I have used this type of tuyere for several years, although itís not usually going for more than a couple of hours, and the fuel is charcoal. It is a bottom blast, supported on bars below a layer of ordinary Victorian house bricks. So long as the air flow is continuous, it does not block up. The stop end can simply be unscrewed if ash accumulates, but I donít usually need to do this while forging. I have also used coke. Charcoal produces very little slag. The benefit of an old sledge hammer head is that slag does not stick to it, even using coke.
Now I want to experiment using a side blast, which is why this tuyere has no stop end.
A note of caution. To fit the pipe to the hammer eye, I had to heat it. It is better not to use galvanised pipe, because of zinc fumes-which can kill! The tubes are not galvanised, although they appear to be, in these pictures.