Numerical Simulation On Unsteady Heat Transfer Of The Large Floating Roof Oil Tank

This paper was financially supported by National Natural Science Foundation ofChina (No.51106020, No.51174042, No.51051002), PetroChina Innovation Foundation（2012D-5006-0610） and Youth Scholar Backbone Supporting Plan Project ofHeilongjiang General Colleges and Universities (1252G005).With the enlargement of Strategic Petroleum Reserve in our country, the constructionquantity of large floating roof tanks at reserve bases is also rising. When floating roof tankis used for oil storage, oil in tank will release heat to the external environment. Most crudeoil produced in China are waxy crude oil, and it starts to solidify after the temperaturedrops to wax precipitation point, so certain thickness of solidificating oil appears on theroof, wall and bottom of the tank, which causes a serious threat to the normal operation ofstorage tank. Solution to this problem is to heat these tanks, but this need quite huge energyfor heating large floating roof tanks, thus reasonable time interval is needed for heating andtemperature-maintaining. Therefore, it is necessary to grasp exactly change of oiltemperature during storage and to choose suitable heating and temperature-maintainingmethods, which helps to optimize the storage process design of large floating roof tank,and it also plays an important role in safety and economic operation of tank farm. Based onthe heat transfer theory，different forms of oil in tank, wax deposition process and threestages of oil temperature drop are summarized in this paper. The heat transfer mechanismbetween oil in tank and external environment is also analyzed. According to theconstruction and layout of floating roof tank, a simplified3-dimension physical model isobtained in accordance with the engineering drawing. Some ineffective factors whichshows no influence to temperature are ignored in this progress. And a mathematical model,including continuity equation, momentum equation and relevant flow regime equation, isestablished. Based on mesh unit type and good mesh quality, a grid division of temperaturevariation computing model is completed with numerical method. Temperature dropprogress in floating roof tank with different reserves or different liquid level is simulatedby FLUENT software. Distribution of temperature field and velocity field is obtained. Theresult indicates that higher fluid level leads to slower axial temperature drop and smallertemperature change of adjacent oil. Thus high level storage is more beneficial for thestability of oil in tank. Compared with measured results, the error of simulation resultmeets the requirements. By simulating coil heating, it is concluded that convection do not leads to good heating results and a stirrer device is also needed.