Study on different gas outlet positions in measurement of gravimetric tar contents in biomass updraft gasifier

Based on the previous experiment, an updraft gasifier has been modified by adding a gas outlet for producer gas at the reduction zone. The gasifier is operated under a variety of conditions that enable investigation on the effect of gas outlet modification on the amount of tar produced. The producer gas is tapped at a gas outlet at the top of the gasifier (conventional mode), a gas outlet in the reduction zone (reduction mode), and combination of the tapping of the gas outlets at the top of the gasifier and in the reduction zone (combination mode). The experimental results show that the tar content from the gas outlet at reduction mode is less than that at the conventional mode, i.e. 81 g (m3-N)-1 and 111 g (m3-N)-1, respectively. Meanwhile, the tar content from the combination mode is about 55 g (m3-N)-1 at the reduction zone and 102 g (m3-N)-1 at the top. Nevertheless, the lower heating values for each mode are similar, that is in the range of 4.6 - 4.9 MJ (m3-N)-1. The hot gas efficiency reaches a maximum of 82 % on gas outlet reduction mode.