The decomposition of NO and N20 by chars has been studied in a fixed bed reactor under steady state conditions. The reactions were studied at temperatures from 673 to 1223 K and at partial NO and N20 pressures in the range of 0.62-3.08 and 0.19-1.92 mbar, respectively. The reactor pressure was 2.5 bar and the space time W/FNo,o(N:O,o )) was either 79280 or 100140 g s/mol for NO and N20 , respectively. Four coals ranging from lignite to anthracite were used as char precursors. N20 was more readily reduced on a coal char surface than NO. The kinetic parameters for the NO and N20 decomposition on a char surface were rather dependent on char structure. Apparent activation energies in the range of 111-181 and 66-104 kJ/mol were obtained for NO and N20 decomposition, respectively. Apparent reaction orders for NO decomposition on the chars ranged from 0.22 to 0.43. In the case of N20, an order of ~ 0.6 was found except for DE53 char that showed an almost zero order at lower temperatures. A large confidence interval was found for the reaction order, which indicates that it is changing with temperature. The rate of NO decomposition by char is strongly enhanced by the presence of CO and N20; this is ascribed to surface oxygen removal. CO had no effect on N20 decomposition, since N20 itself acts as a surface oxygen liberating species. When O2 was added to the NO/char reaction, the NO decomposition increased at the beginning of the addition, but this effect decreased with time because of the rapid combustion of the char. 02 did not affect the N20/char reaction.
NOMENCLATURE
Ea
FNO, o(N20, o) ko n PNO, o(N20, o) T W activation energy (kJ/mol) inlet molar flow of NO(N20) (mol/s) preexponential factor (mol/g s bar n ) reaction order inlet partial NO(N20) pressure (bar) temperature (K) char weight (g)