A method for separating monocyanoamine slurry and a monocyanoamine slurry separation device

Abstract

A slurry separation method for monocyamine production, the method comprising: obtaining reaction slurry containing monocyamine and calcium carbonate through a monocyamine preparation process; the reaction slurry is conveyed to a filtering area by a ring-shaped filter cloth of a belt vacuum filter, under the action of negative pressure, monocyamine filtrate is filtered and separated by penetrating the filter cloth, calcium carbonate solid phase is intercepted on the surface of the filter cloth to form calcium carbonate filter cake, and the calcium carbonate filter cake is scraped off by a scraper when the filter cloth runs to a discharge end; further comprising: setting a spraying area on a ring-shaped running path of the ring-shaped filter cloth, the spraying area is located before the ring-shaped filter cloth enters the filtering area to carry the reaction slurry; during rotation of the ring-shaped filter cloth, the spraying area sprays calcium carbonate slurry to a carrying surface of the ring-shaped filter cloth, and the calcium carbonate slurry forms a continuous calcium carbonate coating on the carrying surface of the ring-shaped filter cloth; the formation of the calcium carbonate coating greatly prolongs the service life of the filter cloth from the original 2 months to more than 8 months.

Description

Technical Field

[0001] This invention belongs to the field of slurry separation technology for cyanamide production, specifically relating to a slurry separation method and a cyanamide slurry separation device for cyanamide production. Background Technology

[0002] Cyanamide is an important fine chemical intermediate widely used in pharmaceuticals, pesticides, flame retardants, and color-fixing agents. Industrially, cyanamide is produced by reacting calcium cyanamide (CaCN2, commonly known as lime nitrogen) with water in the presence of carbon dioxide. The reaction produces cyanamide and calcium carbonate, and the main reaction can be represented as follows: CaCN2+H2O+CO2→H2NCN+CaCO3↓ The resulting slurry needs to undergo solid-liquid separation to obtain cyanamide filtrate (the filtrate typically contains 30%–50% cyanamide by mass), with calcium carbonate as the solid byproduct. In production, a belt vacuum filter (rubber belt or reciprocating disc type) is commonly used for filtration: the annular filter cloth operates continuously, the reaction slurry is applied to the filter cloth via a distributor, and under vacuum negative pressure, the cyanamide filtrate passes through the filter cloth and is drawn away. The calcium carbonate solid phase is retained on the filter cloth surface to form a filter cake. The filter cake is scraped off by a scraper at the discharge end as the filter cloth moves along with it. The filter cloth is then rinsed and reused.

[0003] Existing processes have long suffered from the prominent problem of filter cloth clogging in actual production: filter cloths typically only last about two months before needing replacement due to a significant decrease in filtration flow, severely impacting production continuity and increasing consumable and labor costs. Current cleaning methods for filter cloth clogging have limitations: alkaline cleaning cannot be used because alkaline conditions catalyze the polymerization of cyanamide, increasing the amount of sticky polymers and exacerbating the clogging; acid cleaning can be used, as acids can dissolve the inorganic phase of calcium carbonate.

[0004] However, in actual acid cleaning processes, even after the acid dissolves the inorganic phase of calcium carbonate, the filter cloth still exhibits low filtration flow after secondary use. This indicates that the filter cloth blockage is not caused by calcium carbonate, but rather by other unidentified substances. Therefore, existing methods cannot fundamentally solve the problem of filter cloth clogging in cyanamide production, forcing the filter cloth to be replaced after only one to two months of use. Summary of the Invention

[0005] Based on this, this application provides a slurry separation method for cyanamide production to solve the problem in the prior art that the filter cloth is prone to clogging in cyanamide production, resulting in the filter cloth being forced to be replaced after only about 2 months of use.

[0006] The technical solution to the above-mentioned technical problems in this application is as follows: A slurry separation method for cyanamide production involves a reaction slurry containing cyanamide and calcium carbonate obtained through a cyanamide preparation process. The reaction slurry is conveyed to a filtration zone by an annular filter cloth of a belt vacuum filter. Under negative pressure, the cyanamide filtrate passes through the filter cloth and is separated by vacuum filtration. The calcium carbonate solid phase is trapped on the surface of the filter cloth, forming a calcium carbonate filter cake. The calcium carbonate filter cake is scraped off by a scraper at the discharge end as the filter cloth rotates. The method further includes: setting a spraying area on the annular running path of the filter cloth, the spraying area being located before the annular filter cloth enters the filtration zone to carry the reaction slurry; during the rotation of the annular filter cloth, calcium carbonate slurry is sprayed onto the bearing surface of the annular filter cloth in the spraying area, forming a continuous calcium carbonate coating on the bearing surface of the annular filter cloth; upon discharge, the calcium carbonate coating and the calcium carbonate filter cake are simultaneously scraped off by the scraper, and a new calcium carbonate coating is formed every revolution of the annular filter cloth.

