crushing plant ABSTRACT
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. This paper addresses the critical design parameters as well as the consideration of ore characteristics, geographical location, climatic conditions, expected operational life, expansion potential, safety, environment, and operability and maintainability.
Crushing Plant INTRODUCTION
The fundamental goal for the design of a crushing plant is an installation that meets the required production requirements, operates at competitive cost, complies with today’s tough environmental regulations, and can be built at a reasonable price despite the rising costs of equipment, energy and construction labor. The following industry trends must be taken into account:
Equipment suppliers are offering ever-larger primary crushers , with 1,800 mm (72 in) gyratories expected soon, as well as secondary and tertiary machines of up to 3,000 mm (120 in).
• Rising energy costs are causing owners to increase the integration of mine and mill design, so that they can identify ways of reducing overall electrical power consumption.
• Electronic control of crusher discharge opening and feed rate. With adjustment of a crusher’s discharge opening, as the production continues through an on- line coarse size analysis of the crushed product (digital image analyses). Dance, A. 2001)• More attention is being paid to the impact on crushing circuit design caused by variations in ore characteristics, size distribution, moisture content, ore grade and climatic conditions.
• Operators have always dreamed of reducing the need for crushing equipment; when SAG mills were first introduced, it was hoped that they would eliminate secondary and tertiary circuits. As it turned out, designers are now adding secondary or pebble crushers to SAG circuits, on both greenfield and retrofit projects, to increase feed rate to the SAG mill. In other words, crushing plants, from primary to quaternary circuits, are here to stay.
There are three main steps in designing a good crushing plant: process design, equipment selection, and layout. The first two are dictated by production requirements and design parameters, but the layout can reflect the input, preferences and operational experience of a number of parties.
These can include the owner’s engineering staff, safety personnel, operations and maintenance personnel, equipment manufacturers, and the engineering consultant. Ideally, the consultant combines his knowledge and experience with an understanding of all parties’ needs, to provide a balanced, workable, safe and economic plant design.
Capital Cost
Direct Costs. The largest primary gyratory crushers cost US $2 million or more, while overall crushing plant costs can be as high as $18 million. It’s necessary therefore to estimate crusher installation costs based on equipment costs plus the following direct costs, including construction contractor indirects:
• Earthworks • Mechanical • Concrete • Electrical • Structural steel • Instrumentation. • Architectural
Indirect Costs. Indirect costs can fall within a range of 40 to 60% of the direct costs, and include:
• Construction indirects • Startup and commissioning • Construction equipment • Freight • Spare parts/first fill • Taxes/duties
• Engineering, procurement and construction management (EPCM) • Owner’s costs (relocation, hiring and training personnel, permits, licensing fees, etc).
In addition to the above, a contingency to cover unforeseen costs will be in the range of 10 to 20% of the sum of the direct and indirect costs. The designer must be aware of the project-specific costs of all such elements, so that he can monitor costs and promote methods of reducing total installation costs. In some locations, for example, labor and material costs could make a gabion wall more expensive than a poured concrete wall, which has minimal structural backfill.
Ore Characteristics
Ore characteristics are a critical element in both crusher selection and plant design. Dry ores require greater provisions for dust suppression and collection, including dust enclosures around screens, sealing on conveyor skirts, and vacuum and wash-down systems. Wet, sticky ores can plug chutes, reduce surge capacity, and decrease the live storage capacity of bins and silos. To address this problem, chutes must be easily accessible for clean-up, and large feeder openings must be provided for bins, silos and tunnels. If it is practical to obtain representative ore samples, it is prudent to have testwork conducted to establish ore flow properties, which will influence design parameters.
At virtually all mines, ore characteristics change over time, and it can be costly to “design in” the optimal flexibility required to handle such changes. Some owners stipulate that initial capital investment be kept to a minimum, with design modifications paid for out of the operating budget. This is not always easy to achieve.
Safety and Environment
Safety must be designed into all mining facilities. North American mines must comply with local and national regulations such as OSHA, MSHA, the Mines Act and the WCB. The modern plant includes safety guards around all moving equipment, and emergency pull-cords on both sides of any conveyors with personnel access. The maintenance department and safety officer must keep these safeguards in working order. Ongoing safety training of plant personnel is imperative, and is considered to be one of the most vital and monitored feature of most mining operations.
Dust emissions must comply with the latest regulations for the jurisdiction. Designers must make provisions for the installation of dust abatement, suppression or collection equipment. Spillages from feeders, chutes and conveyors must be minimized. Spill collection can be “designed in” on feeder installations; chute designs can minimize spillage at receiving and discharge points; and conveyor belts can be widened to be more forgiving (e.g., skirting internal back-to-back width can be reduced to allow the belt more side travel.) Skirting should be extended a minimum of three belt widths past the load point. Rules for conveyor and load point design should be used for guidance only, with transfers custom-designed to suit a particular project. It goes without saying that clean plants have lower operating costs. Crushers, screens and dust-collection fans all contribute to high noise levels. Air-cooled lubrication systems are not only noisy, but often leak oil. Well-balanced, choke-fed crushers, dustenclosed screens and dust collector fans with silencers can keep noise levels under control. Recirculating water can be used to cool crusher lubrication systems.
