A method and device for recovering salt from waste liquid of ammonia desulfurization and decyanation

Abstract

The invention relates to the technical field of salt extraction and recovery of waste liquid from ammonia desulfurization and decyanation, and in particular to a method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation and a salt extraction device. The method comprises the following steps: oxidation neutralization, sulfur extraction, primary decolorization treatment, primary concentration and crystallization, secondary decolorization treatment, secondary concentration and crystallization, and by providing a group of activated carbon decolorization treatment before extracting ammonium sulfate and ammonium thiocyanate each time, the adsorption performance of the activated carbon is utilized to adsorb and separate impurities, pigments and heavy metal ions in the waste liquid, so that the extraction purity of both ammonium sulfate and ammonium thiocyanate reaches an optimal level, thereby improving the economic value of salt extraction.

Description

Technical Field

[0001] The invention relates to the technical field of salt extraction and recovery of waste liquid from ammonia desulfurization and decyanation, and in particular to a method and a salt extraction device for salt extraction and recovery of waste liquid from ammonia desulfurization and decyanation. Background Art

[0002] The ammonia-based desulfurization and decyanation process will produce waste liquid containing a variety of salts (such as ammonium thiocyanate, ammonium sulfate, etc.). If these waste liquids are discharged directly, they will cause serious pollution to water bodies and lead to eutrophication of water bodies. The harmful substances in them may also have toxic effects on aquatic organisms and soil ecosystems.

[0003] The salts in the waste liquid are valuable chemical raw materials. For example, ammonium thiocyanate is widely used in printing and dyeing, electroplating and other industries, and ammonium sulfate is a commonly used nitrogen fertilizer. By extracting and recycling salt, resources can be recycled and the production cost of chemical raw materials can be reduced.

[0004] At present, the mainstream method for extracting and recovering salt from waste liquid is evaporation and crystallization. The pretreated waste liquid is heated and evaporated in an evaporator to gradually reduce the solvent (water). When the solution reaches a supersaturated state, the salt will crystallize out. For example, for the recovery of ammonium sulfate, a multi-effect evaporation crystallization process can be used. In this process, the steam is used multiple times to reduce energy consumption. The secondary steam generated by the first-effect evaporator is used as the heating steam for the second-effect evaporator, and so on, which improves energy utilization. The crystallized ammonium sulfate crystals are separated from the mother liquor by centrifugal separation and other methods.

[0005] For example, in the invention patent with patent application number 201910805115.0, a method for purifying ammonium sulfate produced from ammonia desulfurization waste liquid is specifically disclosed, which mentions a technical solution for extracting ammonium sulfate salt from ammonia desulfurization waste liquid by crystallization.

[0006] In addition, in the invention patent with patent application number 201810443698.2, a method for extracting ammonium thiocyanate and ammonium sulfate from the waste liquid of coke oven gas ammonia desulfurization is also specifically disclosed, which also extracts ammonium thiocyanate and ammonium sulfate from the waste liquid of coke oven gas ammonia desulfurization by crystallization method.

[0007] However, in the above-mentioned technical scheme, especially the disclosed technical scheme of the invention patent with patent application number 201810443698.2, when ammonium thiocyanate and ammonium sulfate are extracted by crystallization, due to the small difference in solubility between ammonium sulfate and ammonium thiocyanate, continuous crystallization extraction will still cause the ammonium thiocyanate to contain a large amount of impurities, pigments and heavy metal ions during extraction, resulting in a decrease in the purity of the extracted ammonium thiocyanate. Summary of the invention

[0008] In view of the existing technical problems, the present invention aims to provide a salt extraction method which can improve the purity of ammonium thiocyanate and ammonium sulfate extracted from ammonia desulfurization and decyanation waste liquid as much as possible. Before each extraction of ammonium sulfate and ammonium thiocyanate, a group of activated carbon decolorization treatments are set up, and the adsorption properties of activated carbon are used to adsorb and separate impurities, pigments and heavy metal ions in the waste liquid, so that the extraction purity of both ammonium sulfate and ammonium thiocyanate reaches an optimal level, thereby improving the economic value of salt extraction.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A method for extracting and recovering salt from waste liquid of ammonia desulfurization and decyanation, comprising the following steps:

