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Post by pyrophile on Dec 9, 2013 16:03:41 GMT -8
Hi all Here are my impressions and a few pictures of my first 6 ‘’ (15cm) batch box rocket stove made for a big room dedicated to circus and music.  The water tank above the riser is about 1.8 m high and 1m large, then 5 sq m (5M2). I wanted to avoid too high containers because I think it is not necessary to send heat above humans ‘s heads. In my opinion,lowering the height of the radiator induces to have rather large radiator to keep rather low surface temperatures and then limit convection. But it will be difficult to find a larger tank than this one! This old water tank was free because of 3 or 4 little holes easely repared with refractory paste. The firebox is made with firebricks and the riser with refractory ceramic wool glued around an old inox tube.  The dimensions of the firebox are those of a 8’’ (20cm) system but with a 6’’ (15cm) riser. It is also longer to accept 50 cm logs. The stove was heated for hours (7 at least) with oak (not too dry…) Happily there is no smoke but without a testo I don’t know the quality of the burn. But after some time, the smell was not so good. I had a good draft. BUT I had a big problem with embers! After maybe 2 hours of burning, the firebox was full of embers till the top of the port! I might add a grate and an ash box (with an opening easely closed) to allow air to arrive by below and then burn embers when needed. In a mass stove, this grate burns quickly the embers with a lot of heat. Then I could refill the firebox! It must be also said that oak makes a lot of embers and might not be the best wood for those stoves… The other problem was the surface temperature. After seeing the rose flame leaving the riser, I decided that it was dangeorous for the top of the galvanised water tank (galvanised at around 450 dedrees Celsius?). Then I put a little bell made with the bottom of a water heater on the riser to protect the top and also to homogeinise the surface temperatures.  But the surface temperature was too low. I will then remove this bell to rise the temperature (but I will try to protect the top of the galvanised tank!). I will give you the results when I remove the little iron bell and measure the new temperatures of the tank! I hope this had some interest for you Bye Benoit |
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Post by grizbach on Dec 9, 2013 23:41:05 GMT -8
Benoit, I very much enjoy your build!
I burn hardwood as do you. I also have embers left over. Not to the top of the port though. Once the volatiles are burnt up and the heat subsides enough to open the door without burning my eyebrows, I rake the embers to the front where they can get air to burn. A grate is a fine idea that I have pondered also. It would have to be made replaceable for it would not live long with the heat.
Your inner bell idea is good to protect the galvanize, just too much overkill. You do need something to distribute the heat. Possibly cut the sides away from the inner bell and only leave the top. Or a flat plate of steel in place of your bell.
Good luck,
Terry
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Post by pinhead on Dec 10, 2013 7:01:08 GMT -8
Are you using a metal heat riser wrapped with insulation? If so, it will be gone in no time, unfortunately. You may get a dozen burns at full power before it starts to fail. Other than that, looks good!
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Post by peterberg on Dec 10, 2013 7:22:14 GMT -8
The dimensions of the firebox are those of a 8’’ (20cm) system but with a 6’’ (15cm) riser. It is also longer to accept 50 cm logs. Benoit, It should be completely clear, all the dimensions are derived from the riser's size. So one of two things, you have to scale down the firebox to 6" or you have to scale the riser up to 8". The batch box as it stands, is a tried and tested design. Of course you are free to change it to your liking but what's the point of doing it differently? Moreover, the size of your steel tank is about the maximum which a 6" system is able to drive. First, I highly doubt your stove would run smokeless at all. Second, your ember problem could be from a too low gas velocity in the firebox. The design of the batch box looks ridicously small for a high-performance stove, but that is because you are used to large fire boxes. Please, scale down the firebox and try again, stay very close to the recommended sizes of port and p-channel, firebox and riser. It's a complex stove and highly tuned, change one aspect and it won't perform as expected. And please, don't add a grate. This is adding air under the fuel which will produce a lot more volatiles and the stove won't be able to cope with that. The result will be a chimney which is belching smoke like a do-it-yourself waste incenerator. When the pile of embers is too high, let it be for some time until there's room to add one or two logs. Lengthening the firebox, on the other hand, 8" more won't do any harm but I regard that as the only exeption. Questions: what is the length of the riser, measured from the floor of the firebox? And is this insulated? What happened to be the size of the logs? |
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Post by pinhead on Dec 10, 2013 8:59:29 GMT -8
The dimensions of the firebox are those of a 8’’ (20cm) system but with a 6’’ (15cm) riser. It is also longer to accept 50 cm logs. Benoit, It should be completely clear, all the dimensions are derived from the riser's size. So one of two things, you have to scale down the firebox to 6" or you have to scale the riser up to 8". The batch box as it stands, is a tried and tested design. Of course you are free to change it to your liking but what's the point of doing it differently? Moreover, the size of your steel tank is about the maximum which a 6" system is able to drive. Good catch, Peter. I completely overlooked this statement and I concur. If anything, I would suspect the stove to run better with a slightly undersized batch box rather than oversized. As you mentioned, however, there's no reason to "guess" the dimensions, as the design calls for very specific dimensions if the designed results are to be expected. |
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Post by grizbach on Dec 10, 2013 9:38:52 GMT -8
I assumed Benoit well knew he was over firing the system with his mismatch....to each their own.
