Mitigation of Crystallization Fouling in a Single Heated Tube Using Projectiles of Different Sizes and Hardness

Abstract

Fouling of heat exchangers is a prevalent operating drawback in many process industries. Efficient chemical inhibitors have predominantly been used for many years to combat deposit formation. Nevertheless, new stringent environmental legislations limit their utilization. On-line mitigation techniques, such as propulsion of projectiles at different injection rates, can also be utilized, which can, in turn, minimize the need for chemical inhibitors. Nevertheless, the experimental data are scarce and nonconclusive. In this experimental study, two spherical-type projectiles of different sizes and hardness have been used to clean the inner surface of a single heated tube that was subjected to the deposition of calcium sulfate. Projectiles were then introduced at different injection rate of every 2, 5, 10, 15, and 30 min. The experimental results show that (i) the projectiles would expedite initial nucleation of crystals even if they are soft and easy to propel inside the tube; (ii) fouling can only be mitigated if the projectiles exert a shear force such that the corresponding removal rate is greater than the net rate of the deposition; and finally (iii) harder projectiles with larger surface contact area are more efficient in cleaning the surface compared to those that are softer.