Rice Farming

Efficient, Reliable Conveyors

Match application from rice processing plant to filling a truck
  

By Michel Podevyn

The benefits of four different types of conveyors – flexible screw, aero-mechanical, vacuum and pneumatic – are described for use in rice processing plants or to fill silos or trucks or other applications. The task of any conveyor manufacturer, such as Spiroflow Systems, is to provide the customer with the most optimum solution for their application. We have to assure that the conveyor we jointly select and supply is the most efficient and reliable and is available at the best possible price. Users must also be willing to share information with the supplier to reduce the risk of any future problems.

Following are the main parameters, benefits and disadvantages of the types of conveyor manufactured by Spiroflow Systems and other manufacturing companies. It’s important to select the one best suited to your application.

Flexible screw conveyors
Flexible Screw Conveyors (FSCs) are often the simplest and lowest costing solution for transferring a variety of materials from point A to point B at rates of up to 40 tons an hour over distances of up to 65 feet.
FSCs consist of a special heat-treated and tempered carbon or stainless steel spiral that rotates within an Ultra High Molecular Weight Polyethylene (UHMWPE) food grade tube. This type of conveyor is well suited for powdered, granular or flaked materials with a bulk density up to 150lb/cubic ft.

The term “flexible” means that this conveyor can be curved to some extent, depending on its diameter. This provides the user with the flexibility to route the conveyor around obstacles anywhere between the inlet and outlet. Normally, using only one continuous curve is recommended.

An FSC is designed to operate when full of material; running empty will lead to excessive noise and wear. Having a head of material in the feed hopper is desirable since it helps with the elevation of material upon start-up of the conveyor.

The main benefit of this type of conveyor is its inherent simplicity. This simplicity results in low initial cost, quick installation time and low maintenance.

Aero-mechanical conveyors
The second type of conveyor, the aero-mechanical conveyor (AMC), is ideal for total transfer of products at distances from 10 to 85 feet at rates of up to 120 tons per hour. AMCs are effectively “mechanical vacuum conveying.”

The aero-mechanical conveyor has proven to be a cost efficient method of conveying materials, dust-free and without the need for filtration. The AMC offers total batch transfer, operation at any angle (including vertical) without any loss of capacity and contaminant free delivery. For easy cleaning, they can also be supplied with access panels. Besides straight-line operation, AMCs are available in a multitude of “round the corner” configurations.

Unlike vacuum or pneumatic systems, the AMC has a very important advantage in that it does not need a cyclone, or filter, to separate the product from the air. This not only saves in capital cost but also reduces maintenance and eliminates environmental issues since the air carrying the material is recycled and not released at the outlet.

One disadvantage of an AMC is that maintenance can range from moderate to high. Rope tension needs to be adjusted regularly during the all-important start-up period and then checked periodically. Rope life depends upon on the length of the conveyor, the number of starts and stops, solids loading and whether routine inspection and tensioning is properly performed.

Despite this drawback, properly maintained rope and disk assemblies on arduous duties have been known to last 14 years and more.

The effort, worry and cost of this regular maintenance can be avoided by selecting an AMC with an integral automatic rope tension monitoring and adjustment system, such as the patented system now offered by Spiroflow Systems.

Vacuum conveyors
The third conveyor type, vacuum conveyors, is the obvious choice where products need to be conveyed over longer distances and torturous routes. Vacuum conveying is usually restricted to throughputs of around 10 tons/hour at distances up to 330 feet.

A vacuum conveyor uses air to convey materials through an enclosed pipeline. It provides a solution for users requiring a system that is easy to route, has few moving parts, is dust tight in operation and empties a product leaving minimum residue.

Vacuum systems are normally the only conveying choice for customers that want to suck material out of bags or other open top containers such as kegs and drums. These type systems are also ideal for applications with multiple inlets.

Reverse jet self-cleaning filters clean the conveying air and return the air to the atmosphere after use.

Pneumatic conveyors
Pneumatic conveyors are probably the most versatile of all conveying systems, with the main negative aspect being cost considerations. With these conveyors, there is virtually no limitation on capacity, product type, distance or routing. Lean phase systems (where the ratio of product to air is low) can move mountains of product. Dense phase or plug flow systems can move “slugs” of product at lower speeds with minimal degradation.

Positive pressure pneumatic conveying is generally used to convey materials from a single source to one or multiple destinations. Pneumatic conveying systems are normally the preserve of “big league” applications, such as the rapid discharging of road and rail tankers into silos and the transfer of product from silos to large-scale production processes. Capacities of up to 100 tons per hour are not unusual.

The two main disadvantages for pneumatic conveyors is the relatively high initial installation cost and the amount of filtration required.

In some applications, a mix of different conveyor types is appropriate. In selecting a conveyor, the key is to find a conveyor supplier in which you have confidence and are comfortable in providing you with the right solution for your conveying application. The conveyor supplier also should provide a performance guarantee.

Michel Podevyn is president/CEO of Spiroflow Systems, Inc. For more information, call (704) 291-9595, fax (704) 291-9594, email info@spiroflowsystems.com or visit www.spiroflowsystems.com.


Information required from the user

For the selection process, the user needs to provide the supplier with information such as this:
• Product(s) or material(s) to be conveyed
• Bulk density(ies)
• Condition of the product or material (e.g. moisture content, average particle size and temperature)
• From what is the product being conveyed?
• To what is the product being conveyed?
• Horizontal conveying distance
• Vertical height
• Conveyor route
• Conveying rate in pounds/hour or the batch size over a given time
• Will a pre-weighted batch be conveyed?
• How often/for how long will the conveyor operate each day?
• Will the material be conveyed in a homogenous manner?
• Accessories required (such as a bag tip station, bulk bag discharger or receiver hopper)
• Will conveyor operate in a dusty area?
• Is the conveyor manufacturer supplying the control panel, level sensors and other accessories?
• Will the conveyor be readily accessible for maintenance?
• Length of time conveyor is expected to run between services