Research Of Dangerous Industrial Wastewater Reduction Treatment Based On Vacuum Evaporation Technology

At present,some enterprises can not deal with the dangerous industrial wastewater in a cheap and easy way.In view of this situation,we introduced a new method to deal with the wastewater.The Double-way Phase Change Heat Exchanger(DPCHE)has a single vacuum pump as the power source.Due to the vacuum effect,the wastewater is evaporated into vapour under the low temperature and low pressure condition.Then the vapour is turned into an overheating steam under the high temperature and the high pressure because of the compression.The overheating steam is recirculated in the DPCHE for heat transfer,so the heat is passed from the overheating steam to the wastewater,and overheating steam will condense into clean water.Therefore,the characteristics of this system is to save energy.Based on this principle,this paper presented a quantitative treatment way for dangerous industrial waste water according to the calculation of heat and quality.The results can be concluded as follow:the evaporation temperature should be operated between 75～85℃,the compression ratio should be set at 2～3,heat transfer temperature difference should be controlled in 15～30 ℃.A set of system design parameters were selected as the design reference according to the results.In the case of 20%impurity concentration,the evaporation temperature should be selected between 80(initial)～85℃(terminational),while the corresponding evaporating pressure should be set between 45.3～33.6 kPa.As the evaporation proceeded,the concentration of the concentrate increased,resulting in a sharp decrease in its evaporation pressure.The highest compression ratio of vacuum pump should not extend 3,while the working efficiency should not be less than 75%,and the power should be 3.84～5.54kw.The wastewater treatment rate is 80kg/h,and the mass of wastewater treatment is 480kg per cycle.The recovery rate of pure water is 75%and the final impurity concentration 80%The variation law of process parameters was analyzed by enthalpy-entropy(h-s)diagram,pressure-specific volume(p-v)diagram and temperature-specific entropy(T-s)diagram.The relevant differential equation and integral equation was established and the mass concentration and evaporating pressure were expressed over time.It was found that under the condition of constant feed flow and evaporation temperature,the evaporation pressure decreased with the evaporation time,but the decreasing speed is gradually decline.The concentration of industrial wastewater is a natural logarithmic curve changing over time.Only vacuum pump provides the power for the system.Due to the particularity requirements(smooth exhaust process,big tolerable difference pressure,etc.),the three-lobe Roots vacuum pump is chosen.Based on the basic structure and working principle of Roots vacuum pump,the thermodynamic process of the pumped gas was analyzed by the quantitative calculation formulas.The process can be divided into four stages:inhalation,transportation,recoil and exhaust.The pressure,volume,mass,temperature and internal energy of the gas in the air cavity were derived.This work provides a thermodynamic theoretical basis for the pumping process mechanism of three-lobe Roots vacuum pump,which is helpful for the structural design and performance analysis of the pump.The experiment data were collected and analyzed,and the change trends of collected data were consistent with those values calculated by above-mentioned method.These calculations can be used as the basis of engineering design.