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Post by talltuk on Jun 25, 2014 12:04:12 GMT -8
Hi folks
Long time no post, been armchairing and setting myself up as a self employed Heating Engineer. A huge opportunity has dropped in my lap, the chance to build a massive heater for a Grade 1 listed brewery/barn that is being converted into an event space.
This is going to be in conjunction with English Heritage and Building Control so it could mean some really useful data for RMHs in the UK. I will be posting about design and layout in later posts, once I have done the heat loss calcs and worked out exactly how big I need to build this.
However I just need some quick feedback from people who have used Vacuum formed ceramic fibre for their heat risers and insulating firebrick for their batchboxes.
I want to build this to the highest level, and my first was barrels and cob (still not finished) so I want to do it right first time. How have people found these materials hold up after long use? this won't be fired daily but it will be fired for a long time as this is a huge space to heat.
I have considered refractory tubes but cant find any that are also insulative and don't want to wrap it in superwool if I can avoid it to save space in the barrel, though that is another area I have to look at.
This is a big step for me but I am really, really excited, as is the owner. Expect many more posts as I bounce ideas off you guys, and please don't hesitate to tell me to calm down if I get tiresome ;>
Fire baby Yeah!
Tom
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on Jun 25, 2014 14:29:01 GMT -8
Hi Tom
Sounds like a great project. The riser on my J-tube was insulating fire brick (IFB) and worked great. As long as they are rated to at least 1260C they should be okay.
If the heater is a batch box & bell design, space for added insulation will not be an issue. An option is a refractory octagonal riser with an IFB cladding such as the one on this stove here. More details on the stove build are here. Alternatively, the IFB cladding could be replaced with a high performance board such as WDS Ultra, but the cost is greater!
Andy
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Post by talltuk on Jun 29, 2014 5:24:58 GMT -8
Thanks Andy
Really want to go for batchbox and bench, just in terms of spreading the heat, not sure how to make the top of the firebox but thinking steel used as the p channel. Trying to avoid square risers, and can't cast right noe, though hopefully in the future. Thermalceramics do refractory shapes so considered that with a superwool surround, or maybe just a larger tube of vacuum formed.
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Post by talltuk on Jul 6, 2014 12:28:57 GMT -8
Anyone else got any input?
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Post by peterberg on Jul 6, 2014 23:44:10 GMT -8
However I just need some quick feedback from people who have used Vacuum formed ceramic fibre for their heat risers and insulating firebrick for their batchboxes. Hi Tom, Great opportunity, that's right. Regarding ceramic fibre risers: this will last almost indefinitely as long it's used above the level of the firebox. Mine has been a 150 mm system utilising one of those risers. The inside would feel a bit soft after some months but that wasn't deeper than 5 mm, behind that the binder is protected by the wool itself. Temperature right above the riser has been a bit short of 1000 C on a regular basis. Insulating firebrick, the kind I've seen is too brittle to use in areas where it could be hit by pieces of fuel. Even scraping with a piece of wood could affect the surface. But it's great stuff for building the riser though. As Morticcio remarked, when it's a batch box built into a bell insulating the firebox isn't much of an issue. But this could be built with hard firebrick on its side, refractory slab of whatever kind on top. And hard vermiculite board on top and the sides at the outside of the firebrick. |
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Post by talltuk on Jul 7, 2014 12:45:19 GMT -8
Thanks peter, so firebrick for the batchbox, wrapped in superwool or kaowool, then aybe insulating brick for the riser. was hoping to keep the riser circular but hate transferring from brick to fibre. I had thought about using a formed refractory tube wrapped in wool or a fibre shape as well, to provide durability. Quite fun today as met up with a guy specialising in masonry heaters, who didn't really know why we used insulation and a heat riser, as they use none of this in masonry stoves. don't think I did a great job of explaining it. Just off to start a new thread about this build in experiments group.
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Post by bernardbon on Jul 7, 2014 14:22:26 GMT -8
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Post by Robert on Jul 8, 2014 4:27:12 GMT -8
Quite fun today as met up with a guy specialising in masonry heaters, who didn't really know why we used insulation and a heat riser, as they use none of this in masonry stoves. Hey Talltuk. Great thread. I will follow your build and any exchanges of thought would be great, and on the top of that if you can test your stove with some analyzer would be great. Regarding insulations and riser. I am also becoming a little bit confused on that topic. I started with rockets and now i am going deeper into the world of masonry stoves. I have just returned from Denmark where i just took a course on masonry stove building with Lars Helbro. We was building his very efficient model called a GYMSE. I had a lot of questions regarding insulation of firebox and a riser... he also claimed it is not necessery. So now i really need to understand the topic better. Why do we really insulated a riser and possible the firebox. As far as i understand it is all about keeping a High Temperature for a better combustion. And then we should be possible to see the results on the TESTO regarding Comb.Efficiency. So now is the time to look at them again. From my previous studies of Testo readings from Peter`s stove looks like they are not much superior than the reading from Lars Helbro. He had 92%Eff average and 500PPM of CO. Without a riser insulated and squared shaped. There is also another interesting topic. NOx`es. I been told on the course that if we burn in high temperature the Nitrogen turns into NOx`es which arent so nice. Than with the rocket stove then there is a danger of producing more NOx`es. So those two things i would like to understand better. And if someone who really understand a reason for insulating the risers and what it gives us in returned it would be good. And Peter if you read it could you pleas post the best readings you got from you stove? PS. I am very intersted on what will be our conclusion on this topic. Since more stoves are coming to be build and if all of this insulating issues and risers are not much superior than the other designs, than i would prefer to build next stoves as simple as possible. |
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Post by Daryl on Jul 8, 2014 5:40:06 GMT -8
Looking forward to the answer as well.
