The natural-gas production boom in North America and elsewhere has flared mining-industry interest in switching mobile equipment to LNG power

By Russell A. Carter, Managing Editor

In the era before off-road diesel engine emissions became a point of intense focus for regulatory agencies, fuel choices for large, production-fleet mining equipment were relatively simple for mine operators—mainly, "Do you have diesel, what does it cost, and when can you deliver?"

Even after the U.S. Environmental Protection Agency's early off-road diesel emissions standards and their European Union counterparts came into effect in the mid-1990s, operators' fuel concerns remained largely the same—quantity, availability and price. Fuel cleanliness was mostly an interesting topic of discussion in maintenance-shop lunchrooms and fuel sulphur content wasn't an operational concern for high-horsepower mining engines until more than a decade after the adoption of the Tier 1 standard in North America. Although subsequent Tier 2 standards imposed drastically lower emissions levels than Tier 1 for CO, NOX and particulate matter on off-road engines larger than 750 hp (560 kW), this class of engines was exempted from the even more stringent Tier 3 standards that were applied to less powerful diesels starting in 2006.

However, Tier 4 emissions-control standards for the high-horsepower off-road engines commonly used in mining changed the rules of the game significantly when they became effective in 2011, first as an 'interim' set of standards, followed by final standards in 2015. Engine manufacturers, who had largely been able to meet Tier 1, 2 and 3 standards by applying internal engine tweaks, had to develop design strategies that would allow new diesels to meet Tier 4's extremely low emissions levels without creating disruptive installation, operational and cost-related issues for their OEM and end-user customers. The advanced engine technologies required for Tier 4 compliance, among other things, put a premium on fuel cleanliness and sulphur content. Dirty, contaminated diesel fuel severely shortens the service life of injectors and other extremely fine-tolerance engine components, while previously acceptable fuel sulphur content levels are detrimental to specific emissions-control systems and components needed for Tier 4-level control.

These developments raised the ante for mine operators who need a new haulage fleet to commission a mine, for example, or want to repower to gain the benefits offered by the latest generation of high-horsepower diesels—scenarios that now would be accompanied by the cost of buying, properly storing and filtering the ultra-low-sulphur diesel (ULSD) fuel required by Tier 4-compliant engines. Even in less-regulated countries that don't yet enforce tight emissions standards, diesel-fuel availability and quality control pose problems for fleet operators running Tier 3 or older diesels. Fuel sulphur content in some regions can be as high as 10,000 ppm, compared with levels of about 3,000 ppm that were formerly common in industrialized nations—and 15 ppm in today's ULSD—and these high sulphur levels can shorten the life of certain components. Maintaining proper storage conditions may be difficult, leading to several forms of contamination. In addition, the price of diesel can fluctuate wildly from unpredictable events, despite the government subsidies found in many developing nations.

With fuel and lube costs typically accounting for 40% or more of a large surface mine's annual operating budget and many other operating costs currently on a steep upward climb, mine operators everywhere are anxious to find economical solutions for controlling fuel costs. Biodiesel is becoming a viable alternative in some applications (see sidebar), but even that more environmentally friendly fuel can present availability and storage problems of its own.

Suppose there was a fuel, available in abundant quantities in many global regions, that offered cost savings of 50% or more over diesel, and allowed dual-fuel operation while maintaining current engine performance levels? Too good to be true? Not at all, say a growing contingent of high-horsepower engine builders jumping on the liquefied natural gas (LNG) bandwagon.

Full Throttle on LNG
Just recently, Caterpillar became the latest to publicize its intentions to go full-bore on LNG engine development for mobile applications. Joel Feucht, Caterpillar's director of gas engine strategy for the energy and power systems businesses, made the announcement during his keynote address at HHP Summit 2012, a first-of-its-kind event that examined the economic and environmental benefits of using natural gas in high-horsepower applications.

"We have decided to go all-in on [natural] gas," said Feucht. "We are going to invest because we see a global market long term. Large engines are going gas. It's not debatable; it's our conclusion."

