Bubble analogy and stabilization of core-annular flow

A theory for the stabilization of annular liquid-liquid flow (i.e., core-annular flow) in a horizontal pipe is proposed. Based upon the analysis of the momentum conservation equation in the cross section of the flow, including the effects of peripheral flow in the annulus and interfacial tension, an equation is obtained which describes the interface shape. Results for the height-to-width aspect ratio of the core are compared with laboratory measurements done by the author for a heavy oil-water core-annular flow. A criterion for stabilization of this interesting flow pattern is proposed.123212713

Modeling aspects of oil-water core-annular flows

The annular flow pattern of two immiscible liquids having very different viscosities in a horizontal pipe-also known as 'core-annular flow'-provides an attractive means for the pipeline transportation of heavy oils since the oil tends to occupy the center of the tube, surrounded by a thin annulus of a lubricant fluid (usually water). The correspondent pressure drop is comparable to the flow of water only in the same pipe at the total volumetric flow rate. Recently, successful experiments led by the author and his group indicated that the core flow technology might be even more attractive for heavy oil production in vertical wells, due to the symmetry of the flow and the favorable effect of buoyancy. In this paper, several aspects of core-annular flow modeling are analyzed and discussed in the light of experimental data. First, criteria for existence of stable core flow are proposed, which show the essential role played by interfacial tension. Phenomenological models, based on mass and momentum balances, are developed for volume fraction and pressure drop and compared with data for both horizontal and vertical oil water core flows. The very good agreement observed is encouraging. (C) 2001 Elsevier Science B.V. All rights reserved.3241731SI12714

Wavespeed and volumetric fraction in core annular flow

Kinematic wave theory is used to study the speed of interfacial waves observed in core annular flows of viscous oils with water. The theory; provides a method for measuring the volume fraction of the core. The results obtained by this method are in very good agreement with experimental data. The model also confirms the observation that for oils lighter than water waves move slower than the core in upward flow, faster than the core in downward flow and at the same velocity of the core in horizontal flow. A general correlation for the core fraction in wavy core annular flows at low annulus-to-core viscosity ratio is proposed. (C) 1998 Elsevier Science Ltd. All rights reserved.24696197

Analytical model for interfacial waves in vertical core flow

The vertical annular pipe flow of two immiscible liquids with very different viscosities provides an efficient and low cost method for producing heavy oils in vertical wells using water as a lubricant. The core flow pattern is becoming attractive in the current Brazilian deep water production scenario. Understanding interfacial phenomena present in this flow pattern is crucial for appropriate design of the production system. Assuming that in this axisymmetric flow there is no net force associated with interfacial tension, a differential equation governing the shape of the liquid-liquid interface is derived. An analytical solution is proposed for the prediction of the wave geometry, which depends only on pipe geometry, physical properties and flow rates of the fluids. The comparison between the model predictions and recent experimental data shows a reasonable agreement. (c) 2006 Elsevier B.V. All rights reserved.544173217318

Wettability alteration of internal surfaces of pipelines for use in the transportation of heavy oil via core-flow

A promising technique for heavy oil transportation is the use of water-assisted flow, such as core-annular flow. It is based upon the lubrication of pipeline walls with a thin water film and thereby confining the oil to the central portion of the pipe. Oil adhesion to the pipe wall has, however, been pointed out as a possible hindrance to the efficient employment of this method. A solution to this problem is the utilization of hydrophilic and/or oleophobic material as internal coatings for the pipe wall. This work examines the modification of surfaces as a way to minimize or eliminate altogether the heavy oil adherence to pipeline inner walls in the coreflow method. To obtain hydrophilic/oleophobic surfaces, the oxidation of surfaces and the alteration of the wall roughness were carried out and their effects quantified. The changes in the wetting behavior of the pipe wall are described through contact angle measurements (in the aqueous phase) for oil/water/surface systems. The surfaces examined included PVC, stainless steel, enameled steel, galvanized steel and commercial steel. Salt, pH and temperature effects on the wetting behavior were also investigated. The results indicated a decrease in contact angles upon the oxidation of the pipeline surface as well as the increase of its roughness. Surface oxidation and increase in roughness resulted in the increase of the hydrophilic character of the surfaces. PVC and steels surfaces, without oxidation showed contact angles around 113-150 degrees (i.e., oleophilic behavior). After oxidation, the steels show angles around 14-20 degrees and PVC an angle of 65 degrees. Stainless steel with roughness of 0.24 mu m displayed a contact angle of 35% roughness increase to 2.28 mu m resulted in a contact angle down to 13 degrees. The enameled steel showed a contact angle of 20 degrees, being therefore effective to avoid oil adhesion. Na2SiO3 was effective to lower contact angles of all surfaces being, therefore, effective in reducing fouling. The presence of Na2SiO3 in the solution decreased the contact angles to around 25 degrees, 45 degrees and 20 degrees for systems with glass, PP and stainless steel, respectively. Low temperature and solution pH outside the 4-8 range resulted in lower contact angles. Enameled steel, stainless steel with 2.5 mu m roughness, oxidized polymers or oxidized commercial steel can all be used to better the effectiveness of core-flow in the transportation of heavy oils. (c) 2005 Elsevier B.V. All rights reserved.5141671172