[0011] Step S1, oxidation neutralization, adding a catalyst to the desulfurization waste liquid for neutralization reaction;

[0012] Step S2, sulfur extraction, the salt solution formed by the neutralization reaction in step S1 is filtered through a salt extraction device to filter out the solid phase crude sulfur;

[0013] Step S3, primary decolorization treatment, adding activated carbon to the salt solution after sulfur extraction in step S2, decolorizing the salt solution, and after the treatment is completed, removing the waste activated carbon from the salt solution through a filter press;

[0014] Step S4, primary concentration and crystallization, the salt solution after decolorization in step S3 is sequentially concentrated and crystallized through a concentration kettle and a crystallization kettle to precipitate solid ammonium sulfate, and then filtered and separated through a salt extraction device to separate the ammonium sulfate product;

[0015] Step S5, secondary decolorization treatment, adding activated carbon to the salt solution remaining in step S4 for rough decolorization treatment, after the treatment is completed, the waste activated carbon is removed from the salt solution by a filter press;

[0016] Step S6, secondary concentration and crystallization, the salt solution after the decolorization treatment in step S5 is sequentially concentrated and crystallized through a concentration kettle and a crystallization kettle to precipitate solid phase ammonium thiocyanate, and then filtered and separated through a salt extraction device to separate the ammonium thiocyanate product.

[0017] As an improvement, the waste gas generated by the neutralization reaction in step S1, and the concentrated tail gas generated by the concentration process in step S4 and step S6 are collected and directed to the waste liquid spray tower.

[0018] As an improvement, in step S2, the salt solution after sulfur extraction is a di-salt solution of ammonium sulfate and ammonium thiocyanate.

[0019] As an improvement, the evaporated condensate produced in the condensation process in step S4 and step S6 is treated with reverse osmosis water and then recycled.

[0020] As an improvement, in step S6, the waste liquid generated after the solid phase ammonium thiocyanate is filtered and extracted by a salt extraction device is recycled to the concentration kettle in step S6 to participate in the reaction.

[0021] In addition, the present invention also provides a salt extraction device used in the salt extraction and recovery method of ammonia desulfurization and decyanation waste liquid as described in any of the above items. The salt extraction device is used for the solid-liquid separation work in steps S2, S4 and S6 respectively. The salt extraction device is a horizontal screw centrifuge. When the salt extraction device separates the solid-liquid mixture, the screen drum inside it is arranged to rotate continuously along the axial direction.

[0022] As an improvement, the screen drum is connected to the screw shaft at the central axis of the screen drum through a planetary gear set, and the screen drum is arranged to rotate synchronously with the screw shaft.

[0023] As an improvement, a liquid phase lifting mechanism is provided inside the salt extraction device, and the liquid phase lifted by the sieve cylinder is directed to the top of the sieve cylinder to flush the sieve cylinder.

[0024] As an improvement, the liquid phase lifting mechanism includes a liquid receiving cylinder, a piston assembly and a liquid guiding tube;

[0025] The liquid receiving cylinder is arranged directly below the sieve cylinder, and receives the liquid phase sieved out by the sieve cylinder;

[0026] The piston assembly is disposed between the screen cylinder and the liquid receiving cylinder. The piston in the piston assembly is lifted and slid in the liquid receiving cylinder, and the piston is pressed to squeeze the liquid phase in the liquid receiving cylinder into the liquid guiding tube.

[0027] The liquid guiding pipe surrounds the screen cylinder and is arranged on the inner side wall of the salt extracting device. The liquid guiding pipe is connected to the bottom of the liquid receiving cylinder.

[0028] As an improvement, a liquid receiving bucket and a knocking stick are arranged above the screen cylinder, and the liquid receiving bucket and the knocking stick are arranged parallel to the screen cylinder, and the liquid receiving bucket and the knocking stick are arranged to rotate and swing through a swing arm, and the liquid receiving bucket and the knocking stick are arranged at two ends of the swing arm. The liquid receiving bucket receives the liquid phase lifted by the liquid phase lifting mechanism for centralized dumping, and the knocking stick intermittently knocks the screen cylinder.

