灰斗捕焦器对催化裂化装置旋风分离器性能及流场的影响

EFFECT OF ASH-BUCKET COKE TRAP ON SEPARATION PERFORMANCE AND FLOW FIELD OF CYCLONE SEPARATOR IN FCC UNIT

沉降器顶部旋风分离器(顶旋)升气管外壁焦块脱落堵塞料腿是威胁催化裂化装置长周期稳定运行的重要隐患之一。针对这一问题,提出在顶旋的灰斗内设置网状捕焦器,以拦截脱落的大焦块,避免料腿堵塞的新防治方案,并采用冷模试验与数值模拟的方法对比研究了具有不同结构灰斗旋风分离器的分离效率、压降与流场变化。结果表明:在灰斗中增设捕焦网并拦截焦块后,旋风分离器的压降下降不明显,但分离效率下降0.21~0.91百分点;分离器内分离空间和灰斗中的流体最大切向速度分别下降0.4%和41.2%,同时轴向内旋流上行区增大,导致颗粒夹带增多、颗粒返混逃逸率增大、分离效率降低;增加灰斗高度可以减小颗粒返混逃逸率和内旋流夹带量,恢复甚至提高分离效率,从而实现防治焦块堵塞料腿隐患的目的。

It is one of the most important hidden troubles to threaten the long-term stable operation of catalytic cracking unit that the coke blocks on the outer wall of the vortex finder of the cyclone separator on the top of the settler(top-cyclone).To solve this problem,a new prevention and cure scheme was put forward,which was to set up a network coke trap in the ash bucket of the top cyclone to intercept the large coke falling off and avoid the clogging of the dipleg.The separation efficiency,pressure drop and flow field changes of the cyclone separator with different structures of the ash bucket were investigated in a comparative study with the methods of experiment and numerical simulation.The results showed that the pressure drop of the cyclone separator was not obvious,but the separation efficiency dropped about 0.21-0.91 percentage point after adding coke trap and intercepting coke block in the ash bucket.The maximum tangential velocity of the fluid in the separation space and ash bucket decreased by 0.4%and 41.2%,respectively.At the same time,the upward region of the axial inner swirl increased,resulting in the increase of particle entailing,the increase of particle backmixing escape rate and the decrease of separation efficiency.Increasing the height of the ash bucket can reduce the escape rate and entrainment of particles,restore or even improve the separation efficiency.So,it can be realized to prevent and control the hidden danger of coke blocking the dipleg by installing a coke trap and increasing the height of ash bucket.