Economy meets ecology – crushing with a diesel-electric drive

Langhagen gravel works with its moraine gravel deposit is located on the A 19 road around 50 km outside the city of Rostock, Germany. Around 1 mill. t sand and gravel are processed at the works annually. Besides concrete aggregates, the plant produces high-grade asphalt aggregate and base course materials. The gravel deposit contains boulders up to 1200 mm in size. Some of these are used in gardening and landscaping. The smaller boulders to 700 mm in size are crushed in two stages and screened into different gravel chipping fractions. Cost-efficient primary crushing of these boulders is a challenge for every processor – and also for the Langhagen plant owned by Heidelberger Sand und Kies GmbH.

After several crushers from different suppliers had not shown themselves capable of meeting the producer’s requirements, Metso’s new Lokotrack LT120E, premièred at Steinexpo 2011, was put to the test (Fig. 1). It proved the most effective machine and, in the diesel-electric version, the most cost-efficient solution for this job. In addition, it meets all environmental requirements. A combination of several factors is responsible for the good energy efficiency of the LT120E: thanks to the high mass of its flywheels, the C120 jaw crusher ensures a steady crushing process, while the diesel engine CAT C13 Tier 4 drives the generator with a constant 1500 rpm.

To collect relevant operating experience with the track-mounted machine, the LT120E was hired out after the test. After more than seven months in operation and a crusher running time of over 970 h, Heidelberger Sand und Kies GmbH, subsidiary of the globally operated Heidelberg­Cement Gruppe, is very satisfied with the new Lokotrack. “Despite our extremely difficult-to-crush feed material, we have still achieved good and constant crushing rates. During the entire hire period, there was no unexpected downtime,” says Hans-Jürgen Jeschke, Operating Manager at Langhagen Gravel Works, giving his final verdict on the machine. “It is amazing how well the C120 jaw crusher operates and reliably draws in even the particularly big boulders into the crushing gap (Fig. 2). Here the geometry of the crushing chamber, the crusher kinematics and the crusher jaws optimized for this job work together optimally,” says Jeschke.

Hans-Jürgen Jeschke mentions another important aspect for HeidelbergCement: “With its diesel-electric drive, the Lokotrack LT120E achieves the environmental protection goal set by HeidelbergCement. And when the unit is driven to another job site, we can simply connect it to our power supply and test it in fully electric mode.” For primary crushing to a size acceptable for a secondary crusher, the Lokotrack works twelve hours daily at the Langhagen gravel works.

The new Lokotrack LT120 jaw crusher is available in two versions: as a traditional diesel-hydraulic LT120 or as the diesel-electric LT120E, which gives the customer the option to drive unit diesel-electrically with the 420 kVA generator powered by the diesel engine – or with connection to an external power supply as a fully electrically powered unit. Flexibility in the machine configuration and adaption to the specific requirements are the key features. With the LT120E, crusher, belt conveyor and magnetic separator are driven electrically. In the case of a blockage, the crusher can be operated in reverse. The crawler track, the vibrating feeder and the optional boom with hydraulic hammer are driven by the hydraulic system.