riser sizing for 2 oil drum bell design

after a week of obsessive reading i think i have a rough idea of what i want to build. i have found a source of firebricks and clay. i cant get to them for a few weeks due to the weather so in the meantime i will get the stuff i need to buy sorted out. imy plan is to use matts idea of 2 oil drums as bells connected with 8" pipes. if i use that design as basis for the design i can buy some cardboard tube to make a cast riser. as i don't have any steel tube anyway it makes more sense to go down the cast riser route. what size tube should i get to match the 2 oil drum flue design? i don't want to get this part wrong as this will be the most expensive part of the design. rather than cardboard i could use aluminium tube instead as that may work out cheaper. i will still have the melting issue then though. but aluminium has a quite high burning point i seem to recall. any thoughts anyone?

Bob, it's hard to tell without understanding what you are asking exactly.

Are you talking about 2 barrels side by side, as sometimes seen, one being the "barrel" we usualy see with the heat riser in it, the other one being a bell?

Or a stack of barrels like Peterberg's workshop heater, or else a half barrel systel, as per Matthew Walker's new york restaurant install?

hi, i am thinking the 2 half barrels in a line joined together with a pipe as in Mathew walkers idea. barrels i have, smooth walled 8 inch pipe i would have to find. i can get the spiral wound stuff but been told that is less than ideal.

Hi Bob, so, two halves of a barrel is not much, even if used as a double bell.

A 6 incher J can "feed" a 3 to 4 M² bell. Usualy, if the gases don't sweep the bottom too much.

A barrel is 1.68m² so a pair of them should do you good. I would say, do two bells, not four tho. You cut the ends of the two barrel halves you'll be mating. And tack weld them together. Leaving a strip of the barrel top, at the bottom of the cut stops it from opening.

So for a 6 J you need 4 times 6 for the heat riser, which is 24 inches minimum. I preffer taller heat risers myself.

Hth.

Max.

been doing a few measurements with what i have lying around. i have lots of 11 inch diameter cooking oil drums plenty of 45 gallon oil drums 24inch diameter. if i go for a 6 inch riser that will give me just over 2 inches of insulation around the riser. will this be enough? i will have 6 inches between the outside of the riser and the outside drum. i am not sure how much perlite to get. i can get it in 100 ltr bags for a good price. will i need more than one bag? clay i can get from a local potter. the rest of the build i can work around once i know how big to make the riser. can get the cardboard tubing in any length i want i can always make the drum around the outside of the riser bigger if i have to.

Bob, two inches of perlite clay mix should do the job, if you force a bit on the perlite.

ok got that thanks. as i cant get the cheap clay till the ground dries out a bit i have decided to buy some clay for the riser as i can get on with that while i wait. had a look on ebay and there seems to be lots of different types of clay depending on the end use. prices are all about the same so should i get fire clay for kiln building? it comes in 25 kilo bags delivered to the door for around £20. 25 kilo of clay and 100 litres of perlite would have thought that should be enough. the perlite i can get locally in different grades. apologies if i sound a like i am being too fussy but as there are different options available i might as well get the right stuff. medium perlite 1-5 mm diameter sound like the right stuff?

Well, 20 squids for 25 kils of fire clay sounds good to me.

Tho, what is your perlite? Garden grade or construction grade? The garden one is not too good, as it keeps the water from the mix forever. In France the usual construction grade is efiperl. Don't know what might be available to you in UK.

opps nearly got the horticultural grade. is this this the stuff i need instead?

http://www.william-sinclair.co.uk/industrial/products/perlite/pclg

Yep Bob, that one is suppa duppa! Tho, just basic stuff at your local builder's supplies should be fine.

Bob, sumthin which might intrest you.

http://donkey32.proboards.com/post/10941/thread

very interesting thread on the castable risers. i like the idea of doing it in sections so you can tune it as you experiment.

i had another thought. been looking at robs pellet burning monster, that had the burnt out riser. i was wondering about the failure mode if this were to happen. unlikely to i know as he was shoving a lot of pellets into his. if the riser fails i would have thought the draught would be greatly reduced ,especially if the manifold got blocked up. this would kill the draught leading to the fire blowing smoke into the room i would have expected. it looks like something else happened and the fire kept going in the "right "direction. if you had a heated bench i could see this being quite dangerous if the bench heated up. but with no riser would the fire just bypass the drum and just go straight though the flue?

i am quite risk averse as i have a spike WMO burner in the bus. if i forget to reduce the flow after starting it it turns into a raging monster very quickly, but at least i can see that happening. a failed riser may be a bit more difficult to spot. i am sure i am not the first to think about this, or at least i hope i am not anyway. anyone else had this happen?

Bob, if the path for gases gets blocked, = smokeback. If there's no riser whatsoever, then if there's an external chimney, draft will continue and the barrel will act as a bell. I don't advise rockets without chimneys.

still getting quotes for various items for my build. waiting for a price on the perlite from a builders merchant. got the cardboard tube price sorted. i can just but one if i want. after adding it all up there isn't a great deal of difference between making the riser from fireclay and perlite around a cardboard liner and using ceraboard. a half sheet of 25mm cerabord is about the same price. a full board is 1200mm x1000mm so i assume a half board will be 600mm x 1000mm. not sure if 25mm of ceraboard would be enough insulation around the riser.
if i use ceraboard i may get the burn chamber out of the sheet as well. still need to draw it to confirm i can do that. not sure if ceraboard would be better or not. certainly easier. i could maybe stick to the cast riser and make the burn chamber and feed from ceraboard being as i don't have any firebricks. the firebricks area maybe at an unknown price. i may have to rip a kiln apart to get at them which is a lot of work.
what i don't want to do is build something using the wrong materials and having to buy everything again. that would be a bit disheartening.

