Title:
Evaluation of Different Catalyst Recipes Regarding Tar Conversion in the Gas from Continuously Operated Slow Pyrolysis Reactors
Author(s):
Obernberger, I., Supancic, K., Hargitai, T., Silversand, F., Schlögl, C., Brunner, T.
Document(s):
Paper
Abstract:
The use of biochar instead of fossil carbon sources (e.g. coal, petroleum coke) is a promising option to decarbonise energy and CO2 emission intensive industries. State-of-the-art industrial biochar production typically relies on slow biomass pyrolysis, where the biomass feedstock is converted under absence of an oxidation medium into solids (biochar), condensable gases (tars resp. pyrolysis oil) and permanent gases (CO, CO2, H2, CH4, etc.) at temperatures typically between 350 and 550°C, slow heating rates (< 20K/min) and comparably long residence times (typically 0.3 to several hours). A current R&D project focusses on the development of a new continuous pyrolysis process based on a fixed bed counter-current flow pyrolysis reactor for biochar production and the optimisation of pyrolysis gas utilisation. The novel pyrolysis reactor produces biochar as the main product and an almost dust free pyrolysis gas. The rather high tar content in the gas is removed in a novel tar reforming process, comprising a thermal cracking zone, partial oxidation and a catalytic tar conversion zone. This way, the pyrolysis gas shall be made suitable for direct utilisation in a gas engine for green electricity and heat production, which, together with reduced efforts (no hot gas filter necessary) for pyrolysis gas cleaning, shall improve the economic attractiveness of biochar production considerably. Various catalyst recipes based on coated wire meshes as a catalyst carrier material, Al or Ce/Zr-oxide based washcoats and precious metals as active species have been tested under lab-scale conditions to gain detailed knowledge of the relevant impact factors on tar conversion in pyrolysis gases from biochar production units. The tests revealed that the H2S content (catalyst poison that is present in gases derived from biomass pyrolysis), the gas load and the tar content are the most important parameters that determine tar conversion efficiency. Increased operating temperatures can minimise the negative impact of these parameters. At 950°C, almost complete tar conversion could be achieved at up to 2,000 ppm tar and 12 ppm H2S concentration with a Pt-based catalyst on a Ce/Zr-oxide-based washcoat.
Keywords:
catalytic conversion, tar removal, pyrolysis gas, biomass pyrolysis
Topic:
Biomass Conversion to Intermediate Bioenergy Carriers and Sustainable Biofuels
Subtopic:
Pyrolysis
Event:
32nd European Biomass Conference and Exhibition
Session:
5CO.7.1
Pages:
647 - 655
ISBN:
978-88-89407-24-0
Paper DOI:
10.5071/32ndEUBCE2024-5CO.7.1
Price:
FREE
