Glenn

BTUs, coal vs coke vs charcoal vs wood

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Forges most often use coal, charcoal, and coke for fuels. Very few use wood. I wanted to figure out if it could be used and find the numbers needed in order to base a opinion. This may get a little long so stay with me.

 

Volatile matter is material that is driven off when coal is heated to 950°C (1,742°F) in the absence of air under specified conditions - components of coal, except for moisture, which is liberated usually as a mixture of short & long chain hydrocarbons, aromatic hydrocarbons & some sulphur - measured practically by determining the loss of weight Consists of a mixture of gases, low-boiling-point organic compounds that condense into oils upon cooling, & tars.

 

Burn the volatiles (gases) from coal and you get coke. This is done industrially or when you add coal to a fire in order for it to *coke up* and be raked into the fire to replace the fuel burned to create the heat for forging. This is most often done with bituminous coal (soft coal) but is also done with anthracite coal (hard coal).

 

Burn the volatiles (gases) from wood and you get charcoal. This can be done industrially and then is bagged, or bulk, for sale in the stores. The same thing can be done to on a smaller scale at home. Either way the result is wood (charcoal) that is light weight, and mostly carbon.

 

Reference Indiana Center for Coal Technology Research

 

Anthracite coal is a dense, hard rock with a jetblack color & metallic luster. It contains between 86% and 98% carbon by weight, & it burns slowly, with a pale blue flame & very little smoke. It has a heat value of nearly 15,000 BTUs-per-pound. Most frequently associated with home heating, anthracite is a very small segment of the U.S. coal market. There are 7.3 billion tons of anthracite reserves in the United States, found mostly in 11 northeastern counties in Pennsylvania.

 

Heat Content (Btu/lb) 13,000-15,000 
Moisture < 15% 
Fixed Carbon 85 - 98% 
Ash 10 - 20% 
Sulfur 0.6 - 0.8% 
Chlorine (ppm) 340 ± 40ppm 

 

 

Bituminous coal (in Indiana), contains between 69% & 86% carbon by weight and a heat value of 10,500 to 15,500 BTUs-per-pound.

 

Heat Content (Btu/lb) 11,000-15,000
Moisture  2 - 15% 
Fixed Carbon  45 - 85% 
Ash  3 - 12% 
Sulfur  0.7 – 4.0% 
Chlorine (ppm) 340 ± 40ppm

 

I have found these numbers to be general guide lines and may differ depending on the source you use for information, and the type and location of the coal. Many people throw numbers about without knowing what they actually mean in the forge. There is no magic number that makes coal, blacksmithing coal. I have found most blacksmiths use coal from the 13,000 BTUs to mid to high 14,000 BTUs. It is what is available to them at their location and it works well for them in their forge. Yes, higher the BTUs are better as it is a more efficient fuel based on only BTUs. That is until you burn the end of your stock and it falls off into the fire because the fire and fuel is too hot.

 

United States Department of Agriculture Forest Service publication How To Estimate  Recoverable Heat Energy in Wood or Bark Fuels brochure lists the following woods with 8,000 BTUs to 12,000 BTUs. 


Oregon white oak, Red alder, Western hemlock, and White fir are on the lower 8,000 BTUs range. Cypress, Yellow pine are at 10,000 BTUs and Pitch pine have 12,230 BTUs. Hickory, Red Oak, White ash, White Burch is 9,360 BTUS,  and White Oak is 9,510 BTUs. The bark from trees is from 7,385 BTUs to 10,332 BTUs.  Anyone that has used wood for a fire knows that certain woods burn hotter than others.

 

Density of the fuel

Bituminous mine run coal is 40-50 pounds per cubic foot.  Wood is about is about 40 pounds per cubic foot (average) and a useful number for this discussion. Let us say that both are 40 pounds per cubic foot but the BTU value of wood is half that of the same volume of coal. This means that you will use two times as much wood for the same heat.
 

