CN113955893A - Desulfurization wastewater treatment method and system - Google Patents
Desulfurization wastewater treatment method and system Download PDFInfo
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- CN113955893A CN113955893A CN202111406729.5A CN202111406729A CN113955893A CN 113955893 A CN113955893 A CN 113955893A CN 202111406729 A CN202111406729 A CN 202111406729A CN 113955893 A CN113955893 A CN 113955893A
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
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Abstract
The application provides a desulfurization wastewater treatment method and a treatment system, relates to the technical field of wastewater treatment, and solves the technical problem that magnesium hydroxide obtained by recycling at present is low in purity. The method comprises the following steps: a pretreatment stage: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating the calcium sulfate to obtain a second solution; magnesium hydroxide synthesis stage: and mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage.
Description
Technical Field
The application relates to the technical field of wastewater treatment, in particular to a desulfurization wastewater treatment method and a desulfurization wastewater treatment system.
Background
The desulfurization wastewater of the coal-fired power plant is high-salt and high-hardness wastewater, wherein Mg2+The content is higher. Because of the higher value of magnesium, the Mg in the desulfurization waste water is generally treated2+And (4) recovering.
At present, the calcium method is generally adopted for Mg2+And recovering, and directly putting slaked lime serving as a precipitator into the desulfurization wastewater to generate magnesium hydroxide precipitate and calcium sulfate precipitate. Although this method is economical, the magnesium hydroxide precipitate and the calcium sulfate precipitate are difficult to separate, resulting in a lower purity of the recovered magnesium hydroxide.
Disclosure of Invention
The application provides a desulfurization wastewater treatment method and a treatment system, which can be used for solving the technical problem that magnesium hydroxide obtained by recycling at present is low in purity.
In a first aspect, an embodiment of the present application provides a desulfurization wastewater treatment method, including:
a pretreatment stage: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating the calcium sulfate to obtain a second solution;
magnesium hydroxide synthesis stage: and mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage.
Optionally, in an embodiment, before the mixing at least part of the third solution as the first solution with the desulfurized wastewater in the pretreatment stage, the treatment method further comprises:
adjusting the pH of the third solution to 6-8.
Optionally, in one embodiment, after the magnesium hydroxide synthesis stage, the treatment method further comprises a washing stage:
the cleaning phase comprises: and washing the magnesium hydroxide precipitate by using a washing solution to obtain a magnesium hydroxide product and a cleaning solution.
Optionally, in one embodiment, a part of the third solution is mixed with the desulfurization waste water as the first solution in the pretreatment stage, and the treatment method further comprises a crystallization stage after the magnesium hydroxide synthesis stage:
the crystallization stage comprises: mixing the residual third solution, the cleaning solution and the target solution, reacting to obtain calcium sulfate, and separating calcium sulfate to obtain a fourth solution; wherein the target solution contains sulfate ions.
Optionally, in one embodiment, after the crystallization stage, the treatment process further comprises a nanofiltration treatment stage:
the nanofiltration treatment stage comprises: treating the fourth solution by using a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content of the first nanofiltration solution is greater than the sulfate ion content of the second nanofiltration solution;
at least part of the first nanofiltration solution is mixed as the target solution with the washing liquid and the remaining third solution in the crystallization stage.
Optionally, in one embodiment, the nanofiltration treatment stage is preceded by a filtration stage,
the filtration stage comprises: and filtering the fourth solution to remove suspended matters and colloids in the fourth solution.
Optionally, in one embodiment, after the nanofiltration treatment stage, the treatment process further comprises a concentration stage,
the concentration stage comprises: and treating the second nanofiltration solution by using a concentration process.
Optionally, in an embodiment, before the concentration stage, the treatment method further includes:
washing the magnesium hydroxide precipitate in the washing stage with a portion of the second nanofiltration solution as the washing solution;
the treating the second nanofiltration solution by using a concentration process comprises:
and treating the residual second nanofiltration solution by using a concentration process.
In a second aspect, the present application provides a treatment system for a desulfurization wastewater treatment method provided in the first aspect of the present application, the treatment system includes a pretreatment device, a magnesium hydroxide synthesis device, and a first return line;
wherein the pretreatment device is provided with a first outlet and a first inlet, and the magnesium hydroxide synthesis device is provided with a first inlet and a first outlet;
a first outlet of the pretreatment device is communicated with a first inlet of the magnesium hydroxide synthesis device, a first outlet of the magnesium hydroxide synthesis device is communicated with an inlet of the first return pipeline, and an outlet of the first return pipeline is communicated with the first inlet of the pretreatment device;
the first reflux pipe is used for refluxing at least part of the third solution to the pretreatment device.
Alternatively, in one embodiment, the magnesium hydroxide synthesis apparatus comprises a pH adjusting tank,
the pH adjusting tank is used for adjusting the pH of the third solution to 6-8 before the at least part of the third solution is refluxed to the pretreatment device.
The beneficial effects brought by the embodiment of the application are as follows:
the desulfurization wastewater treatment method provided by the embodiment of the application comprises the following steps: a pretreatment stage: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating the calcium sulfate to obtain a second solution; magnesium hydroxide synthesis stage: mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage; at least part of the third solution rich in calcium ions, which is obtained after magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage to be used as the first solution, sulfate ions in the desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, namely, sulfate radicals are precipitated in the pretreatment stage at first, and then magnesium is precipitated in the magnesium hydroxide synthesis stage, so that the calcium sulfate and the magnesium hydroxide can be precipitated step by step, the phenomenon that a large amount of calcium sulfate precipitates are mixed with the magnesium hydroxide precipitates is avoided, and the purity of the recovered magnesium hydroxide is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts. In the drawings:
FIG. 1 is a schematic flow chart of a desulfurization wastewater treatment method provided by an embodiment of the present application;
FIG. 2 is a schematic flow chart of another desulfurization wastewater treatment method provided by the embodiment of the present application;
FIG. 3 is a schematic flow chart of another desulfurization wastewater treatment method provided by the embodiment of the present application;
FIG. 4 is a schematic structural diagram of a desulfurization wastewater treatment system provided by an embodiment of the present application;
FIG. 5 is a schematic structural diagram of another desulfurization wastewater treatment system provided in the embodiments of the present application.
