Sergio García

Mitigation of biofouling using electromagnetic fields in tubular heat exchangers-condensers cooled by seawater.

Electromagnetic field (EMF) treatment is presented as an alternative physical treatment for the mitigation of biofouling adhered to the tubes of a heat exchanger–condenser cooled by seawater. During an experimental phase, a fouling biofilm was allowed to grow until experimental variables indicated that its growth had stabilised. Subsequently, EMF treatment was applied to seawater to eliminate the biofilm and to maintain the achieved cleanliness. The results showed that EMFs precipitated ions dissolved in the seawater. As a consequence of the application of EMFs, erosion altered the intermolecular bonding of extracellular polymers, causing the destruction of the biofilm matrix and its detachment from the inner surface of the heat exchanger–condenser tubes. This detachment led to the partial removal of a mature biofilm and a partial recovery of the efficiency lost in the heat transfer process by using a physical treatment that is harmless to the marine environment.

Study of the activity of quaternary ammonium compounds in the mitigation of biofouling in heat exchangers–condensers cooled by seawater

The effectiveness of two quaternary ammonium compounds (QACs) (non-oxidising biocides) to reduce the growth of biofilm adhering to the tubes of a heat exchanger-condenser cooled by seawater was evaluated. Their effectiveness was compared to that of a conventional oxidising biocide (sodium hypochlorite [NaOCl]) under the same testing conditions. Each biocide was applied intermittently (6 h on, 6 h off) in a first shock stage (1.5 ppm over 8 days) and a second stabilising stage (0.5 ppm over 20 days). The results showed that the antifouling effectiveness of the first of the QACs (fifth generation) was comparable to that shown by the oxidising power of NaOCl. Although the reaction time was longer than that of NaOCl, both the compounds removed the biofilm, and the tube was practically restored to its clean condition. Treatment with the second of the QACs (fourth generation) allowed for the stabilisation of biofilm growth, but not for its removal. Ecotoxicology studies classified the QACs as environmentally harmless under the testing conditions.

The effect of electromagnetic fields on biofouling in a heat exchange system using seawater

This article discusses the antifouling action of a continuous physical treatment process comprising the application of electromagnetic fields (EMFs) to seawater used as the refrigerant fluid in a heat exchanger-condenser to maintain the initial ‘clean tube’ condition. The results demonstrated that the EMFs accelerated the ionic nucleation of calcium and precipitation as calcium carbonate, which weakened the growing biofilm and reduced its adhesion capacity. Consequently, EMFs induced an erosive effect that reduced biofilm formation and fouling. This treatment allowed for the maintenance of significantly lower fouling factors in the treated tubes compared to a control group of untreated tubes, thereby leading to a higher heat transfer efficiency.

Influence of flow velocity on biofilm growth in a tubular heat exchanger-condenser cooled by seawater

The influence of flow velocity (FV) on the heat transfer process in tubes made from AISI 316L stainless steel in a heat exchanger-condenser cooled by seawater was evaluated based on the characteristics of the resulting biofilm that adhered to the internal surface of the tubes at velocities of 1, 1.2, 1.6, and 3 m s−1. The results demonstrated that at a higher FV, despite being more compact and consistent, the biofilm was thinner with a lower concentration of solids, and smoother, which favoured the heat transfer process within the equipment. However, higher velocities increase the initial cost of the refrigerating water-pumping equipment and its energy consumption cost to compensate for the greater pressure drops produced in the tube. The velocity of 1.6 m s−1 represented the equilibrium between the advantages and disadvantages of the variables analysed for the test conditions in this study.

Impact of the surface roughness of AISI 316L stainless steel on biofilm adhesion in a seawater-cooled tubular heat exchanger-condenser

Abstract The present study evaluated biofilm growth in AISI 316L stainless steel tubes for seawater-cooled exchanger-condensers that had four different arithmetic mean surface roughness values ranging from 0.14 μm to 1.2 μm. The results of fluid frictional resistance and heat transfer resistance regarding biofilm formation in the roughest surface showed increases of 28.2% and 19.1% respectively, compared with the smoothest surface. The biofilm thickness taken at the end of the experiment showed variations of up to 74% between the smoothest and roughest surfaces. The thermal efficiency of the heat transfer process in the tube with the roughest surface was 17.4% greater than that in the tube with the smoothest surface. The results suggest that the finish of the inner surfaces of the tubes in heat exchanger-condensers is critical for improving energy efficiency and avoiding biofilm adhesion. This may be utilised to reduce biofilm adhesion and growth in the design of heat exchanger-condensers.

Mitigation of marine biofouling on tubes of open rack vaporizers using electromagnetic fields

This study quantitatively evaluates the antifouling action of the continuous physical treatment with electromagnetic fields (EMFs) of seawater used as heat exchanger fluid in an open rack vaporizer (ORV) pilot plant to reduce the growth of biofouling on external rib-tube surfaces. The results demonstrate that the biofilm adhered on the treated rib-tubes was reduced by 33% in thickness and by 44% in dissolved solids regarding the biofilm adhered on the untreated control rib-tubes. The lower conductivity and Ca(2+) and Mg(2+) ionic content in the effluent of the treated seawater confirmed that the EMFs accelerated the process of ionic calcium nucleation and precipitation as calcium carbonate. The precipitation of ions dissolved affected the inter-molecular interactions among extracellular polymers, thereby weakening the biofouling film matrix and reducing its adhesion capacity. The drag of small particles by the flow of seawater had an erosive action and decreased the biofouling film thickness. Consequently, the antifouling methods treatment with EMFs allowed reduce the negative effect that the biofouling have for the heat transfer equipment used in the regasification process and keep the highest techno-economic operating conditions.

Parameter estimation of biofouling deposition models on seawater-cooled heat exchangers

The growth of biofilms in seawater-cooled heat exchangers limits the heat exchange of their surfaces, with high impact in the design and maintenance operations. The principal aim of this work has been to study the fit of different biological growth models to the development of biofilms in heat exchangers, with incorporation of the tube surface roughness effects as a main parameter. This study was carried out by rewriting the equations of models with parameters of biological significance. The obtained results have allowed to apply the modified models as a useful tool to predict the biofouling growth. The prediction of the behavior of the biofouling films with different roughness tubes have been compared to the experimental data, with high correlation coefficients.

Improvement of Electromagnetic Fields treatment for biofouling growth control in tubular heat exchanger-condenser cooled by seawater

Biofouling is one of the more important problems of different industries on wide world, which they use to seawater system for your process or they are in contact with seawater. When were not prevented or treated of water on-line, biofouling can cause a lot of problems of loss efficiency. To avoid spending a lot of money on stops to production for cleaning of biofouling, we must to use some procedures in the fighting and control against biofouling on industrial equipment without damage to environment. The influence of flow velocity on Electromagnetic Fields treatment in stainless steel heat exchanger tubes (AISI 316Ti) cooled by seawater was evaluated based on the characteristics of the resulting biofilm that adhered to the internal surface of the tubes at flow velocities of 1, 1.2, 1.6 and 3 m/s. The results showed that the effective of Electromagnetic Fields treatment was increased at a higher flow velocity. Furthermore, the biofilm at a higher flow velocity was thinner with a lower concentration of solids and carbonate calcium, and smoother composition, which favoured the heat transfer process within the equipment.