BULKtalk, Equipment & Technology

BULKtalk: Bulk outside of the box

Steve Davis, Senior bulk handling expert at Advisian, has been involved in projects around the world and seen issues and concepts not often considered in the Australian bulk materials handling world.

The world of bulk materials handling is made up of diverse materials and situations, often dictated by environment.

However, there are some common issues that occur on almost every site. Encrustation from spillage, carryback and dust build-up is one such example I have seen on almost every facility I have been to in recent years.

Some plants have so much encrustation that the structural integrity must be questioned. In many, the structures only had flat surfaces and spillage traps, and there is no access to remove the build-up. In others, there is so much dust that there is a serious risk of secondary dust explosion. Early in my career I worked in a British steelworks where a large roof collapsed due to dust build-up, and recently in South Africa I was concerned for my safety just walking the site.

We need more thought in our designs and more care in our maintenance practices and the data used to determine them. Learning from how other organisations around the world have moved to address these issues can prove valuable.

Travels in Canada and Russia

Australia transports about 1.5 billion tonnes of coal and iron ore via rail each year. Generally, once loaded, it is relatively easy to unload.

However, spare a though for northern hemisphere countries where ores, concentrates and coal commonly freeze solid in transit. The result can be 100-tonne ice blocks in railcars. There are some interesting additions to the train unloading process, which is almost always by rotary tippler.

Methods for managing frozen ores include thaw stations where railcars stand for a period surrounded by radiant heater elements and block breakers where the ice block is tipped onto a grid and a moving rotary hammer device chops the block up. We chose the rotary hammer for an iron concentrate port terminal in Quebec.

Insulating railcars using plywood is common with polyurethane being investigated as a potential alternative. This is often combined with anti-freeze sprays as the train departs. We also included the plywood liner for our railcars.

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Alternative methods exist that use or propose mechanical systems to break up the ice cube, from the use of a jackhammer, through to explosive propelled harpoons over the railcar.

Further to frozen railcars, stockpiles can also freeze. High turnover stockpiles are less likely to encounter this problem, but if the stockpile stands for a few weeks, a thick solid frozen crust can form. This does not appear to be a problem for front-end loaders, but bucket wheel reclaim must consider break out loads in more detail.

In some parts of the world, such as those located above the Arctic circle, the seas freeze for at least six months each year. Mines, however, continue to operate all year round.

At an installation on Canada’s Baffin Island the result is a very large stockpile at the port and high rate reclaim and loading equipment to store 12 months production and load to ships in three to four months. A small fleet of ice breaking cargo ships takes ore from the port.

One lesson learned during my first visit to Fort Mac in Alberta, mid-winter is to ensure the workspaces at these sites are fit for the climate. Where the temperature drops below -30°C, multiple layers of clothes led me to resemble the ‘Michelin Man’.

Standard maintenance access in Australia would be too small for these conditions. Walkways would need to be at least a metre wide. In addition, to account for the heavy gloves, equipment comes with much larger handles. Enclosures are provided with heating to maximise potential activities in the short times allowed in these temperatures. Cold weather carbon steel alloys are mandatory for all structures and platework.

Another lesson I learned from the cold was at a mine producing concentrates in Northern British Columbia, Canada. The road out is frozen for many months, meaning there is no access to transport. The solution was to bag the concentrate into one-tonne flexible intermediate bulk containers (FIBC) and store them in such a way that they froze solid in a slightly constrained shape. As soon as the road opens, the big ice blocks are loaded up and shipped out, with defrosting taking place at the destination.

Heat can also present challenges to catch the unwary. In Australia, we import sulphur granules as there is no viable local source. Typically, granules can be a little dusty but handle well.

Granules have some unusual properties related to phase changes that affect bulk handling. Granules are produced with a surface temperature of approximately 65°C, and then the temperature increases as sulphur experiences a phase change.

In a stockpile the temperature might reach 100°C or more and gradually cool over many days. Much of the world’s sulphur is a by-product of Middle East oil and gas production, where summer temperatures can reach 50°C and above. This does not assist cooling.