Feucht's remarks confirmed that Caterpillar will provide an LNG fuel option for engines across its many high-horsepower lines for mining, rail, construction and other applications. The company recently announced its first expected LNG-powered products will include large mining trucks and the locomotives produced by Electro-Motive Diesel (EMD), a unit of Caterpillar's Progress Rail Services.

"There is huge economic incentive to move to natural gas," Feucht said, noting the price of oil and gas are going to stay disconnected for the foreseeable future, thereby creating an economic incentive to use natural gas in fuel-hungry high-horsepower applications. Current users of natural gas to power high-horsepower equipment are realizing a cost savings of 30% to 50%, and new technologies expanding access, particularly in North America, have contributed to the expanding availability and decreasing cost of natural gas.

Erik Neandross, CEO of Gladstein, Neandross & Associates, which organized the High Horsepower Summit conference, estimates that a single mining truck could save about $500,000 annually by using LNG instead of diesel.

Although the prospect of using natural gas to fuel their trucks has had long-term appeal for many mine operators, until recently it's been an "if you build it, will they come?" type of situation for engine builders. At the MINExpo 2012 trade show held recently in Las Vegas, a product line manager for one of the major engine suppliers described the quandary: "Miners are always looking to be the first to try out new technology, but the second to pay for it."

However, that mindset appears to be changing. Tom Aubee, vice president for global energy at consulting firm Pace Global, which advises mining companies worldwide, noted that mine operators "…are saying to me 'Where can I buy a natural-gas haul truck?' They're ready to go."

Cat's public commitment to development of natural gas fueled mining engines came just a few months after it signed an agreement with Westport, a natural gas engine specialist, to co-develop natural gas technology for off-road equipment. Caterpillar and Westport will combine technologies and expertise, including Westport's High Pressure Direct Injection (HPDI) technology and Cat's off-road engine and machine product technology, to develop the natural gas fuel system. Caterpillar will fund the development program. When the products go to market, Westport expects to participate in the supply of key components.

And it's a sizable market, according to Westport's statistics: With almost 29,000 "units of interest"—in this case, haul trucks in the 100-ton-capacity range and above—in service around the world, and global diesel fuel consumption within that sector pegged at about 1.8 billion U.S. gallons per year, Westport has predicted that the total economic value of fuel cost savings involved in a massive switchover to natural gas from diesel would be in the range of $3.6 billion per year, assuming a $2/gallon savings of LNG energy equivalent over diesel.

"This is a significant opportunity that has the potential to transform important segments of the global off-road equipment industries," said David Demers, CEO of Westport. "We are working with the global leader in engines, locomotives and off-road equipment to develop an attractive natural gas offering for their customers."

"The substantial price difference between natural gas and diesel fuel is resulting in a strong financial incentive to enable off-road applications to take advantage of low natural gas energy costs without sacrificing operational performance," said Demers. "There is also a clear environmental incentive because of the reduced carbon emissions. Adding to the solid business case for this program is the potential to convert existing field units to natural gas—opening up a whole new market opportunity." While the agreements initially focus on engines used in mining trucks and locomotives, the companies will also develop natural gas technology for Caterpillar's other off-road engine lines.

"This agreement does more than pair two leaders in their respective industries," said Steve Fisher, vice president of Caterpillar's Large Power Systems Division. "Many of our customers are asking for natural-gas powered equipment in order to reap the financial and environmental benefits. The program positions Caterpillar to become the first manufacturer to bring HPDI technology to the high horsepower off-road market, offer the broadest product line of natural gas-fueled machines and equipment, and capitalize on the attractiveness of natural gas as an alternate mobile fuel—all within the shortest time frame for our customers."

Westport's HPDI system is based on a patented injector that simultaneously allows tightly controlled quantities of diesel fuel and large quantities of natural gas to be delivered at high pressure to the combustion chamber. The natural gas is injected at the end of the compression stroke. Natural gas requires a higher ignition temperature than diesel, so to assist with ignition, a small amount of diesel fuel is injected into the engine cylinder followed by the main natural gas fuel injection. The ignited diesel fuel acts as a pilot light.

HPDI allows replacement of approximately 95% of the diesel fuel (by energy) with natural gas, according to Westport, but efficiency remains roughly the same as a pure diesel engine. CO2 emissions are reduced by about 22%.

