Urea ammonium nitrate solution and integrated clean production method

Abstract

A urea ammonium nitrate solution and an integrated clean production method are a liquid nitrogen fertilizer production technology, and the method comprises the following steps: premixing a urea melt solution and a part of an ammonium nitrate solution, and introducing the premixed solution into a neutralization reaction system of ammonium nitrate to realize molecular integration of urea and ammonium nitrate in a synthesis stage; performing evaporation concentration, on-line proportion fine adjustment, compound stabilizer treatment, cooling and filtering and the like to obtain a high-stability finished product. According to the invention, solidification and redissolution processes of urea and ammonium nitrate in the traditional process are omitted, so that the energy consumption is obviously reduced; through process innovation and use of the compound stabilizer, the chemical stability (inhibiting ammonia volatilization and nitrite generation) and the physical stability (preventing crystallization) of the product are fundamentally improved, and the product performance is excellent. The whole technological process is short, airtight, clean and low in investment and production cost.

Description

Technical Field

[0001] This invention relates to a liquid nitrogen fertilizer production technology, particularly a urea ammonium nitrate solution and an integrated clean production method. Background Technology

[0002] Urea ammonium nitrate solution is a high-quality liquid nitrogen fertilizer composed of urea, ammonium nitrate, and water. It is widely used in agriculture worldwide due to its high nutrient content, lack of volatile loss, ease of adding micronutrients and pesticides, and suitability for modern irrigation and fertilization. The traditional production process for urea ammonium nitrate solution typically follows a "stepwise synthesis-physical mixing" model: solid urea and solid ammonium nitrate are first produced separately, then dissolved in water, and the final product is obtained through mixing, adjusting the ratio, and filtration. This traditional process has the following significant drawbacks: 1. High energy consumption: Both urea and ammonium nitrate require high-energy-consuming processes such as evaporation, crystallization, granulation, and drying to form solid products, and then energy is required to redissolve them, resulting in serious energy waste.

[0003] 2. Complex process and high investment: It relies on two complete solid fertilizer production units, with a long process flow and high equipment investment and maintenance costs.

[0004] 3. Product Stability Challenges: Urea and ammonium nitrate undergo a slow metathesis reaction in aqueous solution, generating free ammonia and potentially leading to nitrite accumulation, which affects product storage stability and safety. The physical mixing process requires strict temperature and concentration control; otherwise, crystallization may occur, clogging pipelines.

[0005] 4. Environmental pressure: Dust emissions and wastewater treatment are more prominent issues in the production of solid fertilizers.

[0006] To address the aforementioned issues, several solutions have been proposed in existing technologies. One method discloses the direct mixing of urea and ammonium nitrate mother liquor to produce UAN solution, reducing some solid dissolution steps. However, this is essentially still a post-processing mixing of two materials, failing to fundamentally integrate the synthesis pathway, and requires stringent control of impurities in the mother liquor. Another technology attempts to directly introduce urea solution into the ammonium nitrate production process, but this often faces challenges such as complex reaction systems, numerous side reactions, and difficulties in balancing product concentration and stability.

[0007] Therefore, developing an integrated production method for urea ammonium nitrate solution that is simple in process, low in energy consumption, and can fundamentally improve the chemical and physical stability of the product is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a urea ammonium nitrate solution and an integrated clean production method that is characterized by a short process, high stability, and low energy consumption, which can fundamentally improve the chemical and physical stability of the product. This method solves the following problems: the high energy consumption and long process of traditional processes; the stability problems of ammonia volatilization, nitrite accumulation and crystallization during product storage; and the need to improve the environmental friendliness of the production process.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention includes the following steps: S1. Raw material preparation and pre-reaction: Provide urea melt with a concentration of 65%~75% and ammonium nitrate solution with a concentration of 50%~65%. Premix part of the ammonium nitrate solution with all of the urea melt in the first pre-reactor at 85℃~100℃, controlling the molar ratio of urea to ammonium nitrate to be (1.5~2.5):1, and react for 10~30 minutes to form a homogeneous urea-ammonium nitrate premixed melt. This step utilizes the "salting out" effect and complexation of urea on ammonium nitrate to pre-stabilize some ammonium nitrate molecules.

[0010] S2. Neutralization and Integration Reaction: The remaining 5% (by mass) ammonium nitrate solution was continuously fed into an integrated reactor-evaporator with gaseous ammonia or ammonia water at a molar ratio of NH3:HNO3 of (1.02~1.05):1 for neutralization. The reaction temperature was controlled at 120℃~140℃ through evaporative cooling, and the pressure was a slight negative pressure (-5kPa ~ -1kPa). Under vigorous stirring, the urea-ammonium nitrate premixed molten liquid obtained in step S1 was continuously and stably injected into the reaction system. The presence of urea altered the reaction medium, nitric acid, effectively inhibiting the decomposition of ammonium nitrate and the formation of nitrite as side reactions.

