Meanwhile, national laws, as well as directives by the European Union are regulating the limitation in dust emission in various areas. The use of high-performing dust filters and the constant monitoring of their functioning by the professional associations in charge has become the common standard. Even though no global standard has yet been agreed upon, Europe is well on the way to achieving one. The massive use of filters raises the question of how to deal with the huge mountain of separated dust and slags produced. In many cases, the solution exists, but often one’s first reaction to the problem of slags and dust is helplessness.
It must be mentioned that this article does not deal with dust considered as health-threatening or toxic. For these, special disposal regulations are either already in force or have yet to be prepared. It instead, deals with all the other types of dust to be disposed of or recycled; dust which ends up in FIBCs, IBCs, silos, or even on stockpiles after having been separated. No standard addresses the problem of what happens to the dust afterward. Since the stored dust can volatilize again at any time, it must be made “shovelable” i.e. transportable. It is necessary to moisten the dust, which can be done just as well by hand using a hosepipe as using a continuously working twin shaft paddle mixer or, even better, a single shaft ploughshare mixer, both necessarily equipped with a water addition device. In between these exist a variety of alternative systems. The correct consistency of the product is essential not to produce a slurry.
Whether for disposal or recycling, the moisture content must be as low as possible to keep the energy input and costs low.
Here are two examples from the ceramics industry and foundries:
In the first case, the dust is mostly re-used in consideration of the high cost of the product. On recycling, moistening is essential, as these materials tend to develop a great amount of dust and cannot be handled due to their high flowability. The moistening, therefore, must be extremely precise and constant. The moisture content may not be more than 8 – 10%. To obtain this result, a mixer is required that does not exceed a coefficient of mixing quality variation of 2%. Another problem is the strong product cohesion of normally clay dust, especially when moist.
Although in foundries there is no recycling problem, the moisture content must be kept to a minimum because disposal in landfills and incineration plants is calculated by weight. The general rule is the lower the moisture content, the lower the weight. Consequently, the mixers used, must be dustproof and operate highly efficiently to guarantee that there will be no air pollution despite the lowest possible moisture content.
Another aspect not to be neglected is the high wear to which the mixing tools are subjected. This is a problem that almost all types of dust have in common once the liquid has been added.
Reports verify that dust recycling in the ceramics industry is of use for the production process only in part, while for foundries, similar to many other industries, separated dust represents a pure cost.
To solve the problem, various systems have been developed over the years: mixing screw conveyors, twin shaft paddle mixers, ploughshare mixers, and others. Unfortunately, none of these systems has all the features which are important to the operating authority: high efficiency, modest wear, and low purchase cost.
Talking about conditioners the name WAMGROUP® must be mentioned. In the northern Italian town of Modena, in recent times, a great deal of energy has been put into the development of particularly innovative new equipment for this purpose. For smaller throughput rates, especially for the nearby situated ceramics industry, CLAYGRAN® has been developed. WETDUST®, on the other hand, is an option for foundries. Both have in DUSTFIX® their counterpart for applications that require higher mixing capacity.
What is immediately apparent when looking at these machines more carefully, is the varied use of polyurethane-based materials. This gives particularly high resistance to abrasion as well as an optimum efficiency when compared to traditional machines. Besides, the compact design makes the inclusion into existing plants extremely easy.