This paper reviews SINOPEC’s ethylene production in 2020, briefly summarizes the ethylene production from the aspects of safety and environmental protection, feedstock optimization, energy saving and consumption reduction, technology research, long-term operation and maintenance, and puts forward the objectives and important tasks in 2021.

This paper summarizes the development of PetroChina's ethylene business in 2020, including the ethylene production, ethylene yield, yields of ethylene and propylene, processing loss ratio and energy consumption of its subordinate petrochemical enterprises, as well as feedstock optimization, long-term operation, maintenance, technical modification and technical measures. The focus of work concerning long-term optimum operation of ethylene plants in 2021 is put forward.

Since the 800kt/a ethylene plant at PetroChina Sichuan Petrochemical Company Limited was put into operation, its energy consumption index has deviated from the design value. The main energy consumption indexes of ethylene plant are introduced in this paper. By comparing with the indexes of similar ethylene production units, the problems and shortcomings in terms of energy consumption during ethylene production were found. Through the analysis of energy consumption indexes of the plant one by one, some optimization measures were put forward and some improvement schemes were put forward according to the actual production, thus ensuring the stable and efficient operation of ethylene plant and achieving the purposes of increasing ethylene production capacity, reducing energy consumption and improving overall economic benefit. 

Based on the freeze blockage situation in the low-pressure methane side of cold box in an ethylene plant as well as the reaction mechanism of freeze blockage in cold box caused by NOx, the test data of NOx, nitrogen compounds and total-N at different sampling positions in each recuperative stage of cracking process are introduced. The root cause of NOx formation in cold box is that the NO introduced from cracking unit reacts with the O2 in cold box, and NOx is formed from the nitrogen compounds in raw material.

The factors that affect the polymer of styrene products include storage time, storage temperature, oxygen content in tank, pH value of styrene products, TBC content of styrene products and internal anti-corrosion coatings. All of the above factors may cause problems in the quality of styrene products, especially the peeling of anti-corrosion coating and the existence of ferrous ion in inner wall. When the liquid level exceeds the coating that peeled off, styrene reacts with ferrous ion to form polymer, which is dissolved in styrene, resulting in the gradual increase in polymer content of styrene products. In addition, various factors affect the storage quality of styrene products. As for polymer content, besides process operation and external conditions, the construction quality and the selection of anti-corrosion materials are also very important. In order to ensure the storage quality of styrene products, it is necessary to conduct in-depth research and continuous improvement from the aspects of engineering, construction and technology.

The debutanizer of No.2 cracking unit of the ethylene plant in Maoming had been operated for a long time. The unsaturated olefins in the feed polymerized at high temperature and blocked the trays, reducing the separation effect of the debutanizer. As a result, the loss rate of C4 in the bottom of debutanizer increased. To solve the high C4 loss in the debutanizer, the process flow was revamped by utilizing the idle post depentanizer of the No.2 cracking gasoline hydrogenation unit. The debutanizer and the post depentanizer were operated in series, and the material from the bottom of the debutanizer was used as the feed to the depentanizer to further separate and recover C4, thus greatly reducing the loss rate of high value-added C4 products and improving the economic benefit.

The operation of front-end depropanization and front-end hydrogenation process in an 800 kt/a ethylene plant is introduced. The problems occurred during the operation of high pressure and low pressure depropanizer and front-end C2 hydrogenation system are analyzed, and some optimization measures and suggestions are proposed for the problems.

Quench oil dilution steam generator in ethylene plant is used to recover the heat in quench oil to produce dilution steam (DS) for use in cracking furnace, so as to reduce the external supply of medium pressure steam and reduce the energy consumption of the plant. In case of internal leakage of quench oil dilution steam generator, the quench oil will leak into the process water, resulting in the pollution of the dilution steam generator and affecting the stable production of the plant. In serious cases, the plant will be forced to shut down for treatment. In this paper, the causes of internal leakage of the quench oil dilution steam generator in the No.2 ethylene plant in Maoming are analyzed, some corresponding measures are put forward to prevent internal leakage, and some countermeasures for the internal leakage of heat exchanger are proposed.

During the normal operation of centrifugal compressor in the steam cracking unit at PetroChina Liaoyang Petrochemical Company, abnormal pressure fluctuation occurred in the lubricating oil system. Through the exclusion analysis of the influential factors of process and equipment, it was concluded that the failure of self-regulating valve of the lubricating oil system was the main reason for the pressure fluctuation. This problem was completely solved after carrying out targeted check and repair and taking corresponding technical improvement measures.

Cracking gas compressor is the core of ethylene plant, and its ability to maintain efficient operation is critical to the safe and stable operation of ethylene plant. This paper focuses on the problems that had occurred since the startup of a 1000 kt/a ethylene plant, analyzes the causes of these problems, and takes reasonable measures to solve the problems including the full opening of low pressure control valve, the over high SiO2 content of boiler feed water, the increase in shaft displacement due to fouling, the high exhaust steam temperature during turbine startup, the breakdown of mist eliminator of separation tank, the high level of two-stage suction tank and the failure of critical instrument and regulating valve, thus guaranteeing the long period and stable operation of the ethylene plant.

 Taking the ethylene cracking furnaces in the 1500 kt/a ethylene plant at Hengli Petrochemical (Dalian) Chemical Co., LTD. as the example, this paper introduces in detail the process flow of the ethylene cracking furnaces, analyzes the problems in the conventional control scheme and re-designs the control system which includes the average COT temperature control, the branch temperature balance control, the branch temperature "high control" and "low control" and the total feed flow control. The implementation of advanced process control system, such as the hardware and software platform of advanced process control system, the switching logic between advanced control and conventional control and the operation interface of advanced process control system, is introduced. The application of this system improves the control stability of cracking furnace, prolongs the operation cycle of cracking furnace and brings remarkable economic benefits.

Mixed C4 is mainly composed of the acetylene-containing C4 from butadiene extraction plant and MTBE plant and the heavy C4 from light hydrocarbon recovery unit in refinery. This part of C4 components can be used as cracking materials after removing the olefins and alkynes by full hydrogenation. The olefins content of mixed C4 is relatively high, generally accounting for more than 65 mol％. With the operation of the plant, the olefins will be polymerized and coking in the reactor, and then block the pore channel of the catalysts over time, resulting in the decrease of catalyst activity and the increase of bed pressure difference, which will affect the product quality and the operation of the plant. Therefore, the plant has to be shut down for catalyst regeneration. The regeneration process is analyzed, and the regeneration results are evaluated, providing theoretical basis for the subsequent operation of the plant.