Analysis And Optimization Of The Energy-Saving For FCC Unit Of Zipu Refinery

With the rapid development of the social and economic, the demand for light oils were growing quickly. Poor quality of raw material oils and conflict of supply and demand for light oils were determined the technology of converting heavy oils to light oils. The characteristics of low solid residue and metal content, less asphaltenes determined the technology of converting heavy oils to light oils. With the characteristics of less density, low char factor of FCC material, induced some harsh operation conditions, like poor cracking, high gasoline recycle ratio and reaction temperature, which caused the high energy consumption. The energy consumption of FCC account for more than 40% of the energy consumption of refinery, it had a significant for saving energy and improving utilization of oil resources by reducing energy consumption.In this issue, according to the calibration of the material balance, the heat balance, momentum balance, three-link of energy balance and exergy balance of reaction-regeneration system, the main reasons for high energy consumption were calculated and analyzed, the position of the energy loss were confirmed, the practical and feasible measures for optimizing operation were proposed so as to optimize energy and reduce device consumption.Industry results showed that:with the harsh condition of high gasoline recycle ratio(0.54), low catalyst circulation rate(135.3t/h) and low catalyst to oil ratio(5.4), catalytic cracking reaction of 0.2Mt/a FCC leading to low catalytic activity(51), low conversion rate, poor selectivity and product distribution, coke yield as high as 8.8%, which caused the high energy consumption (168.43kg standard oil per ton of feed) by large heat release and low reutilization, higher than the design energy consumption (92.098 kg standard oil per ton of feed).According to the condition of industrial test of low gasoline recycle ratio of 0.2 and high catalyst to oil ratio of 6, results showed that:burning the excess fluidization air and dry gas were resulted from optimal state of regeneration system. High wire speed(1.607), short stay time(2.03min), low oxygen concentration 17%), large steam pressure(larger than 3 times of the normal main steam pressure) and poor catalyst activity caused by catalyst heat collapsed and poor regeneration, the burning heat and reutilization of exhaust-heat boiler were reduced, which caused the energy consumption increased.By choosing the three-link model of energy balance and exergy balance about FCC, the exhaust gas energy loss and exergy loss were account for 88.76% and 53.40% in the conversion and transport link, recycled energy and recycled exergy were account for 99.48% and 29.49% respectively in the use of session, the energy recovery rate was 66.70% and exergy recovery was 53.67% in the recovery session. By transforming the structure of exhaust-heat boiler to improve the heat transfer environment and efficiency of energy conversion; by decreasing the air(23000Nm3/h), stop burning the dry gas and reducing gasoline recycle ratio(0.2), increasing catalyst to oil ratio(6.9) so as to reduce the energy consumption; by optimizing the cold-heat exchanger, reducing the heat transfer exergy loss and so on, which can improve the energy reutilization of exhaust-heat boiler.After conducting energy-saving measures, the total energy consumption of devices was 168.43 kg standard oil per ton of feed, reduced about 23.71%.