The stagnation pressure of a centrifugal compressor system impacts the design of the compressor body?, ?auxiliary systems? (e.g., seals) and ?related process systems? (e.g., suction drums). Rigorous and accurate calculation formulas are derived based on thermodynamic theory. Several simplified formulas are developed. The errors of several calculation methods are compared and analyzed through calculations, and a simplest calculation method is recommended for the stagnation pressure of three key compressors in ethylene plants.

This paper introduces the high exhaust pressure in the driving turbine for propylene refrigeration compressor in the 220 kt/a ethylene plant of a petrochemical company. Through technical research, design optimization and the implementation of technical measures, the working efficiency of the turbine is further improved while eliminating the bottleneck of high exhaust pressure, thus achieving the goal of energy saving and consumption reduction and eliminating the operational hazards in the plant. The operational efficiency of the plant is improved and the cost is reduced through minor modifications in local areas.

In a 1,190 kt/a ethylene plant, seven centrifugal compressors utilizes dry gas seal system. During operation, the failure or damage of the dry gas seal system resulted in the interlock shutdown of cracking gas compressor. This paper briefly explains the principle and control of dry gas seal system, and summarizes the on-site practical experience and application suggestions through typical cases of dry gas seal application over the years.

With heavier and deteriorated cracking feedstocks, an 800 kt/a steam cracking unit faces two major challenges, i.e., the high-load operation control of heavy component separation towers and the increased fouling rates due to the heavier feedstock. This paper analyzes the impact of long-term high-load operation of heavy component separation towers and the material polymerization and fouling on the normal operation of the process system. Some optimization measures are proposed from the aspects of process operation optimization, equipment maintenance strategies and design debottlenecking modifications to ensure the long-term safe production of the heavy component separation towers in steam cracking unit.

The pre-processes of the hydrogen production unit and the methanol unit of a certain company are highly consistent, and the process parameters are similar. Due to the shutdown of reformer in the hydrogen production unit, in order to meet the hydrogen demand for startup after maintenance, high-temperature conversion gas produced by the methanol unit was used as the feed gas for medium-temperature shift reaction in the hydrogen production unit. Through process optimization and the co-production and co-adjustment strategy, the conversion process of methanol unit was closely connected with the process flow of hydrogen production unit including medium-temperature shift, compressor, medium-temperature shift system and feedstock preheating furnace, so as to meet the hydrogen demand for start-up of production units. At the same time, the start-up time of the hydrogen production unit could be reduced from 5 days to 36 hours, greatly improving the emergency hydrogen production capacity of the unit. When the ethylene unit was in operation and the total amount of crude hydrogen and wet hydrogen was 580 kg/h, the optimized process of the new methanol unit and hydrogen production unit could meet the maximum external hydrogen supply of 12,506 m³/h. Through process optimization and co-production and co-adjustment, the operation bottleneck of the hydrogen production unit was eliminated. At the same time, the mutual backup of hydrogen production unit was achieved, the task of guaranteeing hydrogen supply during startup was completed, and the dual goals of technical research and quality improvement with efficiency enhancement were achieved.

Pyrolysis gasoline from ethylene cracker undergoes pre-fractionation to remove C₅ and lighter components and C₉⁺ components, and then undergoes two-stage hydrogenation to hydrogenate olefins into saturated hydrocarbons and remove impurities such as sulfur, nitrogen and oxygen to obtain hydrogenated pyrolysis gasoline. The hydrogenated pyrolysis gasoline is separated by BTX extraction and distillation to obtain products such as benzene, toluene and mixed xylene. In this paper, the technological route and operation key points of BTX aromatics extraction unit with hydrogenated pyrolysis gasoline as the feed are analyzed. It differs from the traditional aromatics extraction in the introduction of raffinate extraction system and water washing coupling process, which recovers benzene from non-aromatic hydrocarbons and removes solvents from non-aromatic hydrocarbons. The technical problem of separating C₈ non-aromatics from aromatics in BTX extraction can be solved, and the solvent quality deterioration caused by the accumulation of heavy components can be solved by the coupling process. The two separation columns of toluene, mixed xylene and heavy aromatics in the aromatics distillation system are integrated into a single column to obtain on-spec toluene and mixed xylene products.

This article focuses on the main operations during the shutdown of quench system of ethylene plant, and analyzes and studies the difficulties in emptying quench oil, the high oil content of quench water, and the easy blockage of discharge valve during the emptying operation. To solve the problem in emptying the quench oil, an optimization method is proposed for the emptying operation of quench system. By utilizing the height difference between the pipeline, tower tank and heat exchanger users of the quench oil system and the inlet pipeline of quench oil delivery pump and heavy fuel oil pump, temporary pipelines are configured to increase the number of available quench oil delivery pumps, improve the delivery flow rate, reduce the workload of operators, and effectively shorten the emptying time of the system and increase the recovery of quench oil. To solve the problem of high oil content of quench water, a method of preliminary separation and recovery of gasoline through cooling and settling is proposed. To solve the problem of easy blockage of discharge valve in the quench system, a backwashing method is proposed.

