Slow pyrolysis of biosolids in a bubbling fluidised bed reactor using biochar, activated char and lime

Slow pyrolysis of biosolids was investigated employing a laboratory scale fluidised bed reactor maintaining the bubbling mode of fluidisation where the primary product was biochar. Low cost bed materials such as natural lime, biosolids derived biochar and activated char of biosolids origin were employed in the investigation. The pyrolysis experiments were mainly conducted in a batch mode at a constant heating rate of 35 degrees C/min, a solids residence time of 60 min and a biosolids to bed material ratio of 1. Experiments were conducted by varying pyrolysis temperatures (500, 700 and 900 degrees C) and bed material. The product characterisation was performed employing various analytical instruments including Scanning Electron Microscope (SEM), Fourier-Transform Infrared (FTIR) spectrometer, Gas Chromatography-Mass Spectrometry (GC/MS) and Brunauer-Emmett-Teller (BET) analyser. The objectives of this work were to identify the most suitable bed material and optimum operating temperature for generating biochar of superior quality as well as cracking down unwanted nitrogenated, oxygenated, polycyclic aromatic compounds (PACs) and aliphatic compounds as these species are difficult to combust or have the potential to cause secondary emissions. The temperature between 700 and 900 degrees C as well as biochar and activated char as bed materials were found to be favourable in obtaining biochar of high porosity and high surface area and in reducing nitrogenated, oxygenated, PACs and aliphatic compounds.