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Title	Enhanced NOx Reduction in Staged Combustion: Technical Application of Premix Technology in Boilers
Creator	Haumann, J.; Knopfli, A.; Sattelmayer, T.
Publisher	Digitized by J. Willard Marriott Library, University of Utah
Date	1994
Spatial Coverage	presented at Maui, Hawaii
Abstract	This paper describes a new approach to the reduct ion of the NOx emissions of oil-fired furnaces (oil no.2 and no.6). The potential of air-staged combust ion was investigated in an experimental and theoretical research program showing a clear advantage for strong air preheat and the use of a premix burner in the first fuel-rich stage instead of a conventional diffusion burner. Using a premix burner (100kWth), the optimum emissions were less than 60% of those from the best diffusion flame in the presence of fuel bound nitrogen. Optimum residence times under substoichiometric conditions were found to be only 100-l50ms. Based on the positive results, this novel technique was developed on an industrial scale using a 2-stage-process for medium size boilers, while large scale power plant boilers will require a 3-stage combustion system. In a cooperative project between a power utility and ABB, a pilot plant of 10MWth was built and intensively tested. The influence of air preheat , oil quality, load variations, primary and secondary equivalence ratios were investigated in a parametric study. Optimum emissions of 27-47ppm (3% 02) for oil no.2 and 04-119ppm NOx for oil no.6 were measured in a load range of 3-10.5MWth while CO and UHC emissions were negligible. A residual 02 content of 0.5-1 % in the stack could be established while maintaining low levels of soot emissions. Based on these results, the potential of the large scale 3-stage process could be estimated to be <=75ppm NOx for a heavy fuel oil with 0.5%N.
Type	Text
Format	application/pdf
Language	eng
Rights	This material may be protected by copyright. Permission required for use in any form. For further information please contact the American Flame Research Committee.
Conversion Specifications	Original scanned with Canon EOS-1Ds Mark II, 16.7 megapixel digital camera and saved as 400 ppi uncompressed TIFF, 16 bit depth.
Scanning Technician	Cliodhna Davis
ARK	ark:/87278/s63n25zc
Setname	uu_afrc
ID	7802
Reference URL	https://collections.lib.utah.edu/ark:/87278/s63n25zc

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Title	Page 13
Format	application/pdf
OCR Text	Show 13 The actual measured NOx values for oil no.2 are shown in this diagram in order to illustrate the thermal NOx-production. No thermal NOx can be found at high recirculation rates (low flame temperatures). Hence the difference NOx - NOxo is a measure for the thermal NOx-production taking the minimum measurement values as a baseline (NOxo). This difference is shown here also for heavy fuel oil. Due to radiation cooling it is to be expected that lower recirculation rates will be necessary for the lower oil qualities. In our case exhaust gas recirculation of 20-2S% for oil no.2 and only lS% for oil nO.6 are sufficient without a significant increase of NOx. IV.4.1nfluence of the primary air preheat The preheat temperature of the primary air is usually fixed by the heat extraction in the impingement cooling of the precombustor . An electrical air preheater was installed in the primary air flow in order to extend the investigated range of the preheat temperatures. This measure also enabled the temperature of the primary air to be controlled independently of the load. As can be seen from the fig. 11, the NOx-emissions are essentially governed by the primary air preheat and only weakly affected by the load variation. The dependence on load is mainly caused by the atomization quality(e.g. droplet size). This finding was verified also in further tests not described here. The lab investigations which were performed up to 47S-S00°C have shown that the NOx concentration continually decreases up to the explored temperature maximum and therefore, a minimum air preheat of T1 ~ SOO C should be striven for. With this preheat value, NOx-emissions of about 100ppm (norm. to 3% 02, heavy fuel oil) are already achievable with the existing test rig. Due to the relatively strong dependence on the primary air preheat, a further reduction of the NOx-emissions can be expected for an optimized premix burner at all load ranges, if air temperatures of about 500°C can be realized.
Setname	uu_afrc
ID	7796
Reference URL	https://collections.lib.utah.edu/ark:/87278/s63n25zc/7796