In mining operations, the layout of crushing plants and ancillary equipment and structures is a crucial factor in meeting production requirements while keeping capital and operational costs to a minimum.

1. Introduction

The primary objective in crafting a crushing plant design is to create an installation that not only fulfils the necessary production criteria but also operates efficiently at a competitive cost while complying with stringent environmental regulations. Additionally, it should be feasible to construct at a reasonable price, considering the escalating expenses associated with equipment, energy, and construction labour.

The design process involves three key phases: process design, equipment selection, and layout. While the first two phases are determined by production requisites and design parameters, the layout can be influenced by input, preferences, and operational insights from various stakeholders. These stakeholders may include the owner’s engineering team, safety personnel, operations and maintenance staff, equipment manufacturers, and the consulting engineer. Ideally, the consultant should leverage their knowledge and expertise to comprehend the unique requirements of all parties involved and deliver a well-balanced, practical, secure, and cost-effective plant design.    

2. Design Parameters

The principal design parameters that drive crushing plant selection and configuration include:

  • Production requirements 
  • Capital cost
  • Ore characteristics 
  • Safety and environment
  • Project location 
  • Life of the plant/expansion plans
  • Operational considerations 
  • Maintenance requirements
  • Climatic conditions

2.1 Production Requirements

Typical production requirements are summarized in the below table.

Table 1: Production Requirements

2.2 Investment Cost

It’s necessary therefore to estimate crusher installation costs based on equipment costs plus the following direct costs, including construction costs:

  • Earthworks
  • Concrete
  • Structural steel
  • Architectural
  • Mechanical
  • Electrical
  • Instrumentation

Apart from the above direct costs, indirect costs can fall within a range of 40 to 60% of the direct costs, and

Include:

  • Construction indirects 
  • Start up and commissioning
  • Construction equipment Freight
  • Spare parts
  • Taxes / duties
  • Engineering, procurement 
  • Owner’s costs (relocation, hiring and training construction management (EPCM) personnel, permits, licensing fees, etc).

Furthermore, apart from these considerations, it is essential to allocate a contingency fund to account for unexpected expenses. This contingency fund typically falls within the range of 10 to 20% of the total of both direct and indirect costs. The designer needs to have a comprehensive understanding of the project’s unique cost components. 

2.3 Ore Characteristics

The nature of the ore plays a pivotal role in both the selection of crushers and the overall plant design. Dry ores necessitate more extensive measures for controlling and collecting dust, such as the installation of dust enclosures around screens, sealing conveyor skirts, and implementing vacuum and wash-down systems. On the other hand, wet and adhesive ores can lead to issues like chute blockages, reduced surge capacity, and decreased storage capacity in bins and silos.

To tackle these challenges, it is crucial to ensure that chutes are readily accessible for cleaning, and that bins, silos, and tunnels feature ample feeder openings. If obtaining representative ore samples is feasible, it is advisable to conduct test work to determine the flow properties of the ore, as these properties will have an impact on the design parameters.

In most mining operations, the characteristics of the ore change over time, and it can be expensive to incorporate the ideal flexibility needed to accommodate these changes. Some owners may insist on minimizing the initial capital investment, with design adjustments financed from the operating budget. However, achieving this balance is not always straightforward.

2.4 Safety and Environment

Safety considerations are a fundamental aspect of designing mining facilities. Crushing plants are required to adhere to local and national regulations all over the World. 

In modern mining plants, safety measures include the installation of protective guards around all moving equipment and the placement of emergency pull-cords on both sides of conveyors with personnel access. It is the responsibility of the maintenance department and the safety officer to ensure that these safety precautions are properly maintained. Continuous safety training for plant personnel is of paramount importance and is closely monitored in most mining operations.

