Comparison of Two Methods of Sampling and Analyzing Tars During AER Biomass Gasification

Abstract

The tar content of product gas is one of the major problems of biomass gasification. In this work, two methods for sampling and analyzing tars were compared: The wet chemical method according to the tar protocol and a solid phase adsorption (SPA) method with Tenax® TA followed by thermal desorption. Both methods are analyzed with gas chromatography (GC) coupled with mass spectrometry (MS). The aim of this paper is to show the feasibility and usefulness of SPA method with Tenax® TA during AER biomass gasification. The SPA method has several advantages compared with conventional used wet chemical method: the sampling time could be shortened from 20­40 minutes to 1 minute and therefore more information can be obtained. Moreover the method is suitable for identifying compounds ranging from C5 to C24 and no solvent is needed. The Adsorption Enhanced Reforming (AER) process involves two coupled fluidised beds: a gasifier and a regenerator (calciner). The in­situ adsorption of carbon dioxide by a sorbent (CaO) during steam gasification in the AER reactor provides the heat necessary for the endothermic gasification reactions. Due to the CO2 capturingthe equilibrium of the water­gas­shift reaction is shifted to the hydrogen product. As a result of the CO2 in­situ capturing the hydrogen concentration is over 75 vol­% in the AER product gas. The used sorbent is then transferred to a regeneration reactor where the CaCO3 is calcined and recycled back to the gasifier. Measurements with both methods SPA as well as wet chemical have been carried out during AER biomass gasification. Results show that with SPA method with Tenax® TA more compounds can be detected and identified, especially light tars can be quantified very well. Furthermore with both methods tar formation during variation of gasification temperature could be shown.