**3.5 Future of the Soultz EGS**

492 Heat Exchangers – Basics Design Applications

Fig. 5. Schematic view of the Soultz' binary power plant after Genter et al. (2010). Each production well can be run separately thanks to the valves. The hot geothermal fluid (around 165°C) is filtered (150 µm) before entering the surface network. After the complete cycle, the fluid is reinjected in the natural rock exchanger thanks to one or two wells : with a reinjection pump in GPK3 and in addition if necessary by gravity in GPK1. The temperature, pressure and flow figures indicated are those obtained during the 8 months circulation test performed in 2008. If the Organic Rankine Cycle dedicated to electricity production is not activated (the last valve being closed), the geothermal fluid goes through 5 exchangers in the cooling cycle (lower part of the figure with the ORMAT aircooling system) in order to be reinjected after filtration (50 µm) at low temperature (around 50 to 67°C). The last of these

avoid mineral precipitations. Locally, in the filtering system, some scaling was observed with barite, celestine, iron oxides, galena and calcite mainly. In order to investigate corrosion and scaling, an innovative corrosion pilot was set up on the surface geothermal loop and tested for the first time between September 2008 and February 2009. Different kinds of steel were investigated for corrosion in the geothermal conditions of re-injection

The liquid hot brine is pumped from the rock reservoir and first filtered in the surface geothermal loop in a self-cleaning 150µm filter. Whether the ORC cycle is or not in function, either the geothermal fluid feeds the ORC exchanger to produce electricity or it feeds the

five exchangers is used only when necessary.

(20bars, < 80°C).

The total cost of the Soultz pilot operating now is 54 M€ (Soultznet, 2011). A prototype of 20- 30 MWe will follow the first pilot presently in production (1.5 MWe). On a longer term, industrial units will be constructed (Soultznet, 2011). Large-scale production units inspired from the Soultz EGS might transform the world of energy since it is clean and sustainable. It preserves fossil fuels and limits the emissions of GHG and allows a continuous production of electricity 8000 hours/year, at night as well as at day, whatever the climate conditions (SoultzNet, 2011).
