Process and device for producing specialty melamine using gas-phase quenching method

Abstract

A process and device for producing specialty melamine using a gas-phase quenching method. The production process comprises: a hot process gas from an outlet of a melamine reactor is in contact with a cold process gas in a crystallizer (6), a generated solid A is discharged from the bottom of the crystallizer (6), and a mixed gas enters a collector (7) for gas-solid separation to obtain a solid B; the solid A is conveyed to a high-pressure collecting device A (63) using a high-pressure conveying gas A, wherein the high-pressure conveying gas A is maintained at 120°C or above during conveying, and upon gas-solid separation in the high-pressure collecting device A (63), the solid A is conveyed to a packaging device A (65) using a low-pressure conveying gas A, wherein it is ensured that the solid A at a conveying end does not exceed 85°C.

Description

A process and equipment for producing specialty melamine via vapor phase quenching

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510184085.1, filed on February 19, 2025, entitled "A process and equipment for producing special melamine by vapor phase quenching", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of melamine production, specifically to a process and equipment for producing special melamine using a vapor-phase quenching method. Background Technology

[0004] Melamine is a widely used basic organic chemical intermediate, primarily used as a raw material for the production of melamine-formaldehyde resin (MF). Besides this, melamine can also be used in wood processing, as a flame retardant, fiber reinforcing agent, water-reducing agent, and formaldehyde scavenger. Melamine is typically produced from urea. According to the reaction equation, 6 molecules of urea produce 1 molecule of melamine, 6 molecules of ammonia, and 3 molecules of carbon dioxide, thus the system is filled with a mixture of gases mainly composed of ammonia and carbon dioxide.

[0005] The production technology of melamine is mainly divided into high-pressure method and low-pressure method. The high-pressure method involves high reaction pressure, the reaction takes place in the liquid phase, the material density is high, and the material requirements are stringent. After the reaction, the material containing melamine is washed with ammonia water, and the melamine is captured in the liquid phase. It is then crystallized and refined from the liquid phase to obtain the solid melamine product. The high-pressure method has high energy consumption and requires significant investment; the technology, materials, and equipment are basically controlled by foreign companies. Domestic melamine production mainly uses the low-pressure method. The characteristics of the low-pressure method, besides the relatively low reaction pressure, are that no liquid water is involved in the entire process, resulting in low energy consumption, less stringent material requirements, domestic production of all key equipment and materials, and relatively lower investment. After the reaction, to obtain the solid melamine product, the process gas containing gaseous melamine is directly contacted with a cold process gas to cool it down. The melamine sublimates from the gaseous state into a solid, and then the solid melamine particles are separated from the process gas. Therefore, this method is also called the low-pressure gas-phase quenching method.

[0006] Currently, the largest single low-pressure vapor phase quenching production line in the industry is less than 60,000 tons / year. For many years, it has been unable to exceed 60,000 tons / year, and scaling up to 100,000 tons / year or even larger has been constrained by many factors, which will be explained in detail below.

[0007] First, increasing production requires an increase in the mass flow rate of the raw materials, and the mass flow rates of the carrier gas and cooling gas must also increase proportionally. If parameters such as temperature and pressure remain constant, it means the density remains constant, leading to a proportional increase in the volumetric flow rate of the entire gas-phase circulation system. The reactor is a fluidized bed reactor, requiring the fluidized carrier gas to enter from the bottom. As it passes through the catalyst bed, the gas distribution is generally uniform, and the upward velocity of the carrier gas within the fluidized bed reactor has a reasonable range, which determines the relationship between production capacity and reactor diameter. Increasing production capacity and the volumetric flow rate of the carrier gas necessitates further increasing the equipment diameter. However, as the equipment diameter increases, achieving uniform gas distribution becomes increasingly difficult. Poor distribution, leading to flow deviation, will cause a rapid decrease in reaction efficiency for the fluidized bed reactor. Furthermore, for materials flowing through pipes, under normal conditions, resistance loss (energy consumption) is proportional to the square root of the flow velocity. To maintain relatively low energy consumption, when production capacity increases, the flow velocity and volumetric flow rate must remain constant. Therefore, an n-fold increase in production capacity means enlarging the pipe diameter by the square root of n. For example, doubling the production capacity means increasing the pipe diameter to the square root of 2 (1.414 times). Considering that the pipe wall thickness also needs to be increased accordingly with the increased pipe diameter, the pipe investment may increase by more than 1.5 times. Similar increases are seen in the investment in various other equipment. Overall, doubling the production capacity leads to approximately 1.5 times the investment in equipment.

[0008] Alternatively, while maintaining a constant reaction temperature and volumetric flow rate, increasing the reaction pressure can also increase the mass flow rate, thereby increasing yield. Since the volumetric flow rate remains constant, it's possible to avoid increasing the size of equipment and piping. However, it's not that simple. This method has its limitations; blindly increasing the pressure can lead to other problems, which will be detailed below.

[0009] In the melamine gas-phase process, the process gas containing melamine products needs to be cooled in the hot gas cooling section to allow high-boiling-point byproducts to precipitate from the gas phase and solidify. These byproducts are then separated from the gas phase using a filter. However, if the cooling temperature is too low, melamine will also precipitate and be filtered out, which is unacceptable. Therefore, the degree of cooling is limited. When the reaction pressure increases, the total gas-phase pressure of the hot process gas increases, and the partial pressure of melamine also increases proportionally. At this point, a higher temperature is required to maintain the gaseous state of melamine, forcing the hot gas cooling section to be set at a higher temperature. In other words, the temperature of the hot process gas increases. Then, in the crystallizer, facing the higher-temperature hot process gas, more cooling gas is needed to counteract it and keep the crystallizer temperature within a reasonable range. The increase in cooling gas volume means an increase in the energy consumption of the cooling fans that power the cooling gas, leading to increased operating costs. Therefore, detailed calculations are required to design an optimal parameter combination that improves production capacity, is engineering-feasible, and does not increase energy consumption—something that is not easily accomplished by those generally working in this field.

[0010] Gas-phase quenching occurs in the crystallizer. The cold process gas comes into direct contact with the hot process gas containing gaseous melamine products within the crystallizer. The melamine cools, changing from a gaseous state to a solid state, mixing with the process gas to form a gas-solid mixture. This mixture flows out from the bottom of the crystallizer and enters the collector through a pipeline. In the collector, gas and solid separate, with the solids collecting at the bottom. The solid powder is then discharged from the collector by a discharge mechanism. The pipeline connecting the crystallizer and the collector, constantly subjected to a two-phase gas-solid flow, is prone to solid accumulation and blockage, which is the bottleneck causing the current short operating cycle of melamine plants. If the plant's production capacity is larger than the current 50,000 tons / year, increasing the solid flow through the pipeline between the crystallizer and the collector will worsen the blockage, significantly shortening the production cycle and causing frequent start-ups and shutdowns. The maintenance time after a shutdown represents lost production time, and a transition period is needed after restarting to gradually improve product quality from substandard to high levels. Therefore, frequent start-ups and shutdowns severely impact normal production, increase costs, and reduce output.

[0011] Furthermore, all current melamine production lines mix melamine of all particle sizes into the same product without particle size classification, limiting its application. High-pressure process products have larger particles and higher bulk density, making them suitable only for melamine-formaldehyde resin adhesives, but not for direct applications such as powder fire extinguishers or fire-retardant coatings. Conventional low-pressure process products have smaller average particle sizes and can be used in various applications, but their wide normal particle size distribution results in inconsistent reaction endpoint times when used in melamine-formaldehyde resin adhesive production, and the adhesive has a short shelf life.

[0012] In summary, given the difficulties in expanding the production capacity of a single unit for producing melamine using the vapor phase quenching method and the shortcomings of existing technologies, there is an urgent need in this field to develop a process and apparatus for large-scale production of specialty melamines using the vapor phase quenching method. Summary of the Invention

[0013] In view of this, this application provides a process for producing special melamine by vapor phase quenching, which can achieve an annual production capacity of 100,000 tons or more with lower energy consumption, filling the technological gap that the annual production capacity of existing single melamine production units cannot exceed 60,000 tons.

[0014] Accordingly, this application also provides an apparatus for producing special melamine using the vapor phase quenching method in the above process.

[0015] In a first aspect, this application provides a process for producing special melamine by vapor phase quenching, comprising the following steps:

[0016] The hot process gas from the outlet of the melamine reactor is cooled by a hot gas cooler and filtered by a hot gas filter before entering the crystallizer and coming into direct contact with the cold process gas. The solid A produced is discharged from the bottom of the crystallizer, and the mixed gas enters the collector for gas-solid separation to obtain solid B.

