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Energy-efficient TBM

Analysis and potential for reducing energy consumption in tunnel boring machines

________________ In times of increasing energy costs, it is important to master the challenge of energy efficiency. To lower the energy needs in tunnelling technology, Herrenknecht AG is developing energy-efficient and energy-cost-saving tunnel boring machines.

Reducing consumption with all our energies

Our focus in product development is to reduce energy consumption through needs-based energy supplies. In addition to optimizing energy consumers, it is also necessary to use energy-saving components.

Starting with the electrical consumers on a TBM and their actually installed powers, a comparison is made of the actual consumption level and the "safety-based" electrical performance level. This process shows that, in a selected Mixshield, after subtracting all of the individual installed electricity consumers, the installed power still has high power reserves.

That is why, first of all, in cooperation with the Electrics Department, the actual parameters on a TBM were ascertained using modern performance counters and the effective values of the voltage and current strengths recorded. These physical parameters are then calculated to analyze important effective, apparent and idle power, as are the phase angle φ, the power factor and the amount of effective energy.

The mean and maximum utilization of the main distributor HV1 calculated from the raw data shows a mean utilization of only 23 percent and a reserve of 77 percent, which moves to approx. 50/50 at maximum utilization. This means that, all in all, more than 50 percent reserve of installed power is still available at absolute peak consumption. An evaluation and presentation of this kind was also carried out for the other main consumers - the slurry pump P2.1 and the cutting wheel drive - with a similarly drastic outcome.

Identifying possible energy savings: Presentation of the power distribution of the main distributor on a Mixshield.

The figure shows the power distribution of the main distributor on a Mixshield over time. For this purpose, an evaluation program was developed, which stores the 2D histograms (x/z-axis) of a tunnelling cycle over time (y-axis). With the help of these 3D graphics, it is possible to recognize energy-saving potentials and optimize tunnelling operations in terms of energy.

The first result achieved has been energy-saving machine lighting. State-of-the-art LED lighting enables considerably lower power consumption than conventional halogen lamps.

However, the focus lies with the main consumers. The slurry circuit in a Mixshield needs the highest percentage of energy. By developing a switch-off criteria for the slurry circuit in ring construction, energy consumption could be considerably reduced. Similarly, a machine design that is more closely oriented towards the actual geological/geotechnical requirements can have a positive influence on a TBM's energy consumption.

Analyzing energy consumption in further tunnel construction projects is resulting in more important information about machine utilization and optimizing the slurry circuit. This subject was not afforded much attention previously because of low energy prices, but in future "energy efficiency" will play a more essential role in the economic viability of tunnel projects.

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