Polymer blockage in reboilers of butadiene distillation towers can significantly reduce the heat transfer efficiency of reboilers, leading to increased energy consumption and insufficient product purity (such as 1,3-butadiene purity < 99.2%), and posing a threat to the long-term operation of the unit. Design defects cause the liquid phase lines of the reboilers in acetylene distillation tower and butadiene distillation tower to be at the lowest point of the entire tower, resulting in the accumulation of polymers and TBC inhibitors, which exacerbates the pipeline blockage and decreases the heat transfer efficiency. No rupture disc is installed upstream the safety valve, and the polymerization of high-concentration butadiene may block or swell the safety valve, posing a safety hazard. Insufficient bypass opening (below 2 turns) of the pressure regulating valve PV24006 results in poor medium fluidity and easy polymer formation in dead legs. In addition, TBC inhibitors need to be accurately added at the designated injection points (the overhead gas phase line and reflux line of acetylene/butadiene towers). Insufficient injection can cause polymerization at the bottom and shorten the operating cycle of reboilers. Excessive injection can lead to equipment blockage and increased costs. Uncontrolled oxygen content and tower pressure can directly trigger polymerization reactions, block the equipment, and force the system to shut down for cleaning.

The abnormal closure of the ethylene feed valve in polyethylene plant caused disturbances in polymerization unit, and emergency measures were taken to avoid the shutdown of the plant. This article uses root cause analysis to investigate the factors causing abnormal valve operation, and ultimately determines that the insufficient power supply of the control system failing to meet the needs of on-site equipment is the cause. The accident potential is eliminated by taking corrective measures, and considerations for the power supply design of control system are proposed.

A comprehensive investigation was conducted on the leakage at the root weld of impulse line of the radiant coil in cracking furnace of a 1.2 Mt/a ethylene plant. Through macroscopic morphology, material testing, metallographic examination, electron microscopy scanning and energy spectrum analysis, it was found that the cracking at this location was due to the decrease in the toughness of small tube structure, resulting in fatigue cracks under structural stress. The reason was that severe stress concentration occurred at the connection between the main pipe and the branch pipe. Material sensitization occurred during long-term service at high temperature, leading to microcracks at the weld seam. These cracks gradually expanded from the outside to the inside, ultimately forming through-thickness cracks and causing leakage.

Ethylene cracking gas main valve assembly is one of the key equipment in ethylene cracking furnace. This paper, based on the engineering example of a newly constructed ethylene plant, discusses the role and importance of the stable operation of cracking gas main valve for the entire process of cracking furnace, elaborates on the optimization of purge steam line for the main valve, and discusses the layout of outlet pipeline of the main valve as well as two design schemes for the support configuration of the main valve.

The tank farm for the 600 kt/a ethylene plant of PetroChina Tarim Petrochemical Company is equipped with eight ethylene spherical tanks with a volume of 3,053 m3. In 2023, the first periodic inspection was carried out for the ethylene spherical tanks after they were put into operation. While strictly implementing the Pressure Vessels Periodical Inspection Regulation, the main damage mechanism and failure mode of the spherical tanks were fully considered. The inspections mainly include document review, macroscopic examination, wall thickness measurement, surface defect detection, ultrasonic testing, hardness testing, and safety accessory inspection. During the process disposal, scaffolding erection, weld grinding and other tasks prior to the inspection, safety technical disclosure was strictly conducted with the construction company, and construction and management were carried out according to the standardized templates, so as to ensure the safe and efficient completion of the inspection.

During the process operation and accident discharge of an ethylene plant, it was found that the back pressure of flare was abnormally increased during equipment emptying and purging as well as acetylene hydrogenation reactor switching and discharging to cold dry flare. During the major overhaul in 2024, endoscopes and tube robots were used to check the inner tube in jacket of the cold dry flare, and the inner tube was found to be severely deformed. The causes of inner tube deformation were analyzed by calculating the parameters of the cold dry flare including daily operation, harsh working conditions and piping design, and targeted solutions were developed to ensure the safe emission of the flare system.

The catalysts in the second stage reactor of the pyrolysis gasoline hydrogenation unit of PetroChina Sichuan Petrochemical Co., Ltd. was unloaded anaerobically for the first time. This paper introduces the anaerobic unloading technology, unloading process and the precautions. Safety risks such as fire, explosion, poisoning and suffocation during catalyst unloading can be effectively reduced through process handling and energy isolation, reliable gas supply system, strict control of the work environment, enhanced process monitoring, strengthened personnel training and education, and proper disposal of spent catalysts.

Cleaning of sewage tanks in chemical plants has always been a high-risk operation in confined spaces. In the past, personnel entered the tanks for cleaning. The site smelled seriously, and the organic hydrocarbon content often exceeded the standard. Personnel suffocation, poisoning, and fire and explosion accidents are prone to occur during the cleaning. The control of the cleaning process has always been a difficulty point. In order to prevent accidents, an advanced mechanical cleaning technology was introduced from the perspective of personal safety, health and environmental protection. It was applied in the cleaning of sewage tank for the first time, and good results were achieved.

In response to the frequent chain accidents of leakage–freeze expansion–fire in domestic ethylene plants with ultra-long service cycle (>30 years) during winter, this paper takes a rupture-and-fire incident on the drain line of an ethylene cracking unit as the example, and reconstructs the release sequence using multi-source data from DCS, GDS, weather stations and surveillance cameras. Using Phast software, a three-stage leakage model of water → liquid hydrocarbon → cracked gas is established and coupled with video frames. It is confirmed that, under conditions of -15 ℃ heat-tracing failure and CUI wall-thinning to 2.06 mm, the DN50 blind-end pipe suffers a 45° shear rupture when internal pressure exceeds the freeze-expansion limit. A four-dimensional closed-loop management strategy of design–inspection–warning–emergency for winter operation of aged units is proposed, providing quantitative bases for standard upgrades of similar installations in the industry.