OCR Text |
Show burner can be employed, introducing into the combustion zone fluegases that have lost considerable thermal energy (enthalpy) by heat transfer in the furnace and beyond, thus reducing reaction temperatures and reactant concentration levels, and this can substantially lower thermal N O x production. However, such forced recirculation is costly. Other approaches to N O x abatement include air staging, fuel staging, and so-called reburning. Lately, interest is developing in serving some of the fuel for non-premix gas burners outside the main burner flow so that this fuel at first mixes, and undergoes some reaction with, product gases in the furnace atmosphere before meeting the combustion air flow. Design principles for a burner incorporating this approach are described in a patent issued to Tokyo Gas (Nakamachi, et al. 1990). The TwinBed II™ burner of the North American Manufacturing Company (North American 1995) employs these principles. The same strategy is facilitated in a research burner designed by the International Flame Research Foundation. The present work has to do with a burner in which all of the fuel gas is served on the outside, directly into the furnace atmosphere, and both fuel and combustion air undergo extensive mixing with furnace gases before meeting each other. The original idea and the initial work came from the Canadian Gas Research Institute (CGRI). Intensive further investigation and development were then pursued at the Centre for Advanced Gas Combustion Technology (CAGCT). This research was sponsored by CGRI, Natural Resources Canada (NRCan, C A N M E T Division), and British Gas pic. A patent on the burner, herein called the C G R I burner, has been applied for (Besick, Rahbar, Becker & Sobiesiak 1995). The research at C A G C T is described in detail in a report (Becker & Sobiesiak 1995) and is the subject of this paper. The specific objectives of the research were to characterize the C G R I burner in respect to: 1. Emissions of N O x and C O 2. Size, shape and appearance of the combustion zone or "flame" 3. Combustion stability 4. Burner interactions in multi-burner operation 5. If possible, effects of scaleup Overall, it was sought to develop guidelines for, (i) the optimization of design in respect to objectives 1-4, and (ii) the management of scaleup. The first form or model of the C G R I burner to be tested was inflexible in all design parameters, very much as an optimized production model might be, but it was soon evident that the optimum design might be significantly different. A second model was then designed for the purposes of the research which permitted wide variation of some of the key parameters, namely the fuel and air port diameters and the fnel port angle. All burners were tested on the C A G C T research furnace, a heavily instrumented furnace which mounts up to three burners of the general type here of interest and permits a wide variation of most of the important furnace operating parameters. The research is significant not only for what it reveals specifically about the C G R I burner but also for drawing attention to the possibilities and challenges of conducting non-premix combustion in a hitherto unorthodox way. In this scheme, as remarked above, both fuel and air are strongly diluted with recirculating combustion products (furnace gases) that have lost 2 |