A comparison between on-line and off-line tar analysis methods applied to common reed pyrolysis

An innovative on-line tar measuring system has been tested using the reference standard for tar sampling (UNI CEN/TS 15439) and off-line analysis approach. Samples of common reed have been characterized by means of physical–chemical and thermal analysis. Several experimental tests have been performed with a bench scale pyrolysis apparatus setting different process temperatures (300–700 °C) and a heating rate of 50 °C min−1. In each test the tar has been collected and analyzed. In addition, tars have been analyzed on-line by a lab scale fluidised bed gasifier – operated without the use of any gasifying agents – coupled with an optical measurement cell, equipped with Light-Emitting Diodes (LEDs) at different wavelengths (265 nm, 285 nm, 300 nm and 365 nm). The spectrum of absorbed light from the tar in the gaseous products has been detected through a photodiode. The total content of Polycyclic Aromatic Hydrocarbons (PAH) detected by the on-line method at 600 °C is 44 mg g−1 of initial feedstock, while the off-line method determined a total PAH content ranging from 2.75 mg to 74.41 mg at 300 °C and 700 °C, respectively. The integration between different analytical approaches on tar characterization has been useful to assess their capability and their potential application to predict tar composition.