Technical Session 21: Spent Grains Session
Heinz Dauth, Münster University of Applied Sciences, Steinfurt, Germany
Co-author(s): Juergen Mueller, Tobias Bosse, and Peter Dettmann, Münster University of Applied Sciences, Steinfurt, Germany
ABSTRACT: HTC was described for the first time in 1913 by a
chemist named Bergius and gained increasing interest for several
applications during the last decade. What does hydrothermal
carbonization mean? In easy to understand terms, it stands for a
thermo-chemical process for the conversion of solid biomass at an
elevated temperature and pressure in the presence of water. The achieved
product differs significantly in its chemical and physical properties
in comparison to the starting material. During the HTC process mainly
water and carbon are dissociated from the biomass. Thus, the energy
density is raised significantly and the heating value is approximately
that of dry, high quality brown coal. As mentioned previously the HTC
process takes place in an aqueous reaction medium so that wet biomass
,like spent grain, can be easily used and is actually preferred. Initial
experiments with spent grain show that this biomass is an ideal
substrate for conversion into “bio-coal.” The advantages of spent grain
are its particle size distribution, chemical properties due to the
composition of the biomass, excellent mechanical compactibility, which
results in a high load capacity (mass loading) in the autoclave, and a
nearly homogeneous distribution of the biomass in the liquid phase
inside the autoclave. Due to the chemical composition of the substrate
the required energy input into the system after initializing the process
is significantly lower compared to other examined substrates. After a
treatment of 5 hr under mild process conditions with respect to
temperature and pressure the resulting product is a coal-water slurry.
The coal fraction can easily be separated and dried. The “bio-coal”
gained from spent grain has a heating value of approximately 27.000
kJ/kg (which is higher than the heating value of brown coal) and has an
ash content of just 6% in relation of dry “bio-coal.” The crop of
“bio-coal” from 1 kg of “wet” spent grain is approximately 12 mass
percent. Furthermore, the process can be enhanced in a way that other
biomass from the brewery, like label residues or sewage sludge, is mixed
with the spent grain. This will be the next step for experimental
examinations. This “bio-coal” from spent grain can serve as a CO2 neutral substitute for fossil coal because by burning “bio-coal,, only that amount of CO2
which was trapped in the plants by means of photosynthesis is released,
making the HTC process a perfectly climate neutral and sustainable
energy process. In summary, the HTC process provides a porous, brittle,
and partly dust-like product that is considerably easier to dry and
convert to thermal energy in a brewery than the original biomass. This
is a clear conceptual advantage for energy use compared to, for example,
the burning or gasification of untreated biomass like spent grain.
Heinz
Dauth graduated with a Dipl.-Ing. degree in food technology and
biotechnology from the Technische Universität München-Weihenstephan in
1993. Afterward he was appointed as a scientific researcher at the Chair
of Process Engineering (Karl Sommer) in Weihenstephan. His doctoral
thesis was completed in 1999 in the field of mechanical process
engineering. He served the Chair of Process Engineering, TU München, as
scientific assistant and university lecturer from 2003 until 2011. His
main research interests are bulk solids technology, dispensing
technology, and hygiene, as well as process engineering for specific
problems in the food and beverage industries. During this time he has
also been working as an assistant professor at the Weihenstephan
University of Applied Sciences, lecturing on mechanical and thermal
process engineering. Since October 2011 he has been a professor at the
Münster University of Applied Sciences in the Faculty of Chemical
Engineering.
