Model for NO formation in recovery boilers

This paper presents a model formation and reduction in recovery boilers. Th e model consists of the following parts: N release during black liquor pyro lysis, NO formation during char combustion, volatile NO formation, NO reduc tion, and NO formation from combustion air Nitrogen release during pyrolysi s is divided into two parts: devolatilization and extended pyrolysis. Durin g devolatilization the fractional nitrogen release is directly proportional to the fractional carbon release, and nitrogen is released as NH3 and N-2. During extended pyrolysis, small amounts of nitrogen are released as N-2 T he formation of NO from char is modeled to depend on whether or not O-2 rea ches the char surface. For the oxidation of the reactive volatile N interme diate NH3, global gas-phase reactions are used. NH3 destruction and oxidati on is catalyzed by Na2CO3 and kinetic expression for the reactions in the a bsence and presence of O-2 are given based on fixed bed reactor experiments . For NO reduction, homogeneous reactions and two heterogeneous processes f or NO reduction are included: reduction by black liquor char and fume parti cles. Laboratory experiments suggest that part of the NO may beformed from the nitrogen in the combustion air.