Controlling dust: operating and cleaning technologies for all needs related to powders and granulates

Mixing and agglomeration processes for bulk goods play an important role in the food production industry. Pudding powders, ready-soups, baking mixes, mueslis and cereals are only a few examples of the applications for these technologies. Behind all these products is a complex technological process that largely determines the products' properties and their quality. The mixing and agglomeration processes used in production have a decisive effect on the quality criteria of colour, flavour, solubility, pourability and shelf life.

One criteria for the quality of dried drink and soup powders is their solubility. Today's consumers demand easily soluble and easy to use instant powders. Superior solubility, especially at low temperatures, can be achieved by reducing the proportion of fine dust in a product as much as possible. This is possible thanks to modern agglomeration processes that are integrated in the drying process. With such processes, the powder is circulated until it has achieved a sufficient grain size and the fine dust is almost entirely bonded.
The other side of the coin is that with the further development of spray drying, the risk of dust explosions in production has increased.

Preventing the "big bang"
Statistics indicate a dust explosion occurs in Germany every day, on average. Whether it's flour, coffee, cocoa or dried plant extracts - if it is fine enough to form a dust cloud, any organic substance can react explosively if exposed to a source of ignition. The conditions necessary to create an explosive atmosphere occur frequently in the production, conveyance and storage of powders, so it's no wonder that the food industry is among the sectors that suffers the most explosions, with a share of about 25 per cent.
In an area that is at risk of explosion, food producers are only allowed to use operating equipment that satisfies the requirements of the European guideline ATEX 100a. Systems that face a higher risk of explosion include spray driers, fluidised-bed granulators, pelletising machines, separators, filters, dust collectors and cyclone separators. For manufacturers of these processing technologies, this means the systems must be developed and designed in such a way that they themselves do not represent a source of ignition and that - in a worst-case scenario - the effects of an explosion would be limited. One of the most frequently used measures is decompression. With this approach, a defined area (explosion diaphragm) on the product tank is destroyed by the explosion and the excess pressure is released in a controlled fashion in area where there is no danger. A problematic aspect is that explosions can spread through pipelines to other parts of the system or facility. These secondary explosions become even more powerful than the original explosion. The spread of explosions is prevented by using fast-closing valves and by blowing in extinguishing powder that isolates an explosion.

The latest trend: designs that are easy to clean
In general, quality standards in the production of food products are increasingly approaching those of the pharmaceuticals industry. With frequent recipe changes and replacement of products with newer versions, the systems and facilities must be as easy to clean as possible and offer the highest degree of flexibility and adaptability. "Hygienic design" is a central focus of decision-making when it comes to investments. And systems for processing bulk goods are no exception to this trend. In addition to design details - no corners or dead spaces, improved flow and discharge characteristics - dismantling that doesn't require any tools is also important for minimising the time needed for cleaning and configuring.
Raw materials and ingredients delivered in sacks are falling out of favour because they represent high expense for manual labour, cleaning and removal. The emerging trend is the use of medium-sized bags (Big Bags), containers and delivery in silo vehicles. With Big Bag delivery, the bags can be coupled at emptying stations without generating any dust, and even products that are hard to handle can be safely emptied. With silo vehicle deliveries, a pneumatic process is used to fill the silos with raw materials. In pneumatic conveyor systems, the dosing devices play a decisive role. Drop gates and blow-through gates are equipped with extraction devices so that the rotor can be removed at the side for cleaning and quickly re-installed. And here too, the cleaner a production system is, the lower the risk of an explosion.