With advantages ranging from low opex and reduced environmental impact to higher overall safety, in-pit crushing and conveying can deliver on its promise—if all the right pieces are carefully put in place
By Russell A. Carter, Managing Editor
Recent surveys show that, to nobody’s surprise, sales of the types of mobile primary production equipment used in conventional truck-and-shovel (T&S) mining have slowed noticeably over the past year or two as project owners take a step back, draw a deep breath and scan the economic landscape for signs of a nascent commodities boom. Many of these same project owners are also taking a second look at their project plans, seeking mining methods and equipment that offer the highest prospect for profitability under current market conditions.
Some will decide that tried-and-true T&S might not be the most efficient solution for their project after all. Others may determine that truck haulage will work for them—but only if they can drastically shorten haul distances and cycle times. Either path may open the door for consideration of in-pit crushing and conveying (IPCC), a concept that has had some difficulty gaining traction as a primary production method, particularly in hard rock applications.
Truck operations and maintenance, diesel fuel management, haul road planning, and dispatch efficiency are familiar concepts to many mine operators. Contrast that with the perceived complexity, downtime concerns and lack of supporting software planning solutions for IPCC mine layout, and it’s easy to understand how producers might feel uneasy about adopting a less-familiar mining system. But despite the industry’s hesitancy, IPCC projects continue to propagate around the globe; for example, Sandvik alone has been involved in major IPCC projects in Brazil, Sweden and Thailand. Metso has been active in promoting IPCC in Mongolia and elsewhere, and Thiess RWE has conducted IPCC studies for customers in Africa, Asia, Australia and South America, among others. ThyssenKrupp Industrial Solutions has been building high-performance mobile crushing plants for decades and has provided IPCC solutions for customers around the world.
This level of interest in IPCC may indicate that mine operators are focusing more on ways to achieve lower cost per ton of material moved and less on production-system flexibility, which has been the hallmark of T&S mining.
The advantages offered by IPCC operations can be significant. Snowden Group, a Perth, Australia-based consulting engineering company, has been involved in more than 30 IPCC studies. The company said IPCC potentially provides benefits such as:
- High volume rock transport rates;
- Relatively low operational costs;
- Low exposure risk for operators;
- High productivity;
- Amenability to a high degree of mechanization and automation; and
- Lower CO2 emissions per site.
Snowden’s experts caution, however, that their experience with IPCC systems confirms that benefits may only be realized under specific circumstances. They recently developed a list of general and specific concerns that require attention from mineral producers interested in investigating the applicability of IPCC to their existing and future operations. Here are the factors that should be considered:
What is the material movement rate of the mine? IPCC provides a competitive alternative to truck-and-shovel in terms of capex and opex when rock movement rates reach at least 30 million metric tons per year (mt/y). Modest material production does not justify the initial investment.
What are the typical haulage cycles? IPCC will only reduce costs if it can replace a sufficient number of trucks with conveyors, versus a pre-existing T&S configuration. In general, IPCC becomes attractive when average truck cycle times exceed 25 minutes, and a large number of truck units may be replaced with conveyors, resulting in opex and capex savings.
How long is the mine life and can more capital be accessed? IPCC is capital intensive and requires a long-life operation in order to take advantage of the reduced opex. Usually, at least five to six years of operation is required to pay back the initial investment.
How cheap is electricity? Electric-powered IPCC equipment offers an alternative to conventional diesel trucks, in particular, when the ratio between electricity price and diesel cost is very low.
How hard are the materials that are being mined? Hardness is a key driver of the selection of a crusher type. It is therefore critical to build a robust geomechanical model of the deposit, which includes UCS data, abrasiveness and size distribution across the several geological domains. The consequences of misjudging the deposit geology and rock properties are, in general, irreversible and very expensive. Once the IPCC configuration is in place, there are few options available to the mine engineer to redress the situation.
What is the variability of the deposit? The success of an IPCC system relies on planning repetitive standard operations. Any topographic or geological variations may be detrimental to productivity of the IPCC system.
Is dilution an important value driver? Using larger equipment such as that required for IPCC may lead to a reduction in mining selectivity, and consequently introducing excessive dilution.
How complex is the mining sequence? Implementation of IPCC implies the design of large pushbacks in order to maintain low vertical advance rates that reduce the relocation frequency of crusher stations. Furthermore, incorporation of highly productive mining systems increases the overall mine capacity but, at the same time, reduces the number of active mining faces, resulting in a limited blending capacity and a variable head grade and ore feed. Only a good balance between these parameters may lead to a viable IPCC configuration. Consequently, mine planning for IPCC requires an additional effort from the mining engineer, when compared with conventional mining. IPCC does not tolerate poor mine planning practices.
