Generation and conversion of carbonaceous fine particles during bubbling fluidized bed gasification of a biomass fuel

This article presents an experimental research concerning the biomass gasification in bubbling fluidized bed. The attention is focused on the part played by comminution phenomena during the conversion of fuel particles, and on the occurrence of post-conversion of elutriated chars in the freeboard. The aim is pursued by means of measurements of bed carbon load, elutriation rate as well as particulate concentration at various heights of the freeboard in a laboratory scale facility equipped with an isokinetic probe. The results of experiments show that fines generation is relevant during gasification, and post-conversion of particles takes place after their release from the bed. The carbon post-conversion in the freeboard achieves a maximum value of 70%, even when the operating conditions are unfavourable for gasification. The results are also confirmed by measurements of gas composition in the freeboard. The laboratory analyses of samples taken during experiments could confirm that a percolative fragmentation takes place in parallel with carbon post-conversion.