[0017] Solid A is transported to a high-pressure collection device A using high-pressure transport gas A, ensuring that the temperature of high-pressure transport gas A remains above 120°C during the transport process. After gas-solid separation in the high-pressure collection device A, solid A is then transported to a packaging device A using low-pressure transport gas A, ensuring that the temperature of solid A at the end of the transport process does not exceed 85°C. The pressure of high-pressure transport gas A is 2 barG to 8 barG and lower than the pressure inside the crystallizer, while the pressure of low-pressure transport gas A is 0.2 barG to 6.5 barG and lower than the pressure of high-pressure transport gas A.

[0018] The production process of this application promptly discharges solid A generated by melamine sublimation in the crystallizer. Only fine particles that cannot settle to the bottom of the crystallizer are carried to the collector by the process gas (i.e., the mixed gas referred to in this application). This significantly reduces the burden on the pipeline between the crystallizer and the collector, preventing blockage. Furthermore, since the material collected at the bottom of the crystallizer has a large particle size and the material collected in the collector has a small particle size, the product material is automatically classified, which can better meet market demand, improve product competitiveness, and increase economic benefits. Furthermore, the production process of this application involves two-stage conveying of solid A discharged from the bottom of the crystallizer (first high-pressure conveying, then low-pressure conveying). The pressure inside the high-pressure conveying pipe is relatively high, and the pressure difference with the crystallizer is relatively small. When the solid product is discharged from the bottom of the crystallizer, the amount of ammonia and carbon dioxide gas carried out with the solid is also very small. At the same time, it is ensured that the temperature of the high-pressure conveying gas A is above 120°C during the high-pressure conveying process. In this way, the ammonia and carbon dioxide gas escaping from the high-pressure conveying pipe can remain in a gaseous state at a relatively high temperature and will not condense into the product, thus avoiding affecting the purity of the product. Then, the ammonia and carbon dioxide gas are separated from the solid product in the high-pressure collector, so there is no ammonia and carbon dioxide gas left when it reaches the low-pressure conveying pipe. At this time, the low-pressure and low-temperature conveying does not have to worry about the sublimation of ammonia and carbon dioxide, and the final temperature of the product is relatively low, so it will not damage the packaging bag.

[0019] In one optional embodiment, the process for producing special melamine using the vapor-phase quenching method provided in this application involves using high-pressure conveying gas B to transport solid B to a high-pressure collecting device B, ensuring that the temperature of the high-pressure conveying gas B is above 120°C during the transport process; after gas-solid separation in the high-pressure collecting device B, low-pressure conveying gas B is used to transport solid B to a packaging device B, ensuring that the temperature of solid B at the end of the transport does not exceed 85°C; the pressure of the high-pressure conveying gas B is 2 barG to 8 barG and lower than the pressure inside the collector, and the pressure of the low-pressure conveying gas B is 0.2 barG to 6.5 barG and lower than the pressure of the high-pressure conveying gas B.

[0020] The solid B obtained from the collector is also conveyed in two stages (high pressure conveying first, then low pressure conveying). As mentioned above, this not only ensures product purity but also prevents the packaging bags from being damaged by heat.

[0021] In one optional embodiment, the process for producing special melamine by vapor phase quenching provided in this application has a mass ratio of cold process gas to hot process gas entering the crystallizer of 2.6 to 3.2.

[0022] In one optional embodiment, the process for producing special melamine by vapor phase quenching provided in this application has a pressure of 4 barG to 9.8 barG inside the crystallizer.

[0023] In one optional embodiment, the process for producing special melamine by vapor phase quenching provided in this application has a bottom discharge amount of 5% to 50% of the total solids in the crystallizer.

[0024] In one optional embodiment, the process for producing special melamine by gas-phase quenching provided in this application has a mass ratio of carrier gas to urea entering the melamine reactor of 3.1 to 4.5.

[0025] In one optional embodiment, the process for producing special melamine by vapor-phase quenching provided in this application has a top temperature of 380°C to 405°C and a top pressure of 5 barG to 10 barG in the melamine reactor.

[0026] The production process described in this application, by controlling the process parameters of the melamine reactor, hot gas cooler, hot gas filter, crystallizer, and collector, can significantly increase output without increasing reactor size, thus avoiding engineering difficulties.

[0027] Secondly, this application also provides a production apparatus for producing special melamine by vapor phase quenching, comprising:

[0028] The crystallizer discharge unit includes a crystallizer discharge device, a high-pressure collecting device A, and a packaging device A. The inlet of the crystallizer discharge device is connected to the bottom of the crystallizer, and the outlet of the crystallizer discharge device is connected to the inlet of the high-pressure collecting device A via a high-pressure conveying pipe A. The lower outlet of the high-pressure collecting device A is connected to the packaging device A via a low-pressure conveying pipe A. The outer wall of the high-pressure conveying pipe A is provided with a heat insulation structure to ensure that the temperature in the high-pressure conveying pipe A is above 120°C, and the pressure in the high-pressure conveying pipe A is 2 barG to 8 barG, which is lower than the pressure in the crystallizer. The outer wall of the low-pressure conveying pipe A is provided with a cooling structure to ensure that the temperature at the end of the low-pressure conveying pipe A does not exceed 85°C, and the pressure in the low-pressure conveying pipe A is 0.2 barG to 6.5 barG, which is lower than the pressure in the high-pressure conveying pipe A.

[0029] The collector discharge unit includes a collector discharge device and a packaging device B. The inlet of the collector discharge device is connected to the bottom of the collector, and the outlet of the collector discharge device is connected to the packaging device B. The inlet of the collector is connected to the upper outlet of the crystallizer.

[0030] The production equipment of this application uses a crystallizer discharge device at the bottom of the crystallizer to promptly discharge solid A generated by melamine sublimation in the crystallizer. Only fine particles that cannot settle to the bottom of the crystallizer are carried to the collector by the process gas (i.e., the mixed gas referred to in this application). This significantly reduces the burden on the pipeline between the crystallizer and the collector, preventing the pipeline from becoming blocked. Furthermore, since the material collected at the bottom of the crystallizer has a large particle size and the material collected by the collector has a small particle size, the product material is automatically classified, which can better meet market demand, improve product competitiveness, and increase economic benefits. Furthermore, the production equipment of this application performs two-stage conveying of solid A discharged from the bottom of the crystallizer (first high-pressure conveying, then low-pressure conveying). The pressure inside the high-pressure conveying pipe is relatively high, and the pressure difference with the crystallizer is relatively small. When the solid product is discharged from the bottom of the crystallizer, the amount of ammonia and carbon dioxide gas carried out with the solid is also very small. At the same time, the outer wall of the high-pressure conveying pipe is equipped with a heat insulation structure to ensure that the temperature of the high-pressure conveying gas A is above 120°C during the high-pressure conveying process. In this way, the ammonia and carbon dioxide gas escaping from the high-pressure conveying pipe can still remain in a gaseous state at a relatively high temperature and will not condense into the product, thus avoiding affecting the purity of the product. Then, the ammonia and carbon dioxide gas are separated from the solid product in the high-pressure collector, so there is no ammonia and carbon dioxide gas when it reaches the low-pressure conveying pipe (which is equipped with a cooling structure on its outer wall). At this time, there is no need to worry about the sublimation of ammonia and carbon dioxide during low-pressure and low-temperature conveying, and the final temperature of the product is relatively low, so it will not burn the packaging bag.

[0031] In one optional embodiment, the production equipment for producing special melamine using the gas-phase quenching method provided in this application includes a screw conveyor as the crystallizer discharge device. Since the gas phase pressure inside the crystallizer is slightly higher than the pressure inside the high-pressure conveying pipe, the process gases (mainly ammonia and carbon dioxide) inside the crystallizer will inevitably leak into the high-pressure conveying pipe along the screw direction. The advantage of using a screw conveyor is that inside the screw conveyor, the propulsion of the screw compresses the product particles, reducing the gap between the particles and the flow path of the process gas, thus reducing the amount of leaked process gas.

[0032] In one optional embodiment, the production equipment for producing special melamine by vapor phase quenching provided in this application has the outlet of the collector discharge device connected to the inlet of the high-pressure collection device B via a high-pressure conveying pipe B, and the lower outlet of the high-pressure collection device B connected to the packaging device B via a low-pressure conveying pipe B.

[0033] The outer wall of the high-pressure conveying pipe B is provided with a heat insulation structure to ensure that the temperature in the high-pressure conveying pipe B is above 120°C, and the pressure in the high-pressure conveying pipe B is 2 barG to 8 barG and lower than the pressure in the trap; the outer wall of the low-pressure conveying pipe B is provided with a cooling structure to ensure that the temperature at the end of the low-pressure conveying pipe B does not exceed 85°C, and the pressure in the low-pressure conveying pipe B is 0.2 barG to 6.5 barG and lower than the pressure in the high-pressure conveying pipe B.

