Due to the arising issue of climate changes and environmental safety, there is a need to replace fossil-based fuels to sustainable renewable energy [1]. For this, the entire worlds energy system is transitioning from fossil to renewable energy, which is a huge technological challenge requiring new technological solutions. This needs to install new decentralized energy plant around the world where electricity is not available from national electric grid systems and the area of low population densities and under difficult to reach geographical conditions. These unserved remote areas have to be met by means of off-grid technologies. Among the off-grid renewable technologies, it is cheap and affordable to use biomass energy for standalone power generation in remote areas [2]. About 7% of primary energy demand mix is currently met by biomass or biomass derived fuels [3]. Use of biomass energy is transformed into producer gas that consists of CO, CO2, H2, CH4, water and tar with other constituents by the gasification process [4]. However, tar content in producer gas is the main problem if it is to be used directly in an engine. Unlike heat applications, power generation demands low tar producer gas that certainly be less than 50 mg/Nm3 to guarantee long lasting performance in the engine generation system [5]. A downdraft moving bed gasifier with an internal recirculation and combustion of pyrolysis gases inside the gasifier offers excellent opportunities for solving the tar problem to a significant extent [6]. Susanto and Beenackers studied a moving bed gasifier (throatless) where recirculation systems reduced tar content in the producer gas below 100 mg/Nm3 [6]. Nonetheless, the technology of internal recirculation of pyrolysis gas and mixing these gases with the gasifying air to burn in the combustion chamber in the combustion zone is not well-established technology and only few studied were performed in this new area of knowledge. So, there is a scope to investigate tar content problem lower than 50 mg/Nm3 considering an easy constructional and operational gasification system. Considering insufficient studies in downdraft moving bed gasifier to reduce tar content in the producer gas, this study was aimed to study a novel design of low-tar biomass (LTB) gasifier with a novel inclined nozzle and combustor. Moreover, the aim is to identify and characterize the parameter of LTB gasifier for optimizing its performance. Furthermore, the resulted producer gas is tested for operation of an internal combustion engine.
1.1 Process Principal
A novel design of low-tar biomass (LTB) gasifier with an inclined nozzle in the pyrolysis zone (Fig. 1(a)) and a separate combustor installed inside the partial oxidation zone (Fig. 1(b)). The design process was focused on a swirling flow created by an inclined nozzle which allows a good mixing between gasifying air and pyrolysis gases in the pyrolysis zone. A separate combustor which has large annular and reverse flow zones with the help of swirl flow. The resulted mixing gases has sucked inside in to the combustor and burning the mixture with the help of induced thermal cracking in the partial oxidation zone which results in turn extremely low tar content in the producer gas.