| Great deals of high concentrations inorganic salts wastewater are discharged by industries ofdyeing and finishing, chemical engineering, paper making, pharmaceuticals and pesticides. Inorganicsalts contained in some wastewater have the value of recycling. If these wastewater are directlydischarged, it will lead to water pollution and waste of resources. There are some problems forconventional multi-effect evaporation, which can treat this kind of waste water, such as high energyconsumption, more corollary equipment and high operating costs. Therefore, it is necessary to developa method which is low energy consumption, low operating costs and compact, to treat highconcentration saline wastewater.In this paper, a method of two-stage mechanical vapor recompression (MVR) was proposed, andthen designed the system process, simulated and analyzed the system, carried out experimental studyand evaluated the performance of the system.First, this paper analyzed the existing salinity wastewater treatment technology andcharacteristics of high concentrations of saline wastewater and put forward a new two-stagemechanical vapor recompression evaporation method. The system process corresponding to the newmethod was designed. The model of main equipment and the computing platform of the system wereestablished and verified by public data. Systems of two-stage MVR, one-effect MVR and three-effectevaporation were analyzed. Overall thermal performances were discussed. Results show thatcompared to the reference system, coefficient of performance and energy efficiency of the new systemis higher. And it can save about75.8%of energy compared with the three-effect evaporation. At thesame time, the influence of the parameters (such as one-stage discharge concentration, evaporationtemperature and temperature difference) on energy consumption of the two-stage MVR system isinvestigated.Following above theoretical analysis, the heater structure is optimized and designed usinggenetic algorithms with the minimum cost targets. The flasher and its structure with feeds from axiswere designed. Then the actual two-stage MVR system device was build which is placed in a dyemanufacturer for the treatment of high concentration of ammonium sulfate wastewater. Actualoperating performances of system at industrial state were studied. The results show that the actualenergy consumption of system is about53.8kWh/t realized the low energy consumption target; theresults of simulation and experiment are in good agreement which shows that the simulation and design model is reliable. The experimental results show that the system recovers ammonium sulfateand discharges clean water, and reaches the treatment requirements.The exergy analysis model of two-stage MVR system considering the influence of salt in thesolution was established. Using above experimental data, the exergy analysis of system had beencarried out at the actual condition. The exergy loss distribution and the effect of compression ratio,evaporation temperature and one-stage discharge concentration on exergy efficiency of the system hadbeen obtained. Improvement measures based on the analysis were suggested. Then, based on theabove logistics exergy, the thermal economics structure theory was introduced to build the thermaleconomics model of two-stage MVR system. The economic cost and distribution was analyzed. Also,the influence of internal and external parameters on the system thermal cost economics was studied.Analysis results showed that compared with single-effect MVR system, system’s exergy efficiencydescribed in this article increase by13.4%and the unit product costs decrease by6.8%.So,theadvantages for the comprehensive performance of two-stage MVR system is obvious. the effect ofinternal operating temperature on thermal cost economics of every component is more than the effectof one-stage discharge concentration; The influence of external electricity price on thermal economicscost of every component is greater than the influence of equipment investment.This paper provides a low energy consumption method for treatment the high concentrationsaline wastewater. The obtained results have a certain theoretical and practical reference value forapplication and development of MVR technology. |
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