Heating from the depth

Messestadt Riem in Munich has been successfully supplied with earth heat for years

Heating plant in Riem with facility for thermal water drilling in the foreground © Stadtwerke München GmbH
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For more than two years, the fair city of Riem has been supplied with district heating in an environmentally friendly way. The special thing about it: the energy comes from over 3, 000 meters depth. Geothermal energy currently covers more than 80 percent of the heat requirement, resulting in CO2 savings of around 7, 000 tons per year. The successful operation shows that the use of geothermal energy also has potential in megacities and can supply large areas with heating energy.

There is a lot of energy inside the globe - volcanoes, geysers and hot springs testify to that. Today, in over 50 countries, there are large power plants that generate electricity with the heat from within the earth. Because if you drill from the surface into the deep, the temperature rises on average by three degrees every 100 meters. At 2, 800 meters, you can expect more than 80 degrees Celsius. Enough to heat with it - without a heat pump and the associated additional power consumption.

Tapped warmer servoire

North-South section through the molasse below Munich © Stadtwerke München GmbH

In Munich, too, the conditions for so-called hydrothermal geothermal energy are very good: deep below the earth's surface there is a huge supply of hot water. The underground water reservoir is located in the so-called Malm limestone, which is extremely porous and jagged, allowing a strong circulation of hot water. A big advantage for the geothermal use, because only then is a sufficiently large flow possible. As early as 2003, two drill holes were drilled over 3, 275 meters and 3, 225 meters into the Malm-Karst in Riem - the heart of today's geothermal plant.

The stored in this layer deep groundwater with a temperature of 98 ° C is pumped through one of the holes up, its heat through heat exchanger to the local heating network and is returned through the other hole again. This is necessary in order not to disturb the water balance in the depth. The natural inflow of water into this layer is very low. On the surface, the two holes were created at a distance of only 15 meters. In the depth, on the other hand, they are about two kilometers apart, as one of the holes was deflected. This prevents the direct inflow of cooled water from the injection well to the wellbore.

"Dismantling" of earth heat

Interior view of the heating plant: heat exchangers in which the thermal water transfers its energy to the district heating circuit Stadtwerke M nchen GmbH

Nevertheless, the geothermal system removes more heat from the underground storage than is naturally replenished in the vicinity of the wells: the heat is "degraded". Therefore, a "Mining Certificate" is required for permission to use the resource. This proves that after 100 years of operation, the water at the extraction point will not have cooled more than 1 degree Celsius. For the geothermal system, two plate heat exchangers are installed in the heating plant, which transfer the heat from the thermal water to the heating water with the least amount of heat, which then transfers the heat to the connected buildings ude brings. Fully automatic control of the pumps and valves ensures that the heat from the earth is optimally fed into the overall system. The plant has a capacity of nine MW and, according to the information provided by the operators, has been in continuous operation to this day. display

(Christian Pletl - SWM Services GmbH, 23.02.2007 - AHE)