Conveying in Cold Temperatures

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During February’s arctic blast, the state of Texas endured prolonged, freezing temperatures to which the region is unaccustomed. As a result, power plants and manufacturers encountered issues with their conveyors freezing. According to climatologists, such wintertime dips may become more frequent due to a weakened jet stream. Utilities and manufacturers in the southern United States, therefore, must plan for similar events to avoid disruptions. In doing so, they can take cues from operations further north to prepare for these weather events.

In northern climes, it’s standard procedure for operations to run their belt conveyors continually when temperatures drop below freezing. They do this because the material inside the conveyor can freeze to the pan and increase the load when the machine starts after a dead stop. Also, the belt itself may freeze to the pan and idlers. Belt idlers can freeze and then wear flat spots that destroy the roller.

When material freezes to a belt, it also creates problems at the conveyor’s head if the operation relies on brushes to knock off material. Brushes don’t remove frozen particles well and fill up with snow, thereby losing their effectiveness.

Belt conveyors can have problems in the extreme cold when operators keep them running, as well. Ice can form on the belt, for example, and decrease friction. When this occurs, the head drum spins in place because it cannot pull the belt.

Chain conveyors have an advantage regarding slippage because they do not operate with a friction drive but with chains and sprockets. The chains cannot slip as belts can. Chains and materials can still freeze to their pans, of course, and designs with large floor-to-chain contact can cause many problems.

Besides mechanical issues, operations can have trouble with the material itself when the weather turns cold. Simply put, the material behaves differently when it’s frozen than when it’s not. It can become more slippery, disallowing operators to elevate it at as steep an angle. Material can also break off in clumps from the storage pile when it freezes. Operators can have difficulty elevating these chunks and, depending on the size of the chunks, may find they lead to clogged chutes or broken chains (conveyor manufacturers do not design their machines to break chunks of ice). In the case of the potential for frozen clumps of material, it is wise to add a massive feeder screw inline to break the clumps. This is fairly common in green wood chips, especially with fresh, whole tree chips.

Operators may have to accommodate other changes in the material. Material may flow differently and surge, or it may become more brittle and require operators to handle it more gently. Every material is different, so operations personnel must determine how their material’s behavior may change, and depending on those changes, they may need to adjust how they handle the material.

Operators may also consider thawing the material to prevent changes, which is what some manufacturers do when they experience extreme winters or regular, albeit temporary, drops into freezing temperatures. They may employ heaters, for example, to warm the material—and keep their conveyors from freezing. A sawmill in North Carolina does this in the wintertime by blowing warm air at the conveyors with makeshift ductwork. If there is a chance the material may refreeze down the line, operators should avoid this practice, however, as the material is more likely to adhere to the belt or conveyor pan.

Manufacturers who deal with the cold also use antifreeze liquids to unstick components and increase belt friction. If the liquid contacts the material being conveyed, it may contaminate it, however, so operation personnel must consider whether this poses an issue. Antifreeze liquids can be expensive and should not be applied continually.

Overusing antifreeze liquids is more of a risk in climates that experience extreme winter cold, of course. But there are other ways to keep conveyors running in the cold, which engineers in the north design permanently into their systems.

According to Paul Janzé, a biomass-handling consultant in British Columbia, operators can equip belt conveyors that work in the extreme cold with large-diameter head pulleys with ceramic or vulcanized diamond-shaped lagging. Drums designed with a greater surface area and better grip are less likely to slip, he says, which reduces the need for antifreeze chemicals. Other designs Janzé recommends for conveying in extreme cold include:

  • Using two, carbide-tipped scrapers to remove material stuck to the belt. If these are not possible, the operation may try thumper rolls or air knives.
  • Increasing chute angles
  • Keeping chute diameters wide to help avoid material from freezing inside them. Adding a UHMW or PTFE plastic liner helps prevent material from sticking in the chutes, as well.

Janzé further says that operations may use belts with vulcanized cleats if they have issues with material falling back down the trough on inclines, but he notes that cleated belts are more difficult to clean. In our experience, cleated belts also have a far shorter lifespan than non-cleated belts. We, therefore, recommend employing premium paddle conveyors to move bulk materials up inclines rather than belt conveyors where possible.

There is only so much manufacturers and power suppliers can do to tweak their current equipment, though. Depending on the severity of the weather or if adjustments like slowing the conveyors are not possible, operations may have to consider replacing or rebuilding their conveyance systems. In applications where paddle or drag conveyors are inappropriate, operators may have to reduce the angle of their inclined belt conveyors. In situations where space is limited, they may consider sandwich belt high-angle conveyors. Sandwich belt conveyors can convey material vertically and protect the material from the elements. They are incredibly costly, however, and require extensive structural support. They also double the amount of drag-back material that collects under the return, and they have many more idlers to maintain.

For biomass, hog fuel, and other lower-density applications, operators may employ SMART Conveyors™ to handle the material. SMART Conveyors™ are a premium dual-chain drag conveyor manufactured by Biomass Engineering & Equipment in Indianapolis, Indiana. Advantages these conveyors provide in cold weather include:

  • Lower chance the chains freeze inside the conveyor when the machine stops, as the chains run along UHMW wear strips and outside the material.
  • Sprocket-and-chain drives do not slip as a drum roller can.
  • Includes an option for emergency aborts. (If conditions upstream are upset, operators can dump the material from the conveyor, which prevents them from having to start a full conveyor.)
  • The fully enclosed structure protects the material from snow and freezing rain.
  • UHMW floor liners are available, which reduce the chances of material sticking to a conveyor’s pan.
  • Paddles support the material, so it cannot slide down the conveyor.
  • Proven performance in cold temperatures. SMART Conveyors™ have been installed as far north as 55° latitude, where they’ve been operating without any reported problems.

If you want performance you can depend on in the cold, SMART Conveyors™ are the best choice for many bulk materials. Don’t get left out in the cold. Make sure your operations are ready for the next winter punch.

 

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