[0034] The solid B obtained from the collector is also conveyed in two stages (high pressure conveying first, then low pressure conveying). As mentioned above, this not only ensures product purity but also prevents the packaging bags from being damaged by heat.

[0035] In an optional embodiment, the production equipment for producing special melamine by gas phase quenching provided in this application further includes: a carrier gas compressor, a carrier gas preheater, a melamine reactor, a hot gas cooler, a crystallizer, a collector, a urea scrubbing tower, and a cooling fan arranged in sequence.

[0036] The upper outlet of the trap is connected to the urea scrubbing tower for cooling the gas to produce recyclable cold process gas.

[0037] The cold air outlet of the urea scrubbing tower is connected to the inlet of the cold air fan, and the outlet of the cold air fan is connected to the cold process gas inlet of the crystallizer.

[0038] The production equipment of this application enables the recycling of cold process gas, thereby reducing production costs. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 is a production process flow diagram of Embodiment 1 of this application.

[0041] Figure 2 is a schematic diagram of the crystallizer discharge unit in Embodiment 1 of this application.

[0042] Figure 3 is a schematic diagram of the structure of the collector discharge unit in Embodiment 1 of this application.

[0043] The reference numerals in the attached drawings are explained as follows: 1. Carrier gas compressor; 2. Carrier gas preheater; 3. Melamine reactor; 4. Hot gas cooler; 5. Hot gas filter; 6. Crystallizer; 7. Collector; 8. Urea scrubbing tower; 9. Cooling fan; 61. Crystallizer discharge device; 62. High-pressure conveying pipe A; 63. High-pressure collecting device A; 64. Low-pressure conveying pipe A; 65. Packaging device A; 71. Collector discharge device; 72. High-pressure conveying pipe B; 73. High-pressure collecting device B; 74. Low-pressure conveying pipe B; 75. Packaging device B. Detailed Implementation

[0044] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0045] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0046] In this application, the term "specialty melamine" refers to melamine products that can meet the special needs of different application scenarios.

[0047] To address the problems existing in the aforementioned related technologies, according to the first aspect of this application, a process for producing special melamine by vapor phase quenching is provided, comprising the following steps:

[0048] The hot process gas from the outlet of the melamine reactor is cooled by a hot gas cooler and filtered by a hot gas filter before entering the crystallizer and coming into direct contact with the cold process gas. The solid A produced is discharged from the bottom of the crystallizer, and the mixed gas enters the collector for gas-solid separation to obtain solid B.

[0049] Solid A is transported to a high-pressure collection device A using high-pressure conveying gas A, ensuring that the temperature of high-pressure conveying gas A is above 120°C during the transport process. For example, the temperature of high-pressure conveying gas A can be 120°C, 130°C, 140°C, 150°C, 160°C, 180°C, 200°C, or any value within the range of these values. After gas-solid separation in the high-pressure collection device A, solid A is then transported to a packaging device A using low-pressure conveying gas A, ensuring that the temperature of solid A at the end of the transport does not exceed 85°C. For example, the temperature of solid A at the end of the transport can be 85°C, 75°C, 65°C, 55°C, 45°C, 35°C, 25°C, or any value within the range of these values. The high-pressure conveying... The pressure of gas A is 2 barG to 8 barG and is lower than the pressure inside the crystallizer. For example, the pressure of high-pressure delivery gas A can be 2 barG, 3 barG, 4 barG, 5 barG, 6 barG, 7 barG, 8 barG, or any value within the range of the above. The pressure of low-pressure delivery gas A is 0.2 barG to 6.5 barG and is lower than the pressure of high-pressure delivery gas A. For example, the pressure of low-pressure delivery gas A can be 0.2 barG, 0.5 barG, 1 barG, 2 barG, 3 barG, 4 barG, 5 barG, 5.5 barG, 6 barG, 6.5 barG, or any value within the range of the above.

[0050] The production process of this application promptly discharges solid A generated by melamine sublimation in the crystallizer. Only fine particles that cannot settle to the bottom of the crystallizer are carried to the collector by the process gas (i.e., the mixed gas referred to in this application). This significantly reduces the burden on the pipeline between the crystallizer and the collector, preventing blockage. Furthermore, since the material collected at the bottom of the crystallizer has a large particle size and the material collected in the collector has a small particle size, the product material is automatically classified, which can better meet market demand, improve product competitiveness, and increase economic benefits. Furthermore, the production process of this application involves two-stage conveying of solid A discharged from the bottom of the crystallizer (first high-pressure conveying, then low-pressure conveying). The pressure inside the high-pressure conveying pipe is relatively high, and the pressure difference with the crystallizer is relatively small. When the solid product is discharged from the bottom of the crystallizer, the amount of ammonia and carbon dioxide gas carried out with the solid is also very small. At the same time, it ensures that the temperature of solid A is above 120°C during the high-pressure conveying process. In this way, the ammonia and carbon dioxide gas escaping from the high-pressure conveying pipe can remain in a gaseous state at a relatively high temperature and will not condense into the product, thus avoiding affecting the purity of the product. Then, the ammonia and carbon dioxide gas are separated from the solid product in the high-pressure collector, so there is no ammonia and carbon dioxide gas left when it reaches the low-pressure conveying pipe. At this time, the low-pressure and low-temperature conveying does not have to worry about the sublimation of ammonia and carbon dioxide, and the final temperature of the product is relatively low, so it will not damage the packaging bag.

[0051] It is understood that “large-scale” as used in this application refers to an annual production capacity of 60,000 tons or more, such as an annual production capacity of 70,000 tons, 80,000 tons, 100,000 tons, 150,000 tons, 200,000 tons, or any of the above values.

[0052] It should be noted that traditional crystallizers completely disregard the issue of material discharge, placing the gas outlet at the center of the bottom of the crystallizer and allowing gas to flow downwards. Even if some solids inside the crystallizer have separated from the gas phase, they cannot be retained and will still flow out of the crystallizer with the gas. However, in this application, by employing technical means commonly known to those skilled in the art to modify and optimize the lower structure of the crystallizer, the solid product can be collected and extracted at the bottom of the crystallizer. Therefore, this application does not require any limitation on the specific structure of the crystallizer; any crystallizer structure that can achieve the separation effect of this application is applicable to this application.

[0053] In one optional embodiment, the process for producing special melamine using the vapor-phase quenching method provided in this application involves using high-pressure conveying gas B to transport solid B to a high-pressure collecting device B, ensuring that the temperature of the high-pressure conveying gas B is above 120°C during the conveying process. For example, the temperature of the high-pressure conveying gas B can be 120°C, 130°C, 140°C, 150°C, 160°C, 180°C, 200°C, or any range thereof. After gas-solid separation in the high-pressure collecting device B, the solid B is then transported to a packaging device B using low-pressure conveying gas B, ensuring that the temperature of the solid B at the end of the conveying process does not exceed 85°C. For example, the temperature of the solid B at the end of the conveying process can be 85°C, 75°C, 65°C, 55°C, 45°C, 35°C, 25°C, or any range thereof. Within the range of values; the pressure of the high-pressure conveying gas B is 2 barG to 8 barG and lower than the pressure inside the trap. For example, the pressure of the high-pressure conveying gas B can be 2 barG, 3 barG, 4 barG, 5 barG, 6 barG, 7 barG, 8 barG, etc., or within any of the above values; the pressure of the low-pressure conveying gas B is 0.2 barG to 6.5 barG and lower than the pressure of the high-pressure conveying gas B. For example, the pressure of the low-pressure conveying gas B can be 0.2 barG, 0.5 barG, 1 barG, 2 barG, 3 barG, 4 barG, 5 barG, 5.5 barG, 6 barG, 6.5 barG, etc., or within any of the above values.

[0054] The solid B obtained from the collector is also conveyed in two stages (high pressure conveying first, then low pressure conveying). As mentioned above, this not only ensures product purity but also prevents the packaging bags from being damaged by heat.

[0055] In one optional embodiment, the process for producing special melamine using the vapor-phase quenching method provided in this application has a mass ratio of cold process gas to hot process gas entering the crystallizer of 2.6 to 3.2. As an example, the mass ratio of cold process gas to hot process gas entering the crystallizer can be, for example, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, or any range of the above values.

