Model for NO formation in recovery boilers

This paper presents a model formation and reduction in recovery boilers. The model consists of the following parts: N release during black liquor pyrolysis, NO formation during char combustion, volatile NO formation, NO reduction, and NO formation from combustion air Nitrogen release during pyrolysis is divided into two parts: devolatilization and extended pyrolysis. During 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 The formation of NO from char is modeled to depend on whether or not O-2 reaches the char surface. For the oxidation of the reactive volatile N intermediate NH3, global gas-phase reactions are used. NH3 destruction and oxidation is catalyzed by Na2CO3 and kinetic expression for the reactions in the absence and presence of O-2 are given based on fixed bed reactor experiments. For NO reduction, homogeneous reactions and two heterogeneous processes for NO reduction are included: reduction by black liquor char and fume particles. Laboratory experiments suggest that part of the NO may beformed from the nitrogen in the combustion air.