[0029] The beneficial effects of the present invention are:

[0030] (1) The present invention provides a group of activated carbon decolorization treatment before extracting ammonium sulfate and ammonium thiocyanate each time, and utilizes the adsorption performance of activated carbon to adsorb and separate impurities, pigments and heavy metal ions in the waste liquid, so that the extraction purity of both ammonium sulfate and ammonium thiocyanate reaches the optimal level, thereby improving the economic value of salt extraction;

[0031] (2) The present invention improves the salt extraction and recovery method, so that the waste gas and waste liquid generated in the salt extraction process can be reused, so that the salt extraction and recovery method forms a closed loop, and the impact and damage of the waste gas and waste liquid generated in the salt extraction process on the environment are reduced as much as possible, while fully improving the economic value of the salt extraction operation;

[0032] (3) The present invention improves the existing salt extraction device (i.e., horizontal screw centrifuge) so that when the salt extraction device performs solid-liquid phase separation, the problem of screen drum blockage due to long-term continuous operation will not occur, thereby increasing the continuous working time of the salt extraction device, reducing the number of maintenance times of the salt extraction device, and improving the working efficiency of the salt extraction device;

[0033] (4) The present invention provides a liquid phase lifting mechanism, and utilizes the liquid phase lifting mechanism to lift the separated liquid phase, so that the liquid phase is directed to the top of the screen drum, and the liquid phase is poured and flushed to form a counter-attack with the liquid phase centrifugally separated by the screen drum, thereby eliminating the centrifugal force and liquid phase impact force on the sieve drum that block the impurities, so that the position of the screen drum facing the pouring of the liquid phase can form a separation area for the blockage impurities, thereby increasing the working time of the screen drum;

[0034] (5) The present invention improves the liquid receiving bucket for pouring the liquid phase and the knocking rod for knocking the screen drum, so that the pouring of the liquid phase from the liquid receiving bucket and the knocking vibration of the screen drum by the knocking rod form an orderly alternation, thereby continuously and online removing the blocking impurities from the screen drum, which can form a better online cleaning effect. At the same time, combined with the rotation and switching of the screen drum itself, it can form a more efficient cleaning effect.

[0035] In summary, the present invention has higher salt extraction purity, less pollution, and the salt extraction equipment has a long working time, a high salt extraction effect, and a small number of maintenance times. It is particularly suitable for the technical field of salt extraction and recovery of waste liquid from ammonia desulfurization and decyanation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the process flow of the method for recovering salt from waste liquid of ammonia desulfurization and decyanation;

[0037] Figure 2 It is a schematic diagram of the three-dimensional structure of an existing horizontal screw centrifuge;

[0038] Figure 3 It is a schematic diagram of the cross-sectional structure of an existing horizontal screw centrifuge;

[0039] Figure 4It is a schematic diagram of the transmission connection between the screen drum and the screw shaft of the present invention;

[0040] Figure 5 It is an enlarged structural schematic diagram of the gear set of the present invention;

[0041] Figure 6 It is a schematic diagram of the assembly of the screen drum and the screw shaft of the present invention;

[0042] Figure 7 It is a schematic diagram of the three-dimensional structure of the screen drum of the present invention;

[0043] Figure 8 This is a schematic diagram of the three-dimensional structure of the screw shaft of the present invention;

[0044] Fig. 9 This is a schematic diagram of the cross-sectional structure of the screen drum of the present invention;

[0045] Fig.10 This is a schematic cross-sectional view of the salt extraction device of the present invention;

[0046] Fig.11 This is a schematic diagram of the three-dimensional structure of the filter bin of the present invention;

[0047] Fig.12 It is a schematic diagram of the enlarged structure of the liquid receiving tube of the present invention;

[0048] Fig.13 This is a schematic diagram of the structure of the lower liquid guide tube of the present invention;

[0049] Fig.14 It is a schematic diagram of the structure of the upper liquid guide tube of the present invention.