Under the right ambient conditions, the granules in the stockpile form an adhered matrix. Factors involved are time, temperature, effective head and humidity. Reclaimers that are specified for free-flowing granules can struggle to reclaim the matrix. Watching scraper reclaimers juddering though the stockpiles of apparently loose granules is uncomfortable and warns of potential failure.

Material properties

In Australia, the bulk handling industry often tests only one or two coarse ore samples for materials handling properties. This is then used to design a materials handling facility for a large non-homogenous ore body for a life span of years. The same properties are also used for all sub fractions of the ore. The cost of testing and difficulty in getting representative samples is the justification.

I have seen projects where test work has been completed and ignored, or not completed at all. I’ve seen others where multiple tests have been completed but not consolidated into any real guidance. These options have resulted in poor handling outcomes that could have been designed out.

Imagine not making nameplate capacity on start-up and the cost of coaxing a facility to operate and all the downtime through all the diverse changes in 20-plus years.

Some organisations are using regular in-pit ore testing results to predict and blend material flow properties to reduce blocked chutes and the like in the process plant. This is proving effective in reducing downtime.

Temperature

Oilsands have interesting properties when temperature is considered. Temperatures in the mine areas vary from -40°C to +35°C. The higher temperatures do not thaw in ground sand, but as soon as it is mined and crushed, we see significant changes in material handling properties.

Frozen or warm is generally ok but there is an interim sticky phase over -4°C to +10°C. In the typical 9000-tonne storage bins, we can see the crushed sand vary between difficult (heated and aerated bins to get flow) and so free flowing that the bin can empty in seconds onto the floor. Typical materials handling testing is at 20°C, so would you consider additional testing at other temperatures for this and similar applications?

Moisture

Transporting bulk with water often creates unloading and storage problems, such as stockpile collapse. Extra water also increases the cost of transport of the ore through displacement.

For example, 10 per cent moisture is 20,000 tonnes of the average cape size ship capacity that has no value. Wet ore in railcars can separate and create havoc when unloading in the dump station, unloading rates are reduced and the rail schedule is impacted. In some situations, this will limit the total capacity of the rail system.

When transferring wet ore by ship, we often see the bottom metre or so of a hold is just wet sludge. This can be so bad that the ship cannot be fully unloaded and is returned with up to five per cent residual material. The wharf and conveying equipment will also likely be covered in spillage from trying to unload as much as possible.

Much of the water is added by random sprays that are used to wet ore on conveyors and elsewhere to manage dust emission. Surely, we can manage dust more effectively and reduce the amount of water added.

Reagents

Reagents are commodities generally used in laboratories for making chemical reactions. But what if your reaction in Australia requires more than 200 tonnes per day?

It turns out that the reagent is produced in a different hemisphere with no regard to handling properties and packaged in 20-kilogram packs. The reagent, like many, is hygroscopic. We needed to assess how to get 10 containers per day to a remote location, and the transport system is complex: truck, train, ship, truck, barge.

The barge operates infrequently so we must store the reagent for up to a month in a hot and humid climate. We want to use container liners for 20-tonne loads, with FIBC as a back-up plan.

The original concept was to test the reagent for the standard suite of handling properties and design assuming these would sustain through travel and storage. After some discussion we completed material tests in a climate chamber and with simulation of vibration and storage.

The conclusion was that the reagent would form a 20-tonne solid block by the time it was needed, so no conventional system could meter the discharge. This allowed us to source an unconventional method that manages the discharge simply.

I am sure there are more diverse materials and situations when it comes to bulk materials handling, and I hope that my experience might drive material flow testing considerations beyond the suite of room temperature flow test that provide valuable data, but sometimes not enough.

A final experience is a potash storage building in Russia. On the outside, a standard steel sheeted building, on the inside, a completely wooden structure. I was told that this material is more cost effective and less prone to corrosion than steel, yet all other structures were steel framed. The photos don’t do it justice.

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