[jeffreyrogers]

Not sure why your comment was dead since it's a good question. The answer is with charcoal, which is how it used to be done. It's less efficient (charcoal isn't as strong as coal so the furnaces have to be smaller) but it worked fine in the past. You obviously couldn't have the same steel output using charcoal. In the past places started running out of trees to turn into charcoal which is why they switched to coal in the first place.