Does the pit have narrow, awkward mining areas? Ideal conditions for IPCC are usually absent in portions of mine sites. In these areas, the system must coexist with truck and shovels in the areas where IPCC is unable to operate efficiently; for example, along narrow and irregular pit boundaries or small pit bottoms. Also, fully mobile systems are typically configured with crushers designed for soft to medium-hard materials. An alternative mining system must be configured for hard rock domains—for example, selecting a semimobile jaw crusher fed by trucks. The greater the presence of these difficult areas, the less amenable the project will be to IPCC, or at least fully mobile IPCC.
Is the company prepared to spend additional pre-strip capital? Before regular production operations take place, IPCC requires the construction of a box cut that creates the necessary space for the equipment, including crusher station, bench and connection conveyors, etc. The total rock movement associated with this excavation may represent a significant volume, and often necessitates the acquisition of additional mining equipment for this task. IPCC systems require the design of sufficient development ahead of production. The result of missing this relevant point may cause a severe impact on mining production. Minimum working space ranges from 100–300 m.
Are the people skilled in running a complex system? IPCC requires a robust operational control system. This can only be achieved if effective personnel are hired and intensive training programs are created. As IPCC is highly vulnerable to uncertainties, special care must be taken to set up a geological control system with the ability to anticipate changes of the rock properties that may compromise mine planning and operations. Geology, mine planning and operations supervision should be well-aligned and integrated with the IPCC requirements.
Equipment innovations continue to bolster IPCC’s appeal. Shown here is Metso’s Lokolink mobile conveying system, which comprises two to three conveyor modules and a discharge hopper. A Metso Lokotrack primary crusher supplies electric power for the conveyors and hydraulics.
To delve a bit deeper into the topic, E&MJ asked Paulo Laymen, a consultant in Snowden’s Belo Horizonte, Brazil, office, to comment on some of the broader trends and issues associated with IPCC.
E&MJ: In what ways, if any, do you think the industry’s trend toward autonomous truck fleets, measured against its rising interest in continuous mining technology, might affect customer interest in IPCC applications?
Most of the advantages/applications of autonomous trucks coincide with those associated with traditional T&S; i.e., short cycle times, relatively modest working space, high vertical advance rates and relatively flexible haul circuits (compared with IPCC), and absence of issues regarding hard material distribution and blending capacity. By contrast, IPCC can potentially improve a mine where cycles times are higher than25 minutes, and annual rock movement exceeds 30 million mt/y. Therefore, it can be concluded that each system has its natural field of application, depending on the particular orebody/mine configuration.
E&MJ: Has there recently been, or do you anticipate, any sort of breakthrough technological advance(s) that contribute to IPCC performance and reliability?
The lack of flexibility of IPCC historically limited its applicability to homogeneous and flat deposits (coal, phosphate, limestone, etc.). Over the last decade, OEMs have worked hard to improve IPCC performance and broaden its field of application to other ore deposits (iron ore, copper) through the introduction of new technologies that reduce downtime and increase operational flexibility with regard to mine geometry and geology. Examples of this include:
- Design of a new generation of crushers (sizers, hybrid crushers) that are able to process a wide variety of rock materials, hard and soft;
- Design of mobile crushers that may be directly fed by mining trucks, avoiding further rehandling through a loader;
- Introduction of intermediate material handling equipment, which allows multibench mining and other configurations;
- High angle/radius conveyors to overcome awkward geometries;
- Mine planning and simulation software that provides the mining engineer with efficient analytical tools; and
- Advanced reconciliation and grade control systems, which assist the mine operator to improve its mining processes.
E&MJ: What type of site/deposit characteristics are most amenable to IPCC? Do weather and environmental conditions have a similar effect on IPCC operations that they have on conventional truck/shovel operations?
The success of an IPCC system relies on planning repetitive standard operations. Any topographic or geological variations may be detrimental to productivity of the IPCC system. This is the main reason why IPCC methods have been traditionally applied to massive homogeneous deposits having large lateral dimensions, flat geometry and a limited number of rock types.
In general, IPCC is less vulnerable to bad weather conditions than T&S, as these systems are generally made up of track-type components. However, caution should be advised under some circumstances; for instance, when a crusher station is to be relocated under unfavorable conditions, planning the relocation to coincide with the dry season. Also, special attention must be paid to waste dumping operations with spreaders in the presence of mixed unstable wet and dry materials—it’s necessary to encapsulate the wet with dry material.