[0050] 10. Filter chamber, 101. Liquid phase chamber, 102. Solid phase chamber, 103. Feed head, 1. Gear set, 11. Sun gear, 12. Planetary gear, 13. Ring gear, 14. Connecting rod, 2. Liquid phase lifting mechanism, 20. Screen cylinder, 201. Filter slit, 202. Filter plate, 203. Baffle, 21. Liquid receiving cylinder, 211. Straight cylinder, 212. Opening, 22. Piston assembly, 221. Piston, 222. Piston motor, 223. Crank connecting rod unit, 23. Liquid guide tube, 231. Lower liquid guide tube, 232. Upper liquid guide tube, 233. Liquid outlet, 3. Liquid receiving bucket, 30. Screw shaft, 301. Propeller blade, 302. Cover plate, 31. Swing arm, 4. Beating stick, 40. Motor. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0053] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0054] Embodiment 1:

[0055] like Figure 1 As shown, a method for extracting and recovering salt from wastewater by ammonia desulfurization and decyanation comprises the following steps:

[0056] Step S1, oxidation neutralization, adding a catalyst to the desulfurization waste liquid for neutralization reaction;

[0057] Step S2, sulfur extraction, the salt solution formed by the neutralization reaction in step S1 is filtered through a salt extraction device to filter out the solid phase crude sulfur;

[0058] Step S3, primary decolorization treatment, adding activated carbon to the salt solution after sulfur extraction in step S2, decolorizing the salt solution, and after the treatment is completed, removing the waste activated carbon from the salt solution through a filter press;

[0059] Step S4, primary concentration and crystallization, the salt solution after decolorization in step S3 is sequentially concentrated and crystallized through a concentration kettle and a crystallization kettle to precipitate solid ammonium sulfate, and then filtered and separated through a salt extraction device to separate the ammonium sulfate product;

[0060] Step S5, secondary decolorization treatment, adding activated carbon to the salt solution remaining in step S4 for rough decolorization treatment, after the treatment is completed, the waste activated carbon is removed from the salt solution by a filter press;

[0061] Step S6, secondary concentration and crystallization, the salt solution after the decolorization treatment in step S5 is sequentially concentrated and crystallized through a concentration kettle and a crystallization kettle to precipitate solid phase ammonium thiocyanate, and then filtered and separated through a salt extraction device to separate the ammonium thiocyanate product.

[0062] Among them, the waste gas generated by the neutralization reaction in the step S1, the concentrated tail gas generated by the concentration process in the step S4 and the step S6 are collected and directed to the waste liquid spray tower, and after being sprayed by the waste liquid spray tower, they are mixed with the desulfurization waste liquid and put into the salt extraction process again to realize closed-loop processing.

[0063] Furthermore, in step S2, the salt solution after sulfur extraction is a mixed solution of ammonium sulfate and ammonium thiocyanate, and then the ammonium sulfate and ammonium thiocyanate in the salt solution are extracted in sequence by gradual evaporation and crystallization.

[0064] Furthermore, the evaporative condensate produced in the condensation process in step S4 and step S6 is recycled again after being treated with reverse osmosis water, the fresh water formed by the evaporative condensate through reverse osmosis water treatment is recycled, and the waste liquid with high concentration is fed into the desulfurization system of the coking plant, thus realizing a closed-loop processing.

[0065] In addition, in step S6, the waste liquid generated after the solid phase ammonium thiocyanate is filtered and extracted by the salt extraction device is reused in the concentration kettle in step S6 to participate in the reaction. The waste liquid generated after the solid phase ammonium thiocyanate is extracted still contains uncrystallized ammonium thiocyanate. The extraction rate of ammonium thiocyanate can be improved by repeated concentration, evaporation and crystallization.

[0066] Specifically, the salt extraction and recovery method of the present application is similar to the technical solution disclosed in the invention patent with patent application number 201810443698.2. The difference is that before the evaporation and crystallization of ammonium sulfate and ammonium thiocyanate for salt extraction, the salt solution is decolorized by adding activated carbon, and at the same time, the activated carbon adsorbs impurities, pigments and heavy metal ions to reduce the impurity content of ammonium sulfate and ammonium thiocyanate after salt extraction, improve the purity of ammonium sulfate and ammonium thiocyanate, and thus increase the economic value after salt extraction.

