Sugar conveying can present a challenge because the material is friable and produces dust that can damage machines and is potentially explosive. While various means of conveying are used, pneumatic conveying systems have become a viable option for many manufacturers.

Conveying Systems for Sugar

There are three main techniques used in the material handling of sugar: gravity flow, mechanical conveying and pneumatic conveying. While gravity flow is simple, it is not very flexible. Mechanical conveying includes bucket, drag and belt conveyors and can be used over short distances. However, the number of moving parts leads to quickly increasing capital, operating and maintenance costs as the conveying distance becomes longer. More complicated paths require more motors and dust collectors, and changes in legislation in some countries require protection devices on each conveyor to safeguard against dust explosions. The risk of product contamination is also relatively high. The complexity of long-distance mechanical conveying exposes the product to multiple sources of possible contamination. Mechanical conveying can be effective and economical provided its use is limited to certain key areas in the plant where it is most suitable.

Dilute phase pneumatic conveying systems are a simple sugar conveying solution with a low capital cost. They use low-pressure, high-velocity air streams that essentially blow the sugar through a pipeline. A positive displacement blower or other fan is used to produce a more or less constant airflow through the pipes, and a heat exchanger is added on its discharge side to eliminate the heating effects of air compression. Rotary valves are used to feed sugar into the system at a controlled rate, and also serve to contain flame propagation in case of a fire or sugar dust explosion. As an additional safety measure, nitrogen can be used as the conveying gas. When the sugar reaches its destination, a separator removes the sugar from the airstream and the material is discharged into a storage container.

When are Pneumatic Systems Suitable for Sugar Conveying?

Because the sugar tends to degrade as it comes into contact with piping components such as elbows, dilute-phase conveying is best used in cases where it does not matter if the particle size is reduced, for example for powdered sugar or where the sugar will be supplied to a mill. The versatility of dilute phase conveying is an advantage, as research shows that some grades of sugar cannot be conveyed with dense-phase systems. In particular, it is not permeable enough for plug flow dense phase conveying. Granulated sugar often needs to be conveyed in the same system as wheat flour due to the range of uses of the product.

Benefits of Dilute Phase Pneumatic Conveying

Dilute-phase pneumatic conveying equipment is simple and easy to operate, and its low capital cost makes it an attractive solution where material degradation is not a concern. The number of moving parts is limited and most equipment is concentrated around the source and destination areas.

The fact that pipelines are enclosed, and that filters are integrated into the points of origin and destination, make for a safe product and reduced dust emissions and hence a cleaner facility. The conveyed sugar is separated from most sources of contamination and does not spread potentially explosive dust. Explosion protection and filtering devices are readily integrated into the system.

There is less need for sources and destinations to be in close proximity, so that flexibility in plant layouts and more widely distributed processes become possible. This flexibility also extends to the ease with which the system can be modified.

The types of components used in pneumatic conveying makes it suited to central control systems that can be monitored and operated remotely. Such systems can make maintenance easier, as components that fail to function properly may be detected automatically. The increased feedback allows for the early detection of problems.

Lifetime Costs

While the operating costs for the system may be higher than for mechanical conveying systems because power consumption is relatively high, the disparity is small for large, long-distance material flows and more complex layouts. Maintenance costs can also be reduced compared to mechanical conveying because fewer moving parts are used.

The benefits of pneumatic conveying can save money in the long term by avoiding production losses from contamination, maintenance problems and some expenditures on safety devices. When the compact and flexible nature of this method is also considered, the reasons for its increasing acceptance for sugar conveying are clear.