Gas cleaning with hot char beds studied by stable isotopes

The chemistry taking place in a high temperature char bed used for binding aromatic tar compounds has been studied in detail. C-13 labelled tar compounds were used to trace the incorporation into the char bed using isotope ratio mass spectrometry (IRMS) and GC MS. Furthermore, compounds labelled with H-2 (deuterium) were used to support proposed reaction mechanisms. It was found that at 700-800 degrees C the aromatic tar compounds bind irreversibly to the char by a radical reaction and, hence, become an integrated part of the char. Thermally induced reactions may occur prior to the binding reaction. The findings explain the tar reducing properties of the char bed in two-stage gasifiers. A living char bed for hot gas cleaning is discussed. (C) 2014 Elsevier B.V. All rights reserved.