Tuyere shape question

[Kozzy]

Attached is a photo of one of the 4 tuyeres on the old school forge I am bringing back to life.  It's a little tough to see but the openings are roughly cone shaped as the refractory has degraded and about 2" in from the face, the refractory is cast around the steel gas lines--looks to be 3/4" pipe.

This is an air fed forge--propane is fed into the blower impellor and then to a distribution header with 4 pipes leading to the tuyeres.  3 have shut-offs so that you can choose 1, 2,3 or 4 burners being lit.

The problem is, I am not sure what the actual shape of the refractory portion of the tuyeres was to begin with--or if it really matters.  Should they be slightly conical to allow some spread?  cylindrical?  If cylindrical, then same diameter as fuel feed pipe or slightly larger?  Cast in some sort of modified mini ribbon burner?

Since you only get one shot at re-casting the refractory (or start again from scratch) I thought it better to ask for opinions rather than just guess.

Oh...those degraded top bricks are 1-1/4 thick for a size reference.

 

[Frosty]

What's the make of the forge? I have an old Johnson Appliance 122A forge out back. It's a gun feeding for nozzles in the chamber. The burner nozzles are rectangular on the flat. I've never converted it to propane let alone lit it, these forges are more inline for a production shop, not a hobbyist. They are serious gas hogs so a person better have enough production to justify one.

Burner nozzle shape is less important with a gun (blown) burner.

If you know the maker you can probably get the specs from the company, Johnson keeps it's manuals, parts lists and parts available online.

Frosty The Lucky.

[ThomasPowers]

You may want to read up on why many propane burners have flares on the end and the appropriate angles for them.