Burners Producing Large Excess Enthalpies

Abstract

The principle of heat recirculation in combustion systems is analyzed for the case where no direct mixing of reactants and products occurs. The concept leads to a general treatment, the restriction of associating flame temperature with the initial mixture stoichiometry and fuel heating value being removed in burners which rely on an enthalpy excess over initial and final states. This has important consequences particularly for reactants of very low heat content. Otherwise nonflammable mixtures may be burned by recirculating heat so as to increase the temperature in the reaction zone without generating a high final temperature. Idealized models are used to demonstrate the potential rewards from application of the principle in the areas of power generation (including direct energy conversion) from gases of low heat content, fuel saving, flame stability (flammability limits and maximum mass throughput rates) and pollutant emission. Experimental results from a simple burner incorporating a counterflow heat exchanger demonstrate the principle.