OCR Text |
Show combustion efficiency in the cement kiln is of paramount importance. Furthermore, the flames must meet stringent requirements with respect to heat release profiles and flame shape, to ensure acceptable product quality :lnd overall process efficiency. High combustion air preheat levels are used, resulting in high flame temperatures and consequential high rates of thermal NOx formation. Legislation on NOx emissions will be applied to the cement industry in the near future. Consequently, techniques for reducing the NOx emissions by combustion modification require evaluation and potential effects on clinker quality and process efficiency needs to be addressed. To address these factors, a consortium of cement manufacturing companies and associated research organisations was formed. This consortium included: Blue Circle Industries, Castle Cement, ENCI/Cimenteries CBR, Ciments Fran~ais, FCT, Fincem, Heracles, Holderbank, IFRF, ltalcementi, KHD, Lafarge Coppee Recherches, Pillard, Unicem and VDZ [1]. In C<K>peration with the consortium members, an experimental programme was thus formulated, funded by the consortium and executed at IJmuiden, to evaluate methods of NOx reduction applicable to cement kilns [1]. The objectives of the experimental campaign were: • to improve the understanding of cement kiln flames • to determine the influence of burner design, operation and fuel type on thermal ~fficiency and NOx formation • to create engineering guide-lines for the effect of fuel variation, fuel efficiency, heat transfer and NOx characteristics • to compare the performance of scaled down versions of industrial burners To satisfy the objectives of the experiments, a semi-industrial scale cement kiln simulator facility of 0.78 m internal diameter was designed and constructed (see Figure 6). The experimental facility consists of two main features: a preheater which provided combustion air at temperatures up to 10000c and the experimental kiln simulating the burning zone (LID = 12) of an industrial kiln with respect to wall temperature distributions and heat fluxes. Four burners were studied during the experimental campaign: a generic mono-channel burner, ao flexible generic multi-channel burner and two scaled down versions of industrial multi-channel burners. The two generic burners were scaled from full scale burners uslng a constant specific mqmentum criterion. |