Diluted exhaust from a selection of Air Force ground support vehicles was subjected to gravimetric, carbon, and size distribution analyses in September 1999. The vehicles operated on diesel and JP-8 fuels. In most cases, the engines involved were similar to civilian counterparts. The tests involved "low" and "high" idle settings but no external loads were imposed. Particle size distribution data, obtained over the 10 to 352 nanometer diameter range using an SMPS instrument, showed that the relative number count of accumulation mode particles increased with respect to nucleation mode particles as the engine rpm increased. The SMPS distributions often explained the main variations in the integrated PM 2.5 gravimetric mass data. Particulate mass derived from the SMPS data and from cascade impactor measurements were well correlated (regression slope 1.02). Empirically determined "elemental" carbon (EC) and "organic" carbon (OC) were the main constituents of the PM 2.5 gravimetric mass (regression slope 0.89). EC contributed less, and OC contributed more to the PM 2.5 mass than was found in some recent studies of exhaust from vehicles operated under external loads. The observed particle nucleation modes were attenuated by coagulation with accumulation mode particles, but it does
SUMMARYConventional fuel rich coal reburning relies upon two primary mechanisms: 1) the reaction of coal volatiles with NO to form HCN, which can subsequently decay to molecular nitrogen (N 2 ) given sufficient residence time at a suitable temperature; and 2), additional NO reduction by reaction of NO with carbon on the coal char surfaces. Recent research has indicated the possibility of HCN release as an additional product during char oxidation, and under appropriate conditions this HCN could provide a third mechanism for reducing NO to N 2 .Lab-scale experiments and kinetic calculations were carried out to identify conditions that might lead to effective coal reburning under oxidizing conditions. The results of the kinetic calculations indicated that, depending on the temperature, oxygen concentrations in the range of 200 ppm to 1000 ppm (0.1%) would provide the greatest levels of gas phase reduction of NO using HCN, and that reductions between 60-80% are possible (in the absence of heterogeneous effects).Experiments using pulverized coal in a laminar flow drop tube furnace demonstrated NO reduction levels as high as 40-50%; however, these experiments were shown to have limited gas/coal contacting. The two different experimental configurations used demonstrated a clear dependence of observed NO reduction efficiency on gas/coal loading. The laboratory results were thus extrapolated to gas/solid loadings more typical of a utility boiler, and this extrapolation indicated that greater levels of NO reductions may well be achievable in a coal-fired boiler application.It was concluded that, given a knowledge of the location of high NO concentrations (obtained for example by CFD modeling), these regions could be targeted with coal injection under slightly oxidizing conditions to obtain NO reductions in excess of the 40-50% levels obtained in the lab-scale experiments. It is recommended that further testing under conventional pulverized coal combustion conditions be pursued to further verify this assertion.3
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