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Post by doudoux on Nov 18, 2021 3:50:37 GMT -8
Hello everyone, It’s my first contribution to this forum, but I’m hanging around here for a few months now. First, thank you all for all your designs, analysis, experiences, tests and advices. It’s an amazing collaborative platform, and I’m more than honored to contribute today.
With two friends, we are designing a wood-fired brewery in France. We want to create a brewery that would work with renewable energy (wood), be as efficient as possible, and emitting as few pollutants as possible. The goal : heat 1000L of clear water from 15°C to 90°C in an open tank, with a batch rocket inspired stove. For the moment, we are working on a reduced size version with a 450 L tank (https://drive.google.com/file/d/1oFHznjea-b7pJimnCbAOj8GTAgGtkn8T/view?usp=sharing). We dimensioned the stove with a 250 mm based heat riser. Smoke exhaust will be 250 mm diameter too. We plan to put the tank over the heat riser. Hot air will hit the bottom of the tank, then move around the tank's wall before going out in the chimney. You will find all the design and dimensions in attachments : - 2D pictures of the design, with a smaller tank (450 L : drive.google.com/drive/folders/12ENevxjz1_HLHXbEWRpkOeGFP1KERuq7?usp=sharing- Theoretical volumes of the firebox, the port and the heat riser : drive.google.com/drive/folders/1g9iu1QSsfaZZUklljRDGIabEW3ekJlgX?usp=sharingI can give you Sketchup file, just ask me ! Here are my questions ! - What do you think about this design ? Would it work, according to your experience ? - As we want to heat the water, we aren’t building a mass stove. We want the maximum heat to reach the water. So, we need to isolate the firebox. What materials would you use : Vermiculite (fragile…), isolating brick, both, anything else… ? Would you isolate intern wall (and protect metal part), outside, or both ? Why ? (So far, I’ve design bricks inside the fire place to represent isolation, but any modification is possible) - Do you know any experiences or anyone that has already built a stove in this purpose, and who could help/inspire us ?
Thank you all for your past and future contributions ! Have a great day. François. |
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fuegos
Full Member
not out of the woods yet
Posts: 177
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Post by fuegos on Nov 18, 2021 6:37:43 GMT -8
Hello François & welcome.the links to your google account are asking for permission so i can't see the second 2 files. It might be a good idea if you could post the sketchup files.A 250 mm system is enormous but the problem as i see it is transfering the heat - direct flow from the riser will degrade the metal. Maybe you need the tank inside some kind of chamber or bell? this sounds like a great project , fire & beer !
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amo
New Member
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Post by amo on Nov 18, 2021 9:37:21 GMT -8
Hello François ! "Les Outils de l'Autonomie" has developped a water boiler based on a DSR core. He used to have a previous version that was a J tube insulated, but it's not present on the website anymore. Maybe you could find some feedback there ? See : www.outils-autonomie.fr/outils/chauffe-eau-%C3%A0-bois-v2/It's seems to be the same philosophy of heat transfert, but in a much smaller scale. Keep us informed of your tests ! |
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Post by doudoux on Nov 22, 2021 2:20:18 GMT -8
Hello everyone ! Here is a new link to the Google file : drive.google.com/drive/folders/12ENevxjz1_HLHXbEWRpkOeGFP1KERuq7?usp=sharingI think It will allow you to access everything. I've added the SketchUp File. I hope you will be able to navigate and use it. Hello François & welcome.the links to your google account are asking for permission so i can't see the second 2 files. It might be a good idea if you could post the sketchup files.A 250 mm system is enormous but the problem as i see it is transfering the heat - direct flow from the riser will degrade the metal. Maybe you need the tank inside some kind of chamber or bell? this sounds like a great project , fire & beer ! I will think about the idea of the bell. The main issues here are, to me : - Enlargement of the stove : it will take more place - A new "layer" means more material (metal or bricks), so it will be more expensive. I need to estimate the additional cost. Still, we need to think about metal degradation... I need to find the balance between metal resistance and fire power. Maybe using a wearing part to protect the tank ? |
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Post by doudoux on Nov 22, 2021 2:25:53 GMT -8
Hello François ! "Les Outils de l'Autonomie" has developped a water boiler based on a DSR core. He used to have a previous version that was a J tube insulated, but it's not present on the website anymore. Maybe you could find some feedback there ? See : www.outils-autonomie.fr/outils/chauffe-eau-%C3%A0-bois-v2/It's seems to be the same philosophy of heat transfert, but in a much smaller scale. Keep us informed of your tests ! Thank you for the link. I've read this before. It's definitely a similar use and philosophy. I like the fact that they reach 33% efficiency rat eon water heating with a non isolated stove ! On the other hand, they use a "closed" tank, but we won't : we want to be able to stir, add something or easily access the tank. I'll try to find some information about the J-tube water boiler. |
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fuegos
Full Member
not out of the woods yet
Posts: 177
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Post by fuegos on Nov 23, 2021 5:28:42 GMT -8
"Maybe using a wearing part to protect the tank ?" a good compromise maybe ?
