Filter bypass (Fiby) & KiBy gas separation tests

Filter bypass (Fiby)

Problem definition:

Thermal water from deep geothermal energy is characterised by a high salt content and a high content of dissolved gases.
When the thermal water is pumped to the surface and cooled down, minerals may precipitate. These precipitates clog pipework and valves and impair heat transfer in the heat exchanger.
This results in high maintenance costs, system downtimes and system failures.

Solution approach:

Precipitation can be prevented or reduced by adding inhibitors or CO2 to the thermal water. Process engineering measures, such as adjusting the pressure in the pipework, are also suitable for reducing or avoiding precipitation processes.
Approach

By simulating extreme situations, situations are simulated in the FiBy test rig in order to force precipitation. The solids that form are separated from the thermal water using filters and can be analysed in terms of type and number. The pressure drop across the filter, the blockage of the filter, is also a criterion for the effectiveness of the measure to prevent precipitation.
As the gas content has a significant influence on the effectiveness of precipitation, the experiments must be carried out directly at the geothermal plant. The water must have the same mineralisation as in the reservoir. Depressurisation or cooling can disturb the sensitive chemical balance of the mineralisation.
 

 

Working principle

The thermal water flow is diverted from the thermal water pipeline above ground and divided into two partial flows. While maintaining pressure and temperature, the water from each partial flow is channelled past an injector. The mass flow is also kept constant, thereby reducing the pipework pressure. After inhibitor or CO2 has been added at the injector, the thermal water is passed through a paper filter, where the solids are collected. The pressure loss across the filter serves as a measure of the amount of minerals that have precipitated out of the water.
 

 

 

Scientific questions

The duration of the injection and the type of inhibitor used can be used to assess which inhibitors are effective at each site and how high the dosage of the inhibitor must be selected in order to achieve an optimal effect.

 

KiBy gas separation tests

Problem definition:

Thermal water contains various gases that are dissolved in the water under the high pressure inside the earth.
If this water is pumped to the earth's surface, the gas can dissolve out of the water when the pressure falls below the so-called degassing pressure. This has an influence on the properties of the thermal water, in particular the solubility of salts and minerals in the thermal water decreases and precipitation occurs.
The degassing pressure depends on the location and is typically between 3 and 20 bar. It is therefore important for the operators of geothermal plants to determine the degassing pressure, the amount of dissolved gas and the gas composition from time to time and then adjust the plant pressure if necessary.
 

 

Solution approach:

The FiBy system has a pipe section that allows the gas in a pipe section to be depressurised to any value up to the ambient pressure. The water is then channelled through a tank. At the bottom of the tank, the inflowing water is discharged again, while the gas that has been extracted from the thermal water is collected in the upper part of the tank. The amount of gas collected is compared to the amount of water that has passed through in order to determine the amount of gas released. The collected gas is analysed in a gas chromatograph. These tests are repeated at different pressures to determine when outgassing begins. At the end, the plant operator knows the degassing pressure and can operate the plant above this pressure accordingly.

 
Gases in thermal water

Typical gas contents in deep geothermal energy are between 0.1-3 litres of gas under standard conditions (30°C, 1 bar) per 1 litre of thermal water. The gases usually contain mainly CO2, but also nitrogen, hydrocarbons such as methane and propane as well as H2S. The dissolution of the gas is not instantaneous and complete. The equilibrium between the dissolved gas and the gas remaining in the water is established gradually. Just as a glass of cola or sparkling water initially releases more CO2 through gas bubbles and later bubbles less and less.
 

Scientific questions
  • How much gas escapes at what pressure
  • What is the composition of the gas 
  • How can the gas be utilised 
  • What is the release rate over time

Utilisation concept:

- thermal utilisation of the gas:

Gas engine CHP (electricity + heat)
Gas turbine (electricity + heat)
Gas burner (heating centre) Condensing boiler systems probably unsuitable

- Heat utilisation:

Coupling into the heating network
Preheating of thermal water (heating network and / or Kalina)
Post-heating Kalina circuit

Questions:

- Measurement of precipitation
- Gas volume as a function of pressure
- Gas composition