Role of Temperature on TAR Characteristics in a Fountain Enhanced Conical Spouted BED Reactor

Role of temperature on tar
characteristics IN A Fountain enhanced conical SPOUTED BED reactoR

M. Cortazar, J. Alvarez, M. Amutio,
L. Santamaria, E. Fernandez, G. Lopez, M. Olazar

Univ. of the Basque Country, Dpt. Chem.
Engineering, PO Box 644– 48080 Bilbao, Spain

maria.cortazar@ehu.eus

Biomass
gasification processes have considerably gained attention for the sustainable
production of syngas which could be used as fuel or
as an intermediate product in the production of other fuels and chemicals.
However, the major challenge of this process is still the high level of tar
presented in the gas, which hinders the improvement of its industrial viability
[1, 2]. This work addresses the influence the temperature has on tar characteristics,
including a detailed tar characterization by means of Fourier transform
infrared spectroscopy (FTIR), gas chromatography coupled with mass spectrometry
(GC/MS) and simulated distillation.

The steam gasification of sawdust (1-2 mm) was carried out in a gasification
pilot plant provided with a fountain confined conical spouted bed reactor. The
influence of gasification temperature on tar concentration and composition was
studied in the 800-900 ºC temperature range. The bed was initially
made up of 100 g of olivine (90-150 um), and a water flowrate
of 1.5 mL/min was used to attain fountain enhanced
regime. All the runs were
carried out in continuous mode by feeding 0.75 g/min of biomass, so steam to biomass (S/B) ratio was maintained at 2. The
analysis of the volatile stream leaving the reactor was conducted on-line, using a CG Agilent 7890 provided with a flame ionization
detector (FID) and a Varian 4900 micro-gas
chromatograph for permanent gases. The identification of the tars
collected in the condensation system was determined in a GC/MS (Shimadazu UP-2010S). Fourier transform infrared spectroscopy (FTIR)
measurements were performed in a Thermo Nicolet 6700 instrument to determine
the organic functional groups in the tar samples. Moreover, tars collected at
different temperatures were fractionated by simulated distillation using a GC (agilent 6890) provided with FID detector and according to
the ASTM-D2887-84 standard.

Not only
does the temperature affect the amount of tar produced, but also the
composition of tar. Tar concentration fell from 49.2 g Nm^-3 (on a
dry basis) at 800 ºC to 6.7 g Nm^-3 operating at 900 ºC. Tar analysis
(FTIR and GC) revealed that its composition was significantly influenced by
temperature, opening a pathway for the evolution of its composition to more
stable species (enhanced when temperature was increased) in the range of
secondary and tertiary tars (of higher molecular weight) due to rearrangement
reactions. The major fraction in the 800-900 ºC range was that of light PAHs,
although tar composition shifted from phenolic
compounds and alkyl-substituted PAHs to more stable and heavier PAHs (non-substituted
species) by increasing temperature, with naphthalene being the major compound
at 850 ºC and 900 ºC. Simulated distillation confirmed that the average boiling
point of the tars increased (especially of those obtained from 800 to 850 ºC)
when the gasification was performed at high temperatures.

References

[1] Alauddin,
Z., Lahijani, P., Mohammadi, M., and Mohamed, A. R. (2010). Renewable & Sustainable Energy Reviews,
14(9), 2852-2862.

[2] Parthasarathy, P., and Narayanan, K. S. (2014). Renewable Energy, 66, 570-579