Understanding microwave heating effects in single mode type cavities—theory and experiment

Robinson, John P.; Kingman, S.W.; Irvine, Derek J.; Licence, Peter; Smith, Alastair D.; Dimitrakis, Georgios; Obermayer, David; Kappe, C. Oliver

doi:10.1039/b922797k

Cited by 166 publications

(156 citation statements)

References 40 publications

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“…Whilst the mechanistic principals were beginning to be understood (Kingman et al, 2000a), it was found that reductions in energy inputs (from >>10kWh/t to <5kWh/t) and residence times (to yield higher throughputs) were required to realise an economically viable process (Kingman and Rowson, 1998). Focussed work using single mode cavities, post-2000 resulted in reductions in the energy required, greater understanding of the breakage mechanism and also characterisation of the electromagnetic properties of such cavities (Kingman et al, 2004c;Kingman et al, 2000b;Robinson et al, 2010a). This yielded important information regarding the spatial distribution and intensity of electromagnetic energy within them.…”

Section: Microwave Processing Of Ores -Technology Development Timelinementioning

confidence: 99%

Towards large scale microwave treatment of ores: Part 1 – Basis of design, construction and commissioning

Buttress

Katrib

Jones

et al. 2017

Minerals Engineering

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Highlights A pilot scale system for microwave treatment of ores is presented  Materials handling concepts and justification for packed bed mass flow are discussed  Microwave applicator and choke modelling is validated against real ores  Control of material flow and presentation is discussed  The operating microwave treatment system performance is described AbstractDespite over thirty years of work, microwave pre-treatment processes for beneficiation of ores have not progressed much further than laboratory testing. In this paper we present a scaleable pilot-scale system for the microwave treatment of ores capable of operating at throughputs of up to 150tph. This has been achieved by confining the electric field produced from two 100kW generators operating at 896MHz in a gravity fed vertical flow system using circular choking structures yielding power densities of at least 6x10 8 W/m 3 in the heated mineral phases. Measured S11 scattering parameters for a quartzite ore (-3.69±0.4dB) in the as-built applicator correlated well with the simulation (-3.25dB), thereby validating our design approach. We then show that by fully integrating the applicator with a materials handling system based on the concept of mass flow, we achieve a reliable, continuous process. The system was used to treat a range of porphyry copper ores. Minerals Engineering 109 (2017) 169-832 http://doi.org/10.1016/j.mineng.2017.03.006 IntroductionMicrowave treatment of metalliferous ores has long been investigated as a means to enhance the recovery of valuable minerals and reduce the comminution resistance of ores (Chen et al., 1984;Walkiewicz et al., 1988;Walkiewicz et al., 1989). The underpinning mechanism and textural characteristics of amenable ores has been described by Batchelor et al. (2015). Selective heating of microwave-absorbent sulphides and metal oxides deported in a microwave-transparent gangue matrix results in differential thermal expansion of the heated phase, yielding micro-fracture around grain margins Jones et al., 2005Jones et al., , 2007Kingman et al., 2004a;Kingman et al., 2004b;Kingman et al., 2000a). Subsequent downstream processing may then yield higher recovery of valuable mineral sulphides and/or lower specific comminution energy, compared to non-microwave treated ore.While the mechanistic principles are well established, the scientific and engineering challenges of developing a commercial scale system are immense. Typical throughputs of a large copper mine can be in excess of 5,000 tph of milled ore (Brininstool, 2015) and a microwave based treatment system would need to handle equivalent throughputs. This is at least an order of magnitude higher than any other microwave process ever built.The following paper details the design, commissioning and operation of a system which was the culmination of over fifteen years of research and development activity. This resulted in a high power microwave treatment process, capable of operating continuously at throughputs of up to 150tph, but crucially, scaleable up to several th...

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Section: Microwave Processing Of Ores -Technology Development Timelinementioning

confidence: 99%

Towards large scale microwave treatment of ores: Part 1 – Basis of design, construction and commissioning

Buttress

Katrib

Jones

et al. 2017

Minerals Engineering

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“…There are a number of techniques whereby spot-measurements of temperature can be made in a microwave environment, however these are point-measurements within a media with a significant temperature distribution. It has also been shown that the addition of a thermocouple causes a significant distortion to the electric field [19], so the readings obtained are partly an artefact of the presence of the thermocouple rather than the behaviour of the sample under study. There are no reliable ways to measure the temperature distribution during microwave heating, so any data interpretation must not rely directly on these measurements.…”

