烧焦罐再生器的数值模拟

Numerical Simulation of Coke Burning Tank Regenerator

流化催化裂化装置是炼油厂中重质油轻质化的重要工艺装置,其中再生器对催化剂烧焦再生、维持反应-再生系统热量平衡、压力平衡都具有重要作用。近年来随着原油逐渐重质化、掺渣比逐渐增大等因素,再生器内由于烧焦不完全产生的CO从密相床层溢出至稀相导致尾燃的问题频繁发生,严重限制了装置的掺渣能力。采用MP-PIC(Multiphase Particle-in-cell)方法对烧焦罐再生器进行深入探究,考察待生剂焦炭含量、操作压力、主风流量、入口氧气含量以及催化剂循环比等对于烧焦反应规律及尾燃趋势的影响。研究结果表明:稀相尾燃的发生主要是因为烧焦罐内烧焦速率低、气相停留时间短。当装置掺渣比增加时,待生剂焦炭含量增加,再生器烧焦负荷增大,虽然高温加速了CO氧化,但再生剂焦炭含量升高;高压有利于降低表观气速,延长气相停留时间,有利于降低尾燃风险;增加主风流量虽然可以提高再生器内平均O_(2)含量,但缩短了气相停留时间,CO燃烧不充分,尾燃风险增加;富氧再生可以明显提高烧焦罐内反应速率并改善整体温度分布,有利于降低尾燃风险,最佳入口O_(2)体积分数为26%;当催化剂循环比大于1.0时,循环剂向待生剂一侧偏流,有利于提高再生器底部起燃温度,改善整体温度分布,从而降低尾燃风险,最佳的催化剂循环比为1.5~2.0之间。

Fluid catalytic cracking(FCC)device is essential for heavy oil lightening in the refinery.Regenerator is vital to catalyst coke burning regeneration and maintaining heat balance and pressure balance of the reaction-regeneration system.In recent years,as the crude oil becomes progressively heavier and the slag mixing ratio steadily increases,the problems of afterburning caused by the CO overflowing from the dense phase bed to the dilute phase after produced by incomplete coke burning in the regenerator occur frequently,which has limited the slag mixing capacity of the device.The method of MP-PIC(Multiphase Particle-in-cell)was used to deeply explore the coke burning tank generator to investigate the influences of coke content of spent catalyst,operating pressure,main air flow,inlet oxygen content and catalyst circulation ratio on the coke burning reaction law and afterburning trends.The research results show that the dilute phase afterburning occurs mainly due to the low burning rate and the short gas phase residence time in the regenerator.With the increase of slag mixing ratio,the coke content of spent catalyst and the coke burning load in the regenerator are also increased.Although high temperature can accelerate the oxidation of CO,the coke content of regenerant is also increased.High pressure can reduce the superficial gas velocity and prolong the gas phase residence time,thus reducing the risk of afterburning.Although the average O_(2) content in the regenerator can be improved through increasing the main air flow rate,the gas phase residence time is shortened,CO combustion is insufficient and the risk of afterburning increases.Oxygen enriched regeneration can significantly increase the reaction rate and improve the overall temperature distribution in the coke burning tank,which can help reduce the risk of afterburning,and the optimal inlet volume fraction of O_(2) is 26%.When the catalyst circulation ratio is greater than 1.0,the circulating agent will flow towards the spent catalyst,which can increase the ignition temperature at the bottom of regenerator,improve the overall temperature distribution,thus reducing the risk of afterburning.The optimal catalyst circulation ratio is between 1.5 and 2.0.