Total recycle process of urea production has solved the core pain points of severe resource waste and significant environmental pollution in traditional processes. This process achieves nearly 100% material utilization by fully recovering unreacted ammonia (NH₃) and carbon dioxide (CO₂) from the urea synthesis process, reducing energy consumption while aligning with the global trend of a low-carbon industry.
This article provides a detailed overview of total recycle process of urea production, including its working principle, main process steps, advantages, and industrial applications.
Total recycle process of urea production is a synthetic method in which unreacted ammonia (NH₃) and carbon dioxide (CO₂) are fully recovered and recycled to the urea synthesis circuit. Unlike partial recycling or direct current processes, this technology ensures almost complete utilization of raw materials.
In this process, urea is produced by reacting ammonia and carbon dioxide at high pressure and temperature, and the unconverted reactants are then effectively separated and recovered.
In the urea synthesis reaction (CO₂ + 2NH₃ → CO (NH₂)₂ + H₂O), under conventional conditions, only 60% to 70% of the raw materials are converted to urea. The full-cycle process captures unreacted NH₃ and CO₂ in the reaction effluent, converts them into the key intermediate methylammonium, and returns them to the recycling tower for recycling. The material utilization rate can reach over 99%.
The main types of urea production full-cycle processes include the aqueous solution full-cycle process (the most widely used), the gas-phase cycle process, and the stripping process. The full-cycle aqueous solution process has become the preferred choice for industry due to its simple process, low investment cost, and adaptability to co-production systems (such as melamine-urea co-production).
Taking the total recycle process of aqueous solution as an example, it consists of five interrelated stages that balance efficiency and stability:
Raw material pretreatment: Preheat liquid ammonia to 170-180 ℃, compress carbon dioxide to 15-20 MPa, and then send it to the synthesis tower.
Reaction conditions: At 180-200 ℃ and 15-20 MPa, ammonia reacts with carbon dioxide to form ammonium formate, which is then dehydrated to produce urea. The reaction effluent contains urea (30%~40%), unreacted NH3, CO2, and moisture.
The synthetic effluent sequentially enters the high-pressure decomposition tower (1.5-2.5 MPa) and the low-pressure decomposition tower (0.3-0.5 MPa).
By using steam or process waste-heat to heat, methylammonium is decomposed into NH3 and CO2, thereby separating it from the urea solution.
After cooling, the NH₃ and CO₂ produced by decomposition are absorbed by an aqueous solution in an absorption tower and regenerated into methylammonium solution.
Key equipment: high-pressure absorption tower, low-pressure absorption tower, and ammonium methane condenser. The regenerated ammonium solution is pumped to the recycling tower for reuse.
The urea solution separated from unreacted materials is concentrated by evaporation (under vacuum or at atmospheric pressure) to a moisture content of less than 0.5%.
Finished product processing: Concentrated urea is processed into granules or pellets to form finished products (agricultural granular urea, industrial pellet urea).
The process generates very little wastewater, and a small amount of effluent can be discharged in compliance with standards or reused as process water after recovering residual ammonia through stripping or ion exchange, achieving near-zero liquid waste discharge.
Compared to traditional partial circulation processes or one-way processes, full circulation processes have revolutionary advantages:
Total recycle process of urea production represents a mature, efficient, and environmentally friendly method of urea manufacturing. By fully recovering and recycling unreacted ammonia and carbon dioxide, this process has significant economic and ecological benefits, making it the cornerstone of the global urea industry today.
Total recycle process of urea production is the core technology of modern chemical manufacturing, balancing efficiency, cost, and environmental responsibility. Its high material utilization rate, low emissions, and adaptability to cogeneration systems make it a key support for meeting global food demand and low-carbon goals.
For production enterprises, adopting full-cycle processes is not only a compliance requirement but also a strategic investment to enhance long-term profitability and establish environmental leadership.
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