First-fractional Bio-oil by Fractional Condensation of Pyrolysis Volatiles

Abstract:

Pyrolysis is an important way of biomass resources utilization. As a liquid product of biomass pyrolysis, biooil has good application prospects in future energy market. However, the problems of low calorific value, high viscosity, high moisture content, high corrosiveness, and poor stability problem exist until now, which constrain further application of biooil. At present, many scholars at home and abroad focus on staged utilization of biooil, by different separation methods to yield the biooils with diverse physical and chemical properties, and then by further purification to obtain the high quality of biooil. Fractional condensation can realize realtime primary separation of biooil, which can facilitate further refinement, so the field has become research focus. In order to achieve the fractional condensation of biooil，various condensation modes were studied in worldwide. Spray condensation were widely used to achieve the aim of rapid condensation because it can quickly reduce the temperature of pyrolysis gas. The tube condensation mainly depending on indirect heat transfer was used in largescale chemical production and its technology was mature, so tube condensation was applied to the research of fractional condensation. Based on the previous researches on fractional condensation unit, a fractional condensation unit using constant temperature condensation was designed, of which condensation levels and heat exchange area can be adjusted flexibly. By the independent design of multilevel condensing unit and adopting camellia seed shells as pyrolysis materials, fractional condensation tests on the pyrolysis volatiles of camellia seed shells at 500℃ were carried out, and three fractional biooil products under the condensation temperature levels of more than 165℃ and 165~120℃, below 120℃ were received. The physical and chemical characteristics of the products were analyzed, and the analysis results of the first two levelfractional products at more than 165℃, 165~120℃ showed that moisture content effectively reduced and gross calorific value was more than 23MJ/kg on average, 44% more than the calorific value obtained by conventional condensation, but kinematic viscosity was not improved. With condensation temperature dropped, kinematic viscosity had significant reduction in each group of biooil and pH value was slightly rose. Combining the thermal analysis curves with comprehensive combustion characteristic index to analyze combustion characteristics of biooil, the results showed that biooils of primary separation obtained by fractional condensation had obvious differences, and YY2 demonstrated the best combustion performance. In conclusion, realtime primary separation of pyrolysis volatiles generally was achieved by dependently designed fractional condensation and the characteristics of each stage’s product were varied. The device designed can provide a reference for design of fractional condensation of pyrolysis volatiles and lay a theoretical foundation for the further application of fractional biooil.