Gassification boiler with a refractory lined primary combustion chamber

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sfriedri

Member
Apr 21, 2008
63
Ontario, Canada
Anyone know of a gassification boiler that has primary and secondary combustion chambers like the EKO or Tarm, but has a refractory lined primary combustion chamber?

I'm considering testing this with my EKO to see how it affects the performance. I'm reasonably happy with the way my EKO currently performs, but I find it still produces a small amount of smoke when it is idling or when the nozzle does not have a good cover of coals. What I call a small amount of smoke is if it dissipates completely with 5-10 feet. I may be holding the unit to a high standard, because I'm comparing it to our Pacific Energy wood stove, which makes absolutely no smoke. The rain cap on the chimney for the wood stove is still bright and shiny after several seasons and I have never cleaned the SS chimney - it is clean. The cap on my EKO chimney is already brownish with only a couple of months of operation.

The EKO does burn cleanly with absolutely no smoke some of the time, but not all the time. I'm thinking of lining the primary chamber for a couple of reasons: 1) to get a higher burn temperature in the upper chamber to reduce the possibility of incomplete combustion after the gasses pass through the secondary chamber, 2) to allow me to run the boiler and storage tank at a lower temperature (say 150*F) when I don't have a high heat load, and 3) to reduce the amount of creosote that forms in the upper chamber. The only thing I'm concerned about is that lining the primary chamber means I may get less heat transfer to the water in this chamber.

I'm thinking of using a heavy weight ceramic fiber board to insulate the chamber, something like this: http://www.rsifibre.com/fiberboard.html

Anyone have any comments on how they think lining the primary chamber will affect performance?
 
BrownianHeatingTech said:
One concern would be creosote trapped between the refractory and the steel wall of the primary combustion chamber, potentially leading to corrosion of the steel.

Joe

Ummm... I don't think that would be a problem. Once that refractory gets hot it will incinerate creosote on either side of it. One concern that I would have is that with all that refractory surface in the primary the wood in "storage" might want to start to combust causing combustion to take place in this chamber. And when that happens I'm thinking that the unit might start puffing due to more and more wood being oxidized and less of a controlled downdraft burn. The Greenwood and seton alike burn upward not downward.
 
Garnification said:
BrownianHeatingTech said:
One concern would be creosote trapped between the refractory and the steel wall of the primary combustion chamber, potentially leading to corrosion of the steel.

Joe

Ummm... I don't think that would be a problem. Once that refractory gets hot it will incinerate creosote on either side of it. One concern that I would have is that with all that refractory surface in the primary the wood in "storage" might want to start to combust causing combustion to take place in this chamber. And when that happens I'm thinking that the unit might start puffing due to more and more wood being oxidized and less of a controlled downdraft burn. The Greenwood and seton alike burn upward not downward.

This was one thing I was wondering about. I'm guessing somewhere along the way during the design of these downdraft gassification boilers that someone tested a lined primary chamber and it did not work well for one reason or another. But without knowing why, the experimenter in me wants to find out what happens. I'm hoping that I get a balance between creating higher temperatures in the primary chamber, but not so high that I get too much combustion of the wood load.
 
Garnification said:
BrownianHeatingTech said:
One concern would be creosote trapped between the refractory and the steel wall of the primary combustion chamber, potentially leading to corrosion of the steel.
Ummm... I don't think that would be a problem. Once that refractory gets hot it will incinerate creosote on either side of it.

It is a problem, and has caused boiler failures in certain European designs.

Some of the newer imports from Europe are using stainless-lined chambers with an air gap behind the stainless, to allow oxygen to get in and burn off the creosote. Even so, they require installation with thermal storage, to prevent excess creosote production while idling.

Joe
 
I’m thinking of using a heavy weight ceramic fiber board to insulate the chamber,

The ceramic board WILL insulate the firebox and maybe even raise the temp of the primary burn. But that insulation will also mean that the water jacket side will be cooler. If it gets cool enough to condense not only creosote but water vapor also you could make a mess of that steel boiler jacket.

I'd give Joe's advice some careful consideration.
 
