A biomass gasifier is a device that converts solid biomass into combustible syngas through partial combustion at high temperatures, typically 700 to 1200 degrees Celsius (1300 to 2200 degrees Fahrenheit). The syngas, composed primarily of carbon monoxide, hydrogen, and methane, can be burned directly for heat or used to fuel an internal combustion engine for electricity generation. Gasification recovers 60 to 85 percent of the biomass energy content. Biomass Gasification covers the energy context and system integration of gasifiers on a homestead.
The most common small-scale gasifier design is the downdraft gasifier, where biomass and air flow downward through the reactor. Downdraft gasifiers produce syngas with low tar content, typically 50 to 500 milligrams per cubic meter, making them suitable for engine use. Updraft gasifiers produce higher tar content, 10000 to 100000 milligrams per cubic meter, and are better suited for direct combustion. Crossdraft gasifiers are a compact design using a high-temperature reaction zone that operates at 1200 to 1500 degrees Celsius (2200 to 2700 degrees Fahrenheit).
Suitable feedstocks include wood chips, pellets, shells, corn cobs, and agricultural residues. Feedstock moisture content must be below 20 percent for efficient gasification, with 10 to 15 percent being optimal. Higher moisture content reduces the gasifier temperature and increases tar production. Feedstock size should be uniform, typically 2 to 5 centimeters (1 to 2 inches), to ensure consistent gas flow. The All Power Labs Power Pallet, a commercially available micro-scale gasifier, processes 7 to 15 kilograms (15 to 35 pounds) of biomass per hour and generates 10 to 15 kilowatts of electrical power.
Biomass gasification technology dates to the mid-19th century, when producer gas was used for lighting and heating. During World War II, fuel shortages in Europe led to widespread adoption of vehicle-mounted gasifiers, called gasogenes, with over 500,000 units in operation. The FEMA biomass gasifier design, published in the early 1980s, documented a small-scale gasifier design suitable for emergency power generation. Interest in gasification has revived with the rise of distributed renewable energy systems.