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"Hydrogen produces only water when burned" This oft-repeated claim is incorrect. Burning hydrogen in air produces NOx and other pollutants, and this confusion

"Hydrogen produces only water when burned" This oft-repeated claim is incorrect. Burning hydrogen in air produces NOx and other pollutants, and this confusion is promoted by fossil fuel companies that persist in telling us that it's fine to keep burning things. Hydrogen is great, but burning it is not sensible, be it by itself, or mixed into natural gas.

Moldoteck 3y ago
Can you pls elaborate why nox is produced? I thought too that burning hydro means just water
- adrian_b 3y ago
  Burning would produce just water only when done in pure oxygen. Normally burning is done in air, which has more nitrogen than oxygen. At the high temperature of the flame, a small part of the nitrogen also burns, producing nitrogen oxides, besides the hydrogen oxide, a.k.a. water.
- RetroTechie 3y ago
  In air: hot nitrogen (~80% of air) + oxygen present -> some nitrogen will react even though it's not the fuel input. Not much different from burning other stuffs in air, really (gasoline / diesel included). Of course the burn conditions have a big effect. And cleanup after the burn (catalysts) is possible. But imho the more sensible thing would be to input the H2 into a fuel cell.
benj111 3y ago
Could you not get it to produce nitrous oxide instead? Or can nox be used as an oxidiser like nitrous oxide? If the byproducts are a liquid an a gas, seems like it would be easy to separate the two. Or is there a cheap source of nitrogen less air/ oxygen?
- amluto 3y ago
  The nitrogen oxides that are produced are gasses at room temperature.
  - benj111 3y ago
    And the water is liquid.
    - amluto 3y ago
      Sure, but if you’re burning H2 in pure O2 you aren’t producing nitrogen oxides, and if you’re burning H2 in air, you end up with a whole lot of N2, CO2, and Ar left over, residual H2 or O2 (because your combustion is not exactly stoichiometric), and a relatively small fraction of nasty nitrogen oxides as side products. (And yes, you can and should condense out the water so you can recover the higher heating value instead of the lower heating value, and H2 will have the nice property that the condensate won’t be especially acidic, unlike boiler condensate from hydrocarbons, which is annoyingly acidic.)
      - benj111 3y ago
        Ah ok. Well the fact remains you have an exhaust with elevated nox. So the 3 options are to stop the nox being created to start with (no nitrogen), convert the nox into something else (nitrous oxide?) or release/store/use the nox for something. I'm not a chemist so I don't know what's possible / economic, thus the question.
thebruce87m 3y ago
Yep, they spend a lot of money trying to convince people that hydrogen is juuuuuuust around the corner, but please keep using our products until it arrives. > “hydrogen lobby, whose main players are fossil gas companies, declared a combined annual expenditure of €58.6m trying to influence Brussels policy making” https://www.rechargenews.com/energy-transition/liebreich-oil-sector-is-lobbying-for-inefficient-hydrogen-cars-because-it-wants-to-delay-electrification-/2-1-1033226 https://www.rechargenews.com/energy-transition/liebreich-oil...
credit_guy 3y ago
It looks to me you just hate fossil fuel companies. Which is fine. But if they can help to get sooner at net zero, you'd rather say no? Hydrogen can produce NOx when burned, if you burn it in air. You can burn it in flue gas (a combination of pure oxygen and CO2). Or you can simply use it in fuel cells to produce electricity. To me the main issue with this discovery that that this "large deposit" is not nearly large enough. At the high end of the estimate it would be 250 million tons of H2, which would replace about 600 million tons of CH4, which would result in about 1.5 gigatons of CO2. That's a lot, but we emit about 50 gigatons of CO2 equivalent each year. We'd need many hundreds of these fields to make a significant dent in our emissions.
- c_o_n_v_e_x 3y ago
  >You can burn it in flue gas (a combination of pure oxygen and CO2). I don't think I quite understand your comment. What type of process equipment has flue gas with only O2 and CO2?
  - credit_guy 3y ago
    This one: https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process
    - c_o_n_v_e_x 3y ago
      Ah, interesting, never come across that before. All the process equipment I've worked with (boilers, furnaces, etc.) combust fuel with ambient air.
Vaslo 3y ago
This comment is a solid of example of letting perfect be the enemy of good.

