Kinetics of Barium Sulfate Deposition and Crystallization Process in the Flowing Tube

Barium sulfate deposition is one of the most serious problems in the flow assurance issues in the industry. The kinetics of barium sulfate deposition inside the flowing tubing has been studied. The deposition process can be divided into two phases: the growth phase, where the deposition rate constant increases with time, and the steady-state phase, wherein the deposition rate remains constant. The result suggests that the barite deposition is governed by a surface-controlled process followed by a mass transport-controlled process. The measured deposition rate along the tubing can be successfully modeled via a heterogeneous reaction equation. Furthermore, the deposition rate constants match well with the coupled-ion diffusion-controlled rate constants, which suggest that the kinetics of barite deposition can be predicted from the fundamental diffusion theory. The measured sizes and crystal number densities follow the predictions of the classical nucleation theory. This result indicates that nucleation is also involved in the scale deposition process. In tubing partially covered with barite, the deposition rate constants ranged from (2.17 to 3.53) x 10(-4) cm/s at 50-120 degrees C. The deposition rate constants increase in the tubing fully covered with barite and become (2.38-9.55) x 10(-4) cm/s over the same temperature range. By comparison with the Graetz-Nusselt theory, the deposition rate constants in the partially covered tubing correspond well with the coupled-ion diffusion control rate constants (1.89-4.41) X 10(-4) cm/s at 50-120 degrees C, which suggest that the barite deposition in the flowing pipe can be described as the coupled-ion diffusion process. The higher deposition rate constants in the fully covered tubing correspond to an increased barite crystal surface area covering the tubing.