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Side Blast Forge, Coal Gas Explosion!


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This is the forge. The blower is connected to the tuyere by a long flex hose.                   This is the hood/chimney sucking the flames from my start up fire.

 

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This picture shows a little smoke being drawn into the hood. Today, the green coal was putting a significant volume of smoke!

 

For the third time today, I fired up my just finished Side Blast forge. I had a good fire going and decided to add a couple shovel full of Bituminous Coal. I was getting a lot of smoke from the new coal that was placed around the edge of the fire to coke up. Since the Blower was off at the time I did a few tasks around the shop. The Supper Sucker Hood was doing a wonderful job of pulling the huge volume of smoke from the newly added coal .

 

I turned the blower on and BOOM! My guess is the coal gas from the new coal had backed up back thru the Tuyere and into the Blower. The BOOM was as loud as a 22. pistol  shot. There wasn't any flying red hot coal luckily. I have heard of coal forges exploding but never thought about it as a problem. If the explosion had been bigger, the red hot coal could have sprayed all over the shop and Nr. 1, me.

Has any of you had a similar experience? What do you suggest to prevent the coal gas explosion in the future?

 

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Not sure how to address this with a  sideblast forge.  In a typical bottom fired forge, the trick I learned is when in "idle" mode with the blower off (banked forge) to keep the ash dump open to induce a flow of air through the grating and bypass the blower.  It doesn't hurt to poke a venting hole in the top of your green coal mound either.  I would also make an effort to avoid banking your green coal with damp coal, or wetting it down after making a mound.  

 

I'm sure someone with more experience with side fired coal forges can be of more help.  Till then I'd be careful, you can get a pretty good "pop" from a coal gas explosion and folks have lost shops for less.

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Same here, I've blown up the flex duct once (loud as a shotgun, nearly had to change my pants and my wife thought I'd blown up the shop) and had a few pops at the guild shop. It is all traceable to wet coal.  The rule is, no damp coal if no blast, and if there's a lot of green coal keep an open flame and crack the ash gate.

Of course you have no ash gate... perhaps make a rule to not put the plate over the fire until it's well coked?

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Thank everyone for identifying the cause of my forge explosion, (I have been formally initiated into a large Forge Explosion Club). I ask very knowledgeable Blacksmiths about the explosion. (Interesting, that all experienced the same forge explosion under the same set of conditions.) The forge explosion is caused by adding green or wet coal over a hot fire and not running the blower.  I received a response from this forum,  Mark Aspery and from ABANA, Bob Valentine. All the responses are basically the same, keep the blower going when green/wet coal is added to the fire. The green coal over a hot fire will make a lot of smoke. The smoke is flammable and will burn the top of the fire. The flammable smoke coming off the top of the fire didn't cause the explosion, this smoke goes up the chimney or burns off.

 

Explosion conditions: The input to the fire is the problem causing the explosion, adding green/wet coal with no air supply. Coal gases formed which  is heavier than air so it settles in the lowest part of the forge system, the tuyere, flex air tube and blower.  Turn the blower on and Boom! 

 

From what I have read since my explosion, the Bellows were always placed high above the forge. If the bellows were placed at or below the forge fire, the coal gas would no only fill the air tube but the large volume of the Bellows.. A Bellows full of coal gas made a very spectacular, damaging and deadly explosion

 

Conclusion: To prevent the Side Blast Forge from exploding after adding green/wet coal , keep the blower running for a positive air flow. 

 

 Using a plate over the fire hot spot increases the heat of the fire, ( something I have been doing this year with very positive results). The plate over the fire reflects some of the escaping heat back into the fire, making the fire hotter. I have been experimenting lately with using a Fire Brick over the fire which appearers to works a little better than the steel plate.  If any one reading about covering the fire with a plate or fire brick, tried this procedure and have either positive or negative results, please respond to report your findings. 

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Overhead bellows can blow up too. The one in the Alex Bealer shop at the Atlanta History Center blew up in 1990 or thereabouts, taking a few square yards of roofing with it.

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