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In June this year, the International Energy Agency confirmed the fact that most experts already knew that the world should work harder to promote the use of hydrogen as a zero-emission energy source.
However, one of the challenges in producing hydrogen is that it requires a lot of energy. According to the International Energy Agency, using electricity alone to produce all of today ’s hydrogen will require 3,600 TWh, which is more than the EU ’s annual electricity generation.
But what if you can use existing energy waste to help hydrogen production? Researchers at the Norwegian University of Science and Technology have developed a new method that uses waste heat from other industrial processes to achieve this goal.
Kjersti Wergeland Krakhella said: "We discovered a method of using heat, which was previously wasted in vain." She is the first author of this paper, which was published in the academic journal "MDPI Energy". "These are low-grade, low-temperature thermal energy-but they can be used to make hydrogen."
1/7 of hydropower output in Norway
Waste heat is exactly what it sounds like-a by-product of industrial processes. From industrial boilers to waste power plants, many industrial processes generate waste heat.
More often, this excess heat will be released into the environment. Energy experts say that the waste heat generated by Norwegian industry and commerce is equivalent to 20TWh of energy each year.
From this perspective, Norway's entire hydropower system generates 140TWh of electricity per year. This means that a lot of waste heat can be used.
Membrane and salt
The researchers used a technique called reverse electrodialysis (RED), which relies on a salt solution and two ion exchange membranes.
To understand the actual work of researchers, we must first understand how RED technology works.
In RED, there is a membrane called anion exchange membrane, or AEM, which allows negatively charged electrons (anions) to pass through the membrane, while another membrane is called a cation exchange membrane, or CEM, which allows positively charged electrons (cations ) Through the membrane.
These membranes separate dilute brine from concentrated brine. Ions migrate from concentrated solutions to dilute solutions. Since two different types of membranes appear alternately, anions and cations are forced to migrate in opposite directions.
When these alternating water columns are sandwiched between two electrodes, the stack can generate enough energy to break the water into hydrogen (on the cathode side) and oxygen (on the anode side).
This method was developed in the 1950s, using salt water and river water for the first time.
However, what Krakhella and her colleagues did was use a salt called potassium nitrate. The use of this salt allows them to use waste heat as part of the process.
Reuse these salts with waste heat
If you run the RED stack described above, at some point, the concentration of concentrated salt solution and diluted salt solution will become closer and closer, so they must be updated.
This means that you need to find a way to increase the salt concentration in the concentrated solution and remove the salt from the dilute solution. This is where waste heat can come into play.
The researchers tested two systems.
The first is to use waste heat to evaporate the water in the concentrated solution to increase its concentration.
The second system uses waste heat to precipitate the salt from the diluted solution (so the salt will be less).
Krakhella said: "If you find a way to remove water or salt, you have completed the task."
Have their own strengths
When the researchers looked at their results, they found that using existing membrane technology, using waste heat to evaporate water in the system, the unit membrane area produced more hydrogen than the precipitation method.
From a cost perspective, this makes it a better choice.
However, the researchers found that in terms of energy requirements, the precipitation process is better. For example, the energy required to produce one cubic meter of hydrogen by precipitation is only 8.2kWh, while the evaporation method is 55kWh.
New system with many possibilities
Although Krakhella's work proves that this concept is feasible, she mainly uses laboratory experimental models and a large number of computer operations. There is still much work to be done, especially in choosing the type of salt used in the production process.
The researchers currently choose potassium nitrate as their salt system, but other salts can also work, she said.
"This is a brand new system," she said. "We need to do more testing on other concentrations of salt."
Film price is the limiting factor
Another factor limiting large-scale hydrogen production is that the membrane itself is still very expensive.
Krakhella hopes that as society seeks to get rid of fossil fuels, the increase in demand will push the price of the film down while improving the characteristics of the film itself.
"The membrane is the most expensive part of our system," Krakhella said. "But everyone knows that we need to do something for the environment. If we don't develop non-polluting energy, the cost may be much higher."
(Original source: Fuel Cell Engineering China New Energy Network Comprehensive)
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