I believe it is possible to weld using charcoal
for fuel . . .
http://www.artistblacksmith.com/articles/forge-welding.htm
Forge Welding
Forge welding is one of the most fundamental techniques of blacksmithing, but one of the trickiest to master. It requires speed, precision, and practice. Practice every time you work. Make it an exercise and when you need it for a project you will have the skill. Forge welding is one of those skills it is best taught one on one, hands on. But it is possible to learn it the hard way.
(Article does continue. Zim.)