Hi, Henk & Til !
So far, nobody seems to have adopted the “balcony roof”;
(a roof over a balcony which does not excist)
The “balcony” is just a spontaneous descripion of a horizontal ring that somebody proposed to be layed on the nozzles…
It soon was modified to be a short cylindrical ring standing loosely on the nozzle-shafts and having a conical roof (funnel) reaching just over the nozzle-tips.
The hollow ring under it acts like a collecting cavity for the outflowing gases from the white-glowing center.
From here the strong nozzle beams suck the tarry gases back into the inferno center, for “final” treatment before reaching the reduction area…
“Yes, we have no bananas…”
It has not been adopted or described in Waine’s book.
It will not deliver heat to the hearth wall in the same amount as when high-glowing char is allowed to be in direct contact with the hearth-wall !
The purpose is to promote targas recirculation into the center,
not preheating primary air outside the hearth.
Outside the hearth-wall a modest preheating of the primary air is anyway taking place.