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How Melamine Production Affects Urea Plants?

For chemical plants that integrate melamine production with urea manufacturing, the mutual influence between the two units is critical for stable operation, cost control, and safety.

This article breaks down how melamine production affects urea plants—and the proven technical retrofits to reduce these risks.

Why Melamine & Urea Plants Are Integrated

Melamine is typically produced from urea via a high-pressure thermal process. The reaction generates large amounts of ammonia (NH₃) and carbon dioxide (CO₂), which are recycled back to the urea unit. This co-production model saves raw materials but creates serious operational challenges for urea plants.

Core Effects of Melamine Production on Urea Plants

Impact on the High-Pressure System

  • The impact on the large urea conversion rate. The urea control reaction step is the dehydration reaction of methylamine. Due to the recovery of melamine and the return of the methylamine solution, the water-to-carbon ratio in the high-pressure system increases, reducing the system’s conversion rate. It is expected that the urea conversion rate will decrease by about 1%.
  • Higher steam consumption: Due to the low average concentration and high water content of the methylamine solution returned by the three melamine plants, along with the large volume of returns, the recovery load of the large urea plant has increased. In order to reduce the loss of ammonia in the medium and low-pressure venting, increase the amount of water added to the system, and thus disrupt the original water balance of the high-pressure coil, the water carbon ratio of the system increases, reaching a maximum of 1.7, and the steam consumption of the system greatly increases.
  • Increased corrosion: Higher loads accelerate the erosion and corrosion of high-pressure equipment and pipelines.

Impact on the Medium-Pressure System

  • Risk of methylamine carryover: Unstable operation of melamine-supporting small urea units can push methylamine into liquid ammonia lines, damaging pump seals and causing shutdowns.
  • Overloaded condensers & absorbers: Large melamine off-gas increases heat and mass transfer load, reducing stability.

Impact on the Low-Pressure System

  • Pressure fluctuations: A poorly concentrated methylamine solution can cause overpressure or pressure drops, leading to ammonia vent loss.
  • Overloaded pumps: Carbonate solution pumps run continuously at full load, with no backup available when dual-pump operation is used.

Impact on Evaporation & Granulation

  • Unstable dilute urine feed: Thin, fluctuating urine from melamine units drops evaporation temperature and causes circulation mode switches.
  • Nozzle clogging: Impurities in recycled urine block granulation nozzles, causing caking and poor product quality.

Impact on Hydrolysis & Desorption System

  • Sharply higher load: Melamine condensate can push hydrolysis capacity from 40 m³/h to over 60 m³/h, causing overload.
  • Level control issues: Condensate tanks struggle to maintain stable levels.

Impact on Ammonia Balance

  • Liquid ammonia inventory drops: Ammonia vent losses increase, forcing urea plant load reductions and CO₂ venting — wasting resources and harming the environment.

conclusion

Melamine production has wide-ranging effects on urea plants, including lower conversion efficiency, equipment overload, product quality issues, and safety risks. With targeted pipeline retrofits and process optimization, plants can greatly reduce these impacts and ensure stable, economical long-term operation.

For integrated melamine–urea complexes, ongoing monitoring and incremental improvements remain essential to maximize output and profit.

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