[0056] In one optional embodiment, the process for producing special melamine using the vapor-phase quenching method provided in this application has a crystallizer pressure of 4 barG to 9.8 barG. As an example, the crystallizer pressure can be 4 barG, 4.5 barG, 5 barG, 5.5 barG, 6 barG, 6.5 barG, 7 barG, 7.5 barG, 8 barG, 8.5 barG, 9 barG, 9.8 barG, or any range thereof.

[0057] In one optional embodiment, the process for producing special melamine by vapor phase quenching provided in this application, wherein the bottom discharge amount of the crystallizer accounts for 5% to 50% of the total solids. As an example, the bottom discharge amount of the crystallizer accounts for 5%, 10%, 20%, 30%, 40%, 50% of the total solids, or any of the above values.

[0058] In one optional embodiment, the process for producing special melamine using the vapor-phase quenching method provided in this application has a carrier gas to urea mass ratio of 3.1 to 4.5 entering the melamine reactor. As an example, the carrier gas to urea mass ratio entering the melamine reactor can be, for example, 3.1, 3.3, 3.5, 3.7, 3.9, 4.1, 4.3, 4.5, or any range of the above values.

[0059] In one optional embodiment, the process for producing special melamine using the vapor-phase quenching method provided in this application has a top temperature of 380°C to 405°C and a top pressure of 5 barG to 10 barG in the melamine reactor. As an example, the top temperature of the melamine reactor can be 380°C, 385°C, 390°C, 395°C, 400°C, 405°C, or any value within the range of these values; the top pressure of the melamine reactor can be 5 barG, 6 barG, 7 barG, 8 barG, 9 barG, 10 barG, or any value within the range of these values.

[0060] The production process described in this application, by controlling the aforementioned process parameters of the melamine reactor, hot gas cooler, hot gas filter, crystallizer, and collector, can significantly increase production output without increasing reactor size, thus avoiding engineering difficulties.

[0061] According to a second aspect of this application, a production apparatus for producing special melamine by vapor phase quenching is also provided, comprising:

[0062] The crystallizer discharge unit includes a crystallizer discharge device, a high-pressure collecting device A, and a packaging device A. The inlet of the crystallizer discharge device is connected to the bottom of the crystallizer, and the outlet of the crystallizer discharge device is connected to the inlet of the high-pressure collecting device A through a high-pressure conveying pipe A. The lower outlet of the high-pressure collecting device A is connected to the packaging device A through a low-pressure conveying pipe A. The outer wall of the high-pressure conveying pipe A is provided with a heat insulation structure, and the outer wall of the low-pressure conveying pipe A is provided with a cooling structure.

[0063] The collector discharge unit includes a collector discharge device and a packaging device B. The inlet of the collector discharge device is connected to the bottom of the collector, and the outlet of the collector discharge device is connected to the packaging device B. The inlet of the collector is connected to the upper outlet of the crystallizer.

[0064] Furthermore, in an optional embodiment, the production equipment for producing special melamine by vapor-phase quenching includes:

[0065] The crystallizer discharge unit includes a crystallizer discharge device, a high-pressure collecting device A, and a packaging device A. The inlet of the crystallizer discharge device is connected to the bottom of the crystallizer, and the outlet of the crystallizer discharge device is connected to the inlet of the high-pressure collecting device A via a high-pressure conveying pipe A. The lower outlet of the high-pressure collecting device A is connected to the packaging device A via a low-pressure conveying pipe A. The outer wall of the high-pressure conveying pipe A is equipped with a heat-insulating structure to ensure that the temperature inside the high-pressure conveying pipe A is above 120°C. For example, the temperature of the high-pressure conveying pipe A can be 120°C, 130°C, 140°C, 150°C, 160°C, 180°C, 200°C, or any value within the range of these values. The pressure inside the high-pressure conveying pipe A is 2 barG to 8 barG and is lower than the pressure inside the crystallizer. For example, the pressure inside the high-pressure conveying pipe A can be 2 barG, 3 barG, 4 barG, etc. The low-pressure delivery pipe A has a cooling structure on its outer wall to ensure that the temperature inside the end of the low-pressure delivery pipe A does not exceed 85°C. For example, the temperature inside the end of the low-pressure delivery pipe A can be 85°C, 75°C, 65°C, 55°C, 45°C, 35°C, 25°C, etc., or within the range of any of the above values. The pressure of the low-pressure delivery pipe A is 0.2 barG to 6.5 barG and is lower than the pressure inside the high-pressure delivery pipe A. For example, the pressure of the low-pressure delivery pipe A can be 0.2 barG, 0.5 barG, 1 barG, 2 barG, 3 barG, 4 barG, 5 barG, 5.5 barG, 6 barG, 6.5 barG, etc., or within the range of any of the above values.

[0066] The collector discharge unit includes a collector discharge device and a packaging device B. The inlet of the collector discharge device is connected to the bottom of the collector, and the outlet of the collector discharge device is connected to the packaging device B. The inlet of the collector is connected to the upper outlet of the crystallizer.

[0067] The production equipment of this application uses a crystallizer discharge device at the bottom of the crystallizer to promptly discharge solid A generated by melamine sublimation in the crystallizer. Only fine particles that cannot settle to the bottom of the crystallizer are carried to the collector by the process gas (i.e., the mixed gas referred to in this application). This significantly reduces the burden on the pipeline between the crystallizer and the collector, preventing the pipeline from becoming blocked. Furthermore, since the material collected at the bottom of the crystallizer has a large particle size and the material collected by the collector has a small particle size, the product material is automatically classified, which can better meet market demand, improve product competitiveness, and increase economic benefits. Furthermore, the production equipment of this application performs two-stage conveying of solid A discharged from the bottom of the crystallizer (first high-pressure conveying, then low-pressure conveying). The pressure inside the high-pressure conveying pipe is relatively high, and the pressure difference with the crystallizer is relatively small. When the solid product is discharged from the bottom of the crystallizer, the amount of ammonia and carbon dioxide gas carried out with the solid is also very small. At the same time, the outer wall of the high-pressure conveying pipe is equipped with a heat insulation structure to ensure that the temperature of solid A is above 120°C during the high-pressure conveying process. In this way, the ammonia and carbon dioxide gas escaping from the high-pressure conveying pipe can remain in a gaseous state at a relatively high temperature and will not condense into the product, thus avoiding affecting the purity of the product. Then, the ammonia and carbon dioxide gas are separated from the solid product in the high-pressure collector, so there is no ammonia and carbon dioxide gas when it reaches the low-pressure conveying pipe (which is equipped with a cooling structure on its outer wall). At this time, there is no need to worry about the sublimation of ammonia and carbon dioxide during low-pressure and low-temperature conveying. The final temperature of the product is relatively low and will not damage the packaging bag.

[0068] In one optional embodiment, the production equipment for producing special melamine using the gas-phase quenching method provided in this application includes a screw conveyor as the crystallizer discharge device. Since the gas phase pressure inside the crystallizer is slightly higher than the pressure inside the high-pressure conveying pipe, the process gases (mainly ammonia and carbon dioxide) inside the crystallizer will inevitably leak into the high-pressure conveying pipe along the screw direction. The advantage of using a screw conveyor is that inside the screw conveyor, the propulsion of the screw compresses the product particles, reducing the gap between the particles and the flow path of the process gas, thus reducing the amount of leaked process gas.

[0069] In one optional embodiment, the production equipment for producing special melamine by vapor phase quenching provided in this application has the outlet of the collector discharge device connected to the inlet of the high-pressure collection device B via a high-pressure conveying pipe B, and the lower outlet of the high-pressure collection device B connected to the packaging device B via a low-pressure conveying pipe B.

[0070] The outer wall of the high-pressure conveying pipe B is equipped with a heat insulation structure to ensure that the temperature inside the high-pressure conveying pipe B is above 120°C. For example, the temperature of the high-pressure conveying pipe B can be 120°C, 130°C, 140°C, 150°C, 160°C, 180°C, 200°C, or any value within the range above. The pressure inside the high-pressure conveying pipe B is 2 barG to 8 barG and lower than the pressure inside the trap. For example, the pressure of the high-pressure conveying pipe B can be 2 barG, 3 barG, 4 barG, 5 barG, 6 barG, 7 barG, 8 barG, or any value within the range above. The outer wall of the low-pressure conveying pipe B is equipped with a cooling system. The structure is designed so that the temperature inside the end of the low-pressure delivery pipe B does not exceed 85°C. For example, the temperature inside the end of the low-pressure delivery pipe B can be 85°C, 75°C, 65°C, 55°C, 45°C, 35°C, 25°C, or any value within the range of the above. The pressure inside the low-pressure delivery pipe B is 0.2 barG to 6.5 barG and is lower than the pressure inside the high-pressure delivery pipe B. For example, the pressure inside the low-pressure delivery pipe B can be 0.2 barG, 0.5 barG, 1 barG, 2 barG, 3 barG, 4 barG, 5 barG, 5.5 barG, 6 barG, 6.5 barG, or any value within the range of the above.

