Environment and ressources

Optimizing energy consumption in tunnelling

In times of climate change and rising energy costs, it is vital to develop energy-saving alternatives. Because in the past energy prices have been lower, less attention was paid to the issue of "energy efficiency" than will be the case in future. In the years to come, energy-saving tunnel boring machines will play an increasingly essential role in the economic viability of tunnel projects. Moving forward, our goal is therefore to produce tunnel boring machines in as environmentally and resource-friendly a way as possible. Herrenknecht AG is taking up this challenge and developing energy-efficient and energy cost-saving tunnel boring machines. The aim is to sustainably reduce energy consumption and CO2 emissions.

Putting all our energy into reducing consumption

As the market leader in mechanized tunnelling technology, Herrenknecht AG takes responsibility and has set itself the goal of reducing the energy consumption of its products by means of demand-driven energy flows. In addition to the optimization of electrical loads in tunnelling, in particular the reuse of components and parts over several project cycles offers an interesting way of saving energy. So-called rebuilding plays a key role here.

Optimizing energy consumption in tunnelling

For safety reasons, a TBM has plenty of reserve capacity in order to have sufficient power in an emergency. A comparison between the actual consumption level and the electrical capacity revealed that Herrenknecht tunnel boring machines still have a high power reserve, even under maximum load. This amounts to around 50% of the power consumption for the main distribution MDB1. A comparison of the actual output of the electrical loads with the safety-related capacity showed that even at medium utilization the power reserve is 77 percent.

The illustration shows the power distribution over time of the main distribution of a Mixshield. With the aid of this 3D graphic it is possible to identify energy-saving potentials and to optimize the energy used for tunnelling.

This has resulted in multiple savings potentials for energy optimization being found:

  • On a Mixshield the slurry circuit consumes the most energy in terms of percentage. With the development of a shutdown criterion for the slurry circuit during ring building, the energy consumption could be substantially reduced.

  • A machine design that adapts even more to the geological/geotechnical requirements can have a positive influence on a TBM's energy consumption.

  • In the design of the machine lighting already, using LED lamps instead of conventional halogen lighting can save significant amounts of energy.

The analysis of further tunnelling projects in terms of energy use brings new findings with regard to machine utilization and the optimization of the slurry circuit.

Low emission rig with hybrid drive 

The HK80CK rig is low in emissions installing pipelines due to its hybrid drive. Instead of a diesel engine, which makes noise protection and exhaust gas purification necessary, the rig is electrically powered. The diesel engine is only needed to drive the machine into position, after which all components, such as separation and mixing plants, transfer tanks, the mobile pre-crushing unit and transfer pump are electrically powered. The drive by the electric motor is environmentally friendly, low in emissions and low in noise. As a result, acceptance of the construction/tunnelling work by the population is increased.

The compact design variant also has flexible product pipes, which require a short boring radius due to the steep entry and exit of the drill rods. Apart from the separately attached control container, all components are on the rig. This makes it easy to transport the machine even in narrow alleyways. The reduced impact on urban space when using the efficient, low-footprint machine is a major step forward in environmental protection and sustainability. 

Reuse through professional rebuilding

A key factor in reducing the carbon footprint of tunnel boring machines is the reuse of as many components as possible over several project cycles. To facilitate this, Herrenknecht has been carrying out professional refurbishing of tunnelling technology for decades – so-called rebuilding. At our Kehl site, tunnelling technology is given a general overhaul after use, adapted to the new, project-specific requirements and prepared for redeployment with a full warranty.

The Product Carbon Footprint represents the sum of the greenhouse gas emissions in the lifecycle of a product, from the extraction of the raw materials required for production to disposal after the end of its operational capability. As part of a potentials analysis, rebuilding was compared with the new production of tunnelling technology to determine what amounts of resources and CO2 can be saved by rebuilding. This concentrated mainly on large steel components. The result was clear: by refurbishing individual TBM components, compared to new production 65% of greenhouse gases, 80% of electricity and 99% of material can be saved.

For the future, the following potentials for savings can be noted:

  • Taking into account the entire life cycle of a tunnel boring machine results in further savings potential.

  • The reuse of tunnel boring equipment after rebuilding will sustainably minimize CO2 emissions.

In order to meet the energy requirements of the future, Herrenknecht AG is working on efficient ways to further reduce the energy consumption and CO2 emissions of tunnel boring machines.

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Steffen Dubé President and General Manager Herrenknecht Tunnelling Systems USA Inc.
Gerhard Goisser Commercial Manager Herrenknecht Tunnelling Systems USA, Inc.

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Steffen Dubé President and General Manager Herrenknecht Tunnelling Systems USA Inc.
Gerhard Goisser Commercial Manager Herrenknecht Tunnelling Systems USA, Inc.