J.P. Hall

Stones in coal, lots of clinkers

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Hi all, I've been having some trouble lately with stones mixed in with coal. The museum I forge at gets bituminous "blacksmithing" coal from Cornwall Coal in Cornwall, NY. The coal itself isn't terrible, a good bit of ash, but not unusable. The problem is that there are a fair amount of stones mixed in. The large ones (1/4 fist size) aren't too difficult to pick out based on texture and density, but I'm sure there are smaller ones that blend right in. In a ~4 hour forging session this past weekend, there were well over a half dozen clinkers to dig out with most being at least fist sized. There was no flux or burned steel in the fire, and the cast iron firepot was cleaned out well before use. I rebuilt the fire two or three times, and often when I started with green coal there was a clinker by the time the whole fire coked over. More than once I noticed as many as one or two stones per scoop of coal.

 

Does anyone else using this supplier have the same issue?

Is there any better way of sorting the coal than picking through each scoopful?

Are there any better suppliers in the Orange County NY/Hudson Valley area? The next closest supplier is Tri-County Coal about an hour away, which I haven't found much information about.

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I had the same problem with stones. Not because of the supply but I had about 150 pounds of coal in sacks that fell apart and the area is loose gravel so when I shoveled it up I got a lot of stone too. I don't think the stone is causing clinkers, but the quality of the coal itself. When I used that coal I lined the hearth with the green coal and picked out the stones before raking the coal to the fire to start it coking. Even when some stones made it into the fire, the clinker problem was no worse than usual which is very low.

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Rocks mass more than coal it's not hard to separate them, even coal shale isn't very hard. If it were large scale you can use wind to separate them like wheat and chaff.

Small scale can be done on a sloped sheet of plywood. Spread a shovel or scoop across the top with a scattering toss, the stones will usually roll farther down the slope. it's a mass and momentum over the friction of the slope that makes them go farther. YOu can also rap the bottom to induce vibration. Vibratory tables are commonly used to separate different density materials.

In the real world of the historical blacksmith shop, separating the coal and stones and cleaning clinker out of the firepot are what apprentices are for.:rolleyes: Kids in the audience LOVE doing things like separating stones and coal, I've had 2-3 at a time doing just that at demos. I DID have to put my foot down about breaking the lumps with hammers or rocks without PPE. NO hitting rocks or the blacksmith will GET YOU! Parents would walk by now and then, smile and wander on. 

Frosty The Lucky.

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Coal is formed in a swamp where the vegetation falls into the water, builds up, and is covered over and compressed into coal.  When they mine the coal, they sometimes get a little of the top and the bottom of the coal seam (read rocks) along with the coal. The coal preparation plants usually remove most of the rocks.

If you have some coal with debris included, fill a bucket full of water and put some of the coal into the bucket. Stir it with your hand. You can then remove any of the sticks from the top. Stir not so vigorously and the coal will rise above the rocks on the bottom but not clear to the top. You can just grab it out with your hand.  Some coal will be left so decant carefully, pour off the water, and remove the coal from the layer above the rocks. 

Cleaning Coal has been discussed before.

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Thanks for the suggestions. I may try out separating the stones out with water. The reason I thought the stones contributed to the clinker was that there appeared to be some partially molten rocks that I pulled out with the clinker. I couldn't tell if it was just the surface, or if it had been melting substantially. I also couldn't tell what type of rocks they were.

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As Glenn mentioned, coal is basically formed from ancient swamp deposits. 

A coal with undue amounts of clinker can usually be attributed to how/where the coal originated (the swamp).  If the area of swamp deposits had occasional influx of silicate fines such as clay, silt or very fine grained sands (such as from a flood) then those sediments would be admixed with the swamp material.  You might not be able to see those silicate fines with the naked eye, but if present, will form clinkers in the forge.  Very thick coal seams such as found in the eastern U. S. probably will tend to have lower fines deposited, but thin coal seams with overlying and underlying sediments (such as the 15 inch thick seam where I buy my coal), probably tend to have more clinker development.  As a side note, which some biologists on here may attest to, some plants may also have some trace amounts of silicates.  Inasmuch as plants had to grow in some type of soil, that trapped soil residue can also contribute to the silicates in coal and hence clinkers.

 

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As mentioned before, IF you want to experience clinker, get a good forge fire going, add more fuel and a double hand full of dirt, sand, etc to the top of the fire. The fire will heat it up and form clinker.