[0071] The solid B obtained from the collector is also conveyed in two stages (high pressure conveying first, then low pressure conveying). As mentioned above, this not only ensures product purity but also prevents the packaging bags from being damaged by heat.

[0072] In an optional embodiment, the production equipment for producing special melamine by gas phase quenching provided in this application further includes: a carrier gas compressor, a carrier gas preheater, a melamine reactor, a hot gas cooler, a crystallizer, a collector, a urea scrubbing tower, and a cooling fan arranged in sequence.

[0073] The upper outlet of the trap is connected to the urea scrubbing tower for cooling the gas to produce recyclable cold process gas.

[0074] The cold air outlet of the urea scrubbing tower is connected to the inlet of the cold air fan, and the outlet of the cold air fan is connected to the cold process gas inlet of the crystallizer.

[0075] The production equipment of this application enables the recycling of cold process gas, thereby reducing production costs.

[0076] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0077] Example 1

[0078] This embodiment provides a production process for large-scale production of specialty melamine (100,000 tons / year) using a vapor-phase quenching method, as shown in Figure 1, including the following steps:

[0079] 117 t / h of hot process gas is pressurized to 7 bar (G) by carrier gas compressor 1, and heated to 405°C by carrier gas preheater 2, before entering the melamine reactor 3 as fluidized carrier gas. 37.5 t / h of urea (carrier gas to urea mass ratio of 3.12) is added to the melamine reactor 3. 3 tons of urea produce 1 ton of melamine. All products other than melamine are represented as ammonia and carbon dioxide. In this embodiment and comparative example, the molar ratio of ammonia to carbon dioxide in all process gases in the entire system is considered to be the theoretical value of 2:1. The efficiency of carrier gas compressor 1 is calculated to be 80%, and the efficiency of cooling fan 9 is calculated to be 70%. The melamine reactor 3 outlet yields 154.5 t / h of hot process gas at a temperature of 405°C and a pressure of 6 bar (G).

[0080] The hot process gas at the outlet of melamine reactor 3 contains 12.5 t / h of melamine, with a mole fraction of 1.78% and a total pressure of 6 bar (G), resulting in a calculated partial pressure of 0.125 bar (A). At this pressure, the theoretical condensation (sublimation) temperature of melamine is calculated to be 337℃, with a 20℃ margin. The operating temperature of hot gas cooler 4 is set at 357℃. The hot process gas from the outlet of hot gas cooler 4 then passes through hot gas filter 5, where the pressure is reduced to 5.7 bar (G), before entering crystallizer 6. Simultaneously, cold process gas is supplied to crystallizer 6 using cold air fan 9, ensuring a mass ratio of cold to hot process gas of 2.65. After the hot and cold process gases mix in crystallizer 6, the temperature becomes 215℃, and the pressure drops to 5.67 bar (G), causing melamine to crystallize into a solid.

[0081] The power of the air cooler 9 is 923 kW, and the power of the carrier air compressor 1 is 1364 kW. According to the formula: unit product energy consumption = (air cooler power + carrier air compressor power) / melamine production, the unit product energy consumption in this embodiment is calculated to be 183 kWh / t melamine.

[0082] 6.25 t / h of melamine solids are separated from the bottom of crystallizer 6. The pipeline from crystallizer 6 to collector 7 contains 6.25 t / h of melamine solids and 552 t / h of process gas, achieving a gas-to-solid ratio of 88. A higher gas-to-solid ratio reduces the likelihood of solids accumulating and clogging the pipeline. The process gas easily carries away the solids, preventing them from depositing in the pipeline from crystallizer 6 to collector 7.

[0083] The process gas pressure at the outlet of trap 7 drops to 5.5 bar (G), and the pressure of the process gas after passing through urea scrubbing tower 8 drops to 5.42 bar (G). This application uses the top pressure of melamine reactor 3 as a representative of the system pressure. All the above pressure values ​​constitute a set of related parameters. In subsequent embodiments and comparative examples, when the top pressure of melamine reactor is changed, all other pressure values ​​change accordingly.

[0084] Referring to Figure 2, 6.25 t / h of melamine solids are discharged from the crystallizer discharge device 61 at the bottom of the crystallizer 6, using 4 t / h of air for transport. The pressure inside the high-pressure transport pipe A 62 is maintained at 2.5 bar (G). The high-pressure transport pipe A 62 is insulated with cotton to reduce heat dissipation, and the temperature at the end of the high-pressure transport pipe A 62 is maintained above 140°C. After reaching the high-pressure collector A 63, the 4 t / h of air separates from the melamine solids, and the solids are collected at the bottom of the high-pressure collector A 63. Then, another 4 t / h of air is used for transport, and the pressure inside the low-pressure transport pipe A 64 is controlled at 0.2 bar (G). The low-pressure transport pipe A 64 is cooled by a circulating water jacket, and the temperature at the end of the low-pressure transport pipe A 64 is reduced to 40°C before reaching the packaging device A 65.

[0085] Please refer to Figure 3. The remaining 6.25 t / h of melamine solids are discharged from the collector discharge device 71 at the bottom of the collector 7, using 3.5 t / h of air for conveying. The pressure inside the high-pressure conveying pipe B 72 is maintained at 2.5 bar (G). The high-pressure conveying pipe B 72 is insulated to reduce heat dissipation, and the temperature at the end of the high-pressure conveying pipe B 72 is maintained above 140°C. After reaching the high-pressure collector B 73, the 3.5 t / h of air separates from the melamine solids, and the solids are collected at the bottom of the high-pressure collector B 73. Then, another 3.5 t / h of air is used for conveying, and the pressure inside the low-pressure conveying pipe B 74 is controlled at 0.2 bar (G). The low-pressure conveying pipe B 74 is cooled by a circulating water jacket, and the temperature at the end of the low-pressure conveying pipe B 74 is reduced to 40°C before reaching the packaging device B 75.

[0086] Packaging unit B 75 yields fine-particle melamine product with a D50 of 15–25 micrometers and a bulk density of 0.4–0.6 g / cm³. 3 Specifically designed for the production of fire-retardant coatings, powder extinguishing agents, or melamine cyanate, and other special applications requiring the use of fine particles.

[0087] Packaging device A 65 yields coarse-particle melamine product. D50 = 50-60 micrometers, bulk density greater than 0.6 g / cm³. 3 This product is specifically designed for applications requiring coarse particles, such as the production of melamine-formaldehyde resin adhesives. Compared to melamine products produced by conventional vapor-phase quenching methods, this product contains fewer fine particles, and the particles are coarse with a narrow particle size distribution. When used in adhesive production, it exhibits good consistency in the reaction endpoint, resulting in adhesives with stable performance.

[0088] Since the pressure difference between the crystallizer, collector, and their respective high-pressure delivery pipes is small, and the leakage rate at the bottom of both the crystallizer and collector is 0.02%, the total leakage is 0.11 t / h. Because the temperatures at the ends of high-pressure delivery pipes A and B are high (above 140℃), ammonia and carbon dioxide will not crystallize into ammonium carbamate. Instead, they will leave the solid product in gaseous form from high-pressure collectors A and B. During low-pressure delivery, the cooling process will also prevent ammonium carbamate crystallization, thus not affecting the final product purity. The product purity can reach 99.5% of the superior grade requirement.

[0089] Example 2

[0090] 143 t / h of hot process gas is pressurized to 9.4 bar (G) by carrier gas compressor 1, and then heated to 380°C by carrier gas preheater 2 before entering melamine reactor 3 as fluidized carrier gas. 37.5 t / h of urea (carrier gas to urea mass ratio of 3.81) is added to melamine reactor 3. 180.5 t / h of hot process gas is obtained at the outlet of melamine reactor 3, with a temperature of 380°C and a pressure of 8 bar (G).

[0091] The hot process gas at the outlet of melamine reactor 3 contains 12.5 t / h of melamine, equivalent to a mole fraction of 1.51%, with a total pressure of 8 bar (G) and a calculated partial pressure of 0.136 bar (A). At this pressure, the theoretical temperature for melamine condensation (sublimation) is calculated to be 339℃, with a 20℃ margin. The operating temperature of hot gas cooler 4 is set at 359℃. The hot process gas from the outlet of hot gas cooler 4 then passes through hot gas filter 5, where the pressure is reduced to 7.7 bar (G), before entering crystallizer 6. Simultaneously, cold process gas is supplied to crystallizer 6 using cold air fan 9, ensuring a mass ratio of cold to hot process gas of 3.05. After the hot and cold process gases mix in crystallizer 6, the temperature becomes 208℃, and the pressure drops to 7.64 bar (G), causing melamine to crystallize into a solid.

