Behavior and Estimation of Nitrogen Oxides Emission In 71 MWe PFBC Boiler

Abstract

71MWe PFBC demonstration plant was successfully operated in the period of 1992 to 1997 in EPDC Wakamatsu Work to complete all the tests of phase I. During the operation, emissions of NOx and N2O ware continuously measured under different load condition and different type of coal and their mixture. Such operational conditions influenced operational parameters such as temperatures of combustion and exhaust gas, pressure in the boiler and oxygen content in the exhaust gas, etc. The effect of such operational parameters on emissions of NOx and N₂O was analyzed.
Since the nitrogen in the fuel was found to be the sole source of NOx and N₂O, the emissions of NOx and N2O were normalized by fuel-N to calculate conversion. The effect of operational parameters on conversion of NOx, that to N₂O and overall conversion of N into nitrogen oxides (NOx +2N₂O) were analyzed. This overall conversion as well as the conversion into N2O was well correlated to the temperature of cyclone gas (T_c) and square root of P_O2 in the exhaust gas. The conversion into NOx was calculated as the difference of overall and N₂O conversions. The concentrations of NOx and N₂O are thus estimated by use of functions of Tc and P_O2 named ASH^TR.
Parameters in the functions were experimentally defined using a coal to establish ASH^TR equations. The equations were confirmed to be applied for other coals and their blends and to estimate the rapid change of NOx concentration due to the rapid change of P_O2 and T_c