Development programs are under way at Caterpillar for both new and existing engines, combustion technology and fuel systems. According to Luis De Leon, Caterpillar vice president with responsibility for the Mining Products Division, work on LNG-powered Cat 793, 795 and 797 trucks is in the early stages, with commercial launch expected within five years.

In addition to offering new LNG products, Caterpillar and EMD are developing retrofit solutions for those who opt to convert existing mining trucks and locomotives to natural gas. Longer term, the company expects to use natural gas technologies in other mining products.

Designing for Dual-fuel Applications
Cummins also announced plans to produce dual-fuel engines for haul trucks. The first engine in the Cummins Dual Fuel portfolio for mining is the QSK60, with other QSK Series engines to follow, including engines capable of meeting EPA Tier 4 Final emissions standards. A release date will be announced in the coming months.

The QSK60, with output of 1,782–2,850 hp (1,329–2,125 kW), is currently available in standard and high-altitude configurations; according to Cummins, both versions will be capable of substantially reducing fuel costs with Cummins Dual Fuel technology.

Cummins said its Dual Fuel engines will use integrated controls that optimize the fuel-substitution rate based on operating conditions, and will seamlessly and automatically transition between diesel fuel and dual-fuel modes. Cummins Dual Fuel technology enables mining equipment to operate in 100% diesel fuel or in dual-fuel mode, giving the customer flexibility depending on natural gas availability at the mine site.

"The rapid expansion and abundance of natural gas in many areas of the world has driven a dramatic cost advantage of natural gas over diesel fuel. The ability to substitute diesel fuel with natural gas drives down the total cost of ownership of equipment," said Mark Levett, vice president–Cummins High-Horsepower Business.

"For operators of high-horsepower mining equipment where power density is critical and large quantities of fuel are burned, Cummins Dual Fuel technology provides an opportunity for a dramatic reduction in dollars spent on fuel while retaining the same power and durability customers have come to expect from Cummins diesel engines," said Levett.

In dual-fuel mode, the substitution rate, which is the percentage of natural gas relative to total fuel flow, is the critical parameter to fuel savings. In typical operating conditions, engines with Cummins Dual Fuel technology can be expected to deliver a maximum substitution rate of 70%.

David Geraghty, executive director–Cummins Mining Business, said, "Engines with Cummins Dual Fuel technology retain the same transient response as a diesel engine, remain on the same torque curve as a diesel engine, and match diesel engine power output while maintaining current service intervals. This technology not only delivers the uptime customers have come to expect from us, but also delivers a rapid return on investment, making it very attractive to mines around the world."

Tognum's MTU diesel group also is looking at dual-fuel engines for mining and other applications, but hasn't yet announced strategy details. According to Tognum America/MTU spokesman Gary Mason, "We've been seeing an increasing amount of interest from our customers in large, mobile, high-speed, natural gas-powered engines. MTU has years of experience with [natural] gas engines in the Onsite Energy business, and we are exploring and prioritizing opportunities to develop mobile gas engines primarily based on our MTU Series 4000 engine platform."

Ready for Retrofit
For operators that prefer not to wait for OEM dual-fuel solutions, Florida, USA-based GFS Corp. is offering aftermarket systems for some of the more popular models of haulage trucks. The company's Evo-MT 7930 system is available for Cat 793 series trucks and the Evo-MT 7770 for Cat 777 series. GFS has sold both types of systems to fleet operators in Wyoming and in the eastern U.S. coal districts.

According to the company, its systems are designed to be installed without major modifications to the chassis or drive engine of the truck, and allow trucks to run on diesel fuel alone in the event of a fault condition or low LNG fuel level. Truck haul capacity is maintained after the Evo-MT System is installed and engine power and torque output is maintained to OEM specifications.

"Our Evo-MT System is able to provide our customers with a 'here and now' solution that can be quickly and seamlessly adopted into their operations, making an immediate impact to the bottom line," GFS President Jason Green said when announcing the Evo-MT 7930's market introduction.

