Among mining leaders, investors and technical specialists worldwide, there is a growing focus on improving energy management practices, as rising costs and concerns for security of supply impact mining revenue.
Energy is one of the largest costs at approximately 30% of total cash operating costs (Deloitte 2016). We know, too, that mine sites are responsible for a significant part of world energy usage. Estimates vary, with some as high as Manouchehri (2015) who considers mining accounts for 7% world energy use, with almost half from crushing and grinding (comminution).
Many regions are facing rising electricity costs. South African electricity prices rose by 9.4% last year. Chilean electricity prices are projected to increase significantly and Canada is also facing increases. Over 2016, Australia’s eastern states experienced a near 50% increase in electricity costs, and, according to the Australia Energy Council, more volatility is predicted.
Rising costs and supply issues are now impacting the bottom line. BHP Billiton recently incurred an unplanned US$105 million half-year cost at its Olympic Dam operations in South Australia, due to high electricity costs and supply disruptions, with planned expansions now at risk.
Compounding the challenges is an increase in the energy intensity of mining, but big inroads can be made by changing the way mines and their plants are managed.
Deloitte (2016) states that with an effective energy-management programme in place, energy consumption can be reduced by an estimated 15-20% in existing mines. It’s best to use a site-wide approach, incorporating production equipment, transport, power and plant. Smart power reticulation and management, including drawdown, power balancing and supply planning can optimise energy use. Energetics (2016 and 2017) cites three key elements:
Driving energy efficiency: It’s best to reduce your demand as much as possible through efficiency programmes. Achieving a predictable, consistent load profile, and classifying critical and non-critical load to support management strategies is vital. Also, shedding non-critical load can reduce idle generation capacity, and defer costly capital upgrades when energy supply is constrained.
Ensuring optimal power supply: While site reticulation systems are typically well designed, over time equipment is added and removed. This can result in poor power factor performance. If your power factor is low, this reduces the capacity of electricity supplied to the site to do work. Power factor improvement may include capacitor bank use and placement, and a load-flow analysis can quickly show improvement potential.
Negotiate the best energy supply contract: Energy is not necessarily a ‘fixed cost’ item. For on-grid sites there’s likely to be an energy contract you should review and charges can be negotiated. Off-grid sites often have contracts with generator companies. Negotiation points include guaranteed heat-rate performance, risk and reward arrangements, and peak period generation performance. Spinning reserve requirements can indicate idle generation capacity, with options to reduce the number of generators used under normal operating conditions.
This is possibly the greatest energy savings opportunity. In a 2017 study, University of Queensland professor Malcolm Powell confirmed the large capex reduction potential in energy efficiency measures. “If we drop the power consumption of a conventional style flowsheet by 40% in a large 3,000 t/h copper plant, this can save $800 million in capital cost of a new comminution circuit alone,” he said.
- High intensity selective blasting can improve comminution throughput and energy consumption;
- Pre-concentration using screening, ore sorting or gravity concentration can remove coarse, barren or low-grade material prior to comminution and concentration. This increases the grade of both mined ore and processed products, and reduces energy per tonne of metal produced;
- Dry comminution processes such as vertical shaft impact crushers, high pressure grinding rolls, and vertical roller mills produce less fine ores and therefore may reduce energy use;
- Stirred mills offer better energy efficiency than conventional ball mills for finer grinding;
- Better classification can reduce overgrinding and thus unnecessary energy consumption;
- Improved wear component design and methods can reduce downtime and increase productivity, increasing throughput over the life of mill liners;
- Intelligent decision-making based on big data analytics can increase throughput, reduce energy consumption and limit downtime;
- Modular, low-height circuit configurations can take plant closer to open-pit or underground mining to divert waste earlier, thus saving transport and process energy;
- Improving autogenous grinding through blast control and partial pre-crushing with pebble extraction can dramatically lower energy use;
- Coarse flotation technologies may enable grinding to coarser size, reducing grinding energy; and
- Novel comminution technologies may improve energy efficiency and liberation, with research showing potential through electrical breakage, microwave treatment and new comminution machines.
Tap into free resources
An independent, not-for-profit industry-funded organisation, CEEC (the Coalition for Energy-Efficient Comminution) promotes an informed debate on energy-efficient comminution through workshops, conference presentations, hosting relevant publications on its website, the annual award of the CEEC Medal, and other strategies.
For example, CEEC offers on its website free access to a powerful comminution benchmarking tool, which can be used by all levels within an organisation. These energy curves tools show where an operation’s comminution performance sits relative to others with comparable ores. The anonymous operating data, kindly supplied by mining companies worldwide, provides a benchmark capturing almost 60% of global copper production, over 30% global of gold production, and smaller (though growing) proportions of other metals. Planned and actual improvements can be plotted, and CEEC will soon enhance the energy tools even further with funding enabled through CEEC’s minerals industry sponsors and the METS Ignited Project Fund.
Barrick has used the CEEC Energy Curves to identify, prioritise and implement changes resulting in 61 million kWh energy savings for US$5 million cost savings per year.
What are the gains?
Energy costs are on the rise. Access and supply is a risk for many miners. A planned approach to reducing your site’s exposure requires an understanding of where energy dollars are spent and the areas in which efficiencies can be achieved.
Such projects not only deliver cost reductions, they also lead to co-benefits such as lower labour, maintenance and capital costs.
With crushing and grinding usually the largest consumer of energy at hard-rock mine sites, improving energy use in comminution is a key area of opportunity which must be exploited.
Learn more at www.ceecthefuture.org/ Go to CEEC News “Energy Management Options for Miners” for more details, examples and references cited in this article