Role of char during reburning of nitrogen oxides. Tenth quarterly report, January 1, 1996--March 31, 1996

Abstract

The four major tasks conducted during this quarter include: (1) extensive investigation in pore structures of chars before and after reactions with NO , CO,, and 02, (2) effects of pyrolysis time on char reactivities, (3) estimations of rates of NO reduction and mass transfer limitations, and, (4) char reactivities at low feed NO concentrations. Pore structure analyses include BET-N{sub 2}, BET-CO{sub 2}, and DR-CO{sub 2} surface areas, pore size distribution, micropore volume, total pore volume, and average pore radius. These studies suggest that neither BET-N{sub 2} nor DR-CO{sub 2} surface area is a normalization factor of chars of different origin. Parameter study reveals that the effectiveness of heterogeneous reburning strongly depends on variables in three areas: (1) the origin of char, (2) char devolatilization temperature and time, and, (3) the competitions of NO with C0{sub 2} and 02 for the active sites on the char surface. The studies on pore structure and on parameter screening signify the importance of transient kinetics (TK) and temperature programmed desorption (TPD) in the future research. These two techniques all lead to the direct measurements of both stable and reactive surface oxygen complexes, reactive surface area, and the Langmuir-Hinshelwood model which has both importance to both fundamental understanding of reaction mechanisms and to industrial practice. Estimation of rate of NO reduction has been established to include the conversions in the nonisothermal and isothermal regions of the flow reactor, and internal mass transfer limitations. Solving a set of equations simultaneously with MathCad gives frequency factor, activation energy, Thiele modulus, and effectiveness factor.