Bright sparks04 January 2019

Skanska and Volvo Construction Equipment have been testing the viability of an ‘electric site’ at a quarry near Gothenburg, Sweden. The results are in...

On account of growing environmental considerations and fuel concerns, vehicle manufacturers are often turning toward electric technology. Although more commonplace among cars, makers of off-road mobile plant, which typically run on red diesel, are also waking up to electrification.

Volvo Construction Equipment (Volvo CE) and its customer Skanska began testing the viability of an ‘electric site’ concept at Skanska’s Vikan Kross quarry, near Gothenburg, Sweden, at the end of August. The site produces aggregates for construction purposes, as well as for asphalt and cement.

Their system, which incorporated electric and autonomous Volvo machines, ran in a real production environment for 10 weeks, with the aim of electrifying each transport stage in the quarry – from excavation to primary crushing, and transport to secondary crushing – while achieving the same output as Skanska’s usual equipment setup (a daily production of 700 tons of aggregate per hour). A negligible amount of diesel power was still used.

Blueprint for transformation

In August, Skanska Sweden CEO Gunnar Hagman said that the electric site “could serve as a blueprint for transforming the efficiency, safety and environmental impact of quarries around the world”.

The research project involved developing new-concept machines, work methods and site management systems that together formed a complete site solution (not a commercial solution for sale today). Joakim Käpynen, production manager for Skanska’s Vikan Kross quarry, explains that Volvo designed and supplied the machines. Skanska’s responsibilities for the project were to run the quarry, make sure operators were on site, and to make sure that the electrical infrastructure there was complete, allowing the machines to connect to the grid. Another task involved setting up and installing a Wi-Fi system to ensure that it could run the management system.

As for the machines, three rigid haulers (dump trucks) were replaced by eight smaller, prototype HX2 autonomous, battery-electric load carriers to transport material from the primary mobile crusher up to the secondary static crusher. These follow an adjustable, pre-programmed GPS path. The system allows the machines to move safely and detect obstacles and people.

Käpynen continues: “The main purpose for using eight to replace three was because they are slower and have less capacity. If we compare our dump trucks against the load carriers, when the trucks are full of material they weigh about 90 tonnes. In the conventional set-up, we are using three of them to transfer pre-crushed material from the Volvo crusher and the plant (dumping spot). The total diesel consumption is approximately more than 100L per hour. Also, if we have a breakdown with a dump truck then we only have 66% running [capacity] left. But, with the HX2, if one breaks then there is like 87.5% left.”

The prototype is an advancement on the HX1, which was revealed in 2016. The next-generation HX2 is a full-electric, battery-driven load carrier that has a load capacity of 15 tonnes and a base machine weight of seven tonnes. There is one electric motor with a rated power of 110kW on each axle and the machine has four-wheel drive and four-wheel steering. The battery pack capacity is 8.9 kWh, while a hydraulic system is used for the steering and bucket tilting actuators.

Käpynen says: “In each HX, you will find two batteries, and they charge each cycle – one cycle is about seven minutes long – and when I say one cycle it is between loading directly from the mobile pre-crusher, driving the path up to the dumping spot, dumping the material into the feeder, and driving to the charging station and charging for around 60 seconds. They then reload.”

The primary crusher on the Skanska site was loaded by a 70t dual-powered, cable-connected EX1 excavator prototype. The base machine for the EX1 was a Volvo EC750 model that had been upgraded to incorporate an electric motor, in addition to the diesel engine. In terms of the operator interface and controls, nothing had changed – it operates in exactly the same way as a conventional Volvo excavator.

“70t is the weight of the excavator machine we are using in the conventional setup and in the electric type. I think it has a bucket of 4.5 cubic metres,” says Käpynen. “One thing I think is very exciting is the power solution. That has been a task for Skanska to design and build. We had to ask: how do we get the power supply to the excavator? The weight is 70 tonnes, it rotates 360° and is around 10 metres long. So, there were a couple of PhD students who looked into the different solutions of how to make the power supply possible for the excavator.

“In the end we decided to make a power solution. Skanska Technology built it; the weight of the construction is about 15 tonnes; and we put the solution above the mobile pre-crusher. The power solution follows and rotates with each movement on the excavator. On the frame of the power solution we also have a transformer.

“Basically, high-voltage cables go into the transformer, and from there low voltage cables come out. Cables go into the power solution and transformer, then through the cable reel, and down to the excavator. To make sure the cables don’t twist together as the excavator rotates, there is a motorised swivel. [Around] 180kV is pumped into it by the cables. Diesel-wise, it uses about 45L per hour for the conventional excavator. That is a huge difference in both cost and energy.”

