Fast Pyrolysis for the Thermochemical Conversion of Biomass
The purpose of pyrolysis is the thermal decomposition of organic macromolecules in order to obtain solid, liquid, and gaseous products. Fast pyrolysis aims at maximizing the yield of liquid bio-oil. Biomass is transformed into an energy dense and economically transportable intermediate. Different alternatives exist as subsequent processing steps: substitution of fossil oil for heating purposes and catalytic upgrading for the synthesis of chemical substances or energy carriers, e.g. for the use in refineries or directly as fuel for engines. The bioliq® concept is different in that the bio-oil is mixed with the char to produce a stable suspension, which is then useable for pressurized entrained flow gasifiers for the production of synthesis gas. The synthesis gas is an excellent raw material for the synthesis of motor fuels and a variety of useful chemicals.
At KIT, fast pyrolysis is conducted in a twin-screw mixing reactor. Dry and comminuted biomass is mixed with a preheated heat carrier and heated up within seconds. Upon heating, pyrolytic conversion takes place within seconds, the pyrolysis products are separated from the heat carrier material, and quickly cooled down in a quench. The heat carrier material is recirculated and heated again in order to achieve a continuous pyrolysis process. In the product recovery section, solids are separated from the pyrolysis products and subsequently liquid products collected in a two-step fractionated condensation.
Fast pyrolysis process scheme including heat carrier cycle, mixing reactor, and product recovery
The focus of the research group is on extending the variety of suitable feedstocks as well as optimization and development of the fast pyrolysis process. Lab tests in combination with different modeling approaches aim at the improvement of critical components such as the pyrolysis reactor and product recovery. A technical lab scale plant (10 kg/h feed capacity) is used for the development of the process by testing new plant components, operation variations, and measurement systems. The results can be transferred to pilot scale and verified in the bioliq® pilot plant with a 500 kg/h plant capacity representative for industrial applications.
Reactor models have been implemented in LIGGGHTS and OpenFoam, which consider the challenges associated with twin-screws. Furthermore, a model of the condensation is developed in AerCoDe. Aspen+ is used to simulate the process; the focus of the associated research is on the development of suitable models that consider the complexity of pyrolysis and the variety of products in the bio-oil.