A Tar Online Measurement System Based on the Absorpion Principle.

Within this work, a very simple but yet fully effective and cheap online measuring system has been tested and evaluated. The analytic method is based on the optical absorption principle. The syngas produced from a lab scale fluidized bed gasifier and post-processed in a methanation reactor has been continuously online monitored and analyzed into an optical measurement cell. In this cell, called TOM (Tar Online Measuring), a UV light stream is produced employing LEDs operating at different wavelengths and transmitted to a spectrometer, positioned on the other side of the cell, by passing through the gas stream. The presence of tar in the gas stream causes a variation of the light transmittance that is recorded from the spectrometer. At the selected UV-wavelengths, only the electronic transitions from energetic levels n to π* and n to σ* are allowed. In plain words, the permanent gas components result transparent unlike tars. The tar concentration is proportional to the light transmittance, or rather to the absorption. Two different experimental approaches have been applied in order to calculate the tar concentration from the light absorption data. The analytic method fulfills its purpose, especially if the tar composition is totally or partially known. In any case, the TOM can be suitable in order to detect tar concentration exceedings, for instance in a feedback sensor. The apparatus itself is finally absolutely cheap.