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Black soot build up. First weeks burning rmh. Need advice

 
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So guys. My build in not yet finished. I wanted to test the stove for a short while before i finish the cob bench.

Its been going good for a few weeks. Firbox is clean. Stove burns hot. Bench is drying and cob is getting harder.

So i opened it up to inspect the inside. I was surprised by the amount of black soot that is sticking to the superwool and well frankly to everything. Its a light powder of black carbon.

I have two areas which i know need to fix.

The seal between my bell chamber and the base is not that as good as it could be. And there seems to be a gab between the riser and port of the firbox. I have seen another thread where clay slip and superwool are mixed to form a more solid seal.

I think when these two things are corrected it will work better but im curious if anyone has had this issue. Can assist me with why there is such a carbon build up .

Thanks in advance for your help
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rocket scientist
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Hi Fraser;  How is the smoke coming out the chimney?  Steam?  Heat shimmers?  Or grey black smoke?
It is possible that is caused by the still wet cob .... But
That looks like over fueling to me.  
Over fueling is a phenomenon that happens with batch box's.
It is common for a hot batch to over fuel directly after adding new wood .
It should only do that for a few minutes before clearing up.

What size is your primary air inlet and what size is your secondary air inlet?
Are they a combined air or separate?
Total air input is apx. 20% of riser size.

 
thomas rubino
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Looking at your picture it looks very tight going from your riser to the bell.
There needs to be plenty of room there for your hot gasses to move.
Do you have dimensions?
 
fraser stewart
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Primary air is 5cm pipe.
Secondary air is 5cm  by 2.5 roughly.

Reading you comments. The riser is wrapped in supperwool. Which i am not sure if it completely necessary. I thought the more insulted the better but could restrict air flow like you state.

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fraser stewart
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thomas rubino wrote:Hi Fraser;  How is the smoke coming out the chimney?  Steam?  Heat shimmers?  Or grey black smoke?
It is possible that is caused by the still wet cob .... But
That looks like over fueling to me.  
Over fueling is a phenomenon that happens with batch box's.
It is common for a hot batch to over fuel directly after adding new wood .
It should only do that for a few minutes before clearing up.

What size is your primary air inlet and what size is your secondary air inlet?
Are they a combined air or separate?
Total air input is apx. 20% of riser size.



The smoke is first steam. Sometimes a little black right at the start. Then it clears up.

This overfuelling seems to be connecting. If i put new fuel. Some smoke around the bell and base seal leaks. Like its choaking and needs a new way out. I have a lever to send it straight up the chimney so when this occures i open it to allow thw smoke to pass both through the bench and straight up. This stops this when it happens. Its not always but thats been my method so far.
 
fraser stewart
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Is the wool on the outside of the heat riser necessary?
Bell has 56cm above riser
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thomas rubino
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Ok Fraser;
Remove the super wool.
Next question what is the riser made of? I can't tell from the photo's.

What I do see is you have super wool and you have stove pipe... Why haven't you made a five minute riser yet?
They have no mass to heat... they are super insulative... Your stove can not burn hot enough to hurt it.
I see it as a win win win.
 
fraser stewart
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I thought i had made a 5 minute riser.
The inner part is superwool
The middel is stainless steel sheet. Made into a pipe and rivited together.
The outer is layer is superwool.

I will take the outer layer superwool off
 
thomas rubino
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Another thing I notice is you need to go inside your firebox and seal the roof up better. Also some of your joints look like they need a touch up as well.
Very important that all the gasses go thru the port and not find other holes to escape from.

Pull the extra super wool and give it a try.  
Let us know how that works.
 
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As Thomas said, remove that outer layer of superwool.

Your side gap is completely wrong! Anything less than 3cm is asking for trouble, better have 5 or 10cm.

 
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Fraser, there are a couple of parameters that are important for the working of the system. Space inside the bell is one, air inlet size is another and let's not forget the bench you have there. So here we go, in no particular order:
The space left and right of the firebox, inside the lower bell seems cramped to me. In order to keep the heater low-friction there should be at least 4 times the system's csa around the firebox area.
Now in order to see whether or not the air inlets are correct one need to know what the size of the system is. So, what is the system size?
Furthermore, of what refractory material is the firebox made of? When this is firebrick, moist need to be driven out and during this process soot will be produced.
Are all the other proportions respected?
 
fraser stewart
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Hey peter.