Dust emissions must comply with the latest regulations applicable to the jurisdiction. Designers must account for the incorporation of equipment for dust containment, suppression, or collection. Efforts should be made to minimize spillages from feeders, chutes, and conveyors. Spill collection can be integrated into feeder installations, chute designs can be optimized to reduce spillage at receiving and discharge points, and conveyor belts can be widened to allow for more flexibility, such as reducing the back-to-back width of skirting to enable the belt to travel more freely. Skirting should extend at least three belt widths past the load point. While standard rules for conveyor and load point design provide guidance, custom-designed transfers are often necessary to suit specific project requirements. It’s worth noting that clean plants tend to have lower operating costs.

Crushers, screens, and dust collection fans can contribute to elevated noise levels. Air-cooled lubrication systems not only generate noise but may also experience oil leaks. Well-balanced, choke-fed crushers, enclosed screens, and dust collector fans equipped with silencers can help maintain acceptable noise levels. Recirculating water can be employed to cool crusher lubrication systems.

2.5 Project Location

The design of a crusher plant can be significantly influenced by various factors related to the project’s location, topography, geotechnical conditions, remoteness, and climate.

Construction costs tend to be notably higher in areas with high altitudes, cold climates, and remote sites. To enhance the economic viability of projects in such locations, modular and pre-assembled structures and plant facilities are often constructed off-site and then transported to the final location. Local labour costs play a significant role in determining the most cost-effective construction materials for a given region. For example, building concrete structures is much more affordable in Mexico compared to Alaska.

Remote projects may face challenges in obtaining spare parts on short notice. Therefore, crushing plant designs should include provisions for laydown areas and workspace for on-site equipment refurbishment and repair. Whenever possible, equipment manufacturers should be encouraged to maintain and supply spare parts in close proximity to the mining operation.

Having access to sound geotechnical information is crucial for selecting the location and designing the layout of a crushing plant. Establishing a primary crushing plant on solid rock can reduce costs associated with concrete and structural steel, providing a more cost-effective solution.

2.6 Life of the plant/expansion plans

The anticipated lifespan of a mine is a critical factor in the design of any crushing plant. For long-term operations with a duration of three to eight years, a meticulous approach to design, layout, and construction is essential. Given that the structure and enclosure of the crushing plant can often constitute the most significant single cost component in a primary crushing facility, it is imperative to tailor these structural and construction costs to match the projected mine life. 

For short-term operations, mobile crushers might be the most suitable choice, as it allows for equipment relocation and reuse. In contrast, long-life mines might find it more cost-effective to employ large concrete structures with fully insulated enclosures. In trade-off studies, short-term operations should prioritize lower capital costs, while long-life installations should focus on minimizing operational costs and enhancing ease of maintenance. 

Planning for expansion is a key consideration in nearly all mining operations, except for the very shortest-lived ones. Even at mines with projected lifespans of only five or six years, it may be necessary to select equipment capable of handling expected increases in throughput. Incorporating expansion plans for most crushing plants during the early planning stages is typically more cost-effective than waiting until the mine is operational before deciding to expand.

Operators are increasingly seeking ways to enhance the throughput of primary crushers, particularly when incorporating larger trucks into their mine planning or operations. 

2.7 Operational Considerations

Designers should prioritize simplicity and cost-effectiveness in their designs to make the plant easy and economical to operate. Many modifications and additions to the plant can be justified by the resulting reductions in operating costs.

Operation rooms should be designed to offer a comfortable, well-ventilated workspace, with access to portable water and nearby toilet facilities. Operators should have clear visibility of all the main components of the crushing facility under their control. This can be achieved through both direct sightlines and the use of TV cameras and monitors.

While it’s challenging to completely eliminate spills, the plant layout should be designed to facilitate swift and efficient clean up. Adequate provisions should be made for appropriate plant cleaning equipment.Wash-down hoses should be carefully located throughout the plant. Sufficient water pressure should be available to clean hard-to-reach areas. Some operators regularly wash down their crushing plants from top to bottom to prevent dust build up on structural steel and equipment, which tends to disperse throughout the plant during operation.

