Fundamental Research Of Semi-dry Dechlorination In Coal-fired Flue Gas To Realize Zero Emission Of Fgd Waste Water

In recent years,the zero emission of FGD waste water in coal-fired power plants has got wide attention.The flue spray evaporation technology has attracted much attention because of its small size,simple process and low cost.But this technology is not yet mature.The excessive waste water may lead to fouling and corrosion issues.When HC1 in the flue gas is largely removed,the discharge rate of FGD waste water will be greatly reduced.In order to solve the problems that caused by excessive waste water,semi-dry dechlorination technology is put forward to attach most chlorine in coal-fired flue gas to fly ash by spraying in alkaline solution.Simultaneously,significantly reduced FGD waste water is used as the solvent of alkali,which could help to realize the target of zero emission of desulfurization waste water.The chemical kinetics model of semi-dry dechlorination is built by CHEMKIN.The reaction process and degree among NaOH and HCl,SO2,SO3 in flue gas atmosphere of coal-fired power plants are studied by CHEMKIN.Experiments are carried out to simulate the flue duct from air preheater to electrostatic precipitator.The effects of Na/Cl,HF,alkali species,SO2 concentration,flue temperature and residence time on HCl reaction efficiency are analyzed.The conclusions are drawn as follow:There is a positive correlation relationship between the reaction efficiency of HCl and Na/Cl.As Na/Cl continues increasing,there is a slower growth of HCl reaction efficiency.The reaction efficiency of SO2 increases linearly with the increase of Na/Cl.The effect of HF on dechlorination is insignificant.There is a certain interference effect of SO2 in flue gas on the removal process of HC1,but the reaction efficiency of HCl is still at a high level.With a fixed value of Na/Cl,a change of 1000 mg/Nm3 in SO2 concentration would change the reaction efficiency of HCl about 13%.For a particular boiler,the concentration of SO2 generally changes in a small range,there will be no significant effect on the stability of the reaction efficiency of HCl.The reaction efficiency of HCl is related to the alkalinity and alkalis are listed from strong to weak as NaOH,Na2CO3 and NaHCO3.The changes of flue temperature will significantly affect the reaction efficiency of HCI.With the temperature rising from 100? to 140?,the reaction efficiency of HCl decreases from 78.67%to 59.23%.With the residence time extending from 0.5s to 2.5s,the reaction efficiency of HCl increases slightly from 68.13%to 73.01%.For a 660WM unit,by analyzing and calculating the amount of FGD waste water,the temperature drop of flue gas,the economy of operation and the influence on fly ash utilization are studied after semi-dry dechlorination.The results show that FGD waste water could be reduced by 71.16%after semi-dry dechlorination.When the reduced waste water is sprayed back to the flue,the temperature drop is only 2.49 ?.The system of semi-dry dechlorination is simple and the cost is relatively low.There is no significant negative effect on the comprehensive utilization of fly ash after semi-dry dechlorination.