E&MJ: One of the concerns voiced about IPCC is, if the system goes down, production stops dead. What is your view of the real, overall track record of major IPCC installations as far as availability? Are there ways to minimize the possibility of major downtime, perhaps through design strategies or proper maintenance approaches, for example?
There are inherent downtimes associated with IPCC systems: crusher station relocations, face and dump conveyor shifts, maintenance, etc. On average, a fully mobile IPCC line may effectively operate 4,300–4,800 hours per year, depending on the specific circumstances of each mine. Obviously, it is possible to reach more than 5,000 hours but, only under exceptional situations that are not relevant for planning purposes.
While a constantly improving maintenance structure is always desirable, mine planning is the most influential parameter in maintaining downtimes at reasonable levels. In this regard, a sound mine plan for IPCC should be configured in such a way that vertical advance rates do not imply an excessive number of crusher relocations per year. As a result, it is important to design large pushbacks that ensure a bench mining sequence. Thus, it is highly recommended to identify which areas are amenable for IPCC and which are not. As the success of IPCC relies on planning repetitive standard operations, it is extremely important to simulate the IPCC operating activities to validate the long-term sequence.
E&MJ: In today’s financial environment, producers moving ahead on new projects and expansions seem to fall into two camps: those looking for a low-risk, quick ROI project implementation strategy, and those that want to reduce operating costs while settling in for the long run. Can IPCC offer benefits to both?
IPCC requires a high initial capital expenditure, which implies a long-life operation in order to take advantage of the reduced opex. Usually, at least five to six years of operation is required to pay back the initial investment. Commodities prices are expected to stay weak for a long period of time with mining companies struggling to reduce their operating costs and market risk exposure. To remain competitive, mining companies will find IPCC an attractive alternative as a result of its low opex profile. Also, it is important to mention that IPCC brings some benefits in terms of CO2 emissions and hazard impact.
E&MJ also spoke with Thomas Gramling, managing director and executive vice president for Tenova TAKRAF Mining & Minerals in Denver, Colorado. TAKRAF is a well-known provider of high-volume bulk materials handling solutions and has installed IPCC systems at Rio Tinto’s Kennecott Copper operation in Utah, USA; Goldcorp’s Peñasquito mine, Mexico’s largest gold producer; and the Buenavista del Cobre copper mine operated by Southern Copper Corp. in the Mexican state of Sonora.
Acknowledging that the global industry is currently in a “holding pattern” for launching new mine projects, he pointed out that mine operators are also intent upon making their existing and future projects more efficient—and that opens avenues for IPCC implementation. These include possible installations at projects with material-handling requirements below the volume baseline threshold previously considered necessary for IPCC operations in the past, and application of IPCC technology to waste handling systems as well as ore transport.
Gramling said TAKRAF sees opportunities to help operators improve IPCC system performance through standardization—in both system control protocol and component commonality. “Our field personnel are constantly helping our customers solve PLC-HMI interface issues for better efficiency. And, we prefer when specifying parts to maintain a high level of interchangeability throughout our systems,” he noted.
He also noted that junior mining companies—not typically regarded as prime IPCC customers—are willing to consider the concept for their greenfield projects. “We’ve been involved in IPCC for almost four decades and we can provide access to knowledge and experience that juniors may not have in this technology. When we talk to them about the opportunities to bring automation, increased safety and faster ROI to their projects through IPCC, they are receptive,” said Gramling. “In the past, IPCC was considered mainly for operations with throughput requirements in the 100,000-ton-per-day and higher range. We can show that lower volume operations—down to perhaps 80,000 tons per day—can benefit as well.
“It also helps that IPCC productivity and reliability are steadily growing,” he continued. “Our recent IPCC projects almost always involve capacity increases, with more material being transported over longer distances. In general, we’re seeing demand for more powerful conveyor systems, with larger components driving longer and stronger belts. Consequently, crusher plant designs have had to improve, scalping technology is being put to better use to increase crusher throughput, and gearless drives for conveyors offer a number of advantages. In recent years, we’ve been able to employ high-powered DEM (Discrete Element Modeling) software, particularly to improve crusher performance.”
Mark Erickson, TAKRAF’s director of mineral processing, added, “Realizing that there are still applications and opportunities for double roll crushers and sizers as part of both IPCC and conventional crushing applications, TAKRAF has developed innovations for both double roll crushers and mineral sizers, including a modular design for the crushing elements that allows these crushing elements to be removed and replaced in-situ, without the need for complete disassembly of the units. Innovations such as these improve the operating time and decrease the operating costs as a result.”