[0092] The power of the air cooler 9 is 1225kw, and the power of the carrier air compressor 1 is 1653kw. According to the formula: unit product energy consumption = (air cooler power + carrier air compressor power) / melamine production, the unit product energy consumption in this embodiment is calculated to be 230kwh / t melamine.

[0093] 4 t / h of melamine solids are separated from the bottom of crystallizer 6. There are 8.5 t / h of melamine solids and 718 t / h of process gas in the pipeline from crystallizer 6 to collector 7. The gas-solid ratio reaches 84, which is high. The process gas can easily carry away the solids, and the solids are not easy to deposit in the pipeline from crystallizer 6 to collector 7.

[0094] The process gas pressure at the outlet of trap 7 drops to 7.44 bar (G), and the pressure of the process gas drops to 7.34 bar (G) after passing through urea scrubbing tower 8.

[0095] 4 t / h of melamine solids are discharged from the crystallizer discharge device 61 at the bottom of crystallizer 6, using 2 t / h of air for conveying. The pressure inside the high-pressure conveying pipe A 62 is maintained at 4 bar (G). The high-pressure conveying pipe A 62 is insulated to reduce heat loss, and the temperature at the end of the high-pressure conveying pipe A 62 is maintained above 150°C. After reaching the high-pressure collector A 63, the 2 t / h of air separates from the melamine solids, and the solids are collected at the bottom of the high-pressure collector A 63. Then, another 2 t / h of air is used for conveying, and the pressure inside the low-pressure conveying pipe A 64 is controlled at 1.5 bar (G). The low-pressure conveying pipe A 64 is cooled by a circulating water jacket, and the temperature at the end of the low-pressure conveying pipe A 64 is reduced to 42°C before reaching the packaging device A 65.

[0096] The remaining 8.5 t / h of melamine solids are discharged from the collector discharge device 71 at the bottom of the collector 7, using 4 t / h of air for conveying. The pressure inside the high-pressure conveying pipe B 72 is maintained at 4 bar (G). The high-pressure conveying pipe B 72 is insulated to reduce heat loss, and the temperature at the end of the high-pressure conveying pipe B 72 is maintained above 150°C. After reaching the high-pressure collector B 73, the 4 t / h of air separates from the melamine solids, and the solids are collected at the bottom of the high-pressure collector B 73. Then, another 4 t / h of air is used for conveying, and the pressure inside the low-pressure conveying pipe B 74 is controlled at 1.5 bar (G). The low-pressure conveying pipe B 74 is cooled by a circulating water jacket, and the temperature at the end of the low-pressure conveying pipe B 74 is reduced to 42°C before reaching the packaging device B 75.

[0097] Packaging unit B 75 yields fine-particle melamine product with a D50 of 15–25 micrometers and a bulk density of 0.4–0.6 g / cm³. 3 Specifically designed for the production of fire-retardant coatings, powder extinguishing agents, or melamine cyanate, and other special applications requiring the use of fine particles.

[0098] Packaging device A 65 yields coarse-particle melamine product. D50 = 50-60 micrometers, bulk density greater than 0.6 g / cm³. 3 This product is specifically designed for applications requiring coarse particles, such as the production of melamine-formaldehyde resin adhesives. Compared to melamine products produced by conventional vapor-phase quenching methods, this product contains fewer fine particles, and the particles are coarse with a narrow particle size distribution. When used in adhesive production, it exhibits good consistency in the reaction endpoint, resulting in adhesives with stable performance.

[0099] The high temperatures inside high-pressure delivery pipes A and B, as in Example 1, will not affect product purity. Product purity can reach 99.5% of the requirements for superior grade products.

[0100] Example 3

[0101] 168 t / h of hot process gas is pressurized to 11.75 bar (G) by carrier gas compressor 1, and then heated to 395°C by carrier gas preheater 2 before entering melamine reactor 3 as fluidized carrier gas. 37.5 t / h of urea (carrier gas to urea mass ratio of 4.48) is fed into melamine reactor 3. 205.5 t / h of hot process gas is obtained at the outlet of melamine reactor 3, with a temperature of 395°C and a pressure of 10 bar (G).

[0102] The hot process gas at the outlet of melamine reactor 3 contains 12.5 t / h of melamine, equivalent to a mole fraction of 1.32%, with a total pressure of 10 bar (G), resulting in a calculated partial pressure of 0.145 bar (A). At this pressure, the theoretical condensation (sublimation) temperature of melamine is calculated to be 340℃, with a 20℃ margin. The operating temperature of hot gas cooler 4 is set at 360℃. The hot process gas from the outlet of hot gas cooler 4 then passes through hot gas filter 5, where the pressure is reduced to 9.7 bar (G), before entering crystallizer 6. Simultaneously, cold process gas is supplied to crystallizer 6 using cold air fan 9, ensuring a mass ratio of cold to hot process gas of 3.19. After the hot and cold process gases mix in crystallizer 6, the temperature becomes 206℃, and the pressure drops to 9.625 bar (G), causing melamine to crystallize into a solid.

[0103] The power of the air cooler 9 is 1467kw, and the power of the carrier air compressor 1 is 1915kw. According to the formula: unit product energy consumption = (air cooler power + carrier air compressor power) / melamine production, the unit product energy consumption in this embodiment is calculated to be 271kwh / t melamine.

[0104] 1.1 t / h of melamine solids are separated from the bottom of crystallizer 6. There are 11.4 t / h of melamine solids and 848 t / h of process gas in the pipeline from crystallizer 6 to collector 7. The gas-solid ratio reaches 74, which is high. The process gas can easily carry away the solids, and the solids are not easy to deposit in the pipeline from crystallizer 6 to collector 7.

[0105] The process gas pressure at the outlet of trap 7 drops to 9.365 bar (G), and the pressure of the process gas drops to 9.255 bar (G) after passing through urea scrubbing tower 8.

[0106] 1.1 t / h of melamine solids are discharged from the crystallizer discharge device 61 at the bottom of crystallizer 6, using 2 t / h of air transport. The pressure inside the high-pressure transport pipe A 62 is maintained at 7 bar (G). The high-pressure transport pipe A 62 is insulated to reduce heat loss, and the temperature at the end of the high-pressure transport pipe A 62 is maintained above 130°C. After reaching the high-pressure collector A 63, the 2 t / h of air separates from the melamine solids, and the solids are collected at the bottom of the high-pressure collector A 63. Then, a 3 t / h stream of air is used for transport, and the pressure inside the low-pressure transport pipe A 64 is controlled at 6 bar (G). The low-pressure transport pipe A 64 is cooled by a circulating water jacket, and the temperature at the end of the low-pressure transport pipe A 64 is reduced to 50°C before reaching the packaging device A 65.

[0107] The remaining 11.4 t / h of melamine solids are discharged from the collector discharge device 71 at the bottom of the collector 7, using 7 t / h of air for conveying. The pressure inside the high-pressure conveying pipe B 72 is maintained at 7 bar (G). The high-pressure conveying pipe B 72 is insulated to reduce heat loss, and the temperature at the end of the high-pressure conveying pipe B 72 is maintained above 130°C. After reaching the high-pressure collector B 73, the 7 t / h of air separates from the melamine solids, and the solids are collected at the bottom of the high-pressure collector B 73. Then, another 7 t / h of air is used for conveying, and the pressure inside the low-pressure conveying pipe B 74 is controlled at 6 bar (G). The low-pressure conveying pipe B 74 is cooled by a circulating water jacket, and the temperature at the end of the low-pressure conveying pipe B 74 is reduced to 50°C before reaching the packaging device B 75.

[0108] Packaging unit B 75 yields fine-particle melamine product with a D50 of 15–25 micrometers and a bulk density of 0.4–0.6 g / cm³. 3 Specifically designed for the production of fire-retardant coatings, powder extinguishing agents, or melamine cyanate, and other special applications requiring the use of fine particles.

[0109] Packaging device A 65 yields coarse-particle melamine product. D50 = 50-60 micrometers, bulk density greater than 0.6 g / cm³. 3 This product is specifically designed for applications requiring coarse particles, such as the production of melamine-formaldehyde resin adhesives. Compared to melamine products produced by conventional vapor-phase quenching methods, this product contains fewer fine particles, and the particles are coarse with a narrow particle size distribution. When used in adhesive production, it exhibits good consistency in the reaction endpoint, resulting in adhesives with stable performance.

