A model for the fouling of M.S.F. plants based on data from operating units

The behaviour of a number of large plants treated with a high performance additive and operated under steady conditions for long periods has been carefully monitored. In time the build-up of insulating deposits (fouling) in the brine heater stopped, the resistance to heat transfer reaching a steady value. Changes in operating conditions resulted in rapid reversible changes in the degree of fouling i.e. this regained its steady value when the operating conditions were returned to their original values. The most important parameter changed was identified as the brine circulating rate or velocity which sets the shear stress at the brine-deposit boundary. The commonly used linear relationship between fouling and time clearly does not explain these plant results. The use of such linear rates to predict the progress of fouling, particularly those obtained over short periods of operation, is shown to be invalid. The observations that a plant will come to different steady values of fouling which change reversibly with specific changes in operating conditions can only be sensibly explained by a two step process of deposition and subsequent removal. Models embracing this behaviour have been proposed in other fields of heat transfer and this approach has proved to be a more meaningful and acceptable technique to describe the plant behaviour. The theory of the model is introduced and the effect of changing parameters on the rate of fouling and steady state value is examined. More research is needed to quantify the factors which control the deposition and removal terms in operating plant. This model is shown to be applicable to plants treated with a polyphosphate based system as well as high performance additives such as ALBRIVAP DSB. Das Verhalten von mit Hochleistungs-Zusatzstoffen behandelten grossen Anlagen wurde auf lange Zeiten im Beharrungszustand sorfältig überwacht. Mit der Zeit hörte die Ansammlung von Verschmutzungsstoffen im Salzlaugenheizer auf, der Widerstand gegen den Wärmeübergang erreichte einen gleichbleibenden Wert. Änderungen der Betriebsbedingungen führten zu schnellen umkehrbaren Veränderungen im Verschmutzungsgrad, d.h. sobald die Betriebsbedingungen wieder auf den ursprünglichen Wert zuruckkehrten, wurde wieder ein gleichförmiger Wert erzielt. Als wichtigster Änderungsparameter wurde die Salzlaugenzirkulationsrate oder die Geschwindigkeit, welche die Scherbeanspruchung in der Grenzschicht zwischen Salzlauge und Ansammlung aufstellt, erkannt. Das