This paper reviews SINOPEC’s ethylene business in 2021, 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 2022.

This paper summarizes the development of PetroChina's ethylene business in 2021, including its subordinate petrochemical enterprises' ethylene production, ethylene yield, yields of ethylene and propylene, processing loss ratio, energy consumption  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 2022 is put forward.

Raw material analysis and cracking performance evaluation of heavy naphtha with an increase of about 10℃ in final boiling point during the operation of ethylene plant were carried out. The results showed that the heavy components of heavy naphtha were mainly concentrated in a distillation range from 90％ boiling point to final boiling point. This raw material was stratified seriously in the storage tank, and the tank switching process had a great impact on the system. Under suitable cracking conditions, the yields of ethylene, propylene and C4 were 33.9％, 14.79％ and 8.56％ respectively. Compared with ordinary naphtha, the yields of hydrogen, propylene and fuel oil in cracking products changed slightly, the yields of methane and ethylene decreased a little, and the yields of mixed C4 and pyrolysis gasoline increased somewhat. It can be a suitable cracking raw material when economic benefit is considered for refinery and petrochemical integration.

Cryogenic methane pump is the key equipment of cryogenic separation technology for ethylene plant. According to the original process technology patent provider, the medium transported by the pump has the process characteristics of light medium, low temperature, inflammable and explosive, so the sealing form of pressure seal tank structure with methanol as the sealing medium was selected. Since the pump was put into operation, the seal had failed frequently, resulting in the frozen blockage of methanol and the serious loss of ethylene in cold box. During the upgrading of the plant, the pump was replaced by permanent magnet canned motor pump to effectively solve the frequent leakage problem in the mechanical seal of cryogenic methane pump and achieve the goal of zero ethylene loss in cryogenic separation area of ethylene plant.

The condenser in propylene rectification tower of ethylene plant is used to condense the gas-phase propylene from the top of propylene rectification tower. Corrosion leakage of tube bundle occurred during its operation. During an overhaul in 2019，the causes of the tube bundle leakage of condenser in propylene rectification tower were found out by macroscopic examination of heat exchanger, cooling water analysis and chemical analysis of corrosion fouling. The analysis results showed that the under-deposit corrosion due to the slime biological fouling at tube side circulating water end is the main cause of the tube bundle leakage of condenser, the shell side process medium is less corrosive, the microbial corrosion and oxygen corrosion in circulating water, the stress relaxation at expansion of tube bundle and tube plate at high temperature and the crevice corrosion at the weld between tube bundle and tube plate also play a certain role in promoting the tube bundle leakage, so corrosion leakage occurred in the tube bundle of condenser under the combined action of these five corrosion forms. Some protection measures such as regular backwashing of condenser, key indicator monitoring of circulating water and anticorrosive coating for condenser tube side were put forward to guarantee the long period, safe and stable operation of the plant.

The DCPD depolymerization system takes C₉ pyrolysis product as the raw material. Common tubular heat exchanger was used as the feed heater for depolymerization material in the original design, and the consumption of high-temperature heat transfer oil was high. The depolymerization system needed to be shut down for cleaning only after 30 days’ operation due to its coking problem. Combining spiral tube heat exchanger (STHE) technology with spiral plate heat exchanger (SPHE) technology can heat the raw materials separately. Reasonable flow rates and retention time were selected respectively for gas and liquid sections, and high-temperature heat transfer oil was replaced by medium-temperature heat transfer oil. The heat exchanger has been operated for more than four consecutive months without any disassembly and cleaning. This technology has reduced the consumption of heat transfer oil and increased the reaction temperature of material and the product yield.

 Cracking gas dryer is an important piece of equipment in ethylene plant which adopts cryogenic separation technology. Starting from the fact that the actual operation cycle of cracking gas dryer is shorter than the design cycle, the process flow of dryer and the molecular sieve regeneration dehydration process were analyzed. It was found that the main factors limiting the operation cycle of dryer include the temperature of cracking gas to dryer, the operating conditions in regeneration stage of dryer and the regeneration frequency. By carrying out bed water penetration test, adjusting the temperature of cracking gas, optimizing the regeneration steps and reducing the regeneration frequency, the operation cycle of cracking gas dryer in ethylene plant was prolonged in the first year after overhaul, the consumption of high pressure steam was reduced, and the goal of cost reduction and efficiency increase was achieved.