[0011] S3. Evaporation Concentration and Component Fine-tuning: The mixture of urea, ammonium nitrate, and water obtained in S2 is evaporated and concentrated in an integrated reactor-evaporator or a connected post-evaporator at 115℃~125℃ and a vacuum of -90kPa~-70kPa. The density of the liquid and the urea / ammonium nitrate ratio are monitored in real time using an online densitometer and a near-infrared analyzer. By slightly adjusting the feed rate of the raw materials (molten urea or ammonium nitrate solution), the total nitrogen content of the final liquid is precisely adjusted to 28%~32%, with the molar ratio of urea nitrogen to ammonium nitrate nitrogen remaining stable at (1.0~1.5):1.

[0012] S4. Stability treatment and cooling: The qualified concentrate obtained from S3 is transferred to a stability processor, where a composite stabilizer is added. The composite stabilizer consists of the following components by weight percentage: diammonium hydrogen phosphate 0.05%–0.15%, hexamethylenetetramine 0.01%–0.05%, citric acid 0.005%–0.02%, with the balance being deionized water. The mixture is stirred at 70°C–85°C for 20–40 minutes. The treated solution is cooled to 30℃~40℃ via a plate heat exchanger.

[0013] S5. Filtration and Storage: The cooled solution is filtered through a precision filter (filtration accuracy ≤10μm) to remove any trace amounts of insoluble impurities, such as nitrite, to obtain a clear and transparent urea ammonium nitrate solution, which is then sent to the finished product storage tank.

[0014] Beneficial effects of the present invention 1. Significant Energy Saving and Consumption Reduction: This invention creatively introduces molten urea directly into the neutralization reaction system of ammonium nitrate, avoiding the huge energy consumption of separately dissolving urea and ammonium nitrate into solids. Utilizing the synergy of reaction heat and evaporation concentration, the entire process has high thermal efficiency, reducing overall energy consumption by approximately 30% to 40% compared to traditional processes.

[0015] 2. Excellent product stability: Chemical stability is achieved through a two-step process of "pre-reaction" and "online neutralization with urea," which enables urea and ammonium nitrate to achieve a more uniform mixture at the molecular level. By utilizing the multiple functions of the composite stabilizer (adjusting pH, complexing metal ions, and blocking nitrosation), the volatilization of ammonia and the formation of nitrite are greatly inhibited. After long-term storage (≥6 months), the nitrite content of the product is far below the national standard limit.

[0016] Physical stability: Precise online proportional control and cooling curve management, combined with the filtration process, ensure that the product does not crystallize and has good fluidity within a wide temperature range (-10℃ to 50℃).

[0017] 3. Short process flow and low investment: The integrated reaction design reduces a large number of intermediate storage tanks, conveying and dissolving equipment, simplifies the process, and reduces fixed asset investment and operation and maintenance costs.

[0018] 4. Environmentally friendly: The entire process is carried out in a closed system with no dust emissions and very little process wastewater. The reaction conditions are mild, which reduces the potential generation of nitrogen oxides, making it a clean production process.

[0019] 5. High product quality: The product concentration can be flexibly adjusted to a higher level of 32%, and it is clear and transparent with good compatibility, making it easy to add other nutrients later. Detailed Implementation

