the structural differences of asphaltenes in Colombian light crude oils from the same field, i.e., the Colorado oilfield, were presented. Colorado crude oil is a light crude with very low content of asphaltenes (<0.3%, w/w) and presents paraffin crystallization problems during its production. In the parafinic deposits, asphaltenes have also been found. In this work, a new methodology is proposed to determine the effects of chemical structure and concentration of asphaltenes on the wax crystallization of the crude oils from the Colorado oilfield. Six crude oils (from different sands) were fractionated in their respective asphaltenes and maltenes. The crystallization properties of crude oils and maltenes were obtained: wax appearance temperature (WAT), pour point, and crystallization enthalpy. Asphaltenes were characterized by nuclear magnetic resonance analysis, mass spectrometry, X-ray diffraction, and Raman spectroscopy, and their main average molecular parameters (AMPs) were calculated. Partial least-squares regression (PLS) analysis was used to understand the influence of asphaltenes chemical structure on the crystallization processes. The proposed characterization−statistical analysis methodology allowed for the understanding of the effect of the average molecular structure of asphaltenes on the crystallization properties of paraffins from the crude oils of the Colorado field. The effect of asphaltenes was analyzed through correlation between the differences in WAT, the differences in pour poin,t and the relative crystallization (C r ) with the AMPs of asphaltenes. The AMPs of the asphaltenes causing the greatest impact on the increase of the crystallization temperature are the pericondensed carbons (C aaa ), ratio of peripheral carbons/aromatic carbons (C p /C ar ), and aromaticity factor ( f a ), and decreases in these properties are attributed to the length of the aliphatic chains (n) and the naphthenic rings (C n ); the concentration of asphaltenes (C oasf ) has little effect. The degree of crystallization is increased by f a and decreased with C aaa , C p /C ar , paraffinic carbons (C s ), and C oasf . The pour point is only increased by f a and decreased withC aaa and C n , and C oasf is negligible.

T his 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. ABSTRACT REVISIÓN DE LOS ESTUDIOS SOBRE INTERACCIÓN ASFALTENOS Y PARAFÍNAS E INCIDENCIA EN SU CRISTALIZACIÓN 40É apresentada uma revisão do efeito que os asfaltenos têm na cristalização de parafinas, nas propriedades de crus parafínicos e nas consequências na garantia de escoamento. Inicialmente são incluídos os estudos de cristalização de n-alcanos puros e de suas misturas onde foi possível entender como ocorre sua precipitação e transições de fases cristalinas, especialmente, por estudos de difração de raios-X (DRX). São analisados os resultados de estudos de cristalização em crus e/ou suas frações e como a presença dos asfaltenos afeta suas propriedades.Sobre a influência dos asfaltenos, os resultados não são conclusivos e em ocasiões são contraditórios: alguns confirmam sua contribuição para diminuir o ponto de fluidez, outros que o aumenta e em alguns casos que não o afeta. Resultados semelhantes são relatados para o ponto de cristalização, a transição de fases e as propriedades reológicas. Também não é possível generalizar qual é a influência da estrutura química dos asfaltenos sobre as propriedades dos crus. Infere-se que possivelmente é devida à interação entre suas cadeias alifáticas com as parafinas e estabelece-se que existe sinergia na coprecipitação pela evidência nas análises dos depósitos orgânicos. Se presenta una revisión del efecto que tienen los asfaltenos en la cristalización de parafinas, en las propiedades de crudos parafínicos y las consecuencias en el aseguramiento de flujo. Inicialmente se incluyen los estudios de cristalización de n-alcanos puros y de sus mezclas donde se ha podido entender como ocurre su precipitación y transiciones de fases cristalinas, especialm...

