Industrial & Engineering Chemistry Research, Vol.59, No.30, 13396-13405, 2020
Continuous Generation of HgCl2 by DBD Nonthermal Plasma. Part I: Influences of the DBD Reactor Structure and Operational Parameters
Accurate on-line measurement of mercury speciation is vital in mercury emission control. A calibrator is an important part in the instrumentation system, which is responsible for the accuracy of mercury concentration detection. The effect of the structure of dielectric barrier discharge (DBD) used for the continuous generation of gaseous HgCl2 was studied. This module can be applied in the mercury continuous emission monitoring system (Hg-CEMS) calibrator. The experimental parameters, including temperature, flow rate, layer of the dielectric, and the material of the dielectric, were investigated. The experimental results showed that a HgCl2 generation efficiency of 88.8% was obtained at 16 kV discharge voltage under the atmosphere of N-2(+) 25 ppm HCl when dual Al2O3 ceramic dielectric discharge was used. Temperature is an important influencing parameter during the DBD process. The higher reaction temperature gave rise to poor HgCl2 generation efficiency and the causes were complex. The effect of flow rate was found to depend on the discharge voltage. The rise of flow rate led to a lower specific energy density (SED) and a better heat dissipation effect. Under the condition of low discharge voltage, the negative effects of SED drop overweighed the positive effect of heat dissipation. In consequence, the HgCl2 generation efficiency dropped, while the result at high discharge voltage was opposite. The experimental results also indicated that dual dielectric DBD (D-DBD) reached higher HgCl2 generation efficiency compared with single dielectric DBD. This outcome arises from the fact that D-DBD could maintain the stability of discharge and achieve a better heat dissipation effect. In addition, using Al2O2 ceramic material as a dielectric was more preferable than quartz in terms of Hg-0 conversion. This study offers an encouraging method for a Hg-CEMS calibrator.