Cracking the conveyor code: solutions for powdered food

Most industries have powdered versions of products or ingredients that will require transport throughout a production facility for further processing. Within the food processing industry, this encompasses a range of products including powdered sugar, flour, coffee, cocoa, food additives, protein concentrates and isolates.

However, there may be challenges in conveying these ingredients if the powder is sticky, hygroscopic or tends to cake or pack. Powdered food products and ingredients can also present health and safety hazards if they become airborne, are combustible or have explosive properties.

The quandary for processors is selecting the right conveyor from the options available, which can involve considering these factors as well as the material’s characteristics, flow rate and other requirements.

“While there are many conveyor options in the market, some are more effective at addressing issues like dust escape and explosion risk as well as caking, packing and cleaning out residue between batches. Processors that minimise or eliminate these issues in the conveyor design will improve their safety, productivity and product quality,” said Don Mackrill, Regional Sales Manager at Automated Handling Solutions (AHS).

AHS can provide a range of material handling equipment and industrial automation solutions, including Spiroflow material handling equipment and control systems integration, and Cablevey Conveyors tubular drag conveying systems for food and beverage and industrial applications.

According to Mackrill, selecting the right mechanical conveyor can be a daunting task.

The most critical aspect to consider is the type of product being conveyed. Issues such as flowability, abrasiveness and cohesiveness should always be considered, whereas product degradation or the need to maintain a blend may be key aspects to consider in some applications.

The distances and rate of speed required to move the material is also a consideration. Does the conveyor need to pick up from or feed multiple locations or follow a complex route around other equipment or structures? Are there any special safety considerations based on area classification, traffic or other processes?

For food-grade applications, hygiene specifications and the ability to clean-in-place are key considerations.

According to Mackrill, there are several categories of enclosed conveyors that meet requirements, including aero mechanical, flexible screw and tubular cable drag designs. However, factors such as the type of and size of the powder and the specific challenges those materials create when conveyed often dictate the choice.

Preventing caking and packing

With powders, care must be taken to avoid the powder caking and clogging the conveyor, which can result in downtime and increased safety hazards during maintenance and cleaning.

An alternative is an aero mechanical conveyor, which uses evenly spaced discs to generate a high velocity air stream to fluidise and convey powdered products. Aero mechanical conveyors like the Aeroflow are totally sealed, tubular systems that are designed to ensure the dust-free transfer of powders without need of additional dust collection systems.

Unlike dilute phase pneumatic conveying systems, aero mechanical systems transport materials at lower speeds, so suspended particles have fewer shear forces. This minimises breakage and caking and packing inside the tube. Because aero mechanical conveyors have near-to-total product transfer capability, any residual product in the system between batches is also minimised. However, if caking or build-up occurs, aero mechanical conveyors can be easily disassembled for regular, quick cleaning.

Containing fugitive dust

For food processors, another priority is containing powdered products within the system, so they do not become airborne. When powder and bulk solids escape the conveyor, the “fugitive dust” can pose health, safety, sanitary and explosive risk, depending on the material and environment. According to OSHA’s (Occupational Safety and Health Administration) definition of combustible dust explosions, any combustible material can burn rapidly when in a finely divided form. If such a dust is suspended in the air in the right concentration, under certain conditions, it can become explosive.

“When conveying powders, understanding the requirements is critical because an explosion can injure people as well as destroy essential equipment, causing lengthy downtime. So, any conveyor system that handles such material must be designed and engineered to comply with all safety codes and have dust mitigation procedures in place,” said Gary Schliebs, a Process Engineer and Director of Plus One Percent…Engineered Solutions, a consulting firm that works in the food industry and globally markets food industry conveyor equipment.

When moving powdered material in a plant, an enclosed system can address concerns over dust containment to deter explosions and prevent environmental contamination.

“One of the best ways to prevent fugitive dust is to use an enclosed conveyor. This prevents spillage, the release of airborne dust, the need for additional clean-up of the surrounding area, as well as the potential for powder contamination from the external environment,” Mackrill said.

Flexible screw conveyors use rotating spiral or open helix screws within tubes to push product along and are mechanically dust tight and totally sealed during operation. Since air is not used as a conveying medium, there is no risk of dust contamination.