I'm trying to help him avoid zinc poisoning.
I agree pinhead, slightly undersized is much better!
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Post by pyrophile on Dec 11, 2013 10:57:29 GMT -8
Hi and Thanks all of you
1. The oversized firebox is due to a change at the last moment of the riser"s diameter that should have been 8''. But it is true that I hoped it would fit! Wrong! I will take it in account for the following one, a 4" system surrounded by standing bricks for a very little mass stove caped with metal to heat quickly the room.
You are right, I will reduce the firebox or make a 8" riser! (The heat was not enough. But I will first remove the little iron bell and glue ceramic wool under the top of the tank to protect it.
2. About smoke, I just wanted to say that it was not smoking in the room! Outsides, I don't know as it was the night!
3. About the grate, I wanted to add a non permanent grate, being used only a few minutes to burn the embers when there are too many, then refill the firebox. But what you say, Peter, is logical : If the velocity is good, embers should not accumulate! Thanks Peter!
4. The riser is one meter high. It is made of an old inox tube surrounded by ceramic wool. The inox should actually disappear, but I hope the wool will keep its form thanks to the refractory "glue"(sodium silicate and very fine chamotte) !
5. About the sizing of the tank I have the impression that it is not too big. At the first trial, with the iron bell in the tank, the outside temperature of the tank was about 150 degrees Celsius. But I aim 250 to heat better the place without melting the galvanisation.
Thank you!
Bye
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Post by satamax on Dec 11, 2013 11:01:53 GMT -8
Benoit, You could always reduce the firebox the way i did on the green machine.
And by the way, inox is called stainless steel in english. Usualy stainless will do.
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Post by pyrophile on Dec 21, 2013 16:31:14 GMT -8
I made a new trial with the 6’’ system connected to a big cylindrical galvanized tank made to heat a uge show room. A movie was played during the trial or the trial done during the movie! The water tank is 1m80 high and 0m95 wide. The riser is made in ceramic wool (surrounding a stainless steel pipe that will disappear) -I reduced the width of the firebox to the good dimensions as advised by everybody, that is 6-7 cm narrower than it was. The height was good, 34cm (the fourth raw you see on the image on the first post is to protect the floor of the stove). -Holes allow to watch inside the bell. -The riser is now a bit higher, about 125cm -I removed the little iron bell in the big bell ( see images at the beginning of the thread -A 2,5cm thick layer of ceramic wool blanket was glued under the top of the bell to protect it from heat (it is galvanized and might melt at 420 degrees Celcius) -I did not check the humidity rate of the wood -I surrounded the bottom of the riser with earthen concrete. 1. The bell’s surface temperature rose from 130 degrees C (first time) to 250°C and more (my little IR thermometer stops working at 250° C. 2. If more than 250°C outsides, how much insides? 3. The riser starts glowing (orange) after a few minutes ! I hope it lasts! This photo was made at the first trial after a few minutes.  4. The pink-orange flame leaves the riser maybe 20cm upon it. But at the end of the burning the flame was 40 cm high, licking the ceramic wool blanket under the top! Waooh! Impressive! A bit too much for me! I don’t know what happened : the “door” badly closed? The two new littles holes bringing fresh air? Dryier pieces of wood? 5. Is this big flame normal? 6. The “draft” of the secondary air pipe is not very big 7. The exhaust pipe was hotter but not measured. Drilling the exhaust pipe during the movie… 8. The problem with too many embers remains but less important 9. The night and the movie didn’t help to examinate the exhaust gases. But I am afraid the stove did smoke… -I think that the bell of this stove (with ceramic wool blanket riser) could be much bigger. Maybe 8 or 10 sq m. -In my second batch box rocket stove I replaced the ceramic wool riser by lightweight firebricks. I feel more confident! -The next trial will be on january.I am a bit afraid by this big flame! (making melt galvanisation?). I don't know if these details are usefull, I hope! And I hope you can help me to solve these problems! Thank you very much ! Benoit |
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Post by pyrophile on Dec 21, 2013 16:39:13 GMT -8
The good orientation! Attachment DeletedBefore the long lasting 20cm high pink-orange flame. (and even higher last time at the end of the firing) 5cm thick ceramic wool blancket should be better than 2,5cm. Benoit |
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Post by pyrophile on Dec 21, 2013 16:40:55 GMT -8
Here!  |
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Post by satamax on Dec 21, 2013 22:37:02 GMT -8
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