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Goodbye to dust

Hygienic bag discharge
Goodbye to dust

There are many possible ways to minimise dust formation during bag discharge. Regardless of whether a simple bag discharge station or one with an integrated filter or isolator technology is involved, it is important to define the requirements precisely. Efficient systems that enable powders and granules to be discharged from bags hygienically can be designed as a stand-alone solution or as part of an overall system.

The author: Clemens Schmitt Marketing, Hecht Technologie

Costs, cleanability and simple handling are key criteria when choosing a bag discharge station for hygienic applications or for handling non-hazardous products, as used in the food industry. The Hecht SE-RVS bag discharge station, for example, meets these requirements and is particularly easy to clean, mainly due to its round design. In addition, it is equipped with a vibrating sieve which holds back contaminants such as scraps of paper and dissolves small lumps.
The associated vibration decoupling is installed internally, which is why the station can do without hygienically critical transition sleeves. If required, the sieve can be replaced quickly and with minimal effort by a sieve with a different mesh size when the product is changed. A separate filter with a fan makes sure that there is always a slight vacuum in the station (aspiration). Dust formation or leakage during the discharge process is thus eliminated to a large extent. The aspiration function can be automatically activated when the front lid is opened.
To discharge a bag, the operator opens the front lid of the discharge station and places the bag on the support table. The bag can then be cut open using a knife and the product emptied onto the vibrating sieve. Lumps in the product and scraps of paper from the bag are retained by the sieve. At the end of the discharge process, the operator closes the lid again. Due to its round shape and split design, the SE-RVS can be cleaned manually without any problems. To do this, the upper part of the bag discharge station is opened (pneumatic springs) and the sieve lifted out by loosening the bayonet locks. The housing and the sieve can then be cleaned separately and quickly reassembled again.
Integrated filter
If the aim is not simply to reduce dust formation but also to keep the product inside the system, bag discharge stations with an integrated filter are needed. In contrast to the solutions with an external filter described above, cleaning, maintenance and particularly the replacement of filter elements can be relatively time-consuming. Usually, the filter elements are only accessible from above the station. This means that the operator first has to climb on top of the bag discharge station and open the cover by loosening the screws before being able to remove the filter elements. The same also applies to installation. To make matters worse, space is frequently limited.
Hecht has accepted this challenge and come up with a solution that allows the filter elements to be integrated in a functional and user-friendly way: up to four elements can be replaced quickly and easily with very little effort and no tools. The operator simply opens the clean gas lid at the back of the bag discharge station and loosens the filter latching mechanism. The filter elements can now be removed and subsequently installed again extremely simply. Product carry-over, as mentioned above, and the associated product loss into an external filter can be avoided by using the PE integrated filter with a PTFE coating and very high separation efficiency. The filter elements are cleaned pneumatically. Owing to the slight vacuum produced by a fan, which can be activated automatically when the front lid is opened, dust formation is reduced to a minimum.
In addition to the standard functions for discharging bags, there is also a wide range of accessories and options to facilitate handling in general and work in a hygienic environment in particular. An empty bag disposal tube and compactor allow the discharged bags to be disposed of cleanly. Mobile designs create added flexibility. Thanks to a front hatch with gloves, sight glass, lateral inlet drawer and special gasket, bags can even be safely discharged at a low occupational exposure limit (OEL) not exceeding 100 µg/m³.
Closed containment solution
However, the more dangerous and sensitive the products or the range of applications, the higher the demands on the discharge system (containment). The interfaces where the prod-uct transfer takes place are especially critical points. Closed containment solutions are a good idea here. In addition to protecting the operator, they also protect the product against (cross-)contamination. This is the only way to ensure the high quality and purity required by the FDA or EMA, for example.
If an isolator is used for bag discharge, protective liner technology allows the bag to be passed in and out again without any contamination. Closed product transfer is thus possible in spite of all the interfaces. This is due to the fact that the isolator is equipped with two continuous liner ports. One protective liner system permits the bag to be passed in while the second serves to pass out the empty bags. The operator pulls a liner that is sealed at the end from the cartridge and pushes the bag into the continuous liner. The liner is sealed after the bag using a special tool and the bag is now enclosed by the protective liner. The operator then uses the gloves to pull the bag into the isolator and empty it without contamination. All operations can be coordinated by looking through the sight glass.
The empty bags and liners are passed out of the isolator in the same way by the second protective liner system. The continuous liner cartridges can also be replaced without contamination. The isolator is operated with a maximum negative pressure of 40 Pa. Leakages are detected by a pressure control. The isolator is designed as a WIP system (washing in place) for easy cleaning. The closed onward transport of the powder is often performed using a vac-uum conveyor system connected to the isolator’s discharge hopper.
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