During lengthy dry periods, thermal power plants sometimes have to be shut down because of a lack of cooling water. The European MATChING project, which has now been completed, investigated various technologies that could resolve this issue, with project results indicating that the innovative membrane technology from VITO may already be useful in power plants on rivers with a higher risk of drought.
Lengthy and extreme dry periods, which will only become more frequent due to global warming, may cause the level of rivers and other watercourses to drop to a level where governments are forced to impose restrictions on water intake. This may not only affect farmers and water authorities, but also energy producers as their thermal power plants constantly require large quantities of cooling water, some of which evaporates in cooling towers rather than flowing straight back into rivers.
Desalination
The European Horizon 2020 MATChING project spent the last three years studying sustainable solutions for the threatened water shortage in the energy sector. VITO was one of 16 partners in the project, which was delivered by a consortium of European energy companies, technology suppliers and knowledge institutions. VITO's main focus was on limiting water usage in cooling towers – and therefore on optimising water intake and the use of cooling water – and on cooling geothermal power plants using groundwater.
One option for limiting usage by cooling towers is to desalinate the water before use. 'Removing ions such as calcium and magnesium means the cooling water can be used for longer, so less has to be pumped in,' say Sofie Van Ermen and Wim De Schepper from VITO. Desalination can be carried out using innovative electrodes; technology developed and patented by VITO. A pilot system using the desalination technology was tested at ENGIE Lab Laborelec in Linkebeek, where two cooling towers operate side by side, allowing the difference in cooling water usage and efficiency to be precisely measured.
The desalination technology was tested for three months on a pilot scale and the results demonstrate that desalinating water first is definitely worth the effort, particularly as it uses very little extra energy. 'We saw a significant reduction in the intake of cooling water,' says Van Ermen, 'and fewer chemicals were also required.'
Avoiding production losses
Although the outlook for the technology is good, there are still some economic question marks about the potential of desalination technology. Significant investment is still required because this technology is still new and experimental,' says Leo De Nocker from VITO. 'And it will not be possible to recoup that investment immediately for all power plants.' But the technology may well be worth the investment for energy producers on rivers with a higher risk of water shortages during dry periods. 'The return on investment is higher because installing it may protect the power plants against being shut down and therefore not being able to produce any electricity,' adds De Nocker. 'We are able to accurately estimate the level of risk of dry periods for some European rivers where power plants are located in countries including Bulgaria, Germany, France, Italy and the United Kingdom. We estimate the production loss for these power plants at 2.5 percent, in the current climate and with today's technology. These risks are expected to increase further due to global warming and the rise in demand for water from a range of sectors. So investing in water conservation will pay off in these cases, as it is cheaper than air cooling. 'The return on investment is also higher in places with harder water (water with a higher mineral content),' says Van Ermen.
The technology can be incorporated into the basic design when new power plants are built, which makes them more climate proof and means they can be used in more sensitive locations. After all, the expectation is that new thermal power stations will still be built in the next few decades – including in Europe. 'And they will ideally be built in locations where they can give the greatest return,' says Van Ermen. 'The results from the MATChING project can help choose those locations, an aspect that has largely been overlooked so far.'
Background
Cooling with groundwater
Low enthalpy geothermal power plants use hot water extracted from underground to supply both electricity and heat above ground, which means that the ORC system (which converts geothermal heat into electricity) has to be cooled. Existing geothermal power plants mainly use (adiabatic) air cooling for this, but the relatively high outside temperatures in summer mean that this impacts the electrical efficiency of the ORC.
So, the MATChING project investigated whether ORCs could be cooled using groundwater from a different, shallower underground aquifer. 'Using a specific aquifer means we have a supply of cooling water with a consistent temperature of 11 °C,' says Johan Van Bael from VITO/EnergyVille. 'And that is in both summer and winter.'
Cooling with groundwater is done via a closed circuit, where the cooling water is injected back underground after use. Simulation results from the MATChING project indicate that this does indeed seem to deliver production benefits. 'Cooling with groundwater in the summer generates seven percent more power than with air cooling,’ says Van Bael. Although that is calculated on top of the energy cost for recooling groundwater in the winter, 'four percent is still counted as energy gain.'
The recently begun GeoSmart research project (also part of H2020) is now investigating whether and how the efficiency and flexibility of geothermal power plants and hybrid cooling methods can be further increased.
