watto
New Member
Posts: 8 
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Post by watto on Sept 29, 2017 6:55:31 GMT -8
Hi Everyone,
New joiner but have been reading up on the great work being gone by the community.
I have been toying with building a batch RMH using a bell in the UK. I am going to use my first attempt to dry out wood fuel and provide some gentle heat to a heater sea ting area around a camp fire. Basically a purely experimental system to see whether I can show one to the Building Regulator before submitting plans to replace my indoor stove.
I was interested in employing magnetite heat storage bricks within the bell (or seating area) to suck up the heat quickly and dissipate it over a longer period of time. - may be using a longer burn time so keeping everything else equal (I understand the need for a strong draw for a seating area and have convinced myself a flue fan is probably sensible even if it used only for the first 10 minutes).
These bricks are the sort used in electrical night storage heaters.
Another concept I was kicking around was putting a copper heater exchanger within a second bell surrounded by or encased within these bricks. Thus protecting the copper heat exchanger from excessive heat movements, direct contact with flue gases and making the unit "retractable" from the bell for servicing (have not thought through how best to do this latter servicing aspect but probably by aligning it with the bell exit)
Has anyone tried using these storage bricks? They are stable to 600 degrees C so may only be suitable for lining the bottom of the first bell and the entirety of the seating area. Any thoughts?
Best wishes
Taj
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Post by Jura on Sept 29, 2017 10:19:35 GMT -8
The magnetite bricks are suitable for the external skin of the stove only as they can not have direct contact with flue gases.
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watto
New Member
Posts: 8
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Post by watto on Sept 29, 2017 12:05:31 GMT -8
Why only the outside? Flue gases should be free of caustic agents and may have moisture but that should be driven off by elevated temp.
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Post by Vortex on Sept 29, 2017 14:20:20 GMT -8
Hi Taj, I've used the Magnetite Storage Heater Bricks in several bell walls and bench tops without any problems. Many people use them for the floors of pizza ovens. Only time I've heard of them failing is where someone tried to use them to replace firebricks inside the firebox of a stove.
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watto
New Member
Posts: 8
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Post by watto on Sept 29, 2017 22:13:09 GMT -8
Thank you Vortex. I assume their use as a heat sink for a water heater also makes sense then. Especially if I use them on the floor of the first bell. The magnesium based bricks are more susceptible to glue gase, but intend to recognise the difference.
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watto
New Member
Posts: 8
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Post by watto on Sept 29, 2017 22:16:41 GMT -8
I was intending to line the brick single skin brick Bell with magnetite bricks. The lining would be loose (no fire resistant mortar) would this cause a problem with the gravity separation of the gases by temperature or will it just equilibrate in time.
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Post by peterberg on Sept 30, 2017 0:25:47 GMT -8
As long as there's enough open space the gases will separate by temperature, no probem. But those magnetite bricks are expanding while warming up so they could "wander off" when stacked dry.
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watto
New Member
Posts: 8
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Post by watto on Sept 30, 2017 7:22:59 GMT -8
Thank you Peter, so can regular mortar be used or in the bell is fire cement needed?
I assume then the magnetite with a second skin of outer brick will work very well. Although there should be around a 5 hour lag before heat starts to be released I to the room
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Post by Orange on Oct 1, 2017 5:16:22 GMT -8
if there are air gaps the heat won't transfer properly. I think magnetite brick are the best for the bench or bell because they have both high - heat transfer (6 W/mK) and heat capacity. so I planned to use them directly for flue tunnel (instead of red bricks) which would result in much faster bench warming.  |
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Post by Jura on Oct 2, 2017 8:23:47 GMT -8
Why only the outside? Flue gases should be free of caustic agents and may have moisture but that should be driven off by elevated temp. It was not about the possibility of base pH of flue gases. AFAIR It was about the soot carbon disrupting the quasi octagonal structure of Fe 3O 4 thus causing it to become crunchy. |
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Post by Orange on Oct 4, 2017 12:25:17 GMT -8
here is the magnezite composition if it helps: 85 - 88 MgO 4 - 6 SiO2 1 - 2 CaO 1 - 2 Al2O3 4 - 5 Fe2O3 if the gasses destroy magnezite, then the second best idea would be to put aluminium or steel plate and magnezite bricks ontop like this:  |
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Post by Jura on Oct 4, 2017 14:06:33 GMT -8
here is the magnezite composition if it helps: You are writing about Magnesite while to OP meant magnetite one of which the main constituent is Fe 3O 4. One may easily distinguish those two with magnet. The magnetite one slightly sticks to the magnet. |
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Post by Jura on Oct 5, 2017 0:14:04 GMT -8
Hi Taj, I've used the Magnetite Storage Heater Bricks in several bell walls and bench tops without any problems. Did you happen to have a chance to inspect them after some period of usage? I always give advantage to experimental data in comparison to pure technological one. |
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Post by Vortex on Oct 5, 2017 2:01:08 GMT -8
I've built 2 stoves using them that have been in use for 3 years and I haven't seen any signs of degradation. I'm building a 3rd stove using them at the moment. I did extensive research on them before deciding to use them and never found any mention of problems, except one where someone used them to line the firebox of a metal box stove. If you look at pizza oven forums they're a favorite for making the floors of the oven.
I take it you're concerned the acidity of the creosote in the channels will cause them to crumble? I just did a ph test on the soot/ash coating from the inside top of my stove bell, it was 6.9, just below neutral. Creosote is mildly acid whereas woodash is highly alkaline. Just for interest I did a test of some woodash from the bottom of my firebox and it went off the scale.
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Post by Jura on Oct 5, 2017 14:33:11 GMT -8
I've built 2 stoves using them that have been in use for 3 years and I haven't seen any signs of degradation. I'm building a 3rd stove using them at the moment. I did extensive research on them before deciding to use them and never found any mention of problems, except one where someone used them to line the firebox of a metal box stove. If you look at pizza oven forums they're a favorite for making the floors of the oven. Great! Then I'm also going to give it a try and place it in a lower part of a bell one day. I take it you're concerned the acidity of the creosote in the channels will cause them to crumble? I just did a ph test on the soot/ash coating from the inside top of my stove bell, it was 6.9, just below neutral. Creosote is mildly acid whereas woodash is highly alkaline. Just for interest I did a test of some woodash from the bottom of my firebox and it went off the scale. Of scale pH  . you are on a good way to start producing your own soap Well It wasn't about the pH. pH was an issue with magnesite bricks. With the magnetite one I do recall one old masonry man having explained it to me as a physical degradation of lamelic structure due to cation exchange under the influence of soot active carbon. I never confirmed it as it is repeated among the masonry bevy in here. I know we shall question everything... but life is too short to apply 5 WHY with every topic we encounter.. I'm still having a huge backlog with a task of delving into geopolymers. |
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. you are on a good way to start producing your own soap