Mechanism of NOx Formation from Nitrogen in the Combustion of the Coals Used in Sintering Process

Abstract

The released NO x during fuel combustion is one of the major air pollutants, directly related to acid rain and photochemical smog. At present, there is not an economical and effective method of inhibiting NO x emission from sintering flue gas. Therefore, controlling the conditions of fuel combustion is extremely required for the reduction in NO x. The current research investigated the effects of different combustion parameters on the formation of NO x for three type of coals. The formation of NO x decreased with increasing temperature and heating rate while it increased when oxygen content in an atmosphere increased. Anthracite coal replacement with coke up to 100 pct promoted a decrease in the formed NO x amount and X NO by 21 and 53 pct, respectively. The addition of CaO and FeO enhanced the conversion of nitrogen to NO x , especially at temperatures below 1273 K (1000°C). Taking both the oxidation reaction to form NO x and reduction reaction of NO x to form N 2 into account, the activation energy (E A) values of anthracite and coke were evaluated to be 2.2 and 3.6 kJ/mol, respectively. The combustion of semi-anthracite coal emitted the largest amount of NO x , but the anthracite coal containing less fuel-N than other coals showed the highest value of X NO , which indicates that nitrogen content in coal is not the major factor affecting the formation of NO x. The change in nitrogen functionality after combustion process might be the reason for the unpredicted results in the X NO. The pyrrolic-N in anthracite coal might be considered to be the major functional form that directly affects the conversion of nitrogen to NO.