Energy Utilization Analysis And System Optimization Of RFCCU

Catalytic cracking, as the secondary process which produces the maximum amount ofgasoline, diesel and other kinds of light oil, occupies an important position in the oil refiningindustry and the national economy. The FCC units, however, are not only effective devices,but also big energy consumers, whose energy consumption accounts for about1/3of the totalrefining energy consumption，especially for RFCC units. Therefore, to scientifically andrationally analyze the energy-use process of RFCC units, to propose concrete and feasiblemeasures for the weaknesses in energy-use process, and to reduce energy consumption ofRFCC units, are of great significance to improve the operation of the devices, to increase theeconomic benefits of the oil refining enterprises, and to promote sustainable socialdevelopment. The thesis is based on the above topic and has done the following research:The study focuses on a certain RFCC unit. Two process simulation models areestablished for the distillation system and the absorption-stabilization system with thecommercial software Aspen Plus. By correct selection of property methods and appropriateadjustment of operation parameters, simulation results can reproduce the actual productioncondition accurately. On the basis of successful process simulation, energy analysis andexergy analysis with three-link model are conducted. Accordingly, the energy and exergybalance flow sheets are created. The results obtained show that for the energy conversionphase, energy loss caused by the emission of flue gas contributes most for the total energyloss, which means that to reduce the flue gas temperature for the waste heat boiler has a largeenergy saving potential. For the energy utilization phase, the large amount of process exergyloss results in the low exergy efficiency. Energy saving should focus on the reduction ofexergy loss of the reaction and distillation process. For the energy recovery phase, it isrelatively low both for the energy efficiency and the exergy efficiency. To reduce the exhaust losses, and to enhance the heat transfer effect are the goals of optimization for this phase.Heat removal distribution is analyzed and optimized for the RFCC distillation column.On the basis of ensuring the product quality and the flow rate of vapor and liquid in thecolumn, the heat removal proportion is re-distributed. The proportion of heat removed fromthe top of the column is decreased, and the proportion of the secondary middle heat recycle isproperly increased, so that the exergy loss of the distillation process is reduced by2025.06MJ/h and the exergy efficiency of the distillation column is raised to81.8%.The temperature of the flue gas discharged from the waste heat boiler is deeplydiscussed. The relationship between the acid dew point temperature of flue gas and thecontent of SO3in flue gas is found according to Müller’s curve, and thus the acid dew pointof this RFCCU is calculated to determine the reasonable flue gas emission temperature tomaximize the heat recovery of the flue gas. The results show that when the flue gas emissiontemperature is reduced to150℃,1665kW of energy and629kW of exergy can be saved.