OCR Text |
Show -6- In APll and AP13, work was concentrated on the external air staged combustion burner concept whilst the results of the more fundamental studies AP12, are equally applicable to both external and internal air staged combustion burner types. The characteristics of the burner types are shown in figure 3. A summary of some main conclusions of the work are as follows [ 3, 4 and 5 U : - - - It was confirmed - in APll - that at the semi-industrial scale, the external air staged burner could be used to fire a range of eleven coals ranging in rank from sub-bituminous to low volatile bituminous, see figure 4. However, the baseline (unstaged) NO x emissions and the NO emissions reduction achieved was clearly x coal dependant. Detailed measurements made in optimised staged and baseline flames produced with two high volatile bituminous coals, gave information on delayed carbon conversion. - Further experiments - AP12 - using the reduced scale burner/flame i simulator- with fo'ur coals in the range sub-bituminous to low volatile ^bituminous gave data on the effect of primary zone stoichiometry and residence time upon NO emissions reduction for V x each individual coal as shown for example in figure 5. i - The third phase - AP13 - executed again at the semi-industrial i scale with an improved external air staged burner, confirmed that the optimum combinations of primary zone stoichiometry and residence time determined in AP12 for a high and medium volatile bituminous coal, could be achieved with such a burner and did give rise to NO emission reductions predicted. Further confirmation x was also gained on the problem of unacceptable carbon conversion. i - Using the results of semi-industrial scale performance trials and relatively simple scaling considerations, NO emission reduction x performance predictions have been made for full scale versions of |