Conveyors should be positioned at a sufficient height above the floor to allow for access to spillage with shovels or plows.

Crushers, chutes, and belts are prone to extensive wear, and their wear parts and plates can be quite heavy. To facilitate maintenance, designers should aim to keep the weight of replacement parts, which must be manually handled. Providing monorails and hoists can greatly assist in the ease of maintenance.

2.8 Maintenance Requirements

To meet their production goals, the plants should be designed for easy access and maintainability. Reducing maintenance requirements to a minimum is key to achieving higher overall operating availability.

Scheduled preventive maintenance at crushing plants requires several crucial actions, including:

  • Replacement of crusher wear parts.
  • Replacement of feeder wear parts.
  • Maintenance of oil and lubrication systems.
  • Regular visual inspections.
  • Maintenance of screen decks.
  • Adjustment of conveyor skirting.
  • Repair of conveyor belts.
  • Electrical and instrumentation adjustments.

Design considerations should include provisions for overhead cranes to facilitate the removal and replacement of crusher wear parts. Adequate supports should be provided for gyratory and conveyor main shafts, and laydown space for cone crusher bowls is essential. Some operators maintain a complete spare screen for major screen maintenance. Trolleys, jib cranes, and pull points should be integrated into the design to make equipment maintenance more straightforward. Oil and lubrication systems should be centralized and designed for easy automatic changes, with well-ventilated centralized lubrication rooms whenever possible. For instance, a line of fine cone crushers should have a central oil receiving area with piping to and from each crusher’s lube package to enable quick and easy oil changes.

Efforts should be made to design conveyor head chutes for easy access, not just through an inspection door but through a man door in the chute itself. Conveyor belt change areas should be provided, and maintenance personnel should have clear visual and rapid access to screen decks for panel replacement.

Collaboration with screen manufacturers is essential to ensure that covers allow for effective access when working on screens. Screening facilities must meet strict dust emission requirements, but many off-the-shelf screen dust covers may not adequately comply with these regulations. Custom-designed covers may be necessary to minimize emissions and provide convenient access to the screen.

2.9 Climatic Conditions

Designing a crushing plant for cold-weather operations or in a desert environment presents unique challenges, particularly when the plant needs to operate year-round. 

Seasonal variations can significantly impact the moisture content of the ore, necessitating adaptability in the crushing plant’s design to accommodate changing material flow characteristics. Higher moisture levels may require steeper angles of withdrawal, and stone-boxes should be designed to prevent clogging. The equipment within the crushing plant must also be adjustable to cope with climatic changes. For instance, screen decks can be designed to maintain production by using wire mesh during the wet season and plastic during the dry season. The choice of screen deck types can be tailored to the seasons and material characteristics to maximize material throughput through the deck openings.

The local climate also influences the type of plant enclosures required. In milder weather climates or desert areas, many crushers are installed with an open face and may not have any enclosures at all. The design of plant structures and enclosures should align with the specific climate conditions and operational requirements of the site.

3. Conclusion

A well-designed plant layout is crucial for striking a balance between capitals and operating costs over the life of a mine. Buildings, infrastructure, and major equipment components represent the primary cost elements of a crushing plant. The designer’s task is to create a layout that aligns with the design criteria, flow sheet, and selected equipment in the most cost-effective configuration. Keeping structural costs low, focusing on ease of maintenance and operation, and incorporating best practices and advancements in fabrication and erection are essential. Input from an experienced mining plant structural engineer can be highly valuable in this process.

Although crushing circuits and ancillaries have seen relatively few changes over the years, the principle of “Keep It Simple” remains a sound strategy when designing a plant. Some may wonder why the design of head chutes has remained largely unchanged for decades, but the reason is straightforward: the traditional, proven methods continue to deliver the best results. However, it’s crucial not to assume that a layout that works well at one mine will be equally effective, or even viable, at another.

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