New project developers as well as mature mine operators are showing renewed interest in in-pit crushing and conveying as a viable alternative to conventional truck and shovel mining By Russell A. Carter, Managing Editor

It’s been well over a year since E&MJ last published an industry-wide report on advances in in-pit crushing and conveying (IPCC), and during that time mining has navigated some rough waters as the global economy tanked, mining investors fled, and commodities prices fell (uranium), rose (gold), and in some cases did both (molybdenum) during an excruciatingly slow and uncertain market recovery.

At the time of that last report, the industry was booming and money flowed freely to equipment vendors as mine developers pushed hard to complete projects while commodity prices were high. Interest in IPCC had been growing and the leading suppliers of IPCC systems had multiple orders on their books.

Fast-forward to today: Access to investment funding has been difficult and in some cases, impossible. Many of the boom-time IPCC system orders have been completed, or are in the final stages of installation. Truck and shovel order backlogs have shrunk, and diesel fuel prices, while still relatively high, have not increased disproportionately since crude oil reached a peak of more than $140 a barrel in June 2008, somewhat blunting at least a few of the perceived advantages that an IPCC approach could claim over conventional truck-and-shovel mining.

Yet, the basic factors—savings in mining costs, fewer workers in the pit, reduced carbon emissions, to name a few—that make IPCC an attractive option in certain applications are still valid. Technical innovations have emerged for both mobile and semi-mobile IPCC systems, and orders continue to be placed.

ThyssenKrupp Robins’ Tom Armesy told E&MJ that, following a downturn in activity after the onset of the world economic crisis, he’s noticed a resurgence of interest in IPCC systems lately, not only from mine operators planning new projects, but also from those who were considering IPCC as a viable option prior to the economic downturn. “What we’re currently seeing not only involves customers who might be planning to include an IPCC system at the initial stage of a project. Other clients are looking at their five- to 10-year mine plans, and realizing that the amount of overburden that must be removed at stage of mining makes it difficult to justify truck and shovel operations.”

ThyssenKrupp Robins is the U.S. mining business unit of ThyssenKrupp Fördertechnik (TKF), a large German industrial group which manufactures a wide range of crushing, materials handling and other types of mining and processing equipment. In total, TKF has installed more than 200 mobile and semi-mobile IPCC systems over the past 50 years or so, and at any given time recently, has eight to 10 systems on order or in various stages of installation.

Armesy noted that recent orders have trended toward fully mobile systems, but hardrock mining clients are also showing interest in higher-capacity semi-mobile systems—up to and including those that call for TKF’s largest primary gyratory crusher, a 63 x 114-in. unit that can handle 10,000–12,000 t/h of throughput, although 8,000–10,000 t/h would be a more typical crushing rate in most applications. However, one of TKF’s semi-mobile systems currently operating at a western U.S. copper mine employs a 60 x 109-in. gyratory and routinely runs at a 10,000-t/h rate.

The interest in higher-capacity systems, said Armesy, is a direct reflection of operator interest in economies of scale, as ore grades gradually subside at mature operations and more material must be moved.

TKF has been active in supplying IPCC systems to the Alberta oil sands operations in Canada, and its double-roll crusher-equipped systems working there can handle up to 11,000 t/h. Higher-capacity systems are in the works for these applications, however, with nominal capacity reaching 14,000 t/h. To provide some idea of the scale of this equipment, the 11,000-t/h systems are equipped with apron feeders 3.4 m wide; the 14,000-t/h units will have 4-m-wide feeders.

Systems for All Scenarios
FLSmidth’s RAHCO business group, based in Spokane, Washington, USA, has developed two new systems for in-pit crushing and conveying, with each taking a different approach: one is designed to work with truck/shovel mining methods; the other is a mobile, conveyor-based system for overburden handling that is similar to previous RAHCO systems designed for this purpose but with additional technological advances.

The Dual Truck Mobile Sizer (DTMS) is intended to fill a gap in current IPCC capabilities. To date, available solutions offer either mobile crushing stations where the shovel feeds the crusher’s hopper, or semi-mobile crushing stations where a truck fleet is employed.

The DTMS bridges these situations by interfacing with trucks yet remaining fully mobile, allowing for the mining flexibility of a truck haulage operation while retaining the low operational costs of conveyor systems.  Integrated material lifting skips eliminate the need for expensive earthen ramps and retaining walls required by conventional semi-mobile, in-pit systems, and reduce truck cycle time.  As mining progresses, the DTMS system is relocated (usually in one shift or less) and crushing continues.

There are two basic DTMS chassis designs. The first has self-propelled crawler tracks while the second has jacking cylinders at each corner for relocation by a conventional crawler transporter. The latter version is intended for sites where multiple DTMS machines are in service, as only a single transporter is required.

According to the company, because the DTMS isn’t “land-locked” with earthen ramps or retaining walls, it is the only truck dump system that can be linked to a shiftable face conveyor. In addition, DTMS can significantly reduce the number of trucks required to service multiple benches by providing needed flexibility while allowing the mobility and high productivity of a conventional shiftable system. When comparing relocation times as well as costs over current systems, RAHCO says the DTMS has a clear advantage. Movement is measured in hours, not weeks, and with costs being proportional to time, significant savings are at hand.

