An experimental study of oil recovery from sewage sludge by low-temperature pyrolysis in a fluidised-bed

Pyrolysis of activated sewage sludge was investigated under inert conditions in a fluidised-bed to study the effects of temperature and gas residence time on the product distribution and composition with an aim to maximise the oil yield. The temperature was varied from 300 to 600 degreesC and the gas residence time from 1.5 to 3.5 s. Three groups of products were produced, namely, a non-condensable gas (NCG) phase, a solid phase (char) and a liquid phase (oil). A maximum of 30% oil yield (wt% daf of sludge fed) was achieved at a pyrolysis temperature of 525 degreesC and a gas residence time of 1.5 s. Higher temperatures and longer gas residence times favoured the formation of NCG, suggesting that secondary cracking reactions had occurred. The oil obtained was analysed using GC-MS and H NMR to determine the oil's composition and structure, a unit structure of the oil was proposed which consisted of aromatic rings connected by hydrocarbons with -OH functional groups attached. (C) 2002 Elsevier Science Ltd. All rights reserved.