Heat-transfer Research And Process Scheme Optimization Of Oil Storage In Alpine Cold Region

In recent years, most of the medium and large scale oil depots' reserves have beenincreased consecutively as our country strategic petroleum reserve progresses, so the oilreserving are increasing in our country. The storage security issues of crude oil in extremelycold areas have been gradually recognized because of high wax content, high freezing pointand high viscosity, the poor low-temperature fluidity, and the objective geographicalenvironment conditions of some areas. There are three existential states of the oil in a storagetank: static state, heating state and turnover process of loading and uploading oil. Research onoil flow and heat-transfer characteristics for different running states is significant informulating rational process scheme, guiding engineering practice, and enriching thetheoretical study of heat-transfer issues in engineering. At present most of the researchesfocus on the tests of oil static state temperature field. Although the direct running datas can begiven, the information is not enough for heat-transfer mechanism and coupling calculating oftransient natural convection velocity field and temperature field. And currently, there is notargeted study on heating state or loading and uploading state. Given that, this paper carriedout the research of oil flow and heat-transfer characteristics during three processes by themethodology of combining numerical models and field tests. And the paper also optimized theoil tank process scheme on the premise of ensuring reserve safety. Detailed research workincludes the following parts:First of all, methodology of combining field tests and numerical models was used to testthe surface temperature distributions and heat loss of large-scale floating roof tank. Testobjects include different positions of different capacity tanks' top and wall. The conclusionsinclude tank surface temperature field distributions, different positions heat loss, and thebuoyancy module and tank wall insulation constructions' coefficient of thermal conductivitywhich are difficult to be determined by theory methods. And the paper evaluated the heatpreservation effect of tanks based on the test results.Secondly, the paper carried out the oil flow and heat-transfer characteristics research ofthree oil states in storage tank: static state, heating state and loading and uploading oil state.For the static state, the paper treated oil temperature drop process as unsteady naturalconvection cooling problem of high Pr value fluid in cylindrical space which has complicatedheat boundary conditions. And the paper built two-dimension axisymmetric model and thenumerical solution method of the process. The results of different work conditions calculationand analysis have shown that the fluid heat-transfer coupled with flow during the process oftemperature drop. There are four temperature drop periods corresponding to natural convection's creation, development, recession and disappearance processes, which are localtemperature drop, quick temperature drop, temperature stratification and heat conductionperiod. On this basis the paper regressed with the floating roof tank different boundariesnatural convection heat-transfer correlation, and presented a new way which can calculate oiltemperature drop. The way can not only predict the oil temperature changing, but also candescribe the oil temperature distributions of different periods in tank. The paper calculated oiltemperature drop in different work conditions by the new way, obtained the influence of tankdiameter, liquid level and thermal insulation construction for oil temperature drop, anddiscussed the optimal condition. For the oil heating state, the paper divided heating type intotwo types: tubular heating and hot oil circulation, according to heat-transfer mechanism. Fortubular heating, the paper established the mathematical model of single heating pipe, verticaland horizontal tubes. And the paper got two experimental relations of single heating pipenatural convection heat-transfer when Ra value is between4.2×104~1×109, Pr value isbetween97~454and Ra value is between1.3×1010~1.7×1012, Pr value is between97~910.The relations are more applicable to thermal calculation analysis of oil tank tubular heating.The heat-transfer characteristics of vertical tubes are different from single heating pipe. Theaverage Nu value of tubes is up to15%more than the single one. The adjacent tubes plumenot only changed the heat-transfer characteristics, but also made top layer Nu value fluctuatesalong with time. The further analysis has shown that the change of plume temperature field isthe main reason for the fluctuation. In contrast, horizontal tubes heat-transfer characteristicschange less, and more stable. The research on hot oil circulation heating process has shownthat this heating way has the characteristics of heated buoyant jets. When heating state isstable, oil temperature hierarchical distribution is along the axis; rather, the performance ofheat-transfer is more excellent. And the bigger the Fr value is, the better the heating effect willbe. As a basis for hot oil circulation heating method adjustment, the Fr value and relativedepth of submergence are taken as the acting factors to regress surface maximum temperaturecalculation model. The comparison of two methods shows that hot oil circulation is moreapplicable to transfer oil depots, and tubes heating is more suitable for strategic oil depots.Field test and numerical compute analysis performed on heat-transfer and flowcharacteristics in oil tank shows that when inlet temperature is higher, oil temperature andvelocity fields have the features of heated buoyant jets. And outlet temperature isapproximately equal to the oil temperature at the same liquid level in tank. The results atdifferent parameters show that oil inlet heat can be in full use when flow is mass andtemperature difference is less.Finally, based on the research work above, the paper established oil storage and transportsystem process scheme optimization models and operation principles using minimized cost ofoperation as objective function and tanks operation mode, heating scheme and insulationscheme as decision variables.