Fast co-pyrolysis of sewage sludge and lignocellulosic biomass in a conical spouted bed reactor

Abstract

Co-pyrolysis of sewage sludge and lignocellulosic biomass has been studied in order to improve the composition of the bio-oil derived from sewage sludge fast pyrolysis as well as progress on the viability of this waste valorization. Fast pyrolysis of a mixture of 50wt.% sewage sludge and 50wt.% pinewood sawdust has been carried out in continuous mode at 500°C in a conical spouted bed reactor (CSBR) and the results obtained have been compared with those obtained in the fast pyrolysis of each raw material separately. Significant synergetic effects have been observed in both the previous thermogravimetric study and the pyrolysis in the bench scale plant, in which gas production is promoted. The bio-oil (55wt.% yield) is mainly composed of oxygenated compounds (49wt.%, with phenols and ketones being the main products) and water (32wt.%), with a lower concentration of nitrogen-containing products (9wt.%) and without any sulphur compound, thus being a suitable raw material for its subsequent valorization. The results obtained prove the capacity of the conical spouted bed reactor for minimizing the reactions of bio-oil transformation into gases (mainly promoted by the catalytic activity of the ash in the sludge), which is due to the low residence time of the volatiles in the reactor.