Characterisation of the producer gas from an open top gasifier: Assessment of different tar analysis approaches

• Comprehensive screening of the tar in the raw producer gas of an open top gasifier.
• Total tar is mainly composed of light aromatic compounds (benzene and toluene).
• Similar gravimetric tar content operating the gasifier with Casuarina woodchip and coconut shell.
• Gravimetric tar in the raw gas of the investigated open top gasifier is 50–80 mg N m−3.

The paper addresses a comprehensive screening procedure of the tar present in the raw producer gas generated by an open top downdraft gasifier developed at the Indian Institute of Science (IISc), Bangalore. The main objectives of this research are the comparison of different approaches for the sampling and analysis of tar (i.e. GC–MS and gravimetric methods), and the assessment of the capability of this gasifier to produce low-tar producer gas.The results of the GC–MS analysis of the collected samples showed that tar is mainly composed of light aromatic compounds, where benzene and toluene account for about 70% of the total detected tar. Contrastingly, the gravimetric tar is roughly one order of magnitude lower than the total tar that was determined by GC–MS analysis on the collected samples. The light and heavy polycyclic aromatic hydrocarbons (PAH) compounds that have a molecular weight higher than 150 g mol−1 account for the gravimetric tars, but the main fraction is GC-undetectable. The two approaches for the analysis of tar have different capabilities and the choice of either the approaches would strongly depend on the selected gasification technology. The detailed experimental analysis evidenced that the IISc open-top reactor design results in a low tar content in the producer gas. The gravimetric tar in the raw gas were measured at 50–80 mg N m−3, with minimum dependence on the choice of the feedstock used (i.e. Casuarina wood chip or coconut shell).