Catalytic unit for gas phase catalysis, more especially for use with wood- and other solid fuel-burning stoves

摘要

Flue gases containing crackable and combustible volatiles e.g. from a wood-burning stove are passed through a catalytic combustor having two spaced catalytic units each having small longitudinally extending catalytic flow passages. Air supplied into a chamber between the two units supports after-combustion of combustible volatiles in the downstream catalytic unit. Some pre-cracking and combustion takes place in the upstream catalytic unit, which serves as a gas collimator and disallows any flow of air from the intermediate chamber into the fire box of the stove, whereby combustion in the fire box can be closely controlled to increase production of combustible volatiles. Each unit may have flow passages which decrease in cross-sectional size and increase in length toward the central portion of the unit, thus encouraging uniformity of flow of the flue gases and of the catalytic reaction over the entire cross section of each unit. The units are surrounded by an air jacket into which air is supplied at one end, and the air is distributed uniformly around the periphery of the intermediate chamber. Each unit has a central bypass opening and a temperature responsive valve which closes the bypass opening when the catalytic unit reaches its threshold temperature of operation. A reflector, preferably with a curved reflective face, reflects radiant heat to the downstream fuel of the combustor, and an exterior heat exchange jacket transfers heat to the surroundings from the hot gases exiting from the combustor. A flame- arresting screen is spaced between the fire box and the combustor to prevent diffusion flames originating in the fire box from lapping on the catalytic flow passages.