Influence of char physicochemical features on the flue gas nitric oxide reduction with chars

Nitric oxide is formed during the combustion of fossil fuels and is subsequ ently oxidized in the atmosphere to NO2. The increasing knowledge of pollut ion problems arising from NOx had led to the introduction of stringent envi ronmental regulations concerning NOx emissions that in most cases, cannot b e met by the only application of combustion modifications, so postcombustio n methods have been developed. The selective catalytic reduction (SCR) is t he only flue gas denitrification technique so far which has been proven to be very effective. However, improvements of the SCR method can be made in t wo aspects: using low-temperature gas (avoiding reheating) and cheap cataly sts. This paper is focused on the reduction of NO to N-2 from stack gases o f stationary sources using nonactivated low-rank coal chars. Physical and c hemical properties of the chars were characterized by different methods and techniques: proximate and ultimate analysis, N-2 and CO2 surface areas, ac id-base titration, AA, XRD, and TPD. The flue gas has been simulated by var ying the water vapor and oxygen content passing through a bed of char with varying reaction temperature and the space velocity. The effect of the diff erent operation conditions on the NO removal capacity of the chars were exa mined. Correlations between the performance of these chars and their physic ochemical features were investigated. An optimal amount of oxygen-functiona l groups on the surface char is needed to obtain high NO removal performanc e. This optimal value can be tailored by char oxidation. The effects of var ying the gas-phase and surface oxygen concentrations were also studied.