Transporte de óleos pesados mediante aquecimento por vapor : uma abordagem analítica e numérica

Abstract

Amongst the innumerable challenges that permeate the production chain of heavy oils, the transportation phase deserves to be highlighted. Due to its high viscosity, heavy oils exhibit considerable flow resistance, requiring auxiliary mechanisms to enable its transportation via pipelines. In this dissertation, a concentric pipeline configuration is proposed, in which steam flows through the inner pipe and oil flows through the annular space of the oil pipe. Analytical and numerical approaches are adopted for the investigation of steam insertion, geometry, thermal insulation, steam quality and system length on the following parameters: temperature, viscosity and pressure of oil, as well as vapor mass fraction of steam. For the first approach, the thermal resistance model associated with the 𝜖 – NTU method is employed. For the second, software Ansys CFX is used in a tridimensional, steady state simulation. The deviations presented by the analytical approach are attributed to the non incorporations of fluctuation, natural convection and steam turbulence effects, which contribute for a non-homogeneous heating of oil. Numerical results reveal that steam insertion elevates the average oil temperature in 1,2% and reduces its average viscosity and initial flow pressure by 8,7% and 24,2%, respectively. A reduction of 24,6% in the ratio between oil pipe and steam pipe radius results in a final oil temperature 1,2% higher and 4,7% lower viscosity. The presence of thermal insulation reduces the heat flux to the external medium in 78,5%. The reduction of steam quality in 30% causes an increase in average oil viscosity of 2,4%. For longer systems, the initial flow pressure required increases significantly and the steam shows more expressive liquid deposits in the lower portion of the coupling. The present study provides an analysis of the concentric coupling between steam and heavy oil under several conditions, explaining the qualitative advantages and disadvantages of some strategies. In addition, it proposes na analytical model capable of predicting the average temperature and viscosity of oil in the outlet, with maximum deviations of 1,3% and 15,6%, respectively, in comparison to the numerical approach.