Formation of NO from combustion of volatiles from municipal solid wastes

An experimental and theoretical study has been performed on the formation o f NO in the combustion of volatiles from municipal solid wastes. Single com ponents and their mixtures were burned in a small-scale, fixed-bed reactor. Numerical simulations using the opposed flow diffusion flame program OPPDI F were performed to obtain a further understanding of the experimental resu lts. Conversion factors for fuel-N to NO were determined for single compone nts of newspaper, cardboard, glossy paper, low-density polyethylene (LDPE), and poly(vinylchloride) (PVC) and their mixtures, using gases with oxygen concentrations of 12, 21, and 40 vol %. For single components experiments a t 100 vol % oxygen were also performed. The conversion factors for paper an d cardboard varied from 0.26 to 0.99. The conversion factor for LDPE and PV C varied from 0.71 to 10.09 and 0.04 to 0.37, respectively. Conversion fact ors higher than 1.0 in the case of LDPE clearly show that NO is formed by t hermal and/or prompt mechanisms. For mixtures, calculated conversion factor s (based on a weighted sum of the conversion factors for single components) were compared with the experimentally determined conversion factors. Mixtu res of paper and cardboard only gave different conversion factors with 40 v ol % of oxygen. For mixtures of paper/cardboard and plastics, however, sign ificant differences in the conversion factors were observed at all oxygen c oncentrations, when comparing experiments on a mixture of paper and plastic s with the weighted sum of the single components. The explanation is found in the different combustion properties for paper/cardboard and plastic, whi ch in this case make the formation of thermal NO from LDPE more favorable f or the single component than in mixtures with other components. The simulat ions with OPPDIF confirmed the trends observed experimentally, and allowed an assessment of the contribution of the different mechanisms of NO formati on. (C) 2001 by The Combustion Institute.