Reference numerals:
30-a desulfurization wastewater treatment system; 301-pretreatment unit; 3011 — a first reaction cell; 3012-a clarification tank; 302-magnesium hydroxide synthesis unit; 3021 — second reaction tank; 3022-sedimentation tank; 3023-pH adjusting tank; 303 — a first return line; 304-a cleaning device; 305 — a crystallization device; 306-a filtration device; 307-a nanofiltration device; 308-a second return line; 309 — third return line; 310-a concentration unit; 311-evaporative crystallization apparatus.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be described in detail and completely with reference to the following specific embodiments of the present application and the accompanying drawings. It should be apparent that the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The features of the terms first and second in the description and in the claims of the present application may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more unless otherwise specified. In addition, "and/or" in the specification and claims means at least one of connected objects, a character "/" generally means that a preceding and succeeding related objects are in an "or" relationship.
In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present application can be understood in a specific case by those of ordinary skill in the art.
As described in the background of the present application, the desulfurization wastewater of coal-fired power plants is a high-salinity and high-hardness wastewater, and generally has the following characteristics: 1) weakly acidic, and the pH is between 4.5 and 7.0; 2) the content of suspended matters (SS) is high, and is generally 2-20 g/L; 3) the salt content is high, and the Total Dissolved Solids (TDS) is up to 20-50 g/L; 4) the hardness is high, and the content of Ca element and Mg element is 1-15 g/L; 5) the content of chlorine element is high, generally 5-20 g/L, and a large amount of sulfate ions are contained. Because of the higher value of magnesium, Mg in the desulfurization wastewater is generally removed2+Converted into magnesium hydroxide for recovery. At present, the calcium method is generally adopted for Mg2+And (4) recovering, namely putting slaked lime serving as a precipitator into the desulfurization wastewater to generate magnesium hydroxide precipitate so as to recover the magnesium hydroxide. Although the method is economical, calcium sulfate precipitation is generated at the same time, and the magnesium hydroxide precipitation and the calcium sulfate precipitation are difficult to separate, so that the recovered magnesium hydroxide has low purity.
In view of the above, the embodiment of the application provides a desulfurization wastewater treatment method, which can be used for solving the technical problem that the purity of the magnesium hydroxide recovered at present is low. As shown in fig. 1, the processing method may include the steps of:
Wherein, the desulfurization wastewater contains a large amount of Mg2+、Ca2+、Cl-、Na+、SO4 2-Etc. of
The first solution is rich in calcium ions, the first solution rich in calcium ions is mixed with the desulfurization wastewater, sulfate ions in the calcium sulfate can be removed in advance by generating calcium sulfate, and the calcium sulfate is further separated out, so that the problem that a large amount of calcium sulfate precipitates are doped in magnesium hydroxide precipitates in the subsequent magnesium hydroxide synthesis stage can be avoided.
The second solution is obtained by mixing and reacting the first solution with the desulfurization wastewater to generate calcium sulfate and further removing the calcium sulfate through solid-liquid separation, wherein the second solution contains a large amount of magnesium ions.
And (3) introducing the second solution from the device corresponding to the pretreatment stage into the device corresponding to the magnesium hydroxide synthesis stage, and then adding calcium hydroxide into the second solution rich in magnesium ions to react to generate magnesium hydroxide precipitate. Through solid-liquid separation, the magnesium hydroxide precipitate can be separated and recovered. The molar ratio of the added amount of the calcium hydroxide to the magnesium ions in the second solution is 1-1.2:1, and the reaction time is 0.5-1 h.
The third solution is obtained by solid-liquid separation and removal of magnesium hydroxide precipitate, and contains a large amount of calcium ions. The third solution rich in calcium ions can be returned to the pretreatment stage of step 101 as the first solution to remove sulfate ions from the desulfurization waste water.
It can be understood that, in the pretreatment stage of step 101, sulfate radicals are precipitated and calcium sulfate is removed to obtain a second solution, and when magnesium ions in the second solution are precipitated in the magnesium hydroxide synthesis stage of step 102, a large amount of calcium sulfate precipitation is avoided, so that a large amount of calcium sulfate precipitation doped in the magnesium hydroxide precipitation is avoided.
In practical applications, part or all of the third solution may be refluxed to the pretreatment stage of step 101 as the first solution. The volume ratio of the backflow amount of the third solution to the desulfurization wastewater in the pretreatment stage in the step 101 is 1-2: 1.
it can be understood that, by using the desulfurization wastewater treatment method provided by the embodiment of the present application, at least a part of the third solution rich in calcium ions, which is obtained after separating magnesium hydroxide precipitate in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, and sulfate ions in the desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, that is, sulfate is precipitated in the pretreatment stage first, and then magnesium is precipitated in the magnesium hydroxide synthesis stage, so that calcium sulfate and magnesium hydroxide can be precipitated step by step, and a large amount of calcium sulfate precipitate is prevented from being mixed with the magnesium hydroxide precipitate, thereby improving the purity of the recovered magnesium hydroxide. On the other hand, at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitate is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage to be used as the first solution to provide a calcium source to precipitate sulfate radicals, so that other calcium reagents are not required to be added in the pretreatment stage, and the treatment cost of the desulfurization wastewater is greatly reduced.
