Effects of the Frequency Conversion Characteristics of Fan and Pump on the Performance of Heat Pump Driven Humidification-Dehumidification Wastewater Treatment System

An experimental study on use of humidification-dehumidification (HDH) technology for treating chemical milling wastewater containing high concentrations of sodium hydroxide and sodium aluminate has been carried out. Heat pump is introduced to simultaneously supply cooling and heating loads of the HDH system. A parametric study is conducted to investigate influence of operational parameters including frequency conversion characteristics of circulating fan and pump on system performance. Performance parameters including pure water production amount (PWPA), pure water recovery rate (PWRR) and gain output ratio (GOR) are analyzed. Results indicate working frequency of pump and fan is not as high as possible, there is an optimal value. With frequency conversion of fan increases, PWPA and PWRR are increased, GOR shows a trend of first increasing and then decreasing, the optimal value of circulated air mass flow rate is 0.44 kg/s. With frequency conversion of pump increases, PWPA and GOR are increased, PWRR is decreased, the optimal value of inlet wastewater mass flow rate is 0.465 kg/s. When system is operating under optimal parameters, PWPA is 9.77 kg/h, PWRR is 0.58% and GOR is 0.781. Compare the indicators before and after treatment, pH, SS, COD, NH4-N and TP of purified water is 9.2, 4 mg/L, 53.2 mg/L, 0.028 mg/L, 0.278 mg/L, respectively. All these parameters decrease 31.9%, 97.6%, 97.5%, 77. 8%, 94.8%, respectively. Although the purified water has not yet reached the direct discharge standard or reclaimed water reuse standard, but HDH method shows feasible in the separation of highly corrosive solutions.