[Stoves] Cross-Current Woodgas Burner with Air Inlet Tubes Angled 45° Downwards - YouTube Vid

[Crispin Pemberton-Pigott]

Dear Julien

 

I agree you are seeing that: 

 

>…When I added a 15 cm riser on top of the burner, the center of the flame became somewhat depressed.  That could mean that there could be a rather interesting circulation pattern going on with some secondary air going down in the center, then circulating up with woodgas at the outside in a toroidal vortex ... or maybe it is just a 'pigment' of my imagination.

It is a toroidal flow probably up on the outside, down in the centre. You should be able to follow small sparks with your gaze because you have a char burn going on at the surface. 

If it is circulating ‘too much’ it will increase the flame height. You can break it up with a few jets pointing in the opposite direction.

The pops you heard drying the refractory is exactly the problem. I suggest the following regimen:

105 for 1 least an hour (use the warming drawer, not the oven) and possible much longer. Then increase it now and then, 15 minutes or 30 minutes, by 25 degrees. The plan is 135 degrees per hour or less, to the highest temperature you can get which is probably 275 C in a baking oven.  This removes ‘crystal water’ meaning H2O bound in the chemistry of the materials. It is not ‘moisture’ in the regular sense but it still makes steam when it comes out. 

The popping is spalling from steam pockets exploding out. The temperature change rate was too high. It doesn’t stop until 600 C but that is hard to do without a clay firing oven. If you can get to 600, hold for 1-3 hrs to get the carbon out of the interior, then you can ramp up to the final firing temperature at 150-200 degrees per hour. That might be 1100-1280.  Modern kilns have ramping software in the controller.

When running the stove you can certainly get a nozzle temp of 900 (glowing) so try to do it gently on the first run.

Regards

Crispin

 

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