This paper studies a new technology which converts C9+ heavy aromatics and non-aromatics into BTX (benzene, toluene and xylene), ethane, propane and a small amount of methane and butane via dealkylation, transalkylation and non-aromatics cracking reactions in the presence of catalysts, and benzene, toluene and mixed xylene can be separated via simple distillation without solvents. It has the characteristics of high value-added products, low energy consumption and eco-friendliness. The economic comparison of this advanced technology with the traditional aromatics extraction technology shows that this new technology can produce considerable economic and social benefits and is worth popularization.

Butadiene is a conjugated diene used in the production of polymers and as a chemical intermediate for several specialty products. Butadiene is produced commercially by two methods, i.e. the physical separation from the steam cracking of paraffinic hydrocarbons and the oxidation dehydrogenation of butene. In this paper, thermal pinch technology is used to analyze the two main process units (dealkylation unit and butadiene extraction unit) of the butene oxidative dehydrogenation unit. Based on the analysis and calculation of the thermal pinch point and heat utilization rate of the heat exchange network, some feasible proposals are put forward for the integration of heat exchange network, which can reduce the utility consumption and improve the efficiency of the unit.

With the enhancement of benefit consciousness and environmental protection consciousness, enterprises are endeavoring to implement low-emission shutdown and startup during the overhaul of production units, so as to protect the environment while minimizing the loss. During the two overhauls of the ethylene plant at SINOPEC Qilu Company in 2013 and 2017, low-emission shutdown and startup was implemented according to the characteristics of the plant. The material loss during the shutdown and startup in 2013 was reduced by more than 1000 tons compared with that during the previous shutdown and startup, and the material loss calculated on the comparable basis during the shutdown and startup in 2017 was reduced by more than 500 tons compared with that in 2009, obtaining better economic and social benefits and achieving low-emission and environmental-friendly shutdown and startup.

In ethylene steam cracking technology, methanol is often used as the sealing fluid for methane pump in cryogenic zone, and the pressure of sealing liquid is required to be higher than the outlet pressure of the pump. Methanol may leak into the medium and be entrained by the process medium into equipment and pipe fittings with relatively small aperture in the cryogenic zone, resulting in frozen blockage and then a dramatic increase in ethylene loss, thus increasing the potential hidden danger of temperature runaway of the mathanation reactor. This paper summarizes the impacts, judgement and countermeasures for methanol leakage.

High temperature wet air oxidation system for spent caustic, as an important environmental treatment unit of ethylene plant, plays an important role in cleaner production. This paper introduces the problems and deficiencies of high pressure wet air oxidation unit for spent caustic during its operation, and puts forward some technical improvement proposals with no major changes to the existing process, so as to guarantee the stable and long period operation of spent caustic oxidation system.

Packing blockage in the upper part of gasoline fractionator (DA101) in ethylene plant led to higher final boiling point of pyrolysis gasoline, and heavy components were entrained to the separation system, resulting in a series of process and quality problems including the over high light components in propylene product, the over high C3 in C4 product, the over high C4 in C5 product and the darker color of C9 and C10 products. A series of measures were taken to ensure the safe and stable operation of the plant until the scheduled overhaul.

Modern chemical enterprises are featured by large-scale unit and continuous production. If there is a leak in the steam and condensate pipelines, online repair welding is required when energy isolation and release is impossible and risk is controllable. In order to prevent the uncontrolled rupture and leakage of the steam and condensate pipelines during repair welding, in addition to the macro inspection of pipelines, the cold and hot state inspection of supports and hangers, the thickness measurement, the out-of-roundness measurement of bends, the hardness test and the creep test, stress calculations are required if necessary to determine the minimum wall thickness and the electrode diameter of the weld. After the welding conditions are met, it is also necessary to pay attention to the fact that the fire work should not be carried out at the same time during the welding with pressure. Only after the blocking and welding of a hot part is completed can the next hot part be blocked and welded.

