Partially -premixed combustion in porous radiant burners
Abstract
Inert porous radiant burners are commonly employed in materials processing and manufacturing (drying, cooking, etc.). In spite of this extensive use, little knowledge was available concerning the operating characteristics and flame structure of such burners until recently. The advent of a new generation of natural gas-fired burners that include an active matrix introduces further challenges and opens new areas of research. The first catalytic heaters were diffusion-type; recent attempts to improve performance suggest that higher firing rates and efficiency can be attained in a partially-premixed mode. Yet, the effects of the partially-premixed air on the catalytic combustion process have to be determined. The objective of the present work is to investigate theoretically and experimentally the performance characteristics of premixed and partially-premixed inert porous burners. A one-dimensional model for solving the conservation equations inside a porous material, including the detailed chemical kinetics for methane-air mixtures, is developed by modifying an existing burner-stabilized flame computer program. The chemical reactions are modeled using the GRI-Mech 2.11 mechanism. An energy equation for the solid matrix is introduced to the original system. The convection heat transfer between the gas and solid phases is characterized by means of a volumetric heat transfer coefficient. The results of the experimental and theoretical investigation on metal-fiber porous radiant burners are presented. The experimental burner consisted of a specially-designed multi-diffuser housing capable of producing a very uniform gas flow distribution. Commercial-grade methane is used to simulate the natural gas. Radiation efficiency, gas and solid temperatures, and pollutant emissions data are obtained at atmospheric pressure for firing rates that cover the industrial operation range of interest. Fuel rich equivalence ratios naturally lead to a partially-premixed flame. It was expected that fuel lean and stoichiometric conditions would yield a conventional premixed flame structure. However, the heat transfer to the solid matrix led to some degree of partially-premixed burning for these conditions as well. An extensive parametric study is carried out to investigate the effects of several parameters on a model burner performance. Emphasis is placed on thermal performance and parameters such as temperature distributions, flame location, the radiation efficiency and pollutant emissions.
Degree
Ph.D.
Advisors
Gore, Purdue University.
Subject Area
Mechanical engineering|Chemical engineering
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