Diesel has long been the fuel of choice for powering mobile mine equipment because of its availability and familiarity, plus the lack of viable alternatives for most haulage applications. Over the past half-decade or so, however, emerging technologies, abundant supplies and low prices for natural gas have expanded the short list of fuel options to include NG in either compressed (CNG) or liquid (LNG) form. Now, with the price of a barrel of oil dropping recently to levels not seen since 2003, mine operators may be faced with an interesting decision-making process going forward: Which of the two fuel choices will best enable them to meet cost and production targets while minimizing current and future environmental, safety and health risks?
Natural gas-fueled haulage vehicles, if published projections of cost savings and environmental advantages turn out to be correct, can meet typical mines’ operational demands without adverse effect on machine performance and maintenance — all it takes is money, for acquisition of dual-fuel conversion kits, refueling facilities, and gas delivery and storage arrangements. In today’s financial environment, money for facility upgrades such as these can itself be a scarce commodity and operators may decide that diesel fuel is the best choice, even when measured against probable requirements for ultra-low sulfur content, better storage and filtration practices to meet the demands of the latest engine designs, and increasingly stringent emissions-related environmental regulations and standards.
Economic factors made 2015 a tough year in many respects for off-highway natural-gas technology developers and advocates, due to slumping haul truck sales, shrinking financial flexibility for mine operators, and cost pressure from lower petroleum prices. Even so, fleet operators continue to register awareness of the prospective long-term benefits of natural gas, along with original equipment manufacturers (OEMs) interested in expanding their product offerings to meet potential future demand. Here are some of the latest developments.
Teck’s Test: A First in Canada
For mine operators with access to natural gas supplies, or that may have business partners willing and able to provide gas, the decision to convert to LNG or dual-fuel NG/diesel — or to just seriously consider conversion — can be reasonably straightforward. For example, Teck Resources recently announced it is piloting the use of LNG as a fuel source in six haul trucks at its Fording River metallurgical coal operation in southeast British Columbia, marking the first use of LNG as a haul truck fuel at a Canadian mine site. Energy utility FortisBC is transporting and supplying LNG to the mine site and is contributing financially to the pilot program.
Because LNG produces virtually no particulate or sulfur dioxide emissions and reduces greenhouse gas (GHG) emissions by up to 20% in comparison to diesel, the company said it believes there is the potential to eliminate approximately 35,000 metric tons (mt) of CO2 emissions annually at the Fording operation, as well as the prospect of cutting fuel costs by more than $20 million annually by adopting LNG and diesel hybrid fuel across its operations.
The pilot, said Teck, is one of the steps it’s taking to achieve its long-term target to reduce annual GHG emissions by 450,000 mt at its operations by 2030. To date, Teck said it has reduced annual emissions by 170,000 mt as the result of initiatives implemented since 2011.
The pilot program is expected to run until mid-2016 and will provide information about the potential of using LNG more broadly across Teck’s haul truck fleet.
The converted trucks at Fording are fueled by a Chart Industries mobile unit designed around Chart’s Orca platform, a self-contained mobile fueling station that provides safe LNG fueling capabilities. The system includes a patented liquid-submersed pump and an integrated meter system that allows operators faster startups and single-hose, zero-loss filling with auto shut-off.
The conversion kits installed on the Fording trucks were supplied by GFS Corp., which reported last year that Arch Coal’s Black Thunder mine, located in Wright, Wyoming, had ordered 10 of its EVO-MT 9300 LNG conversion systems for installation on Komatsu 930E haul trucks. The order is part of Arch Coal’s ongoing program to assess the benefits of using LNG in its mining operations. The EVO-MT Systems will be configured for use with either Cummins or MTU engines.
The converted Komatsu 930E haulers will join Arch’s existing fleet of LNG-powered Komatsu 830E units that have been in operation at Black Thunder since January 2014. GFS said it is currently working with Arch Coal to develop NG+D (natural gas plus diesel) solutions for other applications including additional haul truck models as well as other diesel-powered surface mining equipment.
Arch Coal’s move into LNG-powered haulers follows a similar program at Alpha Natural Resources, another major mine operator in Wyoming’s Powder River Basin. Its subsidiary, Alpha Coal West, began testing LNG technologies developed by GFS Corp. in trucks at its Belle Ayr mine in 2012. After 18 months of daily operation, Alpha Coal West converted its 16 Caterpillar 793 haul trucks at the nearby Eagle Butte mine to LNG.
Alpha contracted with Seattle, Washington-based Plum Energy to build an LNG plant at the Eagle Butte mine, sized to produce 28,500 gallons of LNG a day. In addition, Plum Energy designed an LNG refueling station capable of refueling eight trucks simultaneously.
Alpha Coal West said it expected to use about 6,400 gallons/day of LNG to fuel its trucks. As the plant grows, excess product could be sold to other companies in the area as they convert their haul trucks and other equipment to LNG.
How it Works
In mid-2015, GFS released a new system designed for Cat’s 793D haul truck. The new EVO-MT 7930 System for 793D haul trucks joins the company’s previous offerings for Caterpillar 793B and C model trucks, which have been available since mid-2012. Florida-based GFS Corp. said the new system provides the benefits and features of the previous systems, allowing in-frame conversion of the haul truck engine to LNG+D operation. The conversion process uses components that are installed externally of the engine, without modifications to the cylinders, pistons, fuel injectors or cylinder heads. The system retains the OEM diesel fuel system in its entirety, providing the capability to operate solely on diesel fuel when required.
