Biofilm control in tubular heat exchangers refrigerated by seawater using flow inversion physical treatment

摘要

Biofilm formation is an inevitable consequence that exerts a negative effect on the thermal performance of industrial equipment using seawater as its coolant fluid. The indiscriminate use of chemical antifouling treatments based on toxic biocides to eliminate these biofilms implies the discharge of large amounts of residual biocide in their effluent, which negatively affects the quality of coastal waters. This has led more developed countries to impose ever-stricter legislation to control this matter. Therefore, this paper compares the effectiveness of a flow inversion physical treatment in eliminating the biofilm formed on the internal tube surface of a heat exchanger with that of a traditional chemical treatment with NaClO at 0.8 ppm. The results indicate that it is possible to eliminate a biofilm formed on the inside surfaces of tubes by use of intermittent doses of chemical treatments at low concentrations, but once the first four days in which the biocide reacts and eliminates the biofilm have elapsed, the residual biocide in the effluent is very high. The action of the physical flow inversion treatment is largely evidenced in the reduction of the heat transfer resistance (R-f) and not so markedly on the fluid frictional resistance (f). This led us to combine both methods of treatment thus minimising environmental impact on the marine ecosystem. Scientific relevance of the paper: Biofouling is one of the most serious problems facing numerous industrial processes using seawater as their coolant fluid. Chemical antifouling methods used to mitigate the problem face ever more restrictive legislation regulating water quality. We are hence obliged to seek alternatives that enable said industrial processes comply with current legislation. This paper, therefore, compares a traditional chemical treatment with NaClO and a flow inversion physical treatment to demonstrate the effectiveness of the latter. We, hence, offer an alternative that is not aggressive on the environment or is a combination of a tried and tested traditional chemical treatment method. (C) 2007 Elsevier Ltd. All rights reserved.