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Ammonia stripping in open-recirculating cooling water systems


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A mathematical model was developed to simulate ammonia stripping in wet recirculating cooling systems. The model can be used to predict ammonia concentration in cooling systems using makeup water containing ammonia, such as secondary treated municipal wastewater (MWW). The model revealed that ammonia stripping in a cooling system is a function of makeup water quality, pH, and air and water flow rates in the cooling tower. Pilot-scale cooling towers designed and constructed previously for the investigation of biofouling, scaling, and corrosion issues in the reuse of treated MWW for cooling were used in this study for model verification. Data from pilot-scale testing using a particular ammonia-containing makeup water were used to calibrate the model. The overall mass transfer coefficient based on gas film for ammonia stripping in the cooling tower was found to be 2.3 × 10−3 m/s. Sensitivity analysis showed that even under only slightly alkaline conditions (pH 8), a significant portion of ammonia can be removed through water-to-air stripping, which is consistent with low ammonia measurements in cooling towers reported in the literature. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 489–495, 2013