Experimental Study On Mechanical Vapor Recompression Technology For Salinity Wastewater Treatment

Mechanical vapor recompression technology (MVR) is driven by mechanicalcompressor to compres the secondary steam produced by the evaporator to a higherpressure to improve the quality of steam, the secondary steam enter into the evaporatorand cycle, evaporating the solution to be treated or wastewater in the micro-vacuumstate and low temperature. The core is use of latent heat of secondary steam generatedby system to heat the solution. It’s not only can recycling of water, but also can achieverecycling of heat. Built-in MVR device is to set the vapor compression device inside theevaporation chamber, integrated design into the integration of equipment, with outvapor-liquid separator, reduced the covers and investment costs. The technology ismainly used in chemical, food, pharmaceutical, desalination, and other fields of salinewastewater treatment, it’s not only can recycle water resources, and combined withsubsequent crystallization processing wastewater zero discharge can be realized.In order to study the impact of the raw water salinity and typical ion (calcium ion,sulfate radical) to water quality, water recovery rate and energy consumption, when useMVR to deal with saline wastewater. Based on previous research results, carried out apilot-scale test study on built-in MVR device to deal with different concentration ofsimulated wastewater. According to the operation situation of in the process of the test,water recovery rate, water quality and energy consumption. Analysis of the pilot testtreatment effect of waste water as well as the impact of the raw water salinity,concentration of calcium ion and sulfate radical to water quality, water recovery rate andenergy consumption. The main experimental research conclusions are as follows:①Installation and commissioning test results show that the pilot plant installationquality is good, the evaporator, pipeline and instruments connection close withoutleakage, a complete set of equipment insulation and pressure testing meet the testrequirements, and equipments running steadily.②The single pollutant simulated wastewater treatment test results show that waterconductivity, concentration of total dissolved solids and chloridion of concentrate waterand condensed water are rises with the rising of raw water salinity, and water recoveryrate is decreases with the rising of raw water salinity, the maximum water recovery rateis91.2%. Concentration ratio (measured by chloride ion) is decreases with the rising ofraw water salinity, and the maximum concentration ratio is6.7. The average energyconsumption of per ton water after conversion is23.3kW·h. ③The simulated reverse osmosis condensed water treatment test results show thatwater conductivity, concentration of total dissolved solids and chloridion and sulfateradical and calcium ion of concentrate water and condensed water are rises with therising of raw water salinity. Water recovery rate is decreases with the rising of raw watersalinity, the maximum water recovery rate is85%. Concentration ratio(measured bychloride ion) is decreases with the rising of raw water salinity, the maximumconcentration ratio is6.2. The average energy consumption of per ton water afterconversion is23.0kW·h. Moreover, scaling phenomenon appeared inside of theevaporation tank,This may be caused by calcium precipitates out of the simulated ROcondensed water.④The simulated desulfurization wastewater treatment test results show that waterconductivity, concentration of total dissolved solids and chloridion and sulfate radicaland calcium ion of concentrate water and condensed water are rises with the rising ofraw water salinity. Water recovery rate is decreases with the rising of raw water salinity,the maximum water recovery rate is40.0%. Concentration ratio(measured by chlorideion) is decreases with the rising of raw water salinity, and the maximum concentrationratio is2.5. The average energy consumption of per ton water after conversion is23.5kW·h. Evaporation tank internal appear large scaleing phenomenon, this may be causedby calcium precipitates out of the simulated desulfurization wastewater.⑤Integrated the pilot-scalet test showed that: MVR saline wastewater treatmenttechnology is basically feasible. It not only can recycle high quality condensed water,but also higher concentration and water recovery can greatly reduce the terminalemissions of concentrate of saline wastewater, and laid the groundwork forimplementation of saline wastewater zero emissions. Meanwhile, the energyconsumption of per ton water of MVR treatment technology relative to the otherthermal technique has certain advantages. Moreover, the higher the raw water salinityand the concentration of sulfate radical and calcium ion are, the smaller the waterrecovery and concentration ratio are. Although there are fluctuations of energyconsumption but haven’t changed much. So, when the hardness of raw water is higher,inorder to prevent the evaporation tank internal scale, MVR device will need to increasethe pretreatment of softening process, such as precipitation, filtration and so on.