[0020] The present invention will be further illustrated by the following embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] Example 1: A clean production method for integrated urea-ammonium nitrate solution, characterized by the following steps: S1. Raw material preparation and pre-reaction: Provide urea melt with a concentration of 65%~75% and ammonium nitrate solution with a concentration of 50%~65%. Premix a portion of the ammonium nitrate solution with all of the urea melt in a first pre-reactor at 85℃~100℃, controlling the molar ratio of urea to ammonium nitrate to be (1.5~2.5):1, and react for 10~30 minutes to form a homogeneous urea-ammonium nitrate premixed melt. This step utilizes the "salting out" effect and complexation of urea on ammonium nitrate to pre-stabilize some ammonium nitrate molecules. S2. Neutralization and Integrated Reaction: The remaining 5% (by mass) ammonium nitrate solution and gaseous ammonia or ammonia water are continuously fed into an integrated reaction-evaporator at a molar ratio of NH3:HNO3 of (1.02~1.05):1 for neutralization. The reaction temperature is controlled at 120℃~140℃ by evaporative cooling, and the pressure is a slight negative pressure (-5kPa ~ -1kPa). Under vigorous stirring, the urea-ammonium nitrate premixed molten liquid obtained in step S1 is continuously and stably injected into the reaction system. The presence of urea changes the nitric acid in the reaction, effectively inhibiting the decomposition of ammonium nitrate and the side reaction of nitrite formation. S3. Evaporation Concentration and Component Fine-tuning: The mixed liquid containing urea, ammonium nitrate and water obtained in S2 is evaporated and concentrated in an integrated reactor-evaporator or a connected post-evaporator at 115℃~125℃ and a vacuum of -90kPa~-70kPa. The density of the liquid and the urea / ammonium nitrate ratio are monitored in real time using an online density meter and a near-infrared analyzer. By finely adjusting the feed rate of the raw materials (molten urea or ammonium nitrate solution), the total nitrogen content of the final liquid is precisely adjusted to 28%~32%, with the molar ratio of urea nitrogen to ammonium nitrate nitrogen remaining stable at (1.0~1.5):1. S4. Stabilization Treatment and Cooling: The qualified concentrated solution obtained in S3 is transferred to a stabilization processor, where a composite stabilizer is added. The composite stabilizer consists of the following components by weight percentage: diammonium hydrogen phosphate 0.05%~0.15%, hexamethylenetetramine 0.01%~0.05%, citric acid 0.005%~0.02%, with the balance being deionized water. The solution is stirred at 70℃~85℃ for 20~40 minutes. The treated solution is then cooled to 30℃~40℃ using a plate heat exchanger. S5. Filtration and storage: The cooled solution is filtered through a precision filter (filtration accuracy ≤10μm) to remove any trace amounts of insoluble impurities, such as nitrite, to obtain a clear and transparent urea ammonium nitrate solution, which is then sent to the finished product storage tank. Example

[0022] Prepare a 72% urea molten liquid and a 60% ammonium nitrate solution. Premix 20% of the ammonium nitrate solution with the entire urea molten liquid at 95°C (urea:ammonium nitrate molar ratio = 2.0:1) and react for 20 minutes. Continuously add the remaining 80% ammonium nitrate solution and gaseous ammonia at a molar ratio of NH3:HNO3 = 1.03:1 to an integrated reaction-evaporator (temperature 130°C, pressure -3kPa), while simultaneously injecting the premixed molten liquid stably. After reaction, the solution is evaporated and concentrated at 120°C under a vacuum of -85kPa, with online adjustments to achieve a total nitrogen content of 30% (urea nitrogen:ammonium nitrate nitrogen ≈ 1.2:1). Add a composite stabilizer (0.1% diammonium hydrogen phosphate, 0.03% hexamethylenetetramine, 0.01% citric acid) and treat at 80°C for 30 minutes. Cool to 35°C and filter through a 5μm filter to obtain the finished product UAN-30. Tests showed that the product was clear, showed no crystallization after 7 days of refrigeration at -5℃, and had a nitrite content of only 15mg / kg after 90 days of accelerated storage at 40℃. Example

[0023] Prepare a 68% molten urea solution and a 55% ammonium nitrate solution. Premixing conditions are 90℃ (molar ratio 1.8:1). The integrated neutralization temperature is 125℃, under vacuum of -2 kPa. After evaporation and concentration, adjust the total nitrogen to 28%. The stabilizer formulation consists of 0.08% diammonium hydrogen phosphate, 0.02% hexamethylenetetramine, and 0.015% citric acid. The final product, UAN-28, also exhibits excellent performance and good long-term storage stability.

[0024] Comparative example: The traditional solid dissolution method was used: solid urea and ammonium nitrate were purchased separately and dissolved in hot water according to the specified ratio to prepare a solution with 30% total nitrogen. The prepared product initially showed slight turbidity, and crystals appeared after 24 hours of refrigeration. After 30 days of storage at 40℃, the nitrite content increased to 85 mg / kg, and a slight ammonia odor was observed.

