This article introduces the 20th National Ethylene Annual Meeting during which the delegates exchanged experiences and understandings of enterprises in safety and environmental protection, energy saving and consumption reduction, raw material structure adjustment, refined management, plant optimization, technical modification and the application of new technologies, discussed the concerns of enterprises and the problems encountered, and put forward some suggestions on the development trend and transformation and upgrading strategy of China’s ethylene industry.

In recent years, with the improvement of China's fuel oil standards and the upgrading of refining units, naphtha, which was formerly used as raw materials for ethylene plant, are mostly used as reforming feedstock, leading to the inadequate supply of ethylene raw materials. And the hydrogenation of butadiene tail gas has gradually increased the probability of using butane as ethylene feedstock. Butane is mainly composed of n-butane and isobutane. The experimental data of butane pyrolysis shows that there is a negative benefit in the co cracking of n-butane and isobutane. The higher the isobutane content, the lower the yield of ethylene, the yields of ethylene and propylene and the yields of ethylene, propylene and butadiene are. Therefore, the isobutane content of butane, which is used as ethylene feedstock, should be reduced as much as possible to improve the yield of ethylene, the yields of ethylene and propylene and the yields of ethylene, propylene and butadiene in butane.

PetroChina Sichuan Petrochemical Company Limited is the first large-scale refinery-chemical integration project built in the southwest of China. The construction was started in 2009, and good social benefit and economic benefit have been gained since it was completed and put into operation in early 2014. In order to give full play to the advantages of refinery-chemical integration, increase the production capacity of high value-added product and improve the profitability of the enterprise, technical modification was planned for some units during the 2018 overhaul to adjust product structure, adapt to market demand, and achieve a flexible process flow which produces the products based on feedstock properties.

Mixed C4 is mainly used to produce alkylated gasoline and MTBE. MTBE will be banned in China by 2020, so the combined process of C4 selective polymerization plus 1-butene separation and C4 alkylation is a good way to develop mixed C4 in the future. This combined process can produce not only the industrial isooctane as a blending component for gasoline but also the 1-butene with a concentration of 93％, while the by-product C4 alkane can be used as raw material for ethylene plant. Good economic benefit will be achieved.

In order to meet the different water demands of ethylene oxide (EO) reabsorption system, EO purification system and ethylene glycol (EG) reaction system for the EO reabsorption tower, the amount of dilution water from de-aldehyde line is adjusted to meet the EO concentration requirements of the feed to EG reactor (R-520) on the premise of guaranteeing the absorption of EO, with the aim of meeting the optimum EO concentration of the feed to EO purification tower. ASPEN simulation analysis shows that, based on the patented technology data and the design data of the internals of EO purification tower, and combined with the actual operation data of the EO/EG plant, the EO concentration of the feed to EO purification tower is increased from 8.9％ to 10％ (case 1)/11.18％ (case 2) by reducing the amount of absorption water in the reabsorption tower from design value 381.4 t/h to 333.7 t/h (case 1)/295.7 t/h (case 2), achieving an additional EO production of 27 kt/a (case 1)/56 kt/a (case 2), calculated according to 8,000 hours, without increasing the feed load of EO purification tower.

During the startup of ethylene plant, emissions mainly come from front-end cold box system and deethanization system. This paper introduces the basic process flow of the front-end cold box system and the deethanization system and the possible emission points during operation, analyzes the reasons for the unreasonable emission in combination with the actual situation on site and the startup experiences of other ethylene plants, and proposes some rectification measures to achieve the successful low-emission startup of ethylene plant on the first try. Through analysis of the basic process flow of cold area, some processes are optimized and modified. Startup lines are added without changing the existing process flow, so as to achieve the goals of emission reduction, energy saving and consumption reduction, reduce the total emissions of the system during startup, and reduce the material loss and energy consumption of the ethylene plant.

In the actual operation of the Megaton ethylene plant in Dushanzi, the cracking feedstock is diversified, the impurities are complicated and the switchover of feedstock is frequent. In order to improve the yields of ethylene and propylene, a series of operational change and technological transformation are put forward through the comparative analysis of feedstock to adapt to the processing of different feedstock, so as to maximize the benefit.

This paper studies the problems arose in the long period operation of cracking gas compressor due to light feedstock, including the shorter polymerization fouling period of compressor body, outlet pipes and inter-stage coolers, the decrease in operational efficiency of compressor, the increase in N Factor and first-stage suction pressure, and the rise in operational cost of compressor turbine. By analyzing the reasons for the shorter polymerization fouling period of compressor and the increase in N Factor and first-stage suction pressure, the injection volume of polymerization inhibitor and wash oil was optimized to control the increase of N Factor. A complete decoking of the compressor body and outlet pipes was performed during the overhaul to improve the operational efficiency of the compressor and reduce the inter-stage loss, so as to guarantee the stable, efficient and long period operation of the compressor.