If you can build a coal fire and use it to burn the volatiles (gases) from coal to get coke while you are forging, then why not burn the volatiles (gases) from wood and get charcoal at the same time you are using the charcoal fire for forging? The fuel BTUs of wood is lower than coal meaning you will have to use more wood to get the same heat BTUs than if you used coal for forging. 

 

The fuel size (wood) I found to work best is about the size of a 2x4 and about 4 inches long or about the same size as charcoal fuel. Build a fire and let it burn down into a good bed of embers (hot wood coals). Add more wood so that as you place the metal into the embers (hot wood coals) it forms charcoal and replaces what embers (hot wood coals) that are consumed.  This is no different than burning charcoal as a fuel, except you are making more charcoal from wood as you forge. This is the same as if you were burning coal and making coke as you forge.

 

Can you burn the end off your stock in a good bed of embers (hot wood coals)? Yes as a matter of fact you can. The metal does not care what fuel you use to get it hot. It only matters that it is hot enough to move under the force of a hammer.

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Well I have certainly had wood fires that were hot enough to forge metal with.  For me this fuel (wood) is all around and free for the labor of gathering and processing into useful sizes.  A considerable drawback is the radiant heat differential though.  The coal has a MUCH smaller heating effect on the general area (which includes ME).  My forge is also a bit small for burning wood (being designed for coal).  I do often mix some wood with my coal though... especially when starting a new fire.  I also use the byproducts (wood chips and shavings) of my handle production for fire starter.  This is a good discussion to have IMO.  We need to think through our processes and strategies now and then.  Certainly, in winter, the radiant heat output of wood could be as much advantage as it might be drawback in summer!

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Greetings Glenn,

 

Thanx for all the great info.. I will use this as a reference in the future..  As we all know there are many questions when we demo and your information makes it easy to answer questions...   I'll still keep my trees...

 

Jim  

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Bituminous coal and charcoal have about the same BTU content by WEIGHT; but the density of charcoal is MUCH LESS and so you need a lot more volume to make up that weight.

 

Remember about the first 2000 years of iron working was all done using charcoal; coal use for forging started in the high to late middle ages; but with charcoal use continuing in parallel even to this day.  In smelting charcoal was used in western Europe until Abraham Darby figured out how to use coke in the 1700's (in the USA charcoal fueled blast furnaces in the Hanging Rock region still remained active till about WWI) 

 

Now a forge designed for coal will burn charcoal but not as efficiently as one designed for it will.

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Great topic Glenn.  As a beginer I wundered about which fuel was better.  I like charcoal but have used coke and gas.  the gas is fast but has no "feel".  Coke was great but requires more air than I can supply with any control (shop vac on blow mode).  My charcoal set up uses bellows and the rythem and time lets me think about my next hits.  Each smith will have his favorites but its good to know the science behind it.

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A good companion topic would be how much AIR does one need!.... How may CFM is considered enough for any give firepot (fireball) size.....The comment troubles me that one can't get enough air flow out of blower side of shop vac, and yet I have very small dc blower that moves a lot less air than shop vac and I can literally blow the ash out of fire pot.... One has to wonder just what one expects/needs for air flow...

 

Dale

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Clif, photos of your twyere would be helpful. Supposing all else is open and unrestricted, the grate would be the choke point, or a weak shop vac.

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Not to mention *what* you are doing makes a huge difference on how much air is needed; we were pattern welding yesterday and cranking the blower several times faster as we would with regular smithing.

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I've seen arguments on both sides of whether wood requires more or less air than coal--some swearing it takes more, some assuring that it requires less. I'd like to see the data on that. We use the wood forge with a 50 cfm household exhaust fan, and it is plenty adequate, even for using the foundry attachment for melting aluminum. 

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I measure it by how much cranking we do and for a charcoal fire we crank a LOT slower than for a coal fire.  Some of the difference may be due to the size of the air pathways between the fuel charcoal have larger ones than coal in my usage.