RAHCO also reports that interest is growing in what it describes as a “revolutionary” mobile conveyor-based overburden handling system, of which the first of two systems to be installed is currently undergoing final commissioning. These Triple Track Mobile Sizer (TTMS) systems comprise two 4,000-t/h, crawler-mounted, triple-track mobile hopper/sizers, and a pair of mobile bridge conveyors that operate in series and feed a 350-m mobile stacking conveyor.  Each system has a capacity of 8,000 t/h; total operational capacity is 16,000 t/h.

In operation, a shovel feeds a dedicated 4,000-t/h mobile hopper/sizer.  For maximum efficiency, each shovel and hopper/sizer combination operates independently of the other. Overburden is reduced to 350 mm, an efficient size for the conveyors.

Crushed/resized overburden is then transported along a short telescopic inclined conveyor, transferred at 90° to the longer bridge conveyor and transported to another 90° intersection where the material is transferred to the second bridge conveyor.  At a third 90° transfer station, the overburden is switched to the stacking conveyor for computer-controlled dispersal.

The entire system is mobile and advances at a speed that accommodates numerous variables such as loading rates, conveying distances and overburden distribution and depth.  The only time overburden removal stops is for shovel refueling or regular system maintenance. System alignment is managed by on-board GPS.

Control and mechanical improvements allow the TTMS to strip to a depth of 20 m in a single pass, reducing the operational downtime associated with truck-and-shovel operations. The result, according to RAHCO, is an overburden stripping system that is more effective, more efficient and less expensive than traditional methods.

The two systems being installed include innovative size reduction equipment within the hopper/sizers and improvements to the loading hoppers’ mobility. Each hopper/sizer uses a single FLSmidth-ABON primary low-speed twin-roll sizer driven through a proprietary quad reduction gearbox generating high levels of output torque capable of reducing the uncontrolled ROM feed to a transportable product size for stacking.

The low roll speed protects the sizing elements and drive train from excessive damage or catastrophic failure when tramp metal is encountered in the crushing chamber.  To maximize tooth wear life, it also allows for a more positive bite/engagement on larger feed lumps.

The sizers incorporate “all-oil-bath” lubrication, which eliminates the need for external auto-lube systems.

Each triple track mobile hopper/sizer will carry up to 150 mt of surge capacity and can move even when fully loaded, allowing them to maintain correct position relative to the loading tool. The RAHCO-designed crawler tracks are designed to carry extreme weight and will traverse 20% gradients.

Overall mobility and structural integrity is enhanced by the integration of a series of proprietary knuckle joints along the conveyors.  Designed to allow for the vertical and horizontal movement of each conveyor, the joints are installed longitudinally on 45-m centers.

RAHCO says the system’s overall design will also give site management exceptional control over handling and placing the excavated overburden.  It will allow the original topography to be copied, and environmental restoration and rehabilitation can begin almost immediately if desired. Additionally, the resulting extremely flat benches of stripped overburden means top soil is less likely to erode, making revegetation more successful.

Sandvik’s System: Definitely Different
When Sandvik introduced its PF300 mobile IPCC system in March 2009,  Sandvik’s Thomas Jabs said: “We see strong signs of interest in fully mobile crushing concepts in all the big mining markets. Engineering houses and operating houses worldwide are seeking alternatives to truck intensive mining to reduce maintenance costs, operational costs and to reduce the CO2 footprint. This is where the fully mobile crushing concept perfectly fits and what the PF300 is developed for.”

As E&MJ’s European editor, Kyran Casteel, wrote describing the unit in April 2009: “The PF300 is definitely different.” The machine can be equipped with a sizer, or a double-roll crusher or a hybrid, for any client’s multiple applications: Sandvik does not rely on only one crushing principle but can select and offer the most effective crusher to the client. The hybrid is a roll crusher that combines the advantages of a sizer and a double roll crusher, thereby closing the gap between these two by introducing high inertia crushing and very good intake behavior. It was designed especially to provide higher performance than the common sizer and double roll crushers and also for more critical applications such as abrasive and clogging materials. It is automatically controlled and adjustable from the operator’s control room.

Sandvik said it used new technology to provide stability for the PF300, allowing hydraulic excavators or rope shovels to load the crusher without any temporary support. The PF300’s stability is based on having two sets of crawlers. One set is located at the hopper area where impacts are inevitable from shovel bucket dumping, and the second set is located under the crusher. This  second set is the steering crawler pair and works according to proven design concepts already used in Sandvik mining equipment such as bucketwheel excavators and spreaders. This design minimizes movement of the upper structure from load impacts in the hopper and makes the machine much more stable compared with most of the known design concepts. This not only keeps availability at a high level, but also improves the positioning of the machine.

By shifting the discharge device to a separate system, boom oscillation is uncoupled from hopper loading by the shovel. The PF300 can work in combination with fully mobile belt wagons, transfer conveyors, or load bridges as the connecting downstream link to the face conveyor. The loading bridges are derived from the Sandvik design concept proven on spreaders or bucket wheel excavators and enable the system to work in double or triple block operations, hence reducing shifting sequences of the face conveyors as the mine advances.

Sandvik said the PF300’s initial configuration will provide capacity of approximately 10,000 mt/h, as it sees the highest potential in this class, but higher and lower capacities will be available. The anticipated range will be between 2,000 mt/h and 14,000 mt/h, depending on material density.

In the fourth quarter of 2009,  Sandvik received an order from a Brazilian customer for a complete crushing and materials-handling system that includes a PF300 mobile unit. The system is scheduled to be commissioned in late 2011.