The Geodynamics Enhanced Geothermal System (EGS) Project is based in Innamincka, South Australia. The aim of this project is to harness the power of geothermal brine to generate electricity. To do this, large wells are drilled into the earth as far down as 4km below the surface.  Water is pumped from a producer well to an injector well, with heat removed en-route via heat exchangers. The fluid heated in these exchangers is flashed to vapour and used to drive a turbine and produce power, before being condensed and continuing in a closed loop.

The Injector Well at Innamincka, South Australia

The temperature drop experienced by the geothermal brine causes it to precipitate certain minerals on the heat exchangers surfaces, mainly Stibnite. This mineral forms crystalline deposits in the pipe work of the Brine Cooler and Heat Exchangers, reducing the flow and therefore the conversion efficiency of the system. The client preferred solution is to pump through a combination of water, caustic and glycol at a temperature of 50 – 85 degrees Celsius, which will dissolve the Stibnite build up from the pipes. Dynapumps were invited to design, build and test a system that meets this criterion.

The Caustic Cleaning System at Dynapumps prior to transport.

The Caustic Cleaning Unit comprises of a Caustic Mixing Tank, Waste Tank, Flush Water Tank, several pumps, PLC interface modules, Sampling Sink, Emergency Shower and Wash Station. The Flush Water Pump transfers raw water from the Flush Water Tank to the Caustic Mixing Tank. The Caustic Dosing Pump and Glycol Transfer Pump contribute caustic and glycol respectively to the Caustic Mixing Tank. The Caustic Circulating Pump circulates the liquid until concentrations and temperatures are at desired level. These aspects are monitored by the PLC Interface Modules which can then operate various items in response to the signals.

Samples of the discharge and return liquid must be taken at several intervals to judge when the Caustic Cleaning Unit has completed the process. As the pH levels will be higher than the maximum measurable pH level of 14 for the entire clean, the preferred way to test the progress is by taking and treating samples of the mixture to compare colour. This is done using the sink and taps located at one end of the pump skid. Once the clean is deemed to be complete, the liquid is sent to the Waste Tank.

Samples of the liquid used for visual comparison.

As caustic is highly corrosive it is dangerous to humans and equipment if it isn’t contained within the system. To ensure the safety of the operators and environment several features have been included. The pump transferring caustic has a double mechanical seal and is pressurised to prevent leakage. The flanges have been fitted with PTFE (Teflon) covers to contain caustic leakage should the flange fail. If an accident occurs and an operator comes into contact with caustic there is an insulated Emergency Shower and Eye Wash Station. The shower has been insulated to prevent the water from heating up and burning the user. This is fed from the Flush Water Tank which has been designed so that if the power fails the shower will still run due to the back pressure in the three meter high tank.

The EGS-Geothermal industry is relatively young and requires cutting edge technology to achieve the success the industry is hoping for. This custom made Caustic Cleaning Unit was fully tested and calibrated by Dynapumps prior to delivery to ensure simple installation and operation on site.

Close up of pump skid.

Eye wash safety precaution.

For more information on Dynapumps, please contact us or call 1300 788 579. For more information on the Geodynamics Geothermal Project visit their website at http://www.geodynamics.com.au