A pre-commercial plant is now providing operational data for eventual scaleup and industrial integration of a technology that generates refinery-grade crude oils from biogenic waste, such as agricultural and forestry waste and sewage sludge.
The 12-ton/d demonstration plant (photo), built and operated by the Fraunhofer Institute UMSICHT (Sulzbach-Rosenberg, Germany; umsicht-suro.fraunhofer.de), runs a process known as Thermo-Catalytic Reforming (TCR®), which combines intermediate pyrolysis of sewage sludge with an integrated catalytic reforming step to produce refinery-compatible green crude oils and biochar, a carbon sink. Intermediate pyrolysis refers to processes in the temperature range of 400–500ºC, residence times in the process of about 15 min and heating rates that fall between fast and slow pyrolysis.
The catalytic reforming process used in TCR differs from existing catalytic reforming methods in the type of catalyst used. “Instead of conventional catalysts, the hot char produced in the pyrolysis process is used as a self-regenerating catalyst, assisted by a partial steam reforming, due to the moisture content of the feedstock,” explains Matthias Franke, director of Fraunhofer UMSICHT in Sulzbach-Rosenberg.
“Reforming takes place through contact between the generated hot vapor phase and the catalytically active char bed, without causing catalyst damage or issues with catalyst lifespan,” he continues. In addition to cracking long-chain hydrocarbons, TCR allows enhanced hydrogen formation by the water-gas-shift reaction of steam with carbon and CO. “The reforming process increases the hydrogen content in the gas phase to up to 40%,” Franke says, which can be used for onsite hydrogenation.
The product is a storable oil phase with low acidity, high thermal stability and that can be processed in conventional refineries, Franke notes.
Other key reactions support the high thermal stability and low acidity of the product oils, including decarboxylation of organic acids, Franke says. “A further important reaction is the saturation of reactive intermediate pyrolysis compounds (radical compounds) by the in-situ generated hydrogen. This is an important step to receive thermally stable oil,” he remarks.
In addition to the liquid product and hydrogen-rich synthesis gas, the TCR process also produces biochar, which offers potential for carbon-capture, utilization and storage applications, for example, in agriculture and industry.
The entire process currently sits at a TRL of 7 and Fraunhofer is looking for collaborators to bring the technology to commercial scale, supporting the introduction of green bio-oils for co-refining in existing refinery infrastructure.