Search

This paper reviews the impact of asphaltenes on wax crystallization and on the properties of crude oils, and the consequences thereof on the flow assurance of waxy crude oil. It initially includes studies of the crystallization of both pure n-alkanes as well as the mixtures thereof, because they have led to an understanding of how their precipitation occurs along with their transitions of crystalline phases, particularly, by studies of X-ray diffraction (XRD). This is followed by the studies and results of crystallization in crude oils and/or the fractions thereof and how their properties are affected in the presence of asphaltenes. The results on the influence of asphaltenes are inconclusive and sometimes contradictory: some confirm that their presence decreases pour point, others affirm that it increases it and yet others say there is no effect. Similar results have been reported for properties such as crystallization point, phase transition and rheological properties. The influence of the chemical structure of asphaltenes on the change in crude oil properties has not been generalized either. It has been inferred that is possibly due to the interaction between aliphatic chains of asphaltenes and waxes, and it has been established that there is synergy in coprecipitation due to evidence in the analysis of organic deposits.

This work is aimed to study the wax deposition process on the internal surface of oil production pipelines and the influence of parameters such as flow rate and pipe wall temperature on the deposit thickness for a light crude oil with high paraffinic content considering three different temperature boundary conditions on the pipe wall; two of which assumed a profile temperature on the boundary, fact that has not been considered in previous works, and the third a constant value. The analysis was conducted assuming pseudo steady conditions on the fluid phase. The finite differences method was applied to solve the differential equation system and the solution was implemented numerically using the C++ programming language. The model was validated with the experimental results reported by Singh et al. (2000) and subsequently used to simulate the growth of the paraffin deposits as a function of flow rate and pipe temperature. The results showed that increased flow rates reduce the maximum deposit thickness, as it spreads on a longer distance in the pipe when considering a constant wall temperature or the axial thermal gradient with a positive slope, and the opposite effect is observed when considering the axial thermal gradient with a negative slope.

ABSTRACT A simulation of a pilot plant delayed coking reactor was performed using an in-house computational fluid dynamics (CFD) code. The reactor was modeled as a three-phase dynamic system where the coke is the porous solid phase, the vacuum residue the liquid phase and the distillable product the gas phase. Equations of continuity, momentum, and energy proposed to describe the coking dynamic process where discretized employing the finite volume method and the domain was defined by a 2D structured axisymmetric grid. A PEA algorithm was developed to account for the drag between the fluid phases, and a modified SIMPLEC algorithm achieved the pressure-velocity coupling. The CFD simulator was programmed in C++ code for Linux operating system; all the graphics were constructed in ParaView visualization platform. A full run of 12 hours and the cooling of the resulting coke bed for three different vacuum residues were simulated, the results were compared with experimental data and a good agreement was observed, the simulator demonstrated great potential to be scaled up to industrial level.

ABSTRACT The adhesion forces between bitumen and minerals were measured, using Atomic Force Microscopy (AFM). The AFM enables the study of the interactions between two molecules in a same surface or at interfaces and their behavior. In this case, bitumen samples with different properties were placed in contact with AFM modified tips. The tips were fabricated with minerals found in aggregates used in asphalt mixtures, like silicon dioxide (SiO2) and calcium carbonate (CaCO3). The work of adhesion was obtained measuring adhesion forces for each bitumen-mineral pair. The direct measurement of forces between asphalt and aggregates at interface level through nanoscopic techniques provides a better insight of the system and its characteristics. This will help to improve the selection of bitumen-aggregate combinations used in asphalt mixtures, obtaining systems with higher bond strength, therefore more resistant to failures.