Numerical analysis of asphaltene particles evolution and flocs morphology using DEM-CFD approach

Abstract

The agglomeration and fragmentation of asphaltenes which dictate particle size distribution (PSD) play an important role in deposition behavior of asphaltene. However, the physics underlying the agglomeration/fragmentation processes is grossly missing in the available literature. In this paper, Discrete Element Method (DEM) in combination with a coalescence model is coupled with Computational Fluid Dynamics (CFD) to simulate agglomeration/fragmentation considering asphaltene particles as real/irregular objects in the absence of deposition process. The evolution of asphaltene particles, asphaltene particle size distribution (PSD), and morphology of asphaltene flocs have been examined during the simulation. Also, the effect of fluid velocity (Vf), primary particle concentration (N0), inter-particle bond strength (Fb), and energy barrier (Ub) have been investigated. During asphaltene flocculation, mean floc size increases until a steady-state condition is attained where floc size and mass fractal dimension approximately remains unchanged. The size of asphaltene flocs increases up to 40 μm and fractal dimension values change in the range of 1.45–1.75. Higher Vf leads to the steady-state condition is attained more rapidly along with smaller floc sizes and higher fractal dimensions. Increasing N0 results in faster growth of asphaltene flocs, however, the stable mean asphaltene floc size is approximately insensitive to N0. The presence of larger flocs at higher N0 eventuates the smaller fractal dimensions. As Fb increases, the frequency of small particles decreases, and PSD shifts to larger sizes. Consequently, smaller fractal dimensions are obtained. The floc growth is insensitive to Ub at initial times, whereas the steady-state condition is reached more quickly with a smaller stable floc size for higher values of Ub. The fractal dimension shows a weak dependency on the energy barrier.