filter press effluent to the desulfurization tower.

[0063] In some preferred embodiments, the treatment system further comprises a membrane concentration unit and a solidification unit. The membrane concentration unit is configured to concentrate the nanofiltration product water from the nanofiltration unit to obtain membrane concentration product water and membrane concentration concentrated water. The solidification unit is configured to solidify the membrane concentration concentrated water to obtain sodium chloride. The solidification unit may, for example, adopt an evaporation crystallization device, such as an MVR evaporation crystallizer or a multiple-effect evaporator, to solidify the membrane concentration concentrated water.

[0064] In some embodiments, the tubular membrane treatment unit comprises a concentration tank and a tubular membrane filter; the concentration tank is connected to the dewatering machine to receive the dewatering machine effluent; the water inlet of the tubular membrane filter is connected to the concentration tank to receive the water from the concentration tank; the concentrated water outlet of the tubular membrane filter is connected to the concentration tank to return the concentrated water containing suspended solids obtained from the tubular membrane filter to the concentration tank and mix with the dewatering machine effluent; and the water outlet of the tubular membrane filter is connected to the nanofiltration unit to send the tubular membrane effluent obtained from the tubular membrane filter to the nanofiltration unit.

[0065] In preferred embodiments, the concentration tank is further connected to the desulfurization tower to return the water in the concentration tank to the desulfurization tower when the solid content of the water in the concentration tank reaches a preset solid content.

[0066] The desulfurization wastewater treatment system provided by the present application requires fewer treatment devices and does not need to introduce a traditional triple-tank system to pretreat the desulfurization wastewater discharged from the desulfurization tower, thereby reducing the investment cost and maintenance cost of the triple-tank system. Through the ingenious combination of the dewatering machine, the tubular membrane treatment unit, the nanofiltration unit, the softening unit, and the filter press with the desulfurization tower and the specific material processing flow, the removal of suspended solids can be achieved without using a coagulation and clarification system. At the same time, under the condition of reducing the dosing steps and reducing the overall dosing amount, hardness can be removed, thereby reducing the system operation cost. In addition, by sending part (a small part) of the nanofiltration concentrated water to the softening unit for treatment to remove magnesium ions and the like, the facility size of the magnesium removal softening tank (i.e., the softening unit) can be greatly reduced, thereby reducing the investment cost.

[0067] The treatment method and treatment system provided by the present application are improved based on the existing desulfurization wastewater treatment technology. The devices or treatment units involved (such as the tubular membrane filter, the dewatering machine, the nanofiltration unit, the membrane concentration unit, and the solidification unit) can directly use conventional devices or equipment with corresponding functions in the field, and thus will not be described in detail. Matters not specifically described herein can be understood or known by those skilled in the art based on the conventional technical knowledge or common knowledge in the field, and thus will not be described in detail.

[0068] The present application will be further described below through specific application examples.

[0069] The treatment system used in the following examples for treating desulfurization wastewater is shown in Figure 1 The specific description of the treatment method and treatment system used will be described above, and thus will not be described in detail below.

[0070] In the following examples, the water quality of the desulfurization wastewater in the desulfurization tower to be treated is as follows:

[0071]

[0072] Example 1

[0073] The desulfurization wastewater (9.8 m 3 / h) discharged from the wastewater outlet of the desulfurization tower was sent to a vacuum belt dewatering machine for dewatering, to obtain gypsum and dewatering machine effluent (9.7 m 3 / h), wherein the gypsum production was 740 kg / h, and the water content was 15%;

[0074] The dewatering machine effluent (9.7 m 3 / h) was sent to a concentration tank, and the feed water flow rate of the pipe membrane filter from the concentration tank was 249.6 m 3 / h, the pipe membrane water production (i.e. pipe membrane effluent) flow rate was 9.6 m 3 / h, the thick water flow rate containing suspended solids was 240.0 m 3 / h, the operating pressure of the pipe membrane filter was 0.35 MPa, and the turbidity of the pipe membrane water production was 0.8 NTU; the thick water containing suspended solids was returned to the concentration tank, and when the solid content of the water in the concentration tank reached 4 wt%, the water in the concentration tank was returned to the desulfurization tower at a flow rate of 0.1 m 3 / h;

