The 2011 Manufacturing & Process Innovation winner - ProWave

Prowave vermiculite processing system

e2v Technologies, National Centre for Industrial Microwave Processing at Nottingham

Vermiculite is one of those materials that few people have heard of, but which touches most of our lives in some way. A naturally occurring mineral mined mainly in South Africa, the US and China, it’s used extensively in fireproofing, brake linings, insulation and in many building materials for roofing and flooring. Its most familiar usage is in horticulture, especially for seed cultivation at both the industrial and domestic scale. It’s in hand warmers and the walls of AGA ovens, and used in glassblowing and bead making. It’s even used to incubate reptile eggs.

In its natural state, however, vermiculite is useless. The mineral, which is a form of clay, consists of many layers of mineral ’platelets’, packed close together. To make it useful, it has to undergo a process called exfoliation, which happens when it is heated. The mineral expands, forcing the platelets apart into a high-volume, low-weight configuration.

This process is extremely energy intensive, usually carried out in gas- or oil-fired furnaces. Around 600,000 tonnes of vermiculite is exfoliated per year, and the furnaces generally consume more than 1MWh of energy per tonne of material – and this is on top of the energy expended in mining the material in the first place. The amount of resources consumed, as well as the carbon emissions generated, are considerable.

It’s been known for more than 20 years that vermiculite will also exfoliate when it is microwaved. However, although this was possible at a small scale, expanding it to an industrial-scale process was technically challenging and while energy prices were low and CO2 emissions not a concern, it wasn’t worth the investment to develop an alternative to furnaces.

Now, however, the situation is quite different. This led industrial processing company e2v Technologies, which has a specialist industrial microwave process division, to work with Nottingham University’s Centre for Microwave Processing to develop a solution.

’There has been a long history of research into this field carried out by other organisations,’ said e2v product manager Anthony Fernandez. ’However, none have been able to produce a technically and commercially viable solution.’ Some ’potential stakeholders’ even claimed that the project would be impossible, he added.

Vermiculite is in hand warmers and the walls of AGA ovens, and used in glass blowing and bead making

There were several problems that had to be overcome. First, vermiculite is a natural product. Every sample is different, no load is uniform; composition, liquid content, platelet thickness all vary. ’The system would have to be capable of applying a very accurate power density to a material that varies dramatically in moisture content, platelet diameter and thickness, and particle size distribution,’ Fernandez said. ’In addition, the system had to be capable of treating raw materials sourced from any mine in the world, adding a further level of variability into the process.’

While meeting this criterion, the process also had to be able to apply high-power microwaves, in a controlled, reliable and repeatable manner, while keeping to the required level of throughput for a commercial system and complying with all the microwave regulations in force around the world.

Microwaves exfoliate vermiculite by evaporating the water in the mineral, with the build-up of pressure as the water expands and changes to steam, forcing the layers apart. The key to the process was determining a microwave frequency that would heat only the water and transfer no energy into the bulk material.

’It is this selective heating that offers significant advantages over a traditional furnace, which wastes energy heating the entire bulk material unnecessarily,’ Fernandez said.

However, Fernandez picks out the way the microwaves are applied as the most innovative part of the process. The vermiculite passes through the process on a conveyor belt that sits above the microwave generator; the energy is directed at the bottom of the belt. ’This makes it very challenging to transport the loose granular material through the microwave field and adds significant complexity to the cavity design,’ he said, ’but it is the key to developing a reliable solution, since the exfoliation generates a significant volume of dust and steam that must be extracted immediately, and can only be done effectively from above.’

The process also has highly configurable digital control, which allows operators to fine-tune the process, create production recipes and optimise the various process parameters on the fly to create the exact properties the customer needs in their vermiculite. This control extends to the rate and degree of expansion, which can greatly improve the yield – in this case, referring to the bulk density – of the sample to an unprecedented degree. The Prowave system can achieve yields as low as 80g/litre, compared to furnaces that typically produce 110g/litre. ’A furnace will therefore produce around 9.1m3/tonne, while a microwave system will produce 12.5m3/tonne,’ Fernandez claimed. ’Furthermore, the Prowave system increases the proportion of raw material that is actually processed, significantly reducing the current rejection rater of around 10 per cent.’ As vermiculite is sold by volume rather than mass, this represents a considerable boost to manufacturers’ profit margins.

“A microwave’s selective heating offers significant advantages over a furnace, which wastes energy heating the entire material ”

ANTHONY FERNANDEZ, E2V

A further advantage is that, as the mineral content of vermiculite is transparent to microwaves, the final product is much cooler than that treated in a furnace. The product is delivered at 150°C, so that it can be packaged almost immediately, rather than being fed through cooling systems.

Overall, Fernandez claims, Prowave reduces energy consumption by up to 90 per cent and cuts the process carbon footprint by 85 per cent.

These advances were only possible through collaboration, Fernandez said. ’The key to delivering this project successfully was the formation of a multi-disciplinary team of highly talented chemists, physicists and engineers, and an end-to-end knowledge transfer network including industry experts from the Vermiculite Association, cutting-edge microwave R&D from Nottingham and world-leading power design and global support capabilities from e2v,’ he said. External funding was also significant, he added – a £6.2m grant from the Regional Growth Fund covering e2v’s Essex headquarters helped the company form a dedicated Industrial Processing Systems division. But it’s the final result which is the reward, he added. ’There’s no better indicator of success than direct market feedback, which has been overwhelmingly positive, with the first commercial agreement already in place.’

Category sponsor