This article discusses the problems that the No.1 ethylene plant at PetroChina Dushanzi Petrochemical Company faces in processing light feedstock, including the unstable operation of quench system, analyzes the performance of feedstock, the modification of cracking furnace and the optimized operation of the quench system for processing light feedstock, and provides some feasible operation methods.

This paper introduces the test run process of ethylene pyrolysis furnace, compares the three test runs of SL-Ⅱ ethylene pyrolysis furnace in different periods, and studies the effect of cracking condition changes on the pyrolysis product yields and product benefit. The results show that the test run data can reflect the actual operation of the pyrolysis furnace and provide references for the operation optimization and efficiency improvement of the ethylene plant.

During the actual production of cracking furnace in the ethylene plant at PetroChina Sichuan Petrochemical Co., Ltd., the process and control were inconsistent with the expectations. The load of the gas phase cracking furnace was too high, so through the transformation of fresh propane process, part of the propane was sent to light hydrocarbon furnace for cracking, so as to ensure the stable load of gas phase cracking furnace. The purge gas system was pressurized, so a secondary line was added to the electromagnetic valve which controls the return of purge gas to the hearth of cracking furnace, and the drain pipeline of the purge gas system was led to the coke pool for the formation of a backwater bend, so as to meet the safety and environmental requirements on site. The temperature of super high pressure steam was greatly fluctuated due to the unstable flow of attemperating and pressure reducing water, so the split control of the attemperating and pressure reducing water was optimized, and the linear unstable valve was limited, so as to ensure the stability of the process parameters of super high pressure steam. And the limit method is also used to optimize the split control of fuel gas flow, so as to ensure the stability of fuel gas flow.

The conventional control strategy adopted for the cracking furnace of the 800kt/a ethylene plant at PetroChina Sichuan Petrochemical Co., Ltd. led to some problems including a large fluctuation in average COT, the imbalance of pass temperature and the unstable control of total feed flow. Advanced process control (APC) system was designed for the eight USC tubular reactors, including total feed volume and pass temperature balance control and average COT control. The background and practical needs for the APC system and the system struction, operation interface and securable logic of advanced control are introduced. The application results show that, compared with the conventional control strategy, the APC system has better tracking ability, robustness and disturbance rejection ability, and shows high value in industrial application.

When the main oil pump of cracking gas compressor, propylene compressor and ethylene compressor in ethylene plant fails or drives steam fluctuations, the pressure of lubricating oil decreases to below the set pressure of spare oil pump, and the lubricating oil required by the compressor unit cannot be replenished in time after the startup of the spare pump, resulting in low low pressure interlock shutdown of compressors. Through the calculation of oil circuit data, some measures are put forward including the installation of energy accumulator on lubricating oil main to improve the anti-fluctuation capacity of the oil system of key compressors, so as to reduce the number of unscheduled shutdown of the ethylene plant.

The cracking gas compressor of an 800kt/a ethylene plant in China is large localized compressor unit with three cylinders and five stages, and is designed with three stages of backflow to one-stage suction, four stages of backflow to four-stage suction and five stages of backflow to five-stage suction to prevent the surge. In three years’ operation, there were problems including the operation safety margin of three-stage anti-surge system is low, the action of four-stage anti-surge valve easily leads to compressor trip, and the action of five-stage anti-surge valve easily leads to C2 front-end hydrogenation reactor trip. During the overhaul in 2016, the control system of the cracking gas compressor unit was optimized, the above-mentioned problems were solved successfully, the degree of automation was improved, energy saving and consumption reduction were achieved, and the operation of the compressor unit was stabilized.

Turbine scaling was found simultaneously on the cracking gas compressor, propylene refrigeration compressor and ethylene refrigeration compressor in the 460kt/a ethylene plant at PetroChina Lanzhou Petrochemical Company due to lack of water quality control, resulting in a serious decline in the operating efficiency of turbines, and the plant was forced to reduce the production load. Two online wet steam purging was carried out to improve the operating conditions of the turbines, and the water quality of the boiler was strictly controlled to ensure the long period operation of the plant at high load, thus avoiding the large amount of material discharge due to the shutdown of ethylene plant for scaling treatment.