travellerw t1_iy431ja wrote
Reply to comment by AldoLagana in 'Landmark achievement': Rolls-Royce and easyJet hail successful hydrogen jet engine test by Wagamaga
Traditional hydrolysis of seawater is a super wasteful process. The water must be desalinated first using reverse osmosis or distillation. Then chemicals (usually potassium hydroxide) can be added back to the water to allow "clean" hydrogen to be generated.
Straight hydrolysis of sea water creates chlorine gas. Not only is chlorine gas highly toxic (used as a chemical agent during WWI and WWII), but very hard on equipment. Not to mention you would have to figure out how to dispose of it. Thus the desalination first.
This makes "green" hydrogen from sea water very costly. You are just better off to use that wind and/or solar energy elsewhere as you get more bang for your buck. It also means that green hydrogen simply cannot compete with natural gas derived hydrogen.
That brings up another topic. Hydrogen from natural gas can also be green. The process strips the hydrogen from the natural gas leaving you with the remaining chemicals (mostly carbon). Those chemicals "could" then be returned back down the well. Of course that also adds costs and no company will do it unless regulation requires it.
dbxp t1_iy4q1g7 wrote
I think ATM the focus should be on electrifying the things we can easily and improving the carbon footprint of the grid. Thing like hydrogen powered ships and planes are very much in the R&D phase. Maybe we can even avoid it by offsetting via reforestation and replacing short haul flights with high speed rail.
ArmagedonOverdrive t1_iy5gjs5 wrote
Toyota is testing hydrogen cars out in California right now. They have set up hydrogen fueling centers at gas stations in the Bay Area.
Old_Dave t1_iy5v4o0 wrote
Honda has been doing that for 20yrs in California.
ArmagedonOverdrive t1_iy69vxs wrote
Really? Hydrogen fuel cells? I had only seen adverts for Toyota!
Old_Dave t1_iy6anqe wrote
Their 1st car was the FCX and then the Clarity. They're building a large hydrogen generator to demonstrate commercial power supply for buildings. It's at their Torrence, CA campus. I think it produces 1MW AC and 1150KW DC
travellerw t1_iy6by7e wrote
Agree %100.. Right now its time to grab the low hanging fruit. When there is none of that left, then we move on to the harder problems. If we could eliminate daily personal travel and home heating energy usage that would be HUGE!
paulmclaughlin t1_iy4t1j7 wrote
Hydrolysis is using water to split something else, you're thinking of electrolysis of water.
travellerw t1_iy6bji2 wrote
Thank you.. Yup brain fart..
Robot9P t1_iy4w0a2 wrote
Could we not use fresh water, currently abundant in the Great Lake and similar areas to avoid the desalination and Clorox problems? And I realize fresh water is not endless and with climate change, reliable. But can it jumpstart or fill a void until the tech matures?
travellerw t1_iy6bhhs wrote
We %100 could.. However, its usually a bad idea to make a basic human resource compete with fuel. This is why fuel from crops is a bad idea.
[deleted] t1_iy5bv5c wrote
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No-Yogurtcloset-400 t1_iy63ro6 wrote
Only 2.5% of water on earth is freshwater. Could be tricky to divert so much of that away from agriculture.
dr_jiang t1_iy5ar4z wrote
Commercial aviation burned 95 billion gallons of jet fuel in 2019. Hydrogen has one fourth the energy density of jet fuel, and takes 2.4 gallons of water per kilogram of hydrogen if we're making it through electrolysis.
There's plenty of water in the Great Lakes (for now: we're currently turning it saline). There's not plenty of spare electricity to power the electrolysis plants, or plenty of spare money to build them, or plenty of hydrogen transport and storage infrastructure to get it from the Great Lakes to everywhere planes need to take off from.
Hydrogen has plenty of use cases where it makes sense, and its weaknesses as a fuel can be mitigated. Aviation is not one of them.
Nyrin t1_iy5gq4n wrote
>Hydrogen has one fourth the energy density of jet fuel
Just to call out: as density decreases, fuel requirement goes up a lot worse than linearly. You have to burn fuel at the beginning of the flight to transport the fuel you'll use for the rest of the flight, and the more fuel you need, the more dire that picture looks.
