Starting in the early 1980s, PRM Energy Systems, Inc., began to market gasifi­cation technology for converting biomass to low-energy fuel gases (Bailey and Bailey, 1996). Several commercial plants based on PRM’s air-blown updraft designs for the gasification of rice hulls have been built and operated in Australia, Costa Rica, Malaysia, and the United States. High-silica ash is a salable by-product. An example of this technology is the plant installed in Mississippi in 1995 for the gasification of 300 t/day of rice hulls. The system converts unground rice hulls to fuel gas (121 GJ/h) for an existing boiler — power island which supplies electric power (5 MW capacity) and 6800 kg/h of process steam for parboiling rice. In operation, feedstock is metered into the gasifier by a water-cooled screw conveyor that discharges into the drying and heating zone of the gasifier. The gasifier is a refractory-lined, cylindrical steel shell that is equipped with a fixed grate at the bottom and is mounted in a vertical position. The gasification process is automatically controlled to maintain a preset first-stage gasification zone temperature. Almost all of the ash is removed from the bottom of the gasifier. The low particulate concentration in the product gas makes it possible to direct-fire a boiler without the use of emission control equipment. Total particulate emissions in the boiler exhaust of this plant were determined to be 0.103 kg/GJ.