Bob, if you can get ahold of insulating firebricks, they are wonderfull for burn tunels.

But, are you aware of this?

http://www.laganchimneysystems.com/flue_liners.html I bet they're availlable in UK!

You need one metal tube to put around, and any kind of insulation which can whistand heat (rockwool, superwool, perlite, vermiculite) to pack between the two. They do crack, usualy once, and they're good for years afterwards. You can do the outside tube with any kind of metallic tube, or even with rolled sheet metal, held by wire or rivets. Pish easy to make heat risers that way. And you only need a few bricks to make the burn tunel and feed tube.

Bob,

I would recommend 50 mm thickness for the riser. You can screw 4 panels together using stainless steel screws.

I would not recommend using the board for a burn tunnel. I think if you look at the MSDS on the product, it probably has a lower modulus of rupture after it has been exposed to some particular temperature which you are likely to reach if the board is your burn tunnel. The problem with that is that you will be poking sticks into your feed tube and could easily break out the bottom of the burn tunnel with a stick.

thanks for feedback. i have found a price list for terracotta flue liner in the uk.

http://content.wavin.com/WAXUK.NSF/pages/Hepworth-Terracotta-TPL-010214-EN/$FILE/Terracotta_TPL_010214.pdf

not sure how much they would be after tax and builders merchants bit as well. the handy part is i can get those locally so that is a plus. i like the idea as i could experiment by just packing perlite around them with my old cooking oil drums to hold the perlite in place and pull it apart later if i decided to change the design. will i get away with 2 x 150mm ones which will give me 600mm high or should i go for 3 of them which will give me 900mm?
cindy, will stick to fire brick for the burn tube and feed then. had a look on ebay and i can get a few fire bricks for not a lot of money. not sure what sort they are but a lot better informed after reading erica's very informative article on the different types and their suitability for different parts of the build.
the flue pipe certainly seems to be the easiest option i have come across so far.
as an aside i made a rocket stove out of a log today just to see how they behaved. the log is saturated with water like everything else around here, drilled a couple of holes had several attempts to get to stay alight but after drying some twigs in the oven managed to get it working well enough to boil a pint of water in about 8 minutes. very impressed.

been looking around the web a bit more and found these.

https://www.oilstoves.co.uk/webdocs/prices/ISOKERN_Pumice_08.03.13.pdf

seem as good if not better than the clay ones and about the same price. they are both rated for a 1000C for 30 minutes in a chimney fire but the pumice ones are better insulated apparently according to the sales blurb. suspect the prices wiol be lower than that from a builders merchant. i will do some phoning around tomorrow and report back.

Hi Bob.

Whoah! The Wavin stuff is dire! Forget about the pumice stuff i think. That comes from Schiedel, so, just ask for a Kerastar tube, (here at the bottom of the page http://www.schiedel.co.uk/products/pumice-old/other-schiedel-products/steel ) that's a ready made heat riser! If they can get you one, otherwise

http://www.schiedel.co.uk/products/ceramic-products-and-systems/ceramic/liners

I didn't know Shiedel was selling in uk!

Have a check for Landini SPA if you can find their stuff in uk. I go on the other side of the Italian border, and it costs me 30 euros for 4 tubes to make a rocket J

Well, a little edit. Forget what i said, about teh kerastar, it's bloody expensive.

http://www.bdb.at/Download/preisliste/pdf/50056_Preisliste_2013_KeraStar_ICS.pdf

does the proviso on wavin liners also apply to the terracotta ones as well? the local builders merchants only stock wavin products. the kerastar liners look ideal. haven't dared ask the price though. suspect it is one of those "if you need to ask the price you cant afford it" sort of things.

Bob, Call hepworth terracotta for their specs. I bet it's rated 400C°, and 1000C° for 30 minutes. If there's chamotte in their liners, you should be ok for a heat riser. They crack once then expand and contract, but retail their fireproof properties. And they hold. Well, at least the landini spa ones i use. I've checket the kerastar tubes, a whole 5m system costs more than 2000 euros!

Another uk supplier of clay flue liners in uk i just discovered.

http://www.heidelbergcement.com/NR/rdonlyres/F070043A-6716-445F-8D1D-2269D448CA6C/0/Red_Bank_clay_class1_flue_liners.pdf

hi max, it looks as if they all comply with the 400c 1000c for 30 minutes spec. i looked at the heidelberg ones. sold by hanson in the UK.
ok i think i have a plan at last!
clay liner 150mm ID 600mm high. if i go to 900mm it is getting a bit tall tall by the time i have added the barrel as well. surround it all with loose perlite inside a couple of cooking oil drums about 280mm ID. that should give me around 55mm of perlite around the liner. i will seal the bottom of the drum with fire clay and perlite to stop the loose perlite escaping. and likewise the top with a slope as in the cast design.
sit it on top of a burn chamber and feed made from firebrick. i can get the liner and the perlite from the local builders merchant. the firebrick i am not yet sure about but should be able to find enough to do a test firing at least. the fireclay i can get online.

Bob, carefull, i've just had an info about thoses hanson red bank, Morticio, in another forum said he tried thoses and they failed. I still have to make sure which type they were.

hi max, just got a price for the 150x300mm wavin liners. £22 each. i think i will go for the cardboard tube perlite clay mix as it will be a lot cheaper and has been proved to work ok. i need to get the clay and perlite anyway so we am only talking about the cost of the tube, plus some extra work. the tube will give me about 60mm of insulation if i do that. sounds a lot less risky than the flue liner route,at least on my first build anyway.