Coal combustion models for flame scaling.pdfVIP

Twenty-Second Symposium (International) on Combustion/The Combustion Institute, 1988/pp. 155-164 C O A L C O M B U S T I O N M O D E L S F O R F L A M E S C A L I N G J. s. TRUELOVE Department of Chemical and Materials Engineering The University of Newcastle, NSW 2308 Australia AND R. G. WILLIAMS Electricity Trust of South Australia A theoretical model of a coal flame is applied to interpret and extrapolate pilot-scale test furnace data. The flame model is based on the equations governing conservation of mass, momentum, species and energy and includes physical models for turbulence, volatiles com- bustion, radiation heat transfer and particle dispersion together with phenomenological models to describe coal devolatilization and char combustion. Predictions of flow, temperature and species concentration are compared with measurements in the near-burner ignition zone of pilot-scale and full-scale-boiler flames. Agreement between the predictions and data is gen- erally encouraging. The predictions suggest, and the measurements confirm, that flame char- acteristics near critical ignition are particularly sensitive to burner operating conditions. Test- furnace data for new high-moisture coals are extrapolated to predict flame stability for the thermal conditions in a full-scale boiler. Introduction The testing of new coals in existing full-scale power stations is not practical because of the high cost, and the difficulty in changing and monitoring operating conditions. Consequently, new coals are often tested in pilot-scale combustors. Pilot-scale combustors for flame stability testing typically employ a variable swirl burner and are, ideally, configured to simulate as closely as possible the thermal conditions in a full-scale boiler. Resi- dence-time scaling of the burner and chamber is generally adopted as the best overall approach to achieve similar flame characteristics. 1 However, an exact simulation is not possible due to the