[0075] The pipe membrane effluent was sent to a nanofiltration unit at a flow rate of 9.6 m 3 / h, the operating pressure of the nanofiltration unit was 3.6 MPa, the recovery rate was 50%, and the nanofiltration thick water (calcium sulfate supersaturation reached about 300%) was divided into a first nanofiltration thick water and a second nanofiltration thick water, wherein the first nanofiltration thick water (3.9 m 3 / h) was returned to the desulfurization tower, and the nanofiltration water production (4.8 m 3 / h) was sent to a membrane concentration unit;

[0076] The second nanofiltration thick water (0.9 m 3 / h) was sent to a softening unit (i.e. softening tank), calcium hydroxide and organic sulfur (in this embodiment, organic sulfur TMT-15 was specifically used) were added to the softening tank, the pH value in the softening tank was adjusted to 11.2 by adding calcium hydroxide, and the addition amount of organic sulfur was 8 ppm;

[0077] The suspension in the softening tank (0.9 m 3 / h) was sent to a filter press for filtration, to produce part of the salt (i.e. sludge) for external transportation, and the filtrate (i.e. filter press effluent) 0.8 m 3 / h was returned to the desulfurization tower;

[0078] The nanofiltration water production (salt concentration 11 g / L) was sent to a membrane concentration unit (in this embodiment, a DTRO reverse osmosis device was specifically used), and was concentrated by a high multiple to 130 g / L, to produce recycled water 4.4 m 3 / h, and the water quality of the recycled water was as follows:

[0079]

[0080] The membrane concentration unit obtains membrane concentration concentrated water 0.4 m 3 / h is fed into the MVR evaporation crystallizer (i.e. solidification unit), 44.9 kg / h of sodium chloride is recovered, and high-quality condensed water 0.3 m 3 / h is obtained, which can be returned to the power plant for reuse, and the condensed water quality is as follows.

[0081]

[0082]

[0083] Example 2:

[0084] The desulfurization wastewater (19.6 m 3 / h) discharged from the wastewater outlet of the desulfurization tower is dewatered in a vacuum belt dewatering machine, and gypsum and dewatering machine effluent (19.4 m 3 / h) is obtained, wherein the gypsum production is 1500 kg / h, and the water content is 17%;

[0085] The dewatering machine effluent (19.4 m 3 / h) is fed into the concentration tank, the water flow fed into the tubular membrane filter from the concentration tank is 259.2 m 3 / h, the tubular membrane water flow (i.e. tubular membrane effluent) is 19.2 m 3 / h, the concentrated water flow containing suspended solids is 240.0 m 3 / h, the operating pressure of the tubular membrane filter is 0.38 MPa, and the turbidity of the tubular membrane water is 0.8 NTU; the concentrated water containing suspended solids is returned to the concentration tank, and when the solid content of the water in the concentration tank reaches 5 wt%, the water in the concentration tank is returned to the desulfurization tower at a flow rate of 0.2 m 3 / h;

[0086] The tubular membrane effluent is fed into the nanofiltration unit at a flow rate of 19.2 m 3 / h, the operating pressure of the nanofiltration unit is 3.5 MPa, the recovery rate is 50%, and the nanofiltration concentrated water (calcium sulfate supersaturation reaches about 300%) is divided into a first nanofiltration concentrated water and a second nanofiltration concentrated water, wherein the first nanofiltration concentrated water (7.7 m 3 / h) is returned to the desulfurization tower, and the nanofiltration water (9.6 m 3 / h) is fed into the membrane concentration unit;

[0087] The second nanofiltration concentrated water (1.9 m 3 / h) is fed into the softening unit (i.e. softening tank), calcium hydroxide and organic sulfur (in this embodiment, organic sulfur TMT-15 is specifically used) are added to the softening tank, the pH value in the softening tank is 11.1 by adding calcium hydroxide, and the addition amount of organic sulfur is 6 ppm;

[0088] The suspension in the softening tank (1.9m 3 / h) is sent to a filter press to produce part of the salt (i.e. sludge) for export and the filtrate (i.e. the water from the filter press) 1.7m 3 / h is returned to the desulfurization tower.

