Coal Weight in VS Ash Weight Out?

 
Bustedmp
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Post by Bustedmp » Wed. Oct. 08, 2014 8:56 pm

Not sure if this is the correct spot for this, but here it is anyway. I have been adding 30lbs +/- of coal every 2 days to my stoker, and getting about 30lbs of ash out in 7 to 8 days, at least I think that's how many days ago I changed the ash tub. I will keep track of it this time. But does that sound about right. I'm getting a little over 25% weight out in ashes from my stove. It's burning great, no wasted coal falling into the ash tub, no hot burning coal falling off the grate. I was just curious so I have something to base the differences in coal from different sources. My dad and I both have the same setups, and yet the settings for both stoves are very different with the only difference being where the coal came from.


 
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Lightning
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Post by Lightning » Thu. Oct. 09, 2014 1:40 am

Ash is variable based on where the coal came from. With anthracite, ash content based on weight usually averages 10-15%. Sometimes a little less, sometimes a little more. Last year when I was measuring coal/ash with my hand fed, I was getting around 12-13%.

It's tough to compare ashes from one coal source to another since the burning conditions (heat demand) may change which reflects on how thoroughly the coal is burned. I do a fair amount of experimental comparing and the toughest thing I encounter is keeping the variables the same from one section of time to another.. :lol:

 
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Post by McGiever » Thu. Oct. 09, 2014 7:06 am

Bustedmp wrote:My dad and I both have the same setups, and yet the settings for both stoves are very different with the only difference being where the coal came from.
Perhaps you both have different chimney setups also. :idea:

 
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Post by fifthg » Thu. Oct. 09, 2014 7:49 am

25% is a lot of ash,yet you say it seems to be a complete burn.Some fly ash is lost,so you are not including that,the fly ash lost would add to the 25%.You do not have lab-like conditions,but your comparing coals under your conditions is still fair to the coal,as long as the variables,like draft and heat demand,etc. are the same.Frequently,they are not,but you should be able to notice coal quality differences,anyway,just remember,and maybe note the conditions when you do comparisons.The last guy you want to fool is yourself.

 
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Post by titleist1 » Thu. Oct. 09, 2014 9:56 am

25% does seem a little high for a weight comparison. It would probably be about the % I see for volume. I haven't done a weight comparison for a lot of years but I do check the ash for any unburnt coal. I swap ash pans so when it cools off I crumble it up to look for unburned coal. It is pretty consistent from year to year so I don't bother to weigh it.

 
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Post by Pacowy » Thu. Oct. 09, 2014 11:07 am

It's normal for there to be a small amount of unburned coal in the ash, as it is normal for there to be unburned hydrocarbons in the exhaust from your car. Unburned material can easily add on the order of 10% to the "ash" measurement being made here. I'd suggest focusing on making sure the fuel/air mix produces a proper fire for any given coal, rather than trying to draw too many conclusions about the coal from the ash.

Mike

 
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Post by kstills » Thu. Oct. 09, 2014 11:25 am

Also, from what I've read here, the boilers tend to have more unburnt coal in the ash then the hand feds, for whatever reason. Maybe it's the stokers in general that don't get as complete a burn, whatever it is, I have quite a bit of unburnt coal in my ash.


 
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Post by Pacowy » Thu. Oct. 09, 2014 12:41 pm

Maybe the larger sizes of coal used in hand-fired appliances have less variation in piece size relative to the smaller sizes used in stokers, or maybe some hand-fired users produce fine ash by using excessive air. We may never know. We do know that an optimal fuel/air mix for most stokers does produce a small amount of unburned coal. Not to worry, stoker users, because stokers also produce tangible efficiency benefits.

Mike

 
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Post by Freddy » Thu. Oct. 09, 2014 3:52 pm

The coal I have is some of the last deep mined coal to come from Superior. It's a different color, but I think it comes out the same size and weight as it goes in! LOL Wellll.... not quite, but it makes a HEAVY dense ash. Compared to my buddy Charlie who burns Kimmel, my ash is almost exactly twice the weight of his ash.

