Anthracite Test

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NYEDGE

Member
Sep 19, 2010
86
New York
A while back my friend gave me a bag of anthracite and said it burns very hot and very long.
So, as others have tried, I tried chucking a couple of hand fulls of it in with the wood.
It burned o.k., but most of it did not burn well do to the lack of air passing through a needed coal bed.
Some manufacturers offer add-on components, and some members here have had success with that.

I figured I'd try something different with the coal I still had in hopes to just finish the bag, or give it back to my friend.
What I did was put a bed of the coal on the floor of the fire brick in the bottom chamber so that the flame from the secondary
burn is blowing right on top of it. I only put a bed approximately 1 1/2" high so that the flame still had plenty of room to do it's thing.
After starting a normal fire over a good bed of charcoal I returned after about 15-20 minutes to check on things.
I found that the water temperature had raised much faster than without the coal bed, and with the blower fan off I opened the bottom door to find the coal
glowing an extremely bright orange. The heat coming out of the lower box without the fan was tremendous and I attribute that to the coal.

So now it's time for your thoughts on this.
Do you see any reason not to use this type of coal bed to assist during a regular burn of wood?
The chimney only shows heat vapors coming out with no smoke at all.
I would think that the firebrick would hold up to the coal temperatures, but let me know if you think otherwise.

Thanks.
 
NYEDGE said:
So now it's time for your thoughts on this.
Do you see any reason not to use this type of coal bed to assist during a regular burn of wood?
The chimney only shows heat vapors coming out with no smoke at all.
I would think that the firebrick would hold up to the coal temperatures, but let me know if you think otherwise.

I'd say the goal of tuning the gasification process is to get as complete combustion as possible with minimum excess oxygen going up the flue.

So maybe if there's enough oxygen left over from the wood burning to maintain an efficient coal fire then it would mean the gasification process might not be tuned right. But if the coal fire uses that oxygen then maybe that's a good thing. The only way to know for sure would be to sell your boiler and get a lambda controlled unit.

--ewd
 
I have a 1/2 ton of coal and I was thinking of putting a shallow bed in the upper chamber using a small coal grate. There would be draft ( top to bottom instead of bottom to top) and airspace under the bed. What do you think?
 
ewdudley said:
NYEDGE said:
So now it's time for your thoughts on this.
Do you see any reason not to use this type of coal bed to assist during a regular burn of wood?
The chimney only shows heat vapors coming out with no smoke at all.
I would think that the firebrick would hold up to the coal temperatures, but let me know if you think otherwise.

I'd say the goal of tuning the gasification process is to get as complete combustion as possible with minimum excess oxygen going up the flue.

So maybe if there's enough oxygen left over from the wood burning to maintain an efficient coal fire then it would mean the gasification process might not be tuned right. But if the coal fire uses that oxygen then maybe that's a good thing. The only way to know for sure would be to sell your boiler and get a lambda controlled unit.

--ewd

I follow your thought that the goal is to get as complete combustion as possible, but I'm not to sure on the idea that the boiler should not have any oxygen in the lower chamber.
Not sure why I would sell my unit for a lambda unit. Do you think that a lambda boiler would be so efficient that there would be no oxygen left in the lower chamber?
The boiler's lower chamber is not air tight due to the fact that the exhaust exits out to the chimney, so why can't oxygen be available?
 
IMHO there would have to be excess oxygen in the secondary to get a complete burn just for the wood gasses. With proper heat and oxygen the gasses will burn. With too little oxygen unburned gasses will exit the chimney if they cool below their spontaneous combustion temperature. There still remains the possiblity that there is too much oxygen in the secondary or too little pressure feeding the fire from the primary since the coal is burning so well and it takes the added coal to get the boiler to heat quickly. Good gasification temps will usually range aroud 1800-2300 deg. F and maybe your boiler is not attaining that temp without the coal. However not knowing the exact burn you are getting (as in the right mix for your boiler) you may need the extra air in the secondary. In my EKO40 too much secondary air will actually foil good hot gasification and at times will actually cool the boiler (outdoors in unheated building).
 
Just to clarify things:

My boiler was and is running great!
There is no problem at all raising water temperatures, and the normal flue temps are around 425 - 450.
I only tried this as an experiment, and my unit works fabulous as it is calibrated.
A true blue flame is burning in the second chamber during gasification.

That being said, the flame in the lower chamber is the last stage of the "burn cycle" for the boiler and
under normal conditions the firebrick is glowing orange. I thought that at this point adding additional material (coal),
additional heat/performance could be gained. I'm sure that if you tried the same thing I did in other units, the coal would burn as well.
 
NYEDGE said:
I follow your thought that the goal is to get as complete combustion as possible, but I'm not to sure on the idea that the boiler should not have any oxygen in the lower chamber.
I'm just saying that when a burner is working properly there's a certain amount of what is called 'excess oxygen' in the flue gas. If excess oxygen is too little then the wood combustion won't be complete. If excess oxygen is too much then the wood flame won't be as hot as it could be and also energy is wasted heating both the unneeded oxygen and all the nitrogen that comes with it.

So if the level of excess oxygen is just right for the wood fire then there won't be enough oxygen for the coal fire to burn just right itself, and it's likely there would be unburnt coal gas.

I'm thinking you would need to increase the secondary air flow to the point where the wood combustion would be non-ideal, but then there would be enough oxygen to burn off the coal without sending unburnt coal gas up the flue. It seems like tuning the unit to burn wood plus coal might be pretty tricky with just a pile of coal sitting there in the lower chamber, but that doesn't mean it couldn't be done.