The firebox is made from ceramic fibre board. It is 25mm 1460 degree. Behind it is morgons superwool to prevent air gaps. The system is based on your plans for a 15cm system. The chimney is a 15cm system.

The bench is inspired from matt walkers stratification method. Made from half barrels on stone brick base. Covered in cob

As earlier suggested by thomas i have removed all superwool from the outside of the riser. This was a bit over the top. It made more space when removed. I also removed some which was around the back of the firebox.

Yesturday the burn seems to be more rockety. I also rebuilt the seal and its doing better. I will test more this week and post outcome.

Thanks all of you amazing community

Fraser
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Peter van den Berg
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No soot to form due to evaporating moist then. I mentioned the required space around the firebox already, maybe you should have a look at that whether or not it's wide enough.

So both air inlets are separated from each other and it's a 150 mm system. In the one picture of the firebox' inside I can see a floor channel. The vertical part (stub) should be about 35x35x2 mm, the horizontal part (feed) twice as wide. Two ducts of that same square of the stub would be sufficient, or a duct of 60x40x2 mm. In your configuration it's 50x25 mm, that would be about half the required size.
You might think this isn't that important but in reality it is. I tried 5 different sizes during the development of this specific part and this provided the best performance. The reasoning behind the feed being twice as large is that the stub itself is acting as a narrowing in the gas path and thereby as a venturi. That will result in higher gas speed inside the stub as well as better cooling of that part.

The primary air inlet is round 50 mm, this comes down to 1963 mm². This inlet should be around 15% of the system's csa which is 2655 mm². So in your heater this is too cramped again, although I would regard the floor channel as the main bottleneck.
 
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https://donkey32.proboards.com/thread/1406/calculating-ring-circumference-projection-gap
 
fraser stewart
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Sorry guys but what is meant by csa.

I guess cubic surface area?
 
fraser stewart
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I made the secondary air intake a while ago. I think its based on peters sketch up model measurments  Tonight i will take it out and measure it and post it..

 
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fraser stewart wrote:Sorry guys but what is meant by csa.

I guess cubic surface area?



Cross sectional area.
 
Peter van den Berg
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fraser stewart wrote:I made the secondary air intake a while ago. I think its based on peters sketch up model measurments  Tonight i will take it out and measure it and post it..


The p-channel is the same size rectangle duct throughout, the floor channel is not. It's possible that you've mixed up the properties of the p-channel and the floor channel.
It has happen before, have a look at this information, please note the 2019 modification.
 
fraser stewart
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So guys. Home from work.
I took the seconday air out to measure it.

Im appreciate your imput in helping fine tune my stove. This is the first one i have built and im learning alot each day i have included photos for you to see..


One thing that peter brought up was the secondary air. I started with his sidewinder sketchup. And after inexperimented with ceramic fibre board i made it based on the measurments of his
Brick177.skp file from peters site.
The thing is i wanted to have the bsecondary air in the floor of the firebox. Cant remember why.

In current version I included a pizza stone to protect the floor of the firebox. Perhaps this is a bad move. I dont know. The secondary air sits under this.

Included are the measurments and some photos. Its similiar. Almost identical to the sidewider .skp with the funnel facing forward instead of sideways.

After taking the superwool  from the outside of the riser away. And improving the seal for the bell chamber and bottom with addition of fire-rope. I have noticed a much different burn. No smoke leak and clean exit gasses from the chimney. Lots of steam in the beginning but to be expected i guess from a drying cob bench.

Im trying to understand the engineering calculations of the comments to wrap my head around whats being said but as inearlier started, first ever operational indoor rmh so please be patient.

Fraser
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fraser stewart
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Here it is without pizza stone
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thomas rubino
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Hi Fraser;
It looks to me to be very close to the sketchup picture.
It differs from what I made for mine.
Here is a photo of some new ones I've built.
Note how much closer to the end my stub is compared to yours.
1/2" from the end of the tube was a distance suggested by peter when I built my first one.
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fraser stewart
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Hey thomas.

Do you suggest moving further down.
Right now mine is positioned right infront of the port. When up to temp its red hot.

