Char Nitrogen Conversion to NO_x in a Fluidized Bed

Abstract

Continuous measurements of the CO, CO₂ and NO emissions were made during the burning of batches of char particles of different diameters at temperatures of 750 K to 1000 K. The fractional conversion of fuel nitrogen to NO was derived from the experimental data as a function of char burnout, and shows that the fraction of char-N converted to NO increases with increasing char burnout and with increasing temperature. A simplified model was developed to simulate the fate of char-N during char combustion. A closed form approximate expression was derived for NO emission which lakes into account the influence on the NO formation of the parallel diffusion and chemical reaction of the O₂ into the pores, and the NO partial destruction by the reaction with CO (carbon as catalyst) or with carbon as it diffuses out of particles. The NO emission, expressed as a function of two Thiele moduli, can be used to estimate NO emission for a wide range of parameters. The temperature dependence of NO emission which passes through a maximum at about 1000 K. as well as the dependence of the fractional char-N conversion on char combustion can be explained using the model.

Key words:

• Pollutants
• Coal combustion
• Modeling and simulation