Abstract: A biomass gasification method and apparatus employs a rectangular design and linear injection of feedstock to allow compact modular design to accommodate a wide variety of energy demands with a single-size production unit which can be stacked with others for different energy output demands. The method and construction make use of a long and narrow grate in combination with an air supply system and producer gas return system which uses a down-draft technique to restrict and control by-products and to improve the efficiency of the energy conversion system.