[0067] Specifically, activated carbon absorbs pigments and impurities:

[0068] Color removal: Desulfurization and decyanation wastewater may contain some colored organic substances or metal ion complexes, etc. The presence of these substances will affect the appearance and purity of the final salt extraction product. Activated carbon has a developed pore structure and a huge specific surface area, which can adsorb these colored substances, making the solution after salt extraction clear and improving the color quality of the product. For example, some nitrogen-containing and sulfur-containing complex organic compounds appear dark in the wastewater, and activated carbon can effectively adsorb and remove them.

[0069] Purification of solution: There may be other impurities in the waste liquid, such as tiny particulate matter, some unreacted raw materials or intermediate products produced during the reaction process. Activated carbon can absorb these impurities and purify the solution, thereby improving the purity of the salt extraction product.

[0070] Reduce the content of harmful substances:

[0071] Adsorption of heavy metal ions: Desulfurization and decyanation wastewater may contain a small amount of heavy metal ions, such as mercury, cadmium, lead, etc. These heavy metal ions not only pollute the environment, but also corrode the equipment during the salt extraction process, and if they remain in the salt extraction product, they will affect the quality and application of the product. Activated carbon can adsorb these heavy metal ions, reduce their content in the solution, reduce harm to the environment and equipment, and improve the safety of salt extraction products.

[0072] Absorbing residual ammonia and cyanide: Although desulfurization and decyanation treatments have been carried out, there may still be a small amount of ammonia and cyanide remaining in the wastewater. These substances are not only toxic, but may also interfere with the salt extraction process. Activated carbon can absorb residual ammonia and cyanide, reduce their concentration in the solution, and thus improve the safety and stability of the salt extraction process.

[0073] Improved filtration performance: Before evaporation and crystallization, the solution needs to be filtered to remove solid impurities and insoluble substances. After adding activated carbon, it can absorb some fine particles and aggregate them into larger particles, which are easier to be removed by the filtration equipment. This can improve the efficiency and effect of filtration, reduce the blockage and maintenance frequency of the filtration equipment, and ensure the smooth progress of the salt extraction process.

[0074] Improve product quality and yield: Through the adsorption of activated carbon, impurities, pigments and harmful substances in the waste liquid are removed, making the salt extraction product higher in purity and better in quality. At the same time, the adsorption of activated carbon can also reduce the interference of impurities in the solution on the crystallization process, making it easier for salts to crystallize and precipitate, thereby improving the yield of the product.

[0075] Embodiment 2:

[0076] As 2 to Figure 5As shown, the present invention also provides a salt extraction device used in the ammonia desulfurization and decyanation waste liquid salt extraction and recovery method described in Example 1, and the salt extraction device is used for the solid-liquid separation work in the steps S2, S4 and S6 respectively. The salt extraction device is a horizontal screw centrifuge. When the salt extraction device separates the solid-liquid mixture, the screen drum inside it is arranged to rotate continuously along the axial direction.

[0077] Specifically, if Figure 2 and Figure 3 As shown, the existing salt extraction devices are composed of a filter chamber 10, a screen drum 20, a screw shaft 30 and a motor 40, wherein the filter chamber 10 is divided into a liquid phase chamber 101 and a solid phase chamber 102, and the screen drum 20 is fixedly arranged in the liquid phase chamber 101, and the screw shaft 30 is penetrated in the screen drum 20, and the screw shaft 30 is driven to rotate by the motor 40, and a feed head 103 is arranged on the side of the filter chamber 10 away from the solid phase chamber 102.

[0078] When the salt extraction device separates the solid and the liquid, due to the spiral extrusion of the screw shaft 30, the material is filtered out of the liquid phase from the filter slit 201 of the screen drum 20 into the liquid phase bin 101 through the action of centrifugal force and extrusion force, while the solid phase is retained in the screen drum 20. Through the push of the propeller blades 301 on the screw shaft 30, the solid phase is discharged from the end of the screw shaft 30 into the solid phase bin 102, thereby achieving the purpose of separation of the solid and liquid phases.

