Tar Removal in a Hot Gas Bubble and Spray System for Gas Cleaning in Biomass Gasification

The objective of this project is to develop a tar removal technology which empirically models effective removal of biomass tars in biomass gasification producer gas. Tar removal from the producer gas is a key issue in biomass gasification processes. In this work, a scrubbing and stripping system has been designed which uses biodiesel to absorb the tars from the producer gas followed by tar stripping into hot air and thus the tars are separated from the producer gas and recycled. The advantages of this system include the recycling of the biodiesel and the returning of the tars to the gasification system to recover their energy. In this paper, the details of this system are presented and results from the preliminary tests are discussed. The empirical model quantifies tar vapour composition (determined as naphthalene tar vapours) in the gas phase. It is modelled on a gas stream of vapours of tar samples in nitrogen and hot air for the scrubber and stripper respectively. The tar samples are sampled from raw producer gas which is generated in a gasifier at the Chemical and Process Engineering Department of the University of Canterbury, New Zealand. An equation is developed which theoretically predicts the solubility of tars (taken as naphthalene) in methyl oleate (taken as biodiesel) at different temperatures. The results of the model and theoretical predictions show that higher tar removal efficiencies can be achieved with lower scrubbing temperatures and higher recycling rates of the biodiesel.