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just did my first forging with charcoal tonight. made the charcoal, mixed hardwood pallet wood mostly, but also did a batch of pine branches that the ice brought down last winter. also made a batch of generic spruce charcoal, sourced from crates that snowblowers and snowmobiles are shipped in. forge is made from clay and sand dug from my property. blower is a 100 year old champion that leaks oil like a sieve. have to keep oiling it or it makes funny clanky noises. made a tomahawk from 3/4 inch bar in about 1.5 hrs. compared to gas, it was about 1 hour faster than my propane forge, and 0 carbon footprint. the scale was softer and much less, it came off easily with a wire brush. will try a knife unplugged next time.

 the pine charcoal was by far the fastest burning, but the heat was beautiful, heating the steel in single digit minutes to working heat. the spruce charcoal was borderline useless, and the mixed pallet wood was satisfactory. forge may have to be redesigned to be deeper, but that will be after my next posting.

i bring this up to add more fuel to the charcoal fire discussion.

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I also find less ash with pine. And 2x cut offs are easy to come by. Ad a cheep powerighter saw from harbor freight and your golden.
I am lazy, and i must say that the "live fire method" that Glenn described at the begining of the thead is by far my faverite. Tho i prefer my cut offs at 1 1/2", dosnt mater if its 2x4, 4x4 or 1x stock. Plywood and OSB works as well (might not be so healthy)

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To add a  little more to the fire  ;)  My great Grandfather use to use fir bark off the fire wood.  Doesn't burn to fast and chunks can be used to keep the heat confined.  I've seen my dad use his little rivet forge this way a  few times  so it does work.

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i think i'll be giving the wood chunks a try, as making charcoal for me right now is not an efficient process yet. 

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I built a shaker shovel  made from gravel shaker mesh and so do not use wood in my forge; but have a wood fire close (and down wind) and then just transfer hot coals with the shovel.  I scoop up a good lot, give it a shake to get rid of small pieces and ash and then dump the live coals in the forge when I work with charcoal.

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coal, in my opinion, is nadda due to the fact that it quickly transforms into coke so you can't use it to forge with, anyhow.

Unless, perhaps, you use hard coal....... and I hear two different stories/versions about that;

1. it will not coke. So then, you *would* use coal for forging. Except that is don't coke, so you don't *want* to use it in a forge.

2. it does coke. So then no, you can't use coal because both types coke when burned and thus you can't use it for forging.....cuz it forms coke when heated........

 

I'm getting a head ache thinking about it.

 

Typically, the blacksmiths say hard coal will not coke but the iron/steel industry uses hard coal to form coke for the ovens, so.........

 

I can't think about this any longer.

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Taking bituminous coal and burning off the volital gases makes coke. Coke then makes the coals that transfers heat to the metal. 

It is a simple straight line process.

 

Taking wood and burning off the volital gases makes charcoal. Charcoal then makes the coals that transfers heat to the metal. 

It is again a simple straight line process.

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Mister Reynolds, coal, wood and corn have to be converted to relativly pure carbon to be used as forge fuel. It dosent mater if you comvert it in the forge, by placing it on the outside of your working fire and burn of the volitile chemicals, or if you buy coke or charcoal that have been converted for you.

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guys,

 

you didn't read a word I typed.

 

Was my understanding that the topic is the use of coal etc. for forging.

 My point(s);

 

1. You can't use soft coal for forging because it turns to coke right away when heated or burned. The fire coverts from coal to coke. How you going to keep it from doing so and forge with coal? You can't, so it is a moot point. Unless you are simply refering to the quality or characteristics of the coal used in making of the coke used to forge with.

 

2.Hard coal. If you had read what I had typed, you would have addressed that, but have not. It doesn't matter to me either way; that being I simply find it an oddity that some smiths use hard coal and others will not. Some say it will coke over and others say it will not.

 

3.I have used hard coal and it did not in any way form coke. *That* is the ONLY way in which to "use coal" to forge with,,,as it does not change state (form coke) while being burned in said forge. Use literally ARE using coal to forge with.

 

4.the steel/iron industry uses HARD coal to make coke. How that is possible was another point I made in my original post. 