[0007] Preferably, the spraying area is located on the return section of the annular filter cloth after the scraper and before the reaction slurry filtration area; a coating shaping section of 0.5m to 5m is left between the spraying area and the starting end of the filtration area.

[0008] Preferably, the mass concentration of calcium carbonate in the calcium carbonate slurry is 10% to 25%, and the particle size of the calcium carbonate particles in the calcium carbonate slurry is 10 μm to 30 μm.

[0009] Preferably, the amount of calcium carbonate coating applied is 0.5 kg / m² to 4 kg / m².

[0010] Preferably, after spraying the calcium carbonate slurry, a vacuum is applied to the annular filter cloth below the spraying area for pre-dehydration. The vacuum pressure is -0.02MPa to -0.09MPa, so that the water content of the calcium carbonate coating before entering the filtration area is 25% to 45%.

[0011] Preferably, the calcium carbonate slurry is prepared by mixing and stirring water and calcium carbonate, and then sprayed after being transported by a slurry pump.

[0012] Preferably, the spraying of the calcium carbonate slurry is stopped when the annular filter cloth stops rotating; when the annular filter cloth starts rotating again, the calcium carbonate coating is sprayed first, and then the reaction slurry is added to the annular filter cloth.

[0013] A cyanamide slurry separation device includes a rotating frame, an annular filter cloth mounted on the rotating frame, a reaction slurry distributor positioned above a filtration zone, a vacuum suction mechanism positioned below the filtration zone, a scraper and a cleaning mechanism located at one end of the annular filter cloth, characterized in that it further includes a calcium carbonate slurry spraying device; the calcium carbonate slurry spraying device includes a slurry tank, a slurry pump, a spraying beam, and a plurality of nozzles mounted on the spraying beam, the plurality of nozzles being evenly distributed along the width direction of the annular filter cloth; the spraying beam is positioned on the return section of the filter cloth after the scraper and before the reaction slurry filtration zone, the nozzles facing the bearing surface of the annular filter cloth.

[0014] Preferably, a vacuum filter box is provided below the spraying beam, and the vacuum filter box is located on the side away from the filter cloth bearing surface.

[0015] Compared with the prior art, this application has at least the following advantages: Before filtering the cyanamide filtrate, calcium carbonate slurry is sprayed onto the annular filter cloth 120 to form a calcium carbonate coating. The calcium carbonate coating is scraped off and re-sprayed every turn of the filter cake, which effectively prevents the annular filter cloth 120 from clogging, extending its service life from about one month to about three months. This significantly extends the service life of the filter cloth and is beneficial for continuous production. Furthermore, the sprayed calcium carbonate coating and the calcium carbonate filter cake produced by the process are made of the same material, with continuous interlayer bonding and no separation interface. When the scraper 400 scrapes it off, it peels off in whole sheets without generating debris or dust, and without introducing other impurities into the calcium carbonate filter cake, which is beneficial for subsequent purification and utilization of the calcium carbonate filter cake. In addition, the sprayed calcium carbonate slurry is inexpensive and does not require the use of other filter aids. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a cyanamide slurry separation device.

[0017] Figure 2 This is a schematic diagram of a ring-shaped filter cloth, a calcium carbonate coating, and a calcium carbonate filter cake.

[0018] Figure 3 This is a schematic diagram showing the number of days the annular filter cloth can be used and the suction pressure (uncoated, acid-washed).

[0019] Figure 4 This is a schematic diagram showing the number of days the annular filter cloth is used and the suction pressure (calcium carbonate coating, acid washing).

