What is green hydrogen? | duty

Huge white ball on huge pillars. At the heart of this reservoir, located in the backyard of the Air Liquide facilities in Bécancour, in the Center-du-Québec region, is up to 70 tons of liquefied gas, which is colorless and odorless and tends to play a critical role in the energy transfer: hydrogen.

The smallest atom in the universe is everywhere and nowhere at the same time. It is made up of water, oil, and oil in our bodies. However, in its pure state, its lightness is insurmountable relative to the gravity of our planet, which cannot prevent it from sailing towards infinity and beyond.

In other words, to get hydrogen, it must be produced. “To make hydrogen, you need energy — and a lot of it — because you have to break a water molecule,” says Bertrand Maslot, CEO of Air Liquide Canada, referring to the large electrical cables that supply the French multinational’s Bécancouroises facilities.

“Green” hydrogen, produced from renewable energy, is currently stirring enthusiasm around the world. This clean fuel fuels the dream of a world powered by a molecule similar to fossil hydrocarbons, but is carbon neutral. No new energy is key to this plan: we are talking rather about a new “carrier” of the electricity we already have.

Currently, 90 million tons of hydrogen are produced every year in the world. However, we’re not talking about green hydrogen here: The majority of this production is generated from fossil fuels that undergo a chemical transformation that releases carbon dioxide.2. This highly affordable “gray” hydrogen, which is used primarily in oil refining and fertilizer production, accounts for nearly 2% of global greenhouse gas emissions.

Electrolysis 101

Green hydrogen may be in tune with the times, but the principle underlying its production – “the electrolysis of water” – has been known to scientists for centuries, recalls Pierre Benard, director of the Hydrogen Research Institute at the University of Quebec in Trois-Rivieres.

Basically, it involves immersing two electrodes in water and passing an electric current through them. At the negative electrode, the electrons break up water molecules (H2O) and combines with protons (H+) to produce hydrogen gas (H .).2) and OH . ions. At the anode, OH . ions Oxygen gas generation (O2) and water and donate their electrons.

Conventional electrolysis processes involve adding an alkali metal, such as sodium or potassium, to the water to speed up the electrochemical reaction by providing more OH ions. in aqueous solution. Other modern techniques, such as proton exchange membrane (PEM) electrolysis, do not require these alkali metals.

At Bécancour’s clean factory, large glass cubes contain Air Liquide’s new PEM electrolyzers. The latter started at the end of 2020, and is now producing eight tons of hydrogen per day. “Even today, we have the largest PEM electrolysis capacity here in the world,” says Mr. Masselot, noting that other projects will soon replace his.

Superb plumbing supplies these machines with pure water, after being completely stripped of minerals thanks to a series of filters. PEM electrolyzers have many advantages over alkaline electrolyzers: they are more compact, produce hydrogen without impurities, easily adapt to current changes in the power supply and do not require any chemicals. However, they are more expensive, in part because their electrodes contain metals such as iridium and platinum.

high energy density

Aside from the noise of the running pumps, the engine room is surprisingly quiet. Production, which is fully automated, requires very little manpower. The separated hydrogen exits the electrolyzer in a metal tube, which is transferred to a series of refrigerators. These lower their temperature to below minus 253 degrees Celsius in order to liquefy them – and consume more electricity in the process.

Hydrogen in all its forms is extremely light. At atmospheric pressure, it is seven times less dense than natural gas. As a liquid, it is ten times less dense than gasoline. So hydrogen is huge. However, its strength lies in its high energy density. “Per kilogram, it contains a great deal of chemical energy: three times more than fossil fuels,” notes Professor Benard.

In terms of safety, hydrogen is no more dangerous than fossil fuels. In the event of a leak, a smaller spark could lead to ignition, but because of its lower density, the hydrogen rises very quickly toward the sky, limiting the risk. Mr. Benard explains: “In the event of a traffic accident, the hydrogen will dissipate very quickly. Whereas for gasoline, the fuel remains on the ground and can fuel a fire.”

In the yard of the Bécancour factory, a semi-trailer truck waits as it fills up from the large white ball where the hydrogen stock is. A kind of large thermos on wheels, it can contain up to four tons of liquefied hydrogen. Trucks passing through here deliver their spoils to Canadian or American customers in the sectors of electronics, steel, heat treatment, chemicals, transportation, etc.

The head of Air Liquide confirms this: He has no problem finding takers for his green hydrogen – a product considered “best of the range” at the moment – from industrial customers. “There’s a whole evolution going on,” Mr. Maslott says. Quite frankly, we didn’t see that two years ago. And as we speak, the acceleration continues. »

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