The Formation And Emission Mechanisms Of NO_X In Agriculture Straws &.coal Co-firing Fluidized-bed Combustor

Coal combustion generates a large amount of nitrogen oxides (NOX), which is a major source of air pollution. In order to control the emission of NOX efficiency, the formation and emission mechanisms of NOX from agriculture straws and coal co-firing was studied using fluidized-bed combustor in this paper.Through mass of theoretical and experimental researches, it was believed that fluidized-bed combustion is one kind of clean combustion technique and co-firing of biomass and coal can decrease NOX emission effectively. Furthermore, the agricultural straws is the most abundant biomass resources in our country. Hence the NOX emissions from the co-firing of agriculture straws and coal in fluidized-bed combustor have been investigated in depth.Firstly,relative previous research on NOX was summarized. Based on the studied conclusions,existed problems and background of project, the purpose and main content of the study were put forward.Secondly, the combustion characteristics of coal,agricultural and their mixtures at different ratios was performed using thermo balance analyzer (STA 409C). The results showed that the ignition was shifted to lower temperature and burn out property was upgraded when coal was mixed with agricultural straws, it is consistent with literature when non-straw biomass as sample.Then,the property of NOX emission from agricultural straw combustion(cornstalk and wheat straw),coal combustion(Heshan and Xiaolongtan coal)and co-combustion of biomass and coal were studied in a lab-scale fluidized bed reactor. It can be observed that the NOX emission was decreased greatly with co-firing of coal and agricultural straws. In the bottom of fluidized bed reactor, the fast combustion and pyrolysis of biomass produced a lot of volatile with many reductive ions. The reaction between the reductive ions and oxygen restrained the formation of NOX, hence, the NOX emission decreased with the mass ratio of agricultural straws increasing.At last,combining with models of gas-solid two-phase flow, heat and mass transfer, pulverized coal combustion and NO formation, a set of mathematical models for a lab-scale fluidized bed boiler were established. In terms of commercial CFD code (FLUENT),the gas releasing property and the distribution,especially the emission of NO, in fluidized bed combustor was analyzed.