SEWAGE SLUDGE AND PINEWOOD SAWDUST CO-PYROLYSIS IN A CONICAL SPOUTED BED REACTOR

Co-pyrolysis of both feedstock (a mixture of 50 wt. % of sewage sludge and 50 wt. % of pinewood sawdust) has been carried out at 500 degrees C in a Conical Spouted Bed Reactor (CSBR), which has been proven to be suitable for the individual valorisation of each material, attaining high bio-oil yields (48 wt. % for sewage sludge and 75 wt. % for pinewood). Significant synergetic effects have been observed in both the previous thermogravimetric study and the pyrolysis of the mixture in the bench scale plant, in which gas production is promoted. The bio-oil mainly consists of oxygen-containing compounds (with phenols and ketones being the main products) and water, with concentrations of 48.6 wt. % and 31.6 wt. % respectively. It is noteworthy that no sulphur containing compounds have been detected and the concentration of nitrogen containing compounds is lower than in the bio-oil obtained from isolate sewage sludge. 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.