13 ms·

Batch Box Rocket Stove: Ergonomic, Efficient Wood Combustion

88 points by ShroudedNight 4y ago

tylerag 4y ago
Is this the same as a rocket mass heater? Appears to be a somewhat different design, but same physics. A rocket mass heater is going to have the burner box outside of the bell.
- ShroudedNight 4y ago
  Essentially, yes. The instructions / calculations on the building page are all oriented towards building one for the purposes of space heating. That being said, I'm intrigued to try the 'core' design in something like a pizza oven to see how it performs.
  - InvaderFizz 4y ago
    If you scroll down on the completed projects page, someone made a combo pizza oven and pool heater. It apparently excels at both. Once it's up to temperature, 4 minutes to cook a pizza.
    - ShroudedNight 4y ago
      I had missed that, thanks for pointing it out!
littlestymaar 4y ago
> Higher temperatures result in cleaner combustion. Higher temperatures lead to lower amount of unburned particles, but also lead to NOx production. That's what the WW scandal was about by the way. If you want clean combustion, you need high temperature + SCR[1] [1]: https://en.wikipedia.org/wiki/Selective_catalytic_reduction https://en.wikipedia.org/wiki/Selective_catalytic_reduction
- 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.
kortex 4y ago
An annual problem I have every summer is dealing with smoky campfires when camping. Your bog standard cicle-of-rocks or metal ring fire pit is crazy inefficient, and unless you run continuously in the offgassing phase (bright, tall orange flames, as the wood gas burns off), with lots of convection, you inevitably produce a ton of smoke. This is terrible for all folks, but my asthma-prone lungs get especially cranky. So you either have to continuously feed wood (inefficient and costly), or play the game of shuffling upwind constantly. I usually end up tinkering and modifying the fire pit to try to eek some better air flow patterns, but it's usually a lost cause with open pit fires. I might just cave and get one of those stainless inserts, but what I'd really like is something flatpack that I could assemble into a more efficient burner. I've seen small ones [1] that slot together to make a rocket stove, but nothing campfire sized. I wonder how much demand there would be for such a thing. Seems like there are several products for general "firepit" designs, but without a chimney, these suffer from most of the same problems as open pits. [2][3] Edit: oh, maybe a "tent stove" is what I'm looking for. [1] https://www.amazon.com/Marsh-Kettles-Flat-Rocket-Stove/dp/B07XSLXN4P https://www.amazon.com/Marsh-Kettles-Flat-Rocket-Stove/dp/B0... [2] https://www.amazon.com/Flat-pack-firepit-grill-carry/dp/B086MC4F61 https://www.amazon.com/Flat-pack-firepit-grill-carry/dp/B086... [3] https://www.etsy.com/listing/799723294/flatpack-firepit-portable-collapsible https://www.etsy.com/listing/799723294/flatpack-firepit-port...
- stronglikedan 4y ago
  For those metal ring pits with a cooking grate, you can build the fire on top of the grate for better airflow. If you can get air coming in underneath the fire from all sides, it'll greatly reduce the smoke. And you also reduce the chances of smoke "chasing" the person that's sitting the closest, since they're not blocking a lot of airflow from the sides. Still not peak efficiency, but a lot less smoke.
- leashless 4y ago
  https://www.amazon.com/Quick-Grill-Large-Original-Stainless/dp/B00DNTXCMI/ref=sr_1_7?crid=EFI9TAJG1Z6H&keywords=collapsible+bbq+steel&qid=1674143589&sprefix=collapsible+bbq+steel%2Caps%2C191&sr=8-7 https://www.amazon.com/Quick-Grill-Large-Original-Stainless/... This is dirt cheap, light-ish, and excellent. To get mostly-smokeless performance, leave out the bottom metal plate when you assemble it so it gets continuous air flow right through the device. I used to use https://www.solostove.com/en-us https://www.solostove.com/en-us (car camping only) and it just burns too* clean - no smoke, hot fire, goes through fuel very fast, and all the heat goes straight up. Still love that thing, but actually for an "improved campfire experience" that collapsible grill thing is excellent. Particularly useful: the heat reflects off the inclined metal plates right on to the people sitting around the fire, in exactly the way it does not on a solo stove. It's really good. Makes me happy.
leashless 4y ago
It's not immediately clear what the difference is between this and regular rocket stoves. I think (I could not find a clear description that was short and easy to understand, maybe I missed it) that it has a door on the box where the wood goes in, and a pipe that feeds fresh air into that box to keep the combustion going. Did I get that right?
- davidvd 4y ago
  The difference is that in a normal rocket, you need to keep feeding the fire at regular intervals because the feed tube is so small. In the batch box you load it once and let it burn.
- zdragnar 4y ago
  To add a bit of context to the sibling comment, rocket stoves can work when made out of pretty much any material, because the air flow is not tightly regulated. Batch box's purpose is to allow a more full-sized fire with the efficiency of a rocket stove, and there are several key differences to hit that: - It should be made of a refractory material. Rocket stoves function perfectly well with plate metal or anything, really - All dimensions, especially the air inlets and heat riser, must match a specific set of ratios to preserve the specific airflow needed to maximize burn efficiency. Too much means air will move too quickly, preventing full burn - A choke point between the burn chamber and riser exists to slow down and funnel gasses and heat together. Without this, you don't have enough heat to get full combustion Batch box burners tend to be quite a bit more fussy than a rocket stove to get going, though if a good portion of your exhaust rise is inside and pre-warmed, it should have a strong enough natural draft that starting it isn't much extra effort. I toyed around with the dimensions a bit myself and have something that works really well (cylindrical chamber rather than block), though I don't think I'm getting optimal efficiency out of it.
jollyllama 4y ago
Any reason you couldn't have bells on separate floors? I.e. core and a bell on floor one that leads to a bell on floor two before exiting through a chimney?
CrazyPyroLinux 4y ago
In the US, the Liberator rocket heater is a great option. It's UL listed if you care about that sort of thing. https://rocketheater.com/ https://rocketheater.com/
leke 4y ago
It looks a lot like my father in law's sauna.
wespad 4y ago
This is up there with one of my favorites from Hacker News: The Microhydro Plant https://news.ycombinator.com/item?id=6895582 https://news.ycombinator.com/item?id=6895582 https://news.ycombinator.com/item?id=20075110 https://news.ycombinator.com/item?id=20075110 https://ludens.cl/paradise/turbine/turbine.html https://ludens.cl/paradise/turbine/turbine.html
stevespang 4y ago
[dead]
jonstewart 4y ago
I really like the idea of using a dual bell system, where one is small and steel and the other’s large and masonry. The thing that triggers me to build/add to a fire is feeling cold, so having quick response is nice. But then of course you want heat mass to avoid dumping all of the extra heat out the chimney. If my Hearthstone stove ever goes out, I’d like to build one of these.