In the actual operation process, when the third solution is not available at first, at least part of the third solution cannot be refluxed to the pretreatment stage as the first solution, the pretreatment stage can be skipped, the first batch of desulfurization wastewater directly enters the magnesium hydroxide synthesis stage, calcium hydroxide is added into the first batch of desulfurization wastewater, after a precipitate is separated, the third solution is obtained, at least part of the third solution is refluxed to the next batch of desulfurization wastewater, and the treatment step corresponding to the pretreatment stage is carried out, so that the third solution in the starting step 101 and the step 102 is recycled.
In the step 102 of synthesizing magnesium hydroxide, calcium hydroxide is added to precipitate magnesium ions, so that the third solution obtained after separating magnesium hydroxide precipitate has high hydroxide ion content and high pH, which is generally about 11. If the third solution is directly refluxed to the pretreatment stage as the first solution to precipitate the sulfate radicals in the desulfurization wastewater, a large amount of magnesium hydroxide precipitate may be generated while the calcium sulfate precipitate is generated, so that the calcium sulfate and the magnesium hydroxide cannot be precipitated step by step, and a large amount of magnesium hydroxide precipitate is generated in the pretreatment stage. If the solid-liquid separation is continued in the pretreatment stage to remove the precipitate, the magnesium hydroxide recovered in the magnesium hydroxide synthesis stage may be low in purity, and if the solid-liquid separation is not performed, the magnesium hydroxide recovered in the magnesium hydroxide synthesis stage may be low in purity.
Therefore, in one embodiment, before mixing at least part of the third solution as the first solution with the desulfurization wastewater in the pretreatment stage, the desulfurization wastewater treatment method provided in the examples of the present application further comprises: adjusting the pH of the third solution to 6-8.
The pH of the third solution may be adjusted by adding hydrochloric acid to the third solution.
It can be understood that by adjusting the pH of the third solution to 6 to 8 and then refluxing at least part of the third solution to the pretreatment stage as the first solution, a large amount of magnesium hydroxide precipitate generated in the pretreatment stage can be avoided, and the product quantity and purity of the recovered magnesium hydroxide can be improved.
The magnesium hydroxide precipitate directly separated in the magnesium hydroxide synthesis stage of step 102 generally has a high water content and exists in the form of slurry, and the water content in the magnesium hydroxide precipitate can be further reduced by pressure filtration treatment to obtain a magnesium hydroxide solid precipitate.
Considering that it is difficult to completely remove the sulfate radicals in the desulfurization wastewater in the pretreatment stage of step 101, the residual sulfate radicals in the second solution react with the added calcium hydroxide to generate calcium sulfate in the magnesium hydroxide synthesis stage of step 102, so that the magnesium hydroxide precipitate contains a small amount of calcium sulfate. In order to further improve the purity of the recovered magnesium hydroxide, in an embodiment, after the magnesium hydroxide synthesis stage in step 102, the desulfurization wastewater treatment method provided in the embodiment of the present application further includes step 103, a cleaning stage: the magnesium hydroxide precipitate was washed with a washing solution as shown in fig. 2.
Wherein the washing solution is a sulfate-free or sulfate-less solution. The washing solution is used for washing the magnesium hydroxide sediment containing a small amount of calcium sulfate, and the solubility difference of the calcium sulfate and the magnesium hydroxide in water can be used for dissolving the calcium sulfate, so that the calcium sulfate in the magnesium hydroxide sediment is removed. The washed magnesium hydroxide precipitate can be magnesium hydroxide solid precipitate obtained by filter pressing treatment, wherein the magnesium hydroxide solid precipitate contains a small amount of calcium sulfate solid precipitate. The magnesium hydroxide precipitate is washed by the washing solution, and after solid-liquid separation, a magnesium hydroxide product with higher purity can be obtained, and can be further dried to obtain a final product. After the solid-liquid separation, the cleaning solution remaining after the separation of magnesium hydroxide can also be obtained, and the cleaning solution contains dissolved calcium ions, sulfate ions and the like.
In practice, part of the third solution is returned to the pretreatment stage as the first solution, so that enough calcium source can be provided for the pretreatment stage, and in order to avoid resource waste, in one embodiment, in the step 102 of magnesium hydroxide synthesis stage, at least part of the third solution is mixed with the desulfurization wastewater in the pretreatment stage as the first solution, specifically, part of the third solution is mixed with the desulfurization wastewater in the pretreatment stage as the first solution. Further, after the magnesium hydroxide synthesis stage, the desulfurization wastewater treatment method provided by the embodiment of the present application further includes a step 104 of crystallizing: mixing the residual third solution, the cleaning solution and the target solution, reacting to obtain calcium sulfate, and separating calcium sulfate to obtain a fourth solution; wherein the target solution contains sulfate ions.
Wherein the remaining third solution may refer to the third solution remaining after refluxing a portion of the third solution to the pretreatment stage, being rich in calcium ions. The target solution may specifically be a sulfate-rich solution.
The third solution rich in calcium ions, the cleaning solution containing calcium ions and sulfate ions and the target solution rich in sulfate ions are mixed, the calcium ions in the third solution and the cleaning solution can be precipitated to obtain calcium sulfate precipitate, the recovery of calcium sulfate can be realized, and the resource recovery rate is improved. In specific implementation, the calcium sulfate can be recovered in a normal-temperature crystallizer through a spontaneous crystallization process driven by supersaturation under the normal-temperature condition.
Calcium sulfate can be recovered (also called as recovered gypsum crystal) after solid-liquid separation, and a fourth solution can be obtained after calcium sulfate is separated, wherein the fourth solution still contains more sulfate ions and chloride ions. In one embodiment, after the crystallization stage of step 104, the desulfurization wastewater treatment method provided in the examples of the present application further includes step 105, a nanofiltration treatment stage: treating the fourth solution by using a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content of the first nanofiltration solution is greater than the sulfate ion content of the second nanofiltration solution; at least part of the first nanofiltration solution is mixed as the target solution with the washing liquid and the remaining third solution in the crystallization stage.
