Experimental and numerical investigation of tar destruction under partial oxidation environment

Abstract

Tar in biomass product gas is a major problem because it reduces the reliability of the equipment and enhances pollutant emission. Partial oxidation is effective for reducing tar inside gasifiers. In order to predict tar reduction with partial oxidation technology, knowledge of the fate of tar during partial oxidation process is paramount. A continuous reactor was developed for tar destruction experiment under partial oxidation environment. Tar components and non-condensable gasses were measured and analyzed. Results show that the defined “primary tar” contents share about 60% of the total tar amounts. Phenolics prevail under initial reaction, but it is easy to form PAHs (polycyclic aromatic hydrocarbons) by polymerization reactions under certain ER (actual mass flow rate of oxygen/oxygen required for complete oxidation of biomass feed stock). This process results in an increase of tertiary tar. Hydrogen's evolution curve shows a steep rise with ER, which could be an indicator for the crack of secondary tar. A model was developed for describing partial oxidation of tar. Phenol, toluene, benzene and naphthalene were chosen as model compounds. Fluid flow, chemical mechanism and heat transfer are considered in the model. The calculated total tar amounts are in qualitative agreement with experimental results.