An Engineering Approach for Estimating the Formation of Nitric Oxide from Fuel‐Nitrogen

Abstract

Explicit approximate equations for estimating the conversion factor of fuel‐nitrogen into nitric oxide are presented. They depend on the fuel‐nitrogen mole fraction, the initial nitric oxide mole fraction, and the kinetics‐equilibrium mole fraction of nitric oxide. This last parameter expresses a limiting value of fuel‐nitrogen conversion; it includes the complex nitrogen chemistry and depends thus on combustion conditions. Experimental results demonstrate that the kinetics‐equilibrium mole fraction for fuel‐lean and high‐temperature conditions can be well estimated by the chemical‐equilibrium mole fraction, but for lower temperatures the kinetics‐equilibrium mole fraction has to be described by other correlations.

On the Impact of Non‐CHO Elements on Fuel Properties in Waste Incineration

“…Moreover, as illustrated by Eq. (3), χ NO can also take negative values if fuel‐nitrogen is introduced into a flue gas containing nitric oxide; this is the basis for the selective non‐catalytic reduction (SNCR) process [2, 3]. If the formation of nitric oxide is suppressed by in‐furnace measures, χ NO can be small and negligible (consistent with the ‘standard’ assumption).…”

“…Nitrogen monoxide (NO) is the prevalent oxide of nitrogen formed in a combustion process [2, 3]. Since its Henry's law volatility coefficient is very high ( ≈ 29 000 bar; for comparison: ≈ 4600 bar; ≈ 2300 bar [8]), absorption is not of technical interest so that other technologies are typically applied to suppress its formation, e.g., by low‐NO x burners or staged combustion, or to remove it from the flue gas by selective catalytic (SCR) or non‐catalytic (SNCR) reduction [4].…”

“…Likewise, the conversion factors of halogen compounds are: $${\chi }_{{X}_2} = ( {2 \cdot {y}_{{X}_2}} )/( {2 \cdot {y}_{{X}_2} + {y}_{HX}} )$$ and $${\chi }_{HX} = 1 - {\chi }_{{X}_2}$$. A similar distribution factor can be defined for nitrogen‐containing compounds, although their formation is dominated by kinetics and not by chemical equilibria [3]. Apparently, the limits of these conversion factors are: 0 ≤ χ j ≤ 1; but it should be noted that this is strictly true only if the oxygen carrier for combustion does not contain the respective elements (see also section 3.4 below and the more detailed discussion in [3]).…”

“…A similar distribution factor can be defined for nitrogen‐containing compounds, although their formation is dominated by kinetics and not by chemical equilibria [3]. Apparently, the limits of these conversion factors are: 0 ≤ χ j ≤ 1; but it should be noted that this is strictly true only if the oxygen carrier for combustion does not contain the respective elements (see also section 3.4 below and the more detailed discussion in [3]).…”

“…The conversion factor of fuel‐nitrogen into nitric oxide may be defined as: $$$$\begin{equation}{\chi }_{NO} = \frac{{y_{NO}^{FG} - y_{NO}^{OC}}}{{{{\Sigma}}{y}_{fuel - N}}}\end{equation}$$$$where $$y_{NO}^{FG}$$ is the resulting mole fraction of nitric oxide in the flue gas after completion of the combustion process; $$y_{NO}^{OC}$$ is the mole fraction of nitric oxide in the oxygen carrier before the combustion process has started (if ambient combustion air is used, $$y_{NO}^{OC}$$ = 0, but if the oxygen carrier is a flue gas from a prior combustion zone, $$y_{NO}^{OC}$$ > 0); Σ y fuel − N is the equivalent mole fraction of fuel‐nitrogen atoms in the flue gas prior to its conversion (for details see [3]).…”