And treating the fourth solution containing acid radical ions and chloride ions by a nanofiltration process to respectively obtain a first nanofiltration solution rich in sulfate radicals and a second nanofiltration solution rich in chloride ions. The nanofiltration process is adopted to selectively separate sulfate ions and chloride ions, so that the purity of a sodium chloride product obtained by subsequent evaporation crystallization can be ensured.
In order to avoid calcium sulfate precipitation and scaling in the nanofiltration process, a calcium sulfate scale inhibitor can be added into nanofiltration inlet water to prevent calcium sulfate scaling and realize long-period stable operation. The nanofiltration process has the separation pressure of 0.5MPa-2MPa, and the volume flow ratio of the first nanofiltration solution to the second nanofiltration solution is 1: 1-3. The removal rate of sulfate ions in the second nanofiltration solution is over 98 percent.
And mixing at least part of the first nanofiltration solution rich in sulfate radicals as the target solution with the cleaning solution and the rest of the third solution in the crystallization stage to precipitate calcium sulfate, so that other sulfate radical agents are not required to be added in the crystallization stage, and the treatment cost of the desulfurization wastewater is further reduced. In practical applications, in order to recover as much calcium sulfate as possible in the crystallization stage, the entire first nanofiltration solution may be mixed as the target solution with the cleaning solution and the remaining third solution in the crystallization stage. Considering that when the first nanofiltration solution is refluxed to the crystallization stage, the added calcium sulfate scale inhibitor may be refluxed to the crystallization stage together to prevent the formation of calcium sulfate. Therefore, during the crystallization stage, a scale inhibition and inactivation agent can be further added to destroy the scale inhibition effect of the calcium sulfate scale inhibitor. The addition amount of the scale inhibition and inactivation agent can be 10ppm-30 ppm.
In order to avoid suspended matters, colloids and the like remaining in the fourth solution, the nanofiltration treatment device is blocked in the nanofiltration treatment stage, so that the nanofiltration treatment effect on the fourth solution is not ideal, and in one embodiment, before the nanofiltration treatment stage of step 105, the desulfurization wastewater treatment method provided by the embodiment of the application further comprises a filtration stage: and filtering the fourth solution to remove suspended matters and colloids in the fourth solution.
Wherein, the fourth solution is filtered, and a sand filtration-ultrafiltration treatment process can be specifically adopted.
In order to further save cost, in one embodiment, the desulfurization wastewater treatment method provided in the embodiment of the present application further includes washing the magnesium hydroxide precipitate in the washing stage of step 103 by using the second nanofiltration solution as the washing solution.
The second nanofiltration solution obtained by the nanofiltration process is just a solution with less sulfate radical content, and experiments show that the removal rate of sulfate radical ions in the solution is more than 98 percent, which meets the requirement of washing the solution in the cleaning stage of the step 103. The second nanofiltration solution is used as a washing solution to wash the magnesium hydroxide precipitate in the step 103 washing stage, so that other washing solutions are not required to be added in the step 103 washing stage, and the treatment cost of the desulfurization wastewater is further reduced. In practical applications, a small amount of washing solution can meet the washing requirement of the magnesium hydroxide precipitate, so that only a part of the second nanofiltration solution can be used as the washing solution to wash the magnesium hydroxide precipitate in the step 103 cleaning stage. The mass ratio of the washed magnesium hydroxide solid precipitate to the second nanofiltration solution is 1: 5-1: 20.
In order to further realize resource recycling of the desulfurization wastewater, in an embodiment, after the nanofiltration treatment stage of step 105, the desulfurization wastewater treatment method provided by the embodiment of the present application further includes step 106, a concentration stage: and treating the second nanofiltration solution by using a concentration process.
The second nanofiltration solution treated by the concentration process can be the whole second nanofiltration solution, or the second nanofiltration solution left after part of the second nanofiltration solution is refluxed to the cleaning stage and used as a washing solution. The second nanofiltration solution is rich in chloride ions and sodium ions.
The concentration process may specifically comprise any one or a combination of more of high pressure reverse osmosis, Disc Tube Reverse Osmosis (DTRO) and electrodialysis.
After the concentration process treatment, a sodium chloride concentrated solution can be obtained, wherein the mass fraction of sodium chloride is 10% -15%. In order to further obtain the sodium chloride product for subsequent recovery, storage and reuse, the sodium chloride concentrated solution can be treated by an evaporative crystallization process to obtain the final sodium chloride product with water removed. The evaporative crystallization process can specifically adopt a multi-effect evaporation or steam mechanical recompression evaporation technology. The high-pressure reverse osmosis and DTRO or electrodialysis are adopted for combined concentration in the concentration stage, and the subsequent evaporative crystallization treatment capacity can be greatly reduced, so that the investment and the operation cost of an evaporative crystallization device are reduced.
Therefore, by adopting the desulfurization wastewater treatment method provided by the embodiment of the application, the purity of the recycled magnesium hydroxide is improved, and other resources including calcium sulfate, sodium chloride and the like can be recycled; in addition, the second nanofiltration solution obtained in the step 105 nanofiltration treatment stage is used as a washing solution in the step 103 cleaning stage, and the first nanofiltration solution obtained in the step 105 nanofiltration treatment stage is used as a target solution in the step 104 crystallization stage, so that resources are saved, and the emission of desulfurization wastewater is greatly reduced.
Based on the desulfurization wastewater treatment methods provided in the above embodiments of the present application, the embodiments of the present application also provide a more specific desulfurization wastewater treatment method, and it should be understood that the desulfurization wastewater treatment method is only a specific example and does not represent a limitation to the technical solution of the present application.
