Low shrinkage biuret urea production system
By setting up crystallization centrifugation and crystal reheating units in the urea production system, combined with mother liquor reuse, the problem of high biuret content in urea has been solved, achieving high purity and wide application of urea products.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- HENAN XINLIANXIN FERTILIZER
- Filing Date
- 2025-05-23
- Publication Date
- 2026-06-12
AI Technical Summary
Existing urea production facilities have a high biuret content, which limits the use of urea, especially in high-end industries.
A crystallization centrifugation unit and a crystal reheating unit are set up between the urea synthesis section and the urea granulation tower. The crystallization separation is carried out by taking advantage of the different saturation points of urea and biuret. Combined with the reuse of mother liquor and resource recovery, the biuret content in urea products is reduced.
This technology significantly reduces biuret content while maintaining the purity of urea products, expanding the application range of urea to include high-end agriculture, industry, and medicine, and reducing production costs.
Smart Images
Figure CN224345445U_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of urea preparation technology, specifically a low-biuret urea production system. Background Technology
[0002] Currently, all existing urea production facilities, both domestically and internationally, regardless of whether they utilize the aqueous solution full-cycle method, carbon dioxide stripping method, or ammonia stripping method, must adhere to national standards when producing urea. Specifically, the control index for biuret in agricultural urea is ≤0.9% for superior grade and ≤1.5% for qualified grade. When urea is used as agricultural fertilizer, a biuret content exceeding 1% significantly inhibits crop growth, making it unsuitable for seed fertilizer, seedling fertilizer, or foliar fertilizer. A biuret content exceeding 2% can easily cause plant poisoning, resulting in low germination rates, chlorophyll loss, and incomplete plant development. In industrial urea, excessively high biuret content degrades the resin's bonding and storage properties. Therefore, a relatively high biuret content limits the uses of urea; in other words, biuret content is a crucial indicator for evaluating urea, and a high biuret content prevents its use in high-end, specialized industries.
[0003] There are two ways biuret can be formed: firstly, it can be generated through reactions between raw materials; secondly, during urea granulation, when the temperature exceeds 130℃, urea undergoes a combination reaction to form biuret. The formation of biuret is related to urine concentration, melting temperature, residence time, and ammonia partial pressure. The urea production process generally includes several steps: raw material compression and high-pressure synthesis, medium-pressure decomposition and recovery, low-pressure decomposition and recovery, urea concentration and vacuum condensation, and melt granulation. Due to the complexity and variability of the urea production process, and the fact that urea's melting point is 132.7℃, biuret is an unavoidable byproduct during production. If the production process changes or is not properly controlled, or if the high-temperature period is prolonged, the biuret content will be too high. Utility Model Content
[0004] To overcome the above deficiencies, this utility model provides a low-biuret urea production system to solve the technical problems existing in the prior art.
[0005] The technical solution adopted by this utility model to solve its technical problem is:
[0006] A low-concentration biuret urea production system includes a urea synthesis section and a urea granulation tower. The urea synthesis section is connected to a crystal reheating unit via a crystallization centrifuge unit. The crystal reheating unit is connected to the urea granulation tower via an evaporator and an evaporation separator.
[0007] The beneficial effects of this utility model are as follows: This utility model is based on the design and modification of the existing urea production system. Specifically, a crystallization centrifugal unit is set between the urea synthesis section and the urea granulation tower. Taking advantage of the different saturation points of urea and biuret, urea is crystallized to remove biuret from the urea solution in the urea synthesis section. Under the premise of ensuring that the biuret content of urea crystals is low, urea granulation is carried out through crystal reheating unit and other related equipment to reduce the biuret content in urea products.
[0008] Preferably, the crystallization centrifugation unit includes a crystallizer connected to the urea synthesis section, the outlet of the crystallizer is connected to the urea crystal centrifuge via a slurry conveying pump, and the crystal outlet of the urea crystal centrifuge is connected to the crystal reheating unit.
[0009] Preferably, the slurry circulation outlet of the crystallizer is connected to the slurry circulation inlet of the crystallizer via a slurry circulation pump and a medium-pressure condenser.
[0010] Preferably, the slurry circulation pump is connected to the slurry circulation inlet of the crystallizer through the first heat exchange channel of the medium-pressure condenser; the inlet of the second heat exchange channel of the medium-pressure condenser is connected to the outlet of the medium-pressure separator, and the outlet of the second heat exchange channel of the medium-pressure condenser is connected to the inlet of the sub-high pressure ammonium carbamate collector.