Tonight when i took it out the pizza stone had cracked. I happened to have a thinner stone. So i will try that to see if a tiny extra space makes some difference.

Do you have tips for the primary air. Peter suggests it too small. But dont have any room for doubling it on the door i built.

This photo is taken jut after i typed this
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fraser stewart
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Small update. And new queries.

I have been firing my rmh the past days and i have no issues with heater part. No smoke gaps. Temps are slightly higher. Smoke out of chimney is now steam for first 5/10 minutes then not visable.

I do have another issue though. Perhaps i should make a new thread.

When first burnt stove. The cob bench. Matt walker inspired stratification chamber bench was getting warm and steam was coming off it. Its changed to a little colour so that shows its drying. But the temps are now so low it is worrying.

I opening the last cleanout at the end of the bench to see whats going on and inside was alot of black soot and water dropplets on the inside of barrel. The stove was at the end of a burn cycle but i had expected to feel some heat.

One thing to mention is. The heater and bench are connected with some 15cm stove pipe around which i have not yet added cob. I know this may be the issue but i wanted to be able to adjust the heater part and that way got stuck till that was sorted.

I believe that if i cob around that and the base of the stove that will induce an positive effect. But before i do that can any of you see potensial faults that lead to low temps in a mass bench like i described.

This photo is taken when i just started firing heater some weeks ago
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That is a lot of metal radiating surface area. The duct from manifold to bench is the smallest part. You haven't mentioned the internal surface area of the whole system other than "based on Peter's specs for 15cm" (6"). How does that compare with the recommended ISA for the size of your batch box system? I would be concerned that you might have too much ISA and drawing too much heat, so that there is not enough left to warm the whole bell.
 
fraser stewart
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Glenn Herbert wrote:That is a lot of metal radiating surface area. The duct from manifold to bench is the smallest part. You haven't mentioned the internal surface area of the whole system other than "based on Peter's specs for 15cm" (6"). How does that compare with the recommended ISA for the size of your batch box system? I would be concerned that you might have too much ISA and drawing too much heat, so that there is not enough left to warm the whole bell.



I was reading this again as my secondary air floor channel stub has finally fallen apart.

Q? What does ISA stand for. My guess is inner surface area. Can someone send me a link to what Glen refers to as "recommended ISA"


I am thinking of insultating more of my barrel as i would like towarm the mass better. What do you guys think. Would you recommend it?
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fraser stewart
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P.s. has anyone opions on rvs secondary air floor channel and stub. Went to store and guy there said it draws more heat than steel but not sure what he meant exactly
 
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Hi Frasier;   Your air channel can be repaired. Simply cut off the old stub and weld on a replacement.
If you were in the states I would recommend a RA330 stub.  Installed 8" tall. After 2.5 years of hard long burning. Matt walker has inspected his and there is no degradation at all.
It is showing the potential to be a very long term part, making the upfront costs much lower when amortized over many years.
I am selling these here in the states,(dragontechrmh.com) but shipping to the Netherlands I imagine would be  very expensive.
 
fraser stewart
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thomas rubino wrote:Hi Frasier;   Your air channel can be repaired. Simply cut off the old stub and weld on a replacement.
If you were in the states I would recommend a RA330 stub.  Installed 8" tall. After 2.5 years of hard long burning. Matt walker has inspected his and there is no degradation at all.
It is showing the potential to be a very long term part, making the upfront costs much lower when amortized over many years.
I am selling these here in the states,(dragontechrmh.com) but shipping to the Netherlands I imagine would be  very expensive.



Hey thomas.

I found a website with rolledalloys in europe.
https://www.rolledalloys.com/locations/europe.html

Maybe i will contact them. What is the demenisions of the stub. Is it round pipe. How thick.

Thanks for your help
 
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Hi Frasier;
Yes, that ra330 will floor you with the cost!
Replacing the steel stub for this season is probably a good option.

Tell me what is "RVS"  ?   Do you know what it stands for? (looked it up)    Ahh I see its stainless steel.
Peter mentioned using stainless on his next stub and was hoping for a very long life from it.
Depending on your burning style it might last for quite a bit. Peter only burns once or maybe twice in a day.  Matt burns all day everyday.
If your burning all day everyday then stainless  will have a shortened life.
How short ?  We will have to try one and find out.