Section: Microwave Pyrolysis -A Volumetric Heating Approachmentioning

confidence: 99%

Microwave Pyrolysis of Biomass: Control of Process Parameters for High Pyrolysis Oil Yields and Enhanced Oil Quality

et al. 2015

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The oil yield and quality of pyrolysis oil from microwave heating of biomass was established by studying the behaviour of Larch in microwave processing. This is the first study in biomass pyrolysis to use a microwave processing technique and methodology that is fundamentally scalable, from which the basis of design for a continuous processing system can be derived to maximise oil yield and quality. It is shown systematically that sample size is a vital parameter that has been overlooked by previous work in this field. When sample size is controlled the liquid product yield is comparable to conventional pyrolysis, and can be achieved at an energy input of around 600 kWh/t. The quality of the liquid product is significantly improved compared to conventional pyrolysis processes, which results from the very rapid heating and quenching that can be achieved with microwave processing. The yields of Levoglucosan and phenolic compounds were found to be an order of magnitude higher in microwave pyrolysis when compared with conventional fast pyrolysis. Geometry is a key consideration for the development of a process at scale, and the opportunities and challenges for scale-up are discussed within this paper.

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“…It was noticed that around the edges of internal protruding objects (such as stirrers and temperature probes) the electric field and power density were significantly concentrated ( Figure 8). Furthermore, the volume of solvent present in a reaction vessel has an effect on the distribution of the electric field [190].…”

Section: Microwave Apparatus and The Importance Of Cavity Designmentioning

confidence: 99%

“…The majority of the aforementioned studies in this review report the use of domestic MW which feature built-in agitation devices, temperature monitoring/control of the reaction mixture with either infrared sensors or fibre optic probes and software which enables the user to monitor the temperature/pressure of the reaction [190]. However, one of the main limitations with such devices (and also a limitation of domestic MW ovens) is the relatively low intensity electric field and the absence of reflected power measurements.…”

Section: Microwave Apparatus and The Importance Of Cavity Designmentioning

confidence: 99%

“…Ideally, mapping the power density distribution (preferably in real time) as the feedstock is being pre-treated, (whether for drying purposes, torrefaction, or to induce the necessary structural alternations for increased hydrolysis efficacy for bioethanol or AD conversion routes) would further aid in the development of biomass pre-treatment processes using MW heating. Robinson et al [190] investigated the phenomena that occur within a MW single mode cavity using electromagnetic simulations and heating experiments to show the effects of different factors (including solvent type, vessel material and stirring rate) on the distribution of the electric field, power density and rate of heating. It was noticed that around the edges of internal protruding objects (such as stirrers and temperature probes) the electric field and power density were significantly concentrated ( Figure 8).…”

Section: Microwave Apparatus and The Importance Of Cavity Designmentioning

confidence: 99%

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The application of microwave heating in bioenergy: A review on the microwave pre-treatment and upgrading technologies for biomass

Kostas

Beneroso

Robinson

2017

Renewable and Sustainable Energy Reviews

240

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Bioenergy, derived from biomass and/or biological (or biomass-derived) waste residues, has been acknowledged as a sustainable and clean burning source of renewable energy with the potential to reduce our reliance on fossil fuels (such as oil and natural gas). However, many bioenergy processes require some form of pre-treatment and/or upgrading procedure for biomass to generate a modified residue with more suitable properties and render it more compatible with the specific energy conversion route chosen. Many of these pre-treatments (or upgrading procedures) involve some form of substantive heating of the biomass to achieve this modification. Microwave (MW) heating has attracted much attention in recent years due to the advantages associated with dielectric heating effects. These advantages include rapid and efficient heating in a controlled environment, increasing processing rates and substantially shortening reaction times by up to 80%. However, despite this interest, the growth of industrial MW heating applications for bioenergy production has been hindered by a lack of understanding of the fundamentals of the MW heating mechanism when applied to biomass and waste residues. This article presents a review of the current scientific literature associated with the application of microwave heating for both the pre-treatment and upgrading of various biomass feedstocks across different bioenergy conversion pathways including thermal and biochemical processes. The fundamentals behind microwave heating will be explained, as well as discussion of the imperative areas which require further research and development to bridge the gap between fundamental science in the laboratory and the successful application of this technology at a commercial scale.

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Understanding microwave heating effects in single mode type cavities—theory and experiment

Cited by 166 publications

References 40 publications

Towards large scale microwave treatment of ores: Part 1 – Basis of design, construction and commissioning

Towards large scale microwave treatment of ores: Part 1 – Basis of design, construction and commissioning

Microwave Pyrolysis of Biomass: Control of Process Parameters for High Pyrolysis Oil Yields and Enhanced Oil Quality

The application of microwave heating in bioenergy: A review on the microwave pre-treatment and upgrading technologies for biomass

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