Physical Water Treatment for Fouling Prevention in Heat Exchangers

Abstract

Publisher Summary Physical water treatment (PWT) is an attempt to treat hard water for the purpose of preventing or mitigating fouling using a physical means, without adding chemicals to water. PWT technology prevents or mitigates scale build-up at heat exchangers. The fouling problem starts because of hard water being heated inside heat transfer equipment. The precipitation of dissolved mineral ions and subsequent scale deposit on the heat transfer surface critically depend on water chemistry. In addition to water chemistry, the deposit and removal rates of scale also depend on flow velocity, heat flux, and heat exchanger geometry. The central hypothesis of PWT is bulk precipitation. This chapter focuses on the science behind bulk precipitation, which leads to particulate fouling that produces a soft sludge coating on the heat transfer surface. Thus, for the successful operation of PWT, the ability to remove the soft sludge coating is essential. The various mechanisms of physical water treatment–such as effect of electric and magnetic fields, separation of charges, PWT works at surface via heterogeneous catalysis, and bulk precipitation–along with effect of particles in water on fouling mitigation have been discussed. The chapter also describes the validation methods for the efficiency of PWT and issues involved in the validation of PWT. It is essential to identify the conditions where PWT does and does not work, which in turn helps to understand the fundamental mechanism of PWT. The effectiveness of PWT at laboratory tests, in general, depends on the test conditions, including the flow velocity through permanent magnets, water hardness, and recirculation.