乙烯装置急冷油系统的设计和节能改造

The Design of Quenching Oil System for Ethylene Plants and Technical Revamping Aimed at Raising Energy Efficiency

我国已经投入运转的乙烯装置有27套,总生产能力达1467.5×104t/a,其中除惠州乙烯、扬巴乙烯、原茂名30×104t/a乙烯和一些进行了急冷油系统减黏改造的乙烯装置外,其他多套装置都表现出急冷油系统运转不良,温度、流量、黏度等实际运转参数和设计参数偏离较大,特别是急冷油塔的塔釜、塔顶温度,急冷油黏度,回流汽油量,稀释蒸汽发生量等偏离更大,使装置的能耗较高,稳定运转困难。急冷油的黏度高是急冷油系统存在的主要问题,由此派生出急冷油塔釜温低、稀释蒸汽发生量少、工艺污水量大、能耗高等弊端。改变急冷油塔设备尺寸和型式无法改变急冷油的黏度,必须从工艺流程的设计着手解决黏度问题。提出一种新的急冷油系统工艺流程,其特点包括:设置减黏塔,塔顶温度为250～300℃;设置轻燃料油汽提塔,与减黏塔一起用以控制急冷油的黏度,保持适宜的急冷油塔塔底、塔顶温度;设置盘油循环系统,回收盘油携带的热量,控制和改善急冷油塔的轴向温度分布;用急冷油产生更多的稀释蒸汽,减少中压蒸汽的消耗,减少工艺污水的排放量,节能减排。应用此工艺,在上海赛科乙烯由90×104t/a改扩建为119×104t/a工程和大庆60×104t/a乙烯节能改造项目中,均取得显著成效。

There are now 27 ethylene plants in operation in China with a combined production capacity of 1467.5×104t/a.Except the ethylene plants in the Huizhou ethylene project,Yangzi-BASF project,former Maoming 30×104t/a project and those that have undergone quenching oil system revamping,many plants have met with a series of problems during operation.The quenching oil systems of some plants do not operate very well and in some plants,the actual operating parameters such as temperature,flow rate and viscosity deviate greatly from designed parameters（particularly,the temperature at the bottom and top of the quenching oil tower,the viscosity of the quenching oil,the amount of gasoline refluxed and the amount of dilution steam generated deviate even more dramatically from designs）,resulting in a very high energy consumption by the units and adding to the difficulty of achieving stable operation.The high viscosity of quenching oil is the main problem in the quenching oil system and this problem will result in a series of other problems such as too low temperatures at the top and bottom of the quenching oil tower,low output of dilution steam,large amount of process sewage produced and high energy consumption.Changing the size and type of the quenching oil tower cannot change the viscosity of quenching oil.The viscosity problem can only be resolved by changing the design of the technical process.This article presents a new quenching oil system,which features the addition of a viscosity-reducing tower（the temperature at the top of the column is 250-300℃）,a light fuel oil stripper used in combination with the viscosity-reducing tower to control the viscosity of quenching oil and maintain the appropriate temperatures at the top and bottom of the quenching oil tower,and a disk oil circulating system to recover the heat in disk oil and control and improve the axial temperature distribution in the quenching oil tower and the increase of production of dilution steam using quenching oil to reduce the consumption of medium-pressure steam and the discharge of process sewage and save energy.This new system has been applied in Shanghai SECCO′s ethylene plant expansion program（from 90×104t/a to 119×104t/a） and a project aimed at raising the energy efficiency of a 60×104t/a ethylene plant in Daqing.The application in both projects has yielded excellent results.