Effects And Mechanism Of Competition Of The Flue Gas Composition On No-char Reaction Under High Temperature

Our country is a major energy consumer, with a great coal consumption for along time. Nitrogen oxide pollution caused by the coal is getting worse. That’smeans to control nitrogen oxide emissions of coal-fired power plants is an urgentwork. Studying NO-char reaction helps us to predict the generation of NO in actualcombustion process. Then the study has important guiding significance to controlNOXemissions of coal-fired plants. The author of this paper transformed theSimulator of High-temperature Entrained Flow Reactor. The char samples wereproduced in the reactor. Then, the author completed the experiments of NO-charreactions in the High Temperature Drop Tube Furnace which has been built anddebugged successfully. The influence of different flue gas composition (such asCO2, SO2, O2, H2O, etc.) to NO-char reaction has been studied.Some correlation analysis has been done to the chars, the results shows thatvolatile content of the chars are all at a low level. However, the bituminous charhave a higher conversion rate of volatile while the lean coal and anthracite char islower because of the less volatile content.Through the experimental study concluded that the influence of SO2of thereaction is very small, in the case of the presence of SO2,NO reduction rateincreased from1to7%. The influence of CO2to NO-char reaction is complex.Adding a small amount of CO2can enhance the NO reduction rate, while NOreduction rate changed little when increasing the CO2concentration. Generation ofCO because of the gasification is the main cause that CO2promote the reaction.However, high CO2concentration inhibited the reduction of NO and CO. As thetemperature and H2O concentration upgrade, NO reduction rate increase, and thisphenomenon is more obvious at low temperatures. The main reason that H2Opromote the reaction is the generation of CO and HCN. In terms of lean coal andanthracite, O2inhibited the reduction of NO-char, while the results show thatShenhua bituminous coal, low concentrations of O2can promote the reaction ofNO-char. The best O2concentration is between0.8to1%. The generation of COand the increasing of surface carbon and oxygen functional groups is the importantreason that O2promote the reaction.In the experiments of different ratio of the flue gas, the addition of H2O ismore conducive to the reduction of NO in the case of low O2concentration. In thecase of high concentrations of oxygen, the NO reduction rate of mixed gas is lessthan one-component conditions, X-ray photoelectron spectroscopy (XPS) andmercury porosimetry were used to analyse the char samples. The results shows that the number of carbon-oxygen functional groups increases in the reaction process.The reasons for the high oxygen concentration not conducive to the reduction ofNO is that O2and NO have competition to functional groups in char surface anddecline of the specific surface area. The results of experiments of CO2and O2mixed show that the NO reduction rate of mixed gas is lower than the reduction rateof one component gas. The possible reason is that the consumption of CO generatedby gasification in case of adding O2. In addition, in the presence of CO2is notconducive to reduction of NO. Carbon-oxygen in char surface is increased duringthe reaction process, but the difference of functional groups is not obvious betweendifferent CO2concentration conditions.