CO2-dosing station

... to prevent lime precipitation in geothermal power plants

Principle of a geothermal power plant

Hot thermal water is pumped up from the rock.
The heat is extracted from the thermal water and used.
The cold thermal water is pumped back into the earth.

^{(Illustration from: umweltbundesamt.de)}

Solution equilibrium in the rock (reservoir)

In the rock there is an equilibrium between bound and dissolved
calcium. At depth, due to the high pressure carbon dioxide is dissolved
in the water.

Reaction equation

Lime precipitation in the thermal water circuit

In the technical use of thermal water, the pressure is lower than
in the earth. This results in the degassing of carbon dioxide and
precipitation of lime (CaCO3), which can lead to scaling of plant
components.

Reaction equation

Solutions for the prevention of lime precipitation

• Addition of inhibitors (prevent crystal growth)
  - already successfully tested in a project.
• Addition of carbon dioxide to keep the calcium in solution
  - to be tested shortly in the laboratory and directly on a power plant

Photo CO₂ dosing station

Plant diagram CO₂ dosing station

Principle:
CO₂ is pumped in the liquid state, then expanded and injected