Fast pyrolysis of low and high ash paper waste sludge: Influence of reactor temperature and pellet size

摘要

Paper waste sludge (PWS) is a waste produced in large quantities by the pulp and paper industry, and is usually disposed by landfilling. This study investigates the pyrolytic conversion of PWS as an alternative to its valorisation. Low and high ash PWSs (8.5 and 46.7 wt%) were subjected to fast pyrolysis conversion to maximise the bio-oil yield by optimising the reactor temperature and pellet size. Maximum bio-oil yields of 44.5 ±1.7 daf, wt% at 400 ℃, and 59.9 ± 4.1 daf, wt% at 340 ℃, for an intermediate pellet size of 4.84 ± 0.15 mm, were attained from the conversion of the low and high PWS, respectively. The low optimal reactor temperatures, as well as the high bio-oil yields, make valorisation via fast pyrolysis conversion promising. A significant reduction in the O/C molar ratio of up to 35%, from the high ash PWS to its bio-oil product, led to a 65% increase of the higher heating value. A thermogravimetric study was implemented to investigate the pyrolytic mechanisms behind the increase in bio-oil yield with intermediate pellets sizes. It revealed that the observed increase in non-condensable gas yield, which corresponded to a decrease in the bio-oil yield, was due to the promotion of exothermic reactions for high heating rates using smaller pellet sizes.