| OCR Text |
Show -6- A simplified NOx formation path is shown in figure 2 (6). Most of the gaseous nitrogen pyrolyses either directly or indirectly to HCN. This complex process is not instantaneous but dependent on the conditions in the flame. The HeN then oxidises to NO, figure 3, with this reaction being both temperature and time dependent, figure 4. 2.3 BOx Modelling The above descriptions of NOx formation via the thermal, prompt and fuel NOx routes is a greatly simplified description of extremely complex and still not well understood processes. It therefore follows that modelling these processes is very difficult. Some of the currently available models are capable of predicting the trends of NOx formation with change in flame conditions and fuel type, but the accuracy is poor and sometimes little better than orders of magnitude. Currently, the most reliable methods predicting of NOx emissions from full scale flames is by empirical scale up from test flames. This is the approach adopted in the NOx assessment in section 3. 3. BOx ASSESSMENT The principle objective of the assessment is to establish the reduction in NOx which can be achieved by combustion modifications and to determine whether these modifications will have a detrimental influence on kiln operation and product quality. When undertaking an assessment of this type, it is important that sufficient analysis is undertaken to ensure that the conclusions are representative. However, it is important not to lose the principles in a mass of unnecessary detail. 3.1 SUmmary of the CEMFLAM I Trials The CEMFLAM trials were undertaken on a semi industrial scale kiln O.78m internal diameter and 9.4m long. It was provided with an air heater which could produce secondary air temperature up to lOOOoc and was designed to ensure a fully developed non-swirling, even secondary air flow in the plane of the burner nozzle, figure 5. Four burners were studied during the trials, a generic mono-channel burner, a flexible generic multi-channel burner, a Pillard Rotaflam burner and a KHD burner. These were scaled using a constant specific momentum criterion. All the burners were fired at a constant heat release of 2.5 MW. |
