Mechanical Process Technology Like a long, quiet River
If there were no mechanical process engineering, there’d be no processing industry. It frequently provides the start (crushing, for example) and the end (sorting) of a process. Nevertheless, it´s role has changed in recent years. Whereas previously it tended to be seen more as supporting act, now it takes on the leading roles.
Nothing much has changed in the fundamental techniques used in mechanical process engineering. Whether you’re running screening machines, mills or centrifuges, the technologies they use are centuries old. However, things are bubbling away furiously under (or, more appropriately for mechanical processes, at) the surface, and so many development engineers are currently attempting — if not to outsmart the physics — then to push it to its outer limits at least.
“Generally, we can say for sure that in the past 20 years our understanding of processes has increased substantially. At the same time, the level of process automation has increased, and the theoretical mapping of processes is becoming more and more important. For example, simulating solid matter processes, if we take the discrete element method as an example, is much more realistic today due to the improvement in computing power,” says Dr. Lars Frye, Head of Solids Processing at Bayer Technology Services, giving his impressions of how the sector has developed.
Moreover, in his experience mechanical processes are becoming much more interrelated with other disciplines, such as interface physics. An example of this is electrostatic or steric stabilization in wet grinding attritors, which allows ever-smaller particles to be produced. While 20 years ago this process would have operated in the micrometer range, nanotechnology has since arrived and has now become the practice.
“The material properties of particles can be controlled more precisely“
The opportunities available today in particle analysis also extend significantly further now, and not just in relation to identifying size distribution. The great advances that have been made, for example, in imaging processes reveal detailed insights into a process. While attempts to optimize mechanical processes involved a great deal of empirical work 20 years ago, our understanding of why and how a process operates in practice has grown considerably.
“Today, we’re more likely to know what is happening at the interfaces and the impact this has on the process. At the same time, we’re now able to measure the size of particles and even sometimes the shape of particles inline. As a result, the material properties of particles, such as size, crystal morphology and shape, can be controlled more precisely to suit the purpose,” explains Frye.
It’s not just the particle sizes that have gotten increasingly smaller: the quantities provided for development are also decreasing. “Some years ago, we still needed about 200 ml for conducting trials to characterize bulk goods. Normally now we can do it with 30 ml. And in future we’ll have to make it with just a few grams for our development work in certain circumstances, considering how some active ingredients are expensive to develop and in some cases are customized as well,” says Frye.
The issues that are now being debated by researchers include questions such as: How do I design measuring techniques and equipment in this environment, where the wall effects are no longer negligible, that will still allow work to be carried out in an efficient and reproducible manner? And how can the trend for continuous operations be realized in the solids process engineering sector?
“Will we succeed in accommodating these additional factors and constraints? How, for example, are we going to guarantee continuous dosing of tiny flows of solid material mass?” ponders Frye. Or how can the centrifuges that are frequently used for separating solids and currently operate on a batch basis as such be integrated into continuous processes? “You can’t leverage the physics in continuous processes either, so new solutions need to be found and new equipment needs to be developed,” says Frye of the challenges ahead.
Demands are Increasing
The requirements are also growing on the equipment side as well. Even the mixing stage is much more than a basic processing operation today. It might mean having to coat, agglomerate or disperse, spheronize or condition particles. The focus is on the end product and its properties. As a result, the technical challenges are growing — ultimately, the complexity and differentiation involved in mixing tasks increase — and this requires a precise knowledge of the processes and the customer’s requirements.
“The demands on product properties have increased considerably in the last 20 years, and that’s happened independent of the industry. Our customers are confronted with increasingly complex product properties at the same time as quality demands are increasing, and they’re asking us to come up with a solution for them,” says Reiner Lemperle, Authorized Officer and Head of Sales at plant engineering company, Gebr. Lödige Maschinenbau.
This involves, for example, coping with the fact that particle sizes are becoming increasingly finer and therefore increasingly finer distributions are also required. “For example, we’re certainly having to deal now with sizes in the nano range. Some mechanical processes are also now increasingly combined with thermal processing, which creates new challenges from the point of view of the equipment,” adds Lemperle.
Other changes that affect the equipment have arisen according to Lemperle as a result of adopting the Atex Directive 94/9/EC in 2003. “Of course mechanical equipment was configured, constructed and supplied safely before then, but today there’s a different perspective on how the layout is regarded,” says Lemperle of the developments in safety technology.
Some new developments have also come about through industry-specific initiatives, such as the increasing use of continuous processes in the pharmaceutical industry. “Moving over from what until now was a simple batch-processing approach to continuous production doesn’t just require equipment manufacturers to come up with new developments in the technology but it also calls for structural adjustments on the part of the operator,” Lemperle cites as an additional shift that equipment manufacturers are having to deal with.
This includes, for example, complying with documentation requirements and maintaining close contact with regulatory authorities such as the FDA. However, mixes and mixing times also continue to play an important role. That means the issue of efficiency doesn’t stop at mechanical process engineering: the homogenization of the individual components also needs to happen as quickly and efficiently as possible. A further aspect is the way in which the energy efficiency of drive motors is now deployed and the use of frequency-controlled motors instead of pole-changing motors.
At the Core
Lucrative development potential currently exists in the recovery of raw materials in the form of “urban mining”. There was no role here for mechanical process engineering 20 years ago — before rare earths became the game changers they are today. Due to the protectionist measures of a few — although vital — raw material manufacturing states (such as China), attention in research and development has now shifted to the recycling of strategic materials such as rare earths and precious metals, as well as other high-grade mineral commodities.
When you consider that one ton of PB motherboards contains 30 times more gold than a ton of material extracted from a gold mine, you start to see the mechanical processing of such materials in a different light. However, recovering metals, especially rare earths as well as gold, silver and copper, is a very complicated process and requires high levels of energy, and so specially adapted crushing and sorting processes for extracting metals aim to provide a solution. If the motherboard, for example, is not removed before shredding, it is very difficult — if not impossible — to get at the essential trace elements. In this case, it means losing 75 % of the gold.
Mechanical process engineering with its traditional crushing and sorting disciplines is the starting point for this process chain and has a decisive influence on the subsequent stages in the process, i.e. in dictating whether or not an urban mining operation is even worthwhile. The topic has been flagged up as an issue for the future in a Dechema position paper in 2013.
These examples, whether they involve the handling of minimal flows of material mass where the task pushes the physics to its outer limits or the search for potential future raw materials held in crude flows of recyclable material, demonstrate the huge potential of mechanical process engineering. Although the traditional workhorses of process engineering have performed perfectly well for many years, it’s time for the industry to tackle new challenges.