Vacuum conveyor
Vacuum conveyors convey bulk goods with negative pressure .
Conveying solids with a vacuum
Throughout the process , and process a variety of bulk materials are transported. It can be powdery raw and auxiliary materials, but also the finished end products. With manual handling, all types of containers such as barrels , sacks or big bags are brought into production and emptied openly. The workers are physically stressed by lifting, the dust, the release of harmful substances, the risk of explosion from the solid matter and working on open process containers. Suction conveying under vacuum enables all types of solids to be sucked in, transported and emptied within a closed system without endangering employees.
Functional sequence
- The vacuum pump generates a negative pressure in the separator tank of the vacuum conveyor, so that air is sucked in through the suction opening from a product feed point and transported goods are carried away.
- The air sucked in passes through the filter system installed in the separator container . The sucked-in material is retained by the filter in the separator and collects there. In the case of fine dust, a centrifugal separator in combination with the tangential intake enables higher delivery rates due to the lower filter surface load.
- After the separator tank has been filled, the vacuum pump switches off. The pressure in the separator tank automatically adjusts to the ambient pressure within a few tenths of a second. Now the emptying module located at the bottom of the separator container opens and the sucked-in material falls from the vacuum conveyor directly into the unit to be loaded.
- For emptying, the filter module is cleaned by a counter-blow air pulse. Any filter cake that may have adhered is removed. Piston vibrators and fluidizing units can be used to improve the discharge of material with strongly bridging or sticky material .
- When the emptying module is completely emptied, it closes and the conveying process begins again.
cleaning
The cleaning of vacuum conveyors can be done in different ways, the requirements can vary greatly depending on the product and industry. In addition to the WIP (Washing In Place) method, which requires manual post-cleaning, there is also the fully automatic cleaning, the so-called CIP (Cleaning In Place) method. The CIP process is used particularly for aggressive or dangerous substances, or where cross-contamination is to be avoided. The subsequent fully automatic drying DIP (Drying In Place) makes the vacuum conveyor ready for immediate use again.
Components
Bulk material separation & collection container
With the stainless steel segment construction, the conveyor system can be easily dismantled and cleaned. In this way, the high hygienic requirements of the food and pharmaceutical industries can also be met.
In addition, individual stainless steel modules can be individually optimized according to the specific task. For example, the suction segments in radial or tangential design can be decisive for successful conveyance. The selected material provides the necessary strength (up to 91% vacuum is possible), with low wall thickness and low weight. As a rule, the bulk material collection container is located directly above the part of the system to be filled.
Vacuum pumps
If the conveyor is in frequent use or if a large product flow is desired (even with materials that are difficult to convey), the choice of an external vacuum pump is inevitable. The vacuum pump creates a fine vacuum of approx. 0.1 - 0.3 mbar, which enables delivery even over very long distances. Common industrial vacuum pumps can suck in 1600 m³ / h of air (for comparison: an Olympic swimming pool holds approx. 2500 m³ of water). When selecting the vacuum pumps, it is important to consider the respective requirements. There are special ATEX versions that can be operated in an explosive atmosphere.
If the requirements are not so high, Venturi nozzles can also be used as "pumps".
The vacuum generated with compressed air is maintenance-free; however, the compressed air generator must be serviced. If compressed air is available, they are compact, lightweight and relatively easy to control and regulate. The implementation via the multi-stage Venturi principle ensures economic use with very low flow rates, as no vacuum pump has to be purchased.
This vacuum generator has no rotating parts, does not require lubrication or maintenance, and does not generate any heat during operation. In this way, a vacuum of up to 91% can be generated.
The physical application limit of compressed air-operated vacuum generation is specified by the functional principle. From the atmospheric pressure (approx. 1013 mbar), approx. 910 mbar is available as a maximum negative pressure. A closed water column can thus be sucked up to a height of 9 m. When conveying a product-air mixture (air conveyance), the maximum achievable conveying height is further increased. The sound absorber and exhaust air adapter result in relatively low-noise operation.
With both variants, a wide variety of bulk materials can be sucked, as these pumps can produce high amounts of suction air (air conveyance) and a high vacuum (plug conveyance). They are pneumatically controlled so that suction conveyors can be used in potentially explosive areas without any problems .
The vacuum pumps build the vacuum up and down suddenly. This way of working harmonizes with the discontinuous conveyance, since the separator tank is filled and emptied cyclically. The delivery rate can be regulated in an application-specific and energy-saving manner via the operating pressure and compressed air volume flow.
Realizable funding rates are extremely product-dependent. Bulk density, adherent or bridging character, particle size, surface geometry, moisture content, type of product application point, false air supply and of course the conveying distance and conveying height are decisive parameters. These certainly lead to differences in the conveying capacity of up to 1,000 kg / h, with an identical vacuum conveying system. For vacuum conveying, the majority of conveying tasks are in the range of 10 to 6,000 kg / h, conveying distances up to 80 m and conveying heights up to 30 m, often well below. Its versatility enables fully automatic suction from feed hoppers on the one hand and manual bag emptying on the other hand.
If the vacuum generated by compressed air is no longer sufficient, or if the conveyor is used frequently, an external vacuum pump must be selected.
Filter systems
The sucked in product-air mixture must be separated again in every vacuum conveying system. The speed of the conveyed material is reduced considerably because of the expansion of the cross-section in the separation tank. A large proportion is consequently deposited in the lower segment of the container due to gravity.
In the tangential suction segment, the internal cyclone supports the separation process. A certain amount of dust reaches the filter unit located below the vacuum pump. The service life of a filter can be increased significantly by using large filter surfaces. For example, with ring filter technology, the entire circumference of the vacuum conveyor is used, which enables larger filter surfaces. The discontinuous conveyance enables efficient filter cleaning through the counter-blowing air pulse during the emptying time. How quickly a filter clogs depends on the product to be conveyed, the filter surface and the filter material. Surface filters are used for fine dust, for other applications there are filters made of plastic or stainless steel mesh, which can be wet cleaned if the product is changed frequently, for example with a steam jet device or in an ultrasonic bath ; a CIP and DIP process is also conceivable for stainless steel mesh filters . With an optimal design, depending on the application, filter service lives of 5 to 10 years can be achieved. If normal filter cleaning is not sufficient for particularly adhering materials to be conveyed, the filter unit and separation container can be set in vibration.