Don’t kick up
any dust
Clean handling and cleaning technology for bulk goods handling

Bulk goods are found everywhere in the chemical industry. Some are used as basic materials during further processing, and others are saleable end products. One thing is clear: any time these goods are handled, the amount of dust that is released should be minimized to protect workers and the environment. PROCESS worldwide takes a look at various solutions.

A number of different approaches are used to comply with the requirements of the German Clean Air Act during handling of bulk goods. Closed containers help during shipment and delivery by truck (tank trucks, containers, tarpaulins). Equipment used for continuous material transport must be enclosed or nearly enclosed (conveyor belts, bucket conveyors, worm, screw or pneumatic conveyors). When pneumatic conveying is used, the dust-laden air must be kept within the circuit or fed into dust removal equipment. This must also be done when solids are filled into closed transport containers. Displaced air must be kept under control and fed into dust removal equipment.
It is important to bear in mind that around 70% of the dust generated is explosive in the right concentration, so operators often have to adhere to the new Atex 100a explosion protection directive. The new Anke D1, Anke D3 and MiniHET series from HET-Anke Filtertechnik, which sees itself as the European market leader in self-cleaning submicron particulate filter systems, meet all of the requirements with respect to conductivity and shock resistance in case an explosion occurs.
A special feature of these product families is that no additional explosion protection equipment such as rupture disks or explosion suppression systems are needed in the area where the filter system is used. The supplier emphasizes that this solution ensures that dust does not contaminate the environment if an explosion should occur. This is achieved by taking advantage of the so-called partial filling principle, where the ratio between the volume of raw gas and the volume of clean gas plays a crucial role.

Silo-top filter with conical
filter elements
When silos and containers are filled with bulk goods, the flow of displaced air to the outside must be as unrestricted as possible. Filters mounted on the silos can be used to capture dust particles. Mahle’s folded star-shaped filter elements (cartridge filters) use a new type of element with a particularly high performance density. Conical filter cartridges have the following advantages compared to cylindrical filter elements:
More effective dedusting due to the conical design of the internal chamber. The significantly lower volume of clean gas makes it possible to apply the cleaning pulse more effectively. No additional displacement element is needed.
Reduction of up-current velocity in the element cavity leads to improved dust sedimentation. This facilitates the removal of solids.
Lower air flow resistance. Because the element diameters are designed to match the air flow characteristics, pressure losses are reduced in the raw and clean gas chambers.
Keller Lufttechnik refers to various methods that can be used to achieve separation with almost no residue. Dry separation using a Sinbran filter can be used for very fine and ultra fine dust for example. The long service life of a rigid body filter design and low pressure loss coupled with high separation are the salient features of this filter medium, which is actually a rigid body filter and a membrane filter. Wet separation is a suitable option particularly if explosive, flammable, moist or sticky dust is being handled. Keller’s high-performance wet separators use venturi nozzles. Water is sprayed into the air stream to remove flammable or explosive dust from the air stream.
The PTS – Powder Transfer System from Hecht is a new type of vacuum conveyer system. Its particular strength is dust-free loading of containers at defined atmospheric pressure in various pressure ranges. The PTS product separator differs from conventional systems in some ways:
small membrane filter containing a smooth disk with supporting frame;
it can be quickly disassembled for inspection and maintenance;
minimal product residue in the system due to the cylindrical design of the product separator (no funnel shaped surfaces).
This technology is also suitable for difficult jobs, for example loading reactors in explosive environments. If bulk goods need to be loaded as loose material into tank trucks, flatbed trucks or ships, Agrichema has a solution, namely the modular Telescoper with integrated drive station and triple external cable actuator.
Cleaning: removing
material that will interfere
If the job is to clean bulk good systems, what needs to be done depends on the product and the process. If more than one product is produced, then you must avoid cross-contamination, and the requirements are particularly stringent. Things are more straightforward if all you have to do is keep the equipment clean.
Case example 1:
On bucket wheel feeders, minimizing air leakage, maintaining gentle non-chopping movement of the granulate in the housing and ease of cleaning after frequent product changes are key considerations. For a special application where the requirements were very stringent, Zeppelin added a high-pressure feeder with quick clean mechanism to its product range, which has the following features:
three guide rails to provide stable guidance for the bucket,
non-contact extension and retraction of the bucket wheel.
This new variant is available in versions that can handle up to 150 tons of granulate per hour. The quick-clean feeder is very well suited for high purity media and high-grade color compounds.
Case example 2:
The Toftejorg SaniMidget Retractor (SMR) is a mobile system that can be automatically retracted from the product zone after cleaning has been completed. After that, there is no contact between the product and the system, because the closing plate of the SMR lies flush with the container wall. This is particularly important when you are handling toxic, aggressive or explosive media. The SMR can be used in storage tanks, reactors, mixing containers, spray dryers, etc. with volumes between 0.1 and 10 m3.
Case example 3
Scrapers are used if product remnants from the previous batch have to be completely removed from conveyer systems prior to a product or batch change, for example in the plastics processing industry. Motan produces the Turbo-Pig for dry cleaning of pneumatic conveyer pipes in the DN 50 to DN 250 range.
Case example 4
A company in the plastics production industry grinds PMMA sheets (acrylic glass). A ventilator is used to transport the granulate to the bag filling building which is 80 m away. 6 kg of dust is generated for
every 1000 kg of material that is transported. The solution is as follows: A regenerative compressor sucks in the dusty granulate. An Esta counter-flow separator based on the counter airflow principle separates the granulate from the accompanying dust. After this step, the residual dust content is only 55 g per ton of material transported (in other words 55 ppm). A filter cyclone removes the dust from the air, which falls without pressure via a bucket wheel feeder into a collection bag.
Exhibitors at Powtech, Nuremberg
Agrichema: Hall 9, Booth 424
Esta: Hall 7, Booth 519
Hecht: Hall 9, Booth 421
HET Anke: Hall 9, Booth 302
Keller: Hall 7, Booth 121
Mahle: Hall 9, Booth 623
Motan: Hall 7, Booth 422
Zeppelin: Hall 7, Booth 527