[0020] In the figure: belt vacuum filter 100, rotating frame 110, discharge end guide roller 111, feed end guide roller 112, annular filter cloth 120, reaction slurry distributor 200, vacuum suction mechanism 300, scraper 400, cleaning mechanism 500, calcium carbonate slurry spraying device 600, slurry tank 610, slurry pump 620, spraying beam 630, nozzle 640, vacuum suction filter box 650. Detailed Implementation

[0021] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0022] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," "top," "bottom," "end," "top," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Please refer to Figures 1 to 2A cyanamide slurry separation device uses a belt vacuum filter 100, which includes a rotating frame 110. An annular filter cloth 120 is wound around a drive roller of the rotating frame 110. The drive roller includes a discharge end guide roller 111 and a feed end guide roller 112. Driven by a drive motor, the annular filter cloth 120 rotates continuously around the drive roller. The upper horizontal section of the annular filter cloth 120 is a filtration area. A reaction slurry distributor 200 is provided above the filtration area, and a vacuum suction mechanism 300 is provided below the filtration area. The annular filter cloth 120 turns at the discharge end turning roller 111 (right end). The scraper 400 is located near the side of the annular filter cloth 120. The annular filter cloth 120 enters the return section. A cleaning mechanism 500 is provided on the return section. As the annular filter cloth 120 continues to rotate, after passing the feed end turning roller 112 (left end), a calcium carbonate slurry spraying device 600 is also provided on the side of the feed end turning roller 112. Then the annular filter cloth 120 rotates back to the filtration area, completing one rotation.

[0025] Furthermore, the calcium carbonate slurry spraying device 600 includes a slurry tank 610, a slurry pump 620, a spraying beam 630, and a plurality of nozzles 640 mounted on the spraying beam 630. The prepared calcium carbonate slurry is added to the slurry tank 610 and drawn into the pipeline by the slurry pump 620. The spraying beam 630 is fixedly mounted on one side of the rotating frame 110 and is positioned on the filter cloth return section after the scraper 400 and before the reaction slurry filtration area. The plurality of nozzles 640... The nozzles 640 are evenly distributed along the width direction of the annular filter cloth 120, and are set on the spray beam 630. The nozzles 640 face the bearing surface of the annular filter cloth 120, and the spray coverage areas of adjacent nozzles 640 are connected to each other to ensure that there is no missed spray area in the width direction of the annular filter cloth 120. The nozzles 640 can be arranged in 1 to 3 rows along the operating direction of the annular filter cloth 120, so that the calcium carbonate slurry in the pipeline is sprayed onto the bearing surface of the annular filter cloth 120 through the nozzles 640.

[0026] Furthermore, a vacuum filter box 650 is provided below the spraying beam 630, and the vacuum filter box 650 is located on the side away from the filter cloth bearing surface.

[0027] The process flow is as follows: calcium cyanamide is mixed with water and reacted in the presence of carbon dioxide to obtain a reaction slurry containing cyanamide and calcium carbonate; the reaction slurry is added to the filter cloth through the reaction slurry distributor 200, and the vacuum suction mechanism 300 filters it. The cyanamide filtrate (cyanamide content 30%~50%) passes through the filter cloth and is collected as the product, while the calcium carbonate solid phase forms a calcium carbonate filter cake on the filter cloth; the calcium carbonate filter cake runs to the discharge end and is scraped off by the scraper 400 along with the calcium carbonate coating below it, falling into the filter cake collection tank; after the filter cake is scraped off, the filter cloth is washed by the cleaning mechanism 500 and then runs to the spraying area. Several nozzles 640 evenly spray the calcium carbonate slurry onto the bearing surface of the annular filter cloth 120. The vacuum suction box 650 below the spraying area suctions and dehydrates the calcium carbonate particles, forming a continuous calcium carbonate coating on the cloth surface; the coated annular filter cloth 120 is shaped by the coating layer shaping section and then returns to the filtration area to receive the reaction slurry, entering the next filtration cycle. The calcium carbonate coating is scraped off again along with the calcium carbonate filter cake during the next unloading cycle and flows back into the filter cake collection tank, thus forming a closed-loop cycle of calcium carbonate: scraping-spraying-coating-scraping.

