Kinetic Performance Of Electrochemical Process Applied In Circulating Cooling Water Scaling

The traditional chemical method can not effectively achieve scale inhibition and scale prevention of circulating cooling water system,and the effect of removing scaling ions is not good,which causes secondary pollution to water body.As a new technology,electrochemical descaling has the characteristics of high efficiency,pollution-free and low cost.In this paper,the kinetic characteristics and process of electrochemical descaling were studied,and the kinetic model of electrochemical descaling reaction was constructed,and the influence of operating conditions on the treatment effect was investigated.It provides a certain theoretical basis and technical support for the design and operation of the process.(1)Based on Faraday's first law and electrochemical reaction kinetics equation,a batch reactor(CMB)electrochemical descaling model Cca2+=C0·exp(61k?2J2t2/34L2-k?J?C0't/L)was constructed.The single factor test was designed to verify the model,and the results showed that the experimental data was significantly correlated with the model.Under the condition of batch reaction,the concentration of Ca2+decreases exponentially with the increase of current density.The kinetic model shows that the optimal spacing of the reactor is L=2C/D to minimize the concentration of Ca2+,and the numerical calculation of each group is carried out.The optimal plate spacing of the electrochemical descaling process is determined to be 0.7?1.7cm.For the convenience of equipment processing and process debugging,the optimal plate spacing is 1cm;the Ca2+concentration decreases exponentially with the extension of electrolysis time;The established kinetic model can roughly reflect the change of Ca2+concentration with HCO3-initial concentration.With the increase of HCO3-the initial concentration,the Ca2+concentration decreases continuously.It was proved by SEM and XRD that the scale of the cathode plate was mainly hard and hard calcite,which needs to be removed by external force.(2)Based on the electrochemical descaling model of CMB reactor,the electrochemical descaling reaction kinetic model ?=[1-exp(61/34·k?2J2h2/L2v2-k?J?C0'h/Lv)]×100%of plug flow reactor(PFR)was constructed based on the material balance equation.The single factor test was designed to verify that the test data was significantly correlated with the model.The hardness removal rate increases with the increase of the flow length under the condition of plug flow.When h=17Lv?C0'/61?J,the hardness removal rate reaches the maximum value;the hardness removal rate increases with the increase of current density,but the hardness removal rate increases.The megatrend gradually becomes gentle;the hardness removal rate decreases continuously with the decrease of the flow rate;with the increase of the initial concentration of HCO3-,the hardness removal rate continues to increase,and the rate of increase of the hardness removal rate becomes lower and lower.(3)Establish a correlation model between specific energy consumption and operating conditions 3600·C0[1-exp(61/34·k?2J2h2/L2v2-k?J?C0'h/Lv)]·A·v,calculate and sort the specific energy consumption of each group of tests.The results show that the specific energy consumption increases with the decrease of the flow rate,and the obtained voltage is fitted.It is closer to the actual voltage;the specific energy consumption increases with the increase of current density,and the growth rate increases continuously;with the increase of HCO3 the initial concentration,the specific energy consumption decreases continuously,and the specific energy consumption decreases.Gradually tend to be flat.(4)The pilot test was carried out with the circulating cooling water of the central air conditioning system of an airport as the treatment object.Under the pilot test conditions,due to the interference of magnesium 10ns,scale inhibitors and suspended solids,the hardness removal rate current density is approximately linearly increasing;the flow rate is reduced from 4.17mm/s to 2.08mm/s.The growth rate is faster,and the growth rate of hardness is slowed down when the flow rate is lower than 2.08 mm/s.The results of the specific energy consumption of electrochemical removal of cooling water hardness show that the specific energy consumption and current density are approximately linear;the specific energy consumption decreases with the decrease of flow velocity,and the flow rate is 2.08mm/s is the lowest energy consumption.On this basis,the optimal operating conditions were determined:the residence time was 4 min and the current density was 25.56 A/m2.The presence of scale inhibitors in circulating cooling water was found by XRD pattelns and SEM images to cause distortion of the scale crystals on the cathode plates.Through the above research,the influence of operating conditions on the electrochemical descaling effect is revealed,and the theoretical system of electrochemical descaling kinetics is enriched.In the small and medium-sized circulating cooling water system with circulating water volume of 1000m3/h,compared with the traditional chemical chemical method,the electrochemical descaling equipment can save the operating cost by 235,000 yuan,with considerable economic benefits and good environmental benefits.