 

Non of the above four points were addressed. Simply food for thought that is all. Not arguing the fact that we make coke from coal in our forge or buy it outright.

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guys,
 
you didn't read a word I typed.
 
Was my understanding that the topic is the use of coal etc. for forging.
 My point(s);
 
1. You can't use soft coal for forging because it turns to coke right away when heated or burned. The fire coverts from coal to coke. How you going to keep it from doing so and forge with coal? You can't, so it is a moot point. Unless you are simply refering to the quality or characteristics of the coal used in making of the coke used to forge with.


I would suggest that it does not turn to coke right away as you have to heat the coal to drive off the volitals. As the volitals are removed it converts to coke, and when the volitals are fully removed it is coke. Take it to the forge and prove the point to yourself.
 

2.Hard coal. I simply find it an oddity that some smiths use hard coal and others will not. Some say it will coke over and others say it will not.


I am blessed with good bituminous coal in this area. Hard Coal (anthracite)is not available in this area. The times I have been able to use anthracite, it took a constant air flow but worked well as a fuel.
 

3.I have used hard coal and it did not in any way form coke. *That* is the ONLY way in which to "use coal" to forge with,,,as it does not change state (form coke) while being burned in said forge. Use literally ARE using coal to forge with.

 
These are the first two sites that yielded results.
Anthracite has 10% volitals and when it cokes it has 2% volitals. Moisture 2% to 15%
Bituminous has volatile matter of 31.73%.  Moisture 15%+
 
Both will release volitals and moisture while being heated.

 

Volatile matter consists of aliphatic carbon atoms (linked in open
chains) or aromatic hydrocarbons (one or more six-carbon rings
characteristic of benzene series) and mineral matter.

 

 

4.the steel/iron industry uses HARD coal to make coke. How that is possible was another point I made in my original post.

 

I do not know their process, Maybe you should direct that question toward them.

 

 

-----------Bottom line---------------------------

If you want to make the iron hot so you can pound on it, light the forge. If the fire does not get hot then you MUST change something or your never going to get anything done at the anvil.

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You forgot to mention great experience straining at gnats and swallowing camels!

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OK all, as an old geologist I need to clear up some confusion about coal and coke.

 

Among coals there are thermal (steam) coals which are mainly used for creating steam in power plants.  There are also metallurgical coals which are used to produce coke for steel production.  They differ in various qualities including heat value, amount of volatiles, amount of non-carbon content, etc..  The most important quality for a good coking coal is the index of caking/plasticity which is the ability, when heated in a non-oxygen atmosphere to become plastic and give off the volatiles and then reform as a solid.  Heating coals are pretty common and account for the vast majority of coal reserves.  Good coking coal is much less common.

 

Whether a particular coal is hard (anthracite) or soft (bituminous or sub-bituminous) has little to do with being a good coking coal.

 

I burn coke almost exclusively because I am right in town and I don't want to annoy my neighbors.  It works well but you do have to keep air going to the fire.  If I turn around to do something on the bench or go into the house for more than about 5-10 minutes it will go out where a coal fire would just die down and be able to be brought up again with more air.  Coke does produce clinkers because the coking process does not remove the involatiles.

 

If you know the origin of your coal you may be able to find out its index of plasticity or caking.  I don't recall what a good number is but the higher is better.  You could compare it to the caking index of a known poor coking coal, e.g. Wyoming sub-bituminous coal which is pretty crappy coking or blacksmithing coal.  Also, if your coal slakes (disintegrates) when exposed to the weather it is probably a sub-bituminous, non-coking coal.  That was my first forge fuel and it wasn't pretty.

 

I used to be able to get good blacksmith coal locally and was told that it came from the #3 seam of a coal mine in Oklahoma.

 

And, yes, coal in a forge turns into coke on the edges of the fire.  That is why your fire may start out smoky but then clear up and why you should rake coal into the fire from the sides rather than dumping green coal on top. 

 

Carbonaceously,

 

George M.  

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