Simulation And Optimization Of Heat Exchanger Network In Atmospheric And Vacuum Distillation Units

In the 21 st century, energy problem has become a serious challenge to China and even the whole world. Among them, coal, oil, gas--- as the non-renewable energy, the amount of their reserve is becoming fewer and fewer, however, their consumption has continued to increase. Only in the year 2014, China’s consumption of crude oil was as high as 519 million tons, but our country’s total production was only 211 million tons. Moreover, China has developed with the extensive mode of economic growth for so long a time, which makes a huge energy consumption throughout the petrochemical industry. During the refining process of crude oil, as its first technological process---atmospheric and vacuum crude distillation, it determines the level of quality of the oil production. However, it takes about a quarter of the whole energy amount for a refinery. As it can be seen, the level of technology and energy consumption of the atmospheric and vacuum crude distillation unit has an important impact on energy conservation and optimization as well as economic improvement for the enterprise。At present, China’s refining industry has increasingly focused on basic device design and optimization. In response to this situation, author of this paper intends to use the Aspen plus process simulation software to simulate the chemical process of atmospheric and vacuum distillation unit and its heat exchanger network in order to redesign the system and achieve global energy optimization.Huizhou refinery’s atmospheric and vacuum distillation unit has been chosen as the simulation object in this paper.As the first refinery centralized processes high acid heavy marine oil in the world, Huizhou refinery has many characteristics in their device and technology that many petrochemical companies do not have. In addition, the refinery’s crude oil processing capacity is 12 million tons / year, a huge amount of which makes the actual operating units too many and complex when connected with each other. Before modeling, by drawing its process principle diagram to modify and redesign part of actual process, so that the accuracy of simulation calculations can be guaranteed. During the simulation, according to the crude nature of the design requirements, set simulation parameters in the Aspen plus simulation software. Then choose the proper physical methods BK10 and convergence algorithm WEGSTEIN to establish operational model of atmospheric and vacuum distillation unit. At last, input the appropriate parameters respectively to get the entire process simulation.Followed by that, extracting the data of all the process streams and utilities stream involved in heat transfer process, then use Aspen pinch software simulate its heat exchanger network. Calculate pinch temperature, amount of heat recovery and utility consumption within the system. Furthermore, in order to verify the correctness of the pinch temperature, choose ten different temperature for △Tmin and calculate the pinch value and minimum utility consumption of the heat exchanger network respectively in order to determine whether the simulation of heat exchanger network is correct or not. By drawing heat exchanger network’s raster image and pinch temperature calculation, it can be seen that the actual final heat exchanger temperature is a little lower than the theoretical value, so the network has some certain potential for improvement. According to the pinch theory: setting a cooling utility upon pinch area or locating a heating utility blow it as well as exchanging heat through it, all this can multiplied increase the system’s utility consumption. On the basis of pinch theory, an improved plan is proposed, which is to divide the heat exchanger network into three part of heat transfer zone : before desalination zone、after desalination zone and after flash distillation tower zone. Then, redesign the processes that violates the theory and has potential to be modified and establish new heat flows. After calculation, it can be found that the final heat-exchanging temperature is increased and the fuel gas consumption of devices is reduced, so the new heat exchanger network can increase the rate of energy recovery in the system. Thus, the transformation plan dose have some certain effect on energy saving and can be a guidance on practical produce.