DaveBP said:
I’m thinking of using a heavy weight ceramic fiber board to insulate the chamber,

The ceramic board WILL insulate the firebox and maybe even raise the temp of the primary burn. But that insulation will also mean that the water jacket side will be cooler. If it gets cool enough to condense not only creosote but water vapor also you could make a mess of that steel boiler jacket.

I'd give Joe's advice some careful consideration.

If I go ahead with this test, I will install the ceramic boards as carefully as I can to minimize any entry of gasses behind the board, using stove cement, but I will also install them so that I can remove them after a while to have a look at what is going on behind them.

The temperature of the inside surface of the steel may not change much. One side is exposed to the boiler water and the thermal conductivity of the steel is fairly high, so I don't expect a large temperature gradient across the thickness of the steel. Also, the gasses in the primary chamber may be higher because of the insulation. So the temperature at the interface between the insulation and steel would also be dependent on the higher temperature in the primary chamber and the thermal conductivity of the insulation. I could do the calculations, but empirical observation will trump theory so I'm just going to test it.

One thing I may do is just put a small patch of ceramic board on a high and low spot in the wall of the chamber and then take it off after a few days to see what the surface of the steel looks like.
 
"Anyone know of a gassification boiler that has primary and secondary combustion chambers like the EKO or Tarm, but has a refractory lined primary combustion chamber?"


sure, it is called a masonry heater...
 
The EKO40 primary air is supposed to be set at 10% as per the new manual. When I got mine I left the settings where they were when I received the boiler. Approx 40%. I tinkered with the air but supposed a roaring secondary was what was desired. Now I am at the 10%/primary and my chimney stays cleaner and I do produce less smoke though I have no idea what my stack temperatures are. Also I am able to burn 5-6" x 20" with splits few hang up problems. 3-4" splits work fine but I find I go through them faster at the lower air setting and produce more smoke and I think that is from over burning in the primary. With no current storage I try for the longer burn time and am going to get creosote from idling. There is a much bluer flame in my secondary when the ash pit door is open. Is your primary air greater than 10%? If so try bumping it down to gain greater oxidation and less carbonizing. That should help reduce the creosote and save fuel but any idling will create smoke because the nozzle is too big for the short purging cycle and the available coals to gassify at 100%. We need an adjustable nozzle mechanism or new design approach that allows longer 100% burns with smaller amounts of fuel with essentially no idle time. (Can I get an engineer?? LOL)
One other thing I have found with my unit is the creosote likes to collect on the upper chamber bypass valve and when not fully sealed I get more smoke. It's a simple thing to fix but makes itself known when it needs to be done....Stay warm
 
kuribo said:
"Anyone know of a gassification boiler that has primary and secondary combustion chambers like the EKO or Tarm, but has a refractory lined primary combustion chamber?"


sure, it is called a masonry heater...

I am not sure if mine qualifies but my primary chamber has refractory on the bottom and steel on the top. The coal bed in the primary is all lined with refractory, and the bottom bricks have three slots to the secondary, the slots are basically the same as the nozzle on the Eko. Maybe this is no different then the Tarm or the Eko. I can say this when you open the top door and look down you are looking at refractory.

I will take a picture when I have the thing down with just coals in it, maybe give you an idea.

Steve
 
I think you'll find the secondary side is designed for a particular amount of gas coming from the primary side. Anything you do to insulate the top part from the water jacket will increase the gasification and increase the wood gas source. So to burn it you will need to let in more air.

So your loads won't last as long, and you'll be kicking out more heat when its running. That makes me think it will idle more and smoke more.
 
slowzuki said:
I think you'll find the secondary side is designed for a particular amount of gas coming from the primary side. Anything you do to insulate the top part from the water jacket will increase the gasification and increase the wood gas source. So to burn it you will need to let in more air.

So your loads won't last as long, and you'll be kicking out more heat when its running. That makes me think it will idle more and smoke more.

Install (more) storage...

One thing to be aware of when increasing output is that you will need more flow through the boiler to take the heat away.

It can also cause lower efficiency, as the heat exchanger has a certain amount of surface area, tuned to a given boiler output - it may not be able to pull the heat out of a larger volume of hot gas...

Joe
 
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