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Spanish Food Processing Industry: Tubular Drag Cable Conveyor Technology Effectively Prevents Dust Explosions

Conveying systems and how they may influence dust explosions
In food manufacturing, conveying systems are crucial for handling raw ingredients, blended mixtures, and finished products. These systems transport food between production, blending, storage, filling, and packaging processes. Various methods are used in food production facilities to move bulk solid ingredients through their production processes, including belt conveyors, screw conveyors, bucket elevators, pneumatic conveyors, tubular drag chain conveyors, and tubular drag cable conveyors.

Each of these systems has different levels of dust production, hygienic design, and clean-in-place functionality to control dust accumulation. This is important as it helps keep dust concentration below minimum explosible concentration levels. The following is an evaluation of the main types of conveyor systems used to transport dry ingredients in food processing and their impact on dust explosions.

Flat-belt conveyors. This specific type of conveyor is designed to handle delicate products with care, but it is important to note that it is vulnerable to contamination from its surroundings if left uncovered. As a precaution, the conveyor must be covered to prevent dust buildup and the potential for cross-contamination. However, this cover will need to be regularly removed and cleaned in between runs, which can be a tedious process.

Additionally, it should be noted that product damage and dust can occur when the product is initially introduced onto the conveyor from a processing machine.

Bucket elevators. Bucket elevators use a continuous line of buckets, either attached on a rubber belt or attached by pins to two endless chains running over tracks and driven by sprockets. Centrifugal force throws the product out of the buckets into a discharge spout as the buckets pass.

This type of conveyor can transport fragile materials with minimized product damage. However, the system can be very dusty, as dust is generated when the ingredients are loaded into the buckets and while the product is being conveyed, resulting in dust buildup.

Auger conveyors. Known as flexible screw conveyors, these conveyors are capable of transporting food ingredients in any direction – vertically, horizontally, or at an angle. They are composed of a flexible stainless-steel screw enclosed in a rigid steel or plastic tube, driven by a motor. The tube rotates around a central shaft, moving the product according to the design and direction of the screw. Once the ingredients reach the end of the tube, they are discharged into a process machine or container for packaging.

However, it is important to note that auger conveyors have limitations, as they can potentially break and produce dust when transporting large amounts of product. It is also important to regularly disassemble the unit for cleaning to maintain internal cleanliness and prevent dust buildup.

Pneumatic conveyors. Air-based pneumatic systems are used to transport ingredients between processes by creating air pressure levels either above or below atmospheric pressure. These systems come in two main types: the dilute phase conveyor and the dense phase conveyor, which differ in speed and pressure. They can operate as a pressure or vacuum system, offering flexibility and the ability to reach multiple destinations with one system.

Additionally, pneumatic conveyors can transport ingredients at high speeds without causing product damage or dust contamination, as any dust is collected in filters. However, it’s important to note that these pressurized streams of air can also pose a hazard if there are any breaches or failures in the pipes, tubes, or ducts, potentially releasing large amounts of combustible dust into the air and exacerbating existing hazards by dispersing settled dust.

Tubular drag chain conveyors. Tubular drag chain conveyors gently transport food products through a sealed tube by utilizing a drag chain that is pulled through a loop. The drag chain has attached solid circular discs (flights) that effectively push food ingredients through the tube. These conveyors utilize a completely enclosed tubing system, which ensures minimal dust is released into the work environment.

Furthermore, compared to other types of conveyors such as bucket, auger, pneumatic, and flat-belt conveyors, tubular chain conveyors offer a higher level of dust removal. Two types of chains, link chain and roller chain, can be used in tubular chain conveyors. However, it is important to note that due to direct immersion within the food being conveyed, dust and food particles may become trapped in spaces between plates, pins, and bushings even after cleaning with dry cleaning or wet-CIP systems.

Mitigating dust explosions
Tubular drag cable conveyors, like their counterpart tubular drag chain conveyors, effectively transport various dry food ingredients through an enclosed tube. The gentle handling of these conveyors accommodates delicate materials such as powders, pellets, flakes, and more, without any separation or release of dust during the transfer process.

Additionally, blended materials with varying sizes, shapes, and densities can be seamlessly transported without any impact on their quality.

Minimized dust accumulation
The tubular drag cable conveyor is specifically designed to minimize dust explosions, unlike tubular drag chain conveyors. Its smooth and uniform surface, along with its nylon seal, greatly reduces the chance of trapping food residue and dust.

This design adheres to the European Hygienic Engineering standards, ensuring that there are no crevices, ledges, or dead spots where dust and food particles can accumulate. Additionally, all inside surfaces have a polished finish with no roughness above 0.8 Ra, promoting efficient product flow and easy cleaning.

Maximized dust removal
Tubular drag cable conveyor systems offer a wider range of options for cleaning dry and wet tube conveyors compared to tubular drag chain conveyors. These include brush boxes, urethane wipers, air knives, in-line sponges, in-line bristle brushes, and a fully automated CIP system with multiple steps for thorough cleaning.

The CIP system ensures that all product contact surfaces come into contact with cleaning solutions at the correct temperature and flow rate, effectively removing all food product residues and dust. This avoids the need for time-consuming manual disassembly and reassembly of system components for cleaning.

Reduced ignition sources
One common cause of dust explosion ignition is mechanical sparks, which can result from various sources such as overheating bearings, belts, or out-of-alignment components. Unlike tubular drag chain conveyors, belt conveyors, augers, and bucket elevators which require pins or bushings that can overheat, the cable used on tubular drag cable conveyors does not have such components.

With low horsepower operation and energy-efficient variable-speed motors of less than 5 HP each, the tubular drag cable conveyor effectively consumes minimal power compared to other conveyor systems.

Minimizing the risk of dust explosions
Conventional mechanical conveying is a well-known method for transporting dry ingredients during food production. However, this system can contribute to dust release in the manufacturing environment at each transfer point along the route.

Additionally, it can lead to dust accumulation within the facility if proper equipment cleaning is not performed. Furthermore, the extensive use of moving parts in conventional mechanical conveying increases the risk of mechanical sparks, making it a potential ignition source for dust explosions.

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