Hydrogen harvesting and applications

"Are there hydrogen "ready" appliances available for the consumer at an affordable price, ie; clothes dryer, etc?"

NO. Any gas burning appliance could be modified/adjusted to burn hydrogen. The question is why would anyone want to do so and pay a premium price for hydrogen over NG, or even propane. Hydrogen is expensive to store and/or transport to point of use. Implementations of new processes might change that.

"Is electrolysis the most cost efficient means to harvesting hydrogen? What is the harvest rate per kg to KW?

As to harvesting/collecting under pressure, Why do you ask? Do you perceive an advantage in doing so?

Would it not be safer to pressurize the "water" and the hydrogen captured would also be pressurized thus eliminating the potential hazard of storage of the hydrogen from 14.7 psi.

Unless things have changed in last few years, I expect most hydrogen is still made using the Bosch process, outlined below.

Steam is blown through white-hot coke, and reaction is H₂O + C = H₂ + CO. A detail is the coke quickly cools and when it reaches red heat the steam is stopped and air blown in, bringing it back to white-hot, when steam is re-started, and so on. The air blow produces a mixture of nitrogen and CO (used as fuel gas) and the product streams are switched same time as steam/air.

More steam is then mixed with the H₂ + CO and passed over a catalyst, giving

H₂ + CO + H₂O = 2H₂ + CO₂. These are separated by scrubbing with water under pressure, which dissolves the CO₂.

so what is the energy balance?

From the steam reaction there is 2 kg hydrogen per 12 kg carbon, but need to air blow also. Per kg carbon, heat absorbed by the steam part is ~ heat given out by the air part, assuming carbon is only burnt to CO. So overall more like 1 kg hydrogen per 12 kg carbon = 0.08 kg/kg.

On a calorific value basis (Cal/gm), H/C = 7831/33888 = 0.23 kg H/kg C. But using electrolysis, and taking eff of power generation as 35%, comes to 0.08. From Guest's post #, I calculate energy in H₂/elec energy ~ 60% (which seems pretty good to me) so it comes down to ~ 0.05. There's more losses in the Bosch process of course, but above figure ignores the fuel value of the CO.

I'm not an expert, and there's a lot more to it, but I wouldn't think there's an advantage in making H₂ by electrolysis from coal-burning electric. If it's nuclear or hydro it's a different story.

Cheers....Codey

A long time ago I worked as the Plant Maintenance Engineer on a plant producing hydrogen as a feedstock to an ammonia synthesis plant.

The plant was a pressurised water one, the reason being that it was a great deal easier (and safer!) to pump the water up to 30bar pressure than to compress the resulting hydrogen to a similar level.

I cannot remember exact details, but I do recall we used approximately 96MW to produce 19000 Nm3/hr of hydrogen. The hydrogen purity was high as any carryover of alkali electrolyte would have 'poisoned' the ammonia synthesis catalyst

I think that with such a plant capital costs are quite high but there are other advantages (one of which is the possible production of heavy water over the years of operation as normal water splits into its constituent gasses easier than heavy water does). The plant was very clean and, with the exception of having to deal with a bit of alkali (for make up due to small leaks) from time to time was environmentally friendly. However, I suppose that overall, that would depend on how you sourced your electricity.

You do need to spend a fair bit on water treatment however, as any impurities going in, stay in.

Oh dear. Electrolysis using renewable sources produces hydrogen, an energy carrier like electricity, at a rate related to the power supplied and the energy of formation of water. Do it that way, and some might say there's some hope for the planet.

There is little point in producing hydrogen from a carbon-based fuel when converting it to a producer gas of some sort does it for less energy input and with less overall CO₂ emissions.

Why not just utilize nuclear power to electrolyze the water to hydrogen?

Let's say I come up with a "consumer" grade hydrogen generator. Are there any "consumer" appliances currently available that are hydrogen compliant? Since there isn't (and I just guessing here), how hard would it be to convert aplliances? Can't hydrogen be treated and used like natural gas or propane?

At this point I am aware that there is a higher KW input than H output potential.

I'm working on that...

Do a google search with the key words being <hydrogen generation>. You will get a long list of methods for hydrogen generation. Distributed Energy Systems has commercial hydrogen generations equipment available and can discuss the economies of the various methods of hydrogen generation. A Japanese company, Japan Fine Ceramics, has developed a method for filtering hydrogen from other elements. Professor Jerry Woodward has patented a method of using an aluminum alloy to strip hydrogen from water. And researchers at Virgina Tech have developed a method of producing hydrogen from sugar biomass.

All of these methods hold great promise of producing hydrogen, the most plentiful of all elements in the universe, at a price that can make the element the fuel of choice for us all. You may note, too, that most of these advances are a result of US government sponsored research and, also, the research into Nanotechnology. Science is working hard to develop the tool we in engineering will need to make this world safer and a pollution free energy consumer.

While some day there may be a better way to produce hydrogen, the current method for industrial applications is steam methane reforming with the following reaction:

H2O(v) + CH4 <--> 3H2 + CO

CO is then converted to CO2 in the shift reactor:

CO + H2O <--> CO2 + H2

The process typically runs around 400 psig. Steam is fed in excess to keep from coking solid carbon out on the catalyst in the furnace. Furnace temperatures are above 1500 °F and the primary reaction is endothermic, so you burn a lot of methane to heat the process up and keep it running. Typically, you also burn whatever offgases are left over in the process stream after you separate the hydrogen.

Typically, electrolysis is only used to produce ultra-high purity hydrogen for electronics or some other sensitive customer. Otherwise, it is not economical to produce through electrolysis. As other posters have stated, current methane-burning appliances would have to be modified to accomodate the different gas, burner tips and other things might have to be changed. Hydrogen does not have a very high BTU value and is not considered an efficient fuel, although it burns clean.

