The fact that it reaches melting temperatures means nothing. You need
energy density, (unpressurized) gases do not carry much energy, because they are very very thin compared to hot coals in normal forge. Cooking stove propane flame is around 2000 C and it would not heat anything bigger than a needle to some decent forging (yellow heat) temperature. I would suggest that you will make a testing model from dry stacked regular bricks, experiment and see if it can heat metal to the temperature you want to work with. If it can, you can replace basic bricks with quality refractory material.