| In this paper, the mechanism of photocatalytic oxidation and liquidadsorption removal coal fired flue gas mercury were studied. Firstly, currentsituation of China‘s coal consumption and pollution was analyzed, presentsituation of coal fired flue gas mercury emissions and its harm were discussed,coal fired flue gas mercury control methods were introduced, the influencefactors and the reaction kinetics of photocatalytic oxidation removal mercurywas reviewed, liquid oxidation and adsorption of flue gas mercury wasreviewed. Then, in this paper, the experimental study on TiO2photocatalyticoxidation removal mercury was taken by using the photocatalytic reactor. Aphotocatalytic oxidation reaction kinetics model was set up, the kineticparameters and the reaction rate equation are obtained. Mercury liquid removalexperiments were taken by using the simulated flue gas bubbling reactor.According to the experimental data, the parameters of mass transfer andreaction kinetics were calculated, then the kinetics parameters were obtained.Combined with the experimental data, a comprehensive analysis was made.There are mainly four parts in this paper:(1) Self-developed lab-scaledsimulated flue gas mercury photocatalytic oxidation removal device and fluegas liquid adsorption device.(2) The experimental study on TiO2photocatalyticoxidation removal mercury was taken by using the photocatalytic reactor,mainly discussed the effect of reaction temperature, UV light intensity andcatalyst adopting. Using orthogonal test discussed the different effect of thethree factors on mercury photocatalytic oxidation.(3) The reaction mechanismon TiO2surface was studied, and a photocatalytic oxidation reaction kineticsmodel was set up, the kinetic parameters and the reaction rate equation areobtained.(4) Simulated flue gas mercury liquid removal experiments weretaken by using the simulated flue gas bubbling reactor, mainly discussed initialconcentration of KMnO4solution, pH and reaction temperature, exploring themechanism of Hg0and KMnO4reaction, and the parameters of mass transferand reaction kinetics were calculated.According to the study in this paper, some conclusion can be obtained:(1) In the mercury photocatalytic oxidation removal experimental study,reaction temperature, UV light intensity and catalyst adopting all show great effect on flue gas mercury removal efficiency. With the rising of reactiontemperature, Hg0removal efficiency will decrease. With the rising of UV lightintensity, Hg0removal efficiency will increase. With the rising of catalystadopting, Hg0removal efficiency will increase.(2) In the TiO2photocatalytic oxidation mercury removal orthogonal test,three factors have effect on mercury removal efficiency in different degree,their relationship is B (UV light intensity)> C (TiO2adopting)> A (reactiontemperature). Factor B has the biggest effect on mercury removal efficiency.Efficiency of A2B2C3is the best of all, the corresponding parameters areA22=55℃, B2=279.82μW·cm-, C3=0.6g, the efficiency is89.8%, while theefficiency of the reactor can reach100%. Factor A (reaction temperature) is notsignificant under level0.2, factor B (UV light intensity) and factor C (TiO2adopting) have some influence under level0.2. It can be seen from the resultsof range analysis and variance analysis that factor B and factor C are thedominant factors, so, in order to ensure high mercury removal efficience, thelight intensity and the amount of TiO2should be their best value. Factor A havesome influence on photocatalytic removal of mercury, but it‘s not obvious asthe other two factors do. So, there is no need to ensure the optimal value oftemperature, and the limit of the location where the photocatalytic reactiondevice installed in the back-end flue can be extended appropriately.(3) TiO2photocatalytic oxidation on Hg0removal process is consists oftwo parts, which are adsorption process and photocatalytic oxidation process.Adsorption process fit for the Langmuir-Hinshelwood adsorption isothermmodel, Langmuir adsorption equilibrium constant is KHg=1.0×10-12cm3·mol-1,the reaction rate equation is rHg=2.32×1012×1×10-11cHg(t)/[1+1×10-11cHg(t)].(4) In the simulated flue gas mercury KMnO4solution adsorptionexperiment, initial KMnO4solution concentration, pH and reaction temperatureare three most important factors that influence the Hg0removal efficiency. Hg0removal efficiency is improved with the increase of KMnO4initialconcentration and the decrease of pH value and reaction temperature.(5) The reaction between Hg0and KMnO4is a complex gas-liquid masstransfer reaction process. E and KG/kLincreases with the increase of KMnO4initial concentration, which indicates that the effect of chemical reaction onmass transfer increases and the liquid membrane resistance decreases, so theHg0removal efficiency is improved. On the other hand, KG/kLreduces with theincrease of reaction temperature which means that the liquid membraneresistance grows up, leading to lower Hg0removal efficiency. |
PDF Full Text Request