Numerical study on the temperature drop characteristics of waxy crude oil in a double-plate floating roof oil tank

Abstract Physical and mathematical models for the temperature drop process of the waxy crude oil in a double-plate floating roof oil tank are established with the consideration of non-Newtonian behavior and wax precipitation accompanying the phase change of waxy crude oil. Accordingly, an integrative numerical procedure is developed for the calculation. In this study, non-Newtonian behavior is described by power-law equation. Wax precipitation is described by the enthalpy-porous media theory, in which the gel oil interface is tracked. The computer code is validated by the results in literatures. Based on the verified computer code, characteristics of temperature drop in the tank are studied and the influences of wax precipitation amount and non-Newtonian behavior on the temperature drop process are analyzed in detail. The results show that when oil is not gelled, the oil tank can be divided into two parts: (1) the top and middle part of approximate uniform temperature; (2) the bottom part of stratified distribution of temperature. It is also found that increasing of the wax precipitation amount will slow down the temperature drop process and extend the duration of the temporal stable period. Furthermore, when oil temperature is between abnormal point and thixotropy appearance point, whether considering the non-Newtonian behavior or not covers certain influence on temperature drop process, and different non-Newtonian behaviors play less effect. When oil temperature is below thixotropy appearance point, strengthening of the non-Newtonian behavior will slow down the temperature drop process slightly.