Biomass Pyrolysis in a Fluidized Bed Reactor. Part 2:  Experimental Validation of Model Results

Abstract

Various types of cylindrical biomass particles (pine, beech, bamboo, demolition wood) have been pyrolyzed in a batch-wise operated fluid bed laboratory setup. Conversion times, product yields, and product compositions were measured as a function of the particle size (0.7-17 mm), the vapor's residence time (0.25-6 s), the position of the biomass particles in the bed (dense bed or splash zone), and the fluid bed temperature (250-800 °C). For pyrolysis temperatures between 450 and 550 °C, the bio-oil yield appeared to be maximal (in this work: about 65 wt %), while the water content of the bio-oil is minimal. The position of the biomass particles in the fluid bed, either in the dense bed or in the splash zone, does not affect the conversion time and product yields to a large extent during pyrolysis at 500 °C. In the small fluid bed used for this work, with a char hold-up of up to 5 vol % (or 0.7 wt %), the residence time of the pyrolysis vapors is not that critical. At typical fast pyrolysis temperatures of around 500 °C, it appeared sufficient to keep this residence time below 5 s to prevent significant secondary cracking of the produced vapors to noncondensable gas. Up to a diameter of 17 mm, the particle size has only a minor effect on the total liquid yield. However, for particles larger than 3 mm, the water content of the produced bio-oil increases significantly. The experimental results are further compared with predictions from a one-dimensional (1D) and a two-dimensional (2D) single-particle pyrolysis model. Such models appeared to have a limited predictive power due to large uncertainties in the kinetics and selectivity of the biomass decomposition. Moreover, the product quality cannot be predicted at all.

Biofuels Production through Biomass Pyrolysis —A Technological Review

“…At first, pyrolysis reactor developers had assumed that small biomass particles size (less than 1 mm) and very short residence time would achieve high bio-oil yield, however later research has found different results. Particle size and vapour residence time have little effect on bio-oil yield, whereas those parameters greatly affect bio-oil composition [66,67]. With the continuation of pyrolysis technology development, a number of reactor designs have been explored to optimize the pyrolysis performance and to produce high quality bio-oil.…”

Elucidation of the interaction among cellulose, xylan, and lignin in steam gasification of woody biomass

“…[21][22][23][24][25][26][27][28][29][30][31][32][33][34] Many of the reaction models assume that the three major components of real biomass (cellulose, hemicellulose, and lignin) are pyrolyzed independently without interaction. [21][22][23] Yang et al 21 investigated the roles of the three components in pyrolysis using a thermogravimetric analyzer (TGA).…”

Valorization of agroindustrial solid residues and residues from biofuel production chains by thermochemical conversion: a review, citing Brazil as a case study

“…The energy yield in bio-oil and char (heating value 24-32 MJ.kg -1 ) together is about 90% (Bridgwater and Peacocke, 2000;Mohan et al, 2006); for bio-oil derived from wood, it has been reported to be approximately 55-65% (Venderbosch and Prins, 2010). Some research results have shown that the oil yield is much less dependent on biomass particle size and vapor residence times than originally assumed (Wang et al, 2005(Wang et al, , 2006, although the oil composition is sensitive to these parameters (Venderbosch and Prins, 2010).…”

“…The remainder is contained in the (tar-rich) pyrolysis gas, which has to be used on site and is not available for Biomass-to-liquid production if the FischerTropsch process is located elsewhere. Not considered to be a feasible general option because of the low efficiency Bio-oil, char and pyrolysis gas (70%, 20% and 10% of biomass energy, respectively) (Wang et al, 2005) ~1200 (bio-oil)…”