According to GFS, the system interfaces with the engine cooling circuit in order to supply high-temperature coolant to a heat exchanger/vaporizer for efficient conversion of the LNG from a liquid to a vapor state. Once the LNG is converted to a vapor phase, it is delivered to the engine’s air-intake system at a point upstream of the turbo-compressor inlets using low-restriction air-gas mixing technology. Installation is performed using conventional shop tools and equipment and requires about 6 to 8 hours to complete.
LNG is carried on board the haul truck in a storage “pod” that includes double-walled, vacuum insulated cryogenic tanks, LNG vaporizer, cryogenic safety controls, high and low pressure gas regulators, gas flow meter and sensors. The pod is a pre-fabricated assembly that minimizes installation downtime. Pods are shipped to the mine site completely assembled and tested and can be installed using overhead shop cranes or mobile lifting systems. The LNG pod is designed for specific haul truck configurations and/or duty cycles and normally includes sufficient LNG storage capacity for a 12-hour refueling cycle.
CNG Advancing in Australia
In Australia, a program got under way last year to test a prototype high-density compressed natural gas (CNG) fuel system for haulers, conducted by Mine Energy Solutions (MES), a joint venture company backed by Sime Darby, a multinational conglomerate: and IntelliGas, a privately owned Australian gas technology specialist that has developed a suite of components and processes for the production, storage, dispensing and utilization of High Density Compressed Natural Gas (HDCNG). Sime Darby owns a Caterpillar dealership in Queensland, Australia, where the tests were conducted.
According to MES, the Cat 789C truck used in the test was converted to run on HDCNG, which is compressed, transported, stored and dispensed at more than 350 bar (5,076 psi) pressure. It has approximately twice the energy density of conventional CNG and about 65% the energy density of LNG, has less space and weight demands than CNG and poses none of the handling and other issues that result from the cryogenic nature of LNG.
MES Executive Director Craig James said, “An average diesel displacement of more than 80% is being achieved over the full range of drive cycle conditions simulated by the trials, without loss of torque or power.”
Reports following the tests indicated truck operators remarked about improved comfort in the truck cab due to reduced noise and vibration achieved while running on HDCNG. The engine technology is claimed to be retrofittable to any type of manned or automated mining vehicle and the conversion can also be easily reversed.
During system installation, HDCNG fuel packs are mounted on the truck in four fuel cassettes, each containing two lightweight composite cylinders, which are designed to be robotically exchanged at the refueling station in less than five minutes and on both sides of the truck simultaneously. Alternatively, in-pit mobile refueling can be provided.
MES said if the gas supply is interrupted, the engine is still capable of running on pure diesel, reverting automatically if necessary. And, if the converted truck is transferred to a site where natural gas is not available, the dual fuel conversions are reversible.
Making the List
Several years ago, when Caterpillar began to focus intently on the development of LNG-powered mine trucks, one of its engineers listed the program’s objectives, some of which are summarized here:
- Maintain equivalent engine performance vs. diesel;
- Ensure diesel-only mode with partial power;
- Utilize the same footprint on the truck as the diesel equivalent;
- Minimum 12-hour fuel storage on board;
- Accept wide range of LNG fuel quality;
- Same or lower sound levels as diesel-powered truck;
- Similar reliability of diesel truck; and
- Understand site implementation requirements and best practices.
Cat later explained in its Viewpoint magazine that it was working on two types of fuel systems. The first uses Dynamic Gas Blending (DGB), which mixes natural gas with air and combines with diesel for combustion. The article said this system was initially expected to achieve diesel replacement of around 60% with comparable performance to a pure-diesel engine. DGB allows customers to utilize diesel or a combination of diesel and natural gas. This flexibility offers benefits to customers in areas where natural gas supply is not yet reliable.
The second system under development uses High Pressure Direct Injection (HPDI), which injects natural gas directly into the engine, using only a small amount of diesel as an ignition source. Engine test cell evaluations show the HPDI technology is capable of providing greater than 90% diesel substitution and lower greenhouse gas emissions — while operating at diesel equivalent performance.
Its first DGB conversion retrofit kits — for oil and gas applications — were introduced to the market in 2013, and Cat reported that it has since sold hundreds of those kits for the 3512 Series diesel engines. However, mining-related adaptations are in the company’s pipeline as well: Jeff Castleman, strategy manager for Cat’s large mining truck business, told an audience at the HHP Summit last year in Dallas, Texas, that Cat has been running a DGB-equipped, large mine truck at a test site near Tucson, Arizona, and results indicate that customers operating DGB-powered haul trucks could potentially save more than $1 million to as much as $4 million per unit over a 10-year period after the incremental cost of the installation is repaid. He noted that the company believes the overall economic promise of LNG-powered fleets remains valid even at today’s diesel/natural gas price spread, and it is working toward introduction of both factory-installed LNG-powered mine truck options as well as retrofit kits.
This article is adapted from one that was published in the Teck Resources.