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96298 FOULING CONTROL IN SEAWATER BY ON - LINE ACID ADDITION

Picture for 96298 FOULING CONTROL IN SEA WATER BY ON
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Product Number: 51300-96298-SG
ISBN: 96298 1996 CP
Author: G. Saivago, G. Taccani, R. Polimeni, G. Fumagalli, D. Picenoni
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An experimental plant was setup containing once-through test lines supplied with seawater. The pH level of the seawater was maintained at 6.3 by the acids addition. Heat exchange monitoring equipment and channels exposing different metal specimens were installed on each of the lines. Observation by microscope and EDS analyses were carried out both on the specimen surfaces and on the cross section of the fouling after fracturing in liquid N2. The results obtained slow that: -fouling must not confused with its effects or simply with its biological components; - acidifying seawater can prevent the resistance to heat exchange from increasing without impeding its biological activity. Observation by microscope of the fouling cross sections showed that in untreated seawater the foulings on stainless steel were composed of a continuous compact layer, covered by disorderly clusters. These compact layers were found to contain high quantities of corrosion products of the metals. Elements typical of corrosion products of ferrous materials (Fe, Mn) were also found on Pt, copper alloys and plastic materials. The addition of HCI or H2SO4 to the seawater, to bring it to pH 6.3, reduces the amount of fouling adhering to the surfaces, prevents the development of the continuous layer containing iron and prevents significant increases in heat exchange resistance. The addition of CO2 can encourage the development of incoherent fibrous material with high Si content and low Fe content which is of little impediment to heat exchange. The addition of lactic acid can encourage both the abnormal development of biomass and the formation of several, separate, layers on stainless steel surfaces. These layers are easily removed and are of little impediment to the thermal flow. The innermost layer is compact and has a high iron content. The uppermost layer is incoherent, fibrous and similar to that observed where CO2 was added. In both cases the fibres contain N and Cu as well as C and O. A description and discussion will follow of the role played by iron adsorption on the specimen surfaces in the onset and development of the fouling. Keywords: fouling control, biofilm morphology, seawater, thermal resistance, heavy metals, stainless steel, platinum, sulfuric acid, carbon dioxide, lactic acid.
An experimental plant was setup containing once-through test lines supplied with seawater. The pH level of the seawater was maintained at 6.3 by the acids addition. Heat exchange monitoring equipment and channels exposing different metal specimens were installed on each of the lines. Observation by microscope and EDS analyses were carried out both on the specimen surfaces and on the cross section of the fouling after fracturing in liquid N2. The results obtained slow that: -fouling must not confused with its effects or simply with its biological components; - acidifying seawater can prevent the resistance to heat exchange from increasing without impeding its biological activity. Observation by microscope of the fouling cross sections showed that in untreated seawater the foulings on stainless steel were composed of a continuous compact layer, covered by disorderly clusters. These compact layers were found to contain high quantities of corrosion products of the metals. Elements typical of corrosion products of ferrous materials (Fe, Mn) were also found on Pt, copper alloys and plastic materials. The addition of HCI or H2SO4 to the seawater, to bring it to pH 6.3, reduces the amount of fouling adhering to the surfaces, prevents the development of the continuous layer containing iron and prevents significant increases in heat exchange resistance. The addition of CO2 can encourage the development of incoherent fibrous material with high Si content and low Fe content which is of little impediment to heat exchange. The addition of lactic acid can encourage both the abnormal development of biomass and the formation of several, separate, layers on stainless steel surfaces. These layers are easily removed and are of little impediment to the thermal flow. The innermost layer is compact and has a high iron content. The uppermost layer is incoherent, fibrous and similar to that observed where CO2 was added. In both cases the fibres contain N and Cu as well as C and O. A description and discussion will follow of the role played by iron adsorption on the specimen surfaces in the onset and development of the fouling. Keywords: fouling control, biofilm morphology, seawater, thermal resistance, heavy metals, stainless steel, platinum, sulfuric acid, carbon dioxide, lactic acid.
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