District heating pipeline with water from Lake Geneva in La Tour-de-Peilz (CH)

1. Introduction

With a sustainable energy supply and a reduction in CO₂ emissions in mind, the idea of using heat or cold from lakes is becoming increasingly attractive. In Switzerland around 65 % of the energy used for heating buildings still comes from non-renewable fossil energy sources. Since it is precisely on the larger lakes such as Lakes Constance, Zurich, Lucerne or Geneva that the larger towns and cities also lie, the use of the enormous heating potential of the deep lakes at the edge of the Alps strongly suggests itself. Isolated plants are already in operation, as in Zürich, Lausanne or St. Moritz. But the volumes of heat used to date are small. Also, older heat pumps often have poor efficiency levels. This means that too much energy is used for driving the pumps – for the most part electrical power but also by combustion engines in the larger plants – for the useful heat actually gained.

2. CAD LA TOUR-DE-PEILZ district heating project

The aim of the CAD LA TOURDE-PEILZ district heating project is, in the end, to use the energy of the water from Lake Geneva to cover the heating and hot water requirements of around 3,000 households. The technology behind this district heating system combines pumping stations with a network of pipelines and individual heat pumps (Figure 1), whereby the energy of the water from Lake Geneva can be used. The water will be taken 500 m from the lake bank and drawn down to a depth of 70 m, where the temperature is stable (Figure 2). At a temperature of 6 °C it enters the pumping circuit and delivers 3 K to the distribution network between the pumping station and the buildings connected to the circuit. By alternating compression and expansion the high-performance heat pumps use the energy taken from the lake for heating and for the production of domestic hot water for consumers.

3. Great potential for expansion

By the end of 2015 around 15 buildings will be connected to CAD LA TOUR-DE-PEILZ. The network has been designed so that it will grow with the increasing needs of its clients over the course of time, so that in the end it will be supplying more than 300 buildings. By the time the potential is completely taken up, the pumping station will enable a throughput of 3,600 m³ water per hour to be handled, thereby producing 35,000,000 kWh/a. That corresponds to the average consumption of 3,000 households. By using renewable energies the system will prevent the emission of 10,000 tonnes of CO₂ per year. With an investment of 23.5 million Swiss francs for the first stage, CAD LA TOUR-DE- PEILZ will be one of the largest district heating plants in Europe with this technology. The major technical data on the system are:

• buildings connected: ~ 300
• length of the network: 15 km
• volume of water from the lake: 3,600 m³/h
• connected output: 18,500 kW
• energy produced: ~ 35,000,000 kWh/a equivalent
• energy in terms of fuel oil: ~ 3,745,000 litres of fuel oil per year CO₂
• reduction: ~ 10,000 tonnes of CO₂ per year

4. Solution with energy-efficient vonRoll iron pipes

For the construction of piping for district heating, high operational reliability, cost-effective operation and a long working life for the pipeline are decisive criteria for the choice of an appropriate piping system. The vonRoll DUCPUR cast iron pipe with its tried and tested vonRoll HYDROTIGHT thrust resistance system meets these high requirements and was therefore favoured by the project management. The polyurethane-lined pipe, which is produced according to standards EN 545 [1] and EN 15655 [2], has a surface roughness factor of k < 0.01 mm and is thus considered hydraulically smooth in operation. This is a condition required for minimum pressure losses. In addition, because of the thin PUR coating, the hydraulic cross-section of the pipe is comparatively large. Hence this pipe is predestined for a pumping operation where a high energy-related efficiency is crucial as it has a direct influence on the operating costs of the system. Pipes of nominal sizes DN 200 to DN 700 were used in the project.

The district heating pipeline is a closed-circuit system consisting of double pipelines for forward and return flow with inlet and outlet pipelines to the heat exchangers in the buildings. The inlets and outlets of the building connections have been provided with shut-off valves in each case.

As the entire system is several kilometres long, shut-off butterfly valves (Figure 3) or gate valves, also coated with epoxy powder, have also been used for isolating sections of the circuit.

Because the space available was restricted in some places, the route of the pipeline was very challenging. So, after the water extraction point on the bank of the lake and directly behind the pumping station, the pipeline had to be run underneath the railway line using the microtunnelling process. The DN 700 restrained DUCPUR pipes were pulled into the two tunnels via an 8 m deep shaft using castors (Figure 4).

Using the conventional open installation technique, the trench width for the double pipelines (Figure 5) was optimised in such a way that installation was possible with one installation unit. Because access to the pipeline route was restricted in some places, a helicopter had to be used for the transport and installation of the pipes and of components at particularly exposed places (Figures 6 and 7).

5. Stray current risk when laying pipes underneath a railway line

In the context of the project, the transport pipeline had to run beneath a railway line. In the area of influence of direct-current railways metallic structures in the ground are at risk from stray currents. These stray currents occur because of the reverse current between drive wagons and input rectifier which produces a drop in longitudinal voltage in the rails. These stray currents can considerably endanger a longitudinally conductive piping system, i.e. if the electrical resistance of a joint between two pipes is low. The effective interruption of the longitudinal electrical conductivity from pipe to pipe in pipelines of ductile cast iron with porefree coatings is therefore an important aspect for the aim of achieving as long a working life as possible under these limiting conditions. The new SVGW guideline W4-3 [3] recommends using ductile iron pipes with reinforced coating or, depending on the external protection system, using additional protection with electrically isolating socket joints.

Also, in edition no. 06 of Aqua and Gas there is a technical report by the Swiss corrosion protection association (SGK) on corrosion protection concepts for water pipelines [4] which looks at this subject. Potential differences due to different soil conditions necessarily result in a flow of current and hence to accelerated corrosion damage to insufficiently protected metal structures. By using pore-free coated cast iron pipes with electrically isolating socket joints to interrupt the longitudinal conductivity, the possibility of the formation of galvanic elements is greatly reduced. In a series of tests by the SGK lasting three months, the longitudinal electrical conductivity of restrained cast iron pipe systems was recorded using measurement technology equipment. With their high resistance values, vonRoll pipe systems are able to limit possible stray currents [4]. Profiles of the constructions are shown in Figures 8 and 9.

6. Conclusion

The pore-free and smooth PUR lining and the large hydraulic cross-section result in a good hydraulic performance for the transport of lake water, significantly reducing the energy consumption of the pumps used. In combination with the vonRoll HYDROTIGHT restrained push-in joints with high electrical resistance, the pore-free PUR coated system is effectively protected against galvanic corrosion and stray currents – a secure investment in the future.

Bibliography

[1] EN 545: 2010
[2] EN 15655: 2009
[3] SVGW guideline W4-3: 2013
[4] Aqua & Gas no. 06 Galvanische Elemente: Ihre Gefahren und mögliche Schutzmaßnahmen an Wasserleitungen [Galvanic elements: their risks and possible protection measures on water pipelines] 2013, p. 34 ff.

(Primary publication: GUSS-ROHRSYSTEME - Information of the European Association for Ductile Iron Pipe Systems • EADIPS^®, No. 50)

More News and Articles