Abstract
The basic theory of exergy was used to derive the formulae of physical and chemical exergy in the process of pipeline transportation, combined with the effect of wax deposition on the thermodynamic parameters including specific heat, density, chemical potential and concentration gradient. On the basis of this, the expression of various exergy losses were derived, and the exergy balance model was then built in the process. For the case study, a waxy crude oil pipeline in China was selected. The mechanism for how wax deposition affected the physical and chemical exergy loss was studied through analyzing the axial pipeline distribution of pressure, temperature, flow rate and thickness of insulation layer. Finally, under the design flow of 66 × 103 kg·h−1, the orthogonal experimental analysis method was used for comparing the degree of specific factors which could influence the total exergy efficiency. The highest exergy efficiency combination of working conditions was then determined. This research could provide a theoretical basis for guiding safe and economic operation in the actual pipeline transportation process.
Highlights
Most Chinese crude oil is high-pour-point and viscous, waxy crude oil; it generally needs to be heated for transportation [1,2]
The pressure exergy of the oil flow was a function of both temperature and pressure, and it had nothing to do with the properties of crude oil
The pressure exergy decreased with the increase of the temperature, and increased with the increasing of pressure
Summary
Most Chinese crude oil is high-pour-point and viscous, waxy crude oil; it generally needs to be heated for transportation [1,2]. It is noteworthy that many experts and scholars have done a great deal of research into exergy analyses of general pipeline transportation processes, for the pipeline transportation process of waxy crude oil, their studies might be more reasonable and accurate if they had considered wax precipitation, which can impact the physical and chemical exergy. A waxy crude oil transportation pipeline from an oilfield in eastern China was taken as an example, an exergy analysis of the transportation system was carried out, the distribution of various types of exergy loss was provided, and the reasons for this phenomenon were analyzed. According to the working ability for different potential fields, we can divide the exergy into two categories, physical exergy and chemical exergy, in the process of waxy crude oil pipeline transportation [13]
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