Wastewater generated during melamine powder production contains melamine, ammonium organic acids (amelline, ammelide), ammonia, and other organic pollutants. It must be treated appropriately to meet environmental emission standards and recover valuable resources.
This article is based on the industrial practice of a large melamine factory. It introduces a mature hydrolysis-stripping melamine wastewater treatment technology, including the process flow, key operating parameters, and 72-hour full-load performance verification. This technology achieves efficient pollutant removal, resource recovery, and energy conservation, making it suitable for industrial melamine wastewater treatment.
The production of melamine involves side reactions, such as hydrolysis and condensation, resulting in OAT as the main byproduct. Melamine wastewater is rich in ammonia, melamine, and organic nitrogen. If discharged directly, it will result in high COD and nitrogen.
The core principle is to use high-pressure steam to hydrolyze under high temperature and pressure (HHS, 10.0-11.0 MPa). Melamine, urea, and OAT are hydrolyzed back into ammonia and carbon dioxide, which are then recovered as raw materials for melamine factories. The treated water is recycled for use as flushing or cooling water.
The processing system uses high-pressure hydrolysis and steam stripping, with waste heat recovery. The process is stable, efficient, and resource-friendly.
Wastewater from the melamine plant is pumped into the treatment system, and FIC60001 and FIC60002 control the flow rate.
The wastewater flows through the decomposition tower heat exchanger and decomposition tower preheater, and is heated to the required temperature by high-pressure steam (HHS).
The concentration of melamine in wastewater depends on the temperature of the melamine cooling crystallizer:
High temperature in the crystallizer → More melamine dissolved in the mother liquor → Higher solid load on the treatment system → Risk of incomplete hydrolysis and increased solid content in the final discharge.
Lower crystallizer temperature → lower solid load → easier treatment.
Control strategy: Optimize the crystallizer temperature to minimize residual melamine without sacrificing product yield.
The impact of parameter design value deviation:
Pressure 8.4 MPa high pressure → Dissolved more NH in the liquid of ∝/CO ₂ → Higher stripping tower load;
Lower pressure → lower temperature and incomplete hydrolysis.
At a temperature of 277°C, the purity of the liquid at the bottom of the tower is higher (with lower residual solids), but there is more water vapor at the top of the tower. Lower temperature → risk of exceeding emission standards.
In practical operation, the temperature sometimes reaches 284-285℃. Due to control limitations, the temperature is°C (7-8°C higher than the design temperature). This reduces the concentration of free NH3 in the liquid phase and increases the relative CO₂ content, while still achieving the therapeutic goal.
The flow rate of medium-pressure steam (MS) to the reboiler determines the stripping strength:
Too much steam → low NH3 in the bottom water (good), but higher steam in the top water (greater condensation load).
Too little steam → residual NH3 in treated water may exceed emission limits.
Suggested control: Keep the reboiler steam flow rate proportional to the feed rate. For 24t/h wastewater, set FIC60050 ≈ 4700 kg/h
Resource recycling: NH∝, CO₂, and melamine recovered as raw materials;
Energy saving: Recovering waste heat through multi-stage heat exchangers;
Water reuse: Recycling treated water to reduce freshwater consumption;
Stable water output: fully meets environmental requirements;
Safe operation: A complete interlocking system ensures long-term operation.
The hydrolysis stripping technology for melamine wastewater treatment is a reliable, economical, and environmentally friendly solution for industrial melamine factories. By optimizing decomposition temperature, pressure, residence time, and stripping steam, factories can achieve stable emissions, high resource recovery, and sustainable production. This mature technology supports environmental compliance and cost reduction for melamine manufacturers worldwide.
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