Power Plants in northern Germany Project examples for optimizing intakes and outfalls

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1 (Initial page layout) Power Plants in northern Germany Project examples for optimizing intakes and outfalls O. Stoschek* * Coastal and Estuarine Dynamics Department, DHI, Agern Allé 5, Hørsholm, Denmark, DK ( ost@dhigroup.com) Abstract Reliable production of low cost electrical power will in the near future be one of the most challenging infrastructural problems in Germany. Numerous existing power plants (nuclear / coal) need to be replaced within the next 5 to 10 years. All these power plants need cooling water, either taken from an atmospheric cooling tower or directly from rivers and seas. As heated outfall water may potentially affect the surrounding environment and other cooling water systems in the area, and because of recirculation optimization for the system itself is needed, methods for evaluating the effects has to be adopted. Several new plants along the German shoreline have been in the planning phase in the last years. This paper gives a short overview about the planned and realised sites. Three examples from the North Sea coast and the River Elbe were chosen to illustrate different intake and outfall techniques at the seaside, in an estuary and inside a tidal river. Numerical models were used to optimize the shape, size and location of the structures. All examples show the clear demand of on-site investigations to optimize the design for intake and outfall structures. In nearly all cases optimization is needed to stay within the environmental criteria, e.g. the size of the mixing zone. Keywords Numerical Modelling; heat; plumes; near field; far field; 3-dimensional modelling, Mike 3 INTRODUCTION Along the North Sea coast and inside the German tidal rivers cooling water can be taken from a huge natural reserve without giving rise to fresh water problems. Further, due to the proposed climate change in Germany with less and warmer water inside rivers, these shoreline plant locations were extremely attractive. Figure 1 shows the planned power plants in northern Germany. Until now only few of them have been realized. The optimization of the CFPP plant in Hamburg is presented in Stoschek (2008). These power plants were forced to meet certain environmental criteria. For example the EU-FFH directive and local environmental regulations demands that the impact of cooling water on the environment must be defined and minimized. The mixing zone (ΔT<3 C) is not allowed to be larger than 500m and should not block more than 25% of the cross section. In riverine environments additionally minimum oxygen content (80% of the ambient concentration) and maximum absolute temperatures (28 C 30 C) apply. Numerical models can be used to predict this impact on temperature and environmental parameter like oxygen content. The necessary intake and outfall structures for the planned power plants were adapted to the local hydraulic situation. Numerical models were used to optimize the shape, size and location of the structures. Three examples of locations and design of the different Intake / Outfall structures are given in this paper. The first location in Wilhelmshaven can be found at the German coastline without any influence from upstream discharges. The second one is located in Brunsbüttel in the estuary of the River Elbe, a specific brackish environment with 3-dimensional currents. The third example at Stade is located inside the Elbe River in a tidal environment. It is dominated by tides and upstream discharge.

2 Figure 1: planned power plants (black) and realized power plants (red); CFPP=Coal Fired Power Plant, GFPP=Gas Fired Power Plant METHOD To determine the influence of the power plant on the environment and to optimize the intake / outfall location and structures 3-dimensional numerical models (MIKE 3, DHI 2013) were used. The presented models describe in general a meteorological situation in summer time, characterized by high temperatures and low upstream discharge (as far as applicable) - a situation limiting the availability of cooling. The 3-dimensional models provide information about the near field impact on river and sea temperatures at the power plant location for this critical situation. To cover possible future demands and to estimate the mutual effects of different locations, the model runs include in general several different locations and various heat discharges combinations at each location. RESULTS Wilhelmshaven The intake/outfall system of the GdF Suez (former Electrabel) power plant in Wilhelmshaven is located in the vicinity of the newly built Jade Weser Port (Figure 2). This port interrupts the longshore coastal currents leading to a low current situation (lee side effect). Additionally an existing nuclear power plant is located south of the planned area. The task for DHI was to optimize the position of the outfall to obtain the least impact on the existing plant and minimize the recirculation (Figure 3). The location of the intake was fixed at an offshore position in line with the existing port about 1km off the coast. Due to the new port increased sedimentation problems occur. These have to be taken into account as well. The plant discharge cooling water of about 30 m³/s keeping a ΔT of 7K. Five positions for the outfall were suggested (Figure 4). After applying the numerical model for the case the outfall structure was chosen to be put at position 3. The model showed clearly that the impact on the existing plant and the recirculation temperatures from the new plant was lower than at the other positions. Position 1 provides lower recirculation temperatures and higher impact on the neighboring plant while Position 4 and 5 have a vice versa impact.