Moldoteck 3y ago

Can you pls elaborate why nox is produced? I thought too that burning hydro means just water

adrian_b 3y ago
Burning would produce just water only when done in pure oxygen. Normally burning is done in air, which has more nitrogen than oxygen. At the high temperature of the flame, a small part of the nitrogen also burns, producing nitrogen oxides, besides the hydrogen oxide, a.k.a. water.
RetroTechie 3y ago
In air: hot nitrogen (~80% of air) + oxygen present -> some nitrogen will react even though it's not the fuel input. Not much different from burning other stuffs in air, really (gasoline / diesel included). Of course the burn conditions have a big effect. And cleanup after the burn (catalysts) is possible. But imho the more sensible thing would be to input the H2 into a fuel cell.

benj111 3y ago

Could you not get it to produce nitrous oxide instead? Or can nox be used as an oxidiser like nitrous oxide? If the byproducts are a liquid an a gas, seems like it would be easy to separate the two. Or is there a cheap source of nitrogen less air/ oxygen?

amluto 3y ago
The nitrogen oxides that are produced are gasses at room temperature.
- benj111 3y ago
  And the water is liquid.
  - amluto 3y ago
    Sure, but if you’re burning H2 in pure O2 you aren’t producing nitrogen oxides, and if you’re burning H2 in air, you end up with a whole lot of N2, CO2, and Ar left over, residual H2 or O2 (because your combustion is not exactly stoichiometric), and a relatively small fraction of nasty nitrogen oxides as side products. (And yes, you can and should condense out the water so you can recover the higher heating value instead of the lower heating value, and H2 will have the nice property that the condensate won’t be especially acidic, unlike boiler condensate from hydrocarbons, which is annoyingly acidic.)
    - benj111 3y ago
      Ah ok. Well the fact remains you have an exhaust with elevated nox. So the 3 options are to stop the nox being created to start with (no nitrogen), convert the nox into something else (nitrous oxide?) or release/store/use the nox for something. I'm not a chemist so I don't know what's possible / economic, thus the question.

thebruce87m 3y ago

Yep, they spend a lot of money trying to convince people that hydrogen is juuuuuuust around the corner, but please keep using our products until it arrives. > “hydrogen lobby, whose main players are fossil gas companies, declared a combined annual expenditure of €58.6m trying to influence Brussels policy making” https://www.rechargenews.com/energy-transition/liebreich-oil-sector-is-lobbying-for-inefficient-hydrogen-cars-because-it-wants-to-delay-electrification-/2-1-1033226 https://www.rechargenews.com/energy-transition/liebreich-oil...

credit_guy 3y ago

It looks to me you just hate fossil fuel companies. Which is fine. But if they can help to get sooner at net zero, you'd rather say no? Hydrogen can produce NOx when burned, if you burn it in air. You can burn it in flue gas (a combination of pure oxygen and CO2). Or you can simply use it in fuel cells to produce electricity. To me the main issue with this discovery that that this "large deposit" is not nearly large enough. At the high end of the estimate it would be 250 million tons of H2, which would replace about 600 million tons of CH4, which would result in about 1.5 gigatons of CO2. That's a lot, but we emit about 50 gigatons of CO2 equivalent each year. We'd need many hundreds of these fields to make a significant dent in our emissions.

c_o_n_v_e_x 3y ago
>You can burn it in flue gas (a combination of pure oxygen and CO2). I don't think I quite understand your comment. What type of process equipment has flue gas with only O2 and CO2?
- credit_guy 3y ago
  This one: https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process
  - c_o_n_v_e_x 3y ago
    Ah, interesting, never come across that before. All the process equipment I've worked with (boilers, furnaces, etc.) combust fuel with ambient air.

Vaslo 3y ago

This comment is a solid of example of letting perfect be the enemy of good.