Beating buildups and blockages

Once material starts to stick, the buildup is generally fast and dense, slowing the flow, causing spillages and secondary blockages, and ultimately resulting in unscheduled downtime. Compounding these issues, the temptation to find a quick way to shift a blockage, often without the proper risk assessment, safe access, or the correct tools or training, can lead to workers putting themselves at risk.

This is where flow aids come in, innovative devices specifically engineered and installed to promote material flow, clear buildups and prevent clogging, avoiding costly downtime and reducing the associated safety risks. A variety of flow aid technologies are available but to know what will work best for a specific application, the first step is understanding how, where, when and why clogs are happening in a particular vessel. The next step is redesigning the system not only to clear blockages but also eliminates the need for any worker involvement in doing do, using the right flow aids.

Capacities, characteristics and clogging

Understanding the function and maximum load of each vessel in the process is vital, as is an appreciation of the physical properties of the materials passing through, including moisture content and temperature, plus the effect of atmospheric conditions. Wide variations in the size and shape of particles also affects the flow characteristics. Failure to consider these basic factors can lead to the installation of suboptimal designs that increase the likelihood of buildups and blockages.

Further, if a hopper is not designed to carry the required material load at full capacity, a sudden surge of material or a clog can rapidly lead to harm. And even if a hopper or silo is engineered properly, repeated impact and abrasion from loading over years can cause the vessel walls to distort or wear thin, decreasing their ability to perform as designed, compromising structural integrity and increasing the risk of a serious event. 

There are numerous reference guides that explain vessel loading in order to determine the right design, covering load factors such as:

Dead load – The total weight of the structure, including attached components and equipment supported by the structure

Live load – Forces exerted from the stored material, including high and low pressures caused by flow, plus anything independent of the structure such as snow, positive and negative air pressure, wind or seismic load, and any forces from materials stored against the external wall

Thermal load – Caused by temperature differences between the inside and outside faces of the wall

Settling load – Forces from uneven settling and movement of the structure

Clearly, the combined factors that play a part in buildups, blockages and overloading can be complex – the weight, size and type of material, the load velocity, direction and distribution, the design of the vessel, its age and condition, atmospheric conditions, and the monitoring and maintenance regime. Once a major buildup has occurred, the moment the clogged material is released, the force of the surge has been known to overwhelm and damage the structure, the discharge gate, or the skip or conveyor onto which it is flowing. So before releasing a blockage, understanding the weight of the material in the clog itself is important too.

Hopper geometries and discharge points

Discharge points come in varying shapes, depending on the vessel and the material flow characteristics (Fig. 3). Plant manufacturers carefully choose discharge point shapes based on a series of load and flow factors. Spouts that are narrow, such as those found on conical or pyramidal shapes, direct flow in a vertical column either into a chute or specific loading area. Slotted spouts, like those found on the wedge or transition shapes, typically distribute material in a narrowly defined line for loading onto conveyors or into containers such as trains or trucks.

In all cases, the shape of a vessel should match that of the discharge point or it will be prone to clogging. The slope angles in discharge point geometries can also contribute to clogging, depending on material characteristics, the specifications of the application or the placement of the vessel.

Discharge points often feature gates (to halt material flow for incremental filling of skips, rail cars or trucks) and grates (to break up smaller agglomerations or to slow the flow of material when loading onto a conveyor). Either way, sooner or later operators find that these devices can exacerbate clogging by stopping or slowing material at the structural choke point of the vessel.

Unblocking and unsafe practices

Once a clog has been detected, many operators witness unsafe practices that, at the time, may seem like a simple and harmless solution, but frequently cause injuries and are even known to cause fatalities. 

The most common starting point is beating the vessel walls with mallets or other heavy objects to loosen stuck material. Besides the safety risks of manual handling, over time, the more the walls are pounded, the worse the situation becomes, as the bumps and ridges left in the wall from the hammer strikes will form ledges that provide a place for additional material accumulations to start. 

Another hazardous yet popular practice is poking or lancing from underneath the clog at the discharge point. This can result in a sudden surge of falling material, burying or crushing the worker(s) below. Physical lancing from above is also common, often with makeshift platforms that allow easy access but provide little protection should a worker slip and fall into the vessel.

Manually air lancing the blockage from the mouth of the vessel at the top can be an effective option, but only when guardrails are fitted, or a safe access platform is used. Of course, the reach of the lance and the pressurized air stream must match the size of the vessel and the clog. And again, unless a harness is worn, workers could still fall in trying to get the lance down to the clog, even if guardrails are present.

Perhaps the most prevalent cause of worker injuries is entry into the vessel. Along with potentially sinking into the material, especially in the center, the silo or hopper contents could be “bridging” and suddenly release. If a worker enters the vessel and stands on the fragile bridge or on a buildup to the side, a sudden discharge could pull the worker into the cavity causing a serious fall or engulfment.

These unsafe situations and behaviours can be avoided by introducing flow aids to the vessel to mitigate clogs, promote material flow and reduce downtime.

Productivity through prevention

As the term implies, flow aids are components or systems installed to promote the flow of materials through a silo, bin, hopper or chute whilst controlling buildups, overflows and spillage. Flow aids come in a variety of forms, including rotary and linear vibrators, high- and low-pressure air cannons and aeration devices, as well as low-friction linings and optimal chute designs, to encourage the most efficient flow of bulk materials. 

