3 ms·

If one were willing to build a rather more complex device, likely requiring some electric pumps, one could use an oxygen concentrator to supply nearly pure oxyg

by amluto 4y ago

If one were willing to build a rather more complex device, likely requiring some electric pumps, one could use an oxygen concentrator to supply nearly pure oxygen as the input gas. With much less N2 available, production of nitrogen oxides would be reduced. Or you could do this: https://en.m.wikipedia.org/wiki/Chemical_looping_combustion https://en.m.wikipedia.org/wiki/Chemical_looping_combustion Seems like a bit of a stretch for a household device.

credit_guy 4y ago
Your first idea is great. Unfortunately, combustion in pure oxygen runs extremely hot, so hot that it's difficult to find materials to build a stove. https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process
- amluto 4y ago
  Oxygen plus recirculated flue gas in an appropriate ratio would burn cooler.
  - littlestymaar 4y ago
    Only if you cool the flue gas beforehand, otherwise it doesn't change the equation.
littlestymaar 4y ago
> one could use an oxygen concentrator to supply nearly pure oxygen as the input gas. With much less N2 available, production of nitrogen oxides would be reduced. I suspected the amount of energy needed to concentrate oxygen would dwarf the amount of energy of the combustion so I did the calculation: I took the following device[1]: 350W to produce up to 5L of Oxygen per minute. 5L of dioxygen means roughtly 6 gram or 0.18 mol per minute. Pure carbon combustion produces 393 kJ or energy per dioxygen molecule, whereas dihydrogen produces 572kJ per dioxygen molecule. Wood has roughtly as much Carbon as di-hydrogen (glucose, the basic block for cellulose is 6 carbon for 12 hydrogen, I'm voluntary ignoring the oxygen here since I want an upper bound), so when burning wood, for each of our dioxygen molecule we can take ~500kJ/mol as an approximation. That means your device can only produce enough oxygen to sustain a fire generating around 1,5kW of power. (I was wrong) So, even though my intuition was wrong, spending 350W of electricity to get less than 1,5kW of heat out of the wood you're burning doesn't sounds like a great deal. You're much better off with a heat pump at that point… > Or you could do this: > https://en.m.wikipedia.org/wiki/Chemical_looping_combustion https://en.m.wikipedia.org/wiki/Chemical_looping_combustion I had never heard about that, this is so cool! [1]:https://oxystore.fr/concentrateurs-d-oxygene-stationnaires/500-concentrateur-d-oxygene-stationnaire-sysmed-oc-s50.html https://oxystore.fr/concentrateurs-d-oxygene-stationnaires/5...
- amluto 4y ago
  1.5kW for a room heater isn’t bad. In any case, I imagine that an industrial scale oxygen concentrator would be dramatically more efficient.
  - littlestymaar 4y ago
    That's 1.5kW in exchange for 350W + the fuel. Whereas a heat pump gives you the same without the wood at all. (And a basic stove gives you the 1.5W for just wood without electricity nor complex and expensive machine). An industrial scale thing may be more energy efficient, but why bother when you can just get rid of the NOx with catalysis instead…
    - amluto 4y ago
      Your average heat pump doesn’t burn wood, and wood is, in several respects, an excellent fuel. It’s renewable, it’s easy and safe to store, it’s dense, and it’s easy and safe to transport. (Yes, on a large scale, it’s better for everyone to use heat pumps. But heat pumps plus wood for backup in unusually cold weather may also be a good choice.) On an industrial scale, some form of nitrogen-free combustion may simplify CO2 capture. And, if a CO2-capturing plant needs to remove nitrogen from a gas stream, removing it from the intake stream instead of the exhaust stream may eliminate the need for catalytic reduction. Also, the intake gas is clean and cool, and there’s no risk of contamination the zeolite adsorption bed (or whatever gets used) with soot.
      - littlestymaar 4y ago
        > Your average heat pump doesn’t burn wood, and wood is, in several respects, an excellent fuel. It’s renewable, it’s easy and safe to store, it’s dense, and it’s easy and safe to transport. You don't understand: your heat pump roughly generate the same amount of heat without burning anything. Instead of feeding electricity to an oxygen concentrator, you feed it to your heat pump and tada! you have your heat without burning anything! > But heat pumps plus wood for backup in unusually cold weather may also be a good choice.) Sure, but in this case you just need a good stove, if that's only used occasionally then you don't care about a little bit of NOx. > On an industrial scale, some form of nitrogen-free combustion may simplify CO2 capture. Sure, but then it's a completely different topic, at least because a concentrator won't give you nitrogen-free gas, just 8 times less nitrogen, which may not be enough for the needs. CLC is probably better suited for that, or regular air distillation to get pure oxygen.

by amluto 4y ago

credit_guy 4y ago

Your first idea is great. Unfortunately, combustion in pure oxygen runs extremely hot, so hot that it's difficult to find materials to build a stove. https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process https://en.wikipedia.org/wiki/Oxy-fuel_combustion_process

amluto 4y ago
Oxygen plus recirculated flue gas in an appropriate ratio would burn cooler.
- littlestymaar 4y ago
  Only if you cool the flue gas beforehand, otherwise it doesn't change the equation.

littlestymaar 4y ago

> one could use an oxygen concentrator to supply nearly pure oxygen as the input gas. With much less N2 available, production of nitrogen oxides would be reduced. I suspected the amount of energy needed to concentrate oxygen would dwarf the amount of energy of the combustion so I did the calculation: I took the following device[1]: 350W to produce up to 5L of Oxygen per minute. 5L of dioxygen means roughtly 6 gram or 0.18 mol per minute. Pure carbon combustion produces 393 kJ or energy per dioxygen molecule, whereas dihydrogen produces 572kJ per dioxygen molecule. Wood has roughtly as much Carbon as di-hydrogen (glucose, the basic block for cellulose is 6 carbon for 12 hydrogen, I'm voluntary ignoring the oxygen here since I want an upper bound), so when burning wood, for each of our dioxygen molecule we can take ~500kJ/mol as an approximation. That means your device can only produce enough oxygen to sustain a fire generating around 1,5kW of power. (I was wrong) So, even though my intuition was wrong, spending 350W of electricity to get less than 1,5kW of heat out of the wood you're burning doesn't sounds like a great deal. You're much better off with a heat pump at that point… > Or you could do this: > https://en.m.wikipedia.org/wiki/Chemical_looping_combustion https://en.m.wikipedia.org/wiki/Chemical_looping_combustion I had never heard about that, this is so cool! [1]:https://oxystore.fr/concentrateurs-d-oxygene-stationnaires/500-concentrateur-d-oxygene-stationnaire-sysmed-oc-s50.html https://oxystore.fr/concentrateurs-d-oxygene-stationnaires/5...

amluto 4y ago
1.5kW for a room heater isn’t bad. In any case, I imagine that an industrial scale oxygen concentrator would be dramatically more efficient.
- littlestymaar 4y ago
  That's 1.5kW in exchange for 350W + the fuel. Whereas a heat pump gives you the same without the wood at all. (And a basic stove gives you the 1.5W for just wood without electricity nor complex and expensive machine). An industrial scale thing may be more energy efficient, but why bother when you can just get rid of the NOx with catalysis instead…
  - amluto 4y ago
    Your average heat pump doesn’t burn wood, and wood is, in several respects, an excellent fuel. It’s renewable, it’s easy and safe to store, it’s dense, and it’s easy and safe to transport. (Yes, on a large scale, it’s better for everyone to use heat pumps. But heat pumps plus wood for backup in unusually cold weather may also be a good choice.) On an industrial scale, some form of nitrogen-free combustion may simplify CO2 capture. And, if a CO2-capturing plant needs to remove nitrogen from a gas stream, removing it from the intake stream instead of the exhaust stream may eliminate the need for catalytic reduction. Also, the intake gas is clean and cool, and there’s no risk of contamination the zeolite adsorption bed (or whatever gets used) with soot.
    - littlestymaar 4y ago
      > Your average heat pump doesn’t burn wood, and wood is, in several respects, an excellent fuel. It’s renewable, it’s easy and safe to store, it’s dense, and it’s easy and safe to transport. You don't understand: your heat pump roughly generate the same amount of heat without burning anything. Instead of feeding electricity to an oxygen concentrator, you feed it to your heat pump and tada! you have your heat without burning anything! > But heat pumps plus wood for backup in unusually cold weather may also be a good choice.) Sure, but in this case you just need a good stove, if that's only used occasionally then you don't care about a little bit of NOx. > On an industrial scale, some form of nitrogen-free combustion may simplify CO2 capture. Sure, but then it's a completely different topic, at least because a concentrator won't give you nitrogen-free gas, just 8 times less nitrogen, which may not be enough for the needs. CLC is probably better suited for that, or regular air distillation to get pure oxygen.