As shown in the process flow diagram in fig. 3, the desulfurization waste water treatment method comprises the following steps:
a pretreatment stage: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate (gypsum), and separating the calcium sulfate to obtain a second solution;
magnesium hydroxide synthesis stage: mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and refluxing part of the third solution to the pretreatment stage to be used as the first solution to be mixed with the desulfurization wastewater;
a filter pressing stage: carrying out filter pressing on the magnesium hydroxide precipitate separated in the magnesium hydroxide synthesis stage to obtain a magnesium hydroxide solid precipitate;
a cleaning stage: washing the magnesium hydroxide solid precipitate with a washing solution;
and (3) a drying stage: drying the magnesium hydroxide precipitate separated after washing in the washing stage to obtain a final magnesium hydroxide product;
and (3) a crystallization stage: mixing the residual third solution and a cleaning solution obtained after washing and separating magnesium hydroxide precipitate in the cleaning stage with a target solution, reacting to obtain calcium sulfate, and separating the calcium sulfate to obtain a fourth solution;
and (3) a filtering stage: filtering the fourth solution to remove suspended matters and colloids in the fourth solution;
and (3) nanofiltration treatment stage: treating the fourth solution by using a nanofiltration process to obtain a first nanofiltration solution rich in sulfate ions and a second nanofiltration solution rich in chloride ions; refluxing the first nanofiltration solution to the crystallization stage, and mixing the first nanofiltration solution serving as the target solution with the residual third solution and a cleaning solution obtained after washing and separating magnesium hydroxide precipitate in the cleaning stage; refluxing a portion of the second nanofiltration solution to the washing stage as the washing solution to wash the magnesium hydroxide precipitate;
and (3) a concentration stage: treating the residual second nanofiltration solution by using a concentration process to obtain a sodium chloride concentrated solution;
and (3) an evaporation crystallization stage: and (3) treating the sodium chloride concentrated solution by using an evaporative crystallization process to obtain a final sodium chloride product with water removed.
It can be understood that, by using the desulfurization wastewater treatment method provided by the above embodiment of the present application, a part of the third solution rich in calcium ions, which is obtained after separating magnesium hydroxide precipitate in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, and sulfate ions in the desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, that is, sulfate is precipitated in the pretreatment stage first, and then magnesium is precipitated in the magnesium hydroxide synthesis stage, so that calcium sulfate and magnesium hydroxide can be precipitated step by step, and a large amount of calcium sulfate precipitate is prevented from being mixed with the magnesium hydroxide precipitate, thereby improving the purity of the recovered magnesium hydroxide. On the other hand, part of the third solution which is rich in calcium ions and is obtained after magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage is refluxed to the pretreatment stage to be used as the first solution to provide a calcium source; in the cleaning stage, a second nanofiltration solution obtained in the nanofiltration treatment stage is used as a washing solution to provide a sulfate radical source; and in the crystallization stage, the first nanofiltration solution obtained in the nanofiltration treatment stage is used as a target solution, and a calcium agent, a sulfate agent and a washing solution are not required to be added, so that the desulfurization wastewater treatment cost is greatly reduced, and the discharge of desulfurization wastewater is reduced.
Based on the desulfurization wastewater treatment method provided in the foregoing embodiment of the present application, an embodiment of the present application further provides a desulfurization wastewater treatment system 30 corresponding to the desulfurization wastewater treatment method, as shown in fig. 4, the system 30 includes a pretreatment device 301, a magnesium hydroxide synthesis device 302, and a first return line 303; the pretreatment device 301 is provided with a first outlet and a first inlet, and the magnesium hydroxide synthesis device 302 is provided with a first inlet and a first outlet; a first outlet of the pretreatment device 301 is communicated with a first inlet of the magnesium hydroxide synthesis device 302, a first outlet of the magnesium hydroxide synthesis device 302 is communicated with an inlet of the first return pipeline 303, and an outlet of the first return pipeline 303 is communicated with the first inlet of the pretreatment device 301; the first return line 303 is used for returning at least part of the third solution to the pretreatment device 301.
Wherein the preprocessing device 301 corresponds to the preprocessing stage. The pretreatment device 301 may specifically include a first reaction tank 3011 and a clarification tank 3012 connected to each other, as shown in fig. 5. The first reaction tank 3011 can be used for mixing the desulfurization wastewater with the first solution, the mixed solution enters the clarification tank 3012, and sedimentation and stratification are performed in the clarification tank 3012; the clarifier 3012 may have a solution outlet (which may be considered as a first outlet of the pretreatment device 301) from which the second solution flows and enters the magnesium hydroxide synthesis device 302, and a calcium sulfate outlet from which the calcium sulfate precipitate flows for recovery.
The magnesium hydroxide synthesis apparatus 302 corresponds to the magnesium hydroxide synthesis stage. The magnesium hydroxide synthesizing apparatus 302 may specifically include a second reaction tank 3021 and a settling tank 3022 connected as shown in fig. 5. The second reaction tank 3021 is configured to mix the second solution with calcium hydroxide, and the mixed solution enters the sedimentation tank 3022 and is settled and layered in the sedimentation tank 3022; the solution outlet of the sedimentation tank 3022 may be in communication with the inlet of the first recirculation line 303, and the outlet of the first recirculation line 303 may be in communication with the first reaction tank 3011 (the inlet of the first reaction tank 3011 in communication with the outlet of the first recirculation line 303 may be regarded as the first inlet of the pretreatment device 301), and at least a part of the third solution is recirculated to the first reaction tank 3011.