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Crushing Plant Design and Layout Considerations
crushing plant ABSTRACT
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. This paper addresses the critical design parameters as well as the consideration of ore characteristics, geographical location, climatic conditions, expected operational life, expansion potential, safety, environment, and operability and maintainability.
Crushing Plant INTRODUCTION
The fundamental goal for the design of a crushing plant is an installation that meets the required production requirements, operates at competitive cost, complies with today’s tough environmental regulations, and can be built at a reasonable price despite the rising costs of equipment, energy and construction labor. The following industry trends must be taken into account:
Equipment suppliers are offering ever-larger primary crushers , with 1,800 mm (72 in) gyratories expected soon, as well as secondary and tertiary machines of up to 3,000 mm (120 in).
• Rising energy costs are causing owners to increase the integration of mine and mill design, so that they can identify ways of reducing overall electrical power consumption.
• Electronic control of crusher discharge opening and feed rate. With adjustment of a crusher’s discharge opening, as the production continues through an on- line coarse size analysis of the crushed product (digital image analyses). Dance, A. 2001)• More attention is being paid to the impact on crushing circuit design caused by variations in ore characteristics, size distribution, moisture content, ore grade and climatic conditions.
• Operators have always dreamed of reducing the need for crushing equipment; when SAG mills were first introduced, it was hoped that they would eliminate secondary and tertiary circuits. As it turned out, designers are now adding secondary or pebble crushers to SAG circuits, on both greenfield and retrofit projects, to increase feed rate to the SAG mill. In other words, crushing plants, from primary to quaternary circuits, are here to stay.
There are three main steps in designing a good crushing plant: process design, equipment selection, and layout. The first two are dictated by production requirements and design parameters, but the layout can reflect the input, preferences and operational experience of a number of parties.
These can include the owner’s engineering staff, safety personnel, operations and maintenance personnel, equipment manufacturers, and the engineering consultant. Ideally, the consultant combines his knowledge and experience with an understanding of all parties’ needs, to provide a balanced, workable, safe and economic plant design.
Capital Cost
Direct Costs. The largest primary gyratory crushers cost US $2 million or more, while overall crushing plant costs can be as high as $18 million. It’s necessary therefore to estimate crusher installation costs based on equipment costs plus the following direct costs, including construction contractor indirects:
• Earthworks • Mechanical • Concrete • Electrical • Structural steel • Instrumentation. • Architectural
Indirect Costs. Indirect costs can fall within a range of 40 to 60% of the direct costs, and include:
• Construction indirects • Startup and commissioning • Construction equipment • Freight • Spare parts/first fill • Taxes/duties
• Engineering, procurement and construction management (EPCM) • Owner’s costs (relocation, hiring and training personnel, permits, licensing fees, etc).
In addition to the above, a contingency to cover unforeseen costs will be in the range of 10 to 20% of the sum of the direct and indirect costs. The designer must be aware of the project-specific costs of all such elements, so that he can monitor costs and promote methods of reducing total installation costs. In some locations, for example, labor and material costs could make a gabion wall more expensive than a poured concrete wall, which has minimal structural backfill.
Ore Characteristics
Ore characteristics are a critical element in both crusher selection and plant design. Dry ores require greater provisions for dust suppression and collection, including dust enclosures around screens, sealing on conveyor skirts, and vacuum and wash-down systems. Wet, sticky ores can plug chutes, reduce surge capacity, and decrease the live storage capacity of bins and silos. To address this problem, chutes must be easily accessible for clean-up, and large feeder openings must be provided for bins, silos and tunnels. If it is practical to obtain representative ore samples, it is prudent to have testwork conducted to establish ore flow properties, which will influence design parameters.
At virtually all mines, ore characteristics change over time, and it can be costly to “design in” the optimal flexibility required to handle such changes. Some owners stipulate that initial capital investment be kept to a minimum, with design modifications paid for out of the operating budget. This is not always easy to achieve.
Safety and Environment
Safety must be designed into all mining facilities. North American mines must comply with local and national regulations such as OSHA, MSHA, the Mines Act and the WCB. The modern plant includes safety guards around all moving equipment, and emergency pull-cords on both sides of any conveyors with personnel access. The maintenance department and safety officer must keep these safeguards in working order. Ongoing safety training of plant personnel is imperative, and is considered to be one of the most vital and monitored feature of most mining operations.
Dust emissions must comply with the latest regulations for the jurisdiction. Designers must make provisions for the installation of dust abatement, suppression or collection equipment. Spillages from feeders, chutes and conveyors must be minimized. Spill collection can be “designed in” on feeder installations; chute designs can minimize spillage at receiving and discharge points; and conveyor belts can be widened to be more forgiving (e.g., skirting internal back-to-back width can be reduced to allow the belt more side travel.) Skirting should be extended a minimum of three belt widths past the load point. Rules for conveyor and load point design should be used for guidance only, with transfers custom-designed to suit a particular project. It goes without saying that clean plants have lower operating costs. Crushers, screens and dust-collection fans all contribute to high noise levels. Air-cooled lubrication systems are not only noisy, but often leak oil. Well-balanced, choke-fed crushers, dustenclosed screens and dust collector fans with silencers can keep noise levels under control. Recirculating water can be used to cool crusher lubrication systems.