Design and characterization of a two-stage Hencken burner for combustion of solid fuels

During pulverized coal (pc) combustion process, the solid fuel can transition from a reducing to oxidizing environment, and this transition is expected to influence a number of processes, including ignition, flame stability, pollutant formation and char burnout. However, laboratory coal studies typically address either oxidizing or reducing environments, and the effects of this transition are not considered. To consider the effects of transition, a new Hencken burner is developed that allows coal particles to experience a reducing environment followed by a transition to an oxidizing environment (i.e. reducing-oxidizing). This paper describes the characterization of this two-stage Hencken burner. In addition, in a unique approach to operation of the Hencken burner, the flame configurations are operated as both normal and inverse flames, and the stoichiometric mixture fraction is varied to obtain stable soot-free flames. Gas temperatures and oxygen concentrations for the Hencken burner are measured under reducing-to-oxidizing and purely oxidizing environments. The result shows that stable flames with well-controlled conditions and uniform temperatures and species concentrations can be achieved in both flame configurations, and that the inverse flame configuration with high Z_st is more appropriate for sooty-fuels such as ethylene. The two-stage Hencken burner provides a unique system for evaluating the effect of the reducing-oxidizing transition on coal combustion.