3 Due to sedimentation it was not possible to use a diffuser at position 3. Instead an open ended horizontal pipe was used (single point outfall). The velocities at the end of the pipe were increased (1.5m/s) to reduce sedimentation in front of the outfall. The results from the model in terms of mean excess temperature are shown in Figure 4. With this configuration the model showed that the temperatures would be below the allowed 3K in a radius of 500m. Figure 2: Location of the Electrabel plant in Wilhelmshaven Figure 3: Planned intake and outfall location of the Electrabel and neighboring plants

4 Figure 4: Mean excess temperature in Wilhelmshaven Brunsbüttel The SWS plant in Brunsbüttel is located in the brackish and tidal environment in the Elbe estuary in Germany (Figure 1). The intake and outfall are located along the northern river embankment. Two additional power plants (Electrabel CFPP and E.ON nuclear power plant (NPP)) are located in the direct vicinity of the planned one. The task for DHI was to determine the best possible location of the intake and the outfall, i.e. to minimize recirculation effect and minimize the impact on and from the surrounding power plants. The power plant discharges about 55 m³/s at ΔT = 8K (Figure 5). Due to high longshore currents (>1.5m/s) and a tidal volume of more than 40,000 m³/s a full vertical mixture of the cooling water into the riverine water takes place. No stratification effects can be expected at this location. Two locations were identified for the intake and outfall structures. Both locations could however be chosen as either intake or outfall (and vice versa), hence the problem now was to see which one should be the intake and which one the outfall. Tests were performed to determine whether the intake should be located upstream (variant 1a) or downstream (variant 1b) of the outfall (Figure 5). The effects from the NNP nuclear plant also needed to be taken into account in this exercise. Model results showed that variant 1b has less impact on the neighboring plant (Electrabel CFPP being downstream of SWS) and less impact on recirculation compared to the variant 1a (Table 1). The cooling water will be taken downstream of the intake at the port (Figure 5) and will be discharged 850m upstream. The cooling water is vertically and horizontally mixed into the large tidal volume of the river Elbe (Figure 6). The recirculation and the impact on neighboring plants are minimized. The 3 C criterion is not violated in any case. This case showed that a downstream intake can be better than the reversed if other outfalls are located further upstream.

5 Figure 5: Situation at the planned SWS CFPP in Brunsbüttel. Variant 1a: Intake east, Outfall west. Variation 1b: Outfall east, Intake west. Table 1: Maximum and mean temperature increase at the intake of the neighboring NPP and at the SWS intake Temperature increase ΔT (K) Location / Variant Max. Mean Intake NPP Var. 1a Intake NPP Var. 1b Intake SWS Var. 1a Intake SWS Var. 1b Figure 6: Temperature increase (vertical average) at the planned SWS coal fired power plant (CFPP) in Brunsbüttel (variant 1b)

6 Stade The plant in Stade is located upstream of Brunsbüttel in the Elbe River. The location is tidally influenced with a mean tidal discharge of about 6,000m³/s. The upstream discharge is varying in between 200 m³/s to 3,500 m³/s and has an influence on the temperature distribution. The intake is placed landside of a coal pier. Bulk Carriers and sheet pile walls are blocking the cross current distribution of the cooling water. The pier is needed for coal supply. DHI was asked to optimize the position and the length of the pier with respect to stay within the environmental criteria of the mixing zone. It was critical to stay within the 3 C criteria. Figure 7: Intake and outfall location at the riverine location Stade (Sketch: IMS Ingenieurgesellschaft, Hamburg)

7 Figure 8: Current speed during flood period at the surface Figure 9: Current speed during ebb period at the surface The caisson part of the pier was turned into the main current (Figure 8 and Figure 9) and placed as far as possible into the Elbe (Figure 7). Due to the deepening in front of the pier and the shallow area south east of the pier, flow velocities are small. A sheet pile wall was needed to reduce the direct recirculation which originally turns up during flood tide and partly as well during ebb tide due to the small current speed and the limited water depth. The sheet pile wall length was iterated until the 3 C mixing zone criterion was not violated any more and the recirculation remains small. Figure 10 shows the maximum exceedance of the 3 C excess temperature. This value is taken from a sliding 6h mean value. Even though the current speed is small behind the pier, it is possible to keep within the environmental regulations by adopting the structures to the local situation. Additionally the influence of the plant on critical oxygen content situations in the Elbe was evaluated. This is in detail described in Stoschek, et. al (2008).

8 Figure 10: maximum exceedance of 3 C excess temperature (sliding 6 hour mean value) DISCUSSION Three examples for intake and outfall designs at the northern German coast were shown. Each example was adapted to the local situation. Numerical 3D hydraulic models were used to optimize the shape, size and location of the structures. All examples show the clear demand of on-site investigations to optimize the design for intake and outfall structures. In all shown cases optimization was needed to stay within the environmental criteria, e.g. the size of the mixing zone. REFERENCES DHI, MIKE3 Flow Model FM, Hydrodynamic Module, Scientific Documentation, Horsholm, Denmark. Stoschek, et al., Impact of cooling water intrusion on the tidal River Elbe, 31 st International Conference on Coastal Engineering (ICCE), Hamburg, Germany