Microwave processing of materials

Kingman, Samuel William (2018-03)

Thesis (DEng)--Stellenbosch University, 2018.

Thesis

ENGLISH SUMMARY: The world is under increasing pressure to develop new, more energy-efficient technologies that enable the production of less waste and are more sustainable. Material processing through microwave energy has received academic attention in the past few years for potentially delivering environmental benefits for a number of different applications including, food, fine and bulk chemicals, oil and gas, minerals and metals extraction. Despite the potential to deliver a step change in overall process efficiency across a diverse range of sectors, the true economic value of microwave technology has generally not being realised. My work in microwave processing commenced in 1996 with my PhD at the University of Birmingham where I began investigations into the interaction of microwave energy with metal ores in order to reduce grinding energy and improve liberation of valuable minerals. Even at this early stage it became apparent that despite a strong body of literature reporting laboratory studies there was very little knowledge supporting the scale up of microwave technologies for application in industrial processing. Further investigation into other potential application areas such as chemistry, materials processing, drying and food processing demonstrated that similar barriers existed with few if any commercial implementations of basic research realised. I have sought to identify the reasons why scale up of microwave heating is a challenge, to identify solutions to some of the major technical barriers and to develop generic methodologies which can be applied to different material systems across multiple industries. Such barriers relate to a lack of understanding of the interaction of microwaves with materials at a molecular level, lack of a multi-disciplinary approach to scale up, poorly understood value propositions for the use of microwave technology, and a lack of a trained workforce to support technology implementation in industry. Ultimately, it is also true that due to the high capital cost of microwave technology the ability to identify process benefits that can only be delivered through microwave heating alone, rather through cheaper conventional heating technologies is critical for successful commercialisation. Addressing these barriers has led me to develop, in collaboration with colleagues from across the globe, methodologies for the scale up of microwave technology. Identification of the interaction mechanism with the material to be processed, be it bulk or selective heating exemplified through the use of dielectric property measurements at both extremes of temperature and pressure has been reported as has modelling of the impact of rapid heating on material matrices. Studies which have proven the mechanism by which microwaves deliver value through multiple interactions have been reported for numerous different material classes and systems often at the highest power inputs ever reported. Scale up of systems through collaboration with experts in microwave design, materials handling and chemical reaction engineering have been reported for different applications, each providing a basis for the scale up of the technology. In several cases including rock fracture and sorting, oil and drilling waste processing and vermiculite exfoliation this has led to the development of unique microwave technologies. In the case of mineral sorting and fracture this work has directly underpinned the highest throughput microwave processing systems ever built.

AFRIKAANSE OPSOMMING: Die wêreld is onder toenemende druk om nuwe, energiedoeltreffender tegnologieë te ontwikkel wat sal help om afvalproduksie te verminder en wat meer volhoubaar is. Materiaalverwerking deur mikrogolfenergie het in die afgelope paar jaar aandag op akademiese gebied geniet vanweë die moontlike omgewingsvoordele wat dit vir verskillende toepassings, onder meer die onttrekking van voedsel, fyn en growwe chemikalieë, olie en gas, minerale en metale, inhou. Afgesien van die potensiaal om ’n faseverandering in oorhoofse prosesdoeltreffendheid oor ’n uiteenlopende verskeidenheid sektore te kan lewer, word die werklike ekonomiese waarde van mikrogolftegnologie oor die algemeen nog nie besef nie. My werk in mikrogolfverwerking het tydens my PhD-studie in 1995 aan die Universiteit van Birmingham begin met ondersoeke na die interaksie tussen mikrogolfenergie en mataalertse ten einde slypenergie te verminder en die loslating van kosbare minerale te verbeter. Selfs in daardie vroeë stadium was dit duidelik dat ondanks ’n uitgebreide korpus literatuur wat oor laboratoriumondersoeke berig, daar baie min kennis bestaan ter ondersteuning van die opskaling van mikrogolftegnologieë vir toepassing in bedryfsverwerking. Verdere ondersoeke na ander potensiële toepassingsareas soos chemie, materiaalverwerking, droging en voedselverwerking, het bevind dat daar soortgelyke struikelblokke is en dat min, indien enige, kommersiële toepassings vir basiese bewese navorsing gerealiseer het. Ek het ondersoek ingestel na die redes waarom die opskaling van mikrogolfverhitting uitdagings stel ten einde oplossings te vind vir van die belangrikste tegniese struikelblokke, asook om generiese metodologieë te ontwikkel wat op verskillende materiaalsisteme oor verskeie industrieë heen toegepas kan word. Hierdie struikelblokke het te make met ’n gebrek aan insig rakende die interaksie tussen mikrogolwe en materiale op ’n molekulêre vlak, die gebrek aan ’n multidissiplinêre benadering tot opskaling, onvoldoende insig in waardevoorstelle vir die gebruik van mikrogolftegnologie, en ’n gebrek aan ’n opgeleide werksmag om tegnologie-implementering in die bedryf te ondersteun. Uiteindelik moet daar in gedagte gehou word dat vanweë die hoë kapitaalkoste van mikrogolftegnologie, die vermoë om prosesvoordele te identifiseer wat slegs deur mikrogolfverhitting gelewer kan word – in plaas van deur goedkoper, konvensionele verhittingstegnologieë – krities vir suksesvolle kommersialisering is. Tydens die aanpak van hierdie struikelblokke het ek metodologieë vir die opskaling van mikrogolftegnologie in samewerking met kollegas oor die hele wêreld ontwikkel. Identifisering van die interaksiemeganisme met die materiaal wat verwerk moet word, hetsy massa- of selektiewe verhitting, toegelig deur die gebruik van diëlektriese eienskapmetings teen sowel temperatuur- as drukuiterstes, is aangemeld, asook die modellering van die impak van snelverhitting op materiaalmatrikse. Studies is aangemeld ter stawing van die meganisme waarvolgens mikrogolwe deur veelvoudige interaksies vir ’n verskeidenheid materiaalklasse en -sisteme waarde lewer, dikwels teen die hoogste kraginsette wat tot dusver gerapporteer is. Stelselopskaling deur medewerking met kundiges in mikrogolfontwerp, materiaalhantering en chemiesereaksie-ingenieurswese is vir verskillende toepassings aangemeld, wat elkeen ’n basis vir die opskaling van die tegnologie bied. In verskeie gevalle, waaronder rotsbreking en -sortering, olie- en boorafval-verwerking en vermikulietafskilfering, het dit tot die ontwikkeling van unieke mikrogolftegnologieë gelei. In die geval van mineraalsortering en -breking het hierdie werk die direkte motivering verskaf vir die bou van mikrogolfverwerkingstelsels met die hoogste verwerkingskapasiteit tot op hede.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103644
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