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Breaking the cycle of silo buildup

Published by , Editor
World Cement,

Brad Pronschinske, Martin Engineering, explains how the effective use of air cannons can remedy silo buildup and clogging issues, avoiding lost production and increasing safety.

Most cement plants and silos were designed for the needs and environment of the time when they were constructed. However, production demands and shifts in climate are changing the dynamic. Modest changes in moisture content can cause adhesion to silo walls.

Low temperatures and changes in atmospheric pressure – especially if the silo is stagnant for long periods – can contribute to flow changes.

In the past, when material accumulation problems became a recurring issue, processors would usually limp along until the next scheduled shutdown. That could cost a business hundreds of thousands of dollars per day in lost production.

Once coarse material adheres, the buildup is generally fast and dense, eventually requiring downtime to remove. Seeking ways to address it quickly without the proper tools or training can also be the moment when workplace safety degrades.

Air cannons are engineered to safely clear and prevent clogging, promote material flow and avoid costly downtime. To know if the technology will work best for a specific application, the first step is understanding how, where, when and why clogs happen in any given silo. The second step is removing any worker involvement in clearing the clog, aside from pushing a button to activate the cannon if it is not automated or controlled by logistical software.

Silo clogging and safety

Regardless of the cause, the types of clogs in a hopper can pose unique challenges for discharge, as well as very serious safety issues. There are several unsafe practices around silos that too often result in serious worker injuries or fatalities, mainly sudden discharge of adhered material and entrapment.

Poking or lancing from beneath the clog at the spout can result in a sudden surge of falling material, burying or crushing the worker(s) below and seriously damaging the receiving belt. Beating the vessel walls with mallets or other objects to loosen adhered material is common. Operators who engage in this method find this worsens the situation over time as the divots and ripples left from hammer strikes provide places for additional material accumulations to start.

If a worker enters the vessel and stands on the volatile bridge, a sudden discharge could pull the worker into the cavity. Sometimes material buildup on the sides of the vessel reaches higher than the worker and falls from above, causing serious injury or burial.

Material churn

Silos are designed to hold a certain volume of a particular material, so awareness of the maximum load is important. Repeatedly filling and emptying them makes load requirements especially important in those cases, since capacity is reached repeatedly under many conditions. When working with bulk solids, environments with high moisture and freezing regularly experience clogging. Wide variations in the size and shape of the material can also affect the flow characteristics, leading to buildup and clogs.

Arches form when material consistency changes during loading or when the top material contains more moisture. It can also just be caused by gravity. This is very dangerous since material discharge has a long fall distance. The flat top surface can give workers a false sense of stable ground, so vessel entry is ill-advised. Air cannons placed at the upper point of where material begins to adhere keep material flowing toward the discharge spout.

Plugs are generally caused by compacted moist material or the contents that have been left for long periods. Strategically placed air cannons can help loosen material to get it flowing. Sometimes the contents have hardened to such a degree that a silo cleaning service is needed, which utilises the support of the air cannon system to resolve the issue faster, lowering the cost of the service.

Buildups can be caused by several factors: weather, silo design, the way the silo is loaded, a horizontal grain of the metal on the side of the silo, the silica content of the material, etc. Buildups can be economically mitigated using strategically placed air cannons at common collection points to keep material flowing toward the discharge spout.

Ratholes often form over time and reduce the capacity of the silo. Since the material is flowing, they are often ignored by operators, but can severely impact on production. The significant weight put on the thin walls of the silo and structural supports can pose a serious safety issue if buckling or a collapse occurs.

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