[0028] It should be noted that the calcium carbonate spraying area is located on the return section of the annular filter cloth 120, and simultaneously meets two positional conditions: First, it is located after the scraper 400, ensuring that the annular filter cloth 120 being sprayed is a clean filter cloth with the old filter cake and old coating scraped off; second, it is located before the reaction slurry distributor 200, ensuring that the coating layer forms before the reaction slurry. This ensures that the sprayed calcium carbonate coating is firmly bonded to the fibers of the annular filter cloth 120 and free of other impurities. The spraying direction is towards the bearing surface of the annular filter cloth 120 (i.e., the side that contacts the reaction slurry during filtration). A coating shaping section of 0.5m to 5m is left between the spraying area and the starting end of the filtration area, allowing the sprayed layer to be pre-dehydrated under vacuum and surface leveled before shaping, preventing the wet layer from entering the filtration area and being significantly dispersed or washed out of the groove by the falling reaction slurry.

[0029] Furthermore, the calcium carbonate slurry is formed by mixing and stirring water and pure calcium carbonate powder. It should be noted that the calcium carbonate slurry does not contain any external filter aids or alkaline substances (alkaline substances will catalyze the condensation of cyanamide). The calcium carbonate slurry is stirred and dispersed by a stirrer, and the calcium carbonate mass concentration is adjusted to 10% to 25% before pumping and spraying. Generally, a 15% calcium carbonate slurry is sufficient. The particle size of the calcium carbonate particles is usually in the range of 10μm to 30μm, and grinding is not required.

[0030] Furthermore, when the calcium carbonate slurry is pumped to the nozzle 640 by the slurry pump 620, the distance between the nozzle 640 outlet and the bearing surface of the annular filter cloth 120 is 100mm to 500mm. The amount of calcium carbonate coating is 0.5kg / m² to 4kg / m², and the coating thickness is approximately 0.5mm to 5mm. The linear speed of the annular filter cloth 120 is 0.5m / min to 30m / min. When the linear speed of the annular filter cloth 120 is 15m / min, the amount of calcium carbonate coating is 2kg / m², so that the coating amount matches and is adjusted in conjunction with the linear speed. When the linear speed increases, the amount of annular filter cloth 120 passing through the spraying area per unit time increases, and the spraying flow rate increases synchronously, thereby ensuring that the coating thickness is consistent along the operating direction of the annular filter cloth 120.

[0031] Furthermore, after the nozzle 640 sprays, the vacuum suction box 650 below the spray beam 630 applies a vacuum suction pressure of -0.02MPa to -0.09MPa to the annular filter cloth 120, and the liquid (mostly water) in the calcium carbonate slurry passes through the filter cloth to be removed. Subsequently, the filtrate is recovered, and the calcium carbonate particles are sprayed into a layer on the surface of the bearing surface. Before the calcium carbonate coating enters the filtration area, the water content is controlled at 25% to 45%, forming a wet but non-flowing pre-coating with a smooth surface.

[0032] In operation, the annular filter cloth 120 consists of a calcium carbonate coating and a calcium carbonate filter cake. Under vacuum, the liquid phase in the reaction slurry passes through the gaps in the filter cake, the pores of the coating layer, and the filter cloth fibers to become cyanamide filtrate. Fine calcium carbonate particles and other impurities are all intercepted by the calcium carbonate coating and cannot reach the filter cloth fibers. During unloading, the scraper 400 scrapes along the interface between the calcium carbonate coating and the filter cloth. Because the calcium carbonate coating and the calcium carbonate filter cake are made of the same material and are continuous without delamination, they are peeled off as a whole, leaving the surface of the annular filter cloth 120 fibers clean and residue-free.

[0033] The following examples and comparative models will further illustrate this. Prerequisites: The enterprise's cyanamide production line uses calcium cyanamide (calcium cyanide, main component CaCN2) mixed with water and reacted with carbon dioxide to produce a reaction slurry. All experimental examples or comparative examples below use the same batch of the same reaction slurry. The liquid phase cyanamide mass content is maintained at 30%, and the solid phase is mainly calcium carbonate. A rubber belt vacuum filter 100 is used, with several brand-new annular filter cloths 120. The width of the annular filter cloth 120 is 2.0m, and the vacuum degree of the filtration area is 0.04MPa~0.07MPa.

