On-line cleaning technique for mitigation of biofouling in heat exchangers: A case study of a hydroelectric power plant in Brazil

Abstract

An experimental methodology was developed to assess an on-line cleaning technique to mitigate biofouling in plate heat exchangers. The exchangers are used in the cooling system of the journal bearings of hydro-generators of a power plant. The cleaning technology tested consisted of a non-intrusive electronic device wrapped around the water cooling piping that generated an electric field to inhibit the growth of micro-organisms on the heat transfer surfaces. Limnology studies explained the phenomenon of biofouling formation caused by limnophilous microorganisms present in the deepest parts of the reservoir manage to survive in hostile environments under anoxic conditions. Two criteria were adopted to assess the performance of the antifouling technology: a hydrodynamic criterion based on Kakaç’s pressure drop equation for plate heat exchangers and a thermal criterion (index of fouling) that takes into account the heat transfer effectiveness under the clean and fouled conditions of operation. The position of the antifouling device produced better results when installed in the primary cooling circuit. For the conditions studied, the cleaning technique mitigated biofouling but did not eliminate it completely. Excitation of the flow by an electric field diminishes the pressure drop and the index of fouling when compared to the unexcited flow condition. Control and reduction of the fouling thermal resistance is highly desired as it drastically lessens mechanical pumping costs and increases heat transfer performance.