Gas burner question

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I'm in need of a gas burner, i have the grip, now i need to find the correct burner.

I wish use it to weld rings and to anneal some part of plate armour (for large works i have a coal forge).
The question is: the producer express the power in Kw (from 1.4 to 54) and gas usage, how much power i will need?

Thank you all