Problems encountered during the on-site production of the evaporator

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The company has recently started several evaporator projects, and I happen to be in charge of monitoring them; there have been some issues, so I hope the experts can help me analyze them. Our company has a production process for basic copper chloride, which generates wastewater with high ammonia nitrogen levels. This wastewater is currently treated by using a 7.5-ton three-effect evaporator; the ammonia nitrogen concentration in the wastewater is around 10%. During evaporation, the pH is kept at an acidic level of around 3. However, it has been observed in actual production that the heat exchanger in the first stage – the one to which steam is supplied – tends to get clogged quite easily. The heat exchanger is of four-pass type. No tube blockages occurred in the other two stages; logically, if there is a tube blockage in the first stage of crystallization, it should be even more likely to occur in the second stage. However, it was found during on-site production that only the first stage had clogged pipes.