[0110] The high temperatures inside high-pressure delivery pipes A and B, as in Example 1, will not affect product purity. Product purity can reach 99.5% of the requirements for superior grade products.

[0111] Example 4

[0112] A production facility for large-scale production of specialty melamine using a vapor-phase quenching method includes a carrier gas compressor, a carrier gas preheater, a melamine reactor, a hot gas cooler, a crystallizer, a collector, a urea scrubbing tower, and a cooling fan, connected in sequence. It also includes a crystallizer discharge unit and a collector discharge unit.

[0113] The upper outlet of the trap is connected to the urea scrubbing tower for cooling the gas to produce recyclable cold process gas.

[0114] The cold air outlet of the urea scrubbing tower is connected to the inlet of the cold air fan, and the outlet of the cold air fan is connected to the cold process gas inlet of the crystallizer.

[0115] The crystallizer discharge unit includes a crystallizer discharge device 61, a high-pressure collecting device A 63, and a packaging device A 65. The inlet of the crystallizer discharge device 61 is connected to the bottom of the crystallizer 6, and the outlet of the crystallizer discharge device 61 is connected to the inlet of the high-pressure collecting device A 63 through a high-pressure conveying pipe A 62. The lower outlet of the high-pressure collecting device A 63 is connected to the packaging device A 65 through a low-pressure conveying pipe A 64. The outer wall of the high-pressure conveying pipe A is provided with a heat insulation structure to ensure that the temperature in the high-pressure conveying pipe A is above 120°C, and the pressure in the high-pressure conveying pipe A is 2 barG to 8 barG and lower than the pressure in the crystallizer. The outer wall of the low-pressure conveying pipe A is provided with a cooling structure to ensure that the temperature at the end of the low-pressure conveying pipe A does not exceed 85°C, and the pressure in the low-pressure conveying pipe A is 0.2 barG to 6.5 barG and lower than the pressure in the high-pressure conveying pipe A. In this embodiment, the crystallizer discharge device is a screw conveyor.

[0116] The collector discharge unit includes a collector discharge device 71, a high-pressure collection device B 73, and a packaging device B 75. The inlet of the collector discharge device 71 is connected to the bottom of the collector 7, and the inlet of the collector 7 is connected to the upper outlet of the crystallizer 6. The outlet of the collector discharge device 71 is connected to the inlet of the high-pressure collection device B 73 through a high-pressure conveying pipe B 72. The lower outlet of the high-pressure collection device B 73 is connected to the packaging device B 75 through a low-pressure conveying pipe B 74. The outer wall of the high-pressure conveying pipe B is provided with a heat insulation structure to ensure that the temperature in the high-pressure conveying pipe B is above 120°C, and the pressure in the high-pressure conveying pipe B is 2 barG to 8 barG and lower than the pressure in the collector. The outer wall of the low-pressure conveying pipe B is provided with a cooling structure to ensure that the temperature at the end of the low-pressure conveying pipe B does not exceed 85°C, and the pressure in the low-pressure conveying pipe B is 0.2 barG to 6.5 barG and lower than the pressure in the high-pressure conveying pipe B.

[0117] Example 5

[0118] A production facility for large-scale production of specialty melamine using a vapor-phase quenching method includes a carrier gas compressor, a carrier gas preheater, a melamine reactor, a hot gas cooler, a crystallizer, a collector, a urea scrubbing tower, and a cooling fan, connected in sequence. It also includes a crystallizer discharge unit and a collector discharge unit.

[0119] The upper outlet of the trap is connected to the urea scrubbing tower for cooling the gas to produce recyclable cold process gas.

[0120] The cold air outlet of the urea scrubbing tower is connected to the inlet of the cold air fan, and the outlet of the cold air fan is connected to the cold process gas inlet of the crystallizer.

[0121] The crystallizer discharge unit includes a crystallizer discharge device 61, a high-pressure collecting device A 63, and a packaging device A 65. The inlet of the crystallizer discharge device 61 is connected to the bottom of the crystallizer 6, and the outlet of the crystallizer discharge device 61 is connected to the inlet of the high-pressure collecting device A 63 through a high-pressure conveying pipe A 62. The lower outlet of the high-pressure collecting device A 63 is connected to the packaging device A 65 through a low-pressure conveying pipe A 64. The outer wall of the high-pressure conveying pipe A 62 is provided with a heat insulation structure, and the outer wall of the low-pressure conveying pipe A 64 is provided with a cooling structure.

[0122] The collector discharge unit includes a collector discharge device 71, a high-pressure collecting device B 73, and a packaging device B 75. The inlet of the collector discharge device 71 is connected to the bottom of the collector 7, and the inlet of the collector 7 is connected to the upper outlet of the crystallizer 6. The outlet of the collector discharge device 71 is connected to the inlet of the high-pressure collecting device B 73 through a high-pressure conveying pipe B 72. The lower outlet of the high-pressure collecting device B 73 is connected to the packaging device B 75 through a low-pressure conveying pipe B 74. The outer wall of the high-pressure conveying pipe B 72 is provided with a heat insulation structure, and the outer wall of the low-pressure conveying pipe B 74 is provided with a cooling structure.

[0123] Comparative Example 1: 50,000 tons / year production (6.25 t / h)

[0124] The parameters in this comparative example are quite close to those of a typical 50,000-ton plant. It should be noted that this comparative example only represents a hypothetical 50,000-ton process flow and parameters, and does not represent the existence of the corresponding technology in reality.

[0125] 85 t / h of hot process gas is pressurized to 4.4 bar (G) by carrier gas compressor 1, and then heated to 401°C by carrier gas preheater 2 before entering melamine reactor 3 as fluidized carrier gas. 18.75 t / h of urea (carrier gas to urea mass ratio of 4.53) is added to melamine reactor 3. 103.75 t / h of hot process gas is obtained at the outlet of melamine reactor 3, with a temperature of 401°C and a pressure of 3.5 bar (G).

[0126] The hot process gas at the outlet of melamine reactor 3 contains 6.25 t / h of melamine, with a mole fraction of 1.19% and a total pressure of 3.5 bar (G), resulting in a calculated partial pressure of 0.054 bar (A). At this pressure, the theoretical condensation (sublimation) temperature of melamine is calculated to be 316℃, with a 20℃ margin. The operating temperature of hot gas cooler 4 is set at 336℃. The hot process gas from the outlet of hot gas cooler 4 then passes through hot gas filter 5, reducing the pressure to 3.2 bar (G), before entering crystallizer 6. Simultaneously, cold process gas is supplied to crystallizer 6 using cold air fan 9, with a mass ratio of cold to hot process gas of 1.93. After mixing in crystallizer 6, the temperature of the hot and cold process gases becomes 216℃, and the pressure drops to 3.17 bar (G), causing the melamine to crystallize into a solid.

[0127] The process gas pressure at the outlet of trap 7 drops to 3 bar (G), and the pressure of the process gas drops to 2.93 bar (G) after passing through urea scrubbing tower 8.

[0128] The air conditioner fan power is 703kw, and the carrier air compressor power is 1449kw. According to the formula: unit product energy consumption = (air conditioner fan power + carrier air compressor power) / melamine production, the unit product energy consumption in this comparative example is calculated to be 344kwh / t melamine.

[0129] This comparative example crystallizer has no output. The pipeline from the crystallizer to the collector contains 6.25 t / h of melamine solids and 297.5 t / h of process gas, with a gas-to-solid ratio of 48. The solids are not easily blown away by the gas flow, resulting in a short blockage cycle.

[0130] In this comparative example, all solid melamine was discharged from the bottom of the collector, using a 5t / h air conveyor. The conveying pipe was heated by a steam jacket, with an internal pressure of 0.5 bar (G) and a terminal temperature of 130°C. The melamine product was obtained after packaging. The pressure difference between the collector and the conveying pipe was not significant. Assuming a leakage rate of 0.02% at the bottom of the collector, the leaked gas was 0.0595t / h. At 130°C, this leaked gas would not solidify and would not affect the product purity, which was 99.5%. However, the high product temperature during packaging could easily damage the packaging bags.

[0131] The product obtained is a single product, without particle grading. The average particle size D50 is 30–40 micrometers, and the bulk density is 0.45–0.5 g / cm³. 3 It has a wide particle size distribution and can be used to produce melamine-formaldehyde resin adhesive, but the adhesive produced has unstable performance.

[0132] Comparative Example 2: 100,000 tons / year production (12.5 t / h)

[0133] It should be noted that this comparative example only represents a hypothetical 100,000-ton process flow and parameters, and does not represent the existence of the corresponding process technology in reality.