It can be understood that, with the desulfurization wastewater treatment system provided by the embodiment of the present application, at least a part of the third solution rich in calcium ions, which is obtained after separating the magnesium hydroxide precipitate in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, and sulfate ions in the desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, that is, sulfate is precipitated in the pretreatment stage first, and then magnesium is precipitated in the magnesium hydroxide synthesis stage, so that calcium sulfate and magnesium hydroxide can be precipitated step by step, and a large amount of calcium sulfate precipitate is prevented from being mixed with the magnesium hydroxide precipitate, thereby improving the purity of the recovered magnesium hydroxide. On the other hand, at least part of the third solution rich in calcium ions, which is obtained after the magnesium hydroxide precipitate is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage to be used as the first solution to provide a calcium source to precipitate sulfate radicals, so that other calcium reagents are not required to be added in the pretreatment stage, and the treatment cost of the desulfurization wastewater is greatly reduced.
In one embodiment, the magnesium hydroxide synthesis apparatus 302 includes a pH adjusting tank 3023, the pH adjusting tank 3023 being configured to adjust the pH of the third solution to 6 to 8 before the at least part of the third solution is refluxed to the pretreatment apparatus 301.
The magnesium hydroxide synthesizing apparatus 302 may further include a pH adjusting tank 3023 connected to the settling tank 3022 in addition to the second reaction tank 3021 and the settling tank 3022 connected to each other, as shown in fig. 5. The third solution flowing out of the solution outlet of the sedimentation tank 3022 enters the pH adjusting tank 3023, an outlet of the pH adjusting tank 3023 (which can be regarded as a first outlet of the magnesium hydroxide synthesis apparatus 302) is communicated with an inlet of the first return line 303, and the third solution can flow back to the first reaction tank 3011 through the first return line 303 after being pH adjusted.
It can be understood that, by adjusting the pH of the third solution and then refluxing at least part of the third solution to the pretreatment device 301 as the first solution, a large amount of magnesium hydroxide precipitate generated in the pretreatment stage can be avoided, and the product quantity and purity of the recovered magnesium hydroxide can be further improved.
In one embodiment, the desulfurization wastewater treatment system 30 provided in the embodiment of the present application further includes a cleaning device 304, wherein the cleaning device 304 is connected to the magnesium hydroxide synthesis device 302; the cleaning device 304 is used for introducing a washing solution to clean the magnesium hydroxide precipitate obtained by the magnesium hydroxide synthesis device 302. The washing device 304 may be specifically connected to the sedimentation tank 3022 of the magnesium hydroxide synthesis apparatus 302.
After washing the magnesium hydroxide precipitate, carrying out solid-liquid separation to obtain the cleaning solution without the magnesium hydroxide precipitate.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a crystallization device 305, where the crystallization device 305 is connected to the magnesium hydroxide synthesis device 302; the crystallizing device 305 is configured to mix the remaining third solution, the cleaning solution, and the target solution after a part of the third solution is refluxed to the pretreatment device 301, and react to obtain calcium sulfate. A fourth solution can be obtained after separation of the calcium sulphate. The crystallization device can be specifically a normal-temperature crystallizer.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a filtering device 306, wherein the filtering device 306 is connected to the crystallization device 305; the filtering device 306 is used for filtering the fourth solution to remove suspended substances and colloids therein.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a nanofiltration device 307, wherein the nanofiltration device 307 is connected to the filtration device 306; the nanofiltration device 307 is configured to treat the fourth solution by using a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content in the first nanofiltration solution is greater than that in the second nanofiltration solution, and the second nanofiltration solution is rich in chloride ions.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a second return line 308, and the nanofiltration device 307 is connected to the crystallization device 305 through the second return line 308; the second return line 308 is used for returning at least part of the first nanofiltration solution to the crystallization device 305.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a third return line 309, and the nanofiltration device 307 is connected to the cleaning device 304 through the third return line 309; the third return line 309 is used for returning a portion of the second nanofiltration solution to the cleaning device 304.
In one embodiment, the desulfurization wastewater treatment system provided in the embodiment of the present application further includes a concentration device 310 and an evaporative crystallization device 311 connected to each other, wherein the concentration device 310 is connected to the nanofiltration device 307; the concentration device 310 is configured to treat the remaining second nanofiltration solution by using a concentration process to obtain a sodium chloride concentrated solution; the evaporative crystallization device 311 is used for processing the sodium chloride concentrated solution by using an evaporative crystallization process to obtain a sodium chloride product.
The desulfurization waste water treatment method and the desulfurization waste water treatment system provided by the embodiments of the present application will be described below with reference to specific application examples, and it should be understood that the following examples are only a few specific embodiments and do not represent limitations to the present application.
Example 1:
the treated water quantity of the desulfurization wastewater of a certain power plant is 10m3The water quality of the desulfurized wastewater and the process stages are shown in Table 1.
TABLE 1 Water quality index
(1) Desulfurization waste water gets into preprocessing device at first, and preprocessing device includes first reaction tank and depositing reservoir, and the third solution that is rich in calcium ion in first reaction tank reacts with desulfurization waste water and gets rid of most sulfate ion in the waste water. The volume ratio of the third solution reflux amount to the desulfurization wastewater is 1:1, gypsum is obtained through solid-liquid separation in a clarification tank after reaction, and the supernatant enters a magnesium hydroxide synthesis device.
(2) The magnesium hydroxide synthesis device comprises a second reaction tank, a sedimentation tank and a pH adjusting tank, calcium hydroxide is added into the second reaction tank to react with magnesium ions in the conveyed supernatant (namely the second solution) to obtain magnesium hydroxide precipitate, magnesium hydroxide slurry is obtained through solid-liquid separation of the precipitate, and the magnesium hydroxide solid is obtained through pressure filtration of the slurry. The molar ratio of the calcium hydroxide addition amount to the magnesium ions in the supernatant is 1.2:1, the reaction time is 1h, and the pH of the effluent of the sedimentation tank (namely the third solution) is adjusted to 6-8.