[0011] Preferably, the mother liquor outlet of the urea crystal centrifuge is connected to a mother liquor pump via a mother liquor tank, and the outlet of the mother liquor pump is connected to the slurry circulation inlet of the crystallizer and the medium-pressure absorption tower, respectively.
[0012] Preferably, the crystal reheating unit includes a screw conveyor connected to the crystallization centrifugal unit, the outlet of the screw conveyor is connected to the inlet of the melt, and the melt is connected to the melt recirculation heater via a melt circulation pump; the melt recirculation heater is connected to the circulation inlet of the melt and the evaporator respectively.
[0013] Preferably, a molten urea pump is provided between the evaporator separator and the urea granulation tower.
[0014] A low-biuret urea production system, manufactured according to the above scheme, uses a crystallization centrifuge unit to crystallize the urea solution from the urea synthesis section, separating the biuret from the urea in the form of crystals, thereby improving the purity of the urea. While improving the purity of the urea, it also reduces the biuret content in the final urea product. Furthermore, this invention includes a crystal reheating unit after the crystallization centrifuge unit, which accelerates the reheating and dissolution of urea crystals, laying the foundation for the continuous production of subsequent urea granules. To fully utilize raw material resources and prevent the accumulation of biuret in the crystallization centrifuge unit, this invention allows the mother liquor to be recycled and reused, and also allows it to enter a medium-pressure absorption tower to recover and reuse ammonia and carbon dioxide in the urea. This system features a reasonable process design, enables resource recovery and reuse, and reduces the biuret content in the urea product while ensuring continuous production of urea granules. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This is a schematic diagram of the structure of this utility model.
[0017] In the diagram: 1. Crystallizer; 2. Slurry circulation pump; 3. Medium-pressure condenser; 4. Slurry transfer pump; 5. Urea crystal centrifuge; 6. Mother liquor tank; 7. Mother liquor pump; 8. Medium-pressure absorption tower; 9. Screw conveyor; 10. Melter; 11. Melt circulation pump; 12. Melter recirculation heater; 13. Circulation inlet and evaporator; 14. Evaporator separator; 15. Melt urea pump; 16. Urea granulation tower; 17. Urea synthesis section; 18. Medium-pressure separator; 19. Sub-high pressure ammonium carbamate collector. Detailed Implementation
[0018] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present utility model.
[0019] The following is in conjunction with the appendix Figure 1To further describe this application in detail, this utility model is a low-concentration biuret urea production system. The production system includes a urea synthesis section 17 and a urea granulation tower 16. The urea synthesis section 17 is connected to a crystal reheating unit through a crystallization centrifuge unit. The crystal reheating unit is connected to the urea granulation tower 16 in sequence through an evaporator 13 and an evaporation separator 14. This invention is an improvement based on the existing urea production system, without disrupting the original urea production process. Its essence is to separate urea and biuret in a urea solution, using a high-purity urea solution as raw material to produce urea granules, thereby reducing the biuret content in the urea granules. This invention incorporates a crystallization centrifuge unit, using a urea solution with a concentration of approximately 68% from the urea synthesis section 17 as raw material. Utilizing the characteristic that the urea content in the urea solution is higher than its saturation point while the biuret content is lower than its saturation point at low temperatures, the approximately 68% urea solution is crystallized in the crystallization centrifuge unit. The crystals are high-purity urea, while the mother liquor contains a large amount of biuret, thus achieving separation. After separation, to achieve continuous production of urea granules, this invention also includes a crystal reheating unit, thereby accelerating the dissolution of urea crystals.
[0020] Furthermore, the crystallization centrifugation unit includes a crystallizer 1 connected to the urea synthesis section 17. The outlet of the crystallizer 1 is connected to the urea crystal centrifuge 5 via a slurry transfer pump 4. The crystal outlet of the urea crystal centrifuge 5 is connected to the crystal reheating unit. The urea solution concentration in the urea synthesis section 17 is approximately 68%, of which the biuret content is approximately 0.42%. After crystallization using the crystallizer 1, the biuret content in the urea crystals is 0.07%. That is, this invention uses urea crystals with a biuret content of 0.07% as raw material when producing urea granules, thereby achieving the characteristic of reducing the biuret content in the urea product.
