Handling Powder And Granulated Ingredients Gently

A typical vacuum dense phase conveying system.

Vacuum dense-phase pneumatic conveying offers a number of significant advantages in powder handling applications. It is specifically designed to handle fragile powders and granulated ingredients gently with its very low conveying speed.

The low velocity ensures a minimal product break down, reduces fat migration and prevents loss of shininess in ingredients. It also enables producers to maintain homogeneity while conveying mixed products. Its design allows smooth air or product separation, which prevents de-mixing and jolts.

The high negative pressure (up to -850 mbar) enables high capacity and a high product concentration at a very low consumption of compressed air—over 100 kg of product per kg of air. It is also designed to be ergonomic as well meet requirements to prevent explosions for maximum safety. Further, it is highly hygienic since no moving parts come into contact with the product.

Pneumatic conveying systems work by generating gas flow (generally air) in a pipeline combined with a pressure difference between the pickup point and the receiving point. In vacuum dense-phase pneumatic conveying, this is generated by a vacuum pump.

The powders and granules are conveyed with the air flow from the point with a higher pressure (atmospheric pressure) to the point with lower pressure (under vacuum conditions). Conveying lines may be either horizontal or vertical and often begin at a pickup hopper and end in a reception hopper designed to withstand a high level of vacuum.

A typical hopper used in pneumatic conveying.

There are currently four different types of vacuum densephase pneumatic conveying available to suit a wide range of product and production needs: continuous, batch, densephase, and semi-dense phase.

The most common system is continuous conveying, in which the starting hopper empties while the reception hopper simultaneously and continuously discharges the powder/granule mix to downstream equipment through a rotary valve.

In batch conveying, the starting hopper empties first, and the reception hopper discharges the powder/granule mix through a butterfly valve, only once a set level of powder is reached.

Dense-phase conveying handles both fragile and very fragile products. It has an instant throughput of up to 20 tons per hour, a pipe length up to 50 m and an elevation up to 18 m. The air speed in dense-phase conveying goes from one to five metres per second at the starting point and from five to 10 metres per second at the end point. This enables a product concentration of up to 100 kg of product per kg of air.

Semi-dense conveying handles fragile products, also with a throughput up to 20 tons per hour, but allowing a pipe length up to 75 m and an elevation of up to 25 m. The air speed is from five to 10 metres per second at the starting point and from 10 to 15 metres per second at the ending point. This system enables a product concentration of up to 60 kg of product per kg of air.

To select the proper pneumatic conveying system for each production scenario, it is important to look at powder characteristics, the conveying distance, the product flow, desired performance and end result as well as building constraints. To ensure the optimal solution, laboratory tests should determine the bulk density, particle size, friction coefficient, flowability, floodability, fragility, heat sensitivity and fat content of the powder and granulated ingredients.

Powders do not behave like other materials. This makes characterisations and trials necessary for every new product application. Segregation, density variation and wettability are product values that have to be clearly understood in order to assure the success of recipes with powders and granulated ingredients.

If possible, producers should also test their chosen powder conveying solution in a test centre or pilot plant to control and validate the breakage rate, de-mixing and other characteristics. Test centres specialised in powder handling solutions let producers simulate any kind of powder handling process, to test the system on sensitive products and validate the line performance. They also enable producers to save time and money since they do not need to stop production in order to conduct trials at their own sites.

Some ingredients handled with vacuum dense-phase pneumatic conveying include:

• Milk powders & derivatives: infant formula, skim milk powder, whole milk powder, milk protein concentrate, sweet whey powder, whey protein concentrate, demineralised whey powder
• Sugar and sweeteners: sugar, lactose, maltodextrin
• Coffee powder
• Coffee mixes: coffee, milk and sugar