Is there an advantage to pressurizing the water to harvest under pressure?

Hydrogen is usually stored under fairly high pressure in cylinders. If the hydrogen is generated by electrolysis then a fairly expensve pump is ususlly required to fill the cylinders. However, there is an outfit in Connecticut that makes an electrolyzer that operates under high pressure eliminating the need for a pump. I don't have the name of the outfit or any particulars, but a demonstration standby power system has been installed at the Chewonski (spelling?) Foundation in Maine to provide backup power using a hydrogen fed fuelcell. The hydrogen is generated on site with the high pressure electrolyzer.

If I understand correctly ALL methods of producing H2 consume more energy than the net value of the H2 produced?? Of course using wind or tideal or solar could be considered differently, but energy from those sources could also have been used elsewhere.

Well, yes, that's true.

Unfortunately, there is such an efficiency loss thru each conversion that trying to shortcut a few is the mystery (if you will).

Example:

Wind> (Eff?) Mechanical> (Eff?) Electrical> (63% Eff) H2> (45% Eff) Electrical/ (80% Eff) Fuel-Heat

(personally calculated - won't promise accuracy - first 2 are too variable)

We have recently reviewed a clip that showed an invention by a broadcast engineer who was able to "Burn" salt water using a radio wave. It does not go into detail but it's my guess that he had a 10Mw freq generator emitting the wave and was able to separate H2 from O2 and ignite it. NOT efficient, but curious all the same.

First of all, if one uses solar cells to produce hydrogen, the cost is the initial cost of the solar cells (currently at about $4.50 per watt, and the hydrolysis reactor. note that not only is pure (wet) hydrogen produce but pure (wet) oxygen is also produced. One can either vent the oxygen to the atmosphere or store the oxygen for other uses. If I were to use my hydrogen in a fuel cell, then I would seriously consider using the oxygen in the fuel cell as well.

Also, since the solid oxide fuel cell reforms CH₄ to 2H₂ + CO to generate its own hydrogen, I would believe that the cost of this hydrogen is simply the cost of the methane feed to the fuel cell. If the methane is obtained through bio-digestion of household waste(s), the cost of the hydrogen is limited to the cost of the gas tight septic tank. Also, teh bio-digestion method produces a mixture, 55% methane and 45% carbon dioxide (wet) but since it is produced from bio-wastes, it does not increase the normal carbon dioxide in the atmosphere. Note, too, that the solid oxide fuel cell will reform other fuels, propane, syn-gas, alcohols, in the same manner as with methane. The only fly in the ointment is that sulfur will poison the fuel cell and thus, all fuels must be sulfur free.

What the heck ever happened to the Japanese process of using very, very high magnification sunlight on a stream of water to disassociate the oxygen from the hydrogen?! This was a really promising technology. Nothing but sunlight and a big-ass lens!

"What the heck ever happened to the Japanese process of using very, very high magnification sunlight on a stream of water to disassociate the oxygen from the hydrogen?! This was a really promising technology. Nothing but sunlight and a big-ass lens!"

More likely to vaporize than dissociate? Maybe we could get a surplus Solar Dish from the currently defunct project(s) in the southwest US and give it a try. Wonder how they kept the dissociated gases from immediately recombining?

Any sources of references?

Unfortunately, no. I saw it on an old episode of NOVA. They had a pipe with water going through it. In one section of the pipe, they had a large lens fitted to the pipe and shining sunlight directly into the water. Mind you, this was some nasty lens. Pinpointing thousands of degrees into the pipe. But that's the extent of it. Never heard anything again.

"Any sources of references?"

"Unfortunately, no. I saw it on an old episode of NOVA."

If it were more than a novelty it would be written up, advertised, sold, or some such.

Someone thought boiling was dissociating the H2O, Oh!

A friend of mine that served in the Navy said that when you entered the engine room, there was always a 2 X 4 at the entrance. The reason for the 2 X 4 was that as you walked among the pipes that were carrying super-heated steam (at least 1400° F), you waved the 2 X 4 in front of you. If the plank suddenly had a piece drop off, you went no further. It meant that there was a leak in the super heated steam pipes, and just as it had cut the 2 X 4, it would cut you in half, as well. Something like the "water knife."

In the demonstration I saw, we are talking about much hotter than 1400° super-heated steam. I'm not one to believe in conspiracy theories. I'm sure no evil cabal bought off the Japanese. I'm just curious as to what happened to the technology.

Super heated steam, in your case, also means super pressured steam, too. steam that hot, when it leaves a pinhole in a pipe comes out at very high velocity in a very thin line. This is like a knife and can easily cut through a 2x4 or a bone. It is not visible until it has traveled several feet and cooled enough to begin to condense. At this point, too, the pressure is far, far less than it was at the pinhole. Escaping steam through a pinhole can, in a short time, also erode the pipe around the pinhole to produce a complete rupture.

I am not an engineer, but have my own idea about the best way.

Have the extrapower of our energy grids as well as solar cells at sea be linked to deep, I mean very deep locations at sea. The pressure that deep will allow hydrogen to be compactly stored, (bottled also if you want for transport to the surface).

The power of the hydrogen/oxygen product can be retrieved by fuel cell technology, underwater , on location, with a power line going back to land.

If you had a closed (at the surface) pipe to the surface and let hydrogen "bubble" up from the depths you could collect and bottle it at the surface, at the depths pressure since a column of H2 would be much less weight than a column of water. Maybe, I think?

Are we on to something here?

How would you separate the H2?

How deep would this need to be?

How would you hold that long of pipe in place?

Thank you all for your input and comments.

This has been a very beneficial thread and the info I have received, I value.

Thanks again.

Keep posting with anything new!