(3) Because the sulfate radicals in the desulfurization wastewater are difficult to completely remove in the pretreatment stage, the magnesium hydroxide solid obtained in the step (2) contains a small amount of calcium sulfate, and the magnesium hydroxide solid is washed by using a second nanofiltration solution with a small sulfate radical content by utilizing the solubility difference of the calcium sulfate and the magnesium hydroxide in water to remove the small amount of calcium sulfate in the magnesium hydroxide solid, wherein the mass ratio of the magnesium hydroxide solid to the second nanofiltration solution is 1: 10. the magnesium hydroxide product is obtained after cleaning and separation, the water content is less than 0.5 percent, the mass fraction of the magnesium hydroxide is more than 97.5 percent, and the standard can reach the I-type standard of the industrial magnesium hydroxide specification (HG/T3607-2007).
(4) And (3) the third solution obtained in the step (2) is rich in calcium ions, one part of the third solution flows back to the pretreatment device to precipitate sulfate ions in the desulfurization wastewater, the other part of the third solution enters a crystallization device to be mixed with the first nanofiltration solution rich in sulfate ions, 20ppm of scale and inactivation agent is added to inactivate the calcium sulfate scale inhibitor, the calcium ions and the sulfate ions react to generate gypsum, and a gypsum product is obtained after separation.
(5) And (4) performing sand filtration-ultrafiltration treatment on the wastewater obtained after the treatment in the step (4) to remove suspended matters and colloids in the water.
(6) The water produced in the step (5) enters a nanofiltration treatment device to obtain a first nanofiltration solution rich in sulfate radicals and a second nanofiltration solution rich in chloride ions, and the nanofiltration concentrated water flows back to a normal-temperature crystallization unit to precipitate calcium ions in the wastewater; adding 15ppm of calcium sulfate scale inhibitor into nanofiltration inlet water, wherein the nanofiltration separation pressure is 1.2MPa, the volume flow ratio of the first nanofiltration solution to the second nanofiltration solution is 1:1, and the removal rate of sulfate radicals in the second nanofiltration solution is over 98 percent.
(7) And part of the second nanofiltration solution enters a cleaning device to clean magnesium hydroxide precipitate, and part of the second nanofiltration solution enters a concentration device to concentrate the second nanofiltration solution by adopting a process combination of electrodialysis and high-pressure reverse osmosis, wherein the NaCl in concentrated water is 13.4 percent.
(8) And (4) allowing the sodium chloride concentrated solution to enter an evaporation crystallization device to recover a sodium chloride product. The evaporative crystallization adopts a multi-effect evaporation technology.
Example 2:
the treated water quantity of the desulfurization wastewater of a certain power plant is 5m3The water quality of the desulfurization waste water and each process section is shown in Table 2,
TABLE 2 Water quality index
(1) Desulfurization waste water gets into preprocessing device at first, and preprocessing device includes first reaction tank and depositing reservoir, and the third solution that is rich in calcium ion in first reaction tank reacts with desulfurization waste water and gets rid of most sulfate ion in the waste water. The volume ratio of the third solution reflux amount to the desulfurization wastewater is 2:1, gypsum is obtained through solid-liquid separation in a clarification tank after reaction, and the supernatant enters a magnesium hydroxide synthesis device.
(2) The magnesium hydroxide synthesis device comprises a second reaction tank, a sedimentation tank and a pH adjusting tank, calcium hydroxide is added into the second reaction tank to react with magnesium ions in the conveyed supernatant (namely the second solution) to obtain magnesium hydroxide precipitate, magnesium hydroxide slurry is obtained through solid-liquid separation of the precipitate, and the magnesium hydroxide solid is obtained through pressure filtration of the slurry. The molar ratio of the calcium hydroxide addition amount to the magnesium ions in the supernatant is 1.1:1, the reaction time is 0.5h, and the pH of the effluent of the sedimentation tank (namely the third solution) is adjusted to 6-8.
(3) Because the sulfate radicals in the desulfurization wastewater are difficult to completely remove in the pretreatment stage, the magnesium hydroxide solid obtained in the step (2) contains a small amount of calcium sulfate, and the magnesium hydroxide solid is washed by using a second nanofiltration solution with a small sulfate radical content by utilizing the solubility difference of the calcium sulfate and the magnesium hydroxide in water to remove the small amount of calcium sulfate in the magnesium hydroxide solid, wherein the mass ratio of the magnesium hydroxide solid to the second nanofiltration solution is 1: 20. the magnesium hydroxide product is obtained after cleaning and separation, the water content is less than 0.5 percent, the mass fraction of the magnesium hydroxide is more than 97.5 percent, and the standard can reach the I-type standard of the industrial magnesium hydroxide specification (HG/T3607-2007).
(4) And (3) the third solution obtained in the step (2) is rich in calcium ions, one part of the third solution flows back to the pretreatment device to precipitate sulfate ions in the desulfurization wastewater, the other part of the third solution enters a crystallization device to be mixed with the first nanofiltration solution rich in sulfate ions, 30ppm of scale and inactivation agent is added to inactivate the calcium sulfate scale inhibitor, the calcium ions and the sulfate ions react to generate gypsum, and a gypsum product is obtained after separation.
(5) And (4) performing sand filtration-ultrafiltration treatment on the wastewater obtained after the treatment in the step (4) to remove suspended matters and colloids in the water.
(6) The water produced in the step (5) enters a nanofiltration treatment device to obtain a first nanofiltration solution rich in sulfate radicals and a second nanofiltration solution rich in chloride ions, and the nanofiltration concentrated water flows back to a normal-temperature crystallization unit to precipitate calcium ions in the wastewater; adding 20ppm of calcium sulfate scale inhibitor into nanofiltration inlet water, wherein the nanofiltration separation pressure is 1.6MPa, the volume flow ratio of the first nanofiltration solution to the second nanofiltration solution is 1:1, and the removal rate of sulfate radicals in the second nanofiltration solution is more than 98%.
