Ultrasonic-time-domain-reflectometry as a real time non-destructive visualisation technique of concentration polarisation and fouling on reverse osmosis membranes

Koen, Louis Johannes (2000-12)

Thesis (MEng)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: Fouling is readily acknowledged as one of the most critical problems limiting the wider application of membranes in liquid separation processes. A better understanding of fouling layer formation and its monitoring is needed in order to improve on existing cleaning techniques. Plant operation can be optimised if fouling can be monitored by noninvasion means either on the plant itself or on an attached monitoring device. The overall scope of this research was to develop a non-destructive, real-time, in situ visualisation technique or device for concentration polarisation and fouling layer monitoring. Ultrasonic-time-domain-reflectometry (UTDR) was employed as a visualisation technique to provide real-time characterisation of the fouling layer. A 24 cm-long rectangular flat sheet aluminium cell was designed and used as separation device for a desalination system. The experimental results obtained using this module confirmed that there are an excellent correspondence between the flux decline behaviour and the UTDR response from the membrane. The ultrasonic technique could effectively detect fouling layer initiation and growth on the membrane in real-time. In addition to the measurement of fouling, the ultrasonic technique was also successfully employed for monitoring membrane cleaning. Since no real-time permeation data is available during cleaning operations in industrial applications, a UTDR monitoring device may prove to be a very valuable technique in optimising cleaning strategies. The technique was further tested on an 8-inch diameter spiral wrap industrial module and good results were obtained. Stagnant zones, as well as flux flow behaviour inside the module could be determined. However, more research IS needed to fully understand the complex phenomena inside a spiral wrap module. Overall, the UTDR technique and its use in monitoring devices have a major impact in the membrane industry due to its extremely powerful capabilities.

AFRIKAANSE OPSOMMING: Membraan-bevuiling of -verstopping is die grootste struikelblok wat die algemene aanwending van membrane vir verskillende watersuiweringsprosesse negatief beinvloed. 'n Beter begrip van membraan-bevuiling, asook beter metingsmetodes daarvan is nodig om op bestaande skoonmaaktegnieke te verbeter. Die hoofdoel van hierdie studie was die ontwikkeling van 'n nie-destruktiewe-in-lyn visuele tegniek vir die meting van konsentrasie polarisasie en membraan-bevuiling. Deur gebruik te maak van ultrasoniese klank golwe, is 'n tegniek ontwikkel wat 'n direkte visuele aanduiding kon gee van die toestand van membraan-bevuiling binnein die module. 'n Reghoekige aluminium-module, 24 cm lank, is ontwerp en gebou waarbinne die membraan geplaas is vir die skeidingsproses. Resultate dui daarop dat daar 'n uitstekende verband bestaan tussen die afname in permeaatvloei en die ultrasoniese eggo vanaf die membraan. Die ultrasoniese tegniek kon die vorming van en toename in membraan-bevuiling doeltreffend karakteriseer. In teenstelling hiermee, is die tegniek ook suksesvol aangewend om die skoonmaak-proses van membrane te ondersoek. Met min of geen data beskikbaar vir die skoonmaak-proses van membrane in die industriële sektor, het die tegniek enorme potensiaal in die optimisering van bestaande skoonmaak-tegnieke. Die tegniek is verder aangewend op 'n industriële 8-duim deursnee spiraal-module en goeie resultate is verkry. Stagnante sones asook vloed-vloei-patrone binne-in die module kon suksesvol bepaal word. Baie navorsing is egter nog nodig om die ingewikkelde data wat gegenereer word tydens die ondersoek van 'n spiraal-module ten volle te verstaan. Die enorme potensiaal en moontlikhede van die ultrasoniese tegniek kan die begin wees van 'n revolusie in die membraan-industrie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52042
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