The steam cracker feedslate and its developing trend are introduced. It is considered that the cracking feedstock has become lighter and lighter. The impact of changes in feedslate on the process and equipment of different systems in ethylene plant is analyzed based on the cracking conditions and cracking gas composition of several typical cracking feedstock. The feedstock properties, the proportion of each feedstock, the process technology and the design margin are different among ethylene plants, and the load change proportion is different among systems and equipment when the cracking feedstock changes. Therefore, calculation shall be done for the systems and equipment in ethylene plant to judge the adaptability of each system to the changes in feedstock. 

This paper briefly introduces the development background of Sinopec CBL gas feedstock cracking furnace technology, the technological development implemented in each stage, the technical characteristics of various types of CBL gas cracking furnaces, the technical level achieved and the industrial application of CBL gas cracking furnace. General considerations for CBL gas cracking furnaces in scaling-up, serialization and standardization are also introduced.

Steady-state simulation was carried out for the propylene distillation unit in a 1000 kt/a ethylene plant by using Aspen Plus software. The multivariable impact factors for the operation optimization of propylene distillation tower were discussed, and the influence of simulation optimization orders on propylene distillation efficiency was analyzed. More reasonable simulation steps were determined for the operation optimization of propylene distillation, i.e., the determination of initial value of analog input, the scope of optimum tower bottom yield, the determination of optimum mass reflux ratio and the other optimization parameters, and the previous optimum value was used as a new initial value of analog input in the optimization of other parameters. More accurate and reasonable operation parameters can be provided for the actual operation.

By analyzing 8 key flare emission vents in a typical ethylene plant, this paper proposes an optimized plan for the design of two ethylene plants sharing interconnected pipelines to reduce energy consumption and environmental pollution. The scheme for reducing emissions under various operating conditions by use of a crossed pipeline is put forward, and the material recovery and emission reduction schemes under abnormal conditions such as startup, shutdown and accident fluctuation are proposed.

The pressure difference indicated by the differential gauge of ethylene distillation tower in the 1000 kt/a ethylene plant in Dushanzi exceeded the design operating value, and the feed load was reduced, restricting the increase of overall processing load of the ethylene plant. Through analysis, it was found that the reason for this problem was the plugging of tray caused by the entrance of green oil generated in C₂ hydrogenation reactor. The plugging was removed successfully by injecting methanol into the proper position, and it was more effective to inject a large amount of methanol within a short period of time than injecting a small amount of methanol within a long period of time.

The propylene refrigeration system of the 460 kt/a ethylene plant at PetroChina Lanzhou Petrochemical Company had problems of long pipeline, many branches, nested loop and complex pipe routing due to its scattered refrigerant users. During the startup and shutdown of the plant, the purge and replacement of this section was difficult, and dead ends were easily left to cause potential safety hazards. Through optimization, three measures including installing recovery pump to recover the materials in system, positive purging and reverse purging were taken to ensure that the purge and replacement of the system can be completed in 2 to 3 days.

The basic situation of using liquefied petroleum gas (LPG) as the cracking raw material for the ethylene plant at SINOPEC Yangzi Petrochemical Co., Ltd. is introduced. Combined with the actual operating conditions of the plant, SPYRO is used in the simulation to demonstrate that the introduction of LPG helps improve the ethylene-propylene yield of the plant, so LPG is high-quality cracking material. Simultaneously, to solve the problems brought by the increasing amount of LPG to the operation of plant, some countermeasures are proposed based on analysis, so as to eliminate the bottleneck of plant operation, improve the plant performance and ensure the long-term and stable operation of the plant.

