Tar formation during black liquor low-temperature gasification was studied both in a full-scale steam reformer and in a small-scale gasifier. In the full-scale unit, gravimetric tar contents in the product gas were determined to correspond to approximately 4.5% of liquor organic carbon. An approximately equal amount of lighter condensable organic compounds was estimated to be present in the product gas. The tar contained phenolics and both substituted and unsubstituted multi-ring compounds. 40% of the tar compounds detected by GC/MS analysis were one-ring compounds. The tars from the small-scale unit were primarily mono-, di- and tri-substituted one and two-ring phenolic compounds. Increasing the gasifier temperature decreased tar formation and increasing black liquor solids feed rate increased tar formation.
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