The fire in a forge gets hot enough to melt many things and roasts the remainder. Clinker is what does not burn in the forge. Simply let the fire cool for a minute or so, the clinker will solidify, and can be removed in one large piece or several pieces. Just remove it, throw it away and add more fuel to get started again. One of the coals I used was power plant coal and you could get a 20-30 minute burn before you needed to clean out the fire pot and rebuild the fire. With the metallurgical coal I use, you can forge for 8-10 hours without a problem.

 

 Coal, Coke, and Rocks
by Glenn Conner

Coal, to many people, is a black rock that sometimes can be burned. To a blacksmith, it is the fuel used in the forge to heat the metal, and comes in two varieties, good and bad. "Good coal" produces high heat, little ash, little clinkers (slag) and makes life so much easier. Bad coal is fussed at, cussed at, and generally returned to the earth as landfill (thrown away).

You will hear a lot about blacksmiths using Pocahontas Coal. Well, Pocahontas Coal is broken down into 10 seams of Pocahontas coals, numbered #1 - #9 and Poca #3 rider. Pocahontas #3,#5,#6,#9, and #3 Rider are the seams that have listed coal production. So when they say Pocahontas Coal, which Pocahontas Coal are they talking about? You have to ask, and if there is a question, ask to see the analysis of the coal. The analysis will usually list the Seam, Type, State it was mined, Ash, Sulfur, BTU, Volatiles, Carbon, Reflectance, and other properties

There are 117 named coal seams in West Virginia. Sixty-five seams are considered mineable. In the year 2000, coal was produced from 50 different coal seams.

coke01.jpg

This is some industrial coke that came from Pennsylvania.

coke02.jpg

It is gray in color, light weight, and about the size of your fist. That is a 2 pound hammer for size comparison.

When I put it into a regular coal forge, it had to have a constant air blast to keep burning, and needed to be about twice as deep as a soft coal fire. It gave off no smoke but the exhaust fumes from the open fire were invisible and gave me a trememdous headache. Second time I used it, I intentionally stayed out of the exhaust fumes from the open fire and no headache.

coal01.jpg

This is what is considered good coal for blacksmithing, it is low ash, low sulfur, high BTU coal of a usable size for the forge. The numbers suggested for good coal are less than 7% ash, less than 1% sulfur and above 14,000 Calorific Value in BTU's. These are not hard numbers but guidelines.

This coal will burn unattended in the forge for 4-6 hours with no additional air. With air it will produce "white hot" steel and with a little more air, burn steel with no problem. You can use air from an electric fan and adjust the air and almost hold a temperature while working several irons in the same fire.

junk00.jpg

This on the other hand is coal from the top or bottom of the seam and contains a lit of sediment, mud, rock or junk. The yellow sometimes looks like rust, but smells a lot more like sulfur when it is burned. Notice what looks like layers in the pieces.

junk01.jpg

This is another photo of the layering in the sample of "coal".

junk03.jpg

When you look closely sometimes you can sometimes see the layers coming apart.

junk04.jpg

They just fall apart or fracture on the layering lines. Some are 1/4 inch or thicker, and some are paper thin, it just depends on the layer.

junk05.jpg

The reason this is considered landfill for a blacksmith is because when it is burned, it produces much less heat as your heating up the junk which does not burn. The layers become more pronounced.

junk06.jpg

Coal is made up primarily of "organic" elements (carbon, hydrogen, oxygen and nitrogen) and "inorganic" elements (primarily silicon, aluminum, iron, calcium, magnesium, titanium, sodium, potassium, and sulfur). Organic elements comprise the combustible body of the coal, whereas the inorganic elements are present in coal in minerals that largely form the ash when the coal is burned. Inorganic elements (e.g. silicon and aluminum) are present in most West Virginia coals in the range of several percent or more in ash forming minerals, but other "inorganic" elements, such as sulfur, present in lesser amounts, may detrimentally impact the use of West Virginia coals. You can decide if this sample was more "organic" or more "inorganic" in nature.

Coal seams are fossilized accumulations of plants which lived and died in swamps that were so devoid of oxygen that few microbes or other critters could survive to feed on their remains. The first phase of coal known as "peat" thus developed. These swamps were interwoven with intricate, meandering river channels which eventually covered things with mud and silt. Subsequent deep burial by more sediments in succeeding geologic ages resulted in heat and pressure which transformed the peat into coal. Generally speaking, every 12 inches of coal thickness represents approximately 10,000 years of continuous peat accumulation. Coal seams in West Virginia average 3 feet in thickness, although they occasionally can be as thick as 25 feet.

