Analysis of the high COD in ammonia-vaporized wastewater

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In our plant’s ammonia vaporization process, the excess ammonia water coming from the cold drum enters ceramic filters and coke filters; after impurities such as tar are removed from it, it goes into an ammonia water heat exchanger where it exchanges heat with the ammonia vaporization wastewater coming from the bottom of the ammonia vaporization tower. The excess ammonia water is heated from 70°C to around 98°C before being fed into the ammonia vaporization tower, where it is directly stripped by steam at a pressure of no less than 0.3 Mpa. The ammonia gas that is vaporized enters an ammonia condenser, where it is cooled using circulating water at around 32°C. The ammonia gas then enters a saturator to be used in the production of ammonium sulfate. The ammonia-vaporized wastewater discharged from the bottom of the tower is exchanged heat with the remaining ammonia water in an ammonia-water heat exchanger; as a result, its temperature drops from 103°C to 70–80°C before it enters the wastewater tank. There, it is cooled by a wastewater pump and a wastewater cooler using primary circulating water until its temperature falls below 45°C, after which it is sent for biochemical treatment. The tar residue discharged from the bottom of the ammonia vaporization tower is manually removed and sent to the coal yard for blending with coal. The pH value of the ammonia-vaporizing wastewater from our factory is generally around 8-8.5, while the ammonia nitrogen level is around 50-140 mg/l. The COD value fluctuates considerably, ranging from about 6000-8000 mg/l. The sulfide level is generally around 200-240 mg/l. I would appreciate it if experts could analyze the reasons for the high COD levels and their fluctuations. Thank you.