Volvo Construction Equipment and Swedish construction and mining company Skanska have recorded impressive initial results from an electric quarry research project. The two companies, working in partnership with the Swedish Energy Agency and two local universities, established an electric site within Skanska’s Vikan Kross Quarry, near Gothenburg in Sweden.
The concept site has been using a diesel electric hybrid wheeled loader, a cable-electric crawler excavator and crushing equipment, plus eight battery-powered autonomous haulers to quarry and transport blasted rock from the quarry face. In normal operation, the site requires a 70-tonne (77-ton) crawler excavator, a diesel-driven mobile crusher, a 50-tonne (55-ton) wheeled loader and three 50-tonne capacity rigid dump trucks to move around 700 tonnes (770-tons) of blasted rock per hour within the quarry. Between them, these machines consume around 3,000 L (792 gal) of diesel in a working day.
The Volvo Skanska partnership worked the electric fleet over a 10-week test period, tackling problems as they arose and constantly assessing production. Though unable to quite match the desired production rate of 700 t/hr, the test fleet did reduce fuel consumption to just 64 L (17 gal) per day, along with 9,320 kW·h of electricity.
To meet that need, Vikan Kross has had to invest to bring an additional 1 MW of electricity in from the grid. However, to prove the low carbon potential of the site, that electricity was supplied from sustainable, non-fossil fuel sources, including wind- and wave-generated power.
In total, the electric site showed a reduction in carbon emissions of 98%, from 8,700 kg/day to just 166 kg/day. That results in a 70% cut in energy costs. As the hauling fleet uses autonomous machines, there was also a 40% reduction in operator costs. Given the potential premium of a production version of these machines, Volvo is confident that it could achieve an overall cost saving of 25% for a customer like Skanska.
“Over the last 10 weeks we’ve made incredible progress, learned a lot and seen huge potential in the electric site solution’s environmental, efficiency, safety and cost benefits,” Uwe Muller, chief project manager at Volvo CE, said at a late November media event demonstrating the site. “In fact, we have decided that we want to learn more, so we will extend our test period with Skanska until the end of 2018. The results we have seen so far confirm that this research project is a step towards transforming the quarry and aggregates industry and creating emission-free quarries.”
Muller commented on some of the challenges and lessons learned during the process: “The challenges include additional production planning and that the system complexity relies on every little thing, including having stable Wi-Fi across the site. Noise levels are lower with the electric machines and there is increased safety, as there are fewer operators and better planning.
“Connectivity and site fleet management are both a challenge and an opportunity. Also, we have been learning about how to service these machines, including needing an IT technician.”
Concept machines at work
Volvo CE has shown each of the concept machines in use before, though this is the first time that they have been put into a working environment together. The 70-tonne EX1 crawler excavator is a dual-powered machine based on the company’s own EC750. It has been modified to incorporate an electric motor alongside the standard model’s diesel engine.
For longer travel around the site, the EX1 uses the machine’s diesel engine to power the hydraulics. However, once at the desired loading location, it is plugged into the grid using a cable that is connected from above the main superstructure, behind the operator’s cab.
The main grid electricity is delivered to the mobile crusher that is positioned below the blasted rock area. The crusher is equipped with a gantry and boom that delivers the power cable to the excavator, through a rotating coupling. When the crusher is moved within the quarry, the gantry’s legs are lifted and the structure is carried by the crusher to the new position.
The stone from the mobile crusher is then loaded by the wheeled loader into haulers and carried to a secondary crusher and conveyor system. Rock can also be stockpiled within the quarry using the loader, or the material can be loaded directly into the haulers from the conveyor feed.
The LX1 prototype wheeled loader is a series hybrid that uses electric drive motors at the wheels and electrically-driven hydraulics. This allows for a much smaller diesel engine to be used, resulting in a 50% fuel saving over a traditional diesel-powered loader. There is an additional saving at the electric site, as the haulers are much smaller than the rigid dump trucks that are traditionally used. This has resulted in the LX1 being a 20-tonne (22-ton) model, rather than the 50-tonne loader that is used with the larger trucks.
The haulers are perhaps the most innovative machines within the quarry. The second-generation HX2 is a totally autonomous machine, with no operator cab. They are powered by lithium-ion batteries, driving two electric traction motors and an electrically-powered hydraulic system. With bi-directional drive, there is no need to maneuver and reverse under the loader, the HX2 simply drives in, gets loaded and then drives out again.
Each hauler has a 15-tonne (16.5-ton) capacity—120 tonnes (132 tons) in total for the eight machines—rather than the 150-tonne (165-ton) combined payload of the three rigid dump trucks. Various difficulties in running and managing autonomous vehicles have meant that the site has yet to match the overall performance of the rigid dump trucks.
Each hauler stops for 1 minute during every haul cycle above an autonomous charging point, which inserts a high-powered charging connection into the battery from below—similar to the catenary charging that Volvo uses on its city buses, which drops from above to part-charge the batteries during stops. This continual boost allows Volvo CE to run the haulers with a smaller battery than would be required for a full day’s operation.
The HX2 haulers are monitored from a central control room within the quarry; however, they run to a programmed GPS route on the haul road and have a vision system that prevents collisions within the site. The wheeled loader operator indicates the desired loading position by toggling a button in the cab when the machine is in the loading position. This point is transmitted to the HX2 haulers, which then park in the required position to be loaded.
Though not provided with a cab, the haulers do have an extended skip at one end. When loading from a conveyor or the crusher, this allows the HX2 haulers to overlap their bodies, with the rearmost machine “pushing” the truck in front. This in turn allows the conveyor to run without stopping, as the haulers move smoothly below the flow of rock as they are filled up.
This does, of course, require substantially more planning and control than a traditional site, where individual operators take responsibility for their part of the production cycle. However, Volvo and Skanska insist that the electric site offers improved safety, with no overuse or misuse of machinery and the potential for improved productivity.
The electric site was never intended to replace Skanska’s existing Vikan Kross operation; it is a possible vision of a future quarry that could contribute to carbon reduction.
“At Volvo CE, we believe in a sustainable future and we are doing our best to build the world we want to live in,” said Melker Jernberg, president of Volvo CE. “You don’t need to choose between safety, sustainability and productivity. You can have them all. With this research, we are combining intelligent machines, automation and electromobility to challenge traditional ways of working in the quarrying industry and explore new alternatives. We will now further mature the technologies involved and the reliability of the concept.”
With more than an estimated 500,000 working quarries around the world, employing more than 4 million people, there are certainly potential carbon reduction and efficiency gains to be made.
“With climate change reshaping our industry, we need to find new, sustainable solutions and build partnerships with organizations that have different competencies,” said Anders Danielsson, president and CEO of Skanska. “Our ambition is that this collaboration with Volvo CE will help us and our customers to reduce our carbon footprint.”Continue reading »