Catalytic Effect Of Calcium On Nitrogen Conversion Mechanism In Pulverized Coal Combustion

Coal is the most important energy resource in China.Our country is under a enormous burden on the ecological environment which is caused by the huge energy consumption and the inefficient use of coal.Nitrogen oxides?NO_x?released during pulverized coal combustion is one of the main pollutants affecting the atmospheric environment.Therefore,it is very important to study the mechanism of NO_x conversion in coal combustion and the catalytic conditions affecting NOx reduction for the improvement of environment.A large number of experimental studies have proved that alkali metals and alkaline earth metals have certain effects on char gasificatin,heterogeneous reaction of NO and cahr fusibility.This paper is focused on the catalytic mechanism of calcium in the heterogeneous reduction reaction of NO and char,the catalytic mechanism of calcium in the heterogeneous reaction of NO and char bound nitrogen,the influence of calcium on coal gasification and the difference of formation of N₂ after gasification.We hope this study can help understand the role of calcium in the NO_x reduction.When NO is adsorbed vertically on the active sites of char,CO molecule is needed to remove oxygen atoms.The existence of calcium reduces the energy barrier of this process.The key step in the heterogeneous reduction reaction of NO is the N₂ release process.The energy barrier of this process is 79.84KJ/mol in model without calcium and 50.80KJ/mol in the model with calcium.NO is adsorbed vertically on pyridine-N to form char?N??NO?group.Oxygen atom is removed by CO.The activation energies of N₂ release steps are show below:247.92KJ/mol in ordinary pyridine-N model;246.01KJ/mol in pyridine-N model with Ca;211.88 KJ/mol in pyridine-N model with CaO.Calcium can directly participate in the heterogeneous reduction of NO.The energy barrier of the reaction rate-determinating step is relaticely high which is above 300KJ/mol.In the process of char gasification,the presence of calcium can accelerate the gasification reaction rate.The gasified char is more easier to release N₂.