Problems And Countermeasures Of Production And Operation Of Atmospheric And Vacuum Distillation Unit Under Very Low Load

In the whole refining unit,atmospheric and vacuum distillation unit is the first process of crude oil processing.The production and operation of atmospheric and vacuum distillation unit determines the processing strategy of the whole refinery.With the aggravation of the complexity and variability of the international energy environment,the processing flexibility of oil refining units determines the overall operation planning of the refinery.This paper studies and practices the problem of how to produce safely and stably in the crude distillation unit with 300 × 104 t/a when the operating flexibility is far lower than the design.（1）In view of the risk of furnace tube coking under very low load,the mechanism and harm of coking are discussed,and the influencing factors leading to furnace tube coking are analyzed.Based on the analysis of the operation state of two heating furnaces under 50%very low load,it is determined that the fluid flow rate and residence time of the furnace tube in the radiation chamber are the key to the coking risk of the furnace tube.Through the optimization and adjustment of atmospheric tower,the extraction rate of atmospheric pressure is reduced and the load of vacuum furnace is increased.By injecting steam into the fluid of the radiation chamber,the space in the tube of its own fluid is reduced and the flow rate is greater.A new control logic is adopted for the combustion control system,which reduces the oxygen content and negative pressure fluctuation range,and reduces oxygen content and negative pressure fluctuation range of the heating furnace.Finally,the purpose of reducing the coking risk of vacuum furnace tube under 50%load is achieved.（2）In view of the fact that the products of the third line and the fourth line under 50%load can not meet the quality standard of lubricating oil raw materials,the reasons for the decline of the division accuracy of the vacuum tower are discussed.The second side line of the vacuum tower is returned to the first middle section of the vacuum tower,and the flow of the first and second middle sections of the vacuum tower is increased at the same time,so as to increase the liquid phase load of the vacuum tower.Iinjecting steam into the furnace tube and increasing tower bottom steam blowing increase the gas-phase load of the vacuum tower,effectively alleviate the phenomenon of liquid leakage and bias flow,and make the gas-liquid two-phase distribution more uniform.The optimization of stripping steam is applied to the adjustment of line 3 and line 4 to meet the quality requirements as lubricating oil raw materials（3）Aiming at the problem that the yield of vacuum residue increases under 50%load,inspired by the operating conditions of different cycle ratios of delayed coking unit,the industrial practice of focusing on residue circulation and supplemented by quench oil circulation has been successfully implemented.After the implementation of residue circulation,the unit operates stably,solves the problem of high yield of vacuum residue,reduces the content of light components in vacuum residue,reduces the risk of coking and thermal cracking of vacuum residue,and improves the kinematic viscosity of the third line and the fourth line.The practical research work of this paper provides experience for the safe continuous production and product quality optimization of atmospheric and vacuum distillation unit under extreme low load,which is of certain reference significance for the production adjustment,energy saving,cost reduction and efficiency increase of atmospheric and vacuum distillation unit,and is also conducive to the long-term safe operation of atmospheric and vacuum distillation unit.