Oh the secondary tube itself (being insulated by ash) should be in fine shape to reuse.
 
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ISA is internal surface area. You can get the proper sizing information at batchrocket.eu.
 
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fraser stewart wrote:I am thinking of insultating more of my barrel as i would like towarm the mass better. What do you guys think. Would you recommend it?



Adding mass around the barrel will definitely help to drive heat further down the system into your bench mass. It has been done many times by the folks here. It can easily be fine tuned to get just the right amount you want without much effort.  You will probably have to put some structure (fibre) into it if your using straight cob as there will be very high movement in this high heat area between dissimilar materials. If your using brick, stone etc. then not so much.  
 
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Glenn Herbert wrote:ISA is internal surface area. You can get the proper sizing information at batchrocket.eu.



So glen.

I read up on batchrocket.eu

Just to check i understand to help others

"For example: a 150 mm system will give you 0.0176715 sq m. Multiplied by 300 will result in 5.3014376 sq m, which rounded off to 5.3 sq m is exactly the recommended maximum value for such a system."

I have read it a few time. Im not sure how you come by 0.0176715 sq m

Peter made a list

"
Riser diameter   /   Internal Surface area

12.5 cm  (5")   ISA 3.7 m²    (39.8 sq ft)
15.0 cm  (6")   ISA 5.3 m²    (57 sq ft)
17.5 cm  (7")   ISA 7.2 m²    (77.5 sq ft)
20.0 cm  (8")   ISA 9.4 m²    (101 sq ft)
22.5 cm  (9")   ISA 11.4 m²  (123 sq ft)
25.0 cm  (10") ISA 14.7 m²  (158 sq ft)
"

So from this i learnt that my 15cm diametre riser will give enough heat for a max of 5.3m2. That is the barrel and the bell (in my case the bench)



Thankyou Peter for this info also
 
Peter van den Berg
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fraser stewart wrote:I have read it a few time. Im not sure how you come by 0.0176715 sq m


I had lots of difficulties to grab the concept of decimal calculation while in primary school.
The 150 mm diameter is equivalent to 15 cm, 1.5 dm or 0.15 m. The formula to calculate the area of a circle is pi R², isn't it? That makes the cross section area of a pipe with that diameter 17671.5 mm², 176.715 cm², 1.76715 dm² or 0.0176715 m², all the same but expressed in a different value. The decimal point shifts one place for lengths, two places for area (²) and three for volume (³) when transposing up or down one step. So, going up three steps from millimeter to meter for area is the same as deviding by 1000000.
Once the teacher explained the above rules to this little boy it started to dawn on me. Sufficient to say, I wasn't a quick learner back then.
 
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Peter van den Berg wrote:

fraser stewart wrote:I have read it a few time. Im not sure how you come by 0.0176715 sq m


I had lots of difficulties to grap the concept of decimal calculation while in primary school.
The 150 mm diameter is equivalent to 15 cm, 1.5 dm or 0.15 m. The formula to calculate the area of a circle is pi R², isn't it? That makes the cross section area of a pipe with that diameter 17671.5 mm², 176.715 cm², 1.76715 dm² or 0.0176715 m², all the same but expressed in a different value. The decimal point shifts one place for lengths, two places for area (²) and three for volume (³) when transposing up or down one step. So, going up three steps from millimeter to meter for area is the same as deviding by 1000000.
Once the teacher explained the above rules to this little boy it started to dawn on me. Sufficient to say, I wasn't a quick learner back then.[/quote

Thanks peter. I was not as attentive in class as you were. Or my treachers never made it so clear as you just did.
Learning each step of the way.

From your text on your website i gather that it is the surface area in cm combined that give you your ideal bell size. So the surface of the barrel around the heat riser and the surface of the barrels in the stratification chamber and the floor. These combined should be the values given in your table. Is that correct?

 
Glenn Herbert
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Almost... the floor never counts when figuring ISA of bells. The roof and sides at and above the level of the exit are what you count. Masonry pillars inside the bell may also count if they are massive enough to store heat. If the firebox and riser are inside the bell, their surfaces don't count.
 
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