Online cleaning of tubular heat exchangers in water service systems using projectiles

In water service processes, tubular heat exchangers are commonly used to provide a heat transfer medium for cooling or heating of which both are subject to fouling of heat transfer surfaces. The deposit would dominantly build up in form of biofouling, crystallization, and/or particulate fouling depending on the operating and surface conditions. This, in turn, may result in more demand for excessive energy consumption due to higher pumping requirements, as well as for offsetting the impact of fouling. In this study, as part of a European project entitled "Clean-Ex," a comprehensive set of experimental runs was carried out for crystallization fouling of CaSO4 with and without projectiles. Due to laboratory restriction, the fouling runs were performed at accelerated conditions to rigorously characterize the impact of projectile cleaning in terms of injection frequencies and various types of projectiles. The experimental results show that cleaning by using projectiles will only take place when no deposit is allowed to form on the surface or if formed, then it is just brittle; hence, the projectiles can remove it due to excessive shear forces. There is also a direct link between the rate of fouling and injection frequencies.