Such solutions can be combined in any number of configurations to complement one another in an integrated system to eliminate clogging and improve overall productivity. Flow aid devices are effective in virtually any bulk material or environment, including heavy duty applications, hazardous materials and extreme temperatures. 

When employing flow aids, it’s critical that the hopper or silo structure is sound and the flow aid device(s) are properly sized and mounted, because their operation can exert additional stresses on the structure. A well designed and maintained vessel will not be damaged by the addition of correctly sized and mounted flow aids.

It’s also important that any flow aid device is used only when discharge gates are open and material can flow as intended. Best practice is to use flow aids as a preventive solution to be controlled by timers or sensors to avoid material buildup, rather than waiting until material accumulates and begins to restrict the flow. Using flow aid devices in a preventive manner not only reduces the chance of clogging but also enhances safety and can even save energy.

Start with engineered vibration

A better alternative to pounding the outside walls of a hopper or chute is the use of engineered vibration, which supplies energy precisely where needed to reduce friction and break up potential accumulations to keep material moving to the discharge opening, without damaging the chute or vessel. The technology is often found on conveyor loading and discharge chutes but can be effectively applied to other process and storage vessels, including silos, bins, hoppers, screens, rail cars, feeders, cyclones and heat exchangers. 

Productivity with a blast

Where vibrators alone may not achieve optimal flow, a highly effective solution for eliminating material accumulation in chutes and vessels is the use of low-pressure air cannons, pioneered and patented by Martin Engineering in the 1970s. Air cannons, or blasters, use a plant’s compressed air system to deliver powerful and carefully timed blasts to dislodge buildups before they become problematic. Air cannons can be mounted on metal, concrete or even wooden surfaces as long as they are structurally sound. The basic components include an air tank, a fast-acting valve with a trigger mechanism and a nozzle to distribute the air in the desired pattern to clear the accumulation most effectively. 

The sudden blast of air released by the valve on an air cannon is directed through a specially designed nozzle, which is strategically positioned in the chute, tower, duct, cyclone or other location. Often installed in an array of several air cannons and precisely sequenced for maximum effect, the devices can be timed to best suit individual process conditions or material characteristics. These air blasts help to break down material accumulations ensuring normal flow is maintained. In order to customize the air cannon installation to the service environment, specific air blast characteristics can be achieved by manipulating the operating pressure, tank volume, valve design and nozzle shape. 

In the past, when material accumulation problems became a recurring issue in hard-to-access enclosed vessels, operators would have to either limp along until the next scheduled shutdown or, more likely, endure expensive unplanned downtime to lance the clogged buildups. Such is the importance of keeping materials flowing that many vessels now feature mountings so that devices such as air cannons and vibrators can be fitted safely with relative ease. The question isn’t about whether to fit flow aids, it’s more about what type, how many and where.

Conclusion

Given the demands and complexities of processing mined materials, buildups and blockages in silos, hoppers and other vessels should be banished with engineered flow aids. The key to success lies in selecting the appropriate flow aid technology based on material properties, vessel design and operating conditions. Moreover, proactive and preventive use of these solutions, rather than reactive measures, is proven to help maintain optimal performance and can even extend the lifespan of storage and transfer equipment. As mining plants increasingly prioritise production efficiency and worker safety, investing in well-designed flow aid systems has become a necessity. By embracing such innovations, producers can achieve smoother operations, maximise throughput, and create a safer working environment, ensuring that materials move through the process without unnecessary interruptions.

Case Study

Problem: The bauxite ship-to-shore handling system at an aluminium smelting plant in UAE faced severe jamming due to the material’s high moisture content, making it sticky and prone to buildup. Blockages occurred at five critical transfer points, from ship unloader to storage yard, disrupting flow efficiency. Daily manual intervention through hammering and poking was required to restore movement, leading to safety risks and excessive manual cleaning time. Repeated mechanical impact caused structural damage to chutes and process vessels, escalating maintenance costs. The recurring stoppages reduced equipment reliability, increased downtime, and directly impacted productivity across the bulk material handling chain.

Solution: Martin Engineering, together with the plant’s in-house team, conducted a site audit and recommended an engineered solution. Eighteen Martin^® Typhoon Air Cannons with nozzles were strategically installed across five different chutes and vessels. The solution included control panels, silencers to reduce blast noise, and supporting accessories for reliable operation. The Martin^® Typhoon Air Cannon features a hybrid valve concept that provides more powerful blasting force to free-flow sticky bauxite material. It uses less air, and simplifies maintenance compared to traditional air cannons, while ensuring effective material flow and improved productivity.

Result: The installation of Martin^® Typhoon Air Cannons successfully resolved the bauxite jamming issues, eliminating the need for daily manual cleaning and preventing further structural damage to chutes and vessels. The powerful air blasts ensured sticky bauxite material flowed smoothly through the system, improving material handling efficiency. As a result, downtime was reduced, plant safety enhanced, and overall productivity increased. The solution has been performing reliably for over two years, with the customer expressing satisfaction. Encouraged by these results, they are now planning to replicate the same Martin flow aid solution across additional locations with similar requirements.