The difficulties in the operation of quench oil system in ethylene plant are analyzed in this article. The causes of polymer blockage in gasoline fractionator are summarized, and the process of polymer blockage is analyzed. It is proposed that the concentration of polymer components and the temperature in gasoline fractionator are the key factors influencing the polymer blockage. The reasons for the tiny coke powder in quench oil system are analyzed, the effective measures for removing coal powder are proposed, and the important parameters to be focused on during the operation of quench oil system are pointed out.  

Ethylene rectifying column is used to separate ethylene product, and its control directly affects the quality and yield of ethylene product. Aspen Plus simulation software was used to analyze the ethylene rectifying column of ethylene plant. The positions of feed tray and sensitive plate in ethylene rectifying column were determined, and the influences of process parameters on ethylene product specifications were obtained by sensitivity analysis. Guided by the simulation, the temperature control of sensitive plate and the level control of tower bottoms were installed, and the control of pressure and return flow in ethylene rectifying tower were optimized, thus increasing the output of ethylene, reducing the energy consumption and improving the overall economic benefit of the plant.

The ethylene compressor of a cracking plant was started up after overhaul, and its over high refrigerant consumption and poor refrigeration effect had a certain impact on the refrigeration system. Through preliminary investigation, it was considered that the over high refrigerant consumption was due to the excessive nitrogen content of ethylene medium, which led to poor refrigeration effect. Further investigation on the dry gas seal structure of compressor unit and the site showed that nitrogen entered the compressor and mixed with ethylene medium due to the reverse connection of the secondary air inlet line with the pressure line of seal cavity, resulting in poor refrigeration effect.

The scaling of steam turbine blade in compressor unit leads to many problems such as increased steam consumption, reduced work efficiency, increased pressure of wheel chamber and increased suction pressure of the first stage of compressor, and turbine blade scaling affects the safe, stable and economic operation of ethylene plant at full load. The reasons for turbine blade scaling are analyzed from the aspect of steam quality, the theory, method, process and results of online cleaning of steam turbine are introduced in detail, and the trends in wheel chamber pressure, conductivity of turbine condensate and concentrations of Na⁺, PO₄^3- and SiO₂ during the cleaning are revealed. Online cleaning technology can successfully solve the turbine blade scaling problem in compressor unit. Finally, the measures for controlling the steam quality are introduced.

This paper introduces the excessive vibration problem of ethane refrigerator during commissioning. After taking some measures including the inspection of foundation bolts of the unit, the spectrum analysis of unit vibration, the return of motor to the factory for treatment and the enhancement of structural support of the unit, the vibration was significantly reduced, which fundamentally solved the excessive vibration problem of the unit.

This paper introduces the single test run technology for turbine of cracking gas compressor in the ethylene plant of a petrochemical company, including the purposes of single test run, the conditions to be met prior to single test run and the steps of putting the auxiliary system into operation prior to single test run. The mechanical properties of turbine such as field trip, long-distance trip, electronic over speed, independent over speed and TTV valve stroke are tested. A specific single test run plan for turbine is put forward according to the construction progress on site and the external restriction factors, and the abnormal situations encountered in the actual single test run and the corresponding solutions are introduced.

This paper introduces five SCR ammonia preparation processes, i.e., liquid ammonia / ammonia water vaporization, urea hydrolysis, urea pyrolysis, ammonia direct injection and urea direct injection. Based on the characteristics of ethylene cracking furnace, these processes are analyzed and compared from the aspects of safety and environmental risk, ammonia conversion rate, system responsiveness and comprehensive cost. None of these ammonia preparation processes can improve the safety and environmental risk level of ethylene plant. Liquid ammonia vaporization method has the best system responsiveness and the lowest economic cost. It is concluded that liquid ammonia vaporization is the preferred SCR ammonia preparation process for ethylene cracking furnace.