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Bauer Separation Technology used for construction of Baltic Sea Pipeline Link

The Baltic Sea Pipeline Link – OPAL (Ostsee Pipeline Anbindungs-Leitung), one of Europe’s largest energy infrastructure projects, will connect Germany and Europe via the North-Stream Pipeline with Russia’s extensive natural gas reserves. The annual capacity of the pipeline will be 36 billion cubic meters (bcm) of natural gas. 

The 470 kilometer long pipeline, which will be constructed within a period of two years, will run from the landing point of the North-Stream Pipeline in Lubmin near Greifswald to Obernhau near the German-Czech border.

For reasons of environmental protection, a trenchless method was selected for the construction of a 1,000 m long microtunnel that crosses the River Peene in the northern section of the project. In addition to crossing under the River Peene, the microtunnel also crosses underneath the eco-logically sensitive littoral zone and a protected riverside forest.  

microtunnel

Launch pit for the microtunnel to cross under the River Peene (Ludwig Pfeiffer GmbH)

Steel-reinforced concrete thrust pipes with an outer diameter of 3,000 mm were jacked into the ground from the launch pit. The soil at the tunnel face was excavated by the rotating cutter head of the tunnel boring machine (TBM). Bentonite slurry was injected into the void between cutter head and tunnel face at an increased pressure via a slurry supply line to counteract the native earth and groundwater pressure and prevent an uncontrolled penetration of soil or groundwater or a loss of stability at the tunnel face (“bentonite shield“). The excavated soil material mixed with bentonite slurry was pumped to a separation plant outside the microtunnel via a return pipe.

Bauer Separation Plant

For the treatment of the soil-bentonite slurry mixture (regeneration and disposal) several plants manufactured by Bauer Maschinen were deployed. The configuration of the plant modules had to be tailored to both the actual volumes generated and also the types of soil being excavated.
The prevailing ground conditions presented an enormous challenge not only for the tunnelling operations but also for slurry separation. Whilst large sections of the route of the microtunnel run through very hard and highly abrasive boulder clay, other sections of the route were dominated by sandy and soft soil formations with many fine particles. 

 
mat
 

Desanding plant BE 500-60 and desilter BDS 250-20 mounted on top of recycling container RB-H35
Desanding Plant BE 500-60
For regeneration of the charged return slurry from the tunnel boring machine (TBM) a Bauer BE 500-60 desanding plant was set up as the first regeneration stage. This plant is designed for processing large volumes (300 – 500 m³/h) and for separating soil particles out from the slurry up to a cut point of  d50 = 60 μm.
For this project the BE 500-60 was equipped for the first time with a new screening system. Due to an enlarged open screen area the dewatering performance of the screen was considerably improved resulting in a much dryer solids discharge.

Desilter BDS 250-20
For the separation of finer soil particles, a Bauer BDS 250-20 desilter was added to the desanding plant as a final treatment stage. This unit is capable of reducing the cut point down to d50 = 20 μm and thus remove at least 50% of the 20 micron particle size from the slurry.

Recycling Container RB-H35
The desanding plant and the desilter unit were mounted on top of a Bauer RB-H35 recycling container, in which the pre-treated slurry discharged from the desanding plant was collected. A horizontal agitator prevented sedimentation of the remaining fine particles after regeneration in the desanding plant.

These fine particles were conveyed to the other end of the container, from where they were then pumped into the Bauer BDS250-20 desilter for final-stage post-treatment.

The recycling container fulfills two purposes:
On the one hand it served as an intermediate storage tank from which pre-treated slurry can be delivered to the desilter for post-treatment. This post-treatment can be carried out in multiple cyles as the desilter unit is operated in a bypass circuit.

On the other hand the horizontal agitator prevents sedimentation of solid particles. When using single container units as combined collection and intermediate storage tank, unchecked sedimentation has frequently caused time-consuming downtimes, because the sedimented deposits had to be cleared from inside the container in a laborious operation.

By deploying a Bauer RB-H35 recycling container this problem is now a thing of the past. 

Decanter BD 50
For regenerating the slurry even further, a Bauer BD 50 decanter was set up complete with flocculant station as an additional regeneration stage. The decanter operated also in a bypass circuit. As it separates the residual slurry into relatively dry solids and clear water, offsite disposal is absolutely no problem.
Operation of the flucculant station was ultimately not required on this site, as the available plants were capable of regenerating the slurries to an adequate level of purity. 

Decanter

Decanter BD 50 – Solids discharge
Some Technical Data regarding Plant Operation:

TBM Penetration Rate 3 cm/min (in hard clayey till material or boulder clay) up to 11 cm/min (in sandy soils)
Solids Discharge Rate Up to 45 m³/h at 11 cm/min penetration of TBM

Feed Slurry

Slurry density    1,25 kg/l

Decanter BD 50 Centrate discharge    1,09 kg/l
Solids discharge    1 m³/h (at decanter speed of 800 rpm)

Period of continuous Operation

6 days per week at 24 hours per day

 
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