Abstract: The traditional zone-by-zone computational approach neglecting particles burnout calculation in furnace heat transfer design is applicable to non air staged combustion. With the extensive air staged low NOx combustion technology, advanced coal combustion model integrated with the heat transfer approach to determine the burnout distribution along the furnace height is of great significance to improve the design accuracy of steam temperature in platen super heater or radiant reheater in the upper zone of the furnace. An improved zone-by-zone computational approach incorporated with a more detailed coal combustion model is developed to determine burnout rate of bituminous coal in tangentially fired furnace with air staging, field tests is carried out in the case boiler covering the regular range of variation of operating loads. The tested furnace conditions are used as inputs for the zone-by-zone computational approach coupled with combustion model to predict coal burnout, results of the simulation provide a clear insight into the burnout processes in air staging combustion. The effects of combustion mode and surface reaction kinetics parameters on burnout are also investigated. Results from the simulations are compared against the measured values, showing a reasonable agreement in most test scenarios. Thermal annealing, ash inhibition and inhomogeneous distribution of oxygen content in flue gas are the main cause of the model error. The computational complexity in the incorporated burnout model are equivalent to that of the traditional zone-by-zone computational approach, and suitable for engineering application.

Key words: power plant, boiler, air staging, coal combustion, modeling, burnout