Gasification of lignite in a dual fluidized bed gasifier — Influence of bed material particle size and the amount of steam

The dual fluidized bed steam gasification system, developed by the Institute of Chemical Engineering at Vienna University of Technology, was originally developed for the utilization of woody biomass as feedstock, but during practical operation of the industrial sized plants of this system it turned out that fuel flexibility is the key issue for economic breakthrough. Therefore, gasification tests were carried out with lignite at different operating conditions at the dual fluidized bed pilot plant at Vienna University of Technology. Tests were performed with an input fuel power of 90 kWth. Olivine was used as bed material and the applied particle size was 370 and 510 μm. The steam-to-carbon ratio was varied between 1.3 and 2.1 kgH2O/kgcarbon. In addition to standard online measurements of the permanent gas components of the product gas, impurities like NH3, H2S and tar were also measured. It turned out that a lower amount of steam for fluidization caused a better performance of the gasification reactor in terms of product gas yield, carbon conversion and water conversion. The high catalytic activity of the lignite ash was also a reason for the high product gas quality producing low amounts of condensable hydrocarbons, like tar.