[HN Gopher] Batch Box Rocket Stove: Ergonomic, Efficient Wood Co...
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Batch Box Rocket Stove: Ergonomic, Efficient Wood Combustion
Author : ShroudedNight
Score : 78 points
Date : 2023-01-19 12:13 UTC (10 hours ago)
(HTM) web link (batchrocket.eu)
(TXT) w3m dump (batchrocket.eu)
| stevespang wrote:
| [dead]
| littlestymaar wrote:
| > 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
| voisin wrote:
| 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 wrote:
| 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 wrote:
| 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
|
| Seems like a bit of a stretch for a household device.
| credit_guy wrote:
| 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
| amluto wrote:
| Oxygen plus recirculated flue gas in an appropriate ratio
| would burn cooler.
| littlestymaar wrote:
| Only if you cool the flue gas beforehand, otherwise it
| doesn't change the equation.
| littlestymaar wrote:
| > 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_combus
| tion
|
| I had never heard about that, this is so cool!
|
| [1]:https://oxystore.fr/concentrateurs-d-oxygene-
| stationnaires/5...
| nanomonkey wrote:
| There are at least one misconception here that I can see
| (I work in gasification technology).
|
| You only need the pure oxygen for producing enough heat
| to pyrolysize the fuel (wood/biomass), once it's broken
| down into tar gas, you can feed it through your charcoal
| layer to further reduce it into syngas. The syngas can
| then be burned at a separate space with air at a lower
| temperature where nitric oxides aren't created.
|
| Utilizing the residual heat in the exhaust gas (flue gas)
| is another means of feeding the pyrolysis phase. As you
| mentioned its also a great source of CO2 and H2O as a
| feedstock for producing CO and H2 from the hot charcoal.
|
| What I'd like to see happen is usage of the "waste"
| oxygen produced while producing hydrogen from
| electrolysis of water. The oxygen could be used to
| produce syngas, and the hydrogen could be fed into this
| fuel stream or used separately for off hour electricity
| production.
| amluto wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| > 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.
| useryman wrote:
| 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?
| TacticalCoder wrote:
| > Higher temperatures lead to lower amount of unburned
| particles, but also lead to NOx production.
|
| Honest question: compared to which pollution if the wood is let
| to rot in nature? For it'll eventually decay too.
| pjc50 wrote:
| Natural decay doesn't produce any oxides of nitrogen because
| it's at a different temperature. It _does_ extract
| nitrogenous compounds, which are returned to the soil, but
| not in the acid form of NOx.
| jhoechtl wrote:
| NOx
| leke wrote:
| It looks a lot like my father in law's sauna.
| tylerag wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| I had missed that, thanks for pointing it out!
| CrazyPyroLinux wrote:
| 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/
| wespad wrote:
| 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=20075110
|
| https://ludens.cl/paradise/turbine/turbine.html
| kortex wrote:
| 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/B0...
|
| [2] https://www.amazon.com/Flat-pack-firepit-grill-
| carry/dp/B086...
|
| [3] https://www.etsy.com/listing/799723294/flatpack-firepit-
| port...
| gorgoiler wrote:
| I repurposed an unused grill lighting thing as a perfect
| miniature outdoor fireplace. I don't know the exact name of the
| device but it is a metal tube 8" wide and 16" tall with a metal
| grille at one end, inserted up the tube a couple of inches:
|
| https://image.dhgate.com/0x0/f2/albu/g9/M00/38/77/rBVaVV7PBK...
|
| Yes, you have to feed it sticks like cookies into a Cookie
| Monster, but it's really good for having a snap fire with lots
| of eat and lots of combustion. Because they are a ubiquitous
| garden accessory they are also very cheap.
| EL_Loco wrote:
| I've used and researched a lot of portable wood stoves. If you
| want a portable rocket stove, the one I would recommend is the
| Virestove. There are some video reviews on youtube that you can
| check out before buying it. I haven't used a more practical one
| yet. If you have the funds, they have it in titanium right now.
| Should be quite lighter than the stainless version. The mini
| version is more portable of course, but doesn't achieve the
| smokeless combustion that the larger version does. I guess it's
| the length of the chimney, but not sure.
|
| For a flat pack grill that's practical and portable, I'd
| recommend you check out the ones made by UCO. They come in
| three sizes as of now. The only downside I find with flat pack
| style grills is that on most of them you have to raise the
| grill to add wood.
|
| Somebody recommended the Firebox line. They're pretty awesome,
| but are regular wood stoves. They will smoke just like any fire
| pit or flat pack grill. No rocket smokeless combustion. The
| stainless version is very well built and will last forever.
| Haven't tried the titanium version, but seem to be well like by
| users. I'd also recommend the Bushbox, by Bushcraft Essentials.
| These towo are the best of the folding style portable wood
| stoves (not rocket style).
|
| links to this stuff (some are available on amazon):
|
| virestove.com
|
| ucogear.com/portable-grills/
|
| bushcraft-essentials.com/en/outdoor-stoves/
|
| fireboxstove.com
|
| I have to say though that I've been using wood stoves to cook
| less and less, mostly because of health concerns. It seems
| every year I find more and more reasons not to be around them.
| pnutjam wrote:
| Something like this? It's not backpack portable, although I
| think there are some out there that are smaller.
| https://www.amazon.com/dp/B09DKTM6NF
| Karrot_Kream wrote:
| If you're in the US, take a look at Firebox [1] that have a
| bunch of options through the price range all of which are
| fairly light. I would suggest going with a biomass stove with
| some thermal mass (easier to keep the burn chamber hot and also
| to stop the wind from pushing your stove around) if you're not
| constrained by backpacking/bikepacking constraints though (e.g.
| car camping or just going to a park/yard for some outdoor bbq.)
| You can make one with tin cans and some filler material
| (there's several guides online) or you can buy something like
| the EcoZoom [2].
|
| Lots of people don't realize that wet wood generates a lot more
| smoke and that it takes wood a while after falling off a tree
| to dry up, so if I'm going by car or by train I often take some
| dry wood with me to keep the smoke dry.
|
| [1]: https://www.fireboxstove.com/index.php?route=common/home
|
| [2]: https://ecozoom.com/
| leashless wrote:
| 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 (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.
| kortex wrote:
| Promising, thanks!
|
| I had a charcoal grill like this once and it worked quite
| well, but something stole it off my lawn literally between
| cooking burgers and cleaning up. Must have still been hot.
| Anyway, I tried replacing it with a similar model, and
| convection was terrible. So it seems subtleties in the design
| which make a big difference.
| leashless wrote:
| Well, at least you got the burger even if they got the
| grill.
|
| That particular device is two completely different animals
| with and without the bottom plate. Mediocre and smokey with
| it, really kind of fantastic without it. The wire mesh
| stops the big lumps from falling through but lets the ash
| go, and the whole thing burns like a chimney stove. Really
| good.
| stronglikedan wrote:
| 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 wrote:
| 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?
| zdragnar wrote:
| 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.
| davidvd wrote:
| 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.
| jollyllama wrote:
| 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?
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(page generated 2023-01-19 23:01 UTC)