Mixing of Pyrolyis Products To Form a Slurry
One important motivation for developing the process, in addition to a reliable introduction of the feed for the entrained flow high-pressure gasifier, was to find an economical solution for transporting the regionally formed crop straw to a large-sized plant without producing escalating costs. The fast pyrolysis plant is located close to an agricultural area. There pyrolysis condensates and char are mixed to give a liquid slurry (sludge), which can then be efficiently transported by train over large distances to centrally located gas generation and synthesis plants. The ideal slurry for the Karlsruhe bio slurry gasification will have a high energy content around 5 kWh/kg, a high density around 1,300 kg/m3, and will be chemically and physically stable over many weeks, to ensure its pumpability and atomizability in the gas generator.
Highly concentrated slurries consisting of pyrolysis tar and char have a viscosity of a few Pascal seconds at room temperature.
The lower heating value of slurries of this type is slightly higher than that of the starting biomass, while its energy density can reach 60 to 65% of that of heating oil in favourable cases. The energy content of the slurries can amount to up to 90% of the original biomass energy and, due to its char content, is overall clearly higher (up to 50%) than that for pyrolysis oil alone.
Slurry Preparation in the Laboratory
In the meantime, we've had extensive experience with colloid mixers, which destroy the particle agglomerates in the slurry already during the admixture of char powder, thus lowering the inter-particle volume.
Optical microscopy
A) Char powder stirred into methanol.
B) Slurry following colloidal degradation of the particles diluted with methanol
C) Resulting particle distribution curves
Slurry Preparation on an Industrial Scale
Depending on the feedstock used, the maximum char content of pumpable slurries can vary considerably. Using the new mixer technology, we have been able to increase the solids content of slurries in our pilot plant scale gasification experiments from 20% to up to 33%. To this end, we have used a continuous colloid mixer, which is adapted to the throughput of a 3-5 MW gasification plant (up to 1 t/h of slurry).
Continuous Colloid Mixer for a Throughput of 1 t/h