Analysis Of Exergy Transfer In The Heating Process Of Crude Oil Floating Roof Tanks With Multiple Links

With the increase in China’s oil consumption and strategic demand for crude oil,large floating roof tanks are widely used in crude oil reserves due to their technological and economic advantages.During the tank storage process,the crude oil will dissipate heat to the external environment,resulting in a decrease in temperature and risks such as oil condensation.To ensure the safe operation of the storage tank,timely heating and temperature maintenance are necessary,but the energy consumption during the heating process accounts for a large proportion of the total energy consumption in the storage area.Therefore,in response to the energy-saving and emission reduction goals proposed in China’s 14 th Five Year Plan,this paper takes a large floating roof tank of 100000 m3 as the research object,analyzes the heat transfer and flow characteristics of the heating process of crude oil coils in the tank through numerical simulation,and evaluates the rationality of energy consumption of the system from the perspective of "energy quality",identifies weak links,and proposes energy-saving ways.According to the relevant theories of heat transfer,the theoretical model of heating process of crude oil floating roof tank coil is established by comprehensively considering the physical properties of crude oil,solar radiant intensity,heating steam temperature,external environmental conditions,and other factors.The temperature field and flow field distribution of crude oil are obtained by numerical simulation using FLUENT software,and the influence of different heating steam temperatures and liquid level heights on the temperature field and flow field is analyzed.Based on the first and second laws of thermodynamics and the theory of transport,a multi-link heat transfer system for the heating process of storage tank coils is constructed from the perspective of " energy quality ".For the convenience of research,each exergy transfer element in the system is listed separately,and the spatiotemporal changes and influencing factors of the exergy transfer coefficient,exergy flow density,and exergy resistance of each exergy transfer elements are analyzed to reveal the relationship between exergy transport rate and transport power and resistance.Considering the cross connection relationship between the basic units of exergy transfer under multi-link correlation,based on the principle of 1-N type heat exchange chain,a composite structure of exergy transfer elements in the heating process of storage tank coils is established.By calculating the output of the exergy transfer elements,the flow rate of input exergy,and its decrease rate,the exergy transfer capacity of the exergy source and exergy sink is expressed.Combined with dynamic exergy transfer and static exergy analysis,three evaluation indexes are determined: exergy resistance rate,exergy loss rate and sensitivity factor value.Based on the evaluation index,the TOPSIS method is used to construct the energy evaluation system of tank coil heating process,which realizes the determination of the weakest link in energy consumption at different times of heating.The relevant theories and methods of non-equilibrium thermodynamics are applied to the heating and temperature maintaining process of crude oil storage tanks.The local entropy production equation of the heating process of storage tank coils is derived through the universal entropy production equation.By analyzing the distribution of flow and heat transfer entropy production rate,it is further verified that the weak link is the sub process of coil pipe wall →oil.Based on the entropy production rate equation,a multi field coupled phenomenological equation for exergy transfer is established for weak sub processes.The basic laws of the interaction between heat transfer and fluid flow are studied,revealing the complex mechanism of the coupling and cooperation between various "forces" and "flows" such as temperature gradients and velocity gradients.This paper aims to identify the weak links in the heating process of crude oil floating roof tank coils through the "energy quality" attribute and dynamic characteristics and proposes corresponding energy-saving methods.The research results obtained are of great significance for improving the utilization efficiency of reserve energy and reducing the cost of reserve energy consumption.