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Forsythe
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Instauratur Ruinae
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Post by Forsythe on Dec 13, 2021 7:53:00 GMT -8
"Maybe using a wearing part to protect the tank ?" a good compromise maybe ? +1 on this. I think the crucial thing with hot water heating systems like this (particularly the one linked at outils-autonomie.fr) is your flow-rate of water through the tubing heat exchanger. If that flow rate is not high enough, the burn unit can melt down and explode… kinda like what happens with a nuclear reactor when the electricity fails. (Think: Fukushima.) Or think of it more like an engine coolant than a water heater: If your flow rate / volume is too low for the amount of heat your “engine” (rocket) is producing, then it will overheat and begin to melt down or spall. …and that’s even if you still have water running through the heat exchanger tube at all. Everywhere I’ve seen water heater coils like this used, it’s always recommended to have the system open and fed by gravity and thermosyphon — which will act independently without electricity. The open-air system allowing for pressure expansion. If something goes wrong (like, say, your pump shuts off or you lose electrical power) then you no longer have water running through the exchanger to cool the tank — and you have water trapped in the exchanger coil which will rapidly turn to steam and create a bomb. Steam expands to 17,000 times the volume of liquid water— and in a setup like that, could do so dangerously quickly. It’s extremely risky to run wood fired water-pump heat-exchanger systems powered by electricity. Almost all of the electrical pump systems are fired by gas or heated by electrical heating element for the critically important safety feature of shutting off the fire if when the pump or the electrical system fail to work properly. Gas flame can have automatic shut-off valves in case a certain, predetermined temperature in the exchanger is exceeded, or in case the pump goes off, or in case the electrical supply is interrupted. You cannot shut-off a rocketstove in that way, and that makes them very dangerous with “water-coolant” / “water heater” exchangers. |
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fuegos
Full Member
not out of the woods yet
Posts: 177
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Post by fuegos on Dec 13, 2021 10:08:32 GMT -8
"If your flow rate / volume is too low for the amount of heat your “engine” (rocket)" then i think the water can flash to steam & explode - a member on here , Gadget , posted at some length about his adventures with water heating, well worth looking up.
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Post by Vortex on Dec 13, 2021 11:58:06 GMT -8
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Forsythe
Full Member
Instauratur Ruinae
Posts: 208
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Post by Forsythe on Dec 13, 2021 14:22:10 GMT -8
Yeah, I should have been more clear in stating those two risks separately:
[ Even *if* you’ve managed to build a functioning, gravity-fed thermosyphon which is open to the air in order to avert an explosion of flash-steam ] — you still have the risk of the coolant water flow-rate not cooling the metal fast enough [ causing the water to flash to steam and blowing out the open-atmosphere safety system ] and *then* resulting in the metal components —now exposed directly to flame without coolant flowing to bring the temps down— being melted-down or spalling from the intense heat.
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masd
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Post by masd on Jun 12, 2022 1:45:58 GMT -8
I cant argue with any of the above (and I realise this post is pretty dormant with the OP not spending any more time on the board). However, I will share my findings, some of which I gained after being doused in boiling water (many times) from my water heating system doing exactly what it was not supposed to. Hopefully they will be of use to someone and also, hopefully, re-awaken this post as I'm still working on future designs.
---- Water expands about 4% when heated from room temp to boiling. To accommodate this you need either an expansion chamber (cheap or free secondhand removed from home heating systems) or, more simply, an open reservoir/header tank
---- Thermosyphons are, in my experience, hard to get working. Given ideal circumstances (more than enough area to build whatever you want in any direction) this will likely be different but I live in a world where limitations always exist. Working within those limitations and trying to negate all the unacceptable effects results in a non-functioning thermosyphon. My solution was to use a central heating pump (Grundfos or similar - again cheap secondhand removed from heating systems). They are low power, lubricated using the water flowing through the system so designed for long life and, most importantly when the pump is turned off water can flow freely through them
Given worst case scenario with a raging fire and a power cut, the system will boil and overflow out of the header tank and douse you with boiling water if you are underneath trying to fix it. Not a terrible worst case scenario in my opinion. I fully concur with the prohibition on building a system which could explode as steam is not something to be messed with lightly.
However, taking a look at home gas boilers, they work in a closed loop with a pump and an expansion chamber. Their safety comes from thermal sensors and switches which can shut down the gas supply immediately should temperatures rise to unacceptable levels. The way I implement something like this is using a KSD9700 thermal switch (I have NO but they are available in NC if that works better with your circuit) triggering at 90 degrees C if I recall. This triggers an alarm (cheap, simple 12v ones are available with internal drivers) and gives me time to head to the fire, shut the air ports and close the damper until things are resolved.
Bearing in mind I live in an area where I dont recall we have ever had a power cut in living memory, I can get away with never having to do an emergency shutdown unless I overfire the burner.
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