[0089] The water produced by the nanofiltration (salt concentration 13g / L) is sent to a membrane concentration unit (in this embodiment, a DTRO reverse osmosis device) for high-concentration to 140g / L, producing 8.7m 3 / h of recycled water, which has the following quality.

[0090]

[0091] The 0.9m 3 / h of concentrated water from the membrane concentration unit is sent to an MVR evaporation crystallizer (i.e. solidification unit) to recover 90.0kg / h of sodium chloride and produce 0.6m 3 / h of high-quality condensed water, which can be returned to the power plant for recycling. The quality of the condensed water is as follows.

[0092]

[0093] The experimental results prove that the treatment method for desulfurization wastewater provided by the present application has a simple process flow, does not need the traditional triple-tank system, and can achieve the removal of harmful ions in the desulfurization wastewater and the resource utilization of salt and water in the wastewater. In addition, the entire zero-emission system mainly adds one kind of medicament, i.e. calcium hydroxide, has fewer types of added medicaments, and has a lower system operation cost.

[0094] It is easy to understand that the above embodiments are only examples for clear illustration and do not mean that the present application is limited to this. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for treating desulfurization wastewater, characterized by, The method comprises the following steps: 1) sending desulfurization wastewater discharged from a desulfurization tower into a dewatering machine to dewater, to obtain gypsum and dewatering machine effluent; 2) sending the dewatering machine effluent into a tubular membrane treatment unit to remove suspended solids in the dewatering machine effluent, to obtain tubular membrane effluent in which the suspended solids are removed; The tubular membrane treatment unit comprises a concentration tank and a tubular membrane filter, the dewatering machine effluent is sent into the concentration tank and then into the tubular membrane filter to be filtered, to obtain concentrated water containing suspended solids and tubular membrane effluent in which the suspended solids are removed, and the concentrated water containing suspended solids is returned to the concentration tank to be mixed with the dewatering machine effluent; When the solid content of water in the concentration tank reaches a preset solid content, the water is returned to the desulfurization tower; the preset solid content is 2wt%-5wt%; 3) sending the tubular membrane effluent into a nanofiltration unit to be separated by nanofiltration, to obtain nanofiltration concentrated water rich in divalent ions and nanofiltration product water rich in monovalent ions; 4) splitting the nanofiltration concentrated water into a first nanofiltration concentrated water and a second nanofiltration concentrated water; returning the first nanofiltration concentrated water to the desulfurization tower, so that calcium ions and sulfate ions in the desulfurization tower generate calcium sulfate; sending the second nanofiltration concentrated water into a softening unit to remove magnesium ions, heavy metals and silicon dioxide therefrom, and obtaining miscellaneous salt and filter press effluent after treatment by a filter press, and returning the filter press effluent to the desulfurization tower; The volume flow rate of the first nanofiltration concentrated water is 75%-90% of the total volume flow rate of the nanofiltration concentrated water, and the volume flow rate of the second nanofiltration concentrated water is 10-25% of the total volume flow rate of the nanofiltration concentrated water.

2. The treatment method according to claim 1, characterized in that, The supersaturation degree of calcium sulfate in the nanofiltration concentrated water reaches 200%-400%.

3. The treatment method according to claim 1 or 2, characterized in that, In step 4), calcium hydroxide and organic sulfur are added to the softening unit to remove magnesium ions, heavy metals and silicon dioxide in the second nanofiltration concentrated water; the amount of calcium hydroxide is determined according to the pH in the softening unit reaching 11-11.5; and the amount of organic sulfur is 5-10ppm; And / or, the dewatering machine in step 1) is a vacuum belt dewatering machine.

4. The treatment method according to claim 1 or 2, characterized in that, Further comprising the following steps: sending the nanofiltration product water obtained in step 3) into a membrane concentration unit to be concentrated, to obtain membrane concentration product water as recycled water and membrane concentration concentrated water; and sending the membrane concentration concentrated water into a solidification unit to be solidified, to obtain sodium chloride.

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