Slow Pyrolysis Performance and Energy Balance of Corn Stover in Continuous Pyrolysis-Based Poly-Generation Systems

In order to analyze pyrolysis performance and energy balance of corn stover pyrolysis, a poly-generation pyrolysis unit that coproduced biochar, pyrolysis gas, and liquids was used. Corn stover was naturally dried and crushed to lengths of 4–7 mm before pyrolysis at 450, 550, and 650 °C. The physical and chemical properties, yield rate, and influence of technological parameters were analyzed. In addition, a full energy balance analysis was carried out. The results show that the quality of corn stover char was primarily affected by pyrolysis temperature and material residence time, where a residence time of at least 30 min was required for conversion in this unit. The higher heating value (HHV) of pyrolysis gases reached ∼20 MJ/Nm3 at pyrolysis temperatures of 550 and 650 °C, providing a useful gaseous fuel. In terms of energy balance, biochar contributing 47.88% accounted for most of the enthalpy of products, followed by pyrolysis gas (36.17%), wood tar (13.14%), and light oil (1.74%), and the last fraction, wood vinegar, accounted for only ∼1.07% of the total product enthalpy. The theoretical energy efficiency of the poly-generation system was 82.1%. Pyrolysis at temperatures of 550 and 650 °C could provide fuel gases that contained enough energy to support the heating requirements of the system. The researcher offers an important new direction for comprehensive development of straw utilization for energy and materials, not only in China, but worldwide.