"We developed the Evo-MT System in direct response to our mining customers who have long sought a practical LNG retrofit option for large mine haul trucks," Green said, describing the product as a "smart, cost effective and sustainable natural gas solution."

GFS promises additional products for Caterpillar vehicles, as well as for Komatsu mine haul truck models, and says it is working on both mechanical and electric drive applications in the 100 to +300 ton class range.

Mid-range, LNG-powered Diesels Ahead
OEMs active in the heavy-duty, medium-horsepower off-road diesel sector are also moving ahead to develop dual-fuel engines. Late in 2011, Volvo Penta introduced a bi-fuel, 16-liter Tier 4 Interim engine that was initially targeted for applications in the North American oil and gas sector, but would be appropriate for mobile-equipment applications in other sectors such as mining. The new TWG1663GE, according to the company, provides fuel cost savings, high power density, and advanced SCR to meet Tier 4 Interim EPA and CARB emissions regulations.

In Volvo Penta's dual-fuel engine system, natural gas is introduced upstream from the turbo-chargers and an electronic air valve controls the amount of natural gas mixed with diesel fuel. Engine compression ignites the diesel fuel, which in turn ignites the natural gas. Bi-fuel blending and combustion control is integrated into the Volvo Engine Management System (EMS). Volvo Penta said its bi-fuel principle enables heavy-duty diesel engines to operate on ratios of up to 70% natural gas and 30% diesel fuel under normal loads, and slightly less natural gas during higher loads. The TWG1663GE can also run exclusively on diesel fuel.

The TWG1663GE also utilizes Volvo's Selective Catalytic Reduction (SCR) technology to reduce NOX and particulate emissions. According to Volvo Penta, the engine's emissions output meets EPA and CARB Tier 4i limits regardless of what proportion the engine blends the two fuels.  

Interestingly, Volvo Penta's SCR technology was a major factor in the agreement the Swedish engine builder entered into in 2011 with Sandvik Mining and Construction. Prior to the agreement, Sandvik had already introduced Volvo Penta engines in several models of its product lines for drilling rigs, loaders and haulers.

"Volvo Penta has been receptive to our requirements during the development and we are pleased with the engineering support they provide us," said Chris Jobburn, senior product support engineer at Sandvik M&C, noting that installing after-treatment systems had proven to be a major issue for many equipment suppliers—but not for Sandvik.

"This is just another regular engine installation," said Seppo Karhu, manager for engine installations at Sandvik M&C, referring to development of the company's first-ever loader with SCR for mining and tunnelling applications.

"With the SCR technology, ventilation rates become so low that it [exhaust is] no longer toxic emissions, but [now] CO2 or fuel consumption sets the limits—and the Volvo engines have low fuel consumption," said Olli Koivisto, global product line manager for Load and Haul.

Volvo Penta was one of the first engine manufacturers to receive stage 3B and Tier 4i certificates from the U.S. Mine Safety and Health Administration (MSHA) and Canada Center for Mineral and Energy Technology (CANMET) for one of its newest engines. Certification was awarded for its 13L Tier 4 interim model, and 'there are more to come,' according to the company.

Volvo said the 350–550-hp TAD1360/61/62/63/64/65VE-series of diesel engines offer a ventilation rate that is among the lowest in the industry for the power category—at about 30 cfm/hp, it is less than one-third the traditional rate of 100 cfm/hp commonly applied to diesel engines operating in underground mines today.

The rising interest in mobile mine equipment fuel-switching sparked by cheaper, more widely available natural gas has pushed another viable fuel—biodiesel—out of the limelight, at least for the time being. However, biodiesel remains an alternative to petrodiesel in many mining applications, and all of the major mining-engine suppliers have approved biodiesel, in various blend proportions, for use in their equipment.

In the underground mining sector, the potential harm caused by miners' exposure to diesel particulate matter (DPM) has long been a matter of concern to all involved—workers, mine operators and regulators. Following the recent announcement by the World Health Organization that, based on the results of a U.S. National Cancer Institute study of miners exposed to diesel exhaust emissions, WHO now regards those emissions as carcinogenic to humans and that level of concern has been elevated exponentially.