Based on the transformation of the seal system for hydrogenation recycle hydrogen compressor, this paper introduces in detail the transformation of the instrument control system, and comprehensively discusses the selection of control system, the optimization of control scheme and the implementation of control functions combined with the actual situation of the unit.

To solve the coking problem of cracking gas compressor (K-3101) in the ethylene plant at PetroChina Dushanzi Petrochemical Company, this paper introduces the coking inhibition mechanism of wash oil injection, water injection and polymerization inhibitor injection, and analyzes the axial force balance of high pressure cylinder (K-3101). The result shows that there is a direct relationship between the coking and the axial displacement of the impeller and internals of cracking gas compressor, and the severity of coking is positively correlated with the magnitude of axial displacement. By adopting inter-stage water injection technology and optimizing polymer inhibitor injection amount and wash oil injection time, the accumulation of polymer on the impeller and internals of compressor can be effectively inhibited, so that the axial displacement will gradually decrease.

In April 2018, high level alarms frequently went off in the fifth-stage suction tank of cracking gas compressor in the ethylene plant in Tianjin. Since this happened after the installation of the fourth-stage discharge cooler (EA207B), technical personnel checked the level gauge of the fifth-stage suction tank, the process parameters, and the pressure difference in cooler (EA207/EA207B). It was concluded that the serious coking and blockage in EA207 made the outlet pipe of EA207 a liquid storage pipe, thus resulting in the high level alarms. By adding a technical transformation pipeline, the water and hydrocarbons accumulated in the outlet pipe of EA207 were discharged to quench tower, successfully solving the problem, eliminating the potential safety hazards in production and ensuring the stable operation of the ethylene plant.

This paper briefly introduces the development background of Sinopec CBL ethylene cracking furnace technology, the development implemented in each stage, the technical characteristics of various types of CBL cracking furnaces, the technical level achieved and the application of CBL ethylene cracking furnaces. The general considerations and specific application cases of CBL cracking furnace serialization are introduced. The different schemes of SEI in modular design,the relevant situation of SEI in standardized design of cracking furnace and how to combinewith new furnace revamp of cracking furnace are introduced.

This paper analyzes the reasons for the over high NOx emissions in exhaust gas after low-NOx burner was used in the 100 kt/a CBL-III cracking furnace. In consideration of the design conditions, working principles and actual operation of the low-NOx burner, the air leakage of the furnace body was blocked. Through adjusting the fan speed and the throttle opening of bottom burner and side wall burner, the oxygen content of exhaust gas was controlled and the thermal field distribution of furnace was optimized to reduce the NOx production in exhaust gas. After the optimization, NOx emissions of cracking furnace during normal operation met the national emission requirements. The influence of oxygen content of exhaust gas on NOx and CO production was explored, and an optimal range of oxygen content was determined. The influence of furnace production load on NOx production was analyzed, and the direction of operation adjustment of cracking furnace was proposed after the load changed. An operation manual was developed for low-NOx burner to guide the routine operation of cracking furnace.

The automatic temperature measurement and intelligent coking diagnosis system for furnace tube jointly developed by SINOPEC Maoming Company and Guangdong University of Petrochemical Technology was applied in the H-115 cracking furnace in Maoming, and the accurate measurement of the outer wall temperature of furnace tubes were achieved. Through the collection, diagnosis and analysis of strategy temperatures, the early detection and early warning of over temperature furnace tube can be achieved, and the manual temperature measurement can be replaced.

8 Linde Pyracrack1-1 cracking furnaces are designed for the Megaton ethylene plant at PetroChina Dushanzi Petrochemical Company, each with an ethylene production capacity of 150 thousand tons per year. The ethylene plant has been operated for 8 years since its startup in September 2009. The fouling in convection section was serious, and the superheating temperature of super-high-pressure steam (SS) in light hydrocarbon cracking furnace was low. By increasing the excess air coefficient, the temperature of SS was only maintained at 465~485 ℃. The energy consumption of cracking furnace was increased, and the thermal efficiency was low. Although manual cleaning was performed and high frequency acoustic wave soot blower was installed, the process requirements could not be met, thus influencing the long term operation of the ethylene plant. The chemical cleaning of convection section effectively solved this problem, improved the thermal efficiency of cracking furnace and reduced the emission of exhaust gas.