Detection of HNCO during the Low-Temperature Combustion of Coal Chars

Abstract

Emissions of nitrogen oxides (NO x ) from combustion sources are significant contributors to a number of detrimental atmospheric environmental effects, including acidic deposition processes and production of photochemical smog. 1 Combustion of coal, both in pulverized-fuel fired furnaces and, increasingly, in fluidized-bed combustors, is an important anthropogenic source of NO x , 1 and in the latter case of nitrous oxide (N 2 O), which has a large greenhouse warming potential. The predominant source of these emissions is the nitrogen bound in the organic structures present in all coals. 2 A significant proportion of coal-bound nitrogen is released during the initial stages (devolatilisation) of combustion as simple gas-phase species (HCN, NH 3 ) and in more complex organics, which are categorized as tar molecules. [3][4][5][6] Oxidation of these nitrogen-containing species results in the conversion of some coal-bound N to NO and some to N 2 . Proportions of NO and N 2 formed are a function of the overall stoichiometry, and the chemistry of this volatile-N is relatively well understood, based on extant models of fuel-N chemistry. 7 However, not all coal-N is volatile, and, depending on the coal, varying amounts are retained in the char matrix, and only released during burnout of the char. The fate of this char-N is much more uncertain. This is although, under staged combustion conditions such as those found in low-NO x burners, it is probable that it is the major source of NO x .Molecular nitrogen (N 2 ), NO, and N 2 O are generally agreed to be the most significant products of char combustion. In fact, for many reported experiments, only two of these products have been measured, and it is assumed that the third product (usually N 2 ) completes the mass balance.

Isocyanic acid in the atmosphere and its possible link to smoke-related health effects

“…In this case the precursors are likely to be nitrogen heterocyclic compounds, although specific precursors have not been identified. Further work on the combustion of coal char at 600°C measured the HNCO emission as 12 AE 4.5% of original fuel nitrogen (26).…”

Isocyanic acid (HNCO) and its fate in the atmosphere: a review

“…Emissions of HNCO into the atmosphere have been quantied from a variety of anthropogenic and natural sources through laboratory experiments and eld measurements. The primary emission sources include biomass burning, 19,20,22,[26][27][28][29] fossil fuel combustion (coal, gasoline, and diesel), 19,[30][31][32][33][34][35][36][37] and cigarette smoke. 19,38,39 The secondary production of HNCO, through the oxidation of amines and amides is also a potential source.…”

“…HNCO has been detected in exhaust gases from three major fossil fuels: coal, 19,31,32 gasoline, 33,37 and diesel 30,34,36,37 (Table 3).…”

Numerical modeling of cloud chemistry effects on isocyanic acid (HNCO)

“…Measurements of biomass burning plumes from controlled laboratory measurements have revealed that HNCO can reach levels as high as 600 ppbv near fires [ Roberts et al ., ]. HNCO is a product of combustion from low‐temperature burning of coal [ Nicholls and Nelson , ], biomass burning [ Roberts et al ., ; Veres et al ., ], and exhaust from new diesel engines that use urea‐selective catalytic converters [ Krocher et al ., ; Chen et al ., ], which are used to reduce NO x emissions. Recent results have shown that even untreated diesel engines emit small amounts of HNCO [ Heeb et al ., , ].…”