Claims

1. Integrated clean production method of urea ammonium nitrate solution, characterized in that: The method comprises the following steps: S1. raw material preparation and pre-reaction: providing a urea melt with a concentration of 65%-75% and an ammonium nitrate solution with a concentration of 50%-65%, pre-mixing part of the ammonium nitrate solution and all the urea melt in a first pre-reactor at 85-100 DEG C, controlling the molar ratio of urea to ammonium nitrate to be (1.5-2.5):1, and reacting for 10-30 minutes to form a uniform urea-ammonium nitrate pre-mixed melt, wherein the step utilizes the "salting-out" effect and complexation of urea on ammonium nitrate to pre-stabilize part of the ammonium nitrate molecules; S2. neutralization and integrated reaction: continuously feeding the remaining 5% ammonium nitrate solution and gaseous ammonia or aqueous ammonia into an integrated reaction-evaporator at a molar ratio of NH3:HNO3 of 1.02-1.05:1 to perform a neutralization reaction, the reaction temperature is controlled at 120-140 DEG C through evaporative cooling, the pressure is micro-negative pressure-5 kPa to -1 kPa, and the urea-ammonium nitrate pre-mixed melt obtained in the step S1 is continuously and stably injected into the reaction system under vigorous stirring; the presence of urea changes the reaction medium nitric acid, effectively inhibiting the decomposition of ammonium nitrate and the generation of nitrite byproducts; S3. evaporation concentration and component fine adjustment: evaporating and concentrating the mixed solution containing urea, ammonium nitrate and water obtained in S2 in the integrated reaction-evaporator or a connected post-evaporator under the conditions of 115-125 DEG C and a vacuum degree of -90 kPa to -70 kPa, and real-time monitoring the density and urea / ammonium nitrate ratio of the solution through an online densimeter and a near-infrared analyzer, and accurately adjusting the total nitrogen content of the final solution to 28%-32% by slightly adjusting the feeding rate of the raw materials (urea melt or ammonium nitrate solution), wherein the molar ratio of urea nitrogen to ammonium nitrate nitrogen is stabilized at 1.0-1.5:1; S4. stability treatment and cooling: conveying the qualified concentrated solution obtained in S3 to a stability treatment device, adding a composite stabilizer to the device, the composite stabilizer is composed of the following components in percentage by weight: 0.05%-0.15% diammonium hydrogen phosphate, 0.01%-0.05% hexamethylenetetramine, 0.005%-0.02% citric acid, and the balance is deionized water; stirring and treating at 70-85 DEG C for 20-40 minutes; and cooling the treated solution to 30-40 DEG C through a plate heat exchanger; S5. filtration and storage: filtering the cooled solution through a precision filter with a filtering accuracy of ≤10 μm to remove possible trace amounts of insoluble impurities nitrite, obtaining a clear and transparent urea ammonium nitrate solution product, and feeding into a product storage tank.

2. The integrated clean production method of urea ammonium nitrate solution according to claim 1, characterized in that: Preparation of a 72% urea melt and a 60% ammonium nitrate solution, pre-mixing 20% of the ammonium nitrate solution with all the urea melt at 95 DEG C (urea:ammonium nitrate molar ratio = 2.0:1), and reacting for 20 minutes. The remaining 80% of the ammonium nitrate solution and the gaseous ammonia are continuously added to the integrated reactor-evaporator at a molar ratio of NH3:HNO3=1.03:1 at a temperature of 130°C and a pressure of -3kPa, while the premixed molten liquid is stably injected. After the reaction, the material liquid is evaporated and concentrated at 120°C and a vacuum of -85kPa, and the total nitrogen is adjusted to 30% online, with urea nitrogen:ammonium nitrate nitrogen ≈1.2:

1. A composite stabilizer (diammonium hydrogen phosphate 0.1%, hexamethylene tetramine 0.03%, and citric acid 0.01%) is added and treated at 80°C for 30 minutes, cooled to 35°C, filtered through a 5μm filter to obtain the finished product UAN-30. The product is clear, no crystallization occurs after 7 days of cold storage at -5°C, and the nitrite content is only 15mg / kg after 90 days of accelerated storage at 40°C.

3. The integrated clean production method of urea ammonium nitrate solution according to claim 1, characterized in that: A 68% urea molten liquid and a 55% ammonium nitrate solution are prepared, and the premixing conditions are 90°C and a molar ratio of 1.8:

1. The integrated neutralization temperature is 125°C, and the vacuum is -2kPa. After evaporation and concentration, the total nitrogen is adjusted to 28%, and the stabilizer formulation is diammonium hydrogen phosphate 0.08%, hexamethylene tetramine 0.02%, and citric acid 0.015%. The final product UAN-28 also has excellent performance and good long-term storage stability.

4. The integrated clean production method of urea ammonium nitrate solution according to claim 1, characterized in that: In step S2, the ammonia source is gaseous ammonia or ammonia water with a concentration of ≥20%.

5. Urea ammonium nitrate solution produced according to the method of any one of claims 1 to 3, characterized in that: The total nitrogen content is 28%~32%, no crystallization occurs after 7 days of storage at -10°C, and the nitrite content is less than 50mg / kg after 90 days of accelerated storage at 40°C. The product does not crystallize in a wide temperature range (-10°C to 50°C) and has good flowability. The product concentration can be flexibly adjusted to a higher level of 32%, and it is clear and transparent, has good compatibility, and is easy to add other nutrient elements subsequently. The nitrite content of the product after long-term storage of ≥6 months is much lower than the national standard limit.