Introduction to the Application of PSA “Comprehensive Industrial Technology for Recovering Ethylene from Refinery Dry Gas”

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According to Sinopec News Network, reporters learned from the recently held “Special Technical Exchange Meeting on Recovering Ethylene from Plant Off-gases” that as of now, 10 industrial units utilizing pressure swing adsorption (PSA) for the purpose of recovering ethylene from plant off-gases have been built and put into operation within China’s petrochemical industry. Song Yichang, a senior expert at Yanshan Petrochemical and a professor-level engineer, explained that the PSA \"industrialized technology for recovering ethylene from dry gas in refineries\" was developed jointly by Yanshan Petrochemical and Sichuan Tianyi Technology Co., Ltd. This technology uses pressure swing adsorption to concentrate hydrocarbons with a molecular weight of C2 or higher in refinery dry gas, followed by further purification of the resulting gas. Its technical advantages include: first, the use of a two-stage pressure swing adsorption process for the adsorption and separation of catalytic cracking dry gas; the adsorbents used have good selectivity, high dynamic adsorption capacity, and a service life of up to 10 years, with an ethylene recovery rate of over 87%, and the process requires low energy consumption ； Secondly, the product gas purification process is well-designed; the deoxidizer has high activity, and the product gas undergoes thorough purification to remove impurities such as hydrogen sulfide, carbon dioxide, arsenic, and oxygen, thereby meeting the requirements for ethylene feed ； Thirdly, depending on the equipment capacity of the ethylene plant, the ethylene-rich gas can be directly fed into the alkali scrubbing system for the cracking gas in that plant to reduce energy consumption, or pre-distillation can be employed to ensure a flexible connection with the ethylene plant. This technology offers significant economic and social benefits, and has won the **Second Prize for Scientific and Technological Progress**. According to Song Yichang, this technology has currently been successfully applied industrially in 8 units at Sinopec’s Maoming Petrochemical and Shanghai Petrochemical plants, as well as in 2 units at CNPC. Through continuous process improvements in production practice, the raw materials used for processing have been expanded from catalytic dry gas to coking dry gas, hydrogenation dry gas, and saturated light hydrocarbons ； Based on the composition of the feed gas, an appropriate grading of adsorbents was used along with optimized PSA operation, thereby increasing the recovery rate of C2-rich gas ； The reliability of key equipment has been improved through the proper selection of vacuum pumps and the use of high-power centrifugal compressors ； It has good technical performance and low energy consumption. In 2016, there were no unplanned shutdowns of the production units at Sinopec in China; the average yield of C2-rich product gas was 35%, with both units in Tianjin achieving yields above 48% ； The energy consumption of the plants averages 58 kilograms of standard oil per ton of feed gas, with the Maoming Petrochemical plant having the lowest consumption at 27.72 kilograms of standard oil per ton of feed gas. To further enhance its technical competitiveness, the technology provider has integrated the advantages of two PSA technologies – those featuring ultra-low energy consumption and low-temperature oil use, as well as high C2 recovery rates – to develop a PSA-based composite normal-temperature oil absorption technology. This technology has now been granted an invention patent, and it is being promoted to refining companies that have a need for it.