The ammonia nitrogen level in the purified water is not up to standard

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Dear everyone, our acidic water stripping unit uses a single-tower process without ammonia extraction via side streams. Over the past week, the ammonia nitrogen level in the purified water has remained above the acceptable threshold, at around 300 ppm, while sulfides have been well controlled, remaining below 5 ppm. The various parameters remain largely unchanged. The top temperature of the tower is 120, the bottom temperature is 128; the pressure at the bottom of the tower ranges from 0.16 to 0.17. The pressure in the reflux tank at the top of the tower is generally between 0.11 and 0.12, while the temperature after air cooling is between 90 and 100. There is a alkali injection process. The pH is 8 without alkali addition, and above 9 after alkali addition. In the past, ammonia nitrogen has been well controlled at around 60 ppm. It was mainly after the replacement of the tower top air cooler that the ammonia nitrogen level became unsatisfactory. The distillation tower was steamed for 3 hours before replacing the air cooling system; the unit operated for about half a year, using acidic water from coking, hydrogenation, catalytic processes, and atmospheric pressure processes as the feedstock. I hope for your guidance! Thank you!