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We have seen how important it is to understand the intrinsic aspects of pneumatic conveying system design like product bulk density. However, it is vital to consider the plant and how it could impact on the pneumatic conveying system design in terms of installation, operation and maintenance. Read on for an overview on several major plant considerations that apply when designing a pneumatic conveying system.
Plant considerations in pneumatic system design
Once in the pneumatic conveying system, material - whether flowing freely or not - generally moves along a production line without problems. There can, however, be issues sometimes loading it onto the line from the pickup point.
It is essential the pneumatic conveying conveyor manufacturer knows what container type is being used to hold the material, as this dictates the pickup method used. Pickup methods used to move material into a pneumatic conveying system include:
The equipment used in the point of material pickup point is often the most highly customised section of a pneumatic conveying system. There are often specific challenges that need to be overcome to ensure that steady feeding of material occurs, as required by the downstream manufacturing process.
An example of where customisation pickup equipment could be required is a plant that uses twin-screw large compounding extruders to produce heater cable. The manufacturing process involves the transfer of powders and polymers from their material containers into the compounding extruder. These exotic powders are very dense and sticky, and thus make the materials transfer process rather challenging.
The difficulty is not in conveying the sticky powders but in ensuring it feeds automatically into the pneumatic conveying system. Utilising components of a system designed for transferring powdered sour cream would be a solution. Similarities in material characteristics would make for a good outcome.
The heater cable manufacturer could unload 25 kg bags of material into bespoke bag dump stations. These would be customised vibrating bins combined with bag dump stations and bulk bag unloaders to create units that allow material flow from the pickup point to the pneumatic conveying system.
A pneumatic conveyor system manufacturer understands the plant’s processes involved with the system, and how upstream equipment can affect downstream equipment. The type of processing equipment being fed - for example volumetric feeders, mixers and extruders, loss in weight feeders and packaging - affects conveyor design.
Loss in weight feeders requires quick refill, so the pneumatic conveyor manufacturer will design the system to take into account the fact that the system will be loading into that type of feeder. Conveyor manufacturers need to know whether there are sanitary constraints that will require the use of 316L stainless steel, or whether 304 stainless steel or carbon steel, will be sufficient.
Some equipment - such as food-grade screw conveyors requiring costly lubricants and considerable maintenance - may need to be replaced by a more hygienic, fully-enclosed pneumatic system, which would protect materials from contaminants. The iron rings securing filters might need to be replaced by stainless steel rings to meet stricter manufacturing standards.
It is essential that each piece of equipment in a pneumatic conveying system is complementary to all other parts of the system. If any piece of equipment is the wrong size, the system will not perform correctly. Vacuum receivers need to handle the airflow from the vacuum source, and balancing the air-to-cloth ratio of filters must take place so there is no filter shredding or binding.
Where it is necessary to convey and dispense blended powder into packaging equipment at high speed, the self-lathering properties of the powder are integral considerations when conveying the powder to the auger fillers. When particles in the powder are too small, the product may lather too quickly. When particles are too large, then lathering might take too long. Changing the blend, density and texture would give inconsistent volumes or fill rates. These are both unacceptable in terms of quality control. Powder can easily change density within auger filler heads, which leads to improper fills. Ensuring the heads are at the proper density and kept full is essential.
For easy loading of material transported by vacuum to customised filter receivers mounted about auger fillers, a system utilising low-profile drum dump stations could be custom designed. Powder levels would be checked at each of the auger filler hoppers, and predetermined volumes of powder would be automatically dispensed to fill the hoppers when the levels in the auger fillers dropped to a certain point.
A system designed for easy maintenance could have a receiver custom designed to ensure easy cleaning and allow for fast, toolless disassembly and reassembly. Manufactured with no crevices and as few welds as possible, the corner welds of interior bends in the drum dump stations are a minimum of 3 mm radius to reduce material accumulation. A valve would be used to purge the pneumatic conveying system at the end of each conveying cycle, preventing blowback powder and making restarts easier.
Equipment customisation does not necessarily focus on materials; facility constraints can also be the reason for modification of equipment. An advantage of pneumatic conveying systems is their small footprint in comparison to other types of material handling equipment - but no matter how small the conveying system, there is always a minimum headroom over processing or packaging equipment.
One way of resolving headroom constraints is by use of positive pressure systems. Other options are filterless material receivers or using scaling valves, which channel material into hoppers directly in low clearance areas.
In areas with severe restrictions in ceiling height, vacuum receivers could perhaps be located externally. Modifications can be made to customise the conveying equipment so it fits in the space. Modifications could also be made to filter lids with venturi systems powered with compressed air, and vacuum generators could be modified to fit small spaces.
Where there is adequate height, standard vacuum pumps with electric motors can be used. In some powder processing plants there may be height restrictions due to them being located in older buildings where there may be low ceilings in many areas might require renovation.
When designing a system, conveyor manufacturers need to know - in addition to material flow rates, material characteristics and downstream equipment processes- where the plant is located and what the surrounding environment is like.
Altitude has an effect on pneumatic conveying in the same way that it affects vacuum source sizing. For example, a plant located at sea level and using a 3.75 kW vacuum pump would, due to lower air density, need to use a 5.5 kW vacuum pump for exactly the same application at 1,500 metres above sea level.
The factors outlined above are crucial when a pneumatic conveyor manufacturer evaluates applications and customises equipment, thereby ensuring their customers’ focus is on manufacturing their products rather than worrying about how they can best transfer material.
Pneuvay is the market leader in the provision of pneumatic conveying system design. We provide services to many large manufacturers, and are known for our best fit and turnkey solutions for processing plants wanting to:
If you have any questions in relation to pneumatic conveying system design, feel free to send on congratulations by calling us on 1300721458 or sending us a message via our Pneuvay website contact page or Pneuvay Facebook page.
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