Underground mines currently can reduce worker exposure to DPM through a number of strategies: improving ventilation, using vehicles with specially sealed and pressurized cabs, improving maintenance, installing emission control devices, and using biodiesel. MSHA, for example, notes that a biodiesel blend of B35 (35% biodiesel, 65% petroleum diesel) or higher produced significantly lower DPM emissions than pure petrodiesel. Although anecdotal data seems to support the claim that biodiesel-fueled underground equipment poses less of a health risk to miners, there hasn't been a conclusive study that proves this assumption. That could change in the near future, however, as focus intensifies on understanding potential benefits of biofuel.

Biodiesel: Burning Brighter More Studies Ahead
For example, the National Institute for Occupational Safety and Health recently awarded a $1.4-million grant to the University of Arizona's College of Public Health and department of mining and geological engineering for a three-year project that will compare exposure and health effects of miners using diesel versus biodiesel-fueled underground mining equipment.

The study's results will have a dual purpose: Researchers want to determine the effects of biodiesel-blend fuels in the mining community, and also apply collected data to establish the beneficial or detrimental effects on members of the general population who are exposed to biodiesel-blend fuels.

"Exposures to diesel particulate in underground mining often exceed existing standards," said Dr. Jeff Burgess, the study's principal investigator. "Biodiesel blends are being employed to reduce these exposures, yet there is no information on whether this increases, decreases or fails to change the toxicity to miners of equipment emissions.

Biodiesel usage has a wider, and older, footprint in Europe but statistics show that the North American market is growing steadily. The EPA increased the amount of biodiesel products that must be blended into fuels in 2013 to 1.28 billion gallons, an increase from the prior threshold of 1 billion gallons. The U.S. Renewable Fuel Standard required biodiesel to be included in U.S. diesel fuel markets beginning in 2010. The level was set at 800 million gallons in 2011, the first full year compliance was required, before it was increased to 1 billion gallons in 2012. After that, the EPA is required to determine how much biodiesel must be blended annually.

Jon Scharingson, director of sales and marketing at Ames, Iowa, USA-based Renewable Energy Group (REG) told E&MJ that demand for biodiesel has grown steadily over the past two years. REG is a leading producer/marketer of biodiesel products, with annual production capacity of 215 million gallons/year from six plants located throughout the central U.S. According to Scharingson, REG sold 150 million gallons in 2011, and is on track to sell significantly more in 2012; its products are delivered to customers in 49 of the 50 states.

Scharingson said REG has established a market position in the underground mining sector in the U.S., largely based on the company's ability to demonstrate successful, uncomplicated use of various blends of biodiesel from B50 up to 100% in underground mining equipment, but also from corporate concerns about reducing worker health risks and the overall carbon footprint at mining operations. There also has been rising interest for biodiesel, in lower blend proportions, from mining companies interested in powering various types of surface equipment.

Using biodiesel in mines does pose some challenges. Like petrodiesel, certain biodiesel blends can gel in cold weather, particularly biodiesel derived from non-soy feedstock. Although most mining equipment operates underground where the temperature is consistently moderate, some mines store items of equipment above ground, subjected to more extreme conditions. When necessary, mines can overcome gelling with methods similar to those used for cold-sensitive chemicals. Methods include moving biodiesel trains or trucks into heated buildings, installing heaters for fuel line filters, using additives that reduce cold effects, and switching between blends seasonally.

Biodiesel refiners and distributors can assist users in controlling diesel gelling problems by recommending the proper product. REG, for example, offers three biodiesel products with different 'cloud point' ratings—cloud point refers to the temperature below which wax in diesel or biowax in biodiesels form a cloudy appearance. The presence of solidified waxes thickens the fuel and clogs fuel filters and injectors.

Engine and biodiesel suppliers are unanimous in emphasizing that, regardless of the biodiesel blend level selected, end users should be sure to verify with their fuel provider that the biodiesel blend meets ASTM D6751 (U.S.) standards or an equivalent specification. In the U.S., biodiesel users are strongly encouraged to purchase biodiesel blends from a BQ-9000 Certified Marketer and to source from a BQ-9000 Accredited Producer, as certified by the National Biodiesel Board.

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