[0079] However, due to the gravity of the material, most of the solid phase and liquid phase are concentrated at the bottom of the screen drum, so the blocking phenomenon at the bottom of the screen drum is much higher than other parts of the screen drum, and the screen drums of existing horizontal screw centrifuges are all fixedly set, and it is impossible to switch the various parts of the screen. Compared with the existing salt extraction device, the salt extraction device of the present invention adds the self-rotation function of the screen drum 20, realizes the switching of various parts of the screen drum 20, and reduces the blocking phenomenon of the screen.

[0080] Embodiment 3:

[0081] like Figure 4 and Figure 5 As shown, the screen drum 20 is transmission-connected to the screw shaft 30 at the central axis of the screen drum through the planetary gear set 1 , and the screen drum 20 is arranged to rotate synchronously with the screw shaft 30 .

[0082] Specifically, the screw shaft 30 is inserted through the end of the solid phase bin 102 and is sleeved with a sun gear 11. The outer ring of the sun gear 11 is evenly distributed with a number of meshing planetary gears 12, and the outer side of the planetary gear 12 is sleeved with a gear ring 13. The gear ring 13 is connected to the sieve drum 20 through a connecting rod 14, and the end of the sieve drum 20 is rotatably mounted on the side wall of the liquid phase bin 101 through a bearing.

[0083] When the screw shaft 30 rotates, it drives the sun gear 11 to rotate, and through the transmission of the planetary gear 12, the ring gear 13 rotates, and then drives the screen drum 20 to rotate. Moreover, through the speed regulation effect of the gear set 1, when the screw shaft 30 rotates rapidly, the self-rotation speed of the screen drum 20 is greatly reduced, thereby avoiding the reduction of the filtering effect of the screen drum 20 due to excessively fast rotation speed.

[0084] In addition, if Fig. 9 As shown, the filter slit 201 on the screen drum 20 is formed by combining a plurality of inclined filter plates 202 in a circular array. When the screw shaft 30 rotates, the inclination direction of the filter plates 202 on the screen drum 20 is staggered with the tangential direction of the screw shaft 30, thereby better avoiding the clogging of the filter slit 201 by impurities.

[0085] like Figures 6 to 8 As shown, it should also be noted that a cover plate 302 covering the planetary gear set 1 is also provided on the screw shaft 30 , and the cover plate 302 is used to protect the planetary gear set 1 , and the cover plate 302 and the screw shaft 30 are threaded or interference fit.

[0086] In addition, a baffle 203 is also provided at the position where the bearing is assembled on the sieve drum 20 to isolate and protect the bearing. When the connecting rod 14 is connected to the sieve drum 20, it is connected to the corresponding baffle 203, and the baffle 203 and the sieve drum 20 are fastened together by threads.

[0087] Embodiment 4:

[0088] like Figures 10 to 14 As shown, a liquid phase lifting mechanism 2 is provided inside the salt extraction device, and the liquid phase lifting mechanism 2 guides the liquid phase filtered out by the sieve cylinder 20 to the top of the sieve cylinder 20 to flush the sieve cylinder 20 .

[0089] Specifically, the liquid phase lifting mechanism 2 includes a liquid receiving cylinder 21, a piston assembly 22 and a liquid guiding tube 23;

[0090] The liquid receiving cylinder 21 is disposed directly below the sieve cylinder 20, and receives the liquid phase sieved out by the sieve cylinder 20;

[0091] The piston assembly 22 is disposed between the sieve cylinder 20 and the liquid receiving cylinder 21. The piston 221 in the piston assembly 22 is lifted and slid in the liquid receiving cylinder 21. The piston 221 is pressed to squeeze the liquid in the liquid receiving cylinder 21 into the liquid guiding tube 23.

[0092] The liquid guide tube 23 surrounds the sieve cylinder 20 and is disposed on the inner side wall of the salt extraction device. The liquid guide tube 23 is connected to the bottom of the liquid receiving cylinder 21 .

