Reaction Kinetics and Reactive Surface Area during Gasification of High-Temperature Biomass Char with CO2

High pressure entrained-flow gasification is an essential step of the bioliq® process chain. In this BtL process, a suspension fuel (slurry) produced from biomass in a fast pyrolysis process is converted to syngas in an oxygen/steam blown entrained flow gasifier (EFG). During the gasification process the slurry undergoes different processes, i.e. evaporation of the liquid phase, rapid char heat-up, secondary pyrolysis of char and char gasification in a CO2- and H2O-rich atmosphere. The latter is the rate-limiting step; thus kinetic data for secondary char gasification is needed for reactor design.
The lab scale experiments presented are designed to simulate the typical reaction conditions a char particle has to undergo in the EFG process, i.e. secondary pyrolysis is conducted applying high heating rates and temperatures. The determination of heterogeneous reaction kinetics of the so produced secondary char with CO2 and H2O as well as first results on the development of morphology and surface chemistry of the secondary char particle are reported.
Secondary pyrolysis of bio-char was carried out in a drop-tube furnace at KIT. Pyrolysis was conducted in nitrogen under atmospheric pressure at 1600 °C and a residence time of 200 ms. ... mehrGas 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.
Heterogeneous reaction kinetic data for intrinsic gasification rates of secondary high-temperature bio-chars was obtained in a pressurized thermogravimetric analyzer (pTGA) as well as a free-fall fixed-bed reactor. Reactivities and activation energies corresponded well comparing both reaction systems.
Surface chemistry in respect of the evolution of reactive surface area during gasification is investigated in a lab-scale quartz glass fixed-bed reactor. These chemisorption experiments were conducted by applying the method of temperature-programmed desorption. The experimental results of all systems are presented.
The presented research work is part of the research conducted within the “Helmholtz Virtual Institute for Gasification Technology, HVI GasTech” (www.hvigastech.org) which is funded by the Helmholtz Research association, HGF. This international research cooperation has been established to develop a knowledge-based simulation tool for the design and scale-up of technical entrained-flow gasifiers for a wide range of feedstock.