[0021] Furthermore, the slurry circulation outlet of the crystallizer 1 is connected to the slurry circulation inlet of the crystallizer 1 via the slurry circulation pump 2 and the medium-pressure condenser 3. During the crystallization process in the crystallizer 1, the medium-pressure condenser 3 can be used to exchange heat with the slurry, causing the water in the slurry to evaporate rapidly in the crystallizer 1, thereby achieving the purpose of rapid crystallization.
[0022] Furthermore, the slurry circulation pump 2 is connected to the slurry circulation inlet of the crystallizer 1 via the first heat exchange channel of the medium-pressure condenser 3; the inlet of the second heat exchange channel of the medium-pressure condenser 3 is connected to the outlet of the medium-pressure separator 18, and the outlet of the second heat exchange channel of the medium-pressure condenser 3 is connected to the inlet of the sub-high pressure ammonium carbamate collector 19. In actual production, this invention utilizes the ammonium carbamate condensate in the medium-pressure separator 18 of a traditional urea system as a heat source to heat the slurry, thereby reducing energy consumption.
[0023] Furthermore, the mother liquor outlet of the urea crystal centrifuge 5 is connected to the mother liquor pump 7 via the mother liquor tank 6. The outlet of the mother liquor pump 7 is connected to the slurry circulation inlet of the crystallizer 1 and the medium-pressure absorption tower 8, respectively. This configuration enables the recovery and reuse of the mother liquor. Furthermore, to prevent biuret from accumulating in the crystallizer 1, the mother liquor pump 7 is connected to both the slurry circulation inlet of the crystallizer 1 and the medium-pressure absorption tower 8. When the biuret content is low, it can be fed into the crystallizer 1 for reuse; when the biuret content is high, it can be fed into the medium-pressure absorption tower 8 to recover and reuse ammonia and carbon dioxide in the urea. In actual use, valves can be installed between the mother liquor pump 7 and the slurry circulation inlet of the crystallizer 1, and between the mother liquor pump 7 and the medium-pressure absorption tower 8, to facilitate control.
[0024] Furthermore, the crystal reheating unit includes a screw conveyor 9 connected to the crystallization centrifugal unit. The outlet of the screw conveyor 9 is connected to the inlet of the melter 10. The melter 10 is connected to the melter recirculation heater 12 via a melt circulation pump 11. The melter recirculation heater 12 is connected to the circulation inlet of the melter 10 and the evaporator 13, respectively. Crystals from the urea crystal centrifuge 5 are fed into the melter 10 via the screw conveyor 9 for dissolution, so that they can be used as raw materials in the subsequent urea granulation equipment. At the same time, in order to accelerate the dissolution of urea crystals, the present invention also provides a melter recirculation heater 12, which can use steam to exchange heat with the urea solution. After heat exchange, part of the solution is sent to the subsequent urea granulation equipment, and the other part is returned to the melter 10 to accelerate the dissolution of urea crystals. The above process can achieve rapid dissolution of urea crystals, laying the foundation for ensuring the continuous operation of the subsequent urea granulation equipment.
[0025] Furthermore, a molten urea pump 15 is provided between the evaporator separator 14 and the urea granulation tower 16.