(7) And part of the second nanofiltration solution enters a cleaning device to clean magnesium hydroxide precipitate, and part of the second nanofiltration solution enters a concentration device to concentrate the second nanofiltration solution by adopting a process combination of electrodialysis and high-pressure reverse osmosis, wherein the NaCl in concentrated water is 13.6 percent.
(8) And (4) allowing the sodium chloride concentrated solution to enter an evaporation crystallization device to recover a sodium chloride product. The evaporative crystallization adopts a multi-effect evaporation technology.
It can be understood that, with the desulfurization wastewater treatment method and treatment system provided by the embodiment of the present application, a part of the third solution rich in calcium ions, which is obtained after magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage, is refluxed to the pretreatment stage as the first solution, and sulfate ions in the desulfurization wastewater are removed in advance by generating calcium sulfate, so that a large amount of calcium sulfate is prevented from being generated in the magnesium hydroxide synthesis stage, that is, sulfate is precipitated in the pretreatment stage first, and then magnesium is precipitated in the magnesium hydroxide synthesis stage, so that calcium sulfate and magnesium hydroxide can be precipitated step by step, and a large amount of calcium sulfate precipitation and magnesium hydroxide precipitation are prevented from being mixed, thereby improving the purity of the recovered magnesium hydroxide. On the other hand, part of the third solution which is rich in calcium ions and is obtained after magnesium hydroxide precipitation is separated in the magnesium hydroxide synthesis stage is refluxed to the pretreatment stage to be used as the first solution to provide a calcium source; in the cleaning stage, a second nanofiltration solution obtained in the nanofiltration treatment stage is used as a washing solution to provide a sulfate radical source; and in the crystallization stage, the first nanofiltration solution obtained in the nanofiltration treatment stage is used as a target solution, and a calcium agent, a sulfate agent and a washing solution are not required to be added, so that the desulfurization wastewater treatment cost is greatly reduced, and the discharge of desulfurization wastewater is reduced.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The above description is only an example of the present application and is not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.
Claims (10)
1. A desulfurization wastewater treatment method is characterized by comprising the following steps:
a pretreatment stage: mixing the desulfurization wastewater with the first solution, reacting to obtain calcium sulfate, and separating the calcium sulfate to obtain a second solution;
magnesium hydroxide synthesis stage: and mixing the second solution with calcium hydroxide, reacting to obtain magnesium hydroxide precipitate, separating the magnesium hydroxide precipitate to obtain a third solution, and mixing at least part of the third solution serving as the first solution with the desulfurization wastewater in the pretreatment stage.
2. The desulfurization wastewater treatment method of claim 1, wherein said mixing at least a portion of the third solution as the first solution with the desulfurization wastewater in the pretreatment stage further comprises:
adjusting the pH of the third solution to 6-8.
3. The desulfurization wastewater treatment method according to claim 2, wherein said treatment method further comprises, after said magnesium hydroxide synthesis stage, a washing stage of:
the cleaning phase comprises: and washing the magnesium hydroxide precipitate by using a washing solution to obtain a magnesium hydroxide product and a cleaning solution.
4. The desulfurization waste water treatment method as set forth in claim 3, wherein a part of the third solution is mixed with the desulfurization waste water as the first solution in the pretreatment stage, and the treatment method further comprises a crystallization stage after the magnesium hydroxide synthesis stage:
the crystallization stage comprises: mixing the residual third solution, the cleaning solution and the target solution, reacting to obtain calcium sulfate, and separating calcium sulfate to obtain a fourth solution; wherein the target solution contains sulfate ions.
5. The desulfurization wastewater treatment process of claim 4, wherein after the crystallization stage, the treatment process further comprises a nanofiltration treatment stage:
the nanofiltration treatment stage comprises: treating the fourth solution by using a nanofiltration process to obtain a first nanofiltration solution and a second nanofiltration solution; wherein the sulfate ion content of the first nanofiltration solution is greater than the sulfate ion content of the second nanofiltration solution;
at least part of the first nanofiltration solution is mixed as the target solution with the washing liquid and the remaining third solution in the crystallization stage.
6. The desulfurization wastewater treatment method according to claim 5, wherein the nanofiltration treatment stage is preceded by a filtration stage,
the filtration stage comprises: and filtering the fourth solution to remove suspended matters and colloids in the fourth solution.
7. The desulfurization wastewater treatment method according to claim 5, wherein said nanofiltration treatment stage is followed by a concentration stage,
the concentration stage comprises: and treating the second nanofiltration solution by using a concentration process.
8. The desulfurization wastewater treatment method of claim 7, wherein prior to the concentration stage, the treatment method further comprises:
washing the magnesium hydroxide precipitate in the washing stage with a portion of the second nanofiltration solution as the washing solution;
the treating the second nanofiltration solution by using a concentration process comprises:
and treating the residual second nanofiltration solution by using a concentration process.
9. A treatment system used in the desulfurization wastewater treatment method according to any one of claims 1 to 8, characterized in that the treatment system comprises a pretreatment device, a magnesium hydroxide synthesis device and a first return line;
wherein the pretreatment device is provided with a first outlet and a first inlet, and the magnesium hydroxide synthesis device is provided with a first inlet and a first outlet;
a first outlet of the pretreatment device is communicated with a first inlet of the magnesium hydroxide synthesis device, a first outlet of the magnesium hydroxide synthesis device is communicated with an inlet of the first return pipeline, and an outlet of the first return pipeline is communicated with the first inlet of the pretreatment device;
the first reflux pipe is used for refluxing at least part of the third solution to the pretreatment device.
10. The desulfurization wastewater treatment system according to claim 9, wherein the magnesium hydroxide synthesis unit includes a pH adjustment tank,
the pH adjusting tank is used for adjusting the pH of the third solution to 6-8 before the at least part of the third solution is refluxed to the pretreatment device.
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