Downdraft Gasifier

The National Renewable Energy Laboratory (Solar Energy Research Institute at that time) designed, built, and operated a 0.9-t/day prototype, downdraft biomass gasifier between 1980 and 1985 (Reed, Levie, and Markson, 1984; Schiefelbein, 1985; Babu and Bain, 1991). In 1985, Syn-Gas, Inc., scaled this process to a 22-t/day plant to develop the concept for the commercial produc­tion of methanol. Feedstocks included wood chips, urban wood waste, and densified RDF. Tests in the 22-t/day plant at 870 to 930°C with cedar wood feedstock and oxygen gave 87 to 91% carbon conversions and dry gas analyses of 39 to 45 mol % carbon monoxide, 24 to 30 mol % carbon dioxide, 5 to 6 mol % methane, and 21 to 22 mol % hydrogen; the remainder was C2-C3 hydrocarbons. The product gas had a lower heating value (wet) of 8.3 to 9.8 MJ/m3 (n).

Directly Heated, High-Temperature, Steam-Oxygen Fluid-Bed Gasification

The Rheinbraun High-Temperature Winkler process is an outgrowth of the successful operation of two atmospheric Winkler gasifiers operated on lig­nite feedstocks in Germany from 1956 to 1964 with a combined capacity of 34,000 m3/h of synthesis gas, and subsequent operation of a 1.3-t/h pilot plant beginning in 1978 (Schrader et ah, 1984). The process was developed by Rheinische Braunkohlenwerke AG and consists of gasification in a pressurized fluid-bed system supplied with oxygen and steam. Operating pressures and temperatures range up to 1013 kPa and 1100°C. The operating results with lignite at 1013 kPa and 1000°C, and oxygen and steam at 0.36 m3 (n)/kg and 0.41 kg/kg of dry lignite, gave 96% carbon conversion and a combined hydrogen-carbon monoxide yield of 1406 m3 (n)/t. At this steam-to-lignite ratio and an exit gas temperature of 900°C, the raw gas contained about 2 mol % methane. These tests provided the information and data needed to construct a demonstration plant to produce 300 million m3 (n)/year of synthesis gas for methanol synthesis at Rheinbraun’s facility. Feedstock tests were con­ducted for customers worldwide with wood, peat, lignite, and coal feedstocks. Rheinbraun reported that each of these feedstocks is suitable for gasification by their process. Wood, especially, can be converted at high reactor through­put rates.