催化裂化装置旋风分离器的料腿排料是一个负压差排料过程。由于对料腿有锁气排料和防止吹通的要求,料腿出口通常安装翼阀或插入密相床层,在料腿内部需要堆积一个料柱形成蓄压去平衡负压差。负压差是料腿出口外部同一水平面位置的床层压力与旋风分离器下部料腿入口处的压力之差。而蓄压是料腿内部上下两端(进出口位置)之间气固两相混合物的压力差。针对单级旋风分离系统料腿物料的流体力学状态进行分析,提出了负压差和蓄压的计算方法,指出料腿的排料条件是内部的蓄压大于其外部的负压差。某沉降器顶旋料腿悬挂在稀相床层中,该料腿内直径为200 mm,催化剂颗粒密度为1 500 kg/m3,料腿内密相段空隙率为76%,旋风分离器压力降(约等于料腿外部的负压差)5.6 k Pa,翼阀排料压力降0.35 k Pa,可计算出料腿内刚好形成排料能力的密相料柱的高度为1.685 m。
The microstructure and properties of the coke samples collected from 4 different wall regions of the cyclone in the reactor of a residue fluid catalytic cracking unit(RFCCU) were analyzed by using the scanning-electron microscope(SEM), and the possible coke formation processes were investigated as well. The results showed that some of the heavy nonvolatile oil droplets entrained in the flowing oil and gas mixture could possibly deposit or collide on the walls by gravity settling or turbulence diffusion, and then were gradually carbonized into solid coke by condensing and polymerization along with dehydrogenation. Meanwhile some of fine catalyst particles also built up and integrated into the solid coke. The coke can be classified into two types, namely, the hard coke and the soft coke, according to its property, composition and microstructure. The soft coke is formed in the oil and gas mixture's stagnant region where the oil droplets and catalyst particles are freely settled on the wall. The soft coke appears to be loose and contains lots of large catalyst particles. However, the hard coke is formed in the oil and gas mixture's flowing region where the oil droplets and catalyst particles diffuse towards the wall. This kind of coke is nonporous and very hard, which contains a few fine catalyst particles. Therefore, it is clear that the oil and gas mixture not only carries the oil droplets and catalyst particles, but also has the effects on their deposition on the wall, which can influence the composition and characteristics of deposited coke.
Li XiaomanSong JianfeiSun GuogangYan ChaoyuWei Yaodong