When the swamp stretches across 2, 3, or more states, one part of the swamp can easily be different from the other, and form coal that, although in the same seam, is different in composition. That is why Poca 3 in Ky, WV and Va may give 3 different analysis results.

For the history buffs: The first reference to coal ( in what is today West Virginia) was in 1742, when John Peter Salley reported an outcropping of coal along a tributary of the Kanawha River. By 1817, coal began to replace charcoal as a fuel for the numerous Kanawha River salt furnaces.

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Some of what Glenn illustrated is getting towards "carbonaceous shale" from what would officially be "coal" geologically.

There is another quality of coal that is significant for a blacksmith, "agglomeration."  This is how "sticky" the coal is when it is burning.  It also is a major factor in how well the coal converts to coke as it is exposed to the heat around the fire.  A good coking coal has a fairly high agglomeration index.  

So, if you can get an analysis of the coal from the supplier you want high heat, low ash, high agglomeration, and as low sulphur as you can find (eastern US coals tend to be higher sulphur than western coals).

In my experience, the rocks in coal tend to be more rounded than the coal fragments.  Because of this my theory is that they do not originate in the coal seam or nearby rock but in the processing after mining. After going through the crusher and screening to make the appropriate fragment size the coal may be stacked in a pile and then loaded with a front end loader into the next process and machine to bag it.  If the sized pile is on a concrete pad all will be well but if it is on the bare ground the loader may scoop up dirt and rocks with the coal, particularly if the loader operator is not well skilled. The last lift from the pile may get the underlying dirt and rocks when the earlier loads did not. I have seen rocks included in bags of coal that are clearly limestone pebbles.  Limestone and coal are from different depositional environments and the limestone must have been introduced into the coal at some point after mining.

I had one batch that had so many rocks that I was tempted to save them and take them back to my supplier and demand an equal weight of coal.

I don't know of any way to separate coal from rock other than what has been suggested above.  Frosty's suggestion of using available children as coal/rock separators probably will work pretty well but I'm not sure the parents will be best pleased by the return of coal black children.  A blacksmith is expected to get black, children get grubby but actually blackened with coal dust may be exceeding expectations.

"By hammer and hand all arts do stand." 

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Great info, guys, thanks. I do like the suggestion of having children sort the coal , but I agree with George. Although, some people have asked to take clinkers home as souvenirs when I explain what they are and why I need to take some time to clean out the fire. Nobody's offered to take the pile of them sitting out back when I mention it though.

I have debated talking to the museum about possibly switching to charcoal, but I would prefer a side blast instead of the bottom that we have. It would definitely cost more, but I wonder if there are any bulk charcoal suppliers. I'm not sure I'd have the time to make my own, either.

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You have a good use for coal clinkers in NY.  Break up the clinkers to pea gravel size and put it into a container about the size of a 2 pound coffee can and put it in the car as winter traction material.  There is nothing better because the fragments have sharp edges.  It is much better than gravel or kitty litter.  Put a bow on each container and give it to all the museum staffers for Xmas.

"By hammer and hand all arts do stand."

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Mr. J. P. Hill,

A good source of bulk charcoal are steak houses.

You might try buying a few hundred pounds of it when they get in the next bulk shipment of the stuff.

Or your desired portion might help them make out a greater amount to get a cheaper price from the supplier.

Give it a try. In the worse situation,  all they say is no.  

They just might say yes.

SLAG.

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When we were running a bloomery every summer in Western PA we used to go buy 40# sacks of charcoal from the producers.  I wish I could remember their name as they had a great moorish revival office building that was built in 1929 with a very nice hand forged railing in the main office...TBI strikes again.

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Thomas,

It may not be a traumatic brain injury.  As we get older two things start to happen to us.  First, you start to lose your memory.  And I don't remember the second thing.

"By hammer and hand all arts do stand."

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Aging has its benefits. For example, I used to be terribly indecisive, but now I'm not so sure.

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Actually there was a major drop in me being able to remember names and increase in aphasia that correlated with the TBI; aging justs puts the icing on the snake so to speak. 

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TBI's silver lining is being a pretty unbeatable excuse. I just don't need one this badly.

Frosty The Lucky. 

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