Abstract
One of the major concerns in petroleum refinery preheat trains is identified as fouling. Fouling impacts the refinery economics and environment heavily. Various approaches to mitigate fouling have not yielded the desired results. This is due to lack of understanding on the effect of influencing forces on crude oil fouling in heat exchangers. Therefore, this study attempts to investigate the effects of various forces such as gravity, Saffman Lift, drag and thermophoretic on crude oil fouling in heat exchangers through Computational Fluid Dynamics (CFD) simulations. From the simulations, it is observed that the higher particle size and particle concentration resulted in higher deposition of particles. Deposition velocities increase for larger sized particles and decrease for small and medium sized particles. The Increased flow velocities and surface roughness increases wall shear and mitigate fouling. Lower temperature gradients at the heat exchanger surface decreases deposition rates due to high thermophoretic forces. The mass deposition rate is reduced by 10.3 and 16.9% with 0.03 and 0.05 Pa, respectively, for 0.14 m/s flow velocity. Also, the mass deposition rate is reduced by 15.6 and 25.1% with 0.03 and 0.05 Pa, respectively, for 0.47 m/s flow velocity. With increased surface roughness from 0.03 to 0.05 mm, the mass deposition rate is reduced by 11.48 and 19.18%, respectively, for 0.14 m/s flow velocity. Also, for 0.47 m/s flow velocity, the mass deposition rate is reduced by 18.84 and 32.92% for 0.03- and 0.05-mm surface roughness, respectively.
Highlights
The impacts of fouling, its mechanisms and the phenomena has been well known globally
The gravitational, lift, thermophoretic and drag forces acing on the particles along the tube are shown in Figures 5-8, respectively and In tube pass 1, the gravitational and drag forces increased along the tube, the lift and thermophoretic forces decreased along the tube
Among all the forces, the gravitational force acting on the asphaltenes particles is observed to be high, the drag and thermophoretic forces are observed to have less impact on the asphaltenes particles
Summary
The impacts of fouling, its mechanisms and the phenomena has been well known globally. The physical and chemical aspects involved in the predominated fouling mechanisms (particulate and chemical reaction fouling) have not been well understood. The computational time for the simulations with Eulerian-Lagrangian approach is high for fluids composed with a high volume of particles. Despite the difficulties with the computational time and power, the Eulerian-Lagrangian approach remains the most considered model to solve the fluid flow modelling involving multi-phases [12]. The CFD studies performed in shell and tube heat exchangers, as reported in literature, did not consider the existence of asphaltenes particles in the bulk fluid as a discrete phase. The discrete-phase models have the capability to analyze the particulate and chemical reaction fouling routes on the heat transfer surfaces, but these simulation models have not been well utilized to understand the fouling phenomena of crude oils. Better understanding of its phenomena can help to assist development of appropriate mitigation strategies [13,14]
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