Ceramic foam low emissions burner for natural gas-fired residential

Abstract

An atmospheric reticulated ceramic foam burner which is retrofittable into existing residential heat exchanger designs has been developed to reduce NO.sub.x and CO emissions. It is operated in a blue flame or substantially radiant mode. The ceramic foam tile used is a three dimensional, web-like structure composed of ceramic struts and voids (or pores) which is permeable and rigid and can withstand the high temperatures found in domestic burners. The foam tile is positioned over a manifold, and is the outlet for the manifold. The manifold inlet is a venturi so that incoming gas is mixed with air in the correct range of proportions before passing through the foam. The pressures used, relative to tile porosity, are such that the gas-air mixture does not burn until it has passed all the way through the foam tile, resulting in a flame above the tile. Additional quantities of (secondary) air can be introduced around the burner to mix and burnout the products of combustion. Thus, by the time of burning, the air-gas mixture has been thoroughly mixed so that the flame can provide complete combustion, thus reducing emissions. In one modification of the invention one or more screens can be placed over the outlet of the foam tiles. In another modification, a series of holes pass through the tiles. Both modifications serve to further mix the air and gas before combustion.