Research On Heat Transfer Characteristics Of Crude Oil Tank During Storage Considering Mechanical Agitation

In recent years,with the increase of China's oil reserves,how to safely and economically store it has become the focus of people's attention.In the process of crude oil storage,especially in the cold area in the north,there is a large temperature difference between the crude oil temperature in the storage tank and the external environment temperature,and the crude oil in the tank continuously radiates outwards,which leads to the poor liquidity of the crude oil in the tank and cannot meet the normal scheduling requirements.In order to ensure that the crude oil in the storage tank can keep a good fluidity to meet the daily demand,in practical production,the tube heating and the installation of agitator are often used to heat and homogenize the crude oil,so as to maintain the oil temperature in the tank.This paper adopts the method of combining experiment and numerical simulation to study the heat transfer law in the tubular heating process under the action of mechanical agitation.The specific contents are as follows:Firstly,a set of experimental equipment based on particle image velocity measurement technology and thermocouple temperature measurement technology is used to study the influence of mechanical agitation on the heat transfer characteristics of tubular heating process,and the basic principle and operation method of the experimental equipment are introduced in detail.In addition,the evolution results of temperature field and velocity field of tubular heating process under mechanical agitation were obtained through experiments.The experimental results show that:under the condition of no agitation,the tank top temperature is high,the tank bottom temperature is low,and the temperature is distributed in layers,which is the heat transfer result dominated by natural convection.However,heat conduction is the main heat transfer mode in the low temperature region below the heating tube.Under the action of mechanical agitation,it can have a good disturbance effect on the area under the heating tube,and has a good improvement effect on the temperature distribution in this area.Moreover,the greater the mechanical agitation power in the tank,the more significant the influence on the flow in this part of the tank,especially the influence of the temperature field in the tank.In the same heating time range(120min),the highest temperature in the storage tank is 42.5?under the action of high-power stirring,which is 3?higher than that under the action of low-power stirring.Secondly,the physical model and mathematical model of tubular heating crude oil storage tank with mechanical agitation were established,and the corresponding solution method was established.The oil flow field in the tank under agitation was numerically simulated,and the oil in the tank was divided into three grades according to the velocity value:high speed region,medium speed region and low speed region.The results show that for the 1000m~3 storage tank studied in this paper,the agitator speed has the greatest influence on the flow field,and the average speed difference between the minimum speed and the maximum speed is nearly 4 times.Agitator installation height and deflection angle have the least influence on the average speed;The results are similar at different mounting heights and deflection angles.Finally,on the basis of the simulation of the flow field in the storage tank,the tubular heating process of the storage tank under the action of mechanical agitation was numerically simulated,and the factors of the tubular heating process under the action of agitation were analyzed from the technological parameters(stirrer speed and heating tube temperature)and structural parameters(stirrer deflection Angle and impeller diameter).According to the numerical simulation results,the storage tank can be divided into three grades:high temperature zone,medium temperature zone and low temperature zone.The results show that:at the same heating temperature,the temperature in the tube heating process under agitation increases faster,and the heating rate is twice that of the tube heating process without agitation.Moreover,agitation has a good improvement effect on the low temperature area under the heating tube,which is consistent with the experimental results.In addition,when the agitation speed doubled from 350rpm,the volume proportion of high-temperature zone in the tank changed from 26%to 87%,and the volume of crude oil in high-temperature zone occupied most of the tank.When the heating tube temperature increases from 60?to 80?,the average temperature rising rate of crude oil in the storage tank increases from 0.1045?/h to 0.293?/h.The higher the heating temperature is,the faster the temperature rising rate is.However,the increase of heating temperature will lead to a larger temperature difference,so the variance will be larger;When the agitator diameter increases from 400mm to 600mm,the temperature variance in the tank decreases,and the volume proportion of the high temperature area in the tank increases from24%to 67%.The tube heating effect is better under the large agitator diameter.In addition,the optimal tubular heating scheme under mechanical stirring was discussed,and the optimal parameter was stirring speed 350rpm.Agitator deflection Angle is 0°;Tubular heating temperature 80?;Stirrer impeller diameter 500mm.