[0026] The specific working process of this utility model is as follows: This utility model is designed based on the existing urea plant 2; in the urea synthesis section, urea synthesis and medium-low pressure decomposition purification to obtain a 68% urea solution (biuret content of about 0.42%) enters the crystallizer 1. The crystallizer 1 is maintained at 0.01 MPa (a) and 65°C. The 68% wt urea solution in the crystallizer 1 causes solid urea to begin to crystallize. At the bottom of the crystallizer 1, the urea solution and urea crystal slurry are stirred using the crystallizer's own agitator. The biuret content in the slurry is maintained at a relatively high level. The urea slurry is kept below its saturation point to prevent crystallization. In crystallizer 1, the urea slurry enters the first heat exchange channel of medium-pressure condenser 3 via slurry circulation pump 2, where it exchanges heat with ammonium carbamate condensate from medium-pressure separator 18. This causes the water in the urea slurry to evaporate in crystallizer 1, accelerating crystallization. Slurry transfer pump 4 sends the slurry to urea crystal centrifuge 5, which separates wet urea crystal cakes and urea solution stream (the so-called "mother liquor"). Mother liquor pump 7 can recycle the mother liquor back to crystallizer 1 for reuse, or send it to the medium-pressure separator 3, depending on the situation. In absorption tower 8, NH3 and CO2 are recovered from the mother liquor. Wet urea crystals are fed into melter 10 via screw conveyor 9, where they mix with molten urea to form a slurry. Melt circulation pump 11 recirculates the slurry to melter recirculation heater 12, where the crystals completely dissolve. The slurry is then heated to 140°C with 0.55 MPa (g) steam. A portion of the produced 97-98% wt urea stream is recirculated back to melter 9, and the remainder is sent to evaporator 13, which operates at 0.0... The urea is concentrated to 99.7% wt using 0.55 MPa (g) steam at 0.3 MPa (a). The concentrated urea melt is then subjected to gas-liquid separation in evaporator 14 (the biuret content in the urea melt after evaporator 14 is 0.25%). The concentrated urea solution at the bottom of evaporator 14, with a temperature of approximately 139°C, is pumped by molten urea pump 15 to granulation tower 16 for granulation. The temperature at the bottom of the granulation tower is 60°C. The final urea product tested has a biuret content of 0.5% or less. In practical applications, this invention can be coupled with existing urea systems, sharing traditional urea synthesis and purification processes. When agricultural urea needs to be produced, traditional techniques can be used to perform primary and secondary vacuum concentration of the urea solution, followed by granulation through a urea granulation tower. When producing urea applicable to industries such as manufacturing, pharmaceuticals, cosmetics, reagents, and high-end agriculture, this invention can be used to produce urea products with a biuret content maintained at 0.5% or below. Furthermore, this invention can also be used in the production of automotive urea solutions without purification, significantly reducing costs for automotive urea solution manufacturers and enhancing their market reach and competitiveness.
[0027] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed utility model.
Claims
1. A low-biuret urea production system, comprising a urea synthesis section (17) and a urea granulation tower (16), characterized in that: The urea synthesis section (17) is connected to the crystal reheating unit through the crystallization centrifuge unit, and the crystal reheating unit is connected to the urea granulation tower (16) in sequence through the evaporator (13) and the evaporation separator (14).
2. The low-biuret urea production system according to claim 1, characterized in that: The crystallization centrifugation unit includes a crystallizer (1) connected to the urea synthesis section (17). The outlet of the crystallizer (1) is connected to the urea crystal centrifuge (5) via a slurry conveying pump (4). The crystal outlet of the urea crystal centrifuge (5) is connected to the crystal reheating unit.
3. The low-biuret urea production system according to claim 2, characterized in that: The slurry circulation outlet of the crystallizer (1) is connected to the slurry circulation inlet of the crystallizer (1) through a slurry circulation pump (2) and a medium-pressure condenser (3).
4. The low-biuret urea production system according to claim 3, characterized in that: The slurry circulation pump (2) is connected to the slurry circulation inlet of the crystallizer (1) through the first heat exchange channel of the medium-pressure condenser (3); the inlet of the second heat exchange channel of the medium-pressure condenser (3) is connected to the outlet of the medium-pressure separator (18), and the outlet of the second heat exchange channel of the medium-pressure condenser (3) is connected to the inlet of the sub-high pressure ammonium carbamate collector (19).
5. A low-biuret urea production system according to claim 3, characterized in that: The mother liquor outlet of the urea crystal centrifuge (5) is connected to the mother liquor pump (7) through the mother liquor tank (6), and the outlet of the mother liquor pump (7) is connected to the slurry circulation inlet of the crystallizer (1) and the medium-pressure absorption tower (8) respectively.
6. A low-biuret urea production system according to claim 1 or 2, characterized in that: The crystal reheating unit includes a screw conveyor (9) connected to the crystallization centrifugal unit. The outlet of the screw conveyor (9) is connected to the inlet of the melter (10). The melter (10) is connected to the melter recirculation heater (12) via a melt circulation pump (11). The melter recirculation heater (12) is connected to the circulation inlet of the melter (10) and the evaporator (13) respectively.
7. The low-biuret urea production system according to claim 1, characterized in that: A molten urea pump (15) is provided between the evaporator separator (14) and the urea granulation tower (16).