88 points by ShroudedNight 4y ago

Is this the same as a rocket mass heater? Appears to be a somewhat different design, but same physics. A rocket mass heater is going to have the burner box outside of the bell.

ShroudedNight 4y ago
Essentially, yes. The instructions / calculations on the building page are all oriented towards building one for the purposes of space heating. That being said, I'm intrigued to try the 'core' design in something like a pizza oven to see how it performs.
- InvaderFizz 4y ago
  If you scroll down on the completed projects page, someone made a combo pizza oven and pool heater. It apparently excels at both. Once it's up to temperature, 4 minutes to cook a pizza.
  - ShroudedNight 4y ago
    I had missed that, thanks for pointing it out!

littlestymaar 4y ago

> Higher temperatures result in cleaner combustion. Higher temperatures lead to lower amount of unburned particles, but also lead to NOx production. That's what the WW scandal was about by the way. If you want clean combustion, you need high temperature + SCR[1] [1]: https://en.wikipedia.org/wiki/Selective_catalytic_reduction https://en.wikipedia.org/wiki/Selective_catalytic_reduction

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.

kortex 4y ago

An annual problem I have every summer is dealing with smoky campfires when camping. Your bog standard cicle-of-rocks or metal ring fire pit is crazy inefficient, and unless you run continuously in the offgassing phase (bright, tall orange flames, as the wood gas burns off), with lots of convection, you inevitably produce a ton of smoke. This is terrible for all folks, but my asthma-prone lungs get especially cranky. So you either have to continuously feed wood (inefficient and costly), or play the game of shuffling upwind constantly. I usually end up tinkering and modifying the fire pit to try to eek some better air flow patterns, but it's usually a lost cause with open pit fires. I might just cave and get one of those stainless inserts, but what I'd really like is something flatpack that I could assemble into a more efficient burner. I've seen small ones [1] that slot together to make a rocket stove, but nothing campfire sized. I wonder how much demand there would be for such a thing. Seems like there are several products for general "firepit" designs, but without a chimney, these suffer from most of the same problems as open pits. [2][3] Edit: oh, maybe a "tent stove" is what I'm looking for. [1] https://www.amazon.com/Marsh-Kettles-Flat-Rocket-Stove/dp/B07XSLXN4P https://www.amazon.com/Marsh-Kettles-Flat-Rocket-Stove/dp/B0... [2] https://www.amazon.com/Flat-pack-firepit-grill-carry/dp/B086MC4F61 https://www.amazon.com/Flat-pack-firepit-grill-carry/dp/B086... [3] https://www.etsy.com/listing/799723294/flatpack-firepit-portable-collapsible https://www.etsy.com/listing/799723294/flatpack-firepit-port...