 
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Post by Lightning » Thu. Oct. 09, 2014 5:36 pm

Pacowy wrote:Maybe the larger sizes of coal used in hand-fired appliances have less variation in piece size relative to the smaller sizes used in stokers, or maybe some hand-fired users produce fine ash by using excessive air. We may never know. We do know that an optimal fuel/air mix for most stokers does produce a small amount of unburned coal. Not to worry, stoker users, because stokers also produce tangible efficiency benefits.

Mike
My speculation, if I may, is that hand feds and stokers are more efficient in different areas. Lets make it a given that both have a heat transfer efficiency of 80% overall and lets look at how each handles the heat energy produced.

In a hand fed, the coal is forced to stay in the fuel bed until it burns up small enough to fall thru the grates during shake down. A stoker with its way of doing things, doesn't know if the coal at the end of the grate is completely burned or not, it gets pushed into the ash bucket. So maybe a hand fed wins out in that department by burning more of the coal its given.

On the other side of that, there is the heat energy to consider. With a hand fed (one like mine anyways) there are "stages" if you will, to the burn cycle. After loading fresh coal, it ignites and the volatiles are baked out of it in the first hour or so. I'm willing to say that a fair portion of that heat energy is lost up the chimney along with the extra secondary air it needs to burn it. After that, I cut back the secondary air and keep more heat in the furnace longer to transfer into the convection air that is pumped thru the house. With a stoker, those volatile gases are always part of the total heat produced that is being absorbed by the vessel instead of leaving thru the chimney. So maybe a stoker wins out in that department by absorbing the heat energy produced more efficiently..

That's just my thoughts on the whole hand fed - stoker efficiency debacle... :lol:

 
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Post by Pacowy » Thu. Oct. 09, 2014 7:01 pm

Yes, capturing the heat of the volatiles is a factor. And if the fuel/air mix is set properly, the unit will run indefinitely at its optimum output. Plus, stokers can alternate between max output and idle on short notice, helping match output to variations in the load.

FWIW, back in the day EFM internally estimated the overall efficiency advantage of its underfeed stokers relative to handfiring to be about 20%. Fortunately this thread is in the stoker section, so maybe the manly men won't notice that one. :lol:

Mike

 
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Post by franco b » Thu. Oct. 09, 2014 7:23 pm

Pacowy wrote:FWIW, back in the day EFM internally estimated the overall efficiency advantage of its underfeed stokers relative to handfiring to be about 20%. Fortunately this thread is in the stoker section, so maybe the manly men won't notice that one.
I can accept that statement because they were comparing , most likely, the hand fired boilers of the day which lacked even a rudimentary combustion chamber. Pretty hard to design something worse.

Stoves however are a different story and the best, I believe, would have no trouble equaling or even surpassing the EFM numbers.

 
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Post by Pacowy » Thu. Oct. 09, 2014 7:36 pm

EFM was comparing use of its stokers to handfiring in the same boiler or furnace. Could you please clarify your point about combustion chambers?

Thanks.

Mike

 
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Post by lsayre » Thu. Oct. 09, 2014 7:48 pm

I'm resolved that my Stockton pea is going to act a lot like Freddy's Superior. Ash pans weigh a ton. Of course, I haven't got to winter yet. Hope things improve by then.

 
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Post by Bustedmp » Thu. Oct. 09, 2014 8:29 pm

My chimney is block with a clay liner 3 stories high, my dads chimney is block also, but stainless lined and only 1 story high. I'm not getting much if any unburnt coal in the ash tub. I am going to keep better track of how much goes in compared to how much comes out for the next week or whenever I need to change out the pan again. I'm not overly concerned about it as long as my house is going to be nice and warm, just curious about it. If I can heat my house for the $543 I spent on 3 1/4 tons of coal for the season compared to last years oil and electric bills, my ash tubs can weigh 50% of what I put in.


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