离心双涡流快速热解器的场流机制及协同强化传热

Field-flow Mechanism and Synergistic Heat Transfer Enhancement of Centrifugal Double Vortex Fast Pyrolyzer

下行床是热解工艺的良好载体,但固含率低制约了传热速率的提高。对此,提出离心双涡流快速热解器(CDVFP)的构想予以解决。采用计算流体力学耦合离散单元法(CFD-DEM)研究CDVFP中气固两相的时空特征和传热过程。结果表明:离心力“场”对双涡“流”的削弱造成气固动量交换规律的逆转。气旋尾端以上,气流结构接近兰金涡,气流向颗粒传递动量;气旋尾端以下,气速低于颗粒速度,动量传递方向逆转。“场”将颗粒聚集在器壁,“流”减缓了颗粒下行速度,局部固含率得以提升。虽然CDVFP中二元颗粒混合的均匀性低于传统下行床,但传热速率更高且热损耗少,设备高度可因此削减约3/4.离心力场与双涡流的协同作用强化了下行床中二元颗粒间的传热。

The downer is a promising pyrolyzer,but the low solid holdup restricts the improvement of heat transfer rate.In this regard,this paper proposed the concept of centrifugal double vortex fast pyrolyzer(CDVFP)to solve it.The spatial and temporal characteristics and heat transfer process of gas-solid two-phase in CDVFP were studied by computational fluid dynamics coupled discrete element method(CFD-DEM).The results show that the weakening of the double vortex“flow”by the centrifugal force“field”causes the reversal of gas-solid momentum exchange law.Above the vortex tail,the airflow structure is close to the Rankine vortex,and the airflow transfers momentum to particles;below the vortex tail,the gas velocity is lower than the particle velocity,and the direction of momentum transfer is reversed.The“field”gathers the particles on the wall of vessel,and the“flow”slows down the particles'downward veloci-ty,thereby increasing local solid holdup.Although the uniformity of binary particle mixing in CDVFP is lower than that of conventional downer,the heat transfer rate is higher and the heat loss is less,so the equipment height can be reduced by about 3/4.The synergistic effect of cen-trifugal force“field”and double vortex“flow”enhances the heat transfer between binary particles in the descending bed.