I am familiar with Lars' work and respect his talent.
I would be careful in saying that across the board insulation is not needed. In my limited experience, a hotter chamber definitely helps with drafting and it follows what I have learned about fire science. As far as burning all of the gases, well, in my opinion, that is why there are so many experimenters out there testing various methods to mix the gases. I am not suggesting one stove is better than another. I will always believe there is more than one way to skin a cat.
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Post by peterberg on Jul 8, 2014 11:05:53 GMT -8
From my previous studies of Testo readings from Peter`s stove looks like they are not much superior than the reading from Lars Helbro. He had 92%Eff average and 500PPM of CO. Hi Robert, In order to compare readings, I have to know at which point Lars started the Testo. And there's one reading missing: the oxygen. The CO will be diluted by air, so the air excess value is very important. More excess air, lower CO numbers. My graphs always start when the oxygen descends below 20% and end when the CO2 is about one miniute lower than 4%. This is what I've done for quite a while, so my graphs are comparable with each other. To satisfy your curiosity: the best measurements of carbon monoxide were between zero and 10 ppm, lowest of oxygen at 5% which is extremely low and highest efficiency 96%. Not necessary all at the same time. During the test run there shouldn't be fiddling with the air intakes, chimney damper or bypass. If you can come up with a graph with additional data like the start and end points I can search for a comparable result. I'm sorry, I've seen some very strange graphs made by people who constantly adjusted the air inlets in order to achieve the best results. Even the start and end of the burn weren't there because those were not good enough. Sometimes in the presented data a couple of minutes were missing because the CO readings were too high for the analizer. Even then this person calculated the averages as if there hasn't been a mountain of CO at all. Those people probably thought it was a competition to produce the nicest graphs, instead of running the stove as if there was no coupled gas analizer. Regarding insulation of the stove: when a batch box is inside a bell I would neglect the fire box, but in my view an insulated riser is important to get the highest draft possible in the shortest time. In the pictures Bernardbon is showing there is a bare riser. In reality these risers are surrounded by as much as 5 cm of superwool when in function. The kind of castable refractory is a 1650 C specification variant, denser and higher thermal shock resistant. |
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Post by Robert on Jul 8, 2014 13:42:10 GMT -8
Peter i do remember visiting you and looking at the Testo:) and i remember highest reading 96%Eff and 10ppm... i been quoting them for many months, and i show the pictures at the workshops as well. And when i quoted the numbers at Lars workshop he asked me if those numbers where highest reading or average. Than i realised that the numbers i have seen at your place was not average. So i was a little bit confused. After i have seen the way Lars builds his stove i was shocked  No secondary air (Lars claims that we do not really need it), From my point of view he ads to much air to the firebox, also he adds air from under the kind of a grate he makes from firebricks... all of this thing i was thinking where not the best. I read previously that secondary air is crucial for clean combustion, that we try to limit excess air as much as possible, that the grate is not needed with wood... and than i see a man who does the things completely different and then shows me his graphs from Testo, which are not so bad. And one thing he said, actually the same thing as you said Peter. "Keep it as simple, as possible". And i wish to follow that path, but also i really would like to build stoves that are really very efficient with low CO, NOx and particle emissions. As for now i believed that the rocket stove concept is the best, and now slowly i need to start understand if it is so, and why it is so. What happens when we make heat risers out of insulating materials and round shapes, and what if we make it simple fire brick squared tower. i know that you Peter have the knowledge and that you have spend lot of time on various experiments, so it will take some time... anyway i asked Lars to send me his graphs, and it would be nice if you could take a look at them. PS> what was really interesting on the workshop was a smoke washer concept presented by Sten Moller. Basically a unit to eliminate a chimney and cool down the gases to 20C to keep all of the heat inside a house. A unit should be placed outside, perfectly in a greenhouse:) And of course it uses a fan. But that is another subject. |
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Post by talltuk on Jul 8, 2014 13:54:39 GMT -8
Bernard - that looks lush, havent got the time or space to setup and experiment with casting right now, hence why I am lookibg at preformed shapes.
Robert - thanks, would love to test this but don't think I will get the money for an analyser that is up to the job just yet.
As for the insulation thing, its similar to the batch in a bell, the firebox is surrounded by heated brick, so doesn't require insulation to keep the heat in, the whole core is very hot. My mate doesn't get the need for a riser though, saying a masonry heater has enough draught without it. Personally I feel it just makes a rocket core more flexible
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Post by peterberg on Jul 9, 2014 0:36:40 GMT -8
Robert,
Again, it's crucial where in the test run the readings are started and stopped. I hope the graphs made by Lars do show the O2 line, that is really important. The start of the run should show slightly above ambient temperature and a value of close to 20% oxygen. If that isn't the case, I have to guess which part of the run is shown.
Tom,
A batch box without a riser isn't a rocket burner anymore. Besides that, I find it strange that a man with considerable skills in the masonry heater department would say some parts are not needed at all. About a very different firebox design, completely unknown to him. But please, go ahead and see what happens.
Years ago, I've built a large Finnish style contraflow heater for a client. Two chimney sweeps and a stove seller advised strongly against it, according to them the thing could never work. But it did, in the most convincing way.
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Post by talltuk on Jul 9, 2014 8:17:41 GMT -8
Peter; I know, luckily he is happy for me to design it anyway I like. Its gonna be interesting combining ideas, got three so far in just one area. Rocket core, masonry heater style heating wall next to it and a metal bell upstairs. Both forms of storage controlled with dampers. Just dont know if we can heat the space flexibly enough without wasting heat.
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No secondary air (Lars claims that we do not really need it), From my point of view he ads to much air to the firebox, also he adds air from under the kind of a grate he makes from firebricks...