Investigation on Blending Ratios of Small Particle Size Spent Tea Waste with Bulk Density Agricultural Residues to Enhance the Performance of Downdraft Gasifier

The increased gasification potential of bulk density agricultural residues such as groundnut shell (GS) and rice husk (RH) could aid in the effective implementation of bioenergy for a wider range of applications. Mixing high-carbon biomass with such feedstocks is an appealing option for improving producer gas (PG) quality. Though spent tea waste (STW) has a high-carbon content due to its small particle size and high-moisture levels, it is not directly used in gasifiers for PG generation. However, it could be a promising secondary biomass in the gasification of GS and RH. To establish this strategy, an appropriate mixing method and a study on the gasification potential of the mixture as feedstock for downdraft gasifiers is essential. In this study, STW was mixed with GS and RH at various mixing ratios and tested in a downdraft gasifier. The experimental results showed that, up to a 40% weight ratio of STW with the primary biomasses, the gasifier could operate continuously without any incomplete gasification. The calorific value, cold gas efficiency and hot gas efficiency improvements for GS/STW blends at the best equivalence ratio (ER) were 19.3%, 19.61% and 18.04%, respectively, whereas for the RH/STW blend, the improvements were 16.2%, 14.5% and 13.81%. The best performance of GS/STW and RH/STW blends was found for ERs of 0.3 and 0.25, respectively, which are different from the optimum ERs for the gasification of primary feedstocks alone.