“There are always going to be mine operators that understand and feel more comfortable running a truck fleet, and in the future they would probably choose to increase efficiency by going to autonomous operations,” Gramling said. “The way IPCC can compete with that mindset is simply by providing data. We have a lot of favorable capex and opex information to offer from our past projects, and we stand behind it. And, we always can point out that unless the trucks are hauling something back to the mine—which is unlikely—truck fleets can only offer 50% availability.”
From the Beginning
Although there is no hard and fast rule preventing an existing T&S operation from being converted to an IPCC setup, industry experts generally agree that in order to wring the highest efficiency from an IPCC operation, the mine should be planned and designed for IPCC from the beginning. Even with that approach in mind, it can still be challenging to pinpoint the exact configuration of an optimal IPCC setup without a great deal of study, particularly in the early stages of a project when mineral resources and economic parameters are subject to change.
A good example is Iron Road Ltd.’s flagship project, the Central Eyre Iron Project (CEIP) located on the Eyre Peninsula, about 330 km northwest of Adelaide, South Australia. Iron Road, an ASX listed company, is focused on the development of magnetite gneiss iron ore deposits in South Australia and claims the Iron Road deposit contains the largest measured-plus-indicated magnetite mineral resource in Australia.
In 2014, Iron Road reported that CEIP had a JORC-compliant total mineral resource of 3.7 billion mt at 16% Fe. In its first quarter 2015 report, the company announced that it recently had been able to add another 819 million mt in mineral resources to the project, increasing its inventory from 3.7 billion mt to 4.5 billion mt. The measured and indicated categories now make up 3.5 billion mt or 77% of the overall mineral resource estimate.
The project’s Definitive Feasibility Study confirmed the commercial case for a mining, beneficiation and infrastructure solution with production of 21.5 million mt/y of premium iron concentrates for export over a projected 25-plus-year mine life. The recently added mineral resources, plus a nearly completed optimization study, may allow the company to expand annual output to 24 million mt/y of concentrates—or even more and with a longer LOM, if planned future drilling programs delineate additional resources.
Almost from the beginning, Iron Road gave serious consideration to making CEIP a fully IPCC operation. It had originally commissioned a consulting firm to explore the viability of an owner-operated, conventional truck-and-shovel approach, but quickly determined that it wouldn’t be the optimal method. The company then focused on a plan that would transition to IPCC after three years of conventional truck-and-shovel mining. The original concept involved semimobile, in-pit gyratory crusher stations that would be moved every two years—taking 14 days for relocation—along with conveyor-system reconfiguration on a quarterly basis—each a 36-hour process. Some of the main advantages of this approach included:
- Being well suited to CEIP’s site characteristics at the time.
- Having an open-pit design optimized for electrically powered Hybrid-IPCC. (Longterm plans call for two pits, the largest measuring 6.5 x 1.2 km.)
- Reduced mining fleet, lower operational manning requirements, and less diesel and consumables expenditures.
- Less infrastructure and logistical support requirements.
- Persistent life-of-mine savings.
However, encouraged by the prospect of achieving even better long-term results, Iron Road engaged the Thiess RWE joint venture (TRWE) to complete an updated detailed mining model, building upon the original detailed work undertaken as part of the Definitive Feasibility Study. This study has included a detailed examination of the benefits that could be achieved by redesigning the pit shell and implementing a IPCC system employing mobile crushers that would be fed by mining shovels or wheel loaders. The advantages of this approach over the semimobile IPCC plan include:
- No significant crusher relocation downtime, as the mobile crushers will advance in concert with the shovels.
- Most of the originally envisaged 32 x 360-mt mobile fleet would not be required.
- Mining operating personnel needs could be further reduced by up to 100.
- The size of the mine fleet workshop can be reduced.
- Diesel consumption reduced from 150,000 liters to 30,000 liters per day.
- A fully modularized solution.
An Iron Road analysis of the fleet size and costs associated with conventional truck-and-shovel, semimobile IPCC and fully mobile IPCC systems shows the following comparisons:
- Conventional loading and haulage would involve 93,350-ton-payload haul trucks, an estimated 1,150 employees, estimated capex of US$1.35 billion and opex of $37.30/dmt.
- Semimobile IPCC would reduce truck fleet size to 32,350-ton haulers, require only 350 employees, and entail capex of just $480 million, with opex of $28.50/dmt.
- IPCC with mobile crushers would further reduce the haulage fleet to 12,350-ton trucks and just 250 employees.
Associated capex and opex figures will be determined by the optimization study currently under way.
In its latest quarterly report, Iron Road said that work is continuing at CEIP to further define development and operating structures that will facilitate strategic investment interest and the arrangement of project finance. Current plans target startup of production in 2018.