stronglikedan 4y ago
For those metal ring pits with a cooking grate, you can build the fire on top of the grate for better airflow. If you can get air coming in underneath the fire from all sides, it'll greatly reduce the smoke. And you also reduce the chances of smoke "chasing" the person that's sitting the closest, since they're not blocking a lot of airflow from the sides. Still not peak efficiency, but a lot less smoke.
leashless 4y ago
https://www.amazon.com/Quick-Grill-Large-Original-Stainless/dp/B00DNTXCMI/ref=sr_1_7?crid=EFI9TAJG1Z6H&keywords=collapsible+bbq+steel&qid=1674143589&sprefix=collapsible+bbq+steel%2Caps%2C191&sr=8-7 https://www.amazon.com/Quick-Grill-Large-Original-Stainless/... This is dirt cheap, light-ish, and excellent. To get mostly-smokeless performance, leave out the bottom metal plate when you assemble it so it gets continuous air flow right through the device. I used to use https://www.solostove.com/en-us https://www.solostove.com/en-us (car camping only) and it just burns too* clean - no smoke, hot fire, goes through fuel very fast, and all the heat goes straight up. Still love that thing, but actually for an "improved campfire experience" that collapsible grill thing is excellent. Particularly useful: the heat reflects off the inclined metal plates right on to the people sitting around the fire, in exactly the way it does not on a solo stove. It's really good. Makes me happy.

leashless 4y ago

It's not immediately clear what the difference is between this and regular rocket stoves. I think (I could not find a clear description that was short and easy to understand, maybe I missed it) that it has a door on the box where the wood goes in, and a pipe that feeds fresh air into that box to keep the combustion going. Did I get that right?

davidvd 4y ago
The difference is that in a normal rocket, you need to keep feeding the fire at regular intervals because the feed tube is so small. In the batch box you load it once and let it burn.
zdragnar 4y ago
To add a bit of context to the sibling comment, rocket stoves can work when made out of pretty much any material, because the air flow is not tightly regulated. Batch box's purpose is to allow a more full-sized fire with the efficiency of a rocket stove, and there are several key differences to hit that: - It should be made of a refractory material. Rocket stoves function perfectly well with plate metal or anything, really - All dimensions, especially the air inlets and heat riser, must match a specific set of ratios to preserve the specific airflow needed to maximize burn efficiency. Too much means air will move too quickly, preventing full burn - A choke point between the burn chamber and riser exists to slow down and funnel gasses and heat together. Without this, you don't have enough heat to get full combustion Batch box burners tend to be quite a bit more fussy than a rocket stove to get going, though if a good portion of your exhaust rise is inside and pre-warmed, it should have a strong enough natural draft that starting it isn't much extra effort. I toyed around with the dimensions a bit myself and have something that works really well (cylindrical chamber rather than block), though I don't think I'm getting optimal efficiency out of it.

jollyllama 4y ago

Any reason you couldn't have bells on separate floors? I.e. core and a bell on floor one that leads to a bell on floor two before exiting through a chimney?

CrazyPyroLinux 4y ago

In the US, the Liberator rocket heater is a great option. It's UL listed if you care about that sort of thing. https://rocketheater.com/ https://rocketheater.com/

leke 4y ago

It looks a lot like my father in law's sauna.

wespad 4y ago

This is up there with one of my favorites from Hacker News: The Microhydro Plant https://news.ycombinator.com/item?id=6895582 https://news.ycombinator.com/item?id=6895582 https://news.ycombinator.com/item?id=20075110 https://news.ycombinator.com/item?id=20075110 https://ludens.cl/paradise/turbine/turbine.html https://ludens.cl/paradise/turbine/turbine.html

stevespang 4y ago

[dead]

jonstewart 4y ago

I really like the idea of using a dual bell system, where one is small and steel and the other’s large and masonry. The thing that triggers me to build/add to a fire is feeling cold, so having quick response is nice. But then of course you want heat mass to avoid dumping all of the extra heat out the chimney. If my Hearthstone stove ever goes out, I’d like to build one of these.