[0093] Among them, the top of the liquid receiving cylinder 21 is set in a trumpet-shaped opening to receive the liquid phase filtered out by the sieve cylinder 20. A straight cylinder 211 with a top opening is set in the sieve cylinder 20, and an opening 212 is opened on the side wall of the straight cylinder 211. The piston 221 is slidably set in the straight cylinder 211. The piston assembly 22 also includes a piston motor 222 and a crank connecting rod unit 223. The piston motor 222 drives the piston 221 to move up and down in the straight cylinder 211 through the crank connecting rod unit 223. The piston 221 squeezes the liquid phase in the straight cylinder 211 and squeezes the liquid phase from the straight cylinder 211 into the liquid guide tube 23. Since the liquid phase in the liquid guide tube 23 is continuously pumped by the pressure formed by the piston 221, the liquid phase is pumped in the liquid guide tube 23 to the top of the sieve cylinder 20, and then sprays and flushes the sieve cylinder 20 from the top of the sieve cylinder 20.

[0094] Furthermore, the liquid guide tube 23 consists of two parts: a lower liquid guide tube 231 and an upper liquid guide tube 232. The lower liquid guide tube 231 is located on the side wall of the liquid phase chamber 101, while the upper liquid guide tube 232 is arranged on the side wall of the upper cover 104 of the filter chamber 10. The upper liquid guide tube 232 and the lower liquid guide tube 231 are interlaced and matched through an interface to form a complete liquid guide tube 23.

[0095] Embodiment 5:

[0096] like Fig.10 and Fig.13 As shown, a liquid receiving bucket 3 is arranged above the sieve cylinder 20, wherein the knocking rod 4 is arranged on one side of the sieve cylinder 20, the liquid receiving bucket 3 and the knocking rod 4 are both arranged parallel to the sieve cylinder 20, and the liquid receiving bucket 3 and the knocking rod 4 are rotatably and swingably arranged through a swing arm 31, the liquid receiving bucket 3 and the knocking rod 4 are respectively arranged at the two ends of the swing arm 31, the liquid receiving bucket 3 receives the liquid phase lifted by the liquid phase lifting mechanism 2 for centralized dumping, and the knocking rod 4 intermittently knocks the sieve cylinder 20.

[0097] Specifically, the mass of the liquid receiving bucket 3 when empty is less than the mass of the knocking rod 4. Therefore, initially, due to the mass of the knocking rod 4, the knocking rod 4 always conflicts with the screen cylinder 20, and at this time the liquid receiving bucket 3 is just located directly below the liquid outlet 233 on the liquid guide tube 23, and the liquid receiving bucket 3 continuously receives the liquid phase. When the liquid phase received by the liquid receiving bucket 3 continues to increase and the mass of the liquid receiving bucket 3 exceeds the mass of the knocking rod 4, the liquid receiving bucket 3 drives the swing arm 31 to rotate and swing, so that the liquid receiving bucket 3 pours all the liquid phase it receives onto the screen cylinder 20, and uses the scouring force of the liquid phase to offset the centrifugal force and extrusion force at the top of the screen cylinder 20, so that the blocked material can be cleaned.

[0098] It is further explained that when the liquid receiving bucket 3 is unloaded, the liquid receiving bucket 3 is located below the liquid outlet 233, and it has a certain inclination angle, and its inclination direction is toward the screen drum 20. Therefore, after the liquid receiving bucket 3 receives a certain liquid phase, the liquid receiving bucket 3 will automatically swing and tilt toward the screen drum 20. After the liquid receiving bucket 3 completes the pouring of the liquid phase, the knocking rod 4 will drive the liquid receiving bucket 3 to return to its initial position again, and at the same time, the knocking rod 4 knocks and vibrates the screen drum 20 to loosen the blocked material.

[0099] It is further explained that when the knocking rod 4 swings to knock and vibrate the screen drum 20, the knocking force of the knocking rod 4 on the screen drum 20 each time can be adjusted by adjusting the height and the inclination angle of the liquid receiving bucket 3.