The exact numbers would depend on a lot of variables (weight and distance chief among them) but most flights, even the smaller and shorter ones that are feasible with hydrogen's energy density, will need way more than four times the fossil fuel amount in hydrogen.
I do think that hydrogen (and even BEV in narrow situations) might have a place in limited aviation scenarios (very short/light flights) but completely agreed that the math just doesn't work for either of these electric modalities to replace fossil fuels in-place for long, heavy flights — and that's not a "point in time, technology will keep getting better" thing.
dr_jiang t1_iy5ip33 wrote
I'd forgotten about the "need gas to haul gas" math. Honestly, I stopped taking hydrogen as aviation fuel seriously when the white papers came in describing the plane passenger economics.
The reference escapes me, but the bottom line was that converting existing airframes to hydrogen meant ripping out 14-20% of seats and paying 60% higher fuel costs. Barring science-fiction level advancements in the underlying technologies, commercial air travel as we know it can't exist in a hydrogen-fueled world.
No industry, no government, and no passenger is going to tolerate that.
[deleted] t1_iy5agi1 wrote
>Hydrogen from natural gas can also be green... Those chemicals "could" then be returned back down the well.
There is currently no way to 100% prevent methane escaping from wells or distribution pipelines. Estimates range from 2%-4% of all natural gas produced leaks into the atmosphere. And fracking has shown us that pumping chemicals back down wells can have very severe consequences. Look at the earthquake data for Oklahoma over the last decade or so.
travellerw t1_iy6cvty wrote
I agree with the leaking, however, there is tons of methane that naturally leaks out from numerous sources in the earths crust. In the grand scheme of things, the leaks would be insignificant "IF" they stopped the general burning of carbon fuels for shipping.
I don't agree with you on putting the chemicals back. Fracking is a completely different process that pumps a hydraulic fluid down the holes . Carbon capture and sequestering from natural gas hydrogen would pump the chemicals back down dead wells. It would not use hydraulic forces to try and create fractures in the crust. Simply put the unwanted chemicals back in a chamber that is now empty.
[deleted] t1_iyahp4i wrote
I think you are confused about what causes earthquakes from fracking. They're not caused by the initial fracturing of the crust, they are caused by wastewater disposal wells, which is exactly the kind of solution you are proposing.
https://www.usgs.gov/faqs/does-fracking-cause-earthquakes
>In Oklahoma, which has the most induced earthquakes in the United States, 2% of earthquakes can be linked to hydraulic fracturing operations. Given the high rate of seismicity in Oklahoma, this means that there are still many earthquakes induced by hydraulic fracturing. The remaining earthquakes are induced by wastewater disposal.
So only 2% of the earthquakes are from the actual fracking, 98% are from wastewater disposal. If waste disposal can trigger that many earthquakes in a relatively inactive zone like Oklahoma, imagine the problems it would cause in a state like California where the majority of the population lives within 30 miles of a fault zone.
tyranicalteabagger t1_iy69d9d wrote
There's a whole nother dimension to this problem also. Compressing the hydrogen to the necessary pressures to get descent energy efficiency uses a ton of energy also. Hydrogen is a really terrible energy storage and transport mechanism.
travellerw t1_iy6df25 wrote
Not to mention hydrogen embrittlement. Hydrogen is a "slippery" molecule and can even escape solid steel pipes. As the molecule passes through the pipe it creates a phenomenon called hydrogen embrittlement. Steel is eventually weakened to the point of failure. This is not only a safety issue, but a maintenance nightmare. Steel pipes need to be replaced a much faster rate when used with Hydrogen. I understand there are coating now to mitigate this problem, but they add cost and complexity.
tyranicalteabagger t1_iy6l0mu wrote
Yeah. That too. Composites mitigate it, but high pressure hydrogen is phenominally dangerous when mistakes or accidents happen. Not even so much fire, but 20000psi suddenly releasing is basically a bomb.
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