Measurement of Gas Composition inside a Recovery Boiler Char Bed, 2004 International Chemical Recovery Conference

The gas composition inside the char bed of an operating recovery boiler was determined by removal of gas through an Inconel tube inserted into the bed through a primary airport. The gas composition was measured using on-line CO/CO2 analysis, GC analysis of gas collected in Tedlar sampling bags and by Draeger tubes (for H2S). The results show a change from a combusting gas above the char surface to a gasification gas with zero or low [CO2], 30-50% [CO], 3% [H2] and 30-50% [N2] at about 12 inches into the bed. The change in gas composition may be described by the shrinking core model with an excess amount of gas produced by CO2 and H2O gasification of carbon at the interface between the upper molten char layer and an exposed carbon layer below it. This implies that the residual organic carbon in the top “active” layer of the bed is fully covered by a smelt film and does not react significantly with the gasification gases present inside the “active” layer.