The gasification of fresh herbage (grass) in supercritical water has been optimized in a lab­scale apparatus and then has been tested in the pilot­plant scale. A high gasification yield is possible. The product gas consists of hydrogen, methane and some short chain hydrocarbons. The pretreatment of fresh herbage is complex. Sand should be removed by washing, size reduction with cutting devices and dilution to less than 10 wt. % DM. An enzymatic treatment at elevated temperatures for 24 h is useful for the subsequent gasification. Optimized process conditions are temperature of 650 °C, pressure of 28 MPa and mean residence time of 2 – 4 min; the resulting gasification yield of 98 % is high, also the hydrogen concentration. CO2 can be removed by a water scrubber at a pressure of 10 – 20 MPa. Due to technical boundaries the reaction temperature in the pilot­plant experiments was lower and consequently the gasification yield was lower.

Proceedings of the 18th European Biomass Conference and Exhibition, 3-7 May 2010, Lyon, France, pp. 562-566