Comparing the composition of light hydrocarbons with that of naphtha as the raw materials to a grassroots 600 kt/a ethylene plant, it was concluded that processing light hydrocarbons has obvious advantages in terms of product yield. Since the CO₂ content of light hydrocarbons in oil fields exceeded the design processing capacity of the plant, a caustic wash tower was installed so that double caustic wash towers were used to achieve the dual purposes of enhancing the anti-CO₂ interference capability and improving the light hydrocarbon processing capacity of the plant. After the implementation, the anti-CO₂ interference capability was increased from 2000 mg/L to 4000 mg/L, the light hydrocarbon processing capacity was increased from 20,040 t/a to 430,162 t/a, and the caustic consumption per ton of light hydrocarbons was reduced from 163.87 kg to 13.70 kg.

This article analyzes the causes of high CO₂ content in the ethylene plant of SINOPEC Guangzhou Company. It is concluded that the high sodium content of the naphtha used as cracking raw material is the reason for the high CO₂ content. At the same time, the high sodium content of naphtha may cause problems such as short operation cycle of furnace tube and CO₂ penetration of caustic wash system. Some adjustment measures are proposed including the quality control of raw materials, the scrubbing and soaking during the coke burning of furnace tubes and the optimization of caustic wash tower, so as to ensure the safe and stable operation of the ethylene plant.

The leakage of furnace tubes in the convection section of cracking furnace of ethylene plant is common in the industry. The locations and causes of leakage vary from plant to plant. All the plants have carried out in-depth study on this problem and developed relevant preventive measures. In view of the leakage in the convection section of cracking furnace in a plant, the appearance inspection of corroded furnace tubes, the chemical composition determination of corroded pipelines, the metallographic inspection, the electron microscope and energy spectrum analysis of pipelines and corrosives, and the XRD analysis of corrosion products were carried out. Through inspection, it was determined that the leakage of furnace tubes in convection section was due to the scaling of phosphorus-containing salts, which resulted in under-deposit corrosion and then the perforation of furnace tubes. Based on the analysis, some measures were put forward such as strengthening the monitoring of phosphorus elements in the materials in furnace tubes and prohibiting the use of phosphorus-containing chemicals, so as to ensure the stable production.

This paper analyzes the problems in the operation of cracking gas valve groups in ethylene plant, and proposes a method of adding external decoking accessories to adjust the cracking gas valve to the proper position while the single gate disc has a direct action. An innovative method for cleaning single gate cracking gas valve is presented, and some proposals are put forward for the applications of external decoking accessories.

Through the cause analysis of the fracture of the second pass furnace tube in the radiation section of cracking furnace F-106, the causes of the fracture were found out, the operation and maintenance methods for cracking furnace were formulated, the service life of cracking furnace tube was prolonged, the maintenance frequency of cracking furnace was reduced, and the single operation cycle of cracking furnace was increased, so as to ensure the production of ethylene and propylene and to improve the benefit of ethylene plant.

This paper analyzes the actual operation of the first stage and second stage catalysts in the second cracking gasoline hydrogenation unit at PetroChina Daqing Petrochemical Company. Through the information collection, reasonable adjustment, detailed analysis and simulation calculation of the operation of catalysts and the familiarization with the properties of the first stage and second stage catalysts, the operation cycle of the catalysts was prolonged. The catalysts have not been replaced since July 2010 (with 4 years of shutdown protection), and good operation effect has been achieved. The product quality meets the requirements, effectively reducing the catalyst investment and producing obvious economic benefits.

Since the 460 kt/a ethylene plant at PetroChina Lanzhou Petrochemical Company was started up after its overhaul in 2016, the activity of catalysts in the first stage of acetylene hydrogenation reactor has decreased significantly. Based on the statistical analysis of the operation data of the plant in this maintenance cycle, it was found that the coking on catalyst surface caused by temperature runaway and the formation of a large amount of green oil were the main reasons for the decrease in activity of acetylene hydrogenation catalyst. Compared with the previous cycle, the higher contents of acetylene and MAPD and the more C₄ components and potential heavy metal in the feed also accelerated the deactivation of catalysts. According to the actual situations, some suggestions for optimizing the operation of the plant were put forward.