Determination of Heterogeneous Reaction Kinetics of High-Temperature Biomass Char

Abstract

The bioliq® BtL-process aims for the production of synthetic fuels from low-grade biomass. The process chain comprises the production of biomass slurry (bio-syncrude) consisting of pyrolysis oil and bio-char, its gasification at pressures up to 80 bar, and the subsequent synthesis of gasoline from syngas. At the Karlsruhe Institute of Technology, KIT, the bioliq® pilot plant with its 5 MWth high-pressure entrained flow gasifier (EFG) is in operation. During the gasification of suspension fuels (slurry) under EFG process conditions, the secondary pyrolysis of bio-char is of major importance for fuel conversion. In this work, experiments to determine secondary pyrolysis and gasification kinetics of bio-char were carried out in the drop-tube reactor, VERA. Pyrolysis was conducted in nitrogen under atmospheric pressure at temperatures ranging from 800 - 1600 °C for a residence time of 200 ms. Gas phase measurements of volatile species as well as collection of secondary chars were employed to gain data on volatile yield and gas phase composition, char chemical composition, morphology and CO₂-reactivity. Intrinsic gasification kinetics of secondary chars were obtained in a pressurized thermogravimetric analyzer (pTGA) as well as a free-fall fixed-bed reactor. Reactivity and activation energies corresponded well comparing both reaction systems. Furthermore, the evolution of reactive surface area during gasification is investigated in a lab-scale quartz glass fixed-bed reactor applying the method of Temperature-Programmed Desorption. The experimental results of all systems are presented and discussed.