OCR Text |
Show than the new source performance standard for a natural gas fired boiler. Limited published data (1,2) show similar incineraror NOx emissions. Startup observations Occasional periods of high NOx emission were observed during the startup period before the trial burn. Attempts were made to correlate the NOx emission rates with operating conditions. However, there are many variables in a commercial incinerator due to multiple burners, multiple fuels on each burner, and the varying composition of liquid and batch-fed solid wastes. The result was a lack of correlation between NOx emission and variables that might be considered significant. There was no correlation of NOx with kiln or afterburner temperature (Figure 3). Also, there was no simple relationship between NOx level and afterburner exit oxygen (Figure 4). The effect of other uncontrolled variables overwhelms the temperature and oxygen dependence of NOx formation under typical conditions. There was no correlation of NOx with total solids feed rate. The solid wastes vary widely in composition, in heating value, and in burning rate which makes total mass of solids feed a poor indicator. Also, low conversion efficiency of fuel nitrogen in non-atomized feed streams to NOx is expected. Other correlations were attempted including total aqueous waste feed rate and even including which operating shift was on duty. One definite correlation was that the highest NOx emissions occur when the kiln is being operated on commercial fuel oil and that high NOx emissions are not observed when burning highly chlorinated wastes (Figure 5). A related correlation is that the narrow angle burner nozzles used for melting out slag rings near the kiln discharge result in higher NOx emissions than the wider angle nozzles that spread out the flame near the feed end. This effect of nozzle angle agrees with published observations (3) on other liquid burner applications. Chlorine Several mechanisms were proposed to explain the observed relationship of chlorine to NOx emissions. One effect may be that the chlorine reduces the heat of combustion and reduces peak flame temperature. The calculated effect is small since replacing a hydrogen with a chlorine on a typical compound has a large effect on the mass ratios but has a much smaller effect on the heat of combustion. Another possibility is that chlorine can react in the primary combustion zone and interfere with prompt NOx formation. Obviously an industrial plant is not the ideal setting to verify this possibility. |