Summary of technical transformation of 10 kt/a food-grade liquid CO2

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Chen Shiping (Sinopec Sichuan Vinylon Plant, Chongqing 401254) 1 Overview In order to reduce carbon dioxide emissions and increase methanol production, the methanol unit of Sichuan Vinylon Plant adopted a system to recover CO2 from the flue gas of the natural gas reformer. In 1998, a flue gas recovery CO2 unit was installed. The liquid CO2 device is a downstream device designed and constructed based on the rich capacity of the flue gas recovery CO2 device. The project was put into trial operation in July 2000. However, due to internal leakage in the evaporator and other reasons, the operation of the device was unstable in the early stage (2000.7~2001.4). After the workshop shut down the internal leakage equipment many times for maintenance, and after exploring and modifying the process parameters, the liquid CO2 device operated very stably, with an annual output of about 4,000 t. However, due to flaws in the initial design of the process, food-grade CO2 cannot be produced and can only be sold as industrial-grade CO2. However, the sales price difference between industrial-grade CO2 and food-grade CO2 is large, resulting in large annual profit losses. Therefore, it is necessary to modify the device to produce food-grade liquid CO2. 2. Process technology selection: After multiple investigations and comparisons, we decided to adopt the international standard food CO2 invention patent technology of Hangzhou Kuaikai High-efficiency Energy-saving New Technology Co., Ltd. The technical general manager of Hangzhou Kuaikai High-efficiency Energy-saving New Technology Co., Ltd. will transform the liquid CO2 production device of our factory. After the transformation, the scale will be an annual production of 10 kt of food CO2 whose quality meets the new national standard. Hangzhou Kuaikai High Efficiency Energy Saving New Technology Co., Ltd. determines the transformation plan based on our factory's CO2 raw gas and existing liquid CO2 process flow and related supporting equipment, so that the quality of the transformed CO2 products can meet the quality standards of Pepsi-Cola and Coca-Cola food-grade liquid CO2 products. The renovation project was designed on March 25, 2005, and was completed on August 25, 2005. Under the guidance of Kuaikai's technical staff, it was put into normal operation on September 9, 2005. After the dehydrocarbon purification device was put into normal operation, all 21 indicators were qualified. Online analysis shows that the total hydrocarbon exported by the dehydrocarbon system is only about 0.5×10-6, and all indicators are within the new national standards and the indicators of Coca-Cola and Pepsi-Cola. On September 29, 2005, the samples were sent to Dalian "Chemical Industrial Gas Quality Supervision and Inspection Center" for testing. Tests show that all indicators not only meet my country's new national standards, Coca-Cola, Pepsi-Cola standards and the International Beverage Association (ISBT) standards, but also have many indicators that are better than the indicators set by the above "Standards", see Tables 1 to 3 for details. http://pub2.hi2000.com/upload1/0801231526443014.jpg Table 2 Coca-Cola Company CO2 Standards http://pub2.hi2000.com/upload1/0801231528011158.jpg Table 3 International Beverage Technology Association It can be seen from the tabulated data that the quality of the project reached the design indicators after it was put into production. 3. The process flow uses a piston air compressor to replenish a certain amount of air at the CO2 raw gas inlet, and enters R801 together with the CO2 raw gas. After being cooled by E801 and separated by S801, it enters the dehydrocarbonization device. The dehydrocarbonization unit uses catalytic oxidation to convert organic matter into CO2 and H2O. The converted CO2 enters the molecular sieve S802A/B after heat exchange with E803, and then undergoes sterilization and impurity removal by S803/804/805C. It enters E804A for cooling, and then enters the purification tower for purification. The purified CO2 enters E805B for cold exchange with ammonia, and finally liquid CO2 enters T801/802. The process flow diagram after the transformation is shown in Figure 1. http://pub2.hi2000.com/upload1/0801231529311022.jpg Figure 1 Process flow after transformation 4 Technical characteristics The original liquid carbon dioxide unit is technically transformed using the international standard food CO2 production process of patented catalytic oxidation dehydrocarbon purification and shallow low-temperature distillation purification developed by Hangzhou Kuaikai High Efficiency and Energy Saving New Technology Co., Ltd. and the dehydrocarbon catalyst supporting the Hubei Provincial Institute of Chemistry. After the transformation, it has the following features. (1) For the removal of toxic and harmful organic substances such as hydrocarbons, acetaldehyde, and oxygen-containing organic substances, the invention patent of Hangzhou Kuaikai High-efficiency Energy-Saving New Technology Co., Ltd. is used, and the internationally recognized catalytic oxidation technology is used to enable toxic and harmful organic substances to be completely burned at a lower temperature (around 400°C). A total hydrocarbon analyzer is configured for production control to ensure the complete removal of hydrocarbons, aldehydes and other oxygen-containing organic matter. (2) Putting the E803 heat exchanger before drying the S802A/B is more conducive to controlling the moisture at a lower level (water content less than 10×10-6). Moisture is analyzed online to ensure timely regeneration of desiccant and control of product moisture. (3) The dehydrocarbonated gas is distilled under shallow low temperature conditions using the new composite purification tower with proprietary technology of Hangzhou Kuaikai High Efficiency and Energy Saving New Technology Co., Ltd. Not only the product purity is high, but the carbon dioxide purity of the tail gas is also high. * * Reduced (less than 80%), which effectively solves the contradiction between gas consumption and purity. (4) The entire process is operated under medium and low pressure and normal and shallow low temperature conditions, so the transformation cost is low. (5) The product quality is good, and all indicators meet or exceed my country's new national standards, Coca-Cola, Pepsi-Cola and the International Society of Beverage Technology (ISBT) standards. 5 Conclusion The successful transformation of the liquid carbon dioxide unit in the methanol workshop of Sichuan Vinylon Factory into food-grade carbon dioxide further illustrates that my country’s independently developed food CO2 production technology can not only localize all equipment and save investment, but also has advanced technology and has fully reached the international advanced level.