O. Moersch

Tar quantification with a new online analyzing method

This paper presents a tar quantification method developed at the University of Stuttgart that allows quasi continuous on-line measurement of the content of condensable hydrocarbons (textquotelefttextquotelefttarstextquoterighttextquoteright) in the gas from biomass gasification. The method is based on the comparison of the total hydrocarbon content of the hot gas and that of the gas with all tars removed. Hot gas from the gasifier is led directly into the set up. Hydrocarbons are measured with a flame ionization detector. The method considerably simplifies tar measurements compared to other methods described in literature. A prototype based on the method has been developed and tested. Experiments with the gas from a fluidized bed gasifier and a fixed bed gasifier have been conducted yielding very good results. Tar contents between 200 and 20 000 mg/m3 have been measured reliably. The experimental procedure is simple and repeatability is good. Sampling and analysis time is two minutes. Continuous on-line monitoring of the tar content in the gas is possible.

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

This article presents an experimental research concerning the biomass gasification in bubbling fluidised 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.