Tidying up

Piles of material on the site, meanwhile, are organised by the LX1, Volvo CE’s prototype electric-hybrid wheel loader. It incorporates a driveline with electric wheel motors, electric-driven hydraulics, an energy storage system, a small diesel engine and new machine architecture, including a new design of the lifting unit.

Uwe Müller, chief project manager for Volvo CE’s electric site project, says: “The secondary crusher only runs during the morning shift, due to capacity differences between the primary and secondary crusher, as well as legal restrictions. As a result, all pre-crushed material at the primary crusher is stockpiled during the afternoon shift with an electric conveyor belt. The following morning, this material is then loaded to the HX2s by a wheel loader.”

As for the site management system, Müller explains that it continuously tracks all performance data in the complete process. “The system, for example, tracks the exact positions of all machines, as well as production statistics of the crusher, wheel loader, and the HX2 load carrier.”In addition, the system also controls the HX2 fleet throughout the entire process.

The results

The test concluded in November, showing reductions of 40% in operator cost, 70% in energy costs, and 98% carbon emissions, across the site.

Volvo CE and Skanska say that the HX2 load carriers proved that they could help take a big step towards achieving a vision where work sites are 10 times more efficient. It calculates efficiency in the transport stage by comparing the energy used for material transported (kWh per tonne).

The LX1 prototype electric hybrid wheel loader, meanwhile, delivered more than a 50% improvement in fuel efficiency at the quarry, as well as a reduction in emissions and noise pollution, compared to its conventional counterpart. As for the EX1 cable-connected excavator prototype: when it was plugged into the grid, no emissions were generated.

These results support the potential for a 25% reduction in total cost of operations, says Volvo CE. However, the reduction in total cost of operations is just a prediction at this stage, as the prototype machines are part of a research project and not commercially available (for that reason,guaranteed figures aren’t available).

Says Müller: “The maximum targeted output of the classical process is approximately 700t/h. Within the test period, it was not possible to reach this target because all of the machines and systems are still prototypes, and more work is needed to secure full system uptime. However, with the experience gained when the full system was up and running, we are able to compare the results from the prototype setup with the classical setup. By extrapolating the performance to a full day, it is possible to see the overall potential.

“In fact, we have decided that we want to learn more, so we will extend our test period with Skanska until the end of the year (2018). The results we have seen so far confirm that this research project is a step towards transforming the quarry and aggregates industry.”

Skanska’s Käpynen concludes: “Skanska wants to build for a better society. We are pushing for [better] safety, ethics, green [performance], and diversity, so that is why we have been doing this project with Volvo. We are striving for the same thing.

“I’m sure in the future we will see more projects where companies are working together. We are all struggling with the climate question [and] you have to dare to think outside the box. If you have been doing things the same for a long time, then try other things.”

BOX OUT: Rolling with the times: mobile plant gets electrified

JCB has developed its first-ever electric digger. The 1.9 tonne mini excavator – known as the 19C-1 E-Tec – can be charged by plugging it into a standard 230V domestic electricity supply. Key features of the 19C-1 E-Tec include three lithium-ion battery packs providing a 312Ah (15kWh) storage capacity and a standard load-sensing hydraulic system. Once fully charged, it is ready to put in a full nominal working day on the building site – digging with the same speed and power as its diesel counterpart.

Paus and Danfoss Mobile Electrification have developed an electric and hybrid vehicle for transporting people in underground mining applications. The MinCa 5.1 is available with either a pure electric drive with 50 kilowatt electric motor and a battery system with 50 kilowatt hours, or as a hybrid drive with 50 kilowatt electric motor, a range extender and a battery system with 20 kilowatt hours.

Volvo CE demonstrated the LX2 electric compact wheel loader in September. The prototype is said to deliver zero emissions, lower noise levels, and reduced operational costs. Its combustion engine has been replaced with a lithium ion battery and electric motors. It is not commercially available.

Hinowa S.p.A. received the Intermat 2018 Innovation Award in the lifting, handling and transport category with the new Lightlift 33.17 Performance IIIS tracked aerial platform. The platform comes with two different equipment options: a Kubota three-cylinder diesel engine or an electric system powered by lithium ion battery packs.

Mecalac was given an award for energy transition at Intermat 2018 for the Mecalac e12, a compact wheeled excavator that runs on electricity. It is said to have a 146-kWh capacity, and produce zero CO2 and particulate emissions.

Adam Offord

Related Companies
Skanska UK plc
Volvo Construction Equipment

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