The CDU/VDU at Dagang Petrochemical Company had crude distillation capacity of 5.0Mt/a and vacuum distillation capacity of 3.25Mt/a after the modification in 2004.After 7 years' operation,there were some problems including packing corrosion,low vacuum of overhead and coking in over evaporation section.In June 2012,the vacuum tower was revamped.The side-draw could be clearly cut and the total draw was improved from 51%~52%to 61%~63%,achieving good results.

The method of using sensible heat to heat re-boilers has been widely used in petrochemical units.If designed improperly,however,the method may also lead to a failure of temperature control for the re-boiler.The stabilizer re-boiler of an FCC gasoline hydrodesulfurization unit uses fluids from high-temperature processes as the heating media and the temperature in the stabilizer kettle is jointly controlled by the primary regulating valve on the primary heating medium line and the pressure difference valve on the bypass line.In the early stage since production start,the temperature of the kettle was difficult to control due to two factors: firstly,the flow rate of the heating medium for the re-boiler was too low and the operation was in the unstable transition boiling range;secondly,the pressure difference between the piping on the two sides of the bypass regulating valve was too large.Countermeasures taken included:properly reducing the operating pressure for the stabilizer,increasing the flow rate of the heating media for the primary piping and reducing that for the bypass line to enable the re-boiler to work within the stable nucleate boiling range;introducing three-way regulating valves in temperature control for the stabilizer to prevent control disorders due to the inability of the pressure difference measurements from the two sides of the bypass regulating valve to accurately reflect the changes in the pressure difference on the primary regulating valve.As a result of the above measures,the temperature control for the stabilizer kettle improved considerably and products produced met required quality specifications.

In a case study of a 5.6 MM TPY delayed coking unit,the two process schemes of fractionator upper pumparound heat removal process(Process Ⅰ) and fractionator overhead cold reflux heat removal process(Process Ⅱ) are simulated and compared by using softwsares ASPEN PLUS and HTRI in respect of product yields,overhead salt deposition,facilities investment and energy consumption.The results demonstrate that: the two processes have the same separation efficiency,there is no impact on the temperature of feedstock to heater;Process II has a lower fractionator overhead steam partial pressure and a higher overhead temperature,which helps to reduce NH4Cl solution and has a greater anti-salt deposition feasibility,but it is not easy to control the online salt washing operation and amount of slop oil is large;When the low-temperature heat can't be reutilized,Process II requires 1.36 MM Yuan RMB more facility investment than Process Ⅰ but has saved 29 kW electricity.Therefore,Process I is recommended when low-temperature heat can be reutilized.

兰州石化公司炼油厂1.8Mt/a汽油加氢脱硫装置,采用法国AXENS公司的Prime G+固定床选择性加氢脱硫工艺。选择性加氢反应器采用HR-845S催化剂,加氢脱硫第一反应器采用HR-806S催化剂,第二反应器采用HR-841S催化剂,采用的催化剂活度高、选择性和稳定性好,在保证脱硫水平的同时,使辛烷值损失最低。因催化剂对进料杂质的限制,该工艺对原料油过滤精度、缓冲罐气封用气种类,较常规加氢精制装置严格。催化剂器外再生,干法硫化,循环氢系统设置脱硫塔,下游无需设置脱硫醇装置。该工艺的典型控制方案,如循环汽油流量控制、选择性加氢氢油比控制、分馏塔轻汽油抽出双串级控制等成熟可靠。在开工初期原料中的硫含量、烯烃含量较大偏离设计值时,通过调整氢气用量、反应器入口温度、轻重汽油切割点等工艺参数,仍能保证产品的质量指标。

Merits and drawbacks of individual and central installing light hydrocarbon recovery units in large refineries were studied.Taking a large refinery as an example,design and optimization of central installing light hydrocarbon recovery unit were introduced.The results show that the central installing saturated gas recovery unit can effectively recover saturated gas from multi-units,which can not only avoid to individually install saturated gas recovery unit and save investment,but also increase yield of light hydrocarbons.

Based on the gasoline blending components produced by a refinery,this article describes two schemes for upgrading the quality of gasoline.The first scheme involves the hydro-desulfurization of cat gasoline and the second scheme adds a light gasoline etherification process to the first scheme.The first scheme uses Axens′s Prime-G+ technology as its cat gasoline hydro-desulfurization technology and CDTECH′s etherification process is selected as the etherification technology used in the second scheme.Blending results show that under the first scheme,the average content of sulfur in all gasoline products produced by the refinery is 18.95g/g and the gasoline products can all be used to produce Beijing Ⅳ or Euro Ⅳ gasoline.However,due to octane value loss in the hydro-desulfurization process,the output of 97 octane value Beijing Ⅳ gasoline is only 6.61×104t/a,accounting for 3.73% of total gasoline output produced.After treatment using the second scheme,all gasoline products produced by the refinery meet the requirements of Beijing Ⅳ and Euro Ⅳ gasoline standards on blending properties and the yield of 97 octane value Beijing Ⅳ gasoline rises to 22.64% from 3.73% in the first scheme.On public works,the consumption of circulating water and 1.0MPa steam in the second scheme is far higher than that of the first scheme,its energy consumption(1524.56MJ per ton of feedstock) doubles that of the first scheme(745.12MJ per ton of feedstock) and the total investment in it is also higher than that in the first scheme.However,as it can consume 5.47×104t of methanol annually,the second scheme can convert relatively cheap methanol to high-value gasoline products by etherification.At current prices,this process raises the value of methanol by about 4000 yuan per ton.After scheme II is adopted,the financial internal rate of return(after tax) and net profit per ton of oil can reach 30.81% and 103.60 yuan per ton,far higher than the 8.80% rate of return and 13.86 yuan/t net profit of scheme I.After comprehensive comparison,the refinery has decided to adopt the second scheme to upgrade its cat gasoline products.

The structure and specialty of plat heat exchanger were introduced and compared with tube and shell heat exchanger in the crude distillation unit.The result shows that the plat heat exchanger can reduce investment,recovery more energy,achieve energy saving and emission reduction.