[0034] Comparative Example 1 (no pre-coating, acid pickling) (1) Calcium cyanamide is mixed with water and reacted with carbon dioxide to obtain a reaction slurry containing cyanamide and calcium carbonate. The reaction slurry is added to the filter cloth by the reaction slurry distributor 200. The running linear speed of the annular filter cloth 120 is 15 m / min. The vacuum suction mechanism 300 filters the filter cloth. The cyanamide filtrate passes through the filter cloth and is collected as a product with a cyanamide content of 30%. The calcium carbonate solid phase forms a calcium carbonate filter cake on the filter cloth. The calcium carbonate filter cake is scraped off by the scraper 400 at the discharge end and falls into the filter cake collection tank. After the filter cake is scraped off, the filter cloth is washed by the cleaning mechanism 500 and then enters the next filtration cycle.

[0035] (2) After the annular filter cloth 120 has been running for 12 days, the filtration flux of the annular filter cloth 120 has decreased significantly, and the suction pressure of the vacuum suction mechanism 300 has increased significantly, changing from the initial suction pressure of -0.05MPa to -0.07MPa. The amount of cyanamide filtrate collected by the suction has decreased sharply, and the annular filter cloth 120 can no longer be used. The annular filter cloth 120 is soaked and rinsed in sections using an oxalic acid solution with a pH of 3.5. Each section is rinsed for 10 minutes until the annular filter cloth 120 is completely soaked and rinsed. The acid solution can effectively dissolve the calcium carbonate remaining in the annular filter cloth 120. After the acid washing is completed, the annular filter cloth 120 is rinsed with clean water and allowed to stand. (3) Continue to start the rotating frame 110 to drive the annular filter cloth 120 to rotate. After acid washing, the suction pressure of the vacuum suction mechanism 300 on the annular filter cloth 120 is -0.06MPa. Continue to filter the monocyanamide filtrate. After 12 days of use, the filter flux of the annular filter cloth 120 drops sharply again, and the suction pressure of the vacuum suction mechanism 300 rises sharply, changing to -0.07MPa again. The amount of monocyanamide filtrate collected by the vacuum suction mechanism decreases sharply. The annular filter cloth 120 can no longer be used. Use an oxalic acid solution with a pH of 3.5 to soak and rinse the annular filter cloth 120 in sections. After rinsing each section for 10 minutes, the annular filter cloth 120 is completely soaked and rinsed. After acid washing, the annular filter cloth 120 is rinsed with clean water and allowed to stand. (4) The annular filter cloth 120 was used again with a suction pressure of -0.065MPa. After 8 days of use, the filter flux of the annular filter cloth 120 dropped significantly again, and the suction pressure of the vacuum suction mechanism 300 changed to -0.07MPa again. Pickling continued. (5) When the annular filter cloth 120 was used again with a suction pressure of -0.067 MPa, after 3 days of use, the filter flux of the annular filter cloth 120 decreased significantly again, and the suction pressure of the vacuum suction mechanism 300 changed to -0.07 MPa again. The annular filter cloth 120 was completely unusable. See details. Figure 3 .

[0036] Example 1 (with coating, pickled) (1) Water and pure calcium carbonate powder are mixed and stirred to adjust the calcium carbonate mass concentration to 15% to form a calcium carbonate slurry, which is then transported by the slurry pump 620. (2) Start the belt vacuum filter 100. The running linear speed of the annular filter cloth 120 is 15m / min. Calcium carbonate slurry is sprayed onto the annular filter cloth 120 through the nozzle 640. The distance between the nozzle 640 outlet and the bearing surface of the annular filter cloth 120 is 300mm. The coating amount of the calcium carbonate coating is 2kg / m². The visual thickness of the sprayed calcium carbonate coating is approximately 1mm. The vacuum suction pressure of the vacuum suction box 650 is -0.02MPa. The liquid in the calcium carbonate slurry passes through the filter cloth and is removed. After passing through a 2m coating shaping section, a wet but non-flowing pre-coating layer with a smooth surface is formed. (3) The annular filter cloth 120 coated with calcium carbonate enters the filtration area. Calcium cyanamide is mixed with water and reacted with the participation of carbon dioxide to obtain a reaction slurry containing monocyanamide and calcium carbonate. The reaction slurry is added to the calcium carbonate coating (filtration area) by the reaction slurry distributor 200. The vacuum suction mechanism 300 filters the cyanamide filtrate through the filter cloth and collects it as a product. The monocyanamide content is 30%. The calcium carbonate solid phase forms a calcium carbonate filter cake on the filter cloth. The calcium carbonate filter cake runs to the discharge end and is scraped off by the scraper 400 along with the calcium carbonate coating below it, falling into the filter cake collection tank. After the filter cake is scraped off, the filter cloth is washed by the cleaning mechanism 500 and then sprayed with a calcium carbonate coating again by the calcium carbonate slurry spraying device 600, and then enters the next filtration cycle.

