syngas

syngas, mixture of primarily hydrogen and carbon monoxide that often also contains some amount of carbon dioxide and methane and that is highly combustible. Syngas is used primarily in the production of hydrocarbon fuels, such as diesel fuel and methanol, and in the production of industrial chemicals, particularly ammonia. Syngas produced from waste materials and other biomass is considered a form of renewable energy.

The utility of syngas as a fuel was realized in Germany during World War II, when gasoline shortages affected transportation for both the military and civilians. At the time, it was known that coal could be converted to liquid hydrocarbons through either the Bergius process, developed by German chemist Friedrich Bergius, or the Fischer-Tropsch (FT) reaction, developed by German chemists Franz Fischer and Hans Tropsch. In the Bergius process, liquid hydrocarbons are produced through hydrogenation of coal dust at high temperature and pressure. In the FT reaction, a mixture of carbon monoxide and hydrogen is converted into liquid hydrocarbon at elevated temperature and normal or elevated pressure in the presence of a catalyst of magnetic iron oxide. Syngas produced by FT synthesis served a critical role in fulfilling fuel needs in South Africa in the 1950s.

Today most syngas is generated via thermal conversion of biomass by gasification, particularly by steam reforming of methane or by partial oxidation. At high temperatures and in the presence of steam or oxygen, gasification converts carbon-containing materials into hydrogen, carbon monoxide, and carbon dioxide, without a need for combustion. The conversion rate of hydrogen- and carbon monoxide-rich biomass into syngas can exceed 99 percent. Following production, however, syngas must be cleansed of harmful materials, such as hydrogen chloride and coal tar. Clean syngas can be burned like natural gas, with a portion going to power the gasification plant and the remainder being sold to utility companies, which also use it primarily for producing electricity.

Syngas is an appealing form of energy for several reasons. In particular, it is renewable, is associated with reduced carbon emissions relative to other energy-generation technologies, and can effectively convert problematic wastes into fuel. However, hydrogen levels and the presence of moisture and tars in the starting components for gasification can be problematic. Hydrogen gas is highly combustible—more so than other fuels used to power internal combustion engines. Thus, to run on syngas, such engines must be modified to minimize the risk of phenomena such as preignition and backfiring, and, even with such modifications, engine output may be reduced significantly.