(441e) Fast Pyrolysis of Pine Biomass in a Gas Solid Vortex Reactor

The increased global concern on the dependence on fossil resources has pushed a development in the research of alternative feedstocks for the petrochemical industry. Thermochemical conversion of lignocellulosic biomass into bio-fuels and high valuable chemicals is one of the promising routes to decrease the fossil fuel dependence [1,2]. Fast pyrolysis is one of the most promising thermochemical routes that has been considered for bio-oil production on large scale due to the high bio-oil yields (up to 70 wt. %) [3,4], its simplicity and relatively low capital investment [5]. In spite of the advantages, fast pyrolysis also faces several challenges. The lack of a complete understanding of the pyrolysis reaction network and kinetics makes the tracking of each individual specie (from feed to product) difficult. Yet some simplified kinetic models match the experimental results closely [6]. Another challenge is the selection of the best reactor technology to provide accurate temperature control and fast entrainment and quenching of the pyrolysis vapors (of the order of ms. instead of s).

Nowadays, the fluidized bed reactor (FBR) is one of the preferred technologies for fast pyrolysis due to its ease in design and operation. However, FBRs suffer from operational limits, eg. the maximum fluidization gas flow, while mass and heat transfer rates are moderate. These limits are observed to decrease in a fluidized bed operating in a centrifugal field. The Gas-Solid Vortex Reactor (GSVR) sustains a rotating solids bed by continuous tangential injection of fluidizing gas through multiple small injection slots. GSVRs are known to offer advantages over conventional fluidized bed reactors in the gravitational field, eg. the bed is more densely packed and gas-solid slip velocities are significantly higher. The latter results in enhanced heat and mass transfer rates.

At the Laboratory for Chemical Technology (LCT, Ghent University), biomass fast pyrolysis is carried out in a GSVR demonstration unit [7]. The goal is to further optimize the bio-oil yield and to determine the bio-oil molecular composition using advanced analytical techniques (GCxGC). The present work focuses on experimentally exploring the bio-oil yield in the GSVR demonstration unit. Additionally, CFD simulations including reaction kinetics of this experimental GSVR are performed [8]. By comparing numerical and experimental results, the performance of the selected kinetic model will be validated. First the elemental and molecular composition of the feedstock, and the biomass particle aspect ratio are closely examined. Fast pyrolysis experiments with pine are performed to determine the yield of the main pyrolysis fractions (i.e., bio-oil, char and non-condensable gases). GSVR is compared with conventional FBRs in terms of their respective pyrolysis product fraction distribution. Next, after each experiment, the elemental and molecular composition of the bio-oil obtained from the GSVR is compared with that of bio-oil from FBR technology.

References

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[2] Czernik, S. and A. V. Bridgwater (2004). "Overview of Applications of Biomass Fast Pyrolysis Oil." Energy & Fuels 18(2): 590-598.

[3] D. Shen, W. Jin, J. Hu, R. Xiao, K. Luo (2015). An overview on fast pyrolysis of the main constituents in lignocellulosic biomass to valued-added chemicals: Structures, pathways and interactions, Renewable Sustainable Energy Rev., 51 761-774.

[4] M.S. Mettler, D.G. Vlachos, P.J. Dauenhauer (2012). Top ten fundamental challenges of biomass pyrolysis for biofuels, Energy Environ. Sci, 5 7797-7809.

[5] Bridgwater, A. V. (2012). "Review of fast pyrolysis of biomass and product upgrading." Biomass and Bioenergy 38: 68-94.

[6] Ranzi, E., et al. (2008). "Chemical Kinetics of Biomass Pyrolysis." Energy & Fuels 22(6): 4292-4300

[7] González Quiroga, Arturo, Pieter Reyniers, Shekhar Kulkarni, Maria del Mar Torregrosa Galindo, Patrice Perreault, Geraldine Heynderickx, Kevin Van Geem, and Guy Marin. (2017). “Design and Cold Flow Testing of a Gas-Solid Vortex Reactor Demonstration Unit for Biomass Fast Pyrolysis.” Chemical Engineering Journal 329: 198–210.

[8] Kulkarni, S., Vandewalle, L., González Quiroga, A., Perreault, P., Heynderickx, G., Van Geem, K., & Marin, G. (2018). Computational fluid dynamics-assisted process intensification study for biomass fast pyrolysis in a gas–solid vortex reactor. ENERGY & FUELS, 32(10), 10169–10183.