Pilot-scale Experimental Research On The Technology Of Coal-fired Flue Gas Dechlorination For Realizing Zero-discharge Of Desulfurization Wastewater

The zero-discharge of desulfurization wastewater has become a hot environmental issue.Coal-fired flue gas dechlorination from is a new technology to achieve zero-discharge of desulfurization wastewater.The atomized alkaline solution is sprayed into the flue before the precipitator to absorb strong acid gases such as HCI.Then the reaction products will be removed with fly ash by precipitator synergistically.By reducing the mass concentration of Cl-in the flue gas at the inlet of the desulfurization tower,the amount of desulfurization wastewater can be reduced effectively.While the desulfurization wastewater after reduction being used as the solvent of alkaline,zero-discharge of desulfurization wastewater will be realized finally.On the basis of the laboratory and chemical dynamics research,the feasibility study of this technology was carried out.The results of the feasibility study show that the efficiency of dechlorination could reach more than 70%,the amount of desulfurization waste water of a 300 MW unit can be reduced from 3.1 m3/h to 0.88 M3/h.In order to verify the results of laboratory and chemical kinetics research,a pilot-scale experimental system was built in a 300MW unit in Zhejiang.The system was aim to study the effects of Na/Cl,base types and base solution concentration on the efficiency of dechlorination by simulating the flue between air preheater and electrostatic precipitator.When NaOH is used as base and the molar ratio of Na/Cl is about 16,the dechlorination efficiency can reach 70%.Although the concentration of base solution has a certain effect on the dechlorination efficiency of flue gas,the concentration of NaOH solution is between 1.69mol/L?5.06mol/L,the efficiency of dechlorination is basically stable.Therefore,when the amount of the desulfurization wastewater is changed,the concentration of base solution can be changed in a certain extent,and the zero discharge of the desulfurization wastewater can be achieved.The research shows that although both the solution of Na2CO3 and NaHCO3 can remove HCl?the efficiency of dechlorination of Na2CO3 and NaHCO3 is lower than that of NaOH.At the same time,the solubility of Na2CO3 or NaHCO3,is much lower than that of NaOH.The maximum concentration of Na2CO3 or NaHCO3 is 1/13 of that of NaOH at the same temperature.When Na2CO3 and NaHCO3 are used as base to make up absorption liquid,the dynamic water balance can not be reached,that is,it is impossible to realize the zero discharge of the desulfurization wastewater.Therefore,it is most appropriate to choose NaOH as the base material.In addition,the technology will not only remove HCl,but also can remove SO2 and SO3 in the flue gas.It has great significance for the prevention of low temperature corrosion,especially under the case of ultra-low emission.It also has certain positive significance for the operation of ESP and WFGD.Compared to other technologies of processing desulfurization wastewater,coal-fired flue gas dechlorination technology has the advantages of simple system,low cost,good security,strong adaptability,no secondary pollution and so on.It has a good application prospect.