Thermal integration of multiple effect evaporator in sugar plant

Besides the largest energy consumption in the process of sugar production, evaporation also presents many opportunities of thermal integration with the remaining of the process. That occurs due to the possibility of making use of the vapor generated during the evaporation operation (vegetal vapor), as a heating source, from extractions to process. Regarding the thermal integration of the multiple effect evaporator (MEE), previous studies showed that, in general, the energy recovery is usually larger when extractions are practiced in the last effects of the operation. Although the results found can be used for development of new projects, as heuristic rules, the application has been limited due to the lack of understanding on the Subject. In the present investigation, a study was carried out by defining equations that can be used as a reference for thermal integration projects, including MEEs. The equations are also helpful for elaborating a systematic way to apply pinch analysis in sugar plant with an algorithm. (C) 2008 Elsevier Ltd. All rights reserved.294170051552

Contact angle measurements and wetting behavior of inner surfaces of pipelines exposed to heavy crude oil and water

The technology of oil flow in pipelines assisted by its confinement within an annular aqueous section, known as core-flow, has emerged as a viable alternative for the transportation of heavy crude oils. The lubricating effect of the aqueous film leads to reduced equivalent viscosities and, hence, low energy consumption. One of the possible problems associated with this technique is the gradual accumulation of oil on the inner pipeline surfaces, requiring the use of cleaning procedures. This work is aimed at investigating the roles of the oil polar components on the wetting of such surfaces by crude oils through contact angle measurements in systems containing heavy oil/aqueous phase/metallic surfaces. Asphaltenes and naphthenic acids were removed from the crude oil, respectively, by flocculation with alkanes and by washing with alkaline solution. As model metallic surfaces, commercial and galvanized steel were used; and the studied aqueous phases comprised pure water, 1% sodium chloride and sodium meta-silicate solutions. Static contact angles were determined via the placement of an oil droplet under the metallic surface in the presence of an aqueous phase. These measurements revealed small influence of the nature of the metallic surfaces on the observed wettability. Significant effects, however, were observed depending on the presence of asphaltenes and naphthenic acids, whose removal reduced the contact angles from an oil-wet behavior (angles above 145 degrees) to a water-wet situation, with angles smaller than 45 degrees and 80 degrees, respectively. Experiments carried out with aqueous phases containing 1% sodium meta-silicate and sodium chloride revealed contact angles smaller than 60 degrees in most cases, confirming their suitability for the prevention of oil deposition onto these surfaces. Moreover, this study confirms that measurements of static contact angles are useful for screening of formulations and surfaces used in oil transportation prior to flow tests. (c) 2005 Elsevier B.V. All rights reserved.514167191

Physico-chemical properties of heavy crude oil-in-water emulsions stabilized by mixtures of ionic and non-ionic ethoxylated nonylphenol surfactants and medium chain alcohols

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This work describes the formulation and evaluation of concentrated, heavy oil-in-water emulsions stabilized by mixtures of ethoxylated surfactants and normal alcohols. The rheology, stability and droplet size of these emulsions were investigated as functions of the emulsification process parameters. The parameters investigated for this study include emulsifier agent composition, presence of additives, pH and salinity of the continuous aqueous phase, emulsification temperature, oil content and emulsion aging. The produced emulsions had viscosities ranging from 30 to 150 mPa s and represent a 30-fold reduction of the crude oil viscosity. Sauter mean diameters of the droplets ranged from 10 to 50 mu m. The emulsions were produced by mixing the oil with an aqueous solution containing medium normal-chain alcohols and small quantities of a mixture of ethoxylated nonylphenol and ethoxylated amine surfactants. The presence of these alcohols led to a sharp decrease in the droplet size of the emulsion. This size decrease had a direct impact on the emulsions' stability and apparent viscosity. The rheological parameters of the aged emulsions were also essentially constant over a 42-day period. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.897A957967Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Experimental investigation on liquid-liquid-gas flow: Flow patterns and pressure-gradient

The use of core-annular flow pattern, where a thin fluid surrounds a viscous one, may be attractive to heavy oil transportation and as an artificial lifting method in heavy oil wells,a situation that can become frequent in the Brazilian offshore scenario. However, in petroleum production, operations gas is frequently present. Therefore, the study of three-phase flow of heavy oil, water and gas is in order. This paper reports pressure drop measurements and three-phase flow patterns observed in horizontal and vertical 2.84-cm W. glass pipes. The focus was a mixture of heavy crude oil (3400 mPa s, 970 kg/m(3) at 20 degrees C), water an air at several combinations of the individual flow rates. Three-phase pressure drop data were compared with single-phase oil and two-phase oil-gas flows to assess the gains due to water injection. In addition. three-phase flow patterns formed inside vertical and slightly inclined 1.0 cm i.d. pipes,are also presented. Thus, scale-up and inclination effects could be qualitatively analyzed. Full-scale onshore-field experiments were conducted in order to investigate the applicability of using water to transport heavy oil in actual lines in the presence of gas. A big steel pipeline (7.7 cm W. and 274 m) conveying a very viscous crude oil (36950 mPa s, 972.1 kg/m(3) at 20 degrees C), natural gas (GOR 15 m(3)/m(3)) and water was used. Onshore-field three-phase flow tests were carried out and pressure gradient data are reported. The observed improvements in oil production rates and the pressure drop reductions obtained are remarkable. (c) 2009 Elsevier B.V. All rights reserved.6541671113ANPFINEPPETROBRA