Study on biomass tar reduction by ash and fluidizing medium in a heterogeneous reaction

Abstract

Since fossil energy resources are exhaustible in the world, renewable biomass is considered as one of the useful future resources for energy and materials. In addition, when the biomass grows, it can contribute to the prevention of global warming by circularly absorbing CO2. There are different biomass utilization technologies such as the pyrolysis and gasification, fermentation and combustion. For example, gaseous components are used as chemical products and used for energy production; these can be produced by the pyrolysis or synthesized by gasification. However, there is the problem that condensable organic compounds, so-called 'tar' will also be generated during the pyrolysis and gasification processes. Most of the tar components are present as gases at higher temperature inside of the reactors. However, a black oily liquid will be formed, leading to the equipment failure when the temperature is cooled down lower than their boiling points. Therefore, appropriate processing is required. As a processing method, catalytic decomposition of tar has been widely studied. In the present study, it was carried out for the thermal decomposition of cellulose in the experimental apparatus connecting two reaction tubes. Tar and gases generated by the thermal decomposition of cellulose in the first reactor can be pyrolyzed with catalytic cracking in the second reactor. Tar contents were firstly cooled and collected. At the same time, the amount of gases was measured by a gas chromatograph with a flame ionization detector and a gas chromatograph with a thermal conductivity detector. Then, K and Ca were selected as the catalyst of alkali metals and alkaline earth metals contained in the waste biomass, which were present in the state of oxide or carbonate during the pyrolysis and gasification. The amount of condensable products was decreased by installing catalytic contents of K2CO3 and Ca(OH)2. Additionally, the amount of gaseous products was increased. It can be concluded that an alkali metal compound (K2CO3) and an alkaline earth compound (CaO) have a catalytic effect to decompose tar contents, which can enhance gaseous production in the secondary reaction.