A new Israeli invention makes it possible to precipitate water with the help of a unique wind turbine whose axis of rotation is vertical, which operates without any use of electricity. This is to deal with the problem of the enormous energy consumption of the desalination process, and to also allow residents of remote areas to enjoy clean water
Yonatan Sher, an angle
It is true that all the streams flow to the sea - but in Israel the sea itself also flows, to the taps of all of us. As the Israelis like to be proud of, our small country is a powerhouse when it comes to water desalination, with five desalination plants spread along the Mediterranean Sea that produce about 75 percent of the country's drinking water consumption, and with plans to build two more in the coming years.
A perfect solution for a desert country? It is possible, but nothing comes for free: to make sea water or brackish water suitable for drinking, the desalination plants in Israel consume a lot of electricity. A new invention, which was recently presented at the biannual national conference for research students at the Grand Water Research Institute at the Technion, offers to solve the energy problem, and may even revolutionize the availability of water desalination around the world. Thus, Technion researchers desalinate water using a unique wind turbine that operates without any use of electricity, which is cheap and easy to use and maintain.
Nice to meet you - a vertical axis turbine
The amount of electricity currently consumed by the desalination processes is About 3.5 kilowatt-hours (kWh) for every cubic meter of water. To illustrate, in 2015, about 4 percent of all electricity produced in Israel was used for desalination purposes. In addition to the heavy environmental cost of the extensive energy consumption, which is mostly produced in Israel by burning fossil fuels, the need for a lot of electricity makes the technology of water desalination and purification difficult to achieve for More than a billion No one around the world has access to clean water.
At the center of the new invention is the use of a wind turbine of a type not many people are familiar with - a vertical axis turbine. The rotation in these turbines takes place around an axis that is perpendicular to the ground (to understand the direction of movement of the turbine blades, imagine a person running around an electric pole) - this is in contrast to the more familiar wind turbines, which rotate around a horizontal axis.
Despite the dominance of horizontal axis turbines, their vertical axis counterparts have several significant advantages - the first of which is their slow rotation speed. "The tip of the wing of a 'normal' turbine rotates at a speed that is approximately 7 times higher than the speed of the wind that reaches it, while the tip of our turbine rotates at approximately the same speed as the wind - that is, up to 7 times slower than traditional wind turbines," explains David Kaiser from the Faculty of Mechanical Engineering at the Technion , who headed the research under the guidance of Prof. David Greenblatt, as part of his doctoral thesis in the Technion's Energy Program - GTEP. "Vertical axis turbines can operate well even at low wind speeds, and be very efficient in producing energy in relation to their rotation speed and size." According to Kaiser, the slow rotation rate makes the vertical axis turbine much quieter than the horizontal axis turbines, and also safer for the birds - who are able to see the blades and not run into them.
According to Kaiser, another advantage of the vertical axis turbines is that the rotation occurs perpendicular to the ground, in a column that stretches along the entire height of the turbine - so that it is possible to place the generators where the electricity is produced or the devices that use the rotational energy close to the ground, and there is no need to place them at the top of the turbine as in those with the axis the horizontal This facilitates their installation and regular operation.
A final significant advantage is that vertical axis turbines can receive wind from any direction to spin. Horizontal axis turbines work optimally when their front faces exactly in the direction of the wind or exactly against the direction of the wind (depending on their design). You can think about them Like an inverted fan - Instead of using electricity to rotate blades that result in the production of wind, which blows in the direction to which the front of the fan is facing - wind that reaches the front causes the blades to rotate, which produces electricity. In contrast to this mode of operation, the blades of vertical axis turbines can be rotated by wind coming from many different directions.
Turbines for small systems
With all these advantages, it begs to be asked: why are vertical axis turbines not always used instead of the familiar axis horizontal ones? "Horizontal axis turbines are still better for producing large amounts of energy, and are the most economically efficient at large sizes," explains Kaiser. In addition, he said, the shaft and bearings (the part that reduces friction during rotation) of vertical-axis wind turbines tend to break down and destroy faster than their horizontal-axis counterparts.