[0134] 170 t / h of hot process gas is pressurized to 15 bar (G) by carrier gas compressor 1, and then heated to 410°C by carrier gas preheater 2 before entering melamine reactor 3 as fluidized carrier gas. 37.5 t / h of urea (carrier gas to urea mass ratio of 4.53) is added to melamine reactor 3. 207.5 t / h of hot process gas is obtained at the outlet of melamine reactor 3, with a temperature of 410°C and a pressure of 12.5 bar (G).

[0135] The hot process gas at the outlet of melamine reactor 3 contains 12.5 t / h of melamine, equivalent to a mole fraction of 1.31%, with a total pressure of 12.5 bar (G) and a calculated partial pressure of 0.177 bar (A). At this pressure, the theoretical temperature for melamine condensation (sublimation) is calculated to be 345℃, with a 20℃ margin. The operating temperature of hot gas cooler 4 is set at 365℃. The hot process gas from the outlet of hot gas cooler 4 then passes through hot gas filter 5, where the pressure is reduced to 12.2 bar (G), before entering crystallizer 6. Simultaneously, cold process gas is supplied to crystallizer 6 using cold air fan 9, with a mass ratio of cold to hot process gas of 3.13. After the hot and cold process gases mix in crystallizer 6, the temperature becomes 209℃, and the pressure drops to 12.05 bar (G), causing melamine to crystallize into a solid.

[0136] The process gas pressure at the outlet of the trap 7 drops to 11.67 bar (G), and the pressure of the process gas drops to 11.5 bar (G) after passing through the urea scrubbing tower 8.

[0137] The air conditioner fan power is 1870kw, and the carrier air compressor power is 1690kw. According to the formula: unit product energy consumption = (air conditioner fan power + carrier air compressor power) / melamine production, the unit product energy consumption in this comparative example is calculated to be 285kwh / t melamine.

[0138] This comparative example crystallizer has no output. The pipeline from the crystallizer to the collector contains 12.5 t / h of melamine solids and 845 t / h of process gas, with a gas-to-solid ratio of 68. The solids are not easily blown away by the gas flow, resulting in a short blockage cycle.

[0139] In this comparative example, all melamine solids were discharged from the bottom of the collector using a 10 t / h air conveyor. Natural heat dissipation was achieved outside the conveyor pipe, with an internal pressure of 0.5 bar (G) and a terminal temperature of 55°C. The melamine product was obtained after packaging. Due to the excessive pressure difference between the conveyor pipe and the collector, assuming a leakage rate of 0.1% at the bottom of the collector, 0.845 t / h of gas was leaked. At 55°C, 30% of this leaked gas converted into ammonium carbamate solids, which were mixed into the product, reducing the product purity by 2% to 97.5%.

[0140] The product obtained is a single product, without particle grading. The average particle size D50 is 30–40 micrometers, and the bulk density is 0.45–0.5 g / cm³. 3 It has a wide particle size distribution and can be used to produce melamine-formaldehyde resin adhesive, but the adhesive produced has unstable performance.

[0141] The above comparison shows that Examples 1-3 have lower unit energy consumption; the gas-solid ratio in the pipeline from the crystallizer to the collector is high, making it less prone to clogging; the product is graded into two specifications according to particle size; the amount of leaked process gas is small and will not affect the purity of the product or damage the packaging bag.

[0142] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A process for producing melamine by vapor-phase quenching, characterized in that, Includes the following steps: The hot process gas from the outlet of the melamine reactor is cooled by a hot gas cooler and filtered by a hot gas filter before entering the crystallizer and coming into direct contact with the cold process gas. The solid A produced is discharged from the bottom of the crystallizer, and the mixed gas enters the collector for gas-solid separation to obtain solid B. Solid A is transported to a high-pressure collection device A using high-pressure transport gas A, ensuring that the temperature of high-pressure transport gas A remains above 120°C during the transport process. After gas-solid separation in the high-pressure collection device A, solid A is then transported to a packaging device A using low-pressure transport gas A, ensuring that the temperature of solid A at the end of the transport process does not exceed 85°C. The pressure of high-pressure transport gas A is 2 barG to 8 barG and lower than the pressure inside the crystallizer, while the pressure of low-pressure transport gas A is 0.2 barG to 6.5 barG and lower than the pressure of high-pressure transport gas A.

2. The process for producing melamine by vapor phase quenching according to claim 1, characterized in that, Solid B is transported to a high-pressure collection device B using high-pressure transport gas B, ensuring that the temperature of the high-pressure transport gas B is above 120°C during the transport process. After gas-solid separation in the high-pressure collection device B, solid B is then transported to a packaging device B using low-pressure transport gas B, ensuring that the temperature of solid B at the end of the transport process does not exceed 85°C. The pressure of the high-pressure transport gas B is 2 barG to 8 barG and lower than the pressure inside the collector, and the pressure of the low-pressure transport gas B is 0.2 barG to 6.5 barG and lower than the pressure of the high-pressure transport gas B.

3. The process for producing melamine by vapor-phase quenching according to claim 1 or 2, characterized in that, The mass ratio of the cold process gas to the hot process gas entering the crystallizer is 2.6 to 3.

2.

4. The process for producing melamine by vapor-phase quenching according to claim 1 or 2, characterized in that, The pressure inside the crystallizer is 4 barG to 9.8 barG.

5. The process for producing melamine by vapor-phase quenching according to claim 1 or 2, characterized in that, The bottom discharge of the crystallizer accounts for 5% to 50% of the total solids.

6. The process for producing melamine by vapor-phase quenching according to claim 1 or 2, characterized in that, The mass ratio of carrier gas to urea entering the melamine reactor is 3.1 to 4.

5.

7. The process for producing melamine by vapor-phase quenching according to claim 1 or 2, characterized in that, The top temperature of the melamine reactor is 380℃~405℃, and the top pressure is 5barG~10barG.

8. An apparatus for producing melamine using a vapor-phase quenching method, characterized in that, include: The crystallizer discharge unit includes a crystallizer discharge device, a high-pressure collecting device A, and a packaging device A. The inlet of the crystallizer discharge device is connected to the bottom of the crystallizer, and the outlet of the crystallizer discharge device is connected to the inlet of the high-pressure collecting device A via a high-pressure conveying pipe A. The lower outlet of the high-pressure collecting device A is connected to the packaging device A via a low-pressure conveying pipe A. The outer wall of the high-pressure conveying pipe A is provided with a heat insulation structure to ensure that the temperature in the high-pressure conveying pipe A is above 120°C, and the pressure in the high-pressure conveying pipe A is 2 barG to 8 barG, which is lower than the pressure in the crystallizer. The outer wall of the low-pressure conveying pipe A is provided with a cooling structure to ensure that the temperature at the end of the low-pressure conveying pipe A does not exceed 85°C, and the pressure in the low-pressure conveying pipe A is 0.2 barG to 6.5 barG, which is lower than the pressure in the high-pressure conveying pipe A. The collector discharge unit includes a collector discharge device and a packaging device B. The inlet of the collector discharge device is connected to the bottom of the collector, and the outlet of the collector discharge device is connected to the packaging device B. The inlet of the collector is connected to the upper outlet of the crystallizer.

9. The equipment for producing melamine by vapor-phase quenching according to claim 8, characterized in that, The crystallizer discharge device is a screw conveyor; And / or, the outlet of the collector discharge device is connected to the inlet of the high-pressure collection device B via a high-pressure conveying pipe B, and the lower outlet of the high-pressure collection device B is connected to the packaging device B via a low-pressure conveying pipe B; The outer wall of the high-pressure conveying pipe B is provided with a heat insulation structure to ensure that the temperature in the high-pressure conveying pipe B is above 120°C, and the pressure in the high-pressure conveying pipe B is 2 barG to 8 barG and lower than the pressure in the trap; the outer wall of the low-pressure conveying pipe B is provided with a cooling structure to ensure that the temperature at the end of the low-pressure conveying pipe B does not exceed 85°C, and the pressure in the low-pressure conveying pipe B is 0.2 barG to 6.5 barG and lower than the pressure in the high-pressure conveying pipe B.

10. The apparatus for producing melamine by vapor-phase quenching according to claim 8 or 9, characterized in that, The equipment also includes: a carrier gas compressor, a carrier gas preheater, a melamine reactor, a hot gas cooler, a crystallizer, a collector, a urea scrubbing tower, and a cooling fan, which are connected in sequence. The upper outlet of the trap is connected to the urea scrubbing tower for cooling the gas to produce recyclable cold process gas. The cold air outlet of the urea scrubbing tower is connected to the inlet of the cold air fan, and the outlet of the cold air fan is connected to the cold process gas inlet of the crystallizer.

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