Study On Recycling Use Of Gas Washing Wastewater From Wet Electrostatic Precipitation

With the demand of coal gas quality by users becoming more and more strict, the wetelectrostatic precipitator(WESP) has been widely used in iron and steel enterprises, owingto the high efficiency of purification. The gas washing water generated in the operationprocess is characterized by large quantity, complex compositions, high suspendedsubstance(SS), high hardness, high alkalinity, unstable water quality. If the wastewaterfrom the WESP is recycled, the problem of water consumption can be solved as well asthe production cost reduced effectively. With the help of great technological innovationproject of Hebei province, the study on the treatment and cycling utilization of gaswashing water from WESP in the iron and steel industry has been carried out.According to the properties of coal gas washing water from WESP, the treatmentprocess with the joint use of chemical coagulation, flocculation and ion exchangesoftening has been put forward. Take the suspended substance, total hardness and totalalkalinity for main factors, the concentrations at 350,365,315 mg/L can be decreased to7,75,70 mg/L after the treatment of two main unit, which achieve the reuse standard. Asmall and efficient system of wastewater treatment and recycling has already beendesigned.Based on the experimental research and theoretical analysis of chemical coagulation,flocculation, ion exchange softening used on the coal gas scrubbing water of WESP, theresults are listed as follows:(1)The optimal conditions that affect the removal efficiency of SS are that PACdosage is 60 mg/L, mixing time is 60s, mixing speed is 90 r/min, the optimumprecipitation time is 6 min, the concentration of SS can be reduced from 350 mg/L to 6.6mg/L, of which the remomal efficiency is 98%.(2)The ion exchange softening and resin regeneration test on washing wastewaterdetermines that the effluent hardness can meet the standard when the running velocity is20 m/h. At the same time, the working exchange capacity of ion exchange colum is 0.543mmol/mL. In addition, the resin regeneration efficiency is 94.9% when the HCl with concentration is 3% as the regenerating agent and the dosage of wet resin is 2 L/L.(3)The removal efficiency of alkalinity during the ion exchange softening process onwashing wastewater is 79.5%, which boosts the application value of this method.(4)The processing of wastewater treatment and recycling as well as thchnologicaleconomic analysis have been designed when the water consumption from WESP is 54m~3/h. The result shows that the running cost of this method is 0.41yuan/m3, which is lowerthan the original treatment processing on gas washing wastewater, The processing ofchemical coagulation and flocculation combined with ion exchange and softening used onthe washing wastewater fromWESP has many advantages, for example, low running cost,small occupation area, simple operation, low price of reagent and no secondary pollution,Therefore, this method is quite suitable to treat and recycle coal gas washing wastewaterfrom WESP.