Abstract:

Due to the differences in heat transfer modes and temperature fields experienced by the pyrolysis volatiles, the heat transfer behaviors and pyrolysis behaviour exhibited by solid heat carrier pyrolysis(SHC) and external thermal ordinary pyrolysis(CP) were different significantly. The heat transfer behaviors and pyrolysis laws of walnut shell(WS) were studied in a small closed fixed bed reactor, with quartz sand(QS) as solid heat carrier under the conditions of QS preheating temperature(PT) of 800℃ and QS to WS mass ratio of 9:1. The heat transfer behaviors of SHC process were investigated by experiment and Fluent simulation, and the temperature field was decoupled into average pyrolysis temperature(T_WS) and volatiles temperature(T_QS-h). The results showed that the experimental data of the maximum temperature of T_WS and T_QS-h(460 and 508℃) were smaller than the data from simulation(490 and 612℃), indicating that there was a heat dissipation phenomenon in the experimental process. The experimental and simulated values of the temperature difference between the average of T_WS(${\bar T}$_WS) and T_QS-h(${\bar T}$_QS-h) were 39 and 72℃, respectively, indicating that the low temperature volatiles through the high temperature QS layer underwent a violent secondary reaction during the escape process. Compared with CP, the char and gas yields of SHC pyrolysis were higher(67.42% and 12.51%, respectiely), while the oil and water yields were lower(8.69% and 11.38%, respectiely). At the same time, the content of very light oil(VLO), light oil(LO) and heavy oil(HO) in the oil under SHC pyrolysis method increased significantly, while the content of residual fraction(CR) decreased and the oil quality increased.

Key words: walnut shells, solid heat carrier, pyrolysis temperature, volatiles reaction temperature, heat transfer behavior, pyrolysis laws