Commercial coke fire size sanity check

[robie1373]

I am using my JABOD with some coke I bought from blacksmith depot. I forge in a close subdevelopment and chose coke to reduce the amount of smoke and stink produced. My neighbors have been cool so far and I'd like to keep it that way.

What I'd like a sanity check on is the layout of the fire pot for coke. In the first few burns I feel like the sweet spot is sitting about 2" below the surface of my table. The truer is 3/4" black gas pipe sitting 3.5" below the surface of the table.  Those dimensions were set based on the assumption of a charcoal fire and I suspect they are less suitable for coke.

When  burning the coke, I shop my fire pit to be 1" below the truyere. I fill up the pit with coke and heap a pile another 3" over the top of the table. The hot spot seems to be sitting from the top of the truyer to 1 or 1.5" above the top.

I'm using a bath fan on a dimmer as a blower and have an elbow sitting loosely over the gas pipe. As a result a fair amount of the air just escapes and I get what seems like a pretty reasonable amount of blast. 

My planned fix is to rais the truyer 1.5" and run a couple more fires in that configuration to see if it is better or worse. 

I'd like to here people's predictions / thoughts on the issue. Am I heading the wrong way? Is some other aspect of my fire the actual problem?
 

[JHCC]

Sounds like you’re on the right track. One of the nice things about the JABOD is the ability to revise and adapt fairly easily. Let us know how it plays out. 

(And it’s “tuyere”, by the way.)

[robie1373]

12 minutes ago, JHCC said:

(And it’s “tuyere”, by the way.)

But the extra 'r' just sounds so much better!

[JHCC]

Tuyerer?

Tuyerest!

[BIGGUNDOCTOR]

Every time I see your handle I remember the house I grew up in, its address was 1373.

Try sealing the fittings better and get more air into the coke. I suspect that will make a big difference.

[robie1373]

I got a bit wrapped around the axel trying to figure out tuyere size for coke. I feel like most of what I’ve read is aimed at charcoal. 

Is approx 7/8 I.d. Appropriate for a coke fire? I do small work. <= 1” 

your comment about more air is making me wonder. 

Also, I’d love to live in a house with that address. 

[JHCC]

That's the ID of my tuyere, and I forge material anywhere from toothpick-sized up to about 2-1/2". I've used both anthracite and bituminous -- the latter cokes up nicely.

 

[Glenn]

I like a 2-1/2 inch opening with a 3/8 piece of stock across the opening as a grate. For a 3 inch opening I like 2 each pieces of 3/8 (maybe 1/2 inch) bar across the opening. Brake drum or rotor fire pot. I like all the air I can get going to the fire and then control the air to get the heat I want from the fuel. YMMV

My current bottom blast forge is in testing mode, a 2-1/2 inch opening with no grate, read zero grate, just a 2-1/2 inch hole in the bottom of the brake rotor fire pot. It works with bituminous coal. Build a fire with sticks, add a little coal and let it coke up, then add more coal. As I said it is a test and works.

Coal size is from coal dust (fines) up to about the size of golf balls. 

[robie1373]

I think I need to check an assumption. When I was reading about tuyere size, I thought I saw a chart recommending different diameter tuyeres for different fuels. Or at least different types of fire. I made the logical leap that they intended to compare different pipe sized with a constant air source. With that assumption I then deduced that the velocity of the airflow must be important. Is that a bogus conclusion?

I'm not trying to turn a box of dirt into a space shuttle, I'm just trying to improve my tool kit for troubleshooting my forge. Thanks as always for the thoughtful and useful responses!

JHCC, May  I ask what kind of blower you are using?

[JHCC]

Stripped-down vacuum cleaner with a radiator hose to carry the exhaust to the tuyere and a variable transformer to adjust the speed. 

 

[robie1373]

Ah. That's capable of a lot more air than my bath fan. I'm starting to see a pattern of indicators. More air. Or at least the availability of more air. 

[robie1373]

Changes! After taking on some advice about air supply I did some shopping today. I found a little vacuum that does a ton of air and fits my tuyere like a glove. Sadly, It does not react well to a dimmer. I had to come up with a plan b. 

I admit to feeling pretty clever about this solution. Until I tried it. The air dumps out the top of the T. I was thinking there would be just a trickle of air going into the fire pot when to top was full open. I didn't account for Bernoulli, though. In fact, I get a vacuum pulling air out of the fire pot and up the T. Sigh.

I'm going to have to do some experiments  to figure out how much of the outlet I need to tape off to ensure I don't get that back draft. Idealy I would like to find a more elegant location for the adjusting cap. 

After a quick test fire, I can confidently say I didn't have nearly enough air. I have ample air now.