Energy from deep underground: Why geothermal energy is taking off
Geothermal energy provides climate-friendly heat and electricity 24/7, independent of the weather or supply chains. However, for many years, large-scale use of geothermal energy remained limited to a handful of countries with favourable geological conditions, such as Iceland or Indonesia. New technologies are fundamentally changing this by allowing geothermal energy to be harnessed in places where access to geothermal heat was previously considered difficult. Modern pumps and valves are playing a crucial role in this breakthrough.
New technologies enable geothermal energy to be harnessed almost anywhere
Despite these advantages, geothermal is still a niche energy source: Less than one percent of the primary energy produced worldwide comes from geothermal energy, as until recently, it could only be used in geologically suitable regions such as sedimentary basins, volcanically active areas or tectonic fault zones.
Here’s why: Geothermal energy plants tap into heat which is stored deep beneath the surface of the Earth by pumping high-temperature water up to the surface via wells. This heat is then used to drive steam turbines to generate electricity or to heat district heating networks. Conventional geothermal plants rely on naturally occurring geothermal waters, usually in the form of mineral-rich brine. The surrounding rock also needs to be sufficiently permeable to allow the brine to flow to the wells. However, these conditions are only found in a handful of regions. New technologies are now overcoming these limitations and making it possible to harness geothermal energy on a much larger scale – in many regions almost everywhere.
In enhanced geothermal systems (left), water is pumped through artificially created fractures in hot rock. In closed-loop geothermal systems (right), the fluid is circulated within a closed subsurface heat exchanger.
These new technologies involve engineering the subsurface deep underground. Enhanced or engineered geothermal systems (EGS), for example, use high pressure to create fractures in the rock through which geothermal energy can be harnessed more effectively. In closed-loop geothermal systems (CLGS), horizontal drilling techniques are used to create complete circuits within the rock which act as giant heat exchangers. Neither method requires brine, as surface water is injected into the subsurface.
On the surface, modern processes likewise ensure greater efficiency: In the Organic Rankine Cycle (ORC), heat is transferred to an organic working fluid with a very low boiling point, such as isopentane or isobutane. This allows a turbine to be operated to generate electricity at relatively low temperatures.
Both of these approaches allow geothermal energy to be tapped in places where it was previously not possible. According to the IEA, drilling at depths of below eight kilometres could unlock a potential of almost 600 terawatts for electricity generation worldwide – making geothermal energy the renewable energy source with the second-highest potential after solar energy(opens in a new tab).
Pumps are key
Pumps and valves play a crucial role in geothermal power plants: They must safely extract, control and return the brine back underground – often at high temperatures and pressures, and under variable operating conditions.
Harnessing geothermal energy places maximum demands on pumps and valves due to the fluid handled, as geothermal brine is highly mineral-rich and corrosive. If it cools down or the pressure conditions change, dissolved minerals may precipitate and crystallise, leading to deposits forming in pipes, valves and pumps. These deposits reduce flow, damage components and can cause malfunctions or even failure. In addition, high temperatures and temperature fluctuations place particular stress on the mechanical seals.
Schematic diagram of a geothermal power plant with an Organic Rankine Cycle: Heat from the hot brine from the production well is transferred in the heat exchanger to a working fluid with a low boiling point, which drives a turbine with generator.
Under these conditions, the pumps must be capable of handling high flow rates and be designed to prevent cavitation (the formation of vapour bubbles, which can cause serious damage to the pumps). A key factor here is a low NPSHr to ensure the pump operates reliably and without cavitation even at low inlet pressure. KSB uses special materials to prevent corrosion and wear, and also offers pumps to API 610 standard which are designed for demanding geothermal applications.
