Plasma Chemical Reaction Dynamics Coupled Cfd Method Flue Gas Purification Mechanism Of The Multi-pollutant Studies

Combined removal technology of multi-Pollutants from coal-combusion flue gas is the development direction of clean coal technology. In addition to the primary SO2 and NOx, the controls of mercury is gradually proposed on the program. Removal of SO2/NO/Hg in simulated flue gas with the Non-Thermal Plasma (NTP) is a prospective approach in future. Although scholars had made extensive studies about Non-Thermal Plasma, but the production of plasma and the theory research of mechanisms are still in elementary stage. For homogeneous mercury oxidation and Non-Thermal Plasma chemical kinetics, there is no uniform reaction mechanism and kinetics model, and it is difficult to make a a reliable theory support of gaseous pollutant control technology by NTP. So revealing the purification process through the mechanism is a hot topic and a urgent problem need to be solved. Based on this background, with the support from the Natural Science Foundation of China "Characteristics of non-thermal plasma assisted photocatalyst on oxidation of elemental mercury in flue gas" (No.50976049), the investigation on the SO2/NOx/Hg purification mechanism by non-thermal plasma is carried out through the approach combined with numerical simulation and experimental verification. The paper consists of the following parts:The literatures on the gaseous pollutant control technology by NTP are summarized and the characteristics of plasma generated by different kinds of gas discharge are compared and analysised. The kinetic simulation of Homogeneous mercury oxidation and SO2/NOx/Hg purification by non-thermal plasma using FLUENT6.2 coupled with CHEMKIN mechanism are conducted. The reaction rate constant of the ionization of N2/O2 by electron-impact dissociation was calculated through the lumped kinetic model of pulse corona discharge and a kinetic model in the system of NO/O2/N2 under pulse corona discharge was obtained. The kinetic mechanism was analyzed by the sensitivity analysis method in CHEMKIN. Cl, HOCl and HCl are the important component in the reaction system contained chlorine and play an important role about the formation and oxidation of Hg0. The concentrations of free radicals(N,O) were predicted and the three-dimensional concentration distribution of SO2/NO/Hg in plasma reactor were also obtained. The simulated results were compared with the ralated experimental results. The results show that coupling calculation solves the problem of the combination of the computation fluid dynamics (CFD) with the complex kinetic mechanism。Cl2 fraction is helpful for the oxidation of Hg0. The reaction temperature is 1353k, pressure latm. In our kinetic calculations,17.5%,32.5%, and 55.4% of the mercury was oxidized in the presence of 50, 100, and 300 ppm Cl2, respectively. It shows that the prediction results in this paper are consistence with related experimental data. When Cl2 concentration increased, the oxidation of mercury is enhanced to a great extent. The increase of Cl concentration accelerates mercury oxidation by reaction with mercury. It is observed that when the total concentration of HC1 has increased slightly, the mercury oxidation has only a little growth remained at 5%. The temperature window for the higher oxidizing rate of the elemental mercury focused on the 950-1150K. The pulse corona discharge removes NO and SO2 effectively, and prompt the oxidation of elemental mercury. O2 fraction and low temperature is helpful for the removal of NO. In our kinetic calculations,90.3%,91.5% and 93.0% of the mercury was oxidized in the presence of 1.5%,4.5%,10% O2, respectively. The presence of O2 enhance the conversion of SO2.18.5%,30.3% and 80.6% of SO2 was oxidized in the presence of 0%,5%,10% O2, respectively.In order to prove correctness of the proposed kinetic model, the gas purification system of NTP is designed and constructed, which include the gas generator, pulse power supply with high voltage, NTP reactor and the gas analysis system. Under the NPT atmosphere, the experiments were carried out to study NO,Hg0 removal mechanism. The results show that voltage plays an effective role to the remove of nitric oxide and elemental mercury. With the Input voltage increasing from 5KV to 7KV, the removal efficiency of and Hg0 and NO can be enhanced from 65% and 61% to 80.83 and 98.2%, respectively. O2,HCl,H2O fraction is helpful for the removal of Hg0. Under the same conditions, good agreement between the simulation results and the experimental data is reached.These works are helpful to reveal the mechanism of homogeneous mercury oxidation and SO2/NO/Hg purification under NTP system, present an important reference value for the optimization of SO2/NO/Hg treating device.