Question: I read a few articles about something called “white hydrogen” that could be used as a fuel with no greenhouse gas emissions. Sounds too good to be true. What can you tell me? — TJR, Harshaw, WI
Answer: White hydrogen isn’t really that new. It’s been around for some time:
In 1987 an unlucky well driller in western Mali lit a cigarette and was immediately engulfed in a flare of burning gas venting from the well. That well was plugged and forgotten for 20 years until prospectors looking for hydrogen rediscovered it.
Since 2010, the village of Bourakébougou has benefited from electricity generated by hydrogen fueled generators. Emissions from the well are an amazing 98% pure H2! Nobody was really looking for white hydrogen because it just wasn’t expected. Hydrogen is the lightest element and diffuses quickly, eventually escaping into space. Discoveries of major deposits of hydrogen happened by accident. We now know of large deposits in multiple locations around the globe.
This could be a big deal. Several commercial processes use a LOT of fossil fuels and cannot easily be converted to run on renewable-sourced electricity: e.g. ore smelting, steel fabrication, concrete production, glass and ceramics manufacturing, and heavy lift cargo (air, rail, road, and sea). They all require huge amounts of energy, or need the temperatures provided by combustible fuels.
But the engines that power this sector can be converted to run on hydrogen with a few minor modifications. And unlike conventional fuels, the only thing emitted by burning hydrogen is water vapor. Converting this sector of our economy to run on hydrogen would have a significant impact on global warming.
The technology for conversion already exists. The hydrogen supplies don’t. That supply can be ramped up by any number of possible production methods. The various methods have been given color names (like “white” hydrogen) that identify the source. The colors have been assigned by a variety of corporate, government, and environmental organizations, so there’s some inconsistencies. They’re not official names defined by chemists.
The following chart shows the array of color terms in use today, with a brief explanation for each. I’ve arranged them in sequence starting with the best method method of hydrogen production and working my way down. The sequence is partly based on my personal opinions, but there’s a lot of consensus in the field.
|HYDROGEN COLOR||DETAILS & COMMENTS|
||With newly discovered techniques, existing boreholes from abandoned oil wells can be seeded with biological and chemical compounds (a proprietary mix) that react with any residual oil to release H2 and CO2. More tests are needed, and a method to prevent the CO2 from escaping is in the works. The term “gold” was coined by Cemvita Factory, the developer of the process. If it works it would be slightly better than “white” hydrogen as no new boreholes would be needed.|
||This refers to hydrogen obtained from underground deposits of the gas. Only a borehole and capture system is needed, and geological surveys show it is both plentiful and at easily accessible depths.|
|YELLOW||This is a relatively new color for hydrogen. It refers to hydrogen made by electrolysis using electricity generated by solar power. It’s a sub-category of “green” hydrogen that claims to be the least expensive method.
|GREEN||Electrolysis of water uses electricity to split water molecules and generate both oxygen and hydrogen gas. If that electricity comes from a renewable source, like photovoltaic or wind farms, the hydrogen is considered to be “green.”|
|PINK||This hydrogen is generated through electrolysis using electricity generated by nuclear energy. The color “pink” is used interchangeably with “purple” or “red.”|
|TURQUOISE||This is a new entry in the hydrogen color charts, and production has yet to be proven at scale. Turquoise hydrogen is made using a process called methane pyrolysis to produce hydrogen and solid carbon. In the future, turquoise may be valued as a low-emission hydrogen if the pyrolysis is powered with renewable energy and the carbon permanently stored or used.|
Natural gas (methane) can be broken down into H2 and CO2 using a process called steam reforming. The methane is mixed with hot steam to do this. But carbon dioxide is also produced, so to qualify as “blue” there must be carbon capture and storage (CCS) as part of the process.
|GREY||This is currently the most common form of production. Hydrogen is created from natural gas, or methane, using the steam reforming process. It’s the same as “blue” hydrogen, but in this case CCS is not used.
Using a process called coal gasification finely powdered coal is mixed with oxygen and steam. The process releases H2, CO, CH4, and H2S, and without CCS ranks as one of the most environmentally unfriendly means of hydrogen synthesis. The coal used here is lignite (hence “brown”). The process continues to be improved, but lacks sufficient CCS at this time.
|BLACK||Pretty much the same as “brown” but uses anthracite coal. The greater energy density of this coal means you get more hydrogen. Unfortunately, you also get more of the CO, CH4, and H2S.|
So assuming we have a sufficient source of hydrogen, and a means to convert existing processes to run on it, how do we store and distribute the fuel to where it’s needed? That may be the tougher question, especially if the fuel must be transported. Hydrogen can be stored in three ways: atmospheric pressure, highly compressed, or in liquid form at very low temperatures. The graphic at top (you knew I’d get around to it) shows the storage options and energy density for 1 kg of hydrogen compared to 1 kg of gasoline.
I didn’t include hydrogen storage by adsorption. This is the newest technology for hydrogen storage, where the gas is adsorbed at room temperature to fine grains of metal (like palladium) in a sealed storage tank at moderate pressures. The grains have a large surface area and can hold 900X their volume of hydrogen, but because the weight of the palladium (density 12 g/cm3) has to be factored in it’s difficult to represent fairly in the graphic. Estimates based on current adsorption methods show the process can reach an energy density twice that of liquid hydrogen. So in the graphic comparison, the volume would be somewhere between highly compressed and liquid H2. Research is ongoing.
Hydrogen gas compressed to 10,000 psi could rival fossil fuels. The challenge is the greater fuel storage volume needed. Tweaking a fuel injector or jet or timing to run on hydrogen is easy, but it’s a bit more of a mod when you need to make your fuel tank 12X greater in volume.
This is a green technology worth pursuing. Estimated reserves of “white” hydrogen are immense, and its potential to mitigate climate change is significant. Some geologists claim “white” hydrogen may be replenished by natural processes faster than we can use it. Further, existing natural gas pipelines can be retrofitted to carry hydrogen, so existing distribution networks could be used. Hydrogen may never supplant batteries for EVs, but for heavy industrial processes it’s an excellent solution.
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