The effect of temperature and steam on the yields of tar compounds in fluidized bed pyrolysis

D. Fuentes-Cano*, A. Gómez-Barea, S. Nilsson, M. Campoy, P. OlleroBioenergy Group. Chemical and Environmental Engineering Department. Escuela Superior de Ingenieros

(University of Seville) Camino de los Descubrimientos s/n. 41092 - Seville. Spain

*corresponding author: Tel.: +34 95 4486045; Fax: +34 95 4461775; e-mail address: dfcano@esi.us.es

Objectives

Experimental

To characterize the tar compounds generated in an FB at different temperatures in inert atmosphere To understand the interaction between tar compounds during thermal treatment and the effect of steam addition

Biomass: 1- wood pellets 2- dried sewage sludge (two dp, 1-1,4mm and 4-5mm)

Fluidized bed reactor with two independent heated zones (bed and freeboard) Four temperatures configurations

Bed material: bauxite (aluminosilicate) Residence time of gassesin the bed: 0.6sin the freeboard: 1s

Fluidizing agent: N2 or N2/H2O (70/30) Five type of tar analyses: gravimetric, aromatics, elemental composition, C-13 and H-1 NMR analyses and size exclusion chromatography .

Operating conditions

Small influence of particle size on tar generation for dried sewage sludge (DSS)

Generation temperature (fluidized bed temperature) has little influence on final tar mixtures when a further thermal treatment is applied

The influence of steam addition is significant for all configuration tests, being higher at higher temperature

Further analysis of tar compounds are on the way to understand the results

Conclusions

Preliminary results

Fluidizing agentN2 (H2O)

N2 (H2O)

Biomass

Freeboard

Fluidized bed

Tar sampling and gas analysis

Experiences without steam

DSS tar yields(ppmw daf)

Tb: 500°CTf: 600°C

Tb: 500°CTf: 800°C

Tb: 800°CTf: 600°C

Tb: 800°CTf: 800°C

Tar class 2 yield 2944 6198 4846 6449Tar class 3 yield 4452 33121 16363 33039Tar class 4 yield 992 8380 2802 10353Tar class 5 yield 228 1290 289 1962Total yield 8615 48989 24300 51802Gravimetric yield 329000 117000 250000 154000

Wood pellets tar yields(ppmw daf)

Tb: 500°C

Tf: 600°C

Tb: 500°C

Tf: 800°C

Tb: 800°C

Tf: 600°C

Tb: 800°C

Tf: 800°C

Tar class 2 yield 1204 4286 5908 4426

Tar class 3 yield 2164 18577 25535 28216

Tar class 4 yield 620 3133 4370 5753

Tar class 5 yield 1065 587 598 911

Total yield 5053 26583 36410 39306

Gravimetric yield 232000 93000 127000 71000

Main findings: Aromatic tars represent only a small fraction of total tar (gravimetric) but aromaticity increases with time exposure to high temperatures Tests (not shown) with different DSS particle diameter have indicated no significant influence on tar yields DSS produces higher tar yield than wood pellets (and the higher proportion of heavy tars) Experiences with steam

Gravimetric tar(wt% daf)

Tb: 500°CTf: 600°C

Tb: 500°CTf: 800°C

Tb: 800°CTf: 600°C

Tb: 800°CTf: 800°C

DSS (no steam) 32,9 11,7 25,0 15,4DSS (30% steam) 23,3 Not finished 13,5 5,8

Wood (no steam) 23,2 9,3 12,7 7,1

Wood (30% steam) 17,7 5,0 8,2 0,1

Main findings: Steam addition reduces gravimetric tar in the 4 configurations Reductions are in the range between 26% (wood, config.1) and 98% (wood, config.4). The reduction increases with temperature

Configurations 1 2 3 4

Fluidized bed temperature (°C)

500 500 800 800

Freeboard temperature (°C)

600 800 600 800