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The flow of a ferrofluid between two parallel infinitely long plates generated by a rotating magnetic field has been studied analytically and numerically using spin diffusion theory for a broad range of frequencies and intensities of the magnetic field. This work was motivated by interest in obtaining better agreement between the theoretical predictions and the experimental observations of the dependence of the flow magnitude on the amplitude and frequency of the magnetic field. These discrepancies have been attributed to the use of asymptotic solutions to assess velocity profiles obtained to moderate magnetic field strength and to the need to use a more accurate magnetization equation to high amplitudes and frequencies of the magnetic field. For such reasons, the objective of this work was to evaluate the effect of the magnetization equations derived by Shliomis [Sov. Phys. JETP 34, 1291 (1972)] (Sh-72) and by Martsenyuk, Raikher, and Shliomis [Sov. Phys. JETP 38, 413 (1974)] (MRSh-74) on the flow predictions of the spin diffusion theory using a simple geometry. It was found that the flow predictions for the two cases studied match with an asymptotic solution in the limit of low field strength when the Langevin parameter α is less than 0.1, for any value of the dimensionless frequency (Ω̃). Marked differences were found in the predictions of flow magnitude dependence on the amplitude and frequency of the magnetic field when Sh-72 or MRSh-74 was used for α&gt;1. Results also show that there is a critical value of frequency above which the velocity of the ferrofluid decreases with increasing magnetic field amplitude. Whereas the value of the critical frequency predicted by the Sh-72 magnetization equation is approximately unity for any value of the magnetic field amplitude, the MRSh-74 equation predicts that the critical frequency increases with increasing magnetic field amplitude. Predictions of the MRSh-74 equation are in qualitative agreement with previously reported experimental velocity profiles in other geometries.

In our previous articles (Energy & Fuels 2017, 31, 133−139 and Energy & Fuels 2017, 31, 8997−9005), it was presented that the asphaltenes of the Colorado field have different chemical structures, and these change the properties of crystallization of the paraffins. In this paper, we present a new way to understand the effects of the chemical structure of the asphaltenes on crude oil rheology, which includes correlating the average molecular parameters (AMPs) and the concentration of the asphaltenes with rheological properties using chemometric methods such as the partial least squares method. The asphaltenes were separated from six crude oil samples (average °API of 38) and were characterized using nuclear magnetic resonance to determine their main molecular parameters. Rheological properties including viscosity, yield stress, and gel temperature were experimentally determined for each of the crude oil samples and their respective maltenes. The results of a multivariate analysis show that the AMPs of the asphaltenes that cause the greatest effects are the ratio of peripheral aromatic carbons to aromatic carbons (C p /C ar ) and pericondensed aromatic carbons (C aaa ), which increase the gel temperature among maltenes and crude oils. The concentration of the asphaltenes (C oasf ) contributes to decreasing this property. An increase in the yield stress is mainly caused by the aliphatic chains of the asphaltenes (n) and the molecular weight (M w ), whereas C oasf causes decrease on the yield stress. Finally, the change in viscosity at 20 °C is increased by C p /C ar and is decreased by C oasf and paraffinic carbons (C s ).

Gas–liquid separators are one type of surface facility among those used in oil fields. In this paper, the study of gas–liquid separation in a cylindrical cyclone separator (GLCC) using computational fluids dynamics was carried out. The multiphase mixture model and the k–ε turbulence model in an air–water mixture with different geometries of the separator varying the inlet angle from 27° to 36° and 45° were used. Later, variables for the volumetric fraction, velocity, and pressure drop in the separator were studied. Finally, a natural gas mixture from a Colombian oil field was simulated using a species transport model. The results showed that a 36° inlet is the most suitable for the separation process due to its capacity to form a high-intensity swirl without produced liquid carry over. Also, it was found that the centrifugal separator could be a suitable alternative compared with conventional gravitational gas–liquid separators.

La simulación de una caldera industrial en CFD se realiza, usualmente, por etapas debido al gran tamaño y a los diferentes fenómenos físicos que ocurren dentro del equipo. En este trabajo, la simulación de una caldera industrial de parrilla se realiza en tres etapas, la primera es el circuito de aire primario, la segunda es el circuito de aire secundario y la tercera corresponde a la caldera. La combustión de bagazo de caña es un fenómeno complejo que involucra vaporización de la humedad, devolatilización y combustión del carbón, de forma que para evaluar esos fenómenos las partículas de bagazo fueron modeladas en un marco Euleriano-Lagrangiano. Las simulaciones fueron desarrolladas en el software comercial ANSYS FLUENT y la tasa de devolatilización fue programada en lenguaje C como una función definida por el usuario. Cuando los resultados de las simulaciones se compararon con datos experimentales, se observó una concordancia satisfactoria. Se realizaron simulaciones con modificaciones en las entradas de aire primario y secundario buscando optimizar el funcionamiento de la caldera y los resultados de esas simulaciones presentaron una mejoría significativa en los parámetros de combustión.

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