Contribution to the Understanding of Secondary Pyrolysis of Biomass-Based Slurry under Entrained-Flow Gasification Conditions

The objective of this study was to gain insight into the secondary pyrolysis of biomass-based slurry under entrained-flow gasification conditions. The focus was set on the types of solid products from secondary pyrolysis, their mechanism of formation, and subsequent conversion behavior. Primary chars and pyrolysis oils from wood and wheat straw were produced in a screw pyrolysis reactor. A suspension fuel (slurry) was prepared composed of primary straw char and straw pyrolysis oil. A drop tube reactor was used to study the secondary pyrolysis of the different fuels at 1200 degrees C and 3 s residence time. The secondary pyrolysis of both chars yielded approximately 60 m% of secondary char. While the wood char reactivity was unchanged by the secondary pyrolysis, the straw char showed signs of massive deactivation, which is most likely explained by the loss of catalytic activity. The secondary pyrolysis of both pyrolysis oils yielded approximately 20 m% of secondary char and soot. Cenospheres could be identified with diameters close to the initial droplet diameter. Oil cenospheres and soot had similar chemical compositions but showed very different reactivities, which is likely to be explained by their different structures. The secondary pyrolysis of the straw-based slurry showed results similar to those of the secondary pyrolysis of oil with primary char particles being embedded in the cenosphere carbon shell. Additional thermogravimetric measurements revealed possible conversion mechanisms of cenospheres from oil and slurry feed.