Sulfur containing organic compounds in the raw producer gas of wood and grass gasification

The detailed description of gas streams in biomass gasification plants is necessary for the correct design and operation of these units. Sulfur containing compounds are usually present in biomass gasification gas, since sulfur is typically found in the feedstock. Sulfur compounds are important contaminants present in the gas streams, since even at concentrations as low as a few ppm they poison catalysts causing significant technical challenges to the production process. The determination of contaminants is often challenging due to their low concentration and the presence of steam and tars in the gas streams. Here a method is presented, which allows the qualitative and quantitative analysis of an extensive number of organic sulfur compounds found in low concentration in biomass gasification gas. The method is a combination of an adequate sampling technique (based on the liquid quench of the sampled gas) and a sensitive analytical equipment (gas chromatograph coupled with a sulfur chemiluminescence detector, CG/SCD). This work shows that several organic sulfur species are found in biomass gasification gas, which are usually not reported, but have to be considered for the design of biomass-based gasification plants. The presence of these compounds is discussed considering the feedstock used, gasification conditions and the sampling technique. Moreover, the results presented here evidence that only measuring thiophene, benzo[b]thiophene and dibenzothiophene in the producer gas can be misleading, since the sum of concentrations of all other organic sulfur compounds could be above the tolerable limits for total sulfur in gasification-based processes.