It's conceivable a lambda unit would detect the unburnt coal gas and would adjust the secondary air accordingly, but it just sounds like a lot of bother.
The boiler's lower chamber is not air tight due to the fact that the exhaust exits out to the chimney, so why can't oxygen be available?

But the lower chamber is air tight when it comes to getting any more oxygen than what is flowing in through the primary and secondary combustion air jets. If the amount or oxygen is just right for burning the wood then the coal fire would be starved to some extent. You're right, there would be some oxygen available but I don't think there would be enough for it to finish what it started.

Cheers --ewd
 
I follow your logic and agree with you for the most part.
At the end of the burn cycle the coal was not completely burned to ash.
I'd say that they reduced approximately 50%. They should continue burning if left for the next time.
So it's not really a typical burning if coal, but since the wood burning aspect is not being compromised,
there must be some gain of heat transfer to the water.
 
A timed test with weighed wood would be in order for both burn scenarios. Starting out at the same temperature for both burns. Light the fire and set the timer and see if it does enhance the heat transfer/gain etc. Might be something to it, might not.

Will
 
Perhaps a cost comparison of how much wood it would take versus the cost of the coal to achieve the same results too.
 
NYEDGE said:
I follow your logic and agree with you for the most part.
At the end of the burn cycle the coal was not completely burned to ash.
I'd say that they reduced approximately 50%. They should continue burning if left for the next time.
So it's not really a typical burning if coal, but since the wood burning aspect is not being compromised,
there must be some gain of heat transfer to the water.

I was thinking that the intense heat would cause to coal to vaporize, whether is actually burned completely or not.

But your test shows that the coal sits in the wood flame without disappearing, so it sounds like for the most part the coal won't go anywhere until it gets enough oxygen to burn, however long that takes, which would definitely make some useful heat.

This might be consistent with what I see with coals -- which are also 'pure carbon' -- that fall through the gasification nozzle. They sit in the secondary chamber for hours until the upper fire turns to coals, and then finally they turn to ash.

Maybe you've invented an automatic excess oxygen scavenging system.

--ewd
 
ewdudley said:
NYEDGE said:
I follow your logic and agree with you for the most part.
At the end of the burn cycle the coal was not completely burned to ash.
I'd say that they reduced approximately 50%. They should continue burning if left for the next time.
So it's not really a typical burning if coal, but since the wood burning aspect is not being compromised,
there must be some gain of heat transfer to the water.

I was thinking that the intense heat would cause to coal to vaporize, whether is actually burned completely or not.

But your test shows that the coal sits in the wood flame without disappearing, so it sounds like for the most part the coal won't go anywhere until it gets enough oxygen to burn, however long that takes, which would definitely make some useful heat.

This might be consistent with what I see with coals -- which are also 'pure carbon' -- that fall through the gasification nozzle. They sit in the secondary chamber for hours until the upper fire turns to coals, and then finally they turn to ash.

Maybe you've invented an automatic excess oxygen scavenging system.

--ewd


You know, now that you mention it, your right about the coals sitting in the lower chamber glowing during the burn.
When the unit was new, the fun thing to do of course was to open the bottom door to see the flame, and show others what was happening.
Now I just load the wood and walk away, except for an occasional check-up on the flame to make sure the secondary air mix is good.
With the lower door open you can see glowing wood coal that dropped as you said. I don't make it a habit to check for un-burnt wood coals
in the lower chamber, but during cleaning of ash there is never any coals, just fine dust. It makes sense that after the wood fire has depleted, the wood coals
can then be completely burnt.

I ran the unit with the same un-touched coal in the lower unit for the second time and maybe 1/2 of the previous amount is now left.
I raked to cold coals to see if the structure was just ash, and what was left was still a solid mass. The top of all the coals were a spent gray color, and the underside
of some of the coal still had the original black hue. The fact that they have now gone through 2 burn cycles and still retain some of there original color and structure
may coincide with your thought that there is not enough air during the main wood burn cycle to burn the coal, but perhaps they are burning post wood burn cycle.

If that's the case then perhaps they are acting as a scavenger of sort and at the least they have been primed during the burn so that they can burn the oxygen at the end of the burn cycle
in order to create additional heat. I will leave the original coals in for now and see how many more cycles I get out of them, and then do a check on the fire brick to make sure that they
are in good shape.
 
Its sounds like the dense structure of the coal only allows it to burn if there is O2, instead of gasify like wood does. So I am guessing that since the coal lasts through the burn cycles, you really dont have any extra O2 left over from the wood burn. If it was to burn up right away it would mean that the 2ndaries are turned up too much. I would call it a poor mans Lambda.
 
As long as the coals stay on the firebrick that sounds like a good deal. With pine I have had coals fall right off the U block in the EKO and they just die. There is a possibility then that you need dense wood to get the "complete burn" you are talking about. In any case there have been times when I could nt get good gasification due to condensation on cold wood maybe now I will add a little coal to the U block to aid warming the unit for quicker sustained output.
Great experiment and great results NYEDGE. Thanks for sharing!
 
I experimented with a bucket full of anthracite last winter. Don't know the type but there were pieces large enough to bridge the nozzle so that's what I did and then added enough to make a bed about an inch deep or so. I then built a fire on top of it and it seemed to work quite well. Lots of heat, nice blue flame, etc. Seems like it would form a nice bed of coals in the upper chamber which is exactly what is needed for good gasification.

The only concern I have is the acid that coal produces. I have never used coal but I understand that it tends to eat up stovepipes unless they are stainless probably due to sulfur content. Don't know if that would shorten the life of the boiler.
 
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