Down draft gasifier

In a down draft gasifier, the primary gasification air is introduced at or above the oxidation zone in the gasifier. The producer gas is removed at the bottom of the apparatus, so that fuel and gas move in the same direction. The main advantage of down draft gasifiers lies in the possibility of producing a tar-free gas suitable for engine applications. A major drawback of down draft equipment lies in its inability to operate on a number of unprocessed fuels. Minor drawbacks of the down draft system, as compared to up draft, are somewhat lower efficiency resulting from the lack of internal heat exchange as well as the lower heating value of the gas. Besides this, the necessity to maintain uniform high temperatures over a given cross-sectional area makes impractical the use of down draft gasifiers in a power range above about 350 kW (shaft power).