[0037] (4) After the annular filter cloth 120 has been running continuously for 15 days, the filtration flux of the annular filter cloth 120 has decreased significantly, and the suction pressure of the vacuum suction mechanism 300 has increased significantly, changing from the initial suction pressure of -0.05MPa to -0.07MPa. The amount of cyanamide filtrate collected by the suction is reduced sharply, and the annular filter cloth 120 can no longer be used. The annular filter cloth 120 is soaked and rinsed in sections using an oxalic acid solution with a pH of 3.5. Each section is rinsed for 10 minutes until the annular filter cloth 120 is completely soaked and rinsed. The acid solution can effectively dissolve the calcium carbonate remaining in the annular filter cloth 120. After the acid washing is completed, the annular filter cloth 120 is rinsed with clean water and allowed to stand. (5) Continue to start the rotating frame 110 to drive the annular filter cloth 120 to rotate. After acid washing, the annular filter cloth 120 is coated with calcium carbonate slurry (the same as the calcium carbonate coating sprayed in step 2 of Example 1) through the nozzle 640. Then, the reaction slurry is added to the calcium carbonate coating through the reaction slurry distributor 200. Continue to filter the cyanamide filtrate. After 15 days of use, the annular filter cloth 120 will be discharged again. The current filtration flux has decreased significantly, and the suction pressure of the vacuum suction mechanism 300 has increased significantly, changing again to -0.07 MPa. The amount of cyanamide filtrate collected by the vacuum suction mechanism has decreased sharply. The annular filter cloth 120 can no longer be used. The annular filter cloth 120 is soaked and rinsed in sections using an oxalic acid solution with a pH of 3.5. Each section is rinsed for 10 minutes until the annular filter cloth 120 is completely soaked and rinsed. After acid washing, the annular filter cloth 120 is rinsed with clean water and allowed to stand. (6) The annular filter cloth 120 was used again with a suction pressure of -0.053 MPa. A calcium carbonate coating and reaction slurry were sprayed on. After 15 days of use, the filter flux of the annular filter cloth 120 decreased significantly again. The suction pressure of the vacuum suction mechanism 300 changed to -0.07 MPa again. Pickling continued. (7) The annular filter cloth 120 was used again with a suction pressure of -0.058 MPa. A calcium carbonate coating and reaction slurry were sprayed on. After 13 days of use, the filter flux of the annular filter cloth 120 decreased significantly again. The suction pressure of the vacuum suction mechanism 300 changed to -0.07 MPa again. Pickling continued. (8) The annular filter cloth 120 was used again with a suction pressure of -0.060 MPa. A calcium carbonate coating and reaction slurry were sprayed on. After 11 days of use, the filter flux of the annular filter cloth 120 decreased significantly again. The suction pressure of the vacuum suction mechanism 300 changed to -0.07 MPa again. Pickling continued. (9) The annular filter cloth 120 was used again with a suction pressure of -0.063 MPa. A calcium carbonate coating and reaction slurry were sprayed on. After 10 days of use, the filter flux of the annular filter cloth 120 decreased significantly again. The suction pressure of the vacuum suction mechanism 300 changed to -0.07 MPa again. Pickling continued. (10) The annular filter cloth 120 was used again with a suction pressure of -0.065MPa. A calcium carbonate coating and reaction slurry were sprayed on. After 5 days of use, the filter flux of the annular filter cloth 120 decreased significantly again. The suction pressure of the vacuum suction mechanism 300 changed to -0.07MPa again. Pickling continued. (11) The annular filter cloth 120 was reused with a suction pressure of -0.068 MPa. A calcium carbonate coating and reaction slurry were sprayed on. After 5 days of use, the annular filter cloth 120 again showed a significant decrease in filtration flux, and the suction pressure of the vacuum suction mechanism 300 changed again to -0.07 MPa. The annular filter cloth 120 was completely unusable. See details... Figure 4 .

