Are you considering pneumatic or aero mechanical conveyors for your application? When working with dry bulk ingredients, moving them from one location to a point of use is an important part of your process that should be carefully considered. The material characteristics of your ingredients along with your application parameters and budget should be thoroughly evaluated to maximize benefits in regard to conveying rate, safety, cleanliness, efficiency and return on investment.
When a dilute phase type of pneumatic transfer system is considered, one should always evaluate another option with considerable benefit – aero mechanical conveying.
An Aero mechanical conveyor transfers product in a dilute phase method. They utilize a vacuum created by the slipstream of discs being pulled through a continuous sealed tube using a sprocket driven by an AC motor gearbox. Pneumatic conveying utilizes a sealed tube arrangement as well, however, the motive air is created by using a blower system.
To determine the best conveying option consider the following factors:
- An aero mechanical conveyor is a balanced system. Ambient air is drawn into the conveyor along with the ingredient. The ingredient is centrifugally discharged at the outlet of the conveyor. The displaced makeup air (or gas) is drawn back into the conveyor creating a balanced system. There is no pressurization at the discharge point of the conveyor, therefore there are no special venting or filtering requirements.
- With a pneumatic system, consideration must be given to the motive air. For a vacuum system, a receiver is utilized that requires venting off of the motive air. Compressed air is also required for backwashing the filters and valves required for proper operation. For pressure systems, venting with filtration is required for the receiving vessel, with exhaust entering into the surrounding area or vented outside the building. One must also determine the potential requirement for dust explosion mitigation for any vessel over 8 cu ft in capacity.
- Vacuum systems generally draw motive air from the surrounding area. Determine if special air conditioning or additional climate control will be required in these areas. This could greatly increase the cost of heating or air conditioning and should be factored into your budget.
Multiple Inlets & Multiple Outlets
- Multiple inlets have no impact on the operation of aero mechanical conveyors. The conveyor should be sized for the maximum required transfer rate so that it is not overloaded. When multiple outlets are utilized, an aero mechanical conveyor should be operated at half speed to ensure proper discharge at each outlet. A tube valve at each outlet provides a smooth path for the ingredient to pass through to subsequent outlets.
- For a vacuum pneumatic system, each outlet requires a separate receiver, its own pressurized air supply for filter cleaning as well as its own feed control valve and diverter valves. Additional piping is also required to feed to each individual usage point. For pressure systems, each receiving point requires venting of the motive air as well as filters, valves, diverters and additional piping to direct product to each use point.
- Spiroflow aero mechanical conveyors are available in three sizes. The 3-inch conveyor delivers up to 9 cu ft/min, the 4” conveyor delivers up to 18 cu ft/min and the 5-inch conveyor delivers up to 36 cu ft/min. The largest drive motor requirement is 7.5 to 10 Hp through a gearbox. With these low Hp requirements, the sound level is generally below 80 – 85 dBA at 5 ft.
- Pneumatic systems require a 20 – 40 Hp blower motor for comparable rates. Both power consumption and sound levels are much greater than those of aero mechanical conveying systems. Due to the sound pressure levels, blowers must have mufflers or be remotely installed. This, in turn, can result in the need for additional transfer line piping or special enclosures for sound suppression. These differences and their associated costs should also be factored into your evaluation.
- Aero mechanical conveyors are very gentle with the ingredient by handling a small pocket of product in a given space, generally at a ratio of 80% gas to 20% product. The disc slipstream carries product around any corners in the system. Since an aero mechanical conveyor handles pockets of ingredient, mixtures are maintained.
- Although pneumatic conveying also utilizes a high gas to product ratio, the entire length of the circuit is under the same pressure or vacuum. The product, through centrifugal force, is hammered in bends and elbows which can cause product degradation as well as wear issues on the conveying tubes. With longer distances, it is possible to experience product separation on mixtures that are a blend of products with differing properties and bulk densities.
- Generally, aero mechanical conveyors will transfer all material introduced into them so cleaning is minimal. The use of air purging for the housings as well as close tolerance sweeps can help to ensure complete product transfer. Toolless hinged access points can be included for easy and fast access for dry cleaning of the system. If dealing with flavor or color changes, a sacrificial material such as salt can scour the entire conveyor quickly and then be disposed of. Wash gates and drains are included when the application requires the system to be washed. The aero mechanical conveyor creates an agitation effect much like a dishwasher that completely washes the inside of the entire conveyor. Once drained, the conveyor can be operated empty to self-dry.
- A pneumatic system can also be cleaned fairly easily by conveying salt as a scouring agent. For wet cleaning a “pig” is pushed through the piping system using compressed air.
There are many variables to consider when evaluating a conveying system to move your ingredients. A full evaluation should consider all alternative technologies with consideration of the ongoing cost of operating the system.
For a complete evaluation of your conveying application contact Spiroflow.
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