Research On Thermal Cracking Characteristic Of Biomass Tar

With energy shortage and environmental pollution problems are getting more and more serious, seeking new renewable clean energy has become an urgent research topic currently. Under this background, the research and utilization of biomass energy are gotten widely attentions by scholars from various countries, the thermochemistry conversion technology of biomass is an effective way for biomass energy conversion, while the tar derived from biomass thermochemistry conversion has always been a difficult problem in this technology. The research about thermal cracking characteristics of biomass tar has been done in this paper, the main contents and results are as follows:Sawdust was chosen as raw materials for biomass pyrolysis experiments, something could be found through the elemental and industrial analysis of sawdust that the main elements in sawdust are C and O, there is a small amount of H and N; The volatile content of sawdust is very high, the content of fixed carbon is relatively low, and the moisture and ash content are the lowest. Then experiments about the influence of reaction temperature to the yield of tar and the chemical composition of tar had been done. The results showed that the yield of tar derived from biomass pyrolysis reached maximum at 500℃, the higher or lower temperature are conducive to the reduction of biomass tar. The hydrocarbons of tar are mainly aromatics and a small amount of aliphatic hydrocarbons, the oxygenated compounds are mainly phenol and its alkyl derivatives, the nitrogen compounds are mainly heterocyclic compounds, such as pyridine, pyrrole and its alkyl derivatives.The tar was chosen as raw material for experiments to discuss its pyrolysis and combustion characteristics under nitrogen and oxygen atmospheres. And the tar was derived from biomass pyrolysis at reaction temperature of 500℃, nitrogen flow rate of 100mL/min, solid phase retention time 10 min. The results showed that the characteristics of tar pyrolysis turned out to be a total wide peak, the weight loss was more quick at the first half, slower at the second half, the overall of tar pyrolysis process could be divided into two parts; The characteristics of tar combustion turned out that there were two peaks, the first peak was more wider than the second peak, and the overall of tar combustion process could be divided into three parts. Through the mechanism analysis of tar pyrolysis could be found that after tar pyrolysis 30 s and 2 min, the main remains were phenolic compounds, and little aliphatic hydrocarbons, and after 2 min most matter has been involved in response.In order to deeply understand the cracking characteristics of the tar, the experiments about the influence of solid-phase retention time, the gas flow and reaction temperature to the cracking characteristics of tar had been done under nitrogen, water vapour and carbon dioxide atmospheres. Through the comparison of the tar cracking reaction under three atmospheres, the results showed that rising temperatures and steam can significantly promote the tar cracking while the high CO2 concentration obviously has inhibition effect on the tar cracking.