[0038] It was found that spraying calcium carbonate slurry onto the annular filter cloth 120 before filtering the cyanamide filtrate to form a calcium carbonate coating, with each ring of the calcium carbonate coating being scraped off and re-sprayed along with the filter cake, effectively prevents the annular filter cloth 120 from clogging, extending its service life from about one month to about three months, significantly prolonging the filter cloth's lifespan and facilitating continuous production. Furthermore, the sprayed calcium carbonate coating and the calcium carbonate filter cake produced by the process are made of the same material, with continuous interlayer bonding and no separation interface. When scraped off by the scraper 400, the coating peels off in whole sheets, without generating debris or dust, and without introducing other impurities into the calcium carbonate filter cake, which is beneficial for subsequent purification and utilization of the calcium carbonate filter cake. In addition, the sprayed calcium carbonate slurry is inexpensive and does not require the use of other filter aids.

[0039] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A slurry separation method for cyanamide production, comprising a reaction slurry containing cyanamide and calcium carbonate obtained through a cyanamide preparation process; wherein the reaction slurry is conveyed to the filtration zone by an annular filter cloth of a belt vacuum filter, and under negative pressure, the cyanamide filtrate is filtered and separated through the filter cloth, and the calcium carbonate solid phase is trapped on the surface of the filter cloth to form a calcium carbonate filter cake, wherein the calcium carbonate filter cake is scraped off by a scraper at the discharge end as the filter cloth rotates; characterized in that... Also includes: A spraying area is set on the annular running path of the annular filter cloth, and the spraying area is located before the annular filter cloth enters the filtration area to carry the reaction slurry; During the rotation of the annular filter cloth, calcium carbonate slurry is sprayed onto the bearing surface of the annular filter cloth in the spraying area, and the calcium carbonate slurry forms a continuous calcium carbonate coating on the bearing surface of the annular filter cloth. When unloading, the calcium carbonate coating and the calcium carbonate filter cake are scraped off by the scraper at the same time, and the annular filter cloth is re-sprayed to form a new calcium carbonate coating every time it rotates once.

2. The slurry separation method for cyanamide production as described in claim 1, characterized in that, The spraying area is located on the return section of the annular filter cloth after the scraper and before the reaction slurry filtration area; a coating shaping section of 0.5m to 5m is left between the spraying area and the starting end of the filtration area.

3. The slurry separation method for cyanamide production as described in claim 1, characterized in that, The calcium carbonate slurry has a calcium carbonate mass concentration of 10% to 25%, and the calcium carbonate particles in the slurry have a particle size of 10 μm to 30 μm.

4. The slurry separation method for cyanamide production as described in claim 1, characterized in that, The amount of calcium carbonate coating applied is 0.5 kg / m² to 4 kg / m².

5. The slurry separation method for cyanamide production as described in claim 1, characterized in that, After the calcium carbonate slurry is sprayed, a vacuum is applied to the annular filter cloth below the spraying area for pre-dehydration. The vacuum pressure is -0.02MPa to -0.09MPa, so that the water content of the calcium carbonate coating before entering the filtration area is 25% to 45%.

6. The slurry separation method for cyanamide production as described in claim 1, characterized in that, The calcium carbonate slurry is prepared by mixing and stirring water and calcium carbonate, and then sprayed after being transported by a slurry pump.

7. The slurry separation method for cyanamide production as described in claim 1, characterized in that, When the annular filter cloth stops rotating, the spraying of the calcium carbonate slurry stops; when the annular filter cloth starts rotating again, the calcium carbonate coating is sprayed first, and then the reaction slurry is added to the annular filter cloth.

8. A cyanamide slurry separation apparatus, employing a slurry separation method for cyanamide production as described in any one of claims 1-7, comprising a rotating frame, an annular filter cloth disposed on the rotating frame, a reaction slurry distributor disposed above a filtration zone, a vacuum suction mechanism disposed below the filtration zone, and a scraper and cleaning mechanism located at one end of the annular filter cloth, characterized in that, It also includes a calcium carbonate slurry spraying device; The calcium carbonate slurry spraying device includes a slurry tank, a slurry pump, a spraying beam, and several nozzles installed on the spraying beam. The several nozzles are evenly distributed along the width direction of the annular filter cloth. The spraying beam is located on the return section of the filter cloth after the scraper and before the reaction slurry filtration area, and the nozzles face the bearing surface of the annular filter cloth.

9. A cyanamide slurry separation device as described in claim 8, characterized in that, A vacuum filter box is provided below the spraying beam, and the vacuum filter box is located on the side away from the filter cloth bearing surface.

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