A combination of economic pressures, technological advances and higher awareness of available options is driving the industry’s interest in saving kilowatts
|The correct choice of grinding mill gearbox lubricant can save an operator thousands of dollars a year per unit in energy reduction and unscheduled downtime costs.|
It’s obvious, even to a casual observer hearing a mile-long coal unit train rumble by or watching haul trucks climb out of a copper pit on a cable channel’s “world’s biggest” documentary, that mining is an energy-intensive industry. But its relationship with energy goes beyond the obvious—apart from being an energy customer, it’s also a supplier to the energy sector, providing fuels such as coal and uranium as well as the iron, copper, and other metals needed for production and generation; and it’s often an energy producer itself, building power facilities in remote locations where there simply is no energy infrastructure of any sort in place.
Mining, at any commercial-level scale, needs energy, and lots of it, but energy costs are rising. Estimates are that those costs currently represent about 15% of the total cost of production. Competition for energy supplies from other industry sectors, along with societal concern for resources and the environment, will no doubt drive future costs even higher. So, it’s not surprising that “energy efficiency” is becoming a popular refrain in mineral-industry corporate planning and reporting.
Working in the industry’s favor is the fact that energy efficiency is a relatively new philosophy for it, and opportunities abound for companies to take steps to increase efficiency in the areas of most concern to them. As excerpts from a 2012 study conducted by consulting company Accenture* pointed out: “Opportunities for energy savings in mining span the exploration, excavation and processing steps of operations. Specific to exploration, companies can use noninvasive technologies such as remote sensing and ground-based technologies to minimize exploratory digging and drilling.
“In the final step of processing materials…energy can be saved by properly sizing and maintaining motor systems, using premium-efficiency motors, and using adjustable speed drives in applications with varying load requirements,” the study noted.
In many instances, the maximum return on energy efficiency efforts will only be realized at new mines, where efficiency-improving equipment and technologies are baked into the project plan from inception. But there also are plenty of opportunities for incremental improvements that may yield other benefits.
As an example, ABB recently launched its SmartVentilation system for mines, described as a “complete solution” to the challenge of providing fresh air and venting toxic gases from underground mines. It also minimizes energy use by ventilating only those areas of a mine that require it. ABB estimates that this ability to work on-demand could reduce a mine’s electricity bill by as much as 50%.
The system is divided into three implementation levels—SmartBasic, SmartMid and SmartPerfect—providing an escalating level of control over the operation of the mine’s intake and exhaust fans. Mine operators have the option of installing one implementation level and upgrading later if necessary.
The system’s fans and drives are delivered in modular form and are controlled with ABB’s System 800xA industrial automation platform. This provides operators, engineers, and mine managers with an easy way to supervise and control ventilation from a central location or using mobile devices.
The volume of services and technologies that may offer similar energy-efficiency gains for other facets of mine operations is constantly expanding, and the scope of potential improvements available to mine operators extends far beyond the capabilities of a brief magazine article to thoroughly address. However, in an attempt to provide a micro-to-macro perspective on the possibilities, E&MJ invited two contributors to describe two very viable—but highly divergent—avenues to lower costs: At the micro level, how proper grease formulation and selection can save thousands of dollars in grinding energy costs; and at the macro end, how a mine-wide energy audit may enable an operator to significantly cut overall energy costs.
|When conducting energy-efficiency improvement projects, Klüber Lubrication uses power and energy analyzers, thermography analysis and other tools to make energy savings ‘visible.’|
LEVERAGING LUBRICATION TO CUT ENERGY COSTS
Daniel Narnhammer, head of global competence center–mining for Klüber Lubrication North America, provided the following example of savings that stand to be gained from the correct choice of grinding mill gearbox lubricant.
Narnhammer pointed out that equipment manufacturers are continually challenged to minimize operating costs by reducing maintenance expenses and service time, as well as improving efficiency of equipment. One immediate and cost-effective way to do so is by using high-quality lubricants in machinery and their components, such as gearboxes. Horizontal grinding mills with large open gears use multi-megawatt gearboxes to drive the pinion. These multistage planetary gearboxes often contain 500 liters or more of traditional mineral gear oils, which costs a few hundred dollars. The table below illustrates a comparison of mineral oil vs. a synthetic oil alternative.
By switching from a mineral oil to synthetic oil, an efficiency improvement of only 2% on a mill drive gearbox can result in a savings of more than $42,000 of energy costs in a given year. How can such savings be explained?By the coefficient of friction:
PAO or polyglycol-based synthetic oils have lower values compared to mineral oils; for example, 0.06µ for mineral oils vs. 0.03µ for polyglycols. By minimizing the friction between the tooth flanks and inside the bearings, the oil contributes to the overall effectiveness of the gearbox.
Additionally, friction losses result in elevated oil bath temperatures. Higher oil temperatures have a negative impact on oil service lifetime. According to the Arrhenius equation, a few degrees lower oil temperature can double the lifetime of the gear oil, which results in reduced disposal and maintenance costs.
Actually, the energy saving calculation isn’t that simple: load factors, churning losses, gear design and surrounding factors have to be considered. This results in a factor, which shows energy consumption per produced good. In the case of grinding mills, it is kWh/ton ore milled. This makes it possible to compare “apples to apples.” Klüber Lubrication uses power and energy analyzers, thermography analysis, and torque measurement devices to make the energy savings visible, as well as statistical methods according to international standards to eliminate influencing factors.
Klüber Lubrication started its energy efficiency program several years ago. Now with more than 100 energy efficiency projects conducted in different industries, they are confident to say: Energy saving projects are among those investments that pay off within a few months, generate quick savings and are not tied to large expenses in new equipment.
