Article pubs.acs.org/IECR
Optimization of Flow Parameters of Heavy Crude Oil-in-Water Emulsions through Pipelines Vahid Hoshyargar and Seyed Nezameddin Ashrafizadeh* Research Laboratory for Advanced Separation Processes, Department of Chemical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846-13114, Iran ABSTRACT: High viscosity and low mobility are the main problems in transporting heavy crude oils through pipelines. The methods which have been used so far to overcome the mentioned problems include heating, upgrading, dilution, core annular flow, and emulsification in water. In this research, the emulsification method is thoroughly evaluated by investigating the rheological properties of crude oil-in-water emulsions. The factors affecting the rheology of a heavy crude oil-in-water emulsion stabilized by sodium carbonate (Na2CO3) as an actuator of natural surfactant (asphaltene) were studied. An Iranian heavy crude oil, namely West-Paydar, was used as the oil phase of the emulsions. The Taguchi method of an L-18 orthogonal array was employed to design the experiments. The viscosity of crude oil was almost Newtonian and about 0.3−11 (Pa·s) in temperatures ranging from 55 to 5 °C, respectively; while that of the emulsions was non-Newtonian and about one-tenth of the used crude oil. The rheological model of Herschel−Bulkley was fitted to the data of both emulsions and heavy crude. A purely mathematical calculation was used to determine the pressure loss per unit length of an assumed pipe. The pressure loss of O/W emulsion was about 90−99% less than that of heavy crude oil. The Herschel−Bulkley model was capable not only to predict the pressure loss at each particular condition, but also to optimize the process parameters according to pressure gradient, temperature, volume fraction, sodium carbonate content, and salinity in a manner to be more close to natural conditions as well as economic terms.
1. INTRODUCTION Crude oil is one of the most actively traded commodities in the world. Worldwide demand for crude oil has been steadily intensifying over the past 20 years, as world demand for crude has grown from 60 to 84 million barrels per day.1 From 1975 to 2000, global demand for crude oil had a growth rate of about 1% average. “Emerging Countries” such as India and China changed this stable growth in the first years of the 21st century due to their dynamic economies which resulted in a remarkable 1.8% global growth in demand for crude oil in 2009.2 The International Energy Agency (IEA) estimates that heavy oil represents at least 50% of the recoverable oil resources of the world. Some important studies suggest that a major portion of the world’s energy requirements would be supplied from fossil fuels such as natural gas, petroleum, and coal (reported by IEA, 2006). As a result, heavy crudes which were not reasonable to be recovered so far, would be important due to the limited amount of available crudes. The market price for heavy crude oil is only about half of the price of light crude oil, which is generally quoted by the media.1 As some instances, Alberta, Orinoco Belt, Gulf of Mexico, and Northeastern China could be noted as growing centers in the use of nonconventional heavy and extra heavy oil resources which are able to produce fuels and petrochemicals.1 The density of heavy crude oil is between 10 and 20 oAPI; that of conventional crudes is ranging between 38 and 40 API. If density is
