Chemical Kinetics Of Nox Reduction By Gas Reburning And Study Of Mechanism Reduction

NO_x emissions of pollutants from coal burning would seriously endangerhuman health, pollute the environment. Recently, China has specified more rigorouslimits for the NO_x emissions. Among the most recent developments for reducingNO_x emissions, reburning technology is considered to be one of the most promisingand cost-effective NO_x reduction strategies for coal combustion systems.The key influencing factors of the gaseous fuel reburning process and thereaction mechanism were analyzed and studied in this thesis. In order to achieve thecoupling of reaction and flow computing, the detailed reaction mechanism of largescale was reduced to the skeletal mechanism which meet the requirements of fluidcomputing.NO reburning process by the gaseous fuel of CH4,CO,H₂ and biomass pyrtedolysis gas was simulabased on the typical gas reburn experiments using chemicalkinetics software Chemkin4.1. The key influencing factors of reburning fuel type,reaction temperature, reburning fuel quantity and the inlet O₂ concentration werestudied. The research results indicate that, CH4 has the highest NO reductionefficiency compared to CO and H₂.The most appropriate temperature is 1350¹400Kfor CH4 as reburn fuel.CH4 has the most important effects on reducing NO in themixed prolysis gas because that the reactive radical CHi produced by thedecomposition of CH4 reacts with NO which is the major way to consume NO. Thekey elementary reactions of gaseous fuel reburning process were obtained withsensitivity method. Comparing to the experiment results, it confirmed the SKG03detailed chemical kinetic model has good applicability for the simulation of gasreburning NO reduction.Using the directed relation graph (DRG) method, a skeletal mechanism wasdeveloped from the SKG03 mechanism which contains 37 species and 218 reactions.The skeletal mechanism showed very good applicability for the simulation of thethree gases reburning NO compared to the detailed mechanism. The couplingrelationships between species and transforming relationships between hydrocarbonradicals in the mechanism were analyzed. The reduced skeletal mechanism wascoupled as the chemical model in the Fluent software. The CH4 reburn process hasbeen computed, the results showed that the Fluent simulation agree with theexperimental results on the forecast trends of NO reduction. The outlet NOconcentration decreased with the reaction temperature increased. The oxidizer andfuel mixed well.CH4 and O₂ reacted quickly and consumed in a short time. For thegas reaction, the calculations in Fluent coupled of detailed chemical kinetics are time possible. However the accuracy need to be further improved. It provided the basis ofpredicting the NO_x reburning performance in engineering applications addingheterogeneous reactions.