LESSONS FROM A MINE ENERGY AUDIT
Ruth Fain, senior environmental scientist, and Dave Mercer, energy and carbon lead at Golder Associates U.K., suggest that one of the best ways for mining companies to cut operating costs while also making operations more efficient, is to identify and eliminate sources of wasted energy. Operators are likely to benefit greatly from harnessing new technologies and energy efficiency measures that simultaneously reduce costs and energy demand.In the following paragraphs, they outline how Golder Associates addressed these concerns when performing an energy audit for one of its mining clients.
Fain and Mercer confirmed that, over the last few years, energy efficiency in mining technology has increased significantly. These advances offer solutions to some of the major challenges operators have historically faced. As a global environmental consultancy with a long history of working in the mining sector, Golder Associates is well positioned to share knowledge and design and implement changes bringing about real, bottom line benefits.
Golder was commissioned to undertake an energy audit and identify potential cost savings at a large mine in Central Asia. While mining at the site began during the first half of the 20th century, the processing plant itself had only been in operation since 2008, and some of the original mining machinery had been upgraded to more modern designs around the same time. The operator had already started to invest in the right places, but in fact, even with such new machinery, many additional savings could still be made.
The operation is huge; in 2011, the mine processed more than 700,000 metric tons (mt) of ore and a planned expansion at the time was focused on increasing production even further. To power these demanding targets, the operator used, and still uses, a combination of electricity from the local power supply grid, and diesel fuel for vehicles furnaces and boilers. On completing the energy audit, the Golder team identified several problems with the local energy supply, which meant that the site was not operating to its maximum potential. Accordingly, Golder provided a set of solutions that would reduce energy costs and increase energy efficiency across the site to support the expansion of mining operations within the existing energy infrastructure.
Grinding Through the Ice
The complex nature of the Central Asian site resulted in its electricity consumption approaching the local grid connection threshold, which meant electricity use was restricted. This is obviously problematic for a mine and was something that needed addressing immediately. The high levels of electrical consumption were partly due to a dewatering facility that was being operated outside of optimum parameters. Inconsistencies in the performance of the crushers were also identified, resulting in out-of-specification ore being delivered to the grinders. This affected their energy performance and the overall throughput of ore.
The energy demands were complicated further by environmental conditions at the site; much of the Eurasian Steppe is renowned for its highly variable and extreme climate. These conditions directly affect the energy intensity of ore processing operations, with significantly more electricity being used across the site in winter. Winter temperatures as low as –40°C can also result in ice forming within the ore, which adversely affects crushing and grinding operations. The crushers require more energy to process the frozen ore, and temperature effects on the machinery also reduce the volume of ore that can be processed during the winter months.
|As ore grades generally decline and haulage distances increase, measurement of haul-fleet fuel consumption becomes more important in any energy-efficiency improvement effort.|
Out With the Old, In With the New
To mitigate the high energy levels and overcome the extreme weather conditions, Golder proposed a series of solutions. For the grinding facilities, it recommended expert control systems for the ball mills rather than the pre-existing practice of loading mills with balls to 1 MW. This recommendation alone had the potential to save more than 820 MWh per year.
Similarly, savings were identified in a proposed new ventilation and lighting system planned by the operator. Taking a value engineering approach to the design, Golder presented an opportunity to implement newer and more advanced energy efficient systems with realistic payback periods. Golder proposed that variable speed drives and ventilation on demand (VOD) systems be installed in order to minimize waste during operational downtime, potentially saving up to 700 MWh per year. An identified reduction in the compressed air pressure to the leaching tanks was also recommended and predicted to save an additional 820 MWh per year.
The high level of diesel consumption was another factor that needed to be addressed. Invoices from the mine showed that diesel was acquired on long-term contracts and represented approximately 60% of the energy purchased in 2011. The mine, like many of its competitors, had in recent years witnessed a gradual increase in diesel consumption. This was due to the continuing decline in ore grades and the need to extract more ore to produce the same amount of mineral. Thus, the huge haul trucks that transport the ore and waste rock had to travel longer distances more frequently, which in turn burned more diesel.
On-site monitoring of diesel consumption at the mine, however, was poor and it was neither possible to predict the level of demand nor assess the performance of the processes that used diesel fuel. As a result, Golder suggested that the management replace the existing fuel meters with newer digital models with the ability to link up with their data systems. This, coupled with a more detailed study of dispensing options, was likely to result in an estimated savings of 5% per year.
Managerial, Not Just Technical
Managerial aspects are often just as important as the technical ones. It’s vital that all management personnel are provided with the essential knowledge and skills to help them understand the importance of good environmental practice, and that they appreciate their individual roles in ensuring compliance, and the business benefits it can bring.
At the Central Asian mine, Golder recommended the site management review their overall processes for energy budgeting and capital planning, and implemented systematic and transparent auditing processes with regular monitoring and reporting of progress toward energy improvement targets. Such reports ensure that energy management work is carefully followed up and can prevent an energy audit becoming a “flash in the pan” and instead carry through long-term operational benefits.
Making the Savings
The energy audit in Central Asia identified a range of technical and managerial improvements to energy efficiency for what initially appeared to be an up-to-date mine site. The findings significantly reduced the demand on a restricted electricity supply, allowing the operator to cut around 3% of the total energy costs.
No two mines are the same, but many of the principles around energy efficiency can be implemented to release much needed capital for other operational costs—a great benefit for any mining company. The lessons learned from the work in Kazakhstan can be transposed and implemented to many mines around the world.
* Sustainable Energy for All: Opportunities for the Global Metals and Mining Industry, 2012.