Atmospheric entrained-flow gasification of biomass and lignite for decentralized applications

The present study deals with the development of a small-scale entrained-flow gasification technology for the decentral use of biomass. Gasification experiments with woody biomass in a wide range of particle diameters dS in the fractions 0.04 < dS < 0.11 mm, 0.20 < dS < 0.25 mm, 0.25 < dS < 0.50 mm, and 0.50 < dS < 1.0 mm were carried out in an atmospheric electrically-heated entrained-flow gasifier at temperatures between 950 and 1100 °C. Power plant lignite in the fraction 0.05 < dS < 0.08 mm was gasified as well for comparison. These low temperatures were chosen in order to verify that an entrained-flow gasification technology operating at mild conditions can be developed. Low investment costs combined with the production of a tar-free syngas make this technology option attractive especially for decentralized applications (< 5 MW fuel input power). The production of a high syngas quality during autothermal operation has still to be demonstrated. A short review of studies prepared for entrained-flow gasification of biomass since 2006 points out the state of the art and most important findings. The concentrations of H2, CO, CO2 and N2 together with carbon conversion, cold gas efficiency and syngas yield resulting from the present work are reported and compared to the respective literature values. Carbon conversion, cold gas efficiency, and specific syngas volume varied strongly with temperature and particle diameter showing values between 63 and 100 wt%, 14 and 61%, and 0.6 and 1.4 m3 kg− 1 (STP), respectively. With the present set up, high cold gas efficiencies were only obtained at temperatures of 1100 °C and particle sizes of less than 0.2 mm. Particle residence times in the gasifier were measured at 25 °C for three sawdust fractions and varied between 1.4 and 3.3 s. These measurements indicate that the particle residence time is not equal to the gas residence time in general. A model for the calculation of particle velocities and residence times at ambient and gasification conditions is presented. The interrelationships between particle residence time, particle diameter, carbon conversion, and temperature are discussed.