固体热载体热解中传热行为的Fluent模拟和实验

Fluent Numerical Simulation and Experimental Study of the Heat TransferBehaviour of Biomass Solid Heat Carrier Pyrolysis

固体热载体热解(SHC)和外热式普通热解(CP)由于传热方式和热解挥发物经历温度场的不同,其传热行为和热解行为存在较大差异。采用小型密闭固定床反应器,以核桃壳(WS)为原料、石英砂(QS)为固体热载体,在石英砂预热温度800℃、QS与WS质量比9∶1条件下研究了传热行为和热解规律。采用实验和Fluent模拟两种方式研究了固体热载体热解过程的传热行为,并将温度场解耦为热解温度(T_(WS))和挥发物温度(T_(QS-h))。研究结果表明:相比于模拟所得的T_(WS)和T_(QS-h)最大值(490和612℃),实验数据(460和508℃)更小,实验过程存在散热现象。T_(WS)平均值(T_(WS))和T_(QS-h)平均值(T_(QS-h))的温差的实验值和模拟值分别为39和72℃,说明低温挥发物在逸出过程中经过高温石英砂层时发生剧烈的二次反应。相比于CP,SHC热解方式下的焦炭得率和气体得率更高,分别为67.42%和12.51%;油得率和水得率更低,分别为8.69%和11.38%。同时,SHC热解方式下的油中极轻馏分(VLO)、轻馏分(LO)和重馏分(HO)含量显著增多,残留分(CR)含量显著减小,油的品质得到提高。

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)(T_(WS))and T_(QS-h)(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.