"However, this problem mainly occurs when the vertical axis turbines are large," says Kaiser. "When they're small, they work well and don't get destroyed quickly." Therefore, when it comes to small systems intended for use in remote places, by people who are not professionals in their operation - the advantages of vertical axis turbines, which, as mentioned, are active even at low wind speeds that come from any direction and are easy to install and operate, make them preferable to horizontal axis turbines.
A small turbine can supply water to a community
The goal of the new research was to develop a simple and small water desalination system that is powered directly by wind energy. The researchers focused on the desalination of brackish water, which has a salt content of up to 1 percent (while the salt content of seawater is over 3 percent). "We realized that in vertical axis wind turbines it is possible to make a direct mechanical connection (that is, without the need to generate electricity and then use it to drive the pump, Y.S.) of water pumps that are on the ground to the axis of rotation, and thus start the desalination process," says Kaiser. That is, the axis of rotation of the turbine blades is directly connected to the axis of the water pump. In the first stage, the researchers connected a water pump to a vertical axis turbine which they placed in a wind tunnel (a kind of large tube with a fan operating at its opening, which produces wind at a controlled speed). They wanted to check if the system could operate optimally without electronic control systems that coordinate the activity of the turbine and the pump - which require electricity.
Unfortunately for the researchers, the results of the first experiment were disappointing. "Approximately 3 percent of the wind's energy was converted into hydraulic power (water pumping power, Y.S.) - which is really inefficient," explains Kaiser. "It took us a while to figure out what went wrong: the size of the turbine was too small for the pump, and the pump was not suitable enough for the system."
However, the researchers did not give up. In the second experiment, they used a unique, larger and more efficient turbine developed in their laboratory: a turbine measuring one meter by 80 centimeters, which uses air vortices to improve its efficiency. In addition, based on their previous results, they built a mathematical model that better estimates which water pump they need. They connected the pump to brackish water and a desalination system in reverse osmosis - The main desalination method used today in Israel and around the world. In this method, seawater or brackish water is transported at high pressure through a semi-conducting membrane: water can pass through it freely, but about 99 percent of the salts are blocked by it. After passing through the membrane, the water is almost completely free of salts and you can drink it.
This time, the experiment ended with tremendous success. "We were able to produce a system that converts about 17-12 percent of the wind energy directly into hydraulic power, for almost any wind speed and for an extremely wide salinity range," says Kaiser. "This is just as efficient - or even more so - than generating electricity from the wind and then converting it to hydraulic energy with an electric pump," says Kaiser. "For example, when the wind speed is five meters per second - its average speed here in Haifa - the system is able to produce between 1,000-500 liters of desalinated water per day and remove about 98.5-93 percent of the salts (depending on the salinity of the water and its pressure)." Although this is a modest amount of water, it should be remembered that the experiment included only a small demonstration system. In the next step, the researchers plan to build a larger system and test its operation in the Negev or Arava, to simulate activity in remote areas where a system is needed to produce fresh drinking water for needy communities.
Good news for those in need of clean water
The simple system developed by the researchers may be real news for energy-poor populations around the world, who do not have access to fresh and clean water. According to the UN, it is about 1.2 billion people today - and according to forecasts, about1.6 billion people in 2030. "Basically, the entire system we developed works without generating electricity and without the need to connect it to a power grid or an energy storage system," says Kaiser. "The system is relatively small and cheap because it does not include any electronic components. Due to the fact that it is mechanical, it is also much easier to operate and repair, and even people who do not have extensive training can set it up and take care of it."
These days, the researchers are in the middle of the process of issuing a patent, so that they can make the system commercial. They hope to place within a few years the first systems that will provide fresh water continuously in the field. According to Kaiser, water desalination is not the only purpose these systems will have: "They can also be used to improve the quality of drinking water in general - it will be possible to connect them to facilities that can clean various kinds of impurities and thus purify the water", he says. "The idea is to develop different systems of combining vertical axis turbines with water purification facilities, all of which will be simple, cheap and easy to operate."
The article was prepared by me Angle - the news agency of the Israeli Association for Ecology and Environmental Sciences
More of the topic in Hayadan:
