4 ms·

What temperatures does this trade off between fewer unburied particles and more NOx production begin to take place? Is it a situation where unburned particles r

by voisin 4y ago

What temperatures does this trade off between fewer unburied particles and more NOx production begin to take place? Is it a situation where unburned particles reduce quickly and dramatically as temperature increases and NOx increases slightly until much higher temperatures or is it closer to 1:1?

littlestymaar 4y ago
It's definitely not 1:1 and for a while, every degree you gain results in less particles and barely any NOx. But to get rid of the remaining particles, you need to reach higher temperatures and then NOx emissions is going to increase. So there is a “sweet spot”, which is what's targeted by car engine manufacturers since air pollution norms have been enacted, but we can agree that the result is not “clean”, it's just “the least bad you can do”.
- 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…
        4y ago
- useryman 4y ago
  I assume there's too much airflow to use a urea-based filter like adblue or something in a home stove. Though, if you could get the stove exhaust to pass through some liquid anyway (like the bubbler in a bong, but larger), wouldn't that deal with particulates effectively?
  - littlestymaar 4y ago
    > I assume there's too much airflow to use a urea-based filter like adblue or something in a home stove. Why, these can be manufactured at the scale you need, and a home stove isn't especially powerful compared to a car or truck engine so even such a filter made for cars would work. > Though, if you could get the stove exhaust to pass through some liquid anyway (like the bubbler in a bong, but larger), wouldn't that deal with particulates effectively? Not really, first of all you'd need your bubbles to be really small for that to work, and then you'd need something (a pump) to push the smoke through the water.

by voisin 4y ago

littlestymaar 4y ago

It's definitely not 1:1 and for a while, every degree you gain results in less particles and barely any NOx. But to get rid of the remaining particles, you need to reach higher temperatures and then NOx emissions is going to increase. So there is a “sweet spot”, which is what's targeted by car engine manufacturers since air pollution norms have been enacted, but we can agree that the result is not “clean”, it's just “the least bad you can do”.

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…
      - 4y ago
useryman 4y ago
I assume there's too much airflow to use a urea-based filter like adblue or something in a home stove. Though, if you could get the stove exhaust to pass through some liquid anyway (like the bubbler in a bong, but larger), wouldn't that deal with particulates effectively?
- littlestymaar 4y ago
  > I assume there's too much airflow to use a urea-based filter like adblue or something in a home stove. Why, these can be manufactured at the scale you need, and a home stove isn't especially powerful compared to a car or truck engine so even such a filter made for cars would work. > Though, if you could get the stove exhaust to pass through some liquid anyway (like the bubbler in a bong, but larger), wouldn't that deal with particulates effectively? Not really, first of all you'd need your bubbles to be really small for that to work, and then you'd need something (a pump) to push the smoke through the water.