Tubular cable drag conveyors are also enclosed and use cables with discs attached at set intervals within a tube to gently pull powder from inlets to discharges.

Because sugar, grains, flour and other powdered food products can combust, it is critical that the conveyor system minimises or eliminates potential sources of ignition, such as sparks or fire. Improper maintenance of conventional open mechanical conveying systems can become an ignition source since they use numerous moving parts. Bearings and out-of-alignment belt conveyors, for example, can be problem areas if they cause sparks or generate heat from friction.

Although enclosed, pneumatic systems can still create a “dust cloud” inside the tube, as well as on exit. Because tubular cable conveyors do not suspend material in high-velocity airstreams, less “energy” is imparted into the conveyance and the slower velocity reduces any friction and heat generated to well below an ignition point, limiting it about -12 to -6°C above ambient temperature.

Another way to mitigate dust accumulation is through sufficient cleaning to remove any potential powdered debris. For this, tubular cable conveyor systems have options for dry and wet cleaning to remove accumulations of dust and food residue. The Iowa-based company Oskaloosa has designed, engineered and serviced enclosed cable and disc tube conveyors for almost 50 years. It can provide cleaning accessories such as brush boxes, urethane wipers, air knives, in-line sponges and in-line bristle brushes, as well as fully automated CIP wet cleaning systems.

Specific powdered food challenges

Although enclosed conveyors can be effectively used to convey powders in the food industry, the choice may be dictated by the specific product and size of powder.

Mackrill offers the following examples:

Sugar

Since powdered sugar is highly flammable and explosive, conveying system design should minimise this risk. In fact, due to recent industrial accidents, government regulatory bodies like OSHA and NFPA (National Fire Protection Association) have issued heightened regulations governing the handling of sugar. Furthermore, powdered sugar tends to pack and cake while conveyed. Like powdered sugar, granulated sugar is highly combustible and potentially explosive, and will ignite at high temperatures.

Enclosed aero mechanical conveyors are ideal for conveying large volumes of both powdered and granulated sugar to the mixer. Any dust created during conveying is contained within the conveyor, reducing the risk of explosions caused by static build-up and sugar dust clouds. In addition to being airtight, aero mechanical conveyors run quietly with minimal energy.

Flour

Flexible screw conveyors are an ideal choice for flour. The flexible screw conveyor’s only moving part, the spiral, continuously mixes as it conveys. The conveyor can be configured with a drop out trap, quick release flanges and a reverse bung that facilitates hygienic flour conveying when switching between different batches of flour.

When conveying flour where degradation is a concern, an aero mechanical conveyor is also a good choice. An aero mechanical conveyor creates an airstream which moves flour up the tubes along with high-speed discs and a stainless-steel cable. The material is transported gently through the airstream between discs, ensuring minimal handling and no dust generation due to the non-friable nature of flour. Any dust generated will remain suspended in the airflow together with the material and will not accumulate or come into contact with any potential ignition sources.

Ground coffee and mixes

When conveying ground coffee or mixes, dust control is of utmost importance due to combustible properties and the need for operator safety. Since ground coffee is hygroscopic, it easily absorbs moisture and is prone to clumping. Maintaining the consistency and size of the ground coffee is also essential for brewing a good final product. In addition, conveying systems processing different types of flavoured coffees or mixes often must be quickly and thoroughly cleaned between product changeovers to prevent flavour cross-contamination.

With these considerations in mind, tubular cable drag conveyors are quickly becoming the conveyor of choice for coffee processors due to safe, gentle movement that minimises dust hazard and product degradation while still offering high throughput. These conveyors provide very versatile layouts and can be used to pick up coffee grounds from different sources for transport over long, complex routes to various destinations.

Given the variety of conveyor choices and powdered food ingredients that must be safely moved during processing, the potential risks warrant a careful examination of the available equipment options in consultation with experts.

In the end, implementing a conveyor that minimises the risk of dust escape and explosion along with problems like caking and packing can be the recipe for better health and safety as well as greater productivity and profitability.

Top image caption: Spiroflow food powder conveying system conveying turmeric powder.