[0100] In addition, it should be noted that in order to prevent the internal components of the salt extraction device from being corroded, the materials of the components are preferably acid- and alkali-resistant materials such as stainless steel and fiberglass.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recovering salt from waste liquid of ammonia desulfurization and decyanation, characterized in that: The following steps are involved: Step S1, oxidation neutralization, adding a catalyst to the desulfurization waste liquid for neutralization reaction; Step S2, sulfur extraction, the salt solution formed by the neutralization reaction in step S1 is filtered through a salt extraction device to filter out the solid phase crude sulfur; Step S3, primary decolorization treatment, adding activated carbon to the salt solution after sulfur extraction in step S2, decolorizing the salt solution, and after the treatment is completed, removing the waste activated carbon from the salt solution through a filter press; Step S4, primary concentration and crystallization, the salt solution after decolorization in step S3 is sequentially concentrated and crystallized through a concentration kettle and a crystallization kettle to precipitate solid ammonium sulfate, and then filtered and separated through a salt extraction device to separate the ammonium sulfate product; Step S5, secondary decolorization treatment, adding activated carbon to the salt solution remaining in step S4 for rough decolorization treatment, after the treatment is completed, the waste activated carbon is removed from the salt solution by a filter press; Step S6, secondary concentration and crystallization, the salt solution after the decolorization treatment in step S5 is sequentially concentrated and crystallized by a concentration kettle and a crystallization kettle to precipitate solid ammonium thiocyanate, and then filtered and separated by a salt extraction device to separate the ammonium thiocyanate product; In steps S2, S4 and S6, when the salt-extracting device separates the solid-liquid mixture, the salt-extracting device is a horizontal screw centrifuge, and the screen drum inside the salt-extracting device is arranged to rotate continuously along the axial direction, and a liquid phase lifting mechanism is arranged inside the salt-extracting device. The liquid phase lifting mechanism guides the liquid phase filtered out by the screen drum to just above the screen drum, and the liquid phase is received by the liquid receiving bucket for centralized dumping to flush the screen drum. After the liquid receiving bucket completes the dumping of the liquid phase, the knocking rod drives the liquid receiving bucket to return to the initial position, and the knocking rod knocks and vibrates the screen once.

2. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: The waste gas generated by the neutralization reaction in step S1, and the concentrated tail gas generated by the concentration process in step S4 and step S6 are collected and directed to the waste liquid spray tower.

3. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: In step S2, the salt solution after sulfur extraction is a di-salt solution of ammonium sulfate and ammonium thiocyanate.

4. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: The evaporated condensate produced in the condensation process in step S4 and step S6 is treated with reverse osmosis water and then recycled.

5. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: In the step S6, the waste liquid generated after the solid phase ammonium thiocyanate is filtered and extracted by the salt extraction device is recycled to the concentration kettle in step S6 to participate in the reaction.

6. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: The screen drum is connected to the screw shaft at the central axis of the screen drum through a planetary gear set, and the screen drum is arranged to rotate synchronously with the screw shaft.

7. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: The liquid phase lifting mechanism comprises a liquid receiving cylinder, a piston assembly and a liquid guiding tube; The liquid receiving cylinder is arranged directly below the sieve cylinder, and receives the liquid phase sieved out by the sieve cylinder; The piston assembly is disposed between the screen cylinder and the liquid receiving cylinder. The piston in the piston assembly is lifted and slid in the liquid receiving cylinder, and the piston is pressed to squeeze the liquid phase in the liquid receiving cylinder into the liquid guiding tube. The liquid guiding pipe surrounds the screen cylinder and is arranged on the inner side wall of the salt extracting device. The liquid guiding pipe is connected with the bottom of the liquid receiving cylinder.

8. The method for extracting and recovering salt from waste liquid from ammonia desulfurization and decyanation according to claim 1, characterized in that: The liquid receiving hopper and the knocking stick are both arranged in parallel with the screen cylinder, and the liquid receiving hopper and the knocking stick